LIBRARY OF CONGRESS. Chap Copyright No 8Mt\\M9 UNITED STATES OF America. ELEMENTS OF MODERN CHEMISTRY. -§-§ ^-§ — o ■ — o — o — rr: o c to c: ^^^^ ^^1^ 0) o C > > en in ELEMENTS OF MODERN CHEMISTRY, BY CHAELES ADOLPHE WURTZ. SIXTH AMERICAN EDITION, REVISED AND ENLARGED BY WM. H. GEEENE, M.D., AND HAERY F. KELLEE, Ph.D. (Steasburg). WITB. A PORTRAIT OF THE AUTHOR AND NUMEROUS ILLUSTRATIONS. PHILADELPHIA: J. B. LIPPINCOTT COMPANY. London: 36 Southampton Street, Covent Garden. 1900. 63714 L.iaetA.s f o1 Ooni.fr««* pVsU CoPtU REC£i*EO ! OCT SO 1900 I Copynght «ntry SLCPNO COPY. Oeiivered to OROEt) DiVISION, i 'oy 21 isau ^'?> \ A Copyright, 1879, by J. B. Lippincott & Co. Copyright, 1895, by J. B. Lippincott Company. Copyright, 1898, by J. B. Lippincott Company. Copyright, 1900, by J. B. Lippincott Company. Electrotyped and Printed by J. B. Lippincott Company, Philadelphia, U.S.A. BIOGMPHICAL SKETCH. Charles Adolphe Wurtz, the most illustrious French chemist of the latter half of the nineteenth century, was born at Strasburg, November 26, 1817, and died at Paris, May 12, 1884. Early in life his tastes led him to scientific studies, and he became a student of medicine under the Faculty of Medi- cine of Strasburg, in which he was appointed Director of Chemistry in 1839. After acquiring the degree of Doctor of Medicine, he continued his chemical studies under the direction of that foremost of chemical teachers, Liebig, at Giessen : here he became intimately associated with such men as Strecker, Will, Fresenius, Hofmann, and Hermann Kopp, many of whom were destined later to make world- wide reputations in the same field with himself. In 1844 he removed to Paris, entering the laboratory of the celebrated Dumas, to whom he became assistant the fol- lowing year. Besides this position, he filled that of Director of Chemistry in the Ecole Centrale des Arts et Manufactures from 1845 to 1850, and in 1847 was chosen Professor agrege at the Paris Ecole de Medecine, in which he became Pro- fessor of Chemistry in 1853, retaining this post until his death. In 1866 he was chosen Dean of the Faculty, at that time troubled by political dissensions which his tact and judgment were well adapted to calm. He took advantage of his administrative position to strengthen and improve the scientific lines of the curriculum, and when he resigned the deanship, in 1874, he had succeeded in establishing a Chair 5 b BIOGRAPHICAL SKETCH. of Organic Chemistry in the Sorbonne and a laboratory of Biological Chemistry in the Medical School. In 1858, Wurtz founded the Societe Chimique de Paris, to which he presented many of his papers. In 1867 he was made a member of the Academy of Sciences (Institute de France), and was chosen president of the same in 1880. He was a brilliant and lucid teacher, an eloquent speaker, and he possessed in a remarkable degree the faculty of in- spiring his audiences with his own enthusiasm. Wurtz's chemical work was accomplished with very modest experimental means, and his aim was always rather to sim- plify than to complicate. His main researches were under- taken with the object of developing the atomic theory, then just beginning to be understood, and while these works covered an extensive field, they are, as A. W. Hofmann has well expressed it, " linked together like the pearls of a neck- lace." His results led him to support enthusiastically the theory of which he became the greatest if not the first champion in France. The best known of Wurtz's writings are his "Atomic Theory," published in the International Scientific Series, his " Elementary Lessons," and his " Dictionnaire de Chimie," published with the collaboration of a number of eminent French chemists. He also wrote a Medical and Biological Chemistry in three volumes. Among the more important of his chemical researches were those on the constitution of the acids of phosphorus, on the cyanuric ethers, compound ammonias, ureas, amides, and glycerol ; in the course of these he discovered the glycols, oxide of ethylene, aldol and paraldol, and hydride of copper, as well as the correct explanation of certain in- teresting cases of anomalous vapor density. ATJTHOE'S PEEFAOE TO THE FIRST AMERICAN EDITION. This book is translated from the fourth French edition by my pupil and friend, M. Grreene, whose perfect familiarity with the French language and thorough competence, at the same time, in chemistry I have had occasion to appreciate. The translation is, then, a faithful, or even improved, representation of the original work, in which he will certainly have detected and corrected some faults. The French editions succeed each other rapidly, showing that this little book responds to an educational need. It has been the endeavor to keep it up with the current of the latest discoveries, and in it to condense a considerable number of exact and well-selected facts, without banishing the theory which binds them together. Thus, the origin and foun- dation of the atomic theory have been given, as far as possible, in historical order. The notions concerning atomicity, so im- portant for the appreciation of the structure of combinations and for the interpretation of chemical reactions, are presented in an elementary form. The reader will remark that the history of the metalloids is relatively more developed than the remainder of the book. Indeed, this is the fundamental part of chemistry, and a fa- miliar knowledge of it is indispensable to the fruitful study of the metals and of organic chemistry. It is also the most at- tractive portion for beginners, for it is the most easily under- stood. Immediately on entering the immense domain of organic 7 o AUTHOR S PREFACE. chemistry, wc find the facts overwhelmingly numerous and complicated. Among all these facts a severe and careful choice has been made, the historical importance and the theo- retical and practical interest of the compounds described being borne in mind. In this respect many additions have been made to the third French edition. Thus, the question of isomerism, upon which the theory of atomicity has thrown so much light, has been treated in a more thorough manner. The chapter on the aromatic compounds has been considerably augmented. The author hopes that these " Elementary Lessons" will be well received by the new public to whom they are presented, and that they will contribute to render attractive and diffuse the knowledge of the science to which he has devoted his life. ADOLPHE WURTZ. Paris, November 20, 1878. The progress of the science has made necessary many changes in the fifth edition of this little book, which has so far retained about the form and scope given to it fifteen years ago. It has been deemed advisable to complete the organic portion, and a large number of additions and corrections have been made. Whole chapters have been added to the history of the cyanogen compounds, the hydrocarbons, the acids, and the aromatic com- pounds. Among these will be particularly noticed the articles on isomerism, the azoic and diazoic compounds, and the pyridic bases, subjects which have acquired great importance during the last few years. Paris, 15tli September^ 1883. PEEFAOE TO NEW EDITION. The considerations wliich guided tlie American editors in the preparation of the fifth edition, have been followed also in the revising of the book for this new edition. Besides making numerous corrections and additions which were ren- dered necessary by the rapid advance of the science, the editor has endeavored to eliminate terms and symbols which are no longer generally current, or which betray the French origin of the work. A new chart showing the spectra of the principal gaseous elements, as well as those of metals, is sub- stituted for that found in the former editions. *r H. F. K. Philadelphia, September 16, 1900. PEEFAOE, Sixteen years ago this translation of Wurtz's " Legons elementaires de Chimie Moderne" was first presented to the public by one of the present editors. The hearty favor with which the book was received by American and English chemists, and the fact that it has now undergone the fifth revision, are sufficient indications of its usefulness. In the preparation of the present edition, the aim has been to preserve as nearly as possible the original plan and character of the work, but at the same time to make such changes as will entitle it to continue to rank as a truly modern text-book. In order that this might be accomplished with the least possible enlargement, some matters of minor importance in an elementary treatise have been omitted, and the new matter which has been introduced will, it is believed, be found to include the latest developments of the science. A number of the original illustrations have been replaced by more modern designs, but in not a few instances it has been deemed desirable to retain cuts, which, while they do not represent the newest forms of apparatus, are yet of great historical value in illustrating the development of chemical experimentation. To meet numerous requests, mention has been made of many matters that are of special interest to the student of medical chemistry. W. H. G. H. F. K. TABLE OF CONTENTS. Introduction — Distinction between Chemical and Physical Ac- tion . • . . . Definition of Chemistry ... Affinity — Molecules — Atoms Chemical Combination .... Decomposition — Double Decomposition , Law of Definite Proportions — Equivalents tions Hypothesis of Atoms .... Gay-Lussac's Law — Atomic Theory Ampere's Law — Avogadro's Law . Law of Specific Heats . . o . Law of Isomorphism — Nomenclature and Notation Table of Elements and Atomic Weights Binary Oxygen Compounds .... Oxygen Acids and Metallic Hydroxides Oxygen Salts Nomenclature of Non-Oxygenized Compounds Alloys and Amalgams Hydrogen Oxygen Ozone . Multiple Propor- Air Argon Water Mineral Waters Sulphur Hydrogen Sulphi Hydrogen Persulphide Oxygen Acids of Sulphur Sulphur Sesquioxide — Sulphur Dioxide Hyposulphurous Acid — Sulphur Trioxide Sulphuric Acid . , , , , PAGE ir-19 . 20 21-23 24-27 27-30 31-36 . 36 . 37 40-42 44 47 49 50 52 53 56 57 58 64 69 73 77 80 92 98 102 105 106 107 110 111 H 12 TABLE OF CONTENTS. PAGE Pyrosulphuric Acid 118 Thiosulphuric Acid ..... c ... . 119 Persulphuric Oxide , . . . 120 Selenium and Tellurium 121 Chlorine 122 Hydrochloric Acid 126 Hypochlorous Oxide and Acid 132 Chlorine Peroxide . . , . 134 Chloric Acid — Perchloric Acid 135 Chloride of Sulphur . . . . . . . . . ,136 Bromine 137 Hydrobromic Acid 138 Hypobromous Acid . . , 139 Bromic Acid — Perbromic Acid — Iodine ...... 140 Hydriodic Acid ,...., 142 Iodine Oxides and Oxygen Acids . . . . . . . 144 Periodic Acid 145 Analogies of Chlorine Group . 145 Fluorine ............ 146 Hydrofluoric Acid .....,. = ., 147 Nitrogen ..... 148 Ammonia ............ 149 Nitrogen Chloride . . . 154 Nitrogen Iodide — Ammonium Amalgam , 165 Ammonium Chloride . . 156 Ammonium Hydrosulphide and Sulphide . . , . . .157 Ammonium Nitrate . . . , . . . . . .158 Ammonium Carbonate . , , . 158 Ammonium Sulphate . . . . . . . . , .159 Hydroxy lamine . , . . . , . , , . .159 Hydrazine — Hydrazoic Acid — Oxygen Compounds of Nitrogen . 160 Nitrous Oxide . 161 Nitric Oxide 163 Nitrogen Trioxide , . . , . . . . . .164 Nitrogen Peroxide — Nitryl Compounds . . „ . . 165, 166 Nitrogen Pentoxide — Nitx'ic Acid . 167 Nitro hydrochloric Acid . . . , . , . . .170 Phosphorus . . . - . . . . . . ,171 Phosphine ,.......,.,.. 175 Phosphorus Trichloride — Phosphorus Pentachloride .... 178 Phosphorus Oxychloride — Compound of Phosphorus with Bromine, Iodine, and Fluorine ....... 179, 180 Compounds of Phosphorus and Oxygen 180 Hypophosphorus Acid ......... 181 Phosphorus Acid 182 Phosphoric Oxide — Phosphoric Acid ,....., 183 Pyrophosphoric Acid ,,.,...... 184 Metaphosphoric Acid ......... 185 Phosphorus and Sulphur— Arsenic ....... 186 Arsine ............ 188 Arsenic Chloride, Bromide, and Iodide — Arsenious Oxide . . . 189 Arsenic Acid ........... 192 Arsenic Sulphides ..,,,.... 193, 194 TABLE OF CONTENTS. 13 PAGE Antimony 195 Stibine .196 Antimonous Oxide — Antimony Antimonate 198 Antimonic Oxide and Acids — Antimony Sulphides . . . 199, 200 Analogies of Nitrogen Group 200 Boron 201 Boron Chloride 202 Boron Fluoride — Boric Acid 203 Silicon ............ 204 Hydrogen Silicide 205 Silicon Chloride 206 Silicon Fluoride . . . . 207 Silica . . . , . 208 Carbon ..... 209-215 Carborundum — Compounds of Carbon and Oxygen . . . .216 Carbon Monoxide .......... 217 Carbonyl Chloride — Carbon Dioxide . , . , . . .219 Carbon Bisulphide 225 Carbon Oxysulphide .......... 226 Compounds of Carbon and Hydrogen 227 Flame 228-231 Theory of Atomicity 232 Chemical Energy — Thermo-Chemistry 240 General Properties of Metals 243 Natural State and Extraction of Metals ...... 247 Alloys 248 Oxides and Metallic Hydroxides ...... 250-257 Sulphides , 257 Chlorides 258 Salts ............. 262 Richter's Laws - , , , . . o . . . . 265 General Properties of Salts , w . , . , . . 267 Supersaturation . . . 271 Electrolysis 274 Arrhenius's Theory — Faraday's Law 276 Berthollet's Laws 277 Nitrates . , 283 Sulphates 285 Carbonates 287 Classification and Atomicity op Metals 289 Mendelejepp's Periodic Law 294 Potassium ....,, 297 Sodium ............ 306 Lithium — Caesium and Rubidium — Spectrum Analysis . . . 315 Silver and its Compounds 317 Calcium 324 Strontium ............ 330 Barium ............ 331 Glucinum 333 2 14 TABLE OF CONTENTS. PAOB Magnesium 334 Zinc 337 Cadmium ............ 342 Lead 343 Copper . . 354 Mercury ..,,.,...... 362 Vanadium ....;.,. 370 Niobium and Tantalum . . .' 371 Gold . . .373 Bismuth .,...,. 377 Aluminium _........... 380 Cerium, Lanthanum, and Didymium ...... 385 Gallium . , , 386 Indium , 387 Rare Earths 388 Iron . . . , 389 Cobalt 401 Nickel 403 Manganese 405 Uranium — Helium .......... 409 Chromium . ........... 410 Molybdenum — Tungsten 414 Tin . . 416 Titanium 421 Germanium — Zirconium . . 422 Thorium 423 Platinum , 424 Metals of the Platinum Group 427 Organic Chemistry — Constitution of Organic Compounds . . 429 Formation of Hydrocarbons 433 Homologous Bodies — Chemical Species 435 Elementary Analysis 436 Determination of Molecular Weight ....... 440 Determination of Melting and Boiling Points 444 Isomerism 445 Functions of Organic Chemistry 447 Monatomic Radicals 448 Polyatomic Radicals 469 Cyanogen Compounds 462 Compounds of Carbon Monoxide 473 Monatomic Alcohols and their Derivatives — Methyl Compounds . 483 Ethyl Compounds 497 Series of saturated Hydrocarbons 517 Petroleum 519 Higher monatomic Alcohols 520 Compound Ammonias 530 Hydrazines . 532 Phosphi'nes • 536 Organo-metallic Compounds 539 Fatty Acids . 541 Formic Compounds 543 Acetic Compounds ... 545 Other Acids of the Series C^^H^nO' . . . '. . . .669 TABLE OF CONTENTS. 15 PAGE Oleic Acid and its Homologues 566 Diatomic Hydrocarbons 568 Hydrocarbons C°H2n-2 . 575 Glycols and their Derivatives 577 Glycerol and its Ethers 586 Natural Fats 590 Soaps — Polyatomic and Polybasic Acids 593 Uric Acid and its Derivatives 624 Polyhydric Alcohols 633 Sugars and Starches 635 Fermentation 646 Glucosides . 657 Aromatic Compounds and their Constitution 662 Benzene and its Derivatives . . . . . . . .671 Phenol . 677 Aniline . 683 Diazobenzene Compounds 686 Rosaniline and its Derivatives 689 Dioxybenzenes , , 692 Toluene and its Derivatives 697 Xylenes and their Derivatives . 714 Trimethylbenzenes and Isomerides , 716 Terpenes and Camphors 718 Unsaturated aromatic Compounds ....... 729 Indigo and its Derivatives . 732 Naphthalene 738 Anthracene and Phenanthrene 741 Furfurane, Thiophene, and Pyrrol . 745 Pyridine and its Derivatives 747 Quinoline 750 Alkaloids 752 Substitutes for Natural Alkaloids 769 Albuminoid Matters, Proteids 770 Products of Animal Disassimilation 782 ELEMENTS OF MODERN CHEMISTRY. INTRODUCTION. The material objects surrounding us present striking and infinite differences. Sulphur is readily distinguished from charcoal, rock-crystal from flint, iron from copper, water from spirit of wine, and wood from ivory. It is known to all that these bodies differ not only in form, density, and structure, but also in their proper substance. They differ, too, in the changes through which they pass under the same conditions. When subjected to the action of heat they receive very differently the impression of that force. They become heated more or less quickly, and transmit the heat with greater or less rapidity throughout their own substance. A short bar of iron cannot be grasped in the hand by one extremity if the other be heated to redness ; under the same conditions a cylinder of charcoal may be handled with impunity. Communicate sufficient heat to water and it is converted into steam ; remove heat from it, and if the cooling be sufficient, it is frozen into ice. Spirit of wine requires less heat to become vaporized, and extreme cold to congeal it. If a magnet be placed among iron filings, they attach themselves in tufts around the two poles; on the con- trary, copper filings are indifferent to the magnetic attraction. Rock-crystal is transparent to light ; flint is opaque. These two bodies are unalterable by fire. They may be heated to red- ness in a furnace, but after the temperature has abated they will be found with their original characters unchanged. It is very different with the coal which we burn in our grates. This body disappears during the combustion, and leaves only a quan- tity of ashes. But it has not been destroyed, and its substance is found in entirety in a certain gas produced by the combus- tion. Like charcoal, sulphur is combustible, and is converted by burning into a gas, the suffocating odor of which is well known. Neither sulphur nor charcoal undergo any alteration when b 8* 17 18 ELEMENTS OF MODERN CHEMISTRY. exposed to damp air ; it is not the same witli iron. In a moist atmosphere this metal experiences a striking and lasting change. Its surface becomes covered with rust and is no longer iron. In the forests, the leaves which fall and remain upon the moist soil are slowly consumed and disappear in the course of seasons. All of these changes, these phenomena, take place daily be- fore our eyes, and are familiar to all of us. On comparison, striking diiFerences are discovered between them : some are but passing, and do not affect the proper nature of the body. They are the results of forces which act at sensible distances, and which leave the body in its primitive state as soon as their action has ceased. A piece of soft iron is attracted by the magnet before contact is established, and when under the mag- netic influence, is capable of attracting other soft iron in its turn : the action of the magnet has made the iron itself mag- netic, but it immediately loses this property when the magnet is withdrawn ; and further, this momentary change in property has brought about no alteration in the intimate nature of the iron. It is found after the experiment in precisely the same condition as before. In the same manner, rock-crystal undergoes no change in its specific identity by the passage of a ray of light. Withdraw from the vapor of water the heat which has been communi- cated to it, and the liquid water is recovered with all its prop- erties. Restore to the ice the heat which was abstracted in its formation, and water is regenerated as before. This is charac- teristic of the changes produced by physical forces. Under the influence of such forces, bodies experience modifications more or less profound, more or less lasting, but which never affect their specific nature. But the iron which rusts undergoes a complete and lasting change in its properties and in its substance. The rust is no longer iron, and vainly would it be sought to isolate the metal by mechanical means, or to discover its presence by the aid of the most powerful microscopes. The metal has disappeared as such ; it has undergone a complete transformation ; it has be- come another body. It has attracted one of the elements of the air, oxygen, and has, moreover, fixed to itself the moisture of the atmosphere. These latter bodies, which differ from iron in substance, have intimately united with the metal itself, and the result of this union, of this combination as it is called, is INTRODTJCTION. 19 a new body, rust or hydrated oxide of iron. In this case tlie alteration is profound, the change is lasting ; the specific nature of the body is affected. This is characteristic of chemical action. In the same manner, when the charcoal and the sulphur are burned in the air, they attract oxygen and combine with it, forming two new bodies that are called carbonic and sul- phurous acids. These phenomena may be rendered more clear by simple and well-known experiments. Experiment 1. — A globe (Fig. 1) is filled with oxygen, a gas which constitutes one of the elements of the atmosphere, and which is eminently fitted to support combustion ; into it is plunged a morsel of charcoal lighted at one end ; immediately the coal glows with a brilliant light, the combination takes place actively, and the charcoal is rapidly consumed. But presently the light becomes paler, the combustion ceases, and the char- coal is extinguished. The oxygen is now nearly or quite con- FlG. 1. Fig. 2. sumed, and the globe is filled with another gas which is no longer oxygen, although it contains that oxygen. It contains also the matter of the charcoal which has disappeared, and these two bodies have combined to form a new body, which is carbonic acid. This latter will not support combustion, but, on the contrary, it extinguishes burning bodies. It is then a body having entirely new properties, and is formed by a chemical action. Experiment 2. — Into another jar filled with oxygen (Fig. 2) is plunged a spoon containing ignited sulphur. The combus- 20 ELEMENTS OF MODERN CHEMISTRY. tion takes place with a beautiful blue flame, and in burning in the oxygen with so much energy, the sulphur unites with the gas and forms with it a new body, which is called anhydrous sulphurous acid. It is a suffocating gas, which extinguishes flame. It reddens, and afterwards bleaches, a solution of blue litmus poured into the jar. These are special properties which do not belong to the oxygen at first contained in the jar. They characterize a new body, the result of the combination of the isulphur with the oxygen, and formed by chemical action. Carbon, sulphur, and oxygen are simple hodies or elements. They are so called because from neither of them can more than one kind of matter be obtained. But when the charcoal in burning unites with the oxygen, the carbonic acid which re- sults from the union contains two kinds of matter, — carbon and oxygen ; and these two elements are united in such an intimate manner that the body which contains both does not resemble either carbon or oxygen : it is endowed with new properties which do not in any manner recall those of the elements which constitute it. In fact, it is a new substance, a compound body formed by the combination of the matter of the charcoal with the matter of the oxygen. Considering the preceding facts, we may give to chemistry the following definition : chemistry studies those intimate ac- tions of bodies upon each other which modify their natures and cause a complete and lasting change in their properties. Iron may be reduced to a fine powder. This may be mixed with sulphur itself reduced to powder, and if the mixture be sufficiently intimate, it will present neither the lemon-yellow color of sulphur nor the gray-black of finelj^-divided iron. Nevertheless, a homogeneous substance cannot be formed in this manner. If the powder be examined under the microscope, the particles of iron may be recognized disseminated among those of the sulphur, but the two are not merged together. By the aid of a magnet the iron may be separated. On the other hand, if the mass be thrown into water, the particles of iron will sink first to the bottom, while the lighter particles of sulphur remain in suspension. Thus, after having triturated the sulphur and iron together, not only can each substance be recognized in the mass, but they can be again separated by mechanical means. Here there has been no chemical action, but simply a mixture. If, however, this mixture be heated, the sulphur will first be seen to melt, , and afterwards the INTRODUCTION. 21 whole mass will blacken and enter into fusion if the tempera- ture be sufficiently elevated. After cooling, it is perfectly ho- mogeneous, and neither iron nor sulphur can be recognized. Both have disappeared as such, and in their place is found a substance having new properties ; it is the sulphide of iron. They have disappeared, but their substance is not lost ; and it may be proved by experiment that the weight of the sul- phide of iron produced is exactly equal to the sum of the weights of the iron and the sulphur. The ponderable matter of the iron is then added to the ponderable matter of the sul- phur, and has formed with it a union so intimate that there results a new body, the smallest particles of which are per- fectly similar to each other and to the entire mass. This ex- ample and a thousand others that might be given prove that when bodies combine there is neither loss nor creation of mat- ter. The result of the combination, that is, the compound body, contains the whole of the substance and nothing more than the substance of the combining bodies. This is an essen- tial characteristic of chemical combination. The force which determines chemical combination is called affimty. It is important that this force be distinguished from another which is often opposed to it, and which is cohesion. In order to reduce to powder a solid substance, such as pyrites or sulphide of iron, it is necessary to overcome the resistance opposed by the particles of the mass to their separa- tion. This resistance is due to a special force, which brings and maintains in relation to each other the homogeneous par- ticles of the sulphide of iron, as indeed of all solid bodies. This is cohesion. The particles which are bound together by this force are not only those minute particles which are visible to the naked eye or under the microscope, and of which the most impalpable powder of a solid body is composed. Such particles still present a magnitude that can be measured ; they must be considered as little masses, so to speak, indivisible by the mechanical means at our command, but formed in reality of particles still smaller. These smallest particles of a solid body which are bound by cohesion are called molecules. They are not in immediate contact with each other. In a perfectly compact and homogeneous mass, such as sulphide of iron, the molecules do not touch each other. Between them exist spaces of considerable magnitude, compared to the real volume of the molecule. This idea must not be confused with that of 22 ELEMENTS OP MODERN CHEMISTRY. porosity, which is caused by those accidental spaces which form visible pores in solid bodies. The intermolecular spaces are those which separate the molecules of a homogeneous and com- pact solid body, and physicists have further been led to believe that even in solid bodies the molecules are not perfectly immo- bile, but that they execute vibratory movements in the spaces which separate them, at the same time maintaining their own relative positions. If a solid body be heated, a part of the heat is employed in raising the temperature, another part serves to increase the distances which separate the molecules : the body expands in becoming heated. But, as the distances between the molecules increase by the action of the heat and the efi'ect of the expan- sion, the molecular attraction necessarily becomes more feeble. Cohesion is thus somewhat diminished, and if the heat be further increased, it may be so much diminished that the mole- cules, which have thus far been maintained in definite rela- tions, can move and glide freely over each other ; the solid body then enters into fusion : it becomes a liquid. The liquid state is produced by a diminution of cohesion, and is charac- terized by a greater mobility of the molecules. But if the liquid body be still further heated, at a certain point the additional heat may produce such a separation of the molecules that, already freed from all mutual attraction, they become completely independent of each other. This is char- acteristic of the gaseous state. It may be stated, then, that cohesion is considerable in solid bodies, but slightly energetic in liquids, and null in gases, and we have just seen that heat, by causing the changes of state of a body, can overcome and even practically abolish this physical force. Chemical force or affinity is at the same time more intimate and more powerful. It modifies the molecules themselves. It brings heterogeneous substances into intimate relations, and thus produces new molecules. A consideration of the examples already cited may indicate more clearly the meaning of this important proposition. We have brought together sulphur and iron, and by their reciprocal action and the aid of heat there has been formed a new body, — sulphide of iron. We know that the smallest mass of sulphur we can obtain is composed of a collection of per- fectly homogeneous molecules, aggregated by cohesion. In each INTRODUCTION. 23 of them but one kind of matter can be found. It is the same with iron : the particles of this metal are perfectly homoge- neous. Sulphur and iron are simple bodies or elements. Let us now consider the sulphide of iron which results from their combination. This body also is formed of a collection of molecules, bound together by cohesion and perfectly similar to each other, but not homogeneous, for in each molecule we dis- tinguish two kinds of matter, — sulphur and iron. It cannot be admitted that these two substances are con- founded in the molecule, or that the effect of the combination of sulphur with iron is an interpenetration of the two bodies so intimate that they both disappear in what might be called a homogeneous mixture. On the contrary, it is supposed that the combination results from the juxtaposition of two infinitely small masses, each of which possesses a real magnitude and a constant weight. These little masses that no force, chemical or physical, can divide further, constitute the atoms. In each molecule of sul- phide of iron there exist two of these masses, — one of sulphur and one of iron ; and the atom of sulphur and the atom of iron are united, but not merged together, by chemical force. And when sulphur combines with iron it is because the atoms of the sulphur arrange themselves in juxtaposition with those of the iron, and it is affinity which brings about the action. When these atoms again separate, the sulphide of iron is said to decompose. When it attracts the atoms of another body, it is said to combine with that body. If sulphide of iron remain for some time exposed to moist air, its surface becomes covered with an efflorescence formed of a saline matter. In this case it has attracted one of the ele- ments of the air, oxygen, with which it has combined to form green vitriol or sulphate of iron. As we shall see later on, we have reason to believe that the molecules of oxygen gas are each formed of two atoms, but these atoms are of the same kind ; the molecules of sulphide of iron, on the contrary, are each formed of two unlike atoms, — one of sulphur and one of iron. These attract four atoms of oxygen, which constitute two molecules of that gas, which group themselves around the atom of sulphur and the atom of iron, forming with them one single molecule, more complex than the original molecule of sulphide of iron, for it contains in addition four atoms of oxygen. 24 ELEMENTS OF MODERN CHEMISTRY. 1 molecule sulphide of iron. 1 molecule oxygen. 1 molecule oxygen. and there results 1 molecule sulphate of iron. 0-©-0 ©-©-0 - It is seen from wliat precedes that the words molecule and atom are far from being synonyms. The chemical molecule constitutes a whole of which the atoms form the parts, and these atoms are held together by affinity. In the preceding figure, this exchange of affinities between the atoms is indi- cated by lines of union. Chemical molecules have been well compared to edifices : the atoms constitute the materials, and it is readily conceived that such molecular edifices diff'er from each other according to the nature, number, and arrangement of the atoms, that is, the materials composing them. An edifice may be enlarged by the addition of new parts : it may be reduced in size or it may be entirely demolished. In the same manner a chemical molecule may be increased by the annexation of new atoms, or diminished by the separation of some of those which it already contains. In the first case there is combination, in the second, decomposition. We may still further consider these phenomena of combina- tion and decomposition. Since the combination of two bodies results from the recip- rocal action of their atoms, and has for efiect a change in the nature of the molecules, it is evident that it can only take place when these atoms, and consequently the molecules, are brought into intimate relations ; or more precisely, when the molecules of one of the bodies enter within the sphere of action of the molecules of the other body. And this sphere of action is very limited, for the affinity or elective attraction of the atoms is only exercised at infinitely small distances. INTRODUCTION. 25 In consequence affinity is often retarded by cohesion, wHcli maintains the relations between the molecules of a solid body. These two forces are frequently in opposition, and that the first may attain the supremacy it is necessary that the other shall yield. To make manifest or to increase the affinity be- tween two bodies, it is then necessary to diminish their cohe- sion. On this condition the molecules can enter within the spheres of their reciprocal attraction, and the atoms of one body can attract those of the other. It has been seen from one of the experiments already cited that in order to combine iron with sulphur it is necessary to elevate the temperature. Now, the heat, by fusing the sul- phur, diminishes its cohesion, and, giving its molecules freedom of motion, puts them into more intimate contact with those of the iron. Chemical action then commences. Instead of heating the sulphur and iron to bring about chemical action, it would be sufficient to moisten the mixture with water. By the intervention of this liquid the particles of sulphur and of iron are, as it were, cemented together and thus brought into more intimate relations. For a stronger reason can chemical action between two solids be facilitated by dissolving them both in water and mixing the solutions. Dis- solved, they themselves assume the liquid state and lose, in great part, their cohesion. The ancients understood the in- fluence of the liquid state upon reactions, and stated it with exaggeration : Corpora non agwit nisi soluta. Although the liquid state facilitates chemical reactions, it does not follow that it always determines them. Frequendy liquids and even gases, after being mixed, must be heated before they will react upon each other. Experiment. — In a glass tube (Fig. 3) two gases, oxygen and hydrogen, are mixed in the proportion of one volume of the first to two of the second. Although the mixture is per- fectly homogeneous and very intimate, and although the cohe- sion of the gaseous molecules is null, no action takes place- But as soon as the mixture is heated by approaching a lighted taper to the mouth of the tube, combination takes place ener- getically. An explosion occurs and the two gases unite, form- ing water. In this case the heat has determined combination by increasing the intensity of the movements which animate the molecules of each gas, and so bringing the molecules of the one within the sphere of attraction of those of the other. B 3 26 ELEMENTS OF MODERN CHEMISTRY. The electric spark produces the same effect, and it probably acts by the heat which it communicates to the mixture. Fig. 3. More rarely combination is brought about by the influence of light. If a small bottle be filled with a mixture of equal volumes of hydrogen and chlorine gases, and then thrown into the air so that it may be struck by the direct rays of the sun, the combination of the two gases takes place instantly and with explosion. Such are some of the conditions which favor or determine chemical combination. Let us now study the circumstances which accompany these phenomena. Experiment. — If sulphur be strongly heated in a small glass flask until it begins to boil, and some copper turnings be then thrown into the flask, a brilliant incandescence takes place im- mediately. It is produced by the combination of the two bodies. Charcoal, sulphur, and phosphorus produce a brilliant light when they are burned in oxygen. Their combination with the gas takes place with evolution of light and heat. When any combustible body whatsoever is burned in the air, the heat and light are developed by the combination of the body with oxygen, one of the elements of the air. In general, all chemical combinations give rise to the production of heat, more or less intense ; in many cases it is accompanied by light ; sometimes it is scarcely perceptible. While heat acts as the determining cause of a great number INTRODUCTION. 27 of combinations, and while it is the result of such combination, it may play still another role in chemical reactions. In place of favoring combination, it may act in the opposite manner, separating atoms which are united by chemical attraction. Mercury retains indefinitely its brilliant surface when ex- posed to the air at ordinary temperatures, but at a temperature near its boiling-point it slowly attracts the oxygen of the air, and becomes covered with an orange-red powder, which is oxide of mercury. In this case heat has assisted the formation of a compound. If, however, this red powder be heated in a small retort to a temperature near redness, it is again resolved into mercury, which appears in drops in the neck of the retort, and into oxygen which may be collected. In this case an intense heat breaks up the compound which is formed at a temperature less elevated ; it occasions a decom- position. Heat acts thus in a great number of cases. A body is said to decompose when the elements composing it are separated from each other. The electric spark may occasion such separation when it is passed through compound gases. If a series of electric dis- charges be passed through ammonia gas, the latter is decom- posed., that is, resolved into its two elements, — nitrogen and hydrogen. In like manner, the current of the voltaic pile decomposes a great number of chemical compounds, the elements of which separate and appear, each at its appropriate pole of the bat- tery. The decomposing action exerted by the electric cur- rent upon chemical compounds was discovered about the com- mencement of the present century by Nicholson and Carlisle. These physicists were the first to decompose water by this agent. Lastly, light may decompose certain bodies, among which are a great number of the compounds of silver. The art of photography is founded upon the decomposing action of light upon certain of these combinations. There is another class of decompositions which it is impor- tant to consider with attention. They are occasioned by the intervention of more powerful affinities than those which maintain united the elements of a compound body. If copper be heated in the air, it attracts oxygen and is con- 28 ELEMENTS OF MODERN CHEMISTRY. verted into a black powder, a compound of oxygen and copper, wliicli is called oxide of copper. The affinity which unites the two bodies is considerable ; it cannot be overcome by the ac- tion of heat alone ; at any ordinary temperature to which the oxide so formed may be exposed, the atoms of copper still re- main intimately associated with those of the oxygen. But if this oxide be mixed with powdered charcoal and then heated, a moment arrives when the affinity of the charcoal for the oxy- gen is superior to that of the copper. The atoms of oxygen then abandon the copper and combine with the charcoal, thus forming a new compound, carbonic acid, which is disengaged in the form of gas. Here there is at the same time decompo- sition and combination. The molecules of oxide of copper are decomposed ; those of carbonic acid are formed. Nothing is created in combinations ; nothing is lost in de- compositions. In the preceding experiment only copper re- mains ; the charcoal and oxygen have disappeared, but their substance is not lost. All of the matter of the charcoal is Fig. 4. found combined with all of the matter of the oxygen in the product of their combination, the carbonic acid, in such a manner that the weight of the latter added to the weight of the copper remaining, exactly represents the weight of the oxide of copper and charcoal INTRODUCTION. 29 Experiment. — Some oxide of mercury, of which we have seen the decomposition by heat, may be placed in a tube through which is passed a current of hydrochloric acid gas, a gas composed of chlorine and hydrogen (Fig. 4). An ener- getic reaction takes place. The orange-red powder is converted into a white crystalline substance, and much heat is produced. At the same time a small quantity of liquid condenses in the bulb. This is water, and the white powder formed is mercuric chloride, or corrosive sublimate, a compound of mercury and chlorine. The hydrochloric acid has converted the mercuric oxide into mercuric chloride. The mercury, at first combined with oxygen, is now combined with chlorine. But what has become of the oxygen ? It has combined with the hydrogen of the hydrochloric acid, forming water. We have brought into presence of each other two compound bodies : Mercuric oxide, Hydrochloric acid, and from their reciprocal action two new compounds result : Mercuric chloride, Water or oxide of hydrogen. This reaction has then occasioned an interchange of elements. The mercury of the mercuric oxide has combined with the chlorine of the hydrochloric acid, and the oxygen has left the mercury and combined with the hydrogen, which was aban- doned by the chlorine. The reaction has been as easy as energetic, thanks to the intervention of two affinities, for the affinity of chlorine for mercury has been aided by that of hy- drogen for oxygen. Two molecules are decomposed, and two new molecules are formed by an exchange which may be rep- resented in the following manner : BEFORE THE REACTION. Mercury + Oxygen = Mercuric oxide. Hydrogen + Chlorine = Hydrochloric acid. DURING THE REACTION. AFTER THE REACTION. Mercury -^ Chlorine = Mercuric chloride. Hydrogen + Oxygen = Water. 30 ELEMENTS OF MODERN CHEMISTRY. Such reactions, characterized by an interchange of elements, are called douhle decompositions. They are the more usual reactions in chemistry. The examples cited have been demonstrated by experiments easy to comprehend and to repeat, and are sufficient to give an idea of chemical phenomena. We have seen how, on the con- tact of two heterogeneous bodies, this elective attraction, which is called affinity and which sets in motion the smallest particles of bodies, comes into play to produce either combination or decomposition ; we have seen how this force modifies the chemical molecules either by interposing other molecules, or under the influence of physical forces, such as heat and elec- tricity. The study of all these phenomena constitutes chem- istry, the science of molecular changes ; a science grand in purpose and in magnitude, since it penetrates to the very nature of the bodies surrounding us ; a science unlimited in its applications, since through it we learn to know and control the powerful forces which are at work in the most intimate structure of matter. If we trace the acquired facts to the most obvious and most certain conclusion, we must admit the existence of a number of bodies, each of which, when submitted to the various tests consisting in the application of physical and chemical forces, furnishes but one and the same substance, and it is impossible to obtain anything else than this substance from the body. We maintain, then, until proved to the contrary, that each of these bodies contains but a single kind of matter, to which the name simple body or element is applied. The chemical forces reside, as has been seen, in the most remote particles, in the atoms of these bodies. In uniting together, the elements form compound bodies, and it has already been stated that such combinations result from the juxtaposition of the atoms which attract each other. The idea of atoms was originally an hypothesis, but in its development it has been found to be supported by so many important facts, and moreover to weave them together in the most natural manner, that it has attained the dignity of a theory. Chemists have universally adopted it, and it has ren- dered immense service to the science. Let us proceed, now, to a consideration of the facts upon which it is based. LAW OF DEFINITE PROPORTIONS. 31 LAW OF DEFINITE PROPORTIONS. Fig. 5. The proportions by weight according to which bodies combine are invari- able for each combination — These proportions are equivalent among themselves — Experiments demonstrating this fact. Experiment. — A test-glass (Fig. 5) contains a liquid which is universally known as sulphuric acid. Although largely di- luted with water, that is, mixed with a large quan- tity of that liquid, it still manifests its presence by energetic properties. It has a very sour and cor- rosive taste, — a quality of an acid. If a few drops of blue litmus solution be added to it the blue color instantly changes to bright red. Another glass contains a solution of caustic potash or potassium hydrate. This substance possesses a strong, lye-like, alkaline taste, very easy to distinguish from that of the acid. The color of the blue litmus is not affected by this liquid, but if a few drops of the litmus solution, previously reddened by an acid, be added, the blue color is immediately restored. This caustic substance has properties which are different from those of acids, and which are called basic or alkaline properties. Potassium hydrate is an alkali or powerful base. If now the alkaline liquid, which has a blue color, be poured drop by drop into the reddened acid, and the mixture be stirred with a glass rod, a moment arrives when the red color of the acid liquid changes to blue. Exactly at this moment we have a solution which has no action upon litmus ; it will not redden the blue solution, neither will it restore the blue color to the red. This may be demonstrated by dipping into it first a red and then a blue litmus-paper. Furthermore, this liquid possesses neither the acid taste of the oil of vitriol nor the alkaline taste of the caustic potash, but its taste is salty. By their mixture and reciprocal action the sulphuric acid and the potash have lost the energetic properties which they 32 ELEMENTS OF MODERN CHEMISTRY. manifested before mixing. Thej are exactly saturated ; they are neutralized. That is, the liquid which now contains both, or more properly the product of their reaction, is neither acid nor alkaline ; it is neutral, and its neutrality is manifested both by its indifference to vegetable colors and by its taste. There is no excess, neither of sulphuric acid nor of potash, but the two bodies have reacted exactly upon each other and both have disappeared, and from their reciprocal action two new bodies result, — a salt called potassium sulphate, and water. Whenever sulphuric acid is thus saturated by potash, there arrives a moment when the ^whole of the acid is precisely neu- tralized by the alkali, and when the two bodies are converted, without residue of either one or the other, into potassium sul- phate and water ; and it is always easy to recognize the instant at which this effect is produced by the action of the liquid upon vegetable colors, such as solution of litmus, or syrup of violets. The latter is reddened by an acid, changed to green by an alkali, and assumes its natural violet tint when the neutral point is reached. Now, it has been found that this last effect IS only produced when the acid and the alkali are mixed in certain proportions, which remain invariable, whatever may be the quantities which are mixed. In other words, it has been found that the quantities of sulphuric acid and potash which reciprocally neutralize each other and form potassium sulphate, maintain a constant ratio to each other. It may be easily proved that when the state of neutrality has been once attained, it is immediately passed and disturbed by the least excess of either acid or base that may be added to the liquid. This is made evident by the immediate change in the color of the liquid to either red or green. Thus, in order to form sulphate of potassium with a given quantity of sulphuric acid, it is necessary to add an invariable quantity of potash ; and if the quantity of sulphuric acid be increased by a third, or in any proportion whatever, it is neces- sary to increase by a third, or in the same proportion, the quan- tity of potash. Experiments of this kind have been made with other acids and other bases, and have introduced into the science the fun- damental notion that these bodies react upon each other in definite proportions to form salts, and that consequently the composition of the latter bodies is perfectly fixed. A given DEFINITE PROPORTIONS. 33 quantity of any acid whatever, invariably saturates a. fixed quantity of the same base. This, then, is the first point. It may be added that similar researches made towards the close of the last century have led to a not less important result, namely, the respective quantities of several acids which satu- rate a given weight of one base are exactly proportional to the quantities of the same acids which saturate a given weight of another base. The law which governs the composition of salts was discovered towards the close of the last century by a G-er- man chemist, Richter. We cannot now expose it in detail ; such development will be better placed and better understood in that part of this work which treats of the formation of salts. For the present it is sufficient to state that the law mentioned is a consequence of the law of definite proportions, and that the latter law is universal. It applies not only to the reaction of acids upon bases, but is true for all chemical combinations. It is generally known as Dalton's first law, and may be thus expressed : the relative weights according to which bodies com- bine are invariable for each combination. There is one feature of the laws which control the composi- tion by weight of bodies that it is important to comprehend well. It may be best illustrated by experiment : 100 gr. of mercury are put into the presence of chlorine gas, a body possessing very powerful affinities. In this man- ner mercuric chloride or corrosive sublimate is formed, and it is found that 35.5 gr. of chlorine are necessary to convert 100 gr. of mercury into this compound. These figures — 100 and 35.5 — express the invariable ratio in which these elements are combined in corrosive sublimate. Here we have the definite proportions. Now let the 135.5 gr. of corrosive sublimate be dissolved in water, and a plate of copper be placed in the solution ; this metal will displace the mercury, and combining with the 35.5 gr. of chlorine will form with it cupric chloride, which will remain in solution, coloring the liquid green. The 100 gr. of mercury are then precipitated, and it will be found that 31.75 gr. of copper have entered the solution and actually combined with 35.5 gr. of chlorine. Into this solution of cupric chloride a plate of zinc is now plunged ; all of the copper is precipitated in its turn, and 33 gr. of zinc enter into combination with the 35.5 gr. of chlorine, forming zinc chloride. I 34 ELEMENTS OF MODERN CHEMISTRY. The 35.5 gr. of chlorine lia^fe now been combined success- ively with 100 gr. of mercury, 31.75 gr. of copper, i 33 gr. of zinc. These numbers, which express the respective quantities of mercury, copper, and zinc which combine with the same quan- tity of chlorine, may be called the equivalents of these metals. In fact, these quantities are equivalent to each other in relation to the same quantity of chlorine, the experiment having shown us that in order to displace 100 gr. of mercury combined with 35.5 gr. of chlorine it is necessary to employ 31.75 gr. of copper or 33 gr. of zinc. To continue, 100 gr. of mercury are combined with oxygen, and it is found that this quantity of the metal requires 8 gr. of oxygen to form the red powder called mercuric oxide. But how much oxygen is necessary to form cupric oxide with 31. V5 gr. of copper? Kemarkable as it seems, exactly 8 gr. are required, and 8 gr. are also requisite to form oxide of zinc with 33 gr. of zinc. 100 gr. of mercury, 31.75 gr. of copper, 33 gr. of zinc, which are equivalent compared to 35.5 gr. of chlorine, are then also equivalent in relation to 8 gr. of oxygen. Chlorine itself may be oxidized, and there exists a gaseous compound of chlorine and oxygen which contains precisely 8 gr. of oxygen for 35.5 gr. of chlorine. Thus, there are required 35.5 gr. of chlorine to form chlorides with. . ill^^^fg^. oTZZlll 8 gr. of oxygen to oxidize { 33 gr. of zinc, and also 8 gr. of oxygen to oxidize 35.5 gr. of chlorine. In general, if A, B, C, combine with D, A, B, C, combine also with E, and further, D combines with E, the letters A, B, C, D, E, representing the weights of the dif- ferent elements which enter into combination, or the propor- tions according to which the bodies combine among themselves. MULTIPLE PROPORTIONS. 35 They are expressed by numbers tbat have been called combin- ing weights or equivalents ; these represent the ratio of weights or the relative weights. They are indeed relative to a unit which has served as a term of comparison, and which is the equivalent of hydrogen. That is, the quantity of hydrogen which combines with 35.5 of chlorine being 1, the equivalent quantities of oxygen, zinc, copper, and mercury will be repre- sented by the numbers 8—33—31.75—100. These are the facts of experiment. Let 33 gr. of zinc be treated with hydrochloric acid, the latter is immediately de- composed ; its chlorine combines with the zinc, forming chlo- ride of zinc, and its hydrogen is disengaged. In this experi- ment the hydrogen of the hydrochloric acid is simply displaced by the zinc. Now, 33 gr. of this metal will displace exactly 1 gr. of hydrogen. It is seen that the numbers which have been given do not express absolute quantities, but merely the relative weights ac- cording to which the bodies combine or replace each other in compounds, these relative weights being compared to that of hydrogen, which is taken as unity. f which represent J equivalent quan- I titles of these I elements. Such is the signification of the numbers. 100 31.75 33 35.5 8 1 of of of of of of mercury, copper, zinc, chlorine, oxygen, hydrogen, This being admitted, in order to determine the equivalent of an element it is sufficient to find the quantity of that ele- ment which combines either with 1 of hydrogen or with a quantity of another element which is equivalent to 1 of hydro- gen, for instance, 8 of oxygen. The notion of equivalent proportions can be understood from the preceding considerations ; it appears as a consequence of the law of definite proportions ; it comprehends certain facts relative to the laws of the composition of bodies, but it by no means represents the full scope of these laws. The following developments add important features. MULTIPLE PROPORTIONS. Two bodies may combine in several proportions. Thus, with oxygen, carbon forms two compounds, both of which are gaseous. The less rich in oxygen is carbon monoxide ; the richer is carbon dioxide, or carbonic acid gas. Dalton was the 36 ELEMENTS OP MODERN CHEMISTRY. first to perceive that for the sarae quantity of carbon, carbonic acid contains exactly twice as much oxygen as carbon monoxide. He made analogous observations concerning the composition of two compounds of carbon and hydrogen, the monocarbide of hydrogen or marsh gas, and the dicarbide of hydrogen or olefiant gas. From these observations he deduced the law of multiple proportions, which may be thus stated : when two bodies^ simple or compound^ unite in several proportions to form several compounds, the iveight of one of these todies being considered as constant, the weights of the other vary according to a simple ratio. Thus, taking up one of the examples given above, carbon unites with oxygen in two proportions : Carbon monoxide contains 16 parts of oxygen to 12 parts of carbon. Carbon dioxide contains 32 parts of oxygen to 12 parts of carbon. The numbers 16 and 32 are in the ratio of 1 : 2. Nitrogen forms five compounds with oxygen ; if such quan- tities of these compounds be taken as contain the same weight of nitrogen, the weights of the oxygen will be proportional to the numbers 1, 2, 3, 4, 5. Nitrogen monoxide contains for 28 parts of nitrogen 16 parts of oxygen. Nitrogen dioxide " 28 '' " 32 " " Nitrogen trioxide " 28 " " 48 " " Nitrogen tetroxide " 28 " " 64 " " Nitrogen pentoxide " 28 " " 80 " " These numbers, 16, 32, 48, 64, 80, are multiples of the first by the numbers 1, 2, 3, 4, 5. Five compounds of manganese and oxygen are known, and similar relations exist between the quantities of oxygen con- tained in these compounds. The first contains 55 parts of manganese to 16 of oxygen. The second " 55 " " 24 " The third " 65 « " 32 " The fourth « 65 " " 48 « The fifth « 55 " " 66 The numbers 16, 24, 32, 48, 56 are in the simple propor- tion 1 : 1.5 : 2 : 3 : 3.5. Such is the law of multiple proportions discovered by Dalton. HYPOTHESIS OF ATOMS. The brilliant researches of Dalton did not terminate with the acquisition of facts : he sought to account for them by a GAY-LUSSAC'S LAWS. — ATOMIC THEORY. 37 theoretical conception. Taking up the old idea of Leucippus and the word of Epicurus, he supposed all ponderable matter to be composed of indivisible particles which he called atoms. He gave a precise meaning to the vague and ancient notion by considering on one hand that the atoms of each kind of matter, of each element, possess an invariable weight, and on the other that combination between different kinds of matter results from the juxtaposition of their atoms. Such is the atomic hypothe- sis, the substance of which we have already indicated in treat- ing of chemical phenomena in a general manner. It permits a simple and rational interpretation of the laws of the compo- sition of bodies, and establishes between these laws a firm bond of theory. Indeed, if the combination of bodies results from the juxta- position of their atoms, the latter being considered as indivisi- ble and possessing a constant weight for each element, it is evident that combination can only take place in definite pro- portions, for these proportions represent the invariable relations between the weights of the atoms which are in juxtaposition. If, on the other hand, one body may combine with another in several proportions, such combination can only take place by the juxtaposition of 1, 2, 3, 4, etc., atoms of one body with one or more atoms of the other. It evidently results that the weight of the latter body being constant, the weights of the other in these various combinations must be multiples of each other. An hypothesis which gives such a simple and precise ex- planation of the facts relative to definite and multiple propor- tions is surely worthy of attention. It acquires still further import and becomes elevated to the rank of a theory when to these facts are added others entirely different from the first, but not less important. GAY-LUSSAC'S LAWS.— ATOMIC THEORY. Gases combine in simple volumetric proportions — Relations which exist between the volumes of gases and their atomic and molecular weights — Equal volumes of gases or vapors contain the same number of molecules — The molecular weights are equal to double the densities compared to hydrogen. Among these new facts it is convenient to first notice those which were discovered by Gray-Lussac, from 1805 to 1808. They relate to the volumes of gases which combine together. 38 ELEMENTS OF MODERN CHEMISTRY. Experiment.— A straight graduated glass tube about one metre long, closed at one end and having two platinum wires soldered through the glass near the closed end, is filled with mercury and inverted over a tall glass mercury cistern (Fig. 6), in the bottom ot which is a thick caoutchouc pad. This tube, which is called a eudiometer, is surrounded by a wider glass tube fitting firmly on a cork passed over the eudiometer. The cork is also perforated for the passage of a bent glass tube through which steam from a boiler can be delivered into the space between the eudiometer-tube and the mantle. The mouth of the eudiometer being about one centimetre Fig. 6. below the level of the mercury, which completely fills the cistern, a mixture of two volumes of hydrogen with one volume of oxygen is now introduced until the level of the mercury in the tube indi- cates the latter to contain exactly 30 cubic centimetres. The wires of the eudiometer are now connected with the poles of an induction- coil, and steam is passed from the boiler until it no longer condenses in the space between the tubes ; that is, when the temperature is 100°. The gases have been expanded by the heat, and the eudiometer must be lowered into the cistern until the level of the mercury in the tube again marks 30 cubic centimetres, when the clamps of the GAY-LUSSAC'S LAWS. — ATOMIC THEORY. 39 stand are so adjusted that tlie upper one is fixed at this mercury level. The tube is now lowered into the mercury until its lower end rests upon the caoutchouc pad ; a spark from the coil is passed in the eudiometer, and this causes the oxygen and hydrogen to com- bine instantly, as is seen by a bright flash. Now, on raising the tube until the mercury in it stands as before, at the level of the upper clamp, it is found that the eudiometer contains only 20 cubic centimetres of gas instead of 30. The 20 cubic centimetres consist of steam formed by the union of 20 cubic centimetres of hydrogen with 10 cubic centimetres of oxygen. As the apparatus cools, the steam will condense to water, and as the latter occupies a very small volume compared with that of the steam, the mercury will rise and fill the tube. Prom the facts thus established we draw the conclusion that 2 volumes of hydrogen exactly combine with 1 volume of oxygen to form 2 volumes of vapor of water. There is thus determined a simple ratio not only between the vol- umes of hydrogen and oxygen which combine, but further, between the volume of vapor of water formed and the sum of the volumes of the composing gases. 3 volumes of the latter are reduced to exactly 2 by the combination. Analogous facts have been discovered for other gases, as shown by the following examples : 2 volumes of nitrogen + 1 volume of oxygen = 2 volumes of nitrogen monoxide. 2 volumes of chlorine -f 1 volume of oxygen = 2 volumes of chlorine monoxide. In other cases the combination of two gases determines a still greater contraction, and the initial volume is reduced one-half. Thus 1 volume of nitrogen + 3 volumes of hydrogen — 2 volumes of ammonia gas. Finally, when two gases combine in equal volumes, their combi- nation usually takes place without contraction; in other words, the volume of the gas produced is equal to the sum of the volumes of the component gases. From these collected facts we may draw tlie following general conclusions : 1. There is a simple relation between the volumes of gases which combine. 2. There is a simple relation between the sum of the volumes of the combining gases and the volume of the gas resulting from the combination. These laws were first signalized by Gay-Lussac, whose name is attached to them. Their importance is immense ; they have added a. notable development to the atomic theory. If the definite proportions by weight in which bodies com- bine represent, according to Dalton, the relative weights of their atoms, it is natural to conclude that the definite and simple proportions by volume in which gases combine , accord- 40 ELEMENTS OF MODERN CHEMISTRY. ing to Gray-Lussac, represent the volumes occupied by the atoms. Under the same volume gases would then contain the same number of atoms. This was first proposed by Am- pere, who based his conclusion on the important consideration that gases dilate and contract nearly equally when submitted to the same variations of temperature and pressure. Within certain Hmits the proposition is true ; it applies to a large num- ber of simple gases. But if equal volumes of these gases, measured, let it be well understood, under the same conditions of temperature and pressure, contain the same number of atoms, it is evident that the weights of these equal volumes should represent the weights of the atoms. In other words, the atomic weights of the simple gases should be proportional to their densities. The densities of gases and vapors represent the weights of these gases or vapors compared to the weight of an equal volume of air. To determine the density, a certain volume of the given gas is weighed, and this weight is divided by that of an equal volume of air, under the same conditions of tempera- ture and pressure. The air is then the unit to which are com- pared the densities of gaseous bodies. On comparing these densities to that of hydrogen,^ which we take as unity, we find that the same numbers express almost exactly the densities and the atomic weights, the unit to which the densities are com- pared, that is, hydrogen, being the same as that to which are compared the atomic weights. The figures in the following table demonstrate this to be the case : Elements. Densities of Gases or Vapors, Air being Unity. Densities, Hydrogen being Unity. Atomic Weights. Hydrogen Oxygen Nitrogen Sulphur (density at 1000°) Chlorine Bromine Iodine 0.0695 1.1015 0.9714 2.22 2.44 5.53 8.716 1 15.9 14 32 35.2 79.7 125.8 1 15.9 14 32 35.5 80 127 1 To do this it is suflBcient to multiply the densities of the gases compared to air by = 14.388, which is the density of the air compared to hy- 0.0695 - f -^ *- drogen as unity. GAY-LUSSAC'S LAWS. — ATOMIC THEORY. 41 It is seen from this table that if the densities of gases be compared to hydrogen as unity, just as the weights of their atoms are compared to hydrogen as unity, the same figures, or very nearly the same figures, express both the densities and the atomic weights. We may add that, for all the elements taken in the gaseous state, there has been determined between the densities referred to hydrogen and the atomic weights, if not equality, at least a simple ratio. These remarkable rela- tions were pointed out by Gay-Lussac. Equal volumes of the simple gases above enumerated con- tain the same number of atoms. Two volumes of hydrogen, then, contain twice as many atoms as one volume of oxygen ; and when these gases combine in the ratio of 2 volumes of the first to 1 of the second, we must admit that each atom of oxy- gen combines with 2 atoms of hydrogen. We say, then, that water is composed of 2 atoms of hydrogen and 1 atom of oxy- gen. These three atoms so united constitute the smallest quantity of water that can exist in the free state. This is called a molecule of water. But what volume does this molecule occupy ? The experi- ment has shown us. We have seen that 2 volumes of hydro- gen, in combining with 1 volume of oxygen, yield 2 volumes of vapor of water. One molecule of water in the gaseous state, then, occupies 2 volumes, if 1 atom of hydrogen occupy 1 volume, and if 1 atom of oxygen occupy 1 volume. It is seen that the volumes represent the atoms, and the relative weights of equal volumes, that is, the densities, represent the weights of the atoms. Let us now consider another compound gas, — ammonia, — composed of hydrogen and nitrogen. A very simple experi- ment will show in what proportion the atoms of these elements are combined in this gas, and the volume occupied by the compound compared with the volumes of its component gases. Experiment. — 100 volumes of ammonia gas are introduced into a tube inverted upon the mercury-trough (Fig. 7), and the walls of which are pierced at the upper end by two plati- num wires, between the ends of which a small space is left. To these wires are attached the extremities of the two con- ducting wires of a RuhmkoriF coil, and the current is passed so that a series of electric sparks traverses the ammonia between the extremities of the wires in the tube. The gas is imme- diately decomposed, and the level of the mercury in the tube 4* 42 ELEMENTS OF MODERN CHEMISTRY. is depressed. When the experiment has terminated it is found that the vohime of the gas has been doubled. Instead of 100 volumes, there are now 200, the gas being measured under the same conditions of temperature and pressure as before. It is found, by an analytical process that will be indicated further on, that these 200 volumes of gas resulting from the decompo- FiG. 7. sition of 100 volumes of ammonia are composed of 150 vol- umes of hydrogen and 50 volumes of nitrogen. These 150 volumes of hydrogen and 50 volumes of nitrogen are condensed by their union into 100 volumes of ammonia. In other words, 3 volumes of hydrogen and 1 volume of nitrogen are combined together in 2 volumes of ammonia. And as the volumes rep- resent atoms, it follows that in ammonia gas 3 atoms of hydro- gen are combined with 1 atom of nitrogen. But the quantity of ammonia containing 1 atom of nitrogen and 3 atoms of hydro- gen is the smallest quantity of ammonia that can exist. It is a molecule of ammonia, and this molecule occupies 2 volumes, if 1 atom of nitrogen or 1 atom of hydrogen occupy 1 volume. Here, then, is another compound gas, — ammonia, — of which the molecule occupies 2 volumes, like that of water. It is the same with all the gases. All of the atoms which are combined to constitute the molecule of a gas or vapor are so condensed that the molecule occupies the same volume as the molecule of hydrogen, of vapor of water, or of ammonia. We may state, then, with the Italian chemist, Avogadro, that equal volumes of gases contain the same number of mole- cules^ and that each of these molecules occupies 2 volumes, if 1 atom of hydrogen occupy 1 volume. It follows that the weight of 2 volumes of any gas, whether elementary or com- pound, represents the weight of its molecule, the weight of GAY-LUSSAC'S LAWS.— ATOMIC THEORY. 43 one volume of hydrogen being 1. But the weight of 2 vol- umes of a gas or vapor is twice its density compared to hy- drogen, for the density is the weight of 1 volume compared with the weight of 1 volume of hydrogen. To find the weight of the molecule (the weight of 2 volumes) of a gas or vapor, it is then only necessary to multiply its density compared to hydrogen (the weight of 1 volume) by 2. The densities of gases and vapors are generally referred to air as unity. To bring them to the hydrogen standard, they are multiplied by the number expressing the relation of the density of hydrogen to that of air, which is -Q.-^^-g-g- = 14.388. The product thus obtained expresses the density compared to hydrogen, that is, the weight of 1 volume. To find the weight of 2 volumes, or the molecular weight, it is then only necessary to multiply the densities compared to air by twice the ratio of the density of the air compared to hydrogen, that is, by the constant factor, — _l 2_ _ ^ ^ 0.0695 — 0.0695 " 28.776. It is seen that if the atomic weights of certain gases can be deduced from a comparison of their densities, this same physi- cal notion may also serve for the determination of the molecu- lar weights of compound gases. The numbers which represent double the densities of gases or vapors compared to hydrogen, express also the molecular weights of these gases or vapors, that is, the sum of the weights of all the atoms in the molecule, the weight of one atom of hydrogen being 1. Considering the examples already given, we may deduce the molecular weights of water and of ammonia from the densities of steam and ammonia gas. The density of vapor of water, determined by Gray-Lussac is 0.6235. To find the molecular weight of water, it is suffi- cient to multiply this figure by 28.776. The product, 17.9, expresses the weight of a molecule of water, which is indeed composed of 2 atoms of hydrogen =2 1 atom of oxygen = 15.9 1 molecule of water z= 17.9 Sir Humphry Davy found for the density of ammonia the 44 ELEMENTS OP MODERN CHEMISTRY. number 0.5901. This being multiplied by 28.776, the prod- uct, 16.98, should represent the weight of one molecule of ammonia. Ammonia contains 3 atoms of hydrogen 3 1 atom of nitrogen ........ 14 1 molecule of ammonia 17 The discovery of the laws which govern the combination of gases by volume has seconded in the most efficacious manner the progress of the atomic theory. In the first place, it has established a marked distinction be- tween the old idea of equivalents and the modern one of atoms. The equivalents represented merely the ponderable proportions according to which bodies combine ; the atomic weights repre- sent the relative weights of the volumes of gases which com- bine. The equivalent of hydrogen — unity — expressed merely that hydrogen was the unit to which were referred the weights of other bodies with which it entered into combination. The atomic weight of hydrogen is the weight of one volume of hydrogen, taken as unity, and to this unit are referred the atomic weights of other bodies. In the second place, the discovery of Gay-Lussac has shown how the atomic weights of simple bodies and the molecular weights of compound bodies can be deduced from the densi- ties of gases and vapors. However, this resource would be insufficient in very many cases. It only applies to gaseous bodies, or such as can be con- verted into vapor without decomposition. Now, there are many substances with which this is impossible, and serious difficul- ties would be encountered in the determination of the atomic weights of certain elements were it not for another physical law, discovered by two French physicists, Dulong and Petit. It denotes the relations which exist between the specific heats and the atomic weights. LAW OF SPECIFIC HEATS. It is known that in order to raise the temperatures of differ- ent bodies through the same number of thermometric degrees very different amounts of heat are required. Thus, one kilo- gramme of water requires 30 times more heat than one kilo- gramme of mercury to raise its temperature one degree, and if the quantity of heat required to raise the temperature of LAW OF SPECIFIC HEATS. 45 one kilogramme of water one degree be represented by 1, tbe quantity required to raise the same weight of mercury one degree will be represented by 0.0333 = ■^. This fraction ex- presses the specific heat of mercury between and 100°. The specific heat of a solid or liquid body is then the amount of heat required to raise the temperature of a certain weight of the body one degree, the amount required to raise the tempera- ture of an equal weight of water one degree being taken as unity. In 1820, Dulong and Petit discovered the remarkable fact that if the figures which express the atomic weights of the elements, liquid or solid, be multiplied by those which express their specific heats, the product obtained is sensibly constant ; in other words, the specific heats of the elements are inversely as their atomic weights. It follows that if such quantities of the elements be taken as represent their atomic weights, the amount of heat required to raise the temperature of each one degree will be sensibly the same. The law discovered by Du- long and Petit may then be expressed, — the atoms of the solid elements possess sensibly the same specific heats. This law permits the deduction of the atomic weights from the specific heats. Indeed, it is evident that if the product of the specific heats by the atomic weights be a constant, that may be called the atomic heat.^ dividing this product by the specific heat should give the atomic weight. The product which represents the atomic heat is approximately 6.4, as may be seen from the followinoj table : Names of the Solid Elements. Specific Heats. Atomic Weights. Products of the Specific Heats by the Atomic Weights. Atomic Heats. Sulphur, between and 100° . . Selenium 0.2026 0.0762 32 79.5 127 80 127 31 75 12 n 28 39.1 6.483 6.058 6.023 6.744 6.873 5.850 6.105 5.52 5.5 5.66 6.500 0.0474 Bromine, between — 78 and — 20° Iodine, between and 100° . . Phosphorus, between -\- 1 and 30° Arsenic 0.0843 0.0541 0.1887 0814 Carbon, diamond, at 600° . . . Boron, crystallized, at 600° . . Silicon, at 1000° 0.46 0.5 0.202 0.1695 46 ELEMENTS OF MODERN CHEMISTRY. TABL^.— Continued. Names of the Solid Elements. Sodium, between — 34 and + 7° . Lithium Thallium' Magnesium Aluminium Manganese Iron Zinc Cadmium Cobalt Nickel Tungsten Molybdenum Lead Bismuth Copper Antimony Tin Mercury, between — 77.5 and — 44° Silver Gold .......... Platinum Palladium Osmium Rhodium Iridium Specific Heats. 0.2934 0.9408 0.03355 0.2499 0.2143 0.1217 0.0110 0.09555 0.05669 0.1068 0.1089 0.0334 0.0722 0.0314 0.0308 0.09515 0.06077 0.05623 0.03247 0.05701 0.0324 0.03293 0.0693 0.031 0.05803 0.03259 Products of the Atomic Specific Heats 'Woi crVi ta by the Atomic Weights. Atomic Heats. 23 6.748 7 > 6.586 204 6.844 24 5.998 27 5.786 65 6.693 56 6.116 66.2 6.230 112 6.349 59 6.301 69 6.424 184 6.146 96 6.931 207 6.499 210 6.468 63.5 6.042 120 6.092 118 6.635 200 6.494 108 6.167 197 6.383 195 6.421 106.5 6.316 191 5.921 104.4 6.058 193 6.291 Carbon, silicon, and boron have long been regarded as ex- ceptions to Dulong and Petit's law. Their specific heats had been determined at comparatively low temperatures, and the products of the numbers obtained by the atomic weights fell much below 6.4. These exceptions have disappeared ; the ex- periments of Weber have shown that the specific heats of carbon, silicon, and boron increase with the temperature, and that for the first two elements they attain limits, where they remain sensibly constant. The figures given in the preceding table for these three elements are those of Weber, and it is seen that on multiplying them by the respective atomic weights of carbon, silicon, and boron, values are obtained which ap- proximate 6.4. It will otherwise be remarked that there are sensible differ- ISOMORPHISM. — CHEMICAL NOMENCLATURE, ETC. 47 ences between the numbers expressing tli« atomic beats of tbe various solid elements, showing that Dulong and Petit's law, although true in its generality and striking in its enunciation, is not free from certain perturbations which give to it the character of an approximate law. It is the same with other physical laws, Mariotte's law, for example. ISOMORPHISM. While considering the atomic theory and the determination of the relative weights of the ultimate particles of bodies, we cannot pass in silence a discovery which has had a great influ- ence upon the development of that theory. It is due to E. Mitscherlich, who, in 1819, made known the law of isomor- phism. This law may be thus stated : there is such a relation between the atomic constitutions of compound bodies belonging to the same group and their crystalline form, that " the same number of atoms combined in the same manner produce the same crystalline form, the latter being independent of the chemical nature of the atoms, and determined solely by their number and arrangement." While this proposition is not strictly true, it has rendered important aid in the study of atomic structure of bodies. We will reconsider it when treating of the general characteristics of salts, but we may remark here that it has been of great value in the determination of certain atomic weights. Indeed, in some cases considerations of a chemical nature cannot decide between two numbers for the atomic weight of a given element. The choice is then deter- mined by the following considerations : such a value must be attributed to the atomic weight that the isomorphous com- pounds formed by the element, and by another to which it is analogous, may be represented by similar atomic formula. The methods employed for the determination of the molec- ular weights of such bodies as cannot be vaporized without de- composition will be described under " Organic Chemistry" (page 442). CHEMICAL NOMENCLATURE AND NOTATION. General Considerations. — Nearly eighty substances are known which have not been resolved into simpler forms of matter, and are consequently considered as simple bodies or elements. By combining together, they form an innumerable multitude of com,pound bodies containing two or more elements. 48 ELEMENTS OF MODERN CHEMISTRY. In order to distinguisli these bodies from each other it is neceS' sary to give a name to each, for each constitutes a distinct sub- stance. The names of the simple bodies have been chosen at will, and in some cases recall some peculiar property of the sub- stances designated. It was formerly the same with compound bodies ; there was no definite rule for their nomenclature. From this there resulted a great complication of words which erabarrassed the exposition of ideas, and often for the same sub- stance there were a number of synonyms, of which the least inconvenience was to uselessly fatigue the memory. Hence chemists have felt the necessity of a regular nomenclature, applicable to compound bodies, and capable of indicating their composition. Such is the principle of the chemical nomen- clature suggested by Guyton de Morveau, and developed by Lavoisier, Berthollet, and Fourcroy. This nomenclature, with some modifications, introduced by the progress of the science, is still adopted. Independently of this language, the rules of which will presently be detailed, chemists have adopted a written nota- tion which expresses in concise form the atomic constitution of compounds. The name of each element is represented by a symbol, which also expresses one atom of the substance. This symbol is the initial letter of the name of the element, or the initial letter with another when the names of two ele- ments begin with the same letter. Thus, H represents one atom of hydrogen weighing 1 ; represents one atom of oxygen weighing 16. By combining these symbols together, it is easy to represent in a precise manner the atomic compo- sition of compound bodies. From such combinations result chemical formulas, the use of which was introduced into the science by Berzelius. In the following table will be seen the names of the ele- ments now known, together with their atomic weights, and the symbols by which the atoms of the elements are represented in the notation. The greater number of the elements possess certain physi- cal properties which characterize them as metals. They are opaque, and possess a peculiar lustre, which does not disappear under the burnisher. They are good conductors of heat and electricity. Other elements, fewer in number, do not possess these prop- CHEMICAL NOMENCLATURE AND NOTATION. 49 Names of the Ele- ments. Aluminium . . . Antimony (stibium] Argon . Arsenic Barium Bismuth Boron . Bromine Cadmium Ca3sium Calcium Carbon Cerium Chlorine . Chromium Cobalt . Copper Erbium Fluorine Gadolinium . Gallium . . Germanium . . Glucinum (beryl Hum) . . Gold (aurum) Helium . . Hydrogen Indium . . Iodine . . . Iridium . . Iron (ferrum) Krypton . . Lanthanum . Lead (plumbum Lithium . . Magnesium . Manganese . Mercury (hyd gyrum) Metargon Molybdenum m o » 5 i-a 1- ^l Al 26.9 Sb 119.5 A 40(?) As 74.46 Ba 136.4 Bi 206.5 B 10.9 Br 79.34 Cd 111.55 Cs 131.9 Ca 39.8 C 11.9 Ce 138.0 CI 35.18 Cr 51.7 Co 51.7 Cu 63.1 Er 164.7 F 18.9 Gd 156 (?) Ga 69.5 Ge 71.9 Gl 9.01 Au 195.7 He 4(?) H 1 In 113.1 I 125.89 Ir 191.7 Fe 55.6 Kr 80(?) La 137.6 Pb 205.36 Li 6.97 Mg 24.1 Mn 54.6 Hg 198.5 A^t 40(?) Mo 95.3 Names of the Ele- ments. Neodymium . . . Neon Nickel Niobium (colum- bium) Nitrogen , . . . Osmium Oxygen Palladium . . . . Phosphorus . . . Platinum . . . . Potassium (kalium) Praseodymium . . Radium Rhodium . . . . Rubidium . . . . Ruthenium . . . Samarium . . . . Scandium . . . . Selenium Silicon Silver (argentum) . Sodium (natrium) . Strontium . . . . Sulphur Tantalum .... Tellurium .... Thallium Thorium Thulium Tin (stannum) . . Titanium .... Tungsten (wolfra- mium) Uranium Vanadium .... Xenon Ytterbium .... Yttrium Zinc Zirconium .... Nd Ne Ni Nb N Os Pd P Pt K Pr Ra Rh Rb Ru Sa Sc Se Si Ag Na Sr S Ta Te Tl Th Tu Sn Ti W U V X Yb Y Zn Zr 2*2 142.5 22(?) 58.25 93.03 13.93 189.6 15.88 106.2 30.76 193.4 38.82 139.4 (?) 102.2 84.75 100.9 149.2 43.8 78.6 28.2 107.11 22.88 86.95 31.83 181.5 126.5 202.61 230.8 169.4 118.1 47.8 182.6 237.8 51 128 (?) 171.9 88.3 64.9 90.6 erties. They are known as the non-metals, or metalloids, and include ARGON. CHLORINE. IODINE. NITROGEN. SILICON. ARSENIC. FLUORINE. KRYPTON. OXYGEN. SULPHUR. BORON. HELIUM. METARGON. PHOSPHORUS. TELLURIUM BROMINE. HYDROGEN. NEON. SELENIUM. XENON. CARBON. C d 5 50 ELEMENTS OF MODERN CHEMISTRY. It is impossible, however, to separate the metals from the non-metals by an exact line of demarcation. Nomenclature of Compound Bodies. — The principle of chemical nomenclature is to indicate the composition of com- pound bodies by their names. Among such compounds the most numerous and the most important are those containing oxygen. They are binary or ternary ; that is, the oxygen in them is combined with one or two other elements. Binary Oxygen Compounds. — We will first consider the more simple oxidized bodies, those which result from the com- bination of oxygen with but one other element, metallic or non-metallic. These compounds are called oxides, and diifer as the element associated with the oxygen is metallic or non- metallic. In combining with non-metallic elements, oxygen generally forms compounds which are the anhydrides of acids, that is, compounds capable of uniting with water to form acids ; with the metals it forms metallic oxides. Experiments. — 1. A small piece of phosphorus is placed in a capsule floating on the surface of mercury. It is ignited and the capsule covered with a bell-jar (Fig. 8). The phos- phorus burns, giving off a thick smoke, which condenses in white flakes on the sides of the bell-jar. This substance re- sults from the combination of the phosphorus with the oxygen of the air : it is phosphorus pentoxide^ oi phosphoric anhydride. CHEMICAL NOMENCLATURE AND NOTATION. 51 2. If lead be heated in the air and maintained for some time in a state of fusion, its brilliant surface becomes tarnished and covered with grayish particles, which are finally converted into a yellow powder. This body is formed by the combina- tion of the lead with oxygen : it is plumbic oxide, or oxide of lead. But, as we have seen, such combination can take place in different proportions. An atom of a body may unite with 1, 2, 3, or more atoms of oxygen, and the names of the com- pounds so formed should indicate the degree of oxidation. Sulphur forms two compounds with oxygen : one contains 2 atoms of oxygen to 1 atom of sulphur ; the other, 3 atoms of oxygen to 1 of sulphur. They are designated by the names sulpliuro? HYPOCHLOROUS ACID. 133 HYPOCHLOROUS ACID. HCIO This acid lias never been obtained in the pure state. An aqueous solution may be prepared by agitating mercuric oxide with water in jars filled witb chlorine gas. The water will tben contain hypochilorous acid and mercuric chloride, and tbere remains a brown powder, wMcb is mercury oxy- chloride. (Balard.) 2HgO + ffO + 2CP = HgO.HgCP + 2HC10 Another method consists in passing chlorine through water holding recently-precipitated calcium carbonate in suspension. The latter disappears, carbonic acid gas is disengaged, and the water becomes charged with calcium chloride and hypochlorous acid. The mixture is distilled, and the acid which passes with the water is condensed in a cooled receiver (Williamson). CaCO^ + 2CP + H^O = CO^ + CaCP + 2HC10 Calcium Carbon Calcium Hypochlorous carbonate. dioxide. chloride. acid. When chlorine is passed into a rather dilute solution of an alkaline hydrate, a chloride and a hypochlorite are formed : 2K0H + 2C1 = KCl H- KCIO + H^O In this manner are prepared solutions containing potas- sium hypochlorite (eau de Javelle), and sodium hypochlorite (Labarraque's solution), extensively used for bleaching and disinfecting. The most important hypochlorite is the cal- cium salt, Ca(ClO)^ which is the principal constituent of bleaching-powder. Properties of Hypochlorous Acid. — Concentrated hypo- chlorous acid, obtained by distilling the aqueous solution, is a dark-yellow liquid, having the peculiar smell of chlorinated lime or bleaching-powder. It is very caustic and rapidly destroys the skin ; its bleaching power is very energetic, double that of the chlorine it contains. Hydrochloric acid decomposes it into chlorine and water. HCIO -f- HCl = CP -f H^O Hypochlorous acid is very unstable except in dilute solu- tions. It decomposes spontaneously into oxygen and hydro- chloric acid. 2HC10 = 2HC1 + 0' 134 ELEMENTS OF MODERN CHEMISTRY. Fig. 47. CHLORINE PEROXIDE. C102 This compound, which was discovered by Sir Humphry Davy, is prepared by the ac- tion of concentrated sulphuric acid upon fused potassium chlorate. The salt is finely pulverized and added in small quantities to sulphuric acid cooled to —10°. The pasty mass is then introduced into a small test-tube fitted with a delivery-tube (Fig. 47), and is gently heated in a water- bath ; the gas disengaged is collected in dry jars by down- ward displacement. 3KC10^ + 2H2SO* = KCIO^ + 2KHS0* + H'^O + 2C10' Potassium Potassium Potassium acid chlorate. perchlorate. sulphate. Chlorine peroxide is a yellow gas having a strong irritating odor. When strongly cooled, it condenses to a dark-red liquid, which boils at 9°, and solidifies at — 79°. Compared to hydrogen, the density of the gas is 33.47 ; hence the mo- lecular weight is 66.94, corresponding to the formula CIO'''. A mixture of this gas with chlorine is disengaged when hydrochloric acid is heated with potassium chlorate. This mixture is called euchloriney and was formerly believed to be a definite compound. 4KC10' + 12HC1 ^ 4KC1 + eH^O + 3C10^ + 9C1 Chlorine peroxide is a dangerous body ; it sometimes decom- poses spontaneously with violent explosions. It is soluble in water, and the solution may be prepared by passing into water the mixture of carbonic acid gas and chlorine peroxide which is evolved when potassium chlorate is heated on a water-bath with an equal quantity of oxalic acid. It acts as a powerful oxidizing agent. A jet of hydrogen sulphide passed into it takes fire spontaneously and continues to burn, and on contact with it sugar and other organic com- CHLORIC ACID — PERCHLORIC ACID. 135 pounds are inflamed. If a drop of sulphuric acid be allowed to fall on a mixture of equal parts of sugar and potassium chlorate, both in powder, the chlorine peroxide disengaged at once ignites the sugar in contact with it, and the potassium chlorate yields its oxygen for the rapid combustion of the entire ma&s. Chlorine peroxide is absorbed by alkaline solutions with the formation of a chlorate and a chlorite. 2K0H -J- CW = KCIO^ -f KCIO- -f- H^O Pota&sium hydroxide. Potassium chlorate. Potassium chlorite. Potassium chlorite is a salt of chlorous acid which has never been isolated. CHLOEIC ACID. HC103 This acid is formed by the spontaneous decomposition of solutions of hypochlorous acid and chlorine peroxide. It may be prepared by treating barium chlorate with dilute sulphuric acid. Barium sulphate precipitates, and is removed by filtration, and the solution of chloric acid is concentrated by evaporation in vacuo. If chlorine be passed into a concentrated solution of an alkaline hydrate, a chloride and a chlorate are formed. 6K0H + 6C1 = 5KC1 -f KCIO^ - SH^O Chloric acid is a syrupy liquid, ordinarily of a yeUow color ; it is not very stable ; at a temperature of -40 "^ it commences to decompose, and at a higher temperature it is resolved into per- chloric acid, chlorine, oxygen, and water. It has extremely energetic oxidizing properties ; when concentrated, it at once inflames sulphui\ phosphonis. alcohol, and paper. It oxidizes sulphurous and phosphorous acids and hydrogen sulphide. With hydrochloric acid it forms water and chlorine. HCIO^ — 5HC1 = 3H-0 -f 3CT PERCHLOPJC ACID. HCIO* This is the most rich in oxygen of all the chlorine acids, and it is a curious circumstance that it is also the most stable. It may be prepared by distilling potassium perchlorate with concentrated sulphuric acid. When a mixture of one part of the former with four parts of the latter is heated to 110°, pure perchloric acid distils over first ; but if the distillation 136 ELEMENTS OF MODERN CHEMISTRY. be continued, the liquid in the receiver is gradually converted into the crystalline monohydrate, HCIO* + H^O. The pure anhydrous acid may be prepared by carefully redistilling this hydrate at a temperature of 110°, part of the acid remaining in the retort as the dihydrate, 2HC10* + 2H'0, which boils at 203°. Perchloric acid is a colorless, volatile liquid having a den- sity of 1.782 at 15.5°. When strongly cooled, it solidifies to a crystalline mass which melts at 15°. It is extremely hygro- scopic : absorbing moisture from the air, it emits dense fumes of the hydrate. Its contact with water is attended by a hiss- ing noise and a great evolution of heat. Its oxidizing powers are so energetic that it explodes on contact with paper, wood, or charcoal. Pure perchloric acid cannot be preserved or distilled : it suffers spontaneous decomposition even in the dark, and ex- plodes with much violence when it is heated. The salts of perchloric acid are very stable compounds. Unlike the chlorates, they are not reduced when heated with hydrochloric acid. Potassium perchlorate, KCIO*, is almost insoluble in water. CHLORIDES OF SULPHUR. When a current of dry chlorine is passed over sulphur heated in a retort, a liquid condenses in the receiver which fumes in the air, has a yellow color, and an irritating, fetid odor. This is sulphurous cliloride^ S^CP. In order that this compound may be formed, the sulphur must be maintained in excess, and the operation must be stopped before it has all disappeared. The product is purified by rectification, that part being collected which passes at 139°. When chlorine is passed for several hours through the chloride of sulphur just described, the yellow color of the latter changes to deep red. The liquid obtained is mobile, fumes in the air, and continually disengages chlorine. It can- not be distilled without decomposition. The product which passes is at first red, but afterwards assumes a lighter color, and when the temperature reaches 139° there remains in the retort only sulphurous chloride, S^CP. The red liquid has a composition which corresponds to the formula SCP, It is called perchloride of sulphur. Carius BROMINE. 137 regards it as a mixture of tlie chloride S^CP with a tetra- chloride, SCI*, corresponding to sulphur dioxide. SO^ sulphur dioxide. SCP sulphur tetrachloride. This tetrachloride has been prepared by Michaelis, but it can only exist at a low temperature ; it decomposes into chlorine and sulphurous chloride, S^CP, as soon as it is removed from the freezing mixture where it has been condensed. The chlorides of sulphur are employed in vulcanizing caoutchouc. BROMINE. Vapor density compared to air 5.393 Vapor density compared to hydrogen .... 79.34 Atomic weight Br = 79.34 Bromine was discovered by Balard in 1826. Preparation. — It is obtained by decomposing potassium bromide by manganese dioxide and sulphuric acid. Potassium sulphate and manganese sulphate are formed, and the bromine is liberated. 2KBr + MnO' + 2WS0' = K^SO* + MnSO* + 2^0 + Br* Potassium Manganese Potassium Manganese bromide. dioxide. sulphate. sulphate. The operation is conducted in a tubulated retort, heated on a sand-bath, and the bromine is condensed in a cooled receiver fitted to the retort by the aid of an adapter. The potassium bromide may be replaced by magnesium bromide, which exists in the mother-liquors obtained in the manufacture of potassium chloride from carnallite and also in certain brine springs. The liberation of bromine from this SJ^lt is effected by the action of chlorine, thus — MgBr^ + CP = MgCP + Br^ Properties. — Bromine is a dark-red liquid, which solidifies at —7.3. Its density at 15° is 2.99. It boils at 63°, and at ordinary temperatures gives off red, irritating vapors, for its vapor tension is considerable even in the cold. It stains the skin yellow, and immediately corrodes the tissues. It dissolves in about 33 times its weight of water at 15°, forming an orange- red solution. At a low temperature it combines with water, forming a crystalline hydrate, Br^-j- lOH^O, analogous to that formed by chlorine. •^ 12* 138 ELEMENTS OF MODERN CHEMISTRY. Bromine dissolves in carbon disulphide, in cUoroform, and in ether. Experiment. — A small quantity of solution of potassium bromide is introduced into a long tube, closed at one end, and the tube is then nearly filled with chlorine-water ; when the two solutions are mixed, the liquor assumes an orange-red color from the liberation of the bromine. The tube is now filled up with ether and agitated briskly, the open end being closed with the finger. The ether passes through the aqueous solution and dissolves out all of the bromine, assuming at the same time a dark-red color. The affinity of bromine for hydrogen is powerful, but not as energetic as that of chlorine. Like chlorine, it has remarkable bleaching properties. HYDKOBROMIC ACID. Density compared to air 2.73 Density compared to hydrogen 40.5 Molecular weight HBr = 80.34 Preparation. — This gas is prepared by the action of water upon phosphorus tribromide. PBr' + gajO' = lajO' + 3HBr Phosphorus tribromide. 3 molecules water. Phosphorous acid. The operation may be conveniently conducted in a doubly- curved tube (Fig. 48). Into the long branch CD fragments of phosphorus are introduced, carefully separated from each other by moistened broken glass. The bromine is introduced into the bend A. The shorter end is then corked, a. delivery-tube adapted to the end D, and the bromine is gently heated until it boils. The vapor comes into contact with the phosphorus and forms phosphorus tribromide, but this is at once decomposed by the water into phosphorous acid and hydrobromic acid. The latter may be collected in jars over the mercury-trough. Amorphous phosphorus may be advantageously employed in this operation, and the process conducted as directed for hydri- odic acid (Personne). Another convenient process for preparing the acid depends upon the action of bromine on benzene in the presence of iron bromide. The gas which is disengaged is purified by passing it over ferrous bromide and anthracene. When a mixture of hydrogen and bromine vapor is passed over heated platinum, the elements unite directly. OXYGEN ACIDS OP BROMINE. 139 Properties. — Hydrobromic acid is a colorless gas, producing dense white fumes in the air. A litre of this gas weighs 3.547 grammes. It liquefies at — 73°, and may be solidified at a lower temperature. It is formed by the union of equal volumes of bromine vapor and hydrogen without condensation, so that its composition corresponds to that of hydrochloric acid. It is very soluble in water ; its concentrated solution fumes in the air, and is very corrosive. Chlorine decomposes hydrobromic acid, liberating bromine. Fig. 48. OXYGEN ACIDS OF BROMINE. There are known three bromine oxygen acids : Hypobromous acid, HBrO Bromic acid, HBrO^ Perbromic acid, HBrO* They correspond to hypochlorous, chloric, and perchloric acids. Hypobromous Acid, HBrO. — When mercuric oxide is agitated with an aqueous solution of bromine, a yellowish liquid is obtained which contains hypobromous acid, and can be distilled in vacuo. W. Dancer has obtained this acid by the action of bromine upon silver oxide suspended in water. 2Br^ _|_ Ag^O + H^O = 2AgBr -f- 2HBrO Silver oxide. Silver bromide. In this process it is necessary to operate rapidly and avoid 140 ELEMENTS OF MODERN CHEMISTRY. the contact of an excess of silver oxide with the hypobromous acid, as the latter would be destroyed by the oxide with evolu- tion of oxygen. 2HBrO + Ag^O = 2AgBr + H^O + 0^ The solution of hypobromous acid has a yellow color and bleaching properties analogous to those of hypochlorous acid. Bromie Acid, HBrOl — Potassium bromide and potassium bromate are formed by the action of bromine upon a concen- trated solution of potassium hydroxide. This reaction is simi- lar to that of chlorine upon potash. Kammerer recommends the preparation of bromie acid by the action of chlorine upon bromine in presence of water. 5CP + Br^ -f 6W0 = lOHCl -f 2HBrO' The hydrochloric acid is driven out by evaporation, and bromie acid remains in the form of a liquid that cannot be con- centrated to a syrupy consistence without partial decomposition. Perbromic Acid, HBrO*. — Kammerer has obtained this acid by decomposing perchloric acid with bromine : chlorine is disengaged. After concentration on a water-bath, the per- bromic acid remains as a colorless oily liquid. It is relatively stable, as are the corresponding chlorine and iodine acids. Like them, it resists the reducing action of sulphurous acid and hydrogen sulphide. IODINE. Vapor density compared to air 8.716 Vapor density compared to hydrogen 125.9 Atomic weight I = 125.9 Iodine was discovered by Courtois in 1811, and was studied by G-ay-Lussac in 1813 and 1814. Natural State. — Iodine is widely disseminated in nature. It is found in the mineral kingdom combined with various metals, such as potassium, sodium, calcium, magnesium, silver, mercury. The alkaline iodides exist in small quantity in sea- water, in a great number of salt-springs, and in certain rock- salts. The sodium nitrate found native in Chili contains traces of sodium iodate, and the mother-liquors from which the nitrate has been deposited contain enough iodate to be profitably employed for the preparation of iodine. The ashes of certain IODINE. 141 sea-plants, such as the algae and fuci, are among the chief sources of iodine. Preparation. — The ashes of sea-weeds, called kelp, are ex- hausted with water and the solution concentrated. Various salts, such as sodium and potassium sulphates and chlorides and sodium carbonate, are deposited, and the potassium iodide, which is contained in smaller quantity than these salts, remains in the mother-liquor. A regulated current of chlorine is passed into this solution as long as it continues to set free iodine, which is deposited as a pulverulent, black precipitate. An excess of chlorine must be avoided, as this would redissolve a portion of the iodine, forming iodine chloride. Still larger quantities of iodine are obtained from Chili salt- petre : the mother-liquor from the nitrates, which contains all the iodine in the form of iodates, is treated with the exact quantity of sulphur dioxide required for its decomposition. 2NaI0^ 4- 5S0^ + 4H^0 ^ P + 4.WS0' + Na^SO* Impure iodine is precipitated and is refined by sublimation. In the laboratory, iodine is set free from the iodides by the action of nitric acid, a nitrate being formed and red vapors disengaged. Properties of Iodine. — The iodine obtained by sublimation occurs as scales or crystalline plates, having a brilliant, dark bluish-gray surface, and a density of 4.948 at 17°. It may be obtained crystallized in rhombic octahedra by exposing to the air a solution of hydriodic acid. Iodine melts at 107°. It boils at about 175°, but volatiHzes sensibly at ordinary temperatures. Its vapor has an intense violet color. A litre of this vapor weighs 11.32 grammes. Above 700° the density of iodine vapor diminishes, while its color becomes deep blue. At very high temperatures the molecule appears to be dissociated into single atoms. Iodine is but very slightly soluble in water ; one part of iodine requires 7000 parts of water for its solution, but com- municates a light-brown color to the whole of that liquid. Alcohol and ether dissolve iodine freely, forming dark-brown solutions. Carbon disnlphide, benzine, and chloroform also dissolve it, assuming a beautiful violet color. Experiment. — If a few drops of chlorine-water be added to a very dilute solution of potassium iodide, the chlorine will 142 ELEMENTS OF MODERN CHEMISTRY. combine with the potassium, displacing the iodine, which will color the liquid brown ; if now the solution be agitated with a small quantity of chloroform, the latter will take up all of the iodine, assuming a violet color. Iodine strikes an intense blue color with starch. The reac- tion is very delicate and permits the detection of the smallest trace of free iodine. Experiment. — If a few drops of a solution of potassium iodide be added to a solution of starch, no coloration takes place, because the iodine is in combination ; but if a drop or two of chlorine-water be added, the iodine will be set free, and combining with the starch will at once produce the character- istic blue color. An excess of chlorine will again destroy the color. HYDRIODIC ACID. Density compared to air 4.443 Density compared to hydrogen 64.1 Molecular weight HI =126.9 Preparation. — Hydriodic acid is prepared by the action of iodine upon phosphorus in presence of water ; phosphorus triiodide is first formed, and this is decomposed into phos- phorous acid and hydriodic acid. PP + |aj0' = lajO' + Phosphorus 3 molecules Phosphorous triiodide. of water. acid. SHI Amorphous phosphorus in powder is introduced into a glass- stoppered retort the neck of which is soldered to the delivery- tube (Fig. 49), and covered with a layer of water ; the iodine is then added, and on the application of a gentle heat a regular current of hydriodic acid is obtained. The gas may be col- lected, like chlorine, by downward displacement in dry jars. Properties. — Hydriodic acid is a colorless gas producing white fumes in the air. It may be condensed to a colorless liquid by strong pressure or intense cold, and can even be solid- ified. Dry oxygen decomposes it at a high temperature, water being formed and the iodine being set at liberty. If a lighted taper be applied to a mixture of hydriodic acid and oxygen, the violet vapor of the iodine set free is instantly apparent. This decomposition of hydriodic acid by oxygen takes place at ordinary temperatures in the presence of water. A solution HYDRIODIC ACID. 143 of hydriodic acid exposed to tlie air rapidly becomes brown, and after a time deposits crystals of iodine. Solution of bydriodic acid is prepared by passing the gas into water cooled to 0°. It may also be made by passing a current of hydrogen sulphide through water holding iodine in suspen- sion ; hydriodic acid is formed, and sulphur is precipitated, H^S + P = 2HI + S The solution of hydriodic acid saturated at 0° has a density of 2, and fumes in the air. When freshly prepared, it is color- FiG. 49. less ; when heated, it loses part of its gas, and finally distils without further alteration at 126°. The solution then con- tains 57.7 per cent, of hydriodic acid. Chlorine and bromine at once decompose hydriodic acid, combining with the hydrogen and setting free the iodine. The experiment may be made by pouring a few drops of bromine into a jar filled with hydriodic acid gas, when the appearance of a violet vapor immediately indicates the liberation of iodine. Potassium, zinc, iron, mercury, and silver decompose hydri- odic acid, but with unequal energies, setting free the hydrogen. 144 ELEMENTS OP MODERN CHEMISTRY. Sulphuric acid also decomposes it, and is itself reduced to suL phurous oxide. ffSO* + 2HI = 2W0 + so^ + r Nitric acid is still more readily reduced by hydriodic acid. 2HN0^ + 2HI = 2ffO -f 2N0^ + P Nitric acid. Nitrogen peroxide. OXIDE AND OXYGEN ACIDS OF IODINE. The only oxide of iodine known with certainty is the pen- toxide, PO^ It combines with water to form iodic acid, HIO^ or HTO^ There is also a periodic acid, H^IO^ corre- sponding to the unknown heptoxide, PO^ IODIC ACID. H2I206 Iodic acid is formed when iodine is subjected to the action of energetic oxidizing agents, such as concentrated nitric acid or a mixture of nitric acid and potassium chlorate. It is also formed by the action of an excess of chlorine on iodine in presence of water. p _|- 5CP -I- 6H^0 == lOHCl + H^PO« Preparation. — Iodic acid may be conveniently prepared by heating iodine and potassium chlorate with dilute nitric acid. The oxygen of the chlorate oxidizes the iodine to iodic acid, and on adding barium nitrate to the liquid, barium iodate is precipitated. The latter salt is decomposed by sulphuric acid ; iodic acid is set free in the solution, and barium sulphate is precipitated ; the filtered solution is concentrated by evapora- tion in vacuo. Properties. — Iodic acid is solid, and crystallizes in hex- agonal tables. When heated to 170° it loses water and is converted into iodic oxide, and at a red heat the latter is decomposed into iodine and oxygen. It is seen that iodic acid is much more stable than its ana- logue, chloric acid ; nevertheless it is easily reduced by bodies avid of oxygen. If sulphurous acid be added to a solution of iodic acid, a precipitate of iodine is formed instantly, but an excess of sul- phurous acid redissolves the precipitate, part of the water being decomposed and hydriodic and sulphuric acids being formed. PERIODIC ACID. 145 Iodic acid is also decomposed by hydriodic acid. If a solu- tion of iodic acid be poured into a solution of starch, no color- ation appears, but the characteristic blue color is at once developed on adding a drop of hydriodic acid. HTO« -f lOHI = GH^O -f 6P PERIODIC ACID. H5I06 = IO(OH)5 This acid has been obtained from disodic periodate, a salt which is precipitated when chlorine is passed through a solu- tion of sodium iodate mixed with sodium hydroxide. Na^PO^ -f 6NaOH + 2CP = 2Na2H^IO« + 4NaCl Sodium iodate. Sodium hydroxide. Disodic periodate. Sodium chloride. The precipitate is dissolved in nitric acid, and lead nitrate is added to the solution ; lead periodate is precipitated, and this salt is exactly decomposed by sulphuric acid ; the liquid is fil- tered to separate the lead sulphate, and evaporated at a gentle heat. Periodic acid crystallizes out in colorless, deliquescent, rhombic prisms. It melts at 133°. When heated to 140°, it is decomposed into iodine pentoxide, water, and oxygen. 2W10' = PO^ -f 5H^0 + 0' Between 180 and 190° periodic oxide abandons oxygen, and is converted into iodic oxide, PO^. Analogy between Chlorine, Bromine, and Iodine. — Chlorine, bromine, and iodine present a striking analogy in their chemical properties, and this analogy is seen in all of their com- pounds. They combine with hydrogen, atom for atom, forming the acids HCl, HBr, HI, and the atoms of chlorine, bromine, and iodine are equivalent to each othei- and to an atom of hydrogen ; each of these elements is monatomic. Their affinities for hydrogen are far from being equal ; in this respect chlorine is more powerful than bromine, and bromine than iodine. The contrary has been noticed regarding their affinities for oxygen, for the oxygen acids of iodine are more stable than those of chlorine. The analogy between these three elements is followed out in the constitution of their oxides and acids, and in their combinations with the metals. The chlorides, iodides, and bromides possess in general the same constitution, and it is to be remarked that the greater num- ber of these binary compounds are soluble in water and are crystal- lizable like salts, of which they otherwise present the characters. Hence the name halogen bodies, which was applied by Berzelius to this group of elements, to indicate that they form salts in combining with the metals. G ^ 13 146 ELEMENTS OF MODERN CHEMISTRt. FLUORINE. F = 19 Fluorine "belongs to ttie group of elements just considered, but its chemical energy is much greater than that of chlorine. It occurs chiefly in combination with calcium, and also with aluminium and sodium, forming the minerals fiuor spar, CaF^, and cryolite, AlF3.3NaP. It was first isolated by Mois- san, who obtained it by the electrolysis of an- hydrous hydrofluoric acid in which hydrogen potassium fluoride was dissolved in order to give the necessary elec- trical conductivity. The decomposition was ef- fected in a U-shaped tube of platinum (Fig. 50) , each limb of which was provided with a side tube, and closed with a fluor spar stop- per carrying and insu- lating the platinum electrodes. To prevent the escape of hydro- fluoric acid, this appa- ratus was cooled to — 40° by the rapid evaporation of methyl chloride surrounding it. A battery of 20 Bunsen cells furnished the current. The affinities of fluorine are so energetic that it cannot be collected like other gases. It acts violently upon water, and readily combines with mercury, but may be received by dry displacement in platinum vessels. Fluorine has a greenish-yellow color and a powerful odor. Its density is 1.26. At — 187° the gas condenses to a yellow liquid. Fluorine combines with hydrogen even in the dark, and with explosive violence. Arsenic, antimony, sulphur, phosphorus, and silicon ignite spontaneously in the gas, and all the metals combine with it directly and, with few exceptions, at ordinary temperatures. Chlorine is displaced by fluorine in most of its compounds. Hydro- fluoric acid and ozone result from its action upon water. Organic compounds, such as alcohol, benzene, turpentine, and even cork, are violently attacked and inflamed by it. Fluorine does not combine with oxygen or argon. HYDROFLUORIC ACID. 147 HYDROFLUORIC ACID. Molecular weiarht HF 20 This compound is prepared by decomposing powdered cal- cium fluoride with sulphuric acid. CaF=^ + H^SO* = CaSO^ + 2HF Calcium fluoride. Calcium sulphate. The operation is conducted in a leaden retort, to which is adapted a receiver of the same metal surrounded by a freezing mixture (Fig. 51). The hydrofluoric acid condenses as a very acid liquid, which fumes strong- ly in the air. Its density is 1.06. In this state it still re- tains water ; but Fremy obtained it ^ anhydrous by de- ^j composing dry hy- ^^^^^^^p^ drogen potassium double fluoride KF, Fig. 51. HF, by heat in a platinum retort. This salt breaks up into potassium fluoride, which remains, and hydrofluoric acid, which is disengaged and must be condensed in a platinum receiver cooled to — 20°. Pure hydrofluoric acid is liquid at ordinary temperatures ; it is very mobile, it freezes at — 92.3° and boils at 19.4°. It is extremely corrosive, and manipulations with it should be con- ducted with great care. Its afiinity for water is so great that each drop of the acid let fall into that liquid produces a hissing noise, as would a red-hot iron. The solution is employed for etching upon glass, for hydrofluoric acid attacks and corrodes that substance. This efl'ect is due to the action of the acid upon the silica of the glass, which it converts into either sili- con fluoride or hydrofluosilicic acid, as will be seen farther on. A design may readily be engraved on glass by covering the glass with a thin coating of wax, through which the design is traced with a sharp point ; the glass is then placed over a leaden capsule containing a mixture of powdered calcium fluoride and 148 ELEMENTS OF MODERN CHEMISTRY. strong sulphuric acid, which is gently heated by a spirit-lamp. Hydrofluoric acid vapor is disengaged and attacks the glass wherever it is not protected by the wax. When the wax is re- moved, the design is found to be permanently etched on the glass. A dilute solution of hydrofluoric acid or a bath of hydro- fluoride of potassium fluoride may be employed instead of tbe vapor in the former experiment, but in this case the etched portions are transparent and not opaque as when produced by the vapor ; they may be rendered opaque by adding a salt, such as potassium or ammonium sulphate, to the bath. NITROGEN. Density compared to air 0.969 Density compared to hydrogen 13.93 Atomic weight N = 13.93 Nitrogen was discovered by Eutherford in 17V2. It is one of the elements of the air, and was first obtained free from oxygen by Lavoisier and Scheele, in 1777. Preparation. — A flat piece of cork, B (Fig. 52), floating in the pneumatic-trough, supports a small capsule containing a fragment of phosphorus. The latter is inflamed, and the capsule immedi- ately covered with a bell-jar. The heat produced by the combustion at first expands the air and drives out a portion, but in a few minutes the water rises in the jar, taking the place of the oxygen which has been consumed. When the phosphorus is extinguished, the experiment has ter- minated. The water gradually dis- solves the white smoke of phosphoric oxide which fills the jar, and there remains a colorless, irrespirable gas that will not support combustion. This gas is nitrogen, still mixed with argon, traces of oxygen, and carbonic acid gas. Nitrogen containing no impurity except argon may be ob- tained by passing a current of air, previously freed from moisture and carbon dioxide, through a porcelain tube containing incan- descent copper. The copper absorbs the oxygen, and nitrogen Fig. 52. AMMONIA. 149 passes out at the end of the tube and may be collected over the pneumatic trough. Pure nitrogen is best obtained by heating a strong solution of ammonium nitrite ] the products are nitrogen and water. (NH4)N0' = 2H^0 -f N^ Ammonium nitrite. Properties. — Nitrogen is a colorless gas, somewhat lighter than the air. A litre of this gas weighs 1.2505 grammes. It extinguishes burning bodies, and is not combustible itself ; it produces no precipitate in lime-water. Water dissolves only -^ of its volume of nitrogen at 0°. Animals are quickly suffo- cated in an atmosphere of pure nitrogen, but the gas does not exert a poisonous influence upon the economy. It can be liquefied at temperatures below — 146° (its critical temperature). Its critical pressure is 35 atmospheres. Under a pressure of one atmosphere this liquid boils at — 190°. The affinities of nitrogen are not energetic. It combines directly with only a very small number of elements, among which may be mentioned magnesium, silicon, boron, and titanium. Under the influence of electrical discharges it will unite with oxygen, form- ing nitrogen peroxide, and with hydrogen, forming ammonia. There are at present known three compounds of nitrogen and hydrogen, — ammonia, NH^, hydrazine, N^H*, and hydra- zoic acid, N^H. AMMONIA. Density compared to air 0.596 Density compared to hydrogen 8.60 Molecular weight NH^ = 16.93 Ammonia was discovered by Priestley, studied by Scheele, and analyzed by Berthollet in 1785. Preparation. — Equal weights of quick-lime and sal am- moniac, both in powder, are rapidly mixed in a mortar, and the mixture introduced into a glass flask, which is then filled up with fragments of quick-lime. A cork and delivery-tube are adapted to the flask, which is then gently heated and the gas disengaged collected over mercury. The calcium oxide or lime decomposes the ammonium chloride (sal ammoniac), with the formation of calcium chloride, ammonia gas, and water; the latter is absorbed by the fragments of lime which fill up the flask. 2NH^C1 -f CaO = 2NH^ + CaCP + H^O Ammonium chloride. Calcium oxide. Ammonia. Calcium chloride. 13* 150 ELEMENTS OF MODERN CHEMISTRY. A solution of ammonia in water may be prepared by passing the gas tbrougb a series of Wolff's bottles, about balf filled with water, excepting the first, which should only contain a small quantity destined to wash the gas. Physical Properties. — Ammonia is a colorless gas, having a powerful and pungent odor, which excites tears. Its taste is burning and caustic. It may be. liquefied by a temperature of — 40°, or at 10° under a pressure of 6i atmospheres. Fara- day's method of liquefying it is as follows : ammonia is passed over dry silver chloride, by which it is absorbed. The silver chloride, saturated with ammonia, is introduced into a bent tube (Fig. 53), the empty limb of which is then sealed at the Fig. 63. Fig. 54. blow-pipe. The end containing the chloride is now heated in a water-bath, while the empty end is cooled in a freezing mix- ture (Fig. 54). The ammonia is driven out from the silver chloride, and condenses into a transparent liquid in the cooler branch. Faraday succeeded in solidifying ammonia by subject- ing this liquid to rapid evaporation. In the solid state it is a white, crystalline, transparent substance, fusible at — 75°, and having only a feeble odor. According to Bunsen, liquid am- monia boils at — 33.7° ; its density at 0° is 0.6233. Ammonia gas is very soluble in water, which dissolves 1000 times its volume at 0°, and about 740 times its volume at 15°. The rapid absorption of ammonia by water may be strik- ingly shown by the following experiment. A bottle, A (Fig. 55) , is filled with ammonia gas, and fitted with a cork, through which passes a tube drawn out at both extremities, and the outer end of which is sealed. If this end be plunged under water and the point be broken off, the water at once rises into AMMONIA. 151 the bottle, forming a fountain, and the vessel becomes filled with water in a very short time. The aqueous solution of ammonia possesses the odor of the gas; it is caustic, and was formerly called vol- atile alkali and spirits of hartshorn. It is largely used in the arts and as a reagent. Its density is 0.882 at 15°. When heated, it loses ammonia gas, the whole of which may be driven out by boiling. Composition of Am- monia. — 200 volumes of ammonia gas are in- troduced into an eudi- ometer, and electric sparks are passed through the gas for some time by means of a RuhmkorfF coil (Fig. 56). ^ When the experiment has terminated, the volume of gas will be found to have doubled. 200 volumes of oxygen are added to the 400 volumes of gas thus obtained, and a spark is passed; an explosion takes place, and after making the Fig. 56. necessary corrections for temperature and pressure, the 600 volumes of gas are found to be reduced to 150 volumes ; 450 volumes have thus disappeared to form water, 152 ELEMENTS OF MODERN CHEMISTRY. These 450 volumes must have contained 300 volumes of hydrogen, 150 volumes of oxygen. Consequently the 200 volumes of ammonia gas, which were decomposed by the spark into 400 volumes, must have been formed by the union of 300 volumes of hydrogen, 100 volumes of nitrogen. The latter gas remains in the eudiometer, together with the 50 volumes of oxygen that were employed in excess. From this analysis it is seen that two volumes of ammonia contain three volumes of hydrogen and one volume of nitrogen, a composition which is expressed by the formula NH^. Chemical Properties. — Ammonia gas is decomposed by a high temperature, as by a series of electric sparks. The experi- ment may be made by passing the gas through a porcelain tube filled with fragments of broken porcelain and heated to white- ness, and collecting the gas resulting from the decomposition in vessels filled with water (Fig. 57). This gas is found to be a mixture of three volumes of hydrogen and one volume of nitrogen. The decomposition takes place more readily if iron, copper, or platinum wires be introduced into the porcelain tube. The AMMONIA. 153 Tig. 58. latter metal is not altered, but the iron and copper become brittle and retain a few per cent, of nitrogen. The decompo- sition of the ammonia seems here to be favored by the formation of metallic nitrides, unstable compounds which are almost entirely decomposed by the pro- longed action of the heat. Ammonia will not burn in air, but will burn in an atmosphere of oxygen. A glass tube about 25 millimetres in diameter and 15 centimetres long is fitted with a cork through which pass two bent tubes, one reaching nearly to the open end of the tube, the other only a little beyond the cork (Fig. 58), and some cotton-wool or loose asbestos is thrust into the wide tube beyond this point. Ammonia gas, conven- iently obtained by heating strong am- monia water, is passed through the longer tube, while oxygen gas is delivered through the shorter. The ammonia may then be ignited, and will burn with a yellow flame. 4NH» + 30^ = 6H^0 + 2^\ A mixture of four volumes of ammonia with three of oxygen will explode on the application of flame. Independently of this rapid combustion, ammonia may undergo slow combustion. A spiral of platinum wire is suspended above a little ammonia water in a beaker (A, Fig. 59). The latter is gently heated, and oxygen is passed through the liquid. The mixed ammonia and oxygen gases in contact with the platinum spiral com- bine and develop so much heat that the spiral is heated to redness. The vessel sometimes becomes filled with white fumes of ammonium nitrite, produced by the slow oxidation of the ammonia. If a mixture of oxygen and ammonia be passed through a heated tube containing spongy platinum, nitric acid and water will be formed and disengaged in vapor. Fig. 59. 154 ELEMENTS OF MODERN CHEMISTRY. Action of Chlorine and Iodine upon Ammonia. — Chlorine instantly decomposes ammonia, combining with its hydrogen. If a drawn-out tube through which a jet of ammonia is escaping be plunged into a bottle filled with dry chlorine (Fig. 60), the ammonia takes fire immediately, and white vapors of ammo- nium chloride are formed. 4NH3 + CP = 3NH*C1 + N If a long tube closed at one end be almost filled with satu- rated chlorine-water, and then filled up with ammonia-water, and quickly inverted on the pneumatic trough, the lighter solution of ammonia will rise through the chlorine-water, and reaction occurs according to the preceding equation. Ammonium chloride remains in solution, while the nitrogen collects in the tube. Nitrogen Chloride. — Under certain con- ditions the nitrogen combines with chlorine, forming a very explosive and dangerous compound, nitrogen chloride, NOP. This is an oily yellow liquid, heavier than water, ^^^^_^^ which explodes violently on contact with '-p ^'TT phosphorus, turpentine, and other combusti- ble substances. A small jar of chlorine is inverted in a saucer containing a solution of ammonium chloride ; the salt is slowly decomposed by the chlorine, with the formation of hydrochloric acid and nitrogen chloride, and a drop of yellow liquid soon collects on the surface. A light tap on the vessel causes it to sink through the solution into the saucer. The jar is now removed and a small piece of phosphorus pushed into the drop of nitrogen chloride by the aid of a long wooden rod. Instantly the nitro- gen chloride explodes and the saucer is broken into pieces. When a warm saturated solution of ammonium chloride is electrolyzed, the chlorine set free at the anode reacts with the solution ; nitrogen chloride is formed, and carried to the sur- face with the escaping gases. If a little turpentine be poured on the surface of the liquid, on contact with this each little globule of the chloride explodes with a flash and a continual crackling is kept up. Nitrogen chloride has been carefully investigated by Gatter- mann, who found that it explodes also when exposed to direct sunlight. AMMONIA. 155 Nitrogen Iodide. — There is another explosive compound analogous to nitrogen chloride, but containing iodine. It is obtained as a black powder by treating powdered iodine with ammonia ; when dry it explodes with great violence on the lightest touch, and sometimes spontaneously. Bunsen has attributed to it the formula N^H^Il According to Stahlschmidt, the composition of nitrogen iodide corresponds to the formula NP, when this body is prepared by the action of an alcoholic solution of iodine upon aqueous am- monia ; but if both bodies be in alcoholic solution, an iodide is obtained having the formula NHI^ If this be correct, these bodies present very simple relations with ammonia. fH fCl n fl 1h Ici U (H Ammonia. Kitrogen chloride. Triiodammonia. Diiodammonia. Trichlorammonia. Nitrogen iodides. The last-named compound has been recently carefully studied by Szuhay, who obtained it by the action of aqueous solution of ammonia upon a strong solution of iodine in potassium iodide. Its hydrogen is replaceable by metals. Action of Potassium upon Ammonia. — When potassium is heated in an atmosphere of ammonia, the brilliant surface of the metal becomes covered with a greenish-black liquid, and at the same time hydrogen is disengaged. The metal entirely disappears little by little, and, on cooling, the liquid solidifies to an olive-green mass. This substance represents ammonia in which one atom of hydrogen has been replaced by an atom of potassium. H > N = Ammonia. H > N = Potassium amide. It reacts with water, forming ammonia and potassium hydrate. KNff -f WO = KOH -I- NH^ Potassium amide. Potassium hydrate. Ammonium Amalgam. — If liquid amalgam of potassium or sodium and mercury be treated with a saturated solution of ammonium chloride, the amalgam increases in volume, assumes a buttery consistence, and is converted into a soft, light mass naving the metallic lustre of mercury. It will retain the im- pression of the finger, and will float upon water ; but it grad- ually decomposes, losing hydrogen and ammonia, and only mercury remains. This unstable body is called ammonium amalgam. Whether it is really an amalgam of the group NH* 156 ELEMENTS OF MODERN CHEMISTRY. with mercury or is simply metallic mercury containing hydrogen and ammonia gases is still doubtful. Although the ammonium group has not been isolated, there can be no doubt that it exists in many compounds, and plays in them a part analogous to that of a metallic atom. Thus ammonium may replace potassium in the potassium salts, pro- ducing compounds similar and analogous to the latter. NHIHCI = (NH^)Cl analogous to KCl Ammonium chloride. Potassium chloride. NH^HNO^ == (NH*)NO^ analogous to KNO^ Ammonium nitrate. Potassium nitrate. NHlffS = ^h}^ analogous to ||s Ammonium sulphydrate. Potassium sulphydrate. CNH7.ffS = NH*}^ analogous to | Ammonium sulphide. Potassium sulphide. AMMONIUM CHLORIDE. This salt was formerly obtained from Egypt, where it was made by subliming the soot produced by the combustion of camel's dung. It is now prepared in large quantities from gas- liquor, or the water condensed in the manufacture and purifi- cation of illuminating gas from coal. This liquor is heated with lime, ammonia is disengaged and is conducted into hydro- chloric acid. Ammonium chloride is obtained by simply evaporating the solution. It is purified by sublimation in stoneware pots which are heated in a furnace out of which the upper parts of the pots project. There the volatilized chloride condenses, and the sublimed product is known in commerce as sal ammoniac, or muriate of ammonia. It generally occurs as white or grayish, compact masses, having a crystalline fibrous structure. Its taste is sharp and salty. It dissolves in two and a half parts of cold, and in its own weight of boiling water. It is deposited from a satu- rated solution in small octahedra, grouped together in needles, and presenting a fern-leaf-like appearance. At a high tem- perature it volatilizes without melting j its vapor is dissociated, but the resulting NH^ and HCl at once recombine on cooling. Ammonium chloride is formed by the union of equal vol- umes of hydrochloric acid and ammonia gases. AMMONIUM HYDROSULPHIDE AND AMMONIUM SULPHIDE. 157 AMMONIUM HYDROSULPHIDE AND AMMONIUM SULPHIDE. Hydrogen sulphide and ammonia gases unite in the cold in two different proportions, forming two compounds, ammo- nium hydrosulphide and ammonium sulphide. H^S -{- NH^ = ^^'1 gen sulphide. Ammonia. Ammonium hydi [2 vol.) (2 vol.) ffS + 2NH» = ™;} Hydrogen sulphide. Ammonia. Ammonium sulphide. (2 vol.) (4 vol.) These compounds are definite, but are decomposed into their elements by heat. Horstmann and Salet have shown that hy- drogen sulphide and ammonia gases may be mixed in all pro- portions without contraction in volume taking place, provided the temperature be maintained above 60°. Ammonium hydrosulphide is generally obtained in solution by saturating aqueous ammonia with hydrogen sulphide. This solution is colorless, but acquires a yellow color on exposure to the air. When a quantity of ammonia is added to it equal to that which it already contains, ammonium sulphide, (NH*)^S, is formed, which corresponds to potassium sulphide, K^S. Ammonium sulphide is largely employed in the laboratory as a reagent for the detection of certain metals. If ammonium sulphide be added to a solution of ferrous sulphate, a double decomposition takes place ; ammonium sul- phate is formed and remains in solution, while ferrous sulphide forms a black precipitate. FeSO* + (NHO^S = FeS + (NH*).2S0* Ferrous sulphate. Ferrous sulphide. Ammonium sulphate. The salts of zinc, manganese, cobalt, and nickel are likewise precipitated as sulphides by ammonium sulphide. The salts of aluminium and chromium are precipitated as hydroxides, hydrogen sulphide being disengaged. The preceding salts are not precipitated by hydrogen sul- phide (the zinc salts are not precipitated if they be acid), but the latter reagent precipitates in the form of sulphides the salts of lead, bismuth, copper, cadmium, mercury, silver, antimony, tin, gold, and platinum. The sulphides of the latter four metals dissolve in an excess of ammonium sulphide. U 158 ELEMENTS OF MODERN CHEMISTRY. The sulphides of arsenic, tin, antimony, gold, and platinum all form compounds with ammonium sulphide, in which the latter plays the part of a base. AMMONIUM NITRATE. (NH^)N03 Ammonium nitrate is prepared by saturating nitric acid with ammonia. It crystallizes in large, transparent, fusible prisms, which are very soluble in water and produce a notable depression of temperature in the act of solution, extending even to — 15°. At 300° ammonium nitrate is decomposed into nitrogen monoxide and water. It is used for the prepa- ration of nitrous oxide, much used as an anaesthetic. AMMONIUM CARBONATE. When dry carbon dioxide and ammonia gases are mixed in the proportion of 2 volumes of the first to 4 volumes of the second, they condense, forming a white powder, which is am- monium carbamate, a compound which was formerly called anhydrous carbonate of ammonia. C0= + 2Nff = CO<^^g, Ammonium carbamate. The ammonium carbonate of commerce is generally consid- ered as a sesquicarbonate. It contains 2[C0'(NH*)^] -|- CO^ -)- 2H^0. It is obtained by heating a mixture of equal parts of ammonium sulphate and chalk in a subliming apparatus. Ammonia and water are disengaged, and the sesquicarbonate of ammonium sublimes. Recently sublimed ammonium sesquicarbonate is transparent and crystalline. It has a strong ammoniacal odor and a sharp caustic taste. When exposed to the air it gradually loses ammonia and is converted into ammonium acid carbonate. Ammonium Acid Carbonate. — This salt, which is com- monly known as bicarbonate of ammonia, may be obtained by passing a current of carbonic acid gas into aqueous ammonia, to saturation. The acid salt separates in right rhombic prisms. The neutral carbonate of ammonium crystallizes from a cooled solution of the sesquicarbonate in ammonia-water. These salts present the following relations to the hypothetical carbonic acid : AMMONIUM SULPHATE — HYDROXYLAMINE. 159 co<0| pf. ONH* CO 0. Antimony trisulphide is used in pyrotechny, adding to the brilliancy of colored fires. Antimony Pentasnlphide, Sb^S^, is obtained as an orange- red powder by passing hydrogen sulphide through a solution of the pentachloride in hydrochloric acid. It is more generally prepared as follows : Finely-pulverized antimony trisulphide is digested with sulphur and a solution of sodium hydrate, or a mixture of sulphur, sodium carbonate, and lime ; the antimony sulphide gradually dissolves in the liquid, and the product of the reaction is a sulphantimonate of sodium, which is deposited in fine crystals from the concentrated liquid. Sb^S^ + 3Na=^S = 2Na3SbS* Sodium sulphide. Sodium sulphantimonate. It is soluble in water, and on the addition of hydrochloric acid to its solution, hydrogen sulphide is disengaged and anti- mony pentasnlphide is precipitated. 2Na^^SbS* + 6HC1 = 6NaCl + Sb'S^ -f 3H^S General Considerations upon the Elements of the Nitro- gen Group. — Nitrogen, phosphorus, arsenic, and antimony, and bismuth might be added, form a group of elements allied by the most striking analogies. This is made manifest by the atomic composition of their compounds, as will be seen in the following synopsis : BORON. 201 HYDROGEN COMPOUNDS. Ammonia. Hydrogen phosphide. Hydrogen arsenide. SbH^ Hydrogen antimonide. CHLORINE COMPOUNDS. NOP PCP AsCP Nitrogen Phosphorus Arsenic trichloride. trichloride. trichloride. SbCP Antimony trichloride. — PCP — SbCP Phosphorus pentachloride. Antimony pentachloride. OXYGEN COMPOUNDS. N*0^(?) V'O' As-'O^ SbW Nitrogen trioxide. Phosphorous oxide. Arsenious oxide. Antimonous oxide. N^O^ FO^ As^O^ Sb^O^ Nitrogen pentoxide. Phosphoric oxide. Arsenic oxide. Antimonic oxide. _ H3P03 H^AsO^ H^SbO^ Phosphorous acid. Arsenious acid. Antimonous acid. HNO^ ___ HSbO^ Nitrous acid. Antimonyl hydrate. HTO* H^AsO* Phosphoric acid. Arsenic acid. HT^O' H*As^O^ msb^o^ Pyrophosphoric acid. Pyro-arsenic acid. Pyro-antimonic acid. HNO^ HPO^ HAsO^ HSbO^ Nitric acid. Metaphosphoric acid. Metarsenic acid. Metantimonic add. If tbe analogy between nitrogen and phosphorus were com- plete, there should be an orthonitric acid, H^NO* = HNO^ + H^O, corresponding to ordinary or orthophosphoric acid. This acid is not known as a definite hydrate, but compounds exist which are derived from it. Thus, bismuth subnitrate, BiNO*, can be regarded as a salt of orthonitric acid, in which three atoms of hydrogen are replaced by one atom of triatomic bismuth. BORON. B -^ 10.9 Boron is found in boric acid and in borates. Among the more important of the latter are sodium borate or borax, calcium borates or horocalcite and colemanite, and calcium sodium borate, known as horonatrocalcite. The elemeot was 202 ELEMENTS OF MODERN CHEMISTRY. first isolated by Gay-Lussac and Thenard in 1808, by fusing boric oxide with potassium. It occurs in several modifications. Preparation. — Amorphous boron is obtained by reducing boric oxide with sodium in an iron crucible. 23^0^ 4- Na^ == SNaBO^ + B Boric oxide. Sodium metaborate. A more convenient method consists in heating an intimate mixture of 100 parts anhydrous borax with 50 parts magne- sium powder to redness in a well-covered crucible. The pow- dered mass is thoroughly washed, first with water then with hydrochloric acid, and dried at 100°. Adamantine boron is prepared by fusing boric oxide with an excess of aluminium. The boron set free is dissolved by the aluminium, and on slow cooling separates in crystals, whose color varies from yellow to dark brown, according to the nature of the impurities, aluminium and carbon, one or both of which they invariably contain. These crystals may be isolated by treating the cold mass with hydrochloric acid. Properties. — Amorphous boron is infusible, but may be volatilized by the intense heat of the electric furnace. When heated to 300° in the air, it burns into boric oxide. Its com- bustion in pure oxygen is very brilliant, and it possesses a singular affinity for nitrogen, with which it combines directly at a red heat, forming a nitride, BN. In an atmosphere of nitric oxide, it burns into a mixture of boric oxide and boron nitride (Wohler and Deville). Boron decomposes water at a red heat, and otherwise behaves as an energetic reducing agent. Adamantine boron crystallizes in quadratic octahedra, having a density of 2.6, and a hardness and brilliancy next to diamond. It is infusible, and strongly resists the action of oxidizing agents and alkaline solutions. Hampe and Joly consider the crystals to be definite compounds of boron with aluminium and carbon. BORON CHLORIDE. BCP Preparation. — This body may be prepared by heating crude amorphous boron in a current of chlorine, or by the action of chlorine on an incandescent mixture of boric oxide and charcoal. B^O^ + 3C + 3CP = 2BCP + SCO Boric oxide. Boron chloride. Carbon monoxide, BORON FLUORIDE. — BORIC ACID. 203 Properties. — In a state of purity, boron chloride is a color- less, mobile, and highly-refractive liquid, boiling at 17°. It fames in the air, and is readily decomposed by water into boric and hydrochloric acids. BCP + 3H^0 = 3HC1 + B(0H)3 BORON FLUORIDE. BF3 Density compared to air 2.31 Density compared to hydrogen 34. Preparation. — Boron flucn^ide was discovered by Gay-Lussac and Thenard in 1810. It is prepared by heating in a glass retort an intimate mixture of one part of boric oxide and two parts of powdered calcium fluoride with twelve parts of sul- phuric acid. The gas disengaged is collected over mercury. 3CaF2 + B^O^ -f 3WS0' = 3CaS0^ + 3W0 -f 2BF^ Calcitim Boric oxide. Calciiun sulphate, iluoride. Properties. — Boron fluoride is a colorless gas, having a suf- focating odor. It produces abundant fumes in the air, and is very soluble in water, which dissolves about 800 times its volume of this gas. Its affinity for water is so great that it carbonizes paper and analogous organic substances, from which it removes the elements of water. The solution of boron fluoride in water is accompanied by a chemical reaction ; when the aqueous solution of this gas, satu- rated at the ordinary temperature, is cooled to 0°, crystals of boric acid are deposited, and a very acid liquid is obtained, known as hydrofluoboric acid ; its composition is expressed by the formula : BF^H = BFIHF BORIC ACID. H3B03 Preparation. — Boric acid was discovered by Homberg in 1702. It is found in the ft^ee state in the craters of certain volcanoes, and exists in solution in the lagoni of Monte- Rotondo, in Tuscany. These are muddy little lakes, through which arise the gaseous emanations from the fissures of a vol- canic soil. The gases {suffioni) contain sensible traces of boric 204 ELEMENTS OF MODERN CHEMISTRY. acid, which is dissolved by the water of the lagoni. On evap- oration, this water furnishes the crude boric acid. Large quantities of boric acid are also obtained from the native borates of sodium, calcium, and magnesium, which are decomposed by dissolving them in hot hydrochloric acid. The boric acid then separates upon cooling. In the laboratory, boric acid is prepared by decomposing a boiling saturated solution of borax or sodium borate with dilute sulphuric acid. The latter is added in small portions until the liquid strongly reddens litmus-paper ; the solution is then allowed to cool, and the boric acid separates in the crystalline form. Properties. — Pure boric acid crystallizes in pearly scales, somewhat greasy to the touch. It dissolves in 25 parts of water at 18°, and is much more soluble in boiling water. The solution is feebly acid, and changes blue litmus solution to a wine color. Boric acid dissolves in alcohol, and the solution burns with a green flame. When heated to 100° it loses one molecule of water, and is converted into metahoric acid, HBOl If the latter be main- tained for a time at a temperature of 140°, it is converted into tetraboric acid, H'B*0^ 4HB02 = H"B*0' + H^O When boric acid is heated in a platinum crucible to a tem- perature near redness, it loses all of its water, melts, and solidi- fies to a transparent glass on cooling. This is boric oxide. 2H^B0^ = B'^0^ -f 3ffO At a red heat this body dissolves a great number of solid sub- stances, particularly the metallic oxides ; it then yields variously colored glasses on cooling. Boric oxide is not decomposed by charcoal at a red heat, but is converted into boron chloride by the simultaneous action of chlorine and charcoal. SILICON. Si = 28.2 Like boron, silicon exists amorphous and in the crystalline form. It was discovered by Berzelius in 1825. Preparation. 1. Amorphous >S'it7zco?i,— Dry sodium silico- SILICON. 205 fluoride is heated with half its weight of metallic sodium : sodium fluoride is formed and silicon is set free. Na=^FlSiF* + 2Na2 = 6NaF + Si Sodium silico-fluoride. Sodium fluoride. On cooling, the mass is exhausted, first with cold, and then with hot, water ; a brown powder of amorphous silicon remains. Impure silicon is readily prepared by heating to redness a mixture of fine quartz sand and magnesium powder in a test-tube. SiO' + 2Mg = 2MgO + Si 2. Crystallized Silicon. — Deville and Caron obtained crys- tallized silicon by projecting a mixture of 3 parts of potassium and silicon double fluoride, 4 parts of zinc, and 1 part of sodium into a red-hot crucible. Fluoride of sodium is formed, and the silicon set free dissolves in the zinc and separates in the crystalline form on cooling; it is isolated from the zinc by dissolving the button in hydrochloric acid; the silicon remains in the form of brilliant laminae or needles. Crystal- lized silicon is most conveniently prepared by reducing the oxide SiO^ by charcoal in the electric furnace (Moissan). Properties. — Amorphous silicon is a brown powder, more dense than water, in which it is insoluble, and producing dark stains on the fingers. When heated in the air, it takes fire and burns with a bright light into silicic oxide, SiO^. Crystallized silicon has a density of 2.49. It may be heated to redness in oxygen without taking fire, but when it is calcined with potassium carbonate the latter is decomposed with a vivid emission of light, potassium silicate being formed and carbon being set free. Crystallized silicon resists the oxidizing action of both potassium nitrate and potassium chlorate, but it dis- solves slowly in a boiling solution of potassium hydrate, hydro- gen being disengaged and potassium silicate being formed. It burns when heated to redness in an atmosphere of chlorine, and takes fire spontaneously in fluorine. HYDEOaEN SILICIDE. Probable formula SiH^ Preparation. — This compound was discovered by Wohler and Bufi'in 1857. Magnesium silicide"^ is introduced into a * This is most readily prepared by heating one part finely pulverized quartz sand with one and a half parts magnesium powder. 18 206 ELEMENTS OF MODERN CHEMISTRY, two-necked bottle, which is then entirely filled with water that has been recently boiled. To one of the necks of the bottle is fitted a funnel-tube which passes to the bottom of the bottle ; to the other, a delivery-tube leading to the pneumatic trough ; this tube also is completely filled with water so that there is no air in the whole apparatus. Concentrated hydrochloric acid is then introduced by the funnel-tube, and immediately reacts with the magnesium silicide, forming magnesium chloride, which dissolves, and gaseous hydrogen silicide, which must be collected in jars filled with recently boiled water. Properties. — The gas thus obtained is not pure hydrogen silicide ; it contains an excess of hydrogen. It is colorless and insoluble in water : water containing air in solution oxidizes it. If bubbles of the gas be allowed to escape through the water of the trough, each bubble takes fire on coming to the surface, producing a bright light and a smoke of silicic oxide, which forms rings like those produced by hydrogen phosphide under similar circumstances, but often colored brown by a portion of silicon SILICON CHLORIDE. SiCl* This compound is formed when silicon is heated to dull red- ness in a current of chlorine, or when the latter gas is passed over an incandescent mixture of charcoal and silica. SiO^ -f C^ + CI* = SiCl* -f 2C0 Preparation. — Precipitated silica, lamp-black, and oil are intimately mixed into a stiff" paste. This paste is made into little balls, which are put into a crucible, the cover of which is then luted on, and the whole is heated to redness in a furnace. When cool, the balls are introduced into a porcelain tube or a clay retort (Fig. 74), which is then heated to bright redness, while a current of carefully-dried chlorine is passed through. The silicon chloride and the carbon monoxide formed are passed through two U tubes surrounded by a mixture of ice and salt. The silicon chloride is thus condensed. An easier method of preparation consists in gently heating in a current of chlorine the crude product obtained by reducing silica with magnesium. Silicon chloride distils, and is condensed in a freezing mixture (Gattermann). Properties. — Silicon chloride is a volatile, colorless liquid, of an irritating odor. It fumes in the air. Its density is 1.52, and it boils at 59°. SILICON TLUORIDE. 207 It is instantly decomposed by water, silicic and hydrochloric acids being formed. A part of the silicic acid is precipitated Fig. 74. in the form of a jelly, while another part remains in solution. The latter is perhaps a hydrate corresponding to the chloride. SiCl* + 4ffO = 4HC1 -f Si(OH)* There exist a tetrabromide of silicon, SiBr*, and a tetraiodide, SiP, both corresponding to the chloride just described. Besides these compounds there are also known the tri-halides, Si^CP, Si^Br«, and Si^P, as well as silicon chloroform, SiHCP, and the analogous compounds of bromine and iodine. SILICOI^ FLUOBIDE. SiF* Density compared to air 3.6 Density compared to hydrogen 52. Preparation. — An intimate mixture of silicious sand and finely-powdered calcium fluoride, or fluor spar, is introduced mto a glass flask (Fig. 75), and a sufficient quantity of sul- phuric acid is added to reduce the whole to a creamy consistence. A gentle heat is applied, and the gas disengaged may be col- lected over mercury. 208 ELEMENTS OF MODERN CHEMISTRY. 2CaF^ -f 2H2SO* -f SiO^ = 2CaS0* + SiF* + 2H20 Calcium fluoride. Silicic oxide. Calcium sulphate. Properties. — S i 1 i c o n fluoride is a, colorless, suf- focating gas, producing white fumes when allow- ed to escape into the air. It may be liquefied by a low temperature and a strong pressure. On con- tact with water it is de- composed, silicic hydrate separating in gelatinous flakes, and hydrofluosili- cic acid being formed. 3SiF* + 4H20 =z 2(H2F2.SiF*) + H2Si03 r IG. 75. Hydrofluosilicic acid. Hydrofluosilicic Acid. — A saturated, aqueous solution of this acid is a highly acid liquid, fuming in the air, and evapor- ating slowly at 40° from a platinum-dish, leaving no residue. It is prepared by passing gaseous silicon fluoride into water under which is a layer of mercury. The delivery-tube must dip beneath the surface of the mercury, so that the silicon flu- oride can only come in contact with the water after passing through the metal ; otherwise the delivery- tube would become obstructed by the deposit of gelatinous silica. Hydrofluosilicic acid is employed as a reagent in the labora- tory. It precipitates the salts of potassium and sodium, form- ing insoluble fluosilicates, R^FlSiF*. SILICA. Si02 Native State. — Silicic oxide is widely diffused in nature. It occurs crystallized in the various quartzes, and as tridymite ; cryptocrystalline, as agate, chalcedony, carnelian, flint, etc. ; granulated, it is found in sandstones and the sand produced by their disaggregation ; in this case it is often mixed with variable quantities of alumina and oxide of iron. Rock-crystal is pure silicic oxide. It occurs as six-sided prisms, terminated by pyramids of six faces (Fig. 76). Amorphous silica exists in various minerals, such as qpaZ and hydropTiane, It is also found in the form of pulverulent SILICA. 209 Fig. 76. deposits and in solution in many running waters, in large proportion in the liot waters of the geysers in Iceland. Properties. — Quartz is colorless when pure ; its density is 2.69, and it is No. 7 in the scale of hardness (page 789). It is very refractory : in the oxyhydrogen flame it undergoes a viscous fusion, but can be melted to a clear liquid, and even volatilized, by means of the electric fur- nace (page 210). It forms a bluish vapor. It is not attacked by acids, with the excep- tion of hydrofluoric acid. Boiling alkaline solutions scarcely afi"ect it, but the amor- phous varieties of silica, such as flint, as well as opal and the other hydrates, dis- solve more readily in boiling solutions of the alkaline hydroxides. All of the varieties of silica, when heated to redness with the alkalies or alkaline car- bonates, combine with the bases, forming silicates which enter into fusion at a high temperature and solidify to a vitreous mass on cooling. Potassium silicate, or soluble glass^ is a transparent mass, soluble in water. When hydrochloric acid is added to this solution, potassium chloride is formed and silicic acid is precipitated as a gelatinous mass, which is not insoluble in water. An aqueous solution of silicic acid may be obtained. If hydrochloric acid be added to a dilute solution of potas- sium silicate, the liquid remains transparent although it contains silicic acid. It may be poured into a dialyser, composed of a piece of parchment-paper stretched over a wooden or glass ring, and floated on the surface of pure water contained in another vessel. The potassium chloride gradually passes through the membrane, as would any crystallizable body, and the silicic acid remains alone dissolved in the water in the dialyser, as all other amorphous bodies which are soluble in water would do. Graham gave the name dialysis to this separation of crys-, tallizable bodies, which he named crystalloids^ from uncrystal- lizable bodies, which he named colloids^ by means of certain membranes. The former bodies pass through the membranes, which are, however, impermeable to the colloids. The silicic acid which remains in solution probably consti- tutes normal or ortho-silicic acid, Si(OH)*. By the loss of a o 18* 210 ELEMENTS OF MODERN CHEMISTRY. molecule of water, this tetrabasic acid would be converted into dibasic metasilicic acid, SiO(OH)l Many of the natural sili- cates represent salts of these acids: olivine^ Mg^SiO*, and garnet^ APCa^(SiO*)^, are orthosilicates, while Wollasfomte, CaSiO^, and enstatite, MgSiO^ are metasilicates. A numerous class of minerals correspond to more complex acids resulting from the condensation of two or more molecules of ortho- and meta-silicic acids. Felspar, for example, has the composition AlKSi^O^, and must be regarded as a salt of the polysilicic acid, H^Si^O^. Grlass is a mixture of potassium or sodium silicate with cal- cium silicate, and generally contains aluminium silicate. It is made by the prolonged fusion of potassium or sodium carbon- ate with pure quartz sand and lime. Flint glass contains lead, introduced in the form of red lead. Colored glasses are ob- tained by adding metallic oxides to the above ingredients. Cuprous oxide gives red glass; cupric oxide, green; cobalt oxide, blue, etc. Soda glass is more fusible than potash glass. The Electric Furnace. — The highest temperatures which were formerly employed in chemical operations were those produced by the oxyhydrogen blow-pipe. This has been Fig. 77. recently supplanted by a device known as the electric fur- nace, in which the energy of powerful electric currents is converted into heat. The temperatures which can be thus reached and maintained far exceed 3000°. Nearly all those bodies which were formerly regarded infusible and non-vola- tile have been melted and vaporized in the electric furnace, and many new products have been obtained by its means. CARBON. 211 A simple forai of electric farnace, constructed hj Moissan, is shown in Tig. 77. It consists of a block of lime, cut in two, hol- lowed out at the centre, and perforated to permit the introduction of the carbon electrodes. The arc formed between these plays upon the substance in the cavity, and is regulated by moving the carbons ; its position is controlled by a powerful magnet. CARBON. C = 11.97 Natural State and Varieties. — The carbon of chemists is pure charcoal. This substance is known to all ; black, friable, light, absolutely fixed, inalterable by the air at ordinary tem- peratures, but combustible when heated in the air, it results from the calcination of organic matters, and particularly wood, in closed vessels. But carbon by no means always reveals these same properties. It occurs in nature under forms so different that it is impossible to apply a general description to all of its known varieties. What could be more different, as far as physical properties are concerned, from the soot deposited by a smoky flame, or the light, porous, and opaque charcoal, than the hard, dense, and transparent substance found in nature iu the form of diamond ? Nevertheless, these bodies are com- posed of one and the same substance, carbon ; alike, they all burn in oxygen at a high temperature, producing carbon dioxide. Among the various forms which carbon assumes, and which constitute one of the most curious examples of dimorphism, the following may be described : Diamond. — This is the hardest of all bodies ; it scratches all others, and can only be trimmed by grinding with its own dust. It is found crystallized in the form of the regular octahedron and various fornas de- rived fi'om it, such as the rhombic dodeca- hedron, trisoctahedron, and hexoctahe- dron. The faces are generally convexly curved (Fig. 78). Moissan has succeeded in obtaining the diamond artificially. He dissolved carbon in molten iron, the temperature being raised yiq. 78. to 3000°. Upon chilling the mass, a portion of the carbon crystallized out, and though exceedingly small, the crystals showed all the characteristics of the diamond. 212 ELEMENTS OF MODERN CHEMISTRY. The density of the diamond is between 3.50 and 3.55. It is a bad conductor of heat and electricity ; it strongly refracts and disperses light. From this latter fact Newton first divined its combustible nature, which was proved, in 1694, by the Floren- tine academicians of del Cimento^ who burned a diamond in the focus of a concave mirror. Lavoisier and Davy repeated this celebrated experiment, and proved that the sole product of the combustion is carbon dioxide. At the temperature of the electric arc the diamond swells up and blackens, being con- verted into graphite. Graphite, or Plumbago. — This is a crystalline variety of carbon, which is found in primitive rocks in brilliant steel-gray foliated masses. It sometimes occurs in hexagonal laminse. It can be scratched with the finger-nail, and leaves a black trace when drawn over paper. Its density is 2.2, and it con- ducts heat and electricity. It burns only at very high tem- peratures; ordinarily, it contains from one to two per cent, of foreign matters. It has been obtained artificially. Molten iron possesses the property of dissolving carbon at a very high temperature, and depositing it on solidifying in hexagonal scales of graphite. Graphite is converted into a yellow substance known as graphitic acid when treated with a mixture of nitric acid and potassium chlorate. The diamond is not attacked by this mixture. Plumbago is used for the manufacture of lead-pencils and crucibles, and as a lubricant, and is sometimes called black lead. There are other natural substances popularly regarded as varieties of carbon, but they are very impure. Their carbon is combined with more or less hydrogen, and they are in fact mixtures of complex hydrocarbons. They are : Anthracite^ a hard and compact variety of carbon containing from 8 to 10 per cent, of earthy matters. Bituminous coal, a brilliant, black variety, strongly impreg- nated with bituminous and earthy matters. It has been pro- duced by the slow decomposition of vegetable matters buried in the earth in the early geological ages. This origin is indi- cated by the impressions of leaves, stems, and fruits, which are evident in certain specimens of this coal. It contains only from 75 to 88 per cent, of carbon. When it is calcined in closed vessels, it disengages combustible gases and products which may be condensed in the liquid form and then separate into two layers. One is aqueous and ammoniacal, while the CARBON. 213 other is composed of tar. The residue of the distillation of bituminous coal is coUe. The interior walls of the cast-iron vessels in which coal is distilled become covered with a coni- pact layer of a gray, dense, hard and sonorous carbon, which is a good conductor of heat and electricity. This is the carbon of gas-retorts, and is produced by the igneous decomposition of hydrocarbons rich in carbon, which are disengaged during the calcination of the coal. Fat coals are those which burn with a long flame, softening in burning ; dry coals burn with a short flame which produces less heat than the preceding. Lignite is a combustible mineral containing less carbon, and more impure than bituminous coal ; it is found in the lower, tertiary formations. Natural jety which is employed for the manufacture of ornaments, is a variety of lignite. Among the artificial carbons, independently of coke, may be mentioned wood charcoal, lamp-black, and animal charcoal. Wood Charcoal. — When wood is calcined in closed vessels it leaves a residue which is ordinary charcoal. It is prepared on the large scale by two processes, carbonization in stacks, which is carried on in the forests, and distillation in closed vessels. Charcoal is amorphous, brittle, and sonorous, a bad conductor of heat and electricity. Its density does not ex- ceed 1.57. The lighter varie- ^^ ties are the more combustible. Its combustion leaves a resi- ( due of one or two per cent, of ash, formed principally of min- \ eral salts, among which the most abundant are the car- bonates of calcium and potas- sium. Lamp-hlack is produced by the incomplete combustion of organic substances rich in car- bon. When rosin or tallow is burned, a dense smoke is pro- duced which is composed of particles of carbon that have escaped combustion. In the arts, lamp-black is procured by burning rosin in cast-iron pots, C (Fig. 79), heated by a fire, F. The vapors given off" are ig- nitedj and the smoke is conducted into a chamber, A, the walls Fig. 79. 214 ELEMENTS OP MODERN CHEMISTRY. of which are hung with canvas. On this the lamp-black is de- posited, and is detached by lowering the cone B, which acts as a scraper. Lamp-black is not pure carbon. It contains tarry and oily matters, from which it may be freed by calcination in a covered crucible. It is used for the manufacture of printing- inks. Animal charcoal is produced by calcining animal matters, such as blood, the debris of skin, horn, bone, etc., in closed vessels. Bone-black or ivory-black contains the calcareous salts, calcium phosphate and carbonate, which form the base of the osseous tissue. The carbon is consequently disseminated through a porous mass. These salts may be extracted by treating the bone-black with dilute hydrochloric acid, by which they are dissolved. The residue, washed with water and dried, is known as washed or purified animal charcoal. Absorbent Properties of Charcoal. — The amorphous and porous varieties of carbon, of which several forms have been described, possess the property of absorbing and retaining in their pores, gases, liquid and solid bodies. It is to this absorp- tive faculty that are due the decolorizing and disinfecting properties of charcoal, which are made use of to a large extent in the arts. If a piece of incandescent charcoal be plunged into mercury that it may cool out of contact with the air, and then be intro- duced into a small jar filled with ammonia or hydrochloric acid over the mercury-trough, the gas is at once absorbed and the mercury rises in the jar. The following table, by Th. de Saussure, indicates the quan- tities of several gases which are absorbed by one volume of charcoal : 1 volume of charcoal absorbs 90 volumes of ammonia. u 85 a hydrochloric acid. « 65 ii sulphur dioxide. <( 65 (( hydrogen sulphide {< 40 (( nitrous oxide. tt 35 ft carbon dioxide. tt 9.42 <( carbon monoxide. tt 9.25 f( oxygen. tt tt 7.50 (( nitrogen. <( tt 1.75 « hydrogen. I Charcoal increases in weight when exposed to the air, for it absorbs and condenses the atmospheric moisture. When plunged into water charged with a small quantity of hydrogen sulphide, it absorbs that gas and removes the odor of the water. CAEBON. 215 The disinfecting properties of charcoal are thus easily explained. It is well known that charcoal will remove the unpleasant odor of corrupted waters, of meats slightly spoiled, and in general of organic matters in a state of putrefaction. A layer of char- coal between two layers of sand is an excellent filter for the clarification of drinking waters. The decolorizing properties of charcoal are another mani- festation of this general faculty of absorption, which is pos- sessed in the highest degree by animal charcoal. If litmus solution or red wine be agitated with a sufficient quantity of animal charcoal and subsequently filtered, the liquids pass through colorless. This property of animal charcoal is largely applied in the arts, particularly for decolorizing sugars and syrups. Chemical Properties - Carbon is distinguished by its pow- erful affinity for oxygen, an affinity which is not, however, exercised ex- cept at high tempera- tures. It only combines with oxygen at a red heat, and remains incan- descent as long as com- bination goes on, the heat produced by the combination being suffi- cient to maintain the incandescence. In pure oxygen it burns with a brilliant light. The product of the combus- tion is carbonic acid gas. By the aid of heat, ^' carbon decomposes a great number of oxy- genized compounds, re- moving and combining with the whole or a part of their oxygen. This decomposition takes place at comparatively low tempera- tures when the oxygenized body does not strongly retain its oxygen ; in this case, carbon dioxide is formed, and the reduc- tion of cupric oxide by charcoal furnishes an example. In the contrary case, the reduction, that is, the decomposition of the 216 ELEMENTS OF MODERN CHEMISTRY. oxidized body, requires a very high temperature ; carbon mo- noxide is then formed. The reduction of zinc oxide by charcoal is an example. If an incandescent charcoal be rapidly plunged under a bell- jar filled with water on the pneumatic trough, bubbles of gas arise and collect in the jar (Fig. 80). They are formed of a mixture of hydrogen, carbon monoxide, and a small quantity of carbon dioxide. These gases are produced by the decom- position of the water by the charcoal, which was red-hot at the moment of contact with the liquid. C -f H=^0 = H^ + CO carbon monoxide. Water gas, a mixture of hydrogen and carbon monoxide, is made, according to this reaction, by passing steam over highly- heated coal, coke, or other form of carbon. Carbon combines directly with sulphur at a high tempera- ture, forming carbon disulphide. Carborundum, CSi. — At the high temperature of the elec- tric furnace and under the influence of the current, carbon reduces silica; the product of the reaction is a transparent green- ish or yellowish mass of crystals having a hardness but little below that of the diamond, and used as a substitute for diamond for cutting and polishing under the name carborundum. It is unaffected by acids, even by hydrofluoric acid, but is decom- posed by fusion with alkalies. This substance is a definite compound of carbon and silicon, as indicated by the formula. Carbides of Boron. — Boric oxide, like silica, is reduced by car- bon in the electric furnace, the boron combining with the excess of carbon to form carbides of definite composition. One of these, B^C^, resembles graphite, but is fusible at very high temperatures. Another carbide, CB^, is said to be harder even than the diamond (Moissan). COMPOUNDS OF CARBON AND OXYGEN. Two compounds of carbon and oxygen are known : Carbon monoxide CO Carbon dioxide, or carbonic acid gas CO^ The latter body, which has long been known as carbonic acid, is the oxide corresponding to the true carbonic acid, which would be CO^ + ff = WGO' This normal carbonic acid is as yet unknown : it is doubtless too unstable to exist in the free state. However, its existence CARBON MONOXIDE. 217 may be admitted, for a corresponding compound is known in sulphocarbonic acid H^CS^. CARBON MONOXIDE. Density compared to air 0.967 Density compared to hydrogen 13.9 Molecular weight CO = 27.78 Preparation. — 1. An intimate mixture of zinc oxide and charcoal may be calcined in a clay retort. ZnO 4- C = CO + Zn 2. A convenient method of preparing carbon monoxide con- sists in beating oxalic acid with an excess of sulphuric acid in a glass flask. The oxalic acid loses the elements of water, which it yields to the sulphuric acid, and breaks up into carbon dioxide and carbon monoxide. en^O* r= CO 4- co^ + H^O Oxalic acid. Carbon monoxide. „arbon dioxide. The mixture of the two gases is passed through a wash-bottle, B (Fig. 81), containing a solution of potassium hydroxide, by K 19 218 ELEMENTS OF MODERN CHEMISTRY. which the carbon dioxide is absorbed, potassium carbonate being formed. The carbon monoxide may then be collected over water. Another excellent method consists in heating a mixture of one part of powdered potassium ferrocyanide with ten parts of concentrated sulphuric acid. The carbon monoxide evolved is practically pure. K*Fe(CN)6 + 6H2SO* + GH^O = 2K2SOHFeSO* + 3(NH*)2SO* + 6C0 Potassium Ferrous ferrocyanide. sulphate. Properties. — Carbon monoxide is a colorless, odorless gas. Its critical conditions are — 139.5° and 35.5 atmospheres ; the liquid boils at — 190° and freezes at — 207°. Carbon monox- ide is neutral, and does not cloud lime-water, which distin- guishes it from carbon dioxide. It extinguishes burning bodies, but is combustible itself, burning in the air with a blue flame, and forming carbon dioxide. It is not only unfit for respira- tion, but is very poisonous, combining with and profoundly altering the red corpuscles of the blood. Composition. — If two volumes of carbon monoxide be mixed with one volume of oxygen in an eudiometer, and a spark be passed, complete combustion takes place, and the three volumes of the mixture are reduced to two volumes of carbon dioxide. This can be verified by passing into the eudiometer a solution of potassium hydrate, which will com- pletely absorb the new gas. It hence follows that two volumes of carbon monoxide con- tain the same quantity of carbon as two volumes of carbon dioxide. Knowing from other circumstances that two volumes of carbon dioxide contain two volumes of oxygen, it follows that two volumes of carbon monoxide contain one volume of oxygen. Its molecular formula is therefore CO. Carbon monoxide undergoes dissociation at a very high temperature, and may be resolved into carbon and oxygen. It is almost insoluble in water, but is absorbed by a solution of cuprous chloride in hydrochloric acid (Doyere and F. Le Blanc). Advantage is taken of this property in volumetric analysis to separate carbon monoxide from certain other gases. When heated for a long time to 100°, in sealed tubes with potassium hydroxide, it combines with the alkali, forming potas- sium formate (Berthelot). CO + KOH = KCHO^ Potassium hydroxide. Potassium formj^te, CARBON DIOXIDE. 219 Action of Chlorine upon Carbon Monoxide. — Under the influence of sunlight, carbon monoxide combines directly with an equal volume of chlorine, forming a gas which is known as carhonyl chloride, or phosgene. The volume of the carbonyl chloride is one-half that of the sum of the combining gases, so that its formula is COCP. Carbonyl chloride may be easily condensed to a colorless liquid, boiling at 8.2°. Its vapor is colorless, produces a suffo- cating sensation, and provokes tears. It is instantly decomposed by water, with the formation of carbon dioxide and hydro- chloric acid. COCP + H^O = 2HC1 + CO^ Its mode of formation, its composition, and its properties indicate its relations to carbon dioxide. 2 volumes CO absorb 2 volumes of chlorine to form 2 volumes CO.Cl* 2 volumes CO absorb 1 volume of oxygen to form 2 volumes CO.O Carbon monoxide thus plays the part of a radical ; it com- bines directly with oxygen or with chlorine to form either oxide or chloride of carbonyl. L. Mond has discovered a remarkable class of compounds of carbon monoxide with certain metals. Nickel carhonyl^ Ni(CO)*, may be considered as the type of these compounds ; it is formed by passing carbon monoxide over finely divided nickel at a temperature of 100°. It condenses at low tempera- tures to a colorless, highly refracting liquid having a density of 1.35, and boiling at 43°. At a temperature below 200°, it decomposes into carbon monoxide and metallic nickel. CARBON DIOXIDE. Density compared to air 1.524 Density compared to hydrogen 21.83 Molecular weight CO^ . = 42.73 This gas was discovered by Black in 1757, and its composi- tion was recognized by Lavoisier in 1776. It is one of the constituents of the atmosphere, and is the product of a great number of reactions which take place on the earth's surface, such as the combustion of carbon and organic matters, respira- tion, and the phenomena of putrefaction and fermentation. It issues from the soil of volcanic countries. 220 ELEMENTS OF MODERN CliEMISTRy. Preparation. — Fragments of marble, which is calcium car- bonate, are introduced into a two-necked bottle fitted with a delivery-tube and a safety -tube (compare Fig. 11, page 60). The bottle is half-filled with water, and hydrochloric acid is gradually added by the funnel-tube. An effervescence im- mediately takes place, due to the disengagement of carbon dioxide. CaCO^ + 2HC1 = CO^ + CaCP -f H^O Calcium carbonate. Calcium chloride. The gas is most conveniently collected by dry downward displacement, like chlorine. When it is desired to prepare large quantities of the gas, a self-regulating generator, such as that described on page 102, is advantageously used. Acid vapors and other impuri- ties are removed by passing the gas through a saturated solu- tion of potassium acid carbonate. Yery pure carbon dioxide is also obtained by heating the acid carbonates of the alkaline metals. 2NaHC0^ r= CO^ + Na^CO^ + H^O Sodium acid carbonate. Sodium carbonate. On a large scale, the gas is manufactured by heating lime- stone or magnesite. Composition. — 1. If carbon be burned in oxygen, the latter is converted into carbon dioxide without changing its volume. Hence two volumes of carbon dioxide contain two volumes of oxygen. These two volumes of oxygen, which represent two atoms, are combined with one atom of carbon, and the compo- sition of a molecule of carbon dioxide is hence expressed by the formula CO^ = 2 volumes. 2. Dumas and Stas determined the centesimal composition of carbon dioxide by burning a known weight of diamond in oxygen, and carefully weighing the carbon dioxide produced. By subtracting the weight of the diamond burned from that of the carbon dioxide, the weight of the oxygen was determined. The apparatus employed is represented in Fig. 82. The increase in weight of the tubes L, M, N, 0, P indicates the quantity of carbon dioxide formed. Dumas and Stas thus found that 100 parts of carbon dioxide contain Carbon 27.27 Oxygen r . . 72.73 100.00 CARBON DIOXIDE. 221 222 ELEMENTS OF MODERN CHEMISTRY. a centesimal relation which corresponds to the proportion of one atom of carbon to two atoms of oxygen : Carbon 11.97 Oxygen 31.76 Physical Properties. — Carbon dioxide is colorless ; it has a feeble, somewhat pungent odor. A litre of this gas at 0°, and under the pressure of 760 millimetres, weighs 1.97 grammes. Fig. 83. It was first liquefied by Faraday. At 0° it requires a pressure of 38.5 atmospheres, and at 31° (its critical tem- perature), 74 atmospheres. The apparatus which is now used for its liquefaction is represented in Fig. 83. It is composed of two reservoirs, A and B, communicating by CARBON DIOXIDE. 223 the metallic tube i. furnished with a stop-cock at each end. The cylinders are made of heavy cast-iron, and are further strengthened by forged iron bands forced over their circum- ference. Each cylinder is movable on a horizontal axis. A. B is the generator ; into it are introduced 1800 grammes of sodium dicarbonate, and a cylindrical copper tube, D, containing 1000 grammes of ordinary sulphuric acid. The cylinder is then closed by a strong screw plug, and a few oscil- lating movements are given to it in order that the sulphuric acid may gTadually inin out upon the sodium dicarbonate. Carbon dioxide is disengaged and is liquefied by its own press- ure as it accumulates in the apparatus. By the effect of the chemical action the temperature is raised to 30 or 40°. and, communication being established between the two cylinders, the carbon dioxide distils rapidly into the receiver, the tem- perature of which is about 15°. The operation is repeated several times, that one or two kilo- gTammes of the liquid may accumulate in the receiver. A tube passes to the bottom of this vessel, and on opening the stop-cock which closes the superior extremity of this tube, a jet of the liquid is thi'own out with force : it is received tangentially in a metallic box. A. A' (Fig. S-i), having very thin sides. In this a portion of the oxide solidifies by reason of the gTeat depression of temperature produced by the change of another portion into the gaseous state. A glittering-white, flaky mass collects in the receiver, having the appear- ance of snow. This is solid carbon dioxide. It is a bad conductor of j_ heat and electricity, and can be ex- ^ ^.^^ g^ posed to the air for a few minutes before it disappears. In reassuming the gaseous form, it pro- duces an intense cold. If it be mixed with ether, the mixture, which is less porous and a better conductor of heat, can produce a lowering of temperature as gTeat as — 90°. By pouring it upon mercury, large masses of that metal may be frozen. Liquid carbon dioxide is now manufactured on a commercial scale, and sold in strong steel cylinders. It is colorless and mobile; has a density of 0.72 at -|-2T°, and 0.98 at — 8°. 224 ELEMENTS OF MODERN CHEMISTRY. This considerable difference between the densities is due to the enormous dilatation which the liquid undergoes between these limits of temperature. Indeed, ten volumes of liquid carbon dioxide at 0° occupy fourteen volumes at 30°. Hence the coeffi- cient of expansion of the liquid is superior to that of the gas. Carbon dioxide is incombustible, and extinguishes burning bodies. If carbon dioxide be poured from one vessel into another containing a lighted candle, it falls upon the flame like water, extinguishing it at once (Fig. 85). Lime-water poured into a jar of carbon dioxide becomes clouded, owing to the formation of insolu- ble calcium carbonate. These experiments permit the easy recognition of carbon dioxide from carbon monoxide. Carbon dioxide dissolves in its own volume of water at 15° under the normal pressure. If the press- ure be increased, the solubility of the gas is increased in the same proportion. Thus, under a press- ure of ten atmospheres one litre of water will dissolve ten litres of carbon dioxide ; but it must be remembered that under a press- ure of ten atmospheres these ten litres are reduced to one litre. Thus, one litre of water, which dissolves one litre of carbon dioxide at the ordinary pressure, dissolves also one litre under a pressure of ten atmospheres, and it may be said that water always dissolves its own volume of carbon dioxide, whatever may be the pressure. Water saturated with carbon dioxide under strong pressure, disengages a portion of the gas as soon as the pressure is removed. Such water is universally known and consumed in large quantities under the name of aerated water or soda water. The solution of carbon dioxide exercises a much more ener- getic solvent action upon certain substances than pure water. It dissolves calcium carbonate, forming a soluble dicarbonate ; it is even capable of dissolving calcium phosphate, transform- ing it into acid phosphate, which is soluble. Carbon dioxide is more soluble in alcohol than in water. CARBON BISULPHIDE. 225 It is undecomposable by heat alone, but may be decomposed or reduced at higb temperatures by contact with bodies avid of oxygen. It is not reduced by hydrogen. With carbon the reduction takes place at a red heat, giving rise to the formation of carbon monoxide, the volume of which is double that of the carbon dioxide employed. CO^ + C = 2C0 Carbon dioxide (2 vols.). Carbon monoxide (4 vols.). CARBON BISULPHIDE. CS2 This body is prepared by passing sulphur vapor over incan- descent charcoal. In the arts, the operation is conducted in cylindrical, cast-iron vessels, filled with charcoal and heated to redness, into which sulphur is introduced. The carbon disul- phide distils, and is condensed in a suitable cooling apparatus. Carbon disulphide is a colorless, very mobile, and highly-re- fracting liquid. Its odor is usually strong and unpleasant, but is rather agreeable when the compound is perfectly pure. Its density at 15° is 1.271, and it boils at 46°. It is very inflam- mable, and burns with a blue flame, producing sulphur dioxide and carbon dioxide. CS^ -f- 30' = 2S0' + CO' Its vapor, mixed with oxygen, explodes when heated. Carbon disulphide corresponds in composition to carbon dioxide. CO^ carbon dioxide. CS' carbon disulphide. It is also analogous to the latter body in its chemical func- tions. While carbon dioxide combines with metallic oxides, forming carbonates, carbon disulphide combines with metallic sulphides, forming sulpho carbonates or thiocarbonates, CO' -f Na'O = Na'CO^ corresponding to H'CO' Sodium oxide. Sodium carbonate. Carbonic acid (hypothetical). CS' + Na'S = Na'CS^ corresponding to H'CS^ Sodium sulphide. Sodium sulphocarbonate. Sulphocarbonic acid. Sodium carbonate and sulphocarbonate possess the same con- stitution. By the action of strong acids they should give anal- ogous products: the one, carbonic acid, H'CO^; the other, 226 ELEMENTS OF MODERN CHEMISTRY. sulphocarbonic acid, H^CS^ The latter body is indeed formed under such circumstances, but normal carbonic acid, if it exist, possesses no stability, and at once decomposes into carbon diox- ide and water. Carbon disulphide is employed in the arts in the manufac- ture of vulcanized caoutchouc, and as a solvent for caoutchouc in the fabrication of goods impermeable to water by the deposit of a thin layer of that substance. It is also employed as a solvent for, and in the extraction of, fats and oils. In the laboratory it is useful as a solvent for sulphur, phosphorus, iodine, oils, fats, etc. CARBON OXYSULPHIDE. Density compared to air 2.1046 Density comiDared to hydrogen 30.4 Molecular weight CSO =59.61 This body was discovered by von Than in 1867. It is inter- mediate between carbon dioxide and carbon disulphide. COO carbon dioxide. CSO carbon oxysulphide. CSS carbon disulphide. Preparation. — It is prepared by decomposing potassium sul- phocyanate by dilute sulphuric acid. Potassium sulphate and sulphocyanic acid are formed, and the latter, in the presence of an excess of sulphuric acid and water, decomposes into am- monia and the gas carbon oxysulphide, which may be collected over mercury ; the ammonia remains combined with the sul- phuric acid in the form of sulphate. CSNH + H^O = NH^ + CSO Sulphocyanic acid. Carbon oxysulphide. Properties. — Carbon oxysulphide is a colorless gas, having an odor like that of carbon disulphide, but also recalling that of hydrogen sulphide. On contact with an incandescent body, even a match pre- senting a spark of fire, it takes fire, burning with a blue flame, and depositing sulphur if the supply of air be insufiicient. With one and a half times its volume of oxygen it constitutes an explosive mixture. 2 volumes of carbon oxysulphide . . = CSO mixed with 3 volumes of oxygen = 0^ yield 2 volumes of carbon dioxide ....=: CO^ and 2 volumes of sulphur dioxide . . . . = SO^ COMPOUNDS OF CARBON AND HYDROGEN. 227 Water dissolves about its own volume of carbon oxysulphide, but the solution decomposes in a few hours, with the formation of hydrogen sulphide and carbon dioxide. CSO + H^O = CO^ + H^S Carbon oxysulphide is absorbed completely, but more slowly than carbon dioxide, by solutions of the alkaline hydroxides ; by a reaction analogous to the preceding, a sulphide and a carbonate are formed. COMPOUNDS OF CARBON AND HYDROaEN. These compounds are numerous and important. Carbon unites with hydrogen in different proportions, and the atoms of carbon and hydrogen may accumulate in considerable numbers in the molecules of their compounds. These combinations are called hydrocarbons or carbides of hydrogen. Hydrogen mono- carbide, or marsh gas, contains only one atom of carbon com- bined with four atoms of hydrogen ; its molecule is therefore represented by the formula CH*. In olefiant gas, or ethylene, two atoms of carbon are united with four atoms of hydrogen; in the volatile liquid known as benzene or benzol, which is ob- tained in large quantities from coal-tar, six atoms of carbon are combined with six atoms of hydrogen. Lastly, the molecule of oil of turpentine contains ten atoms of carbon and sixteen of hydrogen. Hence these substances give us the following formulas : CH* methane, or marsh gas. C^H* ethylene, or olefiant gas. C^H^ benzene. C'^H'^ turpentine. These examples, which might be indefinitely multiplied, show : 1st. That the atoms of carbon unite in various proportions with the atoms of hydrogen to constitute the molecules of the hydro- carbons. 2d. That they accumulate in greater or less numbers to form molecules more and more complex, that is, containing an increasing number of atoms of carbon and hydrogen. All of these bodies must be considered among the organic compounds ; indeed, the latter are nothing more than the com- pounds of carbon, and carbon monoxide and dioxide may also be properly considered as the most simple organic combinations. 228 ELEMENTS OF MODERN CHEMISTRY. Hence if the most strictly rigorous method were adhered to, the description of the compounds of carbon and oxygen would be followed by that of all the other compounds of this element, that is, of all the organic compounds. However, for the pur- poses of study it is advantageous to treat the latter bodies separately, and they will be so considered in this work. The following experiments will expose some of the general proper- ties of the hydrocarbons which have been mentioned : 1. If a lighted taper be applied to a jar of methane, which is also called marsh gas, because it is disengaged from the muddy bottoms of marshes, the gas takes fire and burns with a faintly luminous flame. 2. If the same experiment be repeated with ethylene gas, which contains for the same proportion of hydrogen twice as much carbon as marsh gas, a highly luminous flame results. 3. It is well known that benzene and turpentine take fire when lighted, and burn with bright flames ; but it is also known that their flames are smoky. The hydrocarbons are then combustible; and how could they be otherwise, since they contain only two combustible elements, carbon and hydro- gen? The products of the combustion are water and carbon dioxide, and the forma- tion of the latter gas may be proved by agitating the con- tents of the jars in which the combustion has taken place with lime-water; the latter immediately becomes milky by the precipitation of calcium carbonate. This combustion is more or less complete ; when the gas or vapor which burns contains a large amount of combustible elements, the oxygen of the air may not be present in suflicient quantity to burn them all, that is, to oxidize them completely. Under these conditions it is the hydrogen which is burned by preference, and the carbon partly escapes combustion. STRUCTURE OP FLAME. 229 A flame is a gas or vapor in combustion. This combustion is an oxidation, and it is the oxygen of the air which is the agent. In order that it may take place, it is generally neces- sary that the combustible gas shall be brought to a high tem- perature; but once commenced, the combustion continues of itself, because the heat disengaged by the oxidation is sufficient to maintain the phenomenon. But if a flame be suddenly cooled, the combustion is at once arrested. A flame may be cooled by depressing into it a piece of fine wire gauze. The incandescent gases cannot pass through the meshes of the gauze without being cooled by contact with the metal, which is a good conductor of heat. For this reason, no combustion takes place above the gauze (Fig. 86). If a piece of wire gauze be held over an escaping jet of gas, the latter may be ignited above the gauze, and will burn without the combustion being propagated to the gas below ; the gauze acts as a screen, separating the jet into two portions, the lower cold and invisible, the upper in combustion and luminous. Sir Humphry Davy made a happy ap- plication of these facts in the construction of the miner's safety-lamp. This is an ordinary lamp surrounded by a cylinder of wire gauze (Fig. 87). Such a lamp gives less light than one not protected by an envelope, but it re- moves the danger of explosions of fire- damp, for when an explosive mixture is formed in the galleries of a mine, the gas may penetrate to the interior of the lamp and take fire there, but the flame cannot pass through the cooling envelope of wire gauze. The safety-lamps are now constructed with the lower part of the cylinder of glass, so that there is no diminution in the amount of light given. As the oxidation of combustible elements is the source of heat, it is evident that the difi"erent parts of a flame cannot be 20 Fig. 230 ELEMENTS OF MODERN CHEMISTRY. uniformly hot, for the oxygen of the surrounding air cannot equally attain all portions. The exterior borders are the most intensely heated; they are surrounded by air, and constitute the seat of combustion. From them the heat is radiated not only externally, but also to the interior of the flame, where it produces interesting phenomena. These may be studied by analyzing a flame, that is, considering separately the difi"erent parts \^' of which it is composed. If the flame of a can- dle be examined, it will be found to present three distinct layers, or cones (Fig. 88). 1. A dark central part, a, which surrounds '^ MA ^^^ wick. This is known as the obscure cone, or cone of generation; its temperature is not high. 2. A luminous part, hh' , surrounding the ob- scure cone. This is the centre from which the lio'ht is emitted. It is known as the luminous cone, or cone of decomposition. 3. An exterior envelope, cc', thin, and pro- ducing but little light, yellow towards the sum- mit, e, and bluish towards the base, dd'. It is the cone of complete combustion, and its temperature is the highest. It is easy to account for these phenomena. The material of the candle is melted by the heat Fig. 88. ^^ ^^ flame, the liquid is drawn up into the wick by capillarity, and arrives at the incan- descent summit. There it is decomposed, producing gases and vapors rich in carbon and hydrogen, and which rise around the wick, forming an irregular cone. The gaseous products consti- tuting this cone do not present the same composition through- out. They have been analyzed by H. Sainte-Claire Doville, by the aid of very ingenious processes. The obscure cone is formed of gaseous products holding in suspension finely-divided carbon, which has not yet arrived at incandescence. These products become heated on reaching the more central portions of the flame. Then the carbon, which is set free by the decomposition of gases rich in carbon, is brought to bright incandescence, but it is completely burned only when it reaches the exterior envelope, where the oxygen is in excess. A simple STRUCTURE OF FLAME. 231 experiments will demonstrate that the most luminous portion of the flame holds in suspension finely-divided and incandes- cent carbon. If a porcelain saucer be depressed into this portion, the carbon will be deposited on the vessel as soot. It is this solid and incandescent carbon which causes the luminosity of the flame. The flame of hydrogen, which con- tains only gaseous products, is pale. In the calcium or Drum- mond light it produces great brilliancy because a solid body, lime, is heated to bright incandescence. When the carbon suspended in a flame is in excess in proportion to the supply of oxygen, it is incompletely burned, and is carried into the air. The flame then smokes. At the base of the cone, carbon monoxide and methane, the first products of the decomposition of the candle, burn on con- tact with the air at dd' with a bluish flame. The luminosity of a flame is not necessarily due to the presence in it of solid matter. It depends very largely upon the temperature and the density of the burning gas. The flame of hydrogen, accord- ing to Frankland, is luminous when that gas is burned under strong pressure, and the flame of illuminating gas may be rendered non- luminous by diluting with an indifferent gas, such as nitrogen, and thus reducing the temperature- Illuminating gas is a mixture of hydrogen with various gas- eous hydrocarbons and a small proportion of carbon monoxide. It is manufactured by the destructive dis- tillation of bituminous coal. The aqueous products containing ammonia, and the tarry matters formed during the distilla- tion are condensed, and ih.Q gas is purified by washing with water and passage over slaked lime to remove sulphur and other impurities. Illuminating gas forms an explosive mixture with air, but if the mixture be burned as it is formed, the resulting flame will be almost colorless and will deposit no soot, the whole of the carbon coming in contact with sufficient oxygen for its complete combustion. These conditions are fulfilled in the Bunsen burner (Fig. 89). In this burner, the force of the escaping gas-jet draws in air through holes near the jet in a wider tube, at the end of which the mixture is burned. Fig. 89. 232 ELEMENTS OF MODERN CHEMISTRY. GENEKAL NOTIONS UPON THE NON-METALS. THEORY OF ATOMICITY. From a consideration of the facts acquired in the study of the elements known as non-metals, we may deduce certain gen- eral consequences, and while looking back on the field over which we have passed, we may at the same time fix certain landmarks for the remainder of our course. The elements which we have studied are not alike in their aptitude to enter into combination, nor in the general characters of their compounds. In this respect, analogies and difi'er- ences have been established between them, and these have become the basis of a rational classification. Following the example of Dumas, we may arrange these elements in groups or families, uniting in the same group those which are related by their chemical functions. HYDROGEN. OXYGEN. NITROGEN. SILICON. HELIUM. FLUORINE. SULPHUR. PHOSPHORUS. CARBON. NEON. CHLORINE. SELENIUM. ARSENIC. ARGON. BROMINE. TELLURIUM. ANTIMONY. METARGON IODINE. BORON. XENON. The elements of the last group, which includes argon and helium, are characterized by their inability to form chemical compounds. In order to account for the chemical functions of the other non-metals — that is, for the parts which they play in their com- binations — we must first consider their hydrogen compounds. These constitute the following series HH Hydrogen. HCl Hydrochloric acid. HBr Hydrobromic acid. HI Hydriodic acid. HF Hydrofluoric acid. H^O Water, H^S Hydrogen sulphide. H^Se Hydrogen seleiiide. H^Te Hydrogen telluride. H^N Ammonia Hydrogen phosphide. H^As Hydrogen arsenide. H^Sb Hydrogen antimonido, H^B Hydrogen boride, H*Si Hydrogen silicide. H*C Hydrogen carbide. THEORY OF ATOMICITY. 233 It is seen tliat the first four groups are characterized by the composition of their hydrogen compounds. While the bodies of the first group combine with hydrogen atom for atom, those of the second group require two atoms of hydrogen, those of the third three, and those of the fourth four, to form hydrogen compounds. Hence we may draw the conclusion that the atoms of these non-metals are far from being equivalent in their power of combination with hydrogen. The atoms of chlorine, bromine, and iodine are equivalent to each other in this respect, for each requires but one atom of hydrogen. The atoms of oxygen, sulphur, etc., are equivalent to each other, for each combines with two atoms of hydrogen. The atoms of nitrogen, phosphorus, arsenic, antimony, and boron are equivalent to each other, for each of them unites with three atoms of hydrogen. Lastly, the atoms of carbon and silicon are equivalent, for each can unite with four atoms of hydrogen. But, on the other hand, it is evident that the atoms of chlo- rine, oxygen, nitrogen and carbon are not -equivalent to each other, as regards their power of combination with hydrogen, since each of them unites with a difierent number of atoms of that body. In this respect it may be said that 1 atom of chlorine is equivalent to 1 atom of hydrogen. 1 atom of oxygen " 2 atoms " 1 atom of nitrogen " 3 atoms " 1 atom of carbon " 4 atoms " It is evident that the capacity of combination which resides in the atoms of simple bodies and by which they attract the atoms of hydrogen, is unequal. Leaving aside its intensity, this force is exerted in difi"erent degrees, for it determines the union of 1 atom of chlorine, oxygen, nitrogen, or carbon, with 1, 2, 3, or 4 atoms of hydrogen. This number of hydrogen atoms is the measure of the degree of force which resides in the atoms, — of the capacity of combi- nation which they possess for each other. Hence we conclude that The atoms of chlorine and its associates are monatomic or univaletit. The atoms of oxygen " " diatomic or bivalent. The atoms of nitrogen " " triatomic or trivalent. The atoms of carbon " " tetratomic or quadrivalent. 20* 234 ELEMENTS OF MODERN CHEMISTRY. The capacity of combination which resides in the atoms, and which is exerted in such different manners according to the nature of the atoms, is called atomicity. Atomicity is the relative equivalence of the atoms; it is simple or multiple, and if we consider it in its first degree, we may say that the atoms of chlorine and the atoms of hydrogen are so constituted that a single atom of one attracts a single atom of the other. When they combine, they exchange in some manner a unit of satura- tion, and in the combination of chlorine and hydrogen two of these units of force are neutralized ; two units of saturation or two atomicities are exchanged: the atoms of chlorine and of hydrogen are univalent. The force which resides in an atom of oxygen is more com- plex. It attracts two atoms of hydrogen, and represents the second degree of capacity of combination, and we may say that in each atom of oxygen reside two atomicities, which are satis- fied and exchanged when this atom combines with two atoms of hydrogen. Hence, four atomicities are satisfied by the com- bination. Following the same reasoning, we consider that a triple capa- city of combination is active in an atom of nitrogen when this atom unites with three atoms of hydrogen ; and that six atom- icities are satisfied by the combination. Lastly, tetratomic carbon is provided with four atomicities, which are satisfied by the four atomicities which reside in four atoms of hydrogen. If this neutralization or exchange of two units of saturation be represented by a hyphen, we will have the following formulae : H-Cl H-O-H H H Hydrochloric acid. Water. 1 1 N H-C-H /\ 1 H H H Ammonia. Hydrogen monocarbide. It is seen that in the formulae for water, ammonia and hydro- gen monocarbide, the polyatomic elements, oxygen, nitrogen and carbon, constitute, as it were, the nuclei around which the other atoms are symmetrically grouped. A great many other bodies present the same constitutions as the preceding ; it is evident that a given element in any com- pound may be replaced by another element having the same atomicity, without disturbing the equilibrium of the atomicities, THEORY OF ATOMICITY. 235 Indeed, if we suppose the chlorine, oxygen, nitrogen, and carbon to be replaced by elements of corresponding atomicities, we will have the series of hydrogen compounds already con- sidered. All of the bodies which are classed together in the series belong to the same type. Each contains an equal num- ber of atomicities for the same number of atoms. According to the principle of substitution announced above, it is evident that the hydrogen in each of the hydrogen com- pounds under consideration may be replaced by another mon- atomic element, and the compounds thus formed will still belong to the primitive types. So considered, a great number of compounds possess the same constitution, — that is, the same molecular structure, — as hydrochloric acid, water, ammonia, and methane or hydro- gen monocarbide. Such are those arranged in vertical columns in the following table : Type HCl Type H20 Type NH3 Type 0H4 Cl-Cl H-O-H K CI Free chlorine. Water. 1 1 N Cl-C-Cl /\ 1 H H CI Potassium amide. Carbon tetrachloride. K-Cl Cl-O-Cl CI CI Potassium chloride. Hypochlorous oxide. 1 1 P Cl-Si-Cl /\ 1 CI CI CI Phosphorus trichloride. Silicon tetrachloride. K-I H-O-K CI H Potassium iodide. Potassium hydroxide. 1 1 Sb H-Si-H /\ 1 Ag-I Ag-O-Ag CI CI H Silver iodide. Silver oxide. Antimony trichloride, , Hydrogen silicide. All of these bodies belong to the respective types HCl, H'^O, NH^, CH*, the first three of which were established by Ger- hardt, and have their existence explained by the atomicity of the elements ; that is, by the varying equivalence of their atoms, measured, in the present examples, by the number of hydrogen atoms with which they combine. One atom of oxygen is equivalent to two atoms of hydrogen 236 ELEMENTS OP MODERN CHEMISTRY. or two atoms of chlorine. Hence, in tlie preceding combina^ tions, two atoms of chlorine may be replaced by one atom of oxygen without changing the equilibrium of the atomicities. Thus, the oxides SiO^,CO^ correspond to the chlorides SiCl*, CCl*, and belong to the same type. The four atomicities of an atom of silicon or carbon are saturated by the four atomici- ties of two atoms of oxygen. The trichlorides of phosphorus and antimony, POP and SbCP, which will be found in the preceding table, require an impor- tant remark. They are not saturated with chlorine, and each may combine with two more atoms of that element, producing the compounds POP and SbCP. Thus, while phosphorus exhausts its power of combination with hydrogen in uniting with three atoms of that element in PH^, its capacity of combination with chlorine is only exhausted when it has combined with five atoms ; while it plays the part of a triatomic element in hydrogen phosphide, it is pentatomic in phosphorus pentachloride. From these facts it follows that it is often difficult to meas- ure in an absolute manner the capacity of combination which resides in an atom ; for that capacity varies according to the nature of the elements upon which it is exerted. Affinity is an elective force. A given element does not attract all of the other elements with equal facility ; it selects certain ones by preference, and neglects the others. With one, it may form but a single compound; with another, it may form several. The most important compound of nitrogen and hydrogen is ammonia, NH^, which cannot fix any more atoms of hydrogen. Saturated with hydrogen in ammonia, nitrogen manifests in contact with that element but three atomicities. But let am- monia be brought in contact with a body other than hydrogen, hydrochloric acid, for example, and it will combine with it, forming ammonia hydrochloride, or ammonium chloride. If its capacity of combination is exhausted for hydrogen, HH, it is not exhausted for hydrogen combined with chlorine, HCl. Thus, an atom of nitrogen possesses other affinities than those which it manifests for hydrogen in ammonia. While nitrogen is triatomic in ammonia because it is united with three mon- atomic atoms, it behaves as a pentatomic element in ammonium chloride. The parts which polyatomic elements play in their compounds may be expressed by accents marking the number of atomici- THEOUY OF ATOMICITY. 237 ties or tlie quantivalence of the element, as shown in the following formulae : 0"H^ X"'H' N-H*C1 F"CP P^CP C^'O"^ Water. Ammonia. Ammonium Phospliorus Phosphonis Carbon chloride. trichloride, pentachloride. dioxide. In these compounds, as has been remarked before, the poly- atomic elements form, as it were, the nuclei around which the other elements are grouped. This is an important idea, since it leads to the determination of the constitution of the mole- cules, that is, the arrangement of their atoms. The considera- tions just presented concerning the functions of the elements in compounds alone permit the resolution of this question; they alone lead to the discovery of the relations existing be- tween the atoms in theii' combinations, and to the determina- tion of their relative positions, in a word, to the revelation of the molecular structure. The following developments will demonstrate this fact. We will reconsider certain of the combinations above men- tioned, which have been taken as t3rpes. In water, an atom of diatomic oxygen fixes two atoms of hydrogen. One atom of oxygen can fix two atoms of any monatomic element, forming compounds belonging to the same type as water; but it cannot at the same time fix a monatomic element and a diatomic element. In other words, an atom of hydrogen in water may be replaced by an atom of chlorine, bromine, iodine, or potassium, but not by an atom of oxygen ; and if a second atom of the latter element be joined to the oxygen of water, it will be seen that there remains a free affin- ity which may be satisfied by hydrogen. Hydrogen dioxide would result. H-0"-H H-0"-0"-H Water. Hydrogen dioxide. Hence, we draw the conclusion that in hydrogen peroxide, the two atoms of oxygen are combined with each other, and that in uniting together each atom loses one atomicity, the two others being satisfied by hydrogen. The same considerations are applicable to the compounds of chlorine and oxygen. Hypochlorous acid may be regarded as composed of an atom of chlorine united to the group hydroxyl. Cl-0"-H = Cl(OH)' Hypochlorous acid. 238 ELEMENTS OF MODERN CHEMISTRY. In this compound the chlorine exchanges one unit of satu- ration with the oxygen of the group OH, just as it exchanges one with hydrogen in hydrochloric acid: it is monatomic or univalent. In chloric acid it is combined with two atoms of oxygen and one group, OH. It exchanges 4 atomicities with oxygen, and one with the group OH : Cl^O^-^OH)' Chloric acid. Chlorine thus manifests 5 atomicities in chloric acid ; but it has 7 in perchloric acid. Cl-'O^(OH)' Perchloric acid. Without dwelling on these considerations, we will take one more example. In hydrogen phosphide, one atom of phosphorus is combined with three atoms of hydrogen ; it manifests but three atomici- ties, and these could not neutralize those which reside in three atoms of oxygen, since the latter possess six atomicities. If, then, three atoms of diatomic oxygen were united with one atom of triatomic phosphorus, it is clear that three affinities would remain free, one in each of the three atoms of oxygen. In phosphorous acid, these three affinities of the oxygen atoms are satisfied by three atoms of hydrogen. We may suppose that in the molecule of this compound, the phosphorus is the nucleus around which are grouped three atoms of oxygen, each of which is joined also to one atom of hydrogen. This atomic grouping is indicated in the following formulae : H OH I I P P /\ ^ H H HO OH Hydrogen phosphide. Phosphorous acid. This hydrogen, combined with the oxygen in all of the oxy- gen acids, plays invariably the same part: it saturates the one atomicity which remains free in one atom of oxygen. The oxygen thus combined with an atom of hydrogen, has lost one of its atomicities by the fact of this combination ; it still retains one in the group OH, which represents, as it were, water less one atom of hydrogen. HOH — H = (OHy THEORY OF ATOMICITY. 239 This group is named hydroxyl, and it is evident that, although it cannot exist by itself, it may play the part of a monatomic element, for it retains one free atomicity. It may then replace a monatomic element, such as hydrogen or chlo- rine. Indeed, it plays an important part in the constitution of acids. If we consider the examples which have already been dis- cussed, we will notice that it is this hydroxyl which, by com- bining with an element or group of elements capable of forming acids, confers upon them the characters of acids. So consid- ered, hypochlorous acid is formed by the union of hydroxyl with an atom of chlorine. Cl(OH)' Hypochlorous acid. Sulphuric acid is formed by the union of two hydroxyl groups with sulphurous oxide, and represents in a manner sulphuryl chloride in which the two atoms of chlorine are replaced by two hydroxyl groups. Sulphuryl chloride. Sulphuric acid. Phosphorous acid is formed by the union of three hydroxyl groups with one atom of phosphorus. (Cl f(OH)' F" i Cl F" ] (OH)' (01 ((OH)' Phosphorus trichloride. Phosphorous acid. Lastly, phosphoric acid results from the union of three hy- droxyl groups with one atom of phosphorus already combined with one atom of oxygen (phosphoryl). ( 01 f (OH)' 0"P'^C1 0"P'^(OH)' (Cl ((OH)' Phosphoryl trichloride. Phosphoric acid. Such, according to the theory of atomicity, are the relations existing between the atoms of certain acids ; such, in other words, is the constitution of these acids. It would be easy to extend these considerations to other bodies, but the examples we have chosen are sufficient to indicate the importance of the idea of atomicity, when it is applied to the discovery and definition of 240 ELEMENTS OF MODERN CHEMISTRY. the part played by eacli element in a given compound. By supposing tlie capacities of combination of cblorine, oxygen, sulphur, and phosphorus to be known, we have been able to follow these bodies in their most important combinations, we have seen how they attract and group around themselves other elements. We have thus been able to penetrate the atomic structure of the molecules, and have built up as it were the molecular edifice. It must be remembered, however, that the preceding formulae do not in any manner represent the real positions of the atoms in space. Their sole object is to indi- cate the points of attachment of the affinities, and consequently the mutual relations between the atoms. CHEMICAL ENERGY— THERMO-CHEMISTEY. The study of the elements and compounds already described has shown that combination is usually accompanied by a more or less intense development of energy, while in some cases energy is developed by decomposition. W;e have seen that many compounds are dissociated or separated into their elements by temperatures more or less elevated, and it is not difficult to understand that the amount of energy developed or absorbed in the formation of a compound, is the exact measure of the energy required or developed in its decomposition. The determination of the precise amount of energy developed or absorbed in any chemical reaction is the object of thermo- chemistry. In order to simplify and harmonize results for com- parison, the kilogramme degree is selected as the unit of energy, representing the quantity of heat necessary to raise the tem- perature of one kilogramme of water through one degree centi- grade. This unit is termed a calorie, and the heat of formation or decomposition of a compound is expressed by the number of calories produced by the formation or decomposition of one molecule of the substance, the atom of hydrogen being supposed to weigh one gramme. Thus the heat of formation of carbon dioxide will be the number of calories produced by the perfect combustion of twelve grammes of carbon. When practicable, the heat of formation is determined by the energy of combus- tion. As a general formula, we may consider that the combining atoms possess a quantity of energy in some form, chemical or CHEMICAL ENERGY — ^THERMO-CHEMISTRY. 241 physical, which quantity we may call w. The product of the reaction will possess m ± n energy, ± n being the quantity of energy disengaged by the reaction. It has been found that the amount of energy developed by the formation of any compound from its elements is precisely the same whether the body is formed at once or by several stages (Hess). Thus, the heat of formation of CO^ is the same whether it be formed by C -f 0^ = C0^ or by C + = CO and CO + = C0= In the oxidation of a combustible compound which has been formed with disengagement of energy, less heat should be pro- duced than by the direct oxidation of the constituent elements, since part of their atomic energy has already been disengaged by their combination. Thus, the energy of formation of CH* should be represented by the difference between the heat pro- duced by the combustion of CH*, and that produced by the combustion of C plus that of H* (H = 1 gramme). The energy of formation of CO will be the difference between the energy of combustion of C and that of CO. Direct and indirect methods of reasoning of this kind have enabled the calculation of the energy of formation of a large number of compounds. The physical state of the reacting bodies and of the product is necessarily an important factor in therm o-chemical consider- ations. If the product be gaseous while the reacting bodies be liquid or solid, a certain amount of energy will be required to maintain the matter in the gaseous form, and this quantity must be calculated and added to that actually resulting from the reaction. If, on the contrary, the bodies entering into combination be liquid or gaseous while the result is solid, the direct energy of combination will be lower than the heat de- veloped by the reaction. While the laws governing chemical energy are as yet unde- veloped, it is not difficult to understand the cause of the phe- nomena in which heat is disengaged or absorbed. We must believe that the atoms of any element are endowed with motion, and chemical energy then becomes atomic motion. If the atomic motion be arrested, the energy appears as heat, molecu- lar motion, or in some other form. When two elements manifest energetic affinities for each other, it is because their atoms are moving in such a manner that a portion of the L ^ 2i 242 ELEMENTS OF MODERN CHEMISTEY. atomic motion may be mutually arrested ; this atomic energy is then transformed into heat energy or molecular motion. While all chemical action must be referred to atomic motion, the manner of that motion cannot at present be fully under- stood. Atomic energy, that is, affinity, must be a function of temperature, since the atomic vibrations of the elements may be so varied by an absorption of energy from external sources that, on one hand, the motions of atoms manifesting little affinity for each other may be so harmonized that combination must take place, and, on the other, the harmonious movements of unlike atoms may be rendered so incompatible that those atoms will separate, finding conditions of more stable equilib- rium in molecules of the elementary substances. In this manner we can readily interpret those cases in which decomposition is attended by a development of energy, as with hydrogen dioxide, nitrogen iodide, and many other compounds. In the formation of nitrogen iodide by the action of ammonia on iodine (page 155), ammonium iodide also is formed. 4:NW -f 3P = NP -1- 3NH*I Ammonium iodide is formed with disengagement of energy, but in the above reaction that energy does not become apparent ; the liquid does not become warm ; the energy which disappears from the atoms in the ammonium iodide is transferred to the atoms of nitrogen and iodine, and enables them to combine, forming nitrogen iodide. These atoms then possess greater energy than when in molecules of nitrogen and iodine, and on the least disturbance of the unstable equilibrium the nitrogen iodide is decomposed ; the atoms of nitrogen combine, forming molecules of nitrogen, and the atoms of iodine form molecules of iodine. The energy furnished by the formation of ammo- nium iodide then becomes external explosively. A compound which is formed from its elements with libera- tion of energy is called an exothermic compound, while one which is similarly formed with absorption or disappearance of energy is called an endofhermic compound. All explosive com- pounds are endothermic. As a general rule, in any chemical equation the sum of the energies developed in the formation of the compounds pro- duced must be greater than the sum of the energies developed in the formation of the substances reacting. Unless energy be supplied the reaction is otherwise impossible (Berthelot). METALS. The metals are elements which are good conductors of heat and electricity, and are endowed with a peculiar lustre, which is called the metallic lustre. This definition, it will be ob- served, is founded upon certain physic-al characters rather than upon chemical properties. It is unsatisfactory and wanting in exactness, for it is applicable to bodies which are properly con- sidered as metalloids. Such is antimony, which has already been described, and bismuth, which should be placed beside antimony. Indeed, the distinction between the metals and non-metals is not so well marked that a line which shall sepa- rate these two classes of simple bodies may be sharply drawn. Physical Properties of the Metals. — These will be found in the table on page 244, but the indications there given may be completed by certain other developments. The metals are opaque, but their opacity is not absolute. A sheet of gold-leaf pressed out between two plates of glass allows the passage of a green light. Gold possesses a brilliant lustre and a yellow color, but it loses this lustre when it is reduced to very fine powder. When, however, this powder is rubbed with a hard body, when, for example, it is triturated in an agate mortar, or passed under the burnisher, it acquires a certain degree of cohesion, and again assumes its lustre. It is thus with all the metals. They lose their metallic lustre when finely divided and reassume it on burnishing. The yellow color of gold is not its true color ; the rays which reach the eye are the result of but one reflection, but if light be successively reflected from ten surfaces of gold, the metal will appear of a bright-red color. Under the same circum- stances, copper will appear scarlet, zinc indigo, iron violet, and silver pure yellow (B. Prevost). Most of the metals may be crystallized. Bismuth is the most striking example. If a few kilogrammes of pure bismuth be fused, and the liquid mass be allowed to cool slowly, the 243 244 ELEMENTS OF MODERN CHEMISTRY. !S 2 AS a rt ° « a &.2 ja _^ « £ ° 5 ' cra&H < I I I I o a a :^ o S 5 ^ <1 S Oh S O O M 5 6 H g- : 05 05 O (N o o .2 -S o .2 .2 .2 S oSS^msSoSSiJ ■■3 -o r-l f- r-1 1-; O O o o o o c> o ^^ o 00 CO -* ■* ^ i i i i s i i o o a <6 o o o ?5 O tSl O (X, fl S -B 2 s -^ *§ a _ a oj o .3 S H cc ^ ;^ O &< J o « SS2 .-S o o .S .S 3 (L, cB El cq ►.:? o I a . 21.70 . 21.15 . 21.40 . 19.35 -42° 14.40 '^ . 13.59 . 11.80 . 11.33 . 10.57 . 9.82 . 8.79 , 8.60 . 7.79 . 7.79 . 7.25 . 7.29 . 7.20 . 7.01 . 6.86 . 6.71 . 2.56 . 0.97 . 0.59 5 ai >> .2 1^5 1 il O N <5 <; t» Oi h5 GENERAL PROPERTIES OF METALS. 245 metal will solidify first next to tlie walls of the vessel and on tlie surface, where it is most cooled. If, in a little while, the crust which covers the still liquid metal be pierced, and the latter be poured out, the whole of the interior of the vessel will be found covered with magnificent crystals, arranged in hopper-like pyramids, and presenting brilliant, rainbow-like colors. Other metals, such as copper, lead, antimony, tin, silver, and gold, may be crystallized under certain conditions. Some of the metals are found crystallized in nature. Those metals which may be beaten or rolled into thin laminae are said to be malleable. AA (Fig. 90) represent two steel Fig. 90. rollers capable of moving on their axes in opposite directions. A plate of metal engaged between them will be drawn in, and the rolled sheet will pass out on the other side with a uniform thickness equal to the distance between the two rollers. By diminishing this distance more and more by means of the screws BB, the sheet may gradually be reduced in thickness. Metals which may be drawn out into wires are said to be ductile. The wire-drawing machine is represented in Fig. 91. It consists of a steel plate, ff, firmly fixed in the up- rights CC, which are themselves solidly attached to a bench. The plate is pierced with a series of holes regularly decreasing in diameter. The wire is drawn from the bobbin A, through the holes and around the cylinder B, which is moved by power. That a metal may be drawn into fine wires, it is necessary that it shall olfer a certain resistance to rupture. This is called the tenacity of the metal. It is measured by suspending weights 21* 246 ELEMENTS OF MODERN CHEMISTRY. at the extremities of wires of the same diameter. The metals exhibit every degree of fusibility. Mercury is liquid at ordi- nary temperatures, while osmium cannot be melted in the oxyhydrogen flame. Some metals, such as mercury, potassium, zinc, are readily distilled ; others are scarcely volatilized at the highest attainable temperatures. Chemical Properties of the Metals. — The metals combine with each other and with the metalloids, the energy with which these combinations take place being very variable. In general, Fig. 91. the metals having the strongest affinities are those known as the alkaline metals, because they are obtained from the alkalies. Such are potassium and sodium. All the metals combine directly with chlorine. The chlorides thus formed do not all possess analogous compositions ; they con- tain for one atom of metal a varying number of chlorine atoms. A similar remark applies to the oxides and sulphides formed by the union of oxygen and sulphur with the metals. The power of combination of the latter with chlorine, sulphur, oxy- gen, etc., is far from being the same. In other words, the atoms of the metals combine unequally with the atoms of chlorine, oxygen, etc. ; hence it follows that the atomic composition of the bodies thus formed is different. If the metals be compared together in this respect, analogies and differences will be estab- lished between them, which become the basis for a rational classification. Those metals which form compounds having EXTRACTION OF METALS. 247 analogous atomic constitutions are put into tlie same group. Such principles as these have guided us in the classification of the non-metals, and we will apply them to the metals as soon as we have acquired a general knowledge of their compounds. K'atiiral State and Extraction of the Metals. — Certain metals are found in nature free from all combination. It is thus that gold, silver, copper, bismuth, etc., are met with in the native state. More often the metals are found combined with oxygen, sul- phur, or other non-metals. The natural sulphides are numerous and abundant : those of silver, copper, mercury, lead, and zinc constitute the minerals from which these metals are ordinarily extracted. Iron and tin are obtained from their oxides, which are found in nature. The metals are often found in saline combinations, in the form of chlorides, carbonates, sulphates, phosphates, and silicates. We can only indicate here in a very general manner the methods by the aid of which the metals are extracted from their combinations. If a metal is to be obtained from its oxide, the latter is generally reduced by carbon at a high temperature. A num- ber of oxides resist the reducing action of carbon at the highest temperatures attainable by the combustion of that element in the ordinary furnaces ; with few exceptions, how- ever, they will give up their oxygen to carbon when sub- jected to the intense heat of the arc in the electric furnace (see page 210). Some of the rarer metals have been obtained in this manner. Certain oxides reducible by carbon do not yield pure metal by such reduction, as the metal combines with part of the carbon, forming a carbide from which removal of the carbon is difficult or even impossible. In such cases reduction of the oxide may be accomplished by a more oxidizable metal : thus manganese and chromium oxides may be reduced by aluminium or magnesium. If the ore be a sulphide, it is first roasted, that is, heated in contact with the air. The oxygen of the air then acts upon the sulphur, which is disengaged in the form of sulphur di- oxide, and upon the metal, which remains in the form of oxide ; the latter is afterwards reduced by carbon. The metals are sometimes obtained from their chlorides by heating the latter with sodium, magnesium, aluminium, or other 248 ELEMENTS OF MODERN CHEMISTRY. metal which will combine with the chlorine, forming the cor- responding chloride. Electrolysis of salts, either in aqueous solution or in a state of fusion, is now advantageously employed for the extraction of metals like copper, nickel, aluminium, and magnesium. ALLOYS. The combinations of the metals with each other are called alloys ; amalgams are the alloys formed by mercury. If a small quantity of mercury be heated in a crucible or a capsule, and a morsel of sodium be thrown into it, the latter dissolves instantly ; and by employing the proper proportions of mercury and sodium, the alloy may be obtained in crystals possessing a definite composition. Crystalline combinations of zinc and antimony are known. The most interesting has the composition Sb^Zn^ It is necessary to state that more generally the alloys do not present the characters of definite compounds. Many metals seem to alloy with each other in all proportions, forming mix- tures which are more or less homogeneous ; but this is only in appearance, and it must be admitted that one or more com- pounds exist in such a mixture, remaining dissolved in each other, or mixed with the excess of one of the metals. Such a mixture would form a sensibly homogeneous mass, especially when the molten mixture had been suddenly cooled. But if the cooling be slow, it may happen that the less fusible definite compounds separate from the mixture in the crystalline form, leaving the more fusible compounds which still remain liquid. Such a separation often takes place in large masses of melted alloys which are allowed to cool slowly. The process is called liquation^ and it may be readily conceived that the alloys so cooled are far from homogeneous in composition after their solidification. Conversely, when a mass composed of a mixture of metals and alloys is slowly heated, the more fusible assume the liquid state first, and separate from the others. This difference between the fusing-points of the various defi- nite compounds which may exist in an alloy is taken advantage of in the arts for their separation. Alloys are generally more fusible than their component metals. Thus, there is an alloy which melts at about 66° j ALLOYS. 249 and contains bismuth, 4 parts ; lead, 2 parts ; tin and cadmium, each 1 part. It is known as Wood's fusible metal. The following table gives the composition of some of the more important alloys : Gold coin (United States, France, Germany) Gold coin (Great Britain) . . Gold jewelry i Silver coin (United States) . Silver coin (Great Britain) . Silverware (sterling silver) . Bronze medals ..... Gun-metal . . . Bell-metal . . . Speculum-metal . Aluminium bronze Manganese bronze Red brass . . . White brass . . German silver Type-metal Britannia-metal Hard pewter . Soft pewter Plumbers' solder {Gold 900 1 Copper 100 f Gold 916.6 1 Copper 83.4 I Gold 750-920 I Copper 250-80 {Silver 900 I Copper 100 I Silver 925 I Copper 75 I Silver 925 I Copper 75 f Copper 93.5-95 ^ Tin 6-4 ( Zinc 0.5-1 {Copper 100 (Tin 10 f Copper 78 iTin 22 f Copper 67 ITin 33 I Copper 90-95 I Aluminium 10-5 I Copper 90 \ Manganese 10 /Copper 90 \ Zinc 10 f Copper 65 I Zinc 35 {Copper 50 Zinc 25 Nickel 25 I Lead 80 I Antimony 20 ("Tin J Antimony .... j Bismuth [ Copper (Tin I Lead fTin I Lead I Tin 1 Lead 100 8 1 4 92 8 82 18 66 33 1 The proportion of gold in jewelry is expressed in carats, which signifies twenty-fourths. Thus, pure gold is twenty-four carats fine, while eighteen- carat gold contains eighteen twenty-fourths gold and six twenty-fourths of basfir allnv. of baser alloy. 250 ELEMENTS OF MODERN CHEMISTRY. METALLIC OXIDES AND HYDROXIDES. Formation of Metallic Oxides. — The metals absorb oxygen with very unequal energy. Many of them become oxidized when exposed to the air at temperatures more or less elevated. In this respect it is important to distinguish the action of dry air from that of moist air. Potassium is the only metal that absorbs dry oxygen at ordi- nary temperatures. All of the other metals, with the excep- tion of silver, gold, and platinum, only become oxidized in the air at very high temperatures. Melted lead absorbs oxygen. Mercury becomes oxidized at about 350° ; copper at a dull-red heat. The combination often takes place with the production of luminous heat. Iron burns in oxygen, but it is necessary that the metal be first heated to bright redness that the combustion may take place. However, the finely-divided iron that is obtained by reducing oxide of iron in a current of hydrogen at a comparatively low temperature, will take fire when exposed to the air at ordi- nary temperatures. It is pyrophoric, and the fine state of division of the metal favors the oxidation. If the powder be projected into the air, each particle takes fire and burns with a bright flash. A bright sheet of iron will indefinitely preserve its brilliant surface in dry air, but if a drop of water be placed upon it, or if it be exposed to the action of a moist atmosphere, rust makes its appearance in a short time. This rust is ferric hydrate, for the metal has at the same time absorbed oxygen and water. It is generally admitted that it is the oxygen of the air dis- solved in the water that first fixes upon the metal, and that the combination is favored by the presence of carbon dioxide. However it may be, the spot of rust once formed constitutes a Voltaic couple with the iron itself, and the current so estab- lished decomposes the water. The oxidation then proceeds rapidly, the oxygen of the decomposed water combining with the metal. It is possible that hydrogen dioxide may play a part in oxi- dations ; it may be formed as a secondary product during the METALLIC OXIDES AND HYDROXIDES. 251 decomposition of the water, and fix directly upon the metals, converting them into hydroxides (Weltzien). 2Fe + 3ffO^ = 2FeO^H3 Iron. Hydrogen dioxide. Ferric hydroxide. Mg -f- H^O^ = MgO^H^ Magaesium. Magnesium hydroxide. Indeed, the oxidation of metals in moist air always produces hydroxides, and not oxides. Composition and Classification of the Oxides. — It has already been remarked that the metals differ as to the number of oxygen atoms with which they combine ; besides this, the same metal may form several compounds with oxygen, con- stituting different degrees of oxidation. Hence the oxides present different compositions, and the differences exercise a marked influence upon the properties of the compounds. 1. Certain oxides present the same atomic constitution as water. Two atoms of metal are combined with one atom of oxygen. Ag^O silver oxide. Cu^O cuprous oxide. Hg^O mercurous oxide. Au^O aurous oxide. TPO thallous oxide. 2. One atom of certain metals can combine with one atom of oxygen ; the oxides of the general formula MO result. BaO barium oxide. SrO strontium oxide. CaO calcium oxide. MgO magnesium oxide. MnO manganous oxide. FeO ferrous oxide. ZnO zinc oxide. PbO lead oxide. CuO cupric oxide. HgO mercuric oxide. SnO stannous oxide. The metallic oxides containing but one atom of oxygen are generally energetic bases ; that is, they react energetically with the acids, forming salts. 3. The sesquioxides are those which contain two atoms of metal and three atoms of oxygen. Such is antimony oxide, that has already been studied ; the oxides of bismuth, gold, etc., present an analogous composition. 252 ELEMENTS OF MODERN CHEMISTRY. Sb^O^ antimony sesquioxide. Bi^QS bismuth sesquioxide. Au^QS gold sesquioxide. Fe^QS ferric oxide. Mn^QS manganic oxide. Cr^QS chromic oxide. Al^QS aluminium oxide. 4. A large number of oxides contain two atoms of oxygen. Ba02 barium dioxide. SrO^ strontium dioxide. Mn02 manganese dioxide. PbO^ lead dioxide. Sn02 stannic oxide. The first four are incapable of uniting with acids to form corresponding salts. With hydrochloric acid, they yield either hydrogen peroxide or chlorine. BaO'^ + 2HC1 = BaCP + H^O^ MnO^ + 4HC1 = MnCP + 2H20 + CP "When manganese dioxide is heated with sulphuric acid oxygen is disengaged, and manganous sulphate is formed. H^SO* + MnO^ = MnSO* -f H^O + Sulphuric acid. Manganese dioxide. Manganous sulphate. As to stannic oxide, it is the anhydride of a metallic acid. SnO^ -f H^O = H^SnO^ stannic acid. 5. The oxides which contain three atoms of oxygen possess acid characters still more marked than stannic oxide. Chro- mium trioxide, CrO^ is well known, and manganic and ferric anhydrides would present analogous compositions. 6. There is a class of oxides still more complex than the preceding ; they can be regarded as formed by the union of two oxides, and they have been named saline oxides. Such are Ferroso-ferric oxide Fe^O* = FeO + Fe^O^, or magnetic oxide of iron. Manganoso-manganic oxide Mn^O* = Mn^O^ -f MnO, or red oxide of manganese. Diplumboso-plumbic oxide Pb^O* = PbO^ + 2PbO, or red oxide of lead. The first two contain one molecule of a sesquioxide, combined with one molecule of a monoxide ; the last, one molecule of a dioxide and two molecules of a monoxide. METALLIC OXIDES. 253 Chemical Properties of the Oxides. — Some of the oxides are fixed, that is, undecomposable by heat; others lose the whole or a part of their oxygen at temperatures more or less elevated. The oxides of the noble metals, such as silver, gold, and platinum, are decomposed by heat alone into metal and oxygen. We have seen that mercuric oxide is decomposed by a dull-red heat. Many of the oxides that contain two or three atoms of oxygen lose a part of the latter element when heated to redness. Such are the dioxides of manganese, lead, and barium. The oxides containing but one atom of oxygen are among the most stable. Some of them absorb oxygen when they are heated in contact with air, forming higher oxides. Among these are the monoxides of manganese, iron, lead, and tin. Hydrogen reduces the greater number of the oxides at tem- peratures more or less elevated ; water is formed, and the metal is set at liberty. If a current of dry hydrogen be passed over ferric oxide heated in a glass bulb (Fig. 92), the oxide is reduced, and a black powder is obtained which is finely divided and pyropho- ric iron. Vapor of water escapes at the same time by the drawn-out point of the bulb. Fe^O' + 3H^ = 3H^0 -f 2Fe Ferric oxide. Iron. 22 254 ELEMENTS OF MODERN CHEMISTRY. The ferric oxide may be replaced by cupric oxide, CuO. If this oxide be heated in a current of hydrogen, it is reduced, and the action is so energetic that it gives rise to the produc- tion of light and heat. Carbon reduces the greater number of the oxides with for- mation of either carbon dioxide or monoxide. It is even more energetic in its action than hydrogen, for it decomposes oxides which are irreducible by the latter element, such as those of potassium and sodium. The various oxides require for their reduction more or less heat, according to the degree of energy with which they retain their oxygen. If the reduction be difficult, a high temperature is required, and carbon monoxide is formed; otherwise carbon dioxide is the product. The oxides of calcium, barium, strontium, and aluminium are not reducible by carbon, except at the high temperature of the electric arc. A small quantity of cupric oxide may be reduced by char- FiQ. 93. coal by heating the mixture in a glass tube by the aid of a spirit-lamp (Fig. 93). Carbon dioxide is disengaged. 2CuO + C == 2Cu + CO^ Cupric oxide. Copper. But to reduce zinc oxide by charcoal, the mixture must be METALLIC OXIDES. 255 heated to bright redness in a clay or u'on retort, and in this case carbon monoxide is evolved, ZnO -f- C =: Zn -I- CO Zinc oxide. Zinc. Chlorine decomposes nearly all of the oxides at a high tem- perature. It drives out the oxygen and combines with the metal, forming a chloride. Some of the oxides are in-educible by carbon, and resist also the action of chlorine. Such an oxide is aluminium oxide, or alumina. But if these oxides be submitted to the simultaneous action of chlorine and carbon at a high temperature, they are converted into chlorides, and carbon monoxide is disengaged. An intimate mixture of alumina and charcoal may be intro- duced into a porcelain tube, BB (Fig, 94), which is heated to Fig. 94. bright redness, and a current of dry chlorine then passed through. In this case, carbon monoxide is disengaged, while aluminium chloride is formed and volatilizes and may be con- densed in a cooled receiver. Sulphur decomposes all of the oxides except alumina and its analogues. The reaction takes place at a high temperature, and gives rise to the formation of a sulphide and sulphur di- oxide, or a sulphide and a sulphate if the latter be not decom- posable by heat. 256 ELEMENTS OP MODERN CHEMISTRY. If sulphur be heated with cupric oxide, cupric sulphide is formed and sulphur dioxide is evolved. 2CuO + 3S = 2CuS + SO^ Cupric oxide. Cupric sulphide. However, if calcium oxide (lime) or lead oxide, PbO, be heated with sulphur, a sulphate and a sulphide are formed. 4CaO + 2S''' = 3CaS + CaSO* Calcium oxide. Calcium sulphide. Calcium sulphate. Action of Water upon the Oxides — Metallic Hydroxides and Acids. — If some fragments of barium oxide (baryta) be sprinkled with cold water, an energetic reaction immediately takes place. The water unites with the metallic oxide with so much energy that the heat disengaged is sufficient to convert a portion of the water into vapor. The barium oxide is con- verted into hydroxide. BaO 4- H^'O = Ba(0H)2 Barium oxide. Barium hydroxide. In the same manner, the oxides of potassium and sodium energetically absorb the elements of water, being converted into hydroxides. K^O + H^O = 2K0H Potassium oxide. Potassium hydroxide. The hydroxides of potassium and sodium are soluble in water, and their solutions are caustic, changing tincture of violet to a green color and restoring the blue color to reddened litmus solution. These hydroxides constitute the alkalies. The hydroxides of barium, strontium, and calcium are like- wise soluble in water to a certain extent, and their solutions are also somewhat caustic. Other hydroxides are insoluble ; they may be obtained by double decomposition by precipitating the corresponding salts with an alkali. If a solution of potassium hydroxide be poured into a solu- tion of cupric sulphate, a light-blue precipitate of cupric hydroxide is formed. CuSO^ + 2K0H = K^SO* + Cu(OH)^ Cupric sulphate. Potassium hydroxide. Potassium sulphate. Cupric hydroxide. But if this precipitate be heated, even in the liquid in which it was formed, it changes to brown, and is converted into oxide by losing its water. Cu(OH)^ — H^O -- CuO SULPHIDES. 257 A great number of metallic hydroxides undergo the same decomposition when they are heated. There are true metallic acids which contain the elements of an oxide plus the elements of water. Such are H^CrO' = CrO' + H^O Chromic acid. Chromium trioxide. H^MnO* = MnO^ + H=^0 Maogauic acid. Manganese trioxide. As far as their constitution is concerned, these metallic acids may be compared to sulphuric acid. H^SO^ = 80=^ -I- WO They also resemble sulphuric acid in their chemical func- tions ; each contains two atoms of basic hydrogen, that is, two atoms of hydrogen which are replaceable by a metal. SULPHIDES. Sulphur has a great tendency to unite with the metals, and the union often takes place with a vivid evolution of heat. Copper-turnings and iron-filings burn in the vapor of sulphur. The phenomena which favor or determine, and those which accompany this combination, have already been indicated, and we have seen that the presence of a small quantity of water favors chemical union in a mixture of sulphur and iron-filings. In composition the sulphides are analogous to the oxides. The more important of the transformations which they may undergo are the following: Oxygen decomposes all of the sulphides at a temperature more or less elevated. Finely-divided potassium sulphide, obtained by calcining the sulphate with an excess of charcoal, is a black powder, but it becomes incandescent on contact with oxygen, and if thrown into the air it produces a shower of sparks. It is known as Gay-Lussac's pyrophorus. Its fine state of division favors the absorption of oxygen, and the latter converts it into sulphate. K^S 4- 0* = K^SO^ Potassium sulphide. Potassium sulphate. Dry oxygen acts in the same manner upon all the sulphides when the corresponding sulphates are stable at high tempera- tures. In the contrary case, sulphur dioxide is formed, and r 22* 258 ELEMENTS OF MODERN CHEMISTRY. a residue of oxide or even of metal is obtained, if the oxide be decomposable by heat. If zinc sulphide be roasted, it is converted into zinc oxide, and sulphur dioxide is evolved; but if sulphide of mercury- be heated in a current of air, metallic mercury is obtained. HgS + 0^ = Hg + SO^ Mercuric sulphide. Mercury. Moist oxygen acts upon the sulphides more readily than the dry gas. It unites with them at ordinary temperatures, form- ing sulphates. FeS 4- 0* = FeSO* Sulphide of iron. Ferrous sulphate. Chlorine attacks all of the sulphides, forming metallic chlo- rides and sulphur chloride, if the dry method be employed, or with deposition of sulphur if the reaction take place in presence of water. Water dissolves the alkaline sulphides as well as those of cal- cium, barium, and strontium ; the sulphides of the other metals are insoluble in water. Hydrogen sulphide combines with certain sulphides, convert- ing them into hydrosulphides. The analogy will be noticed between this reaction and that of water upon the oxides. K^S + ffS = 2KSH Potassium sulphide. Potassium hydrosulphlde. K^O -h H^O = 2K0H Potassium oxide. Potassium hydroxide. CHLORIDES. Chlorine, bromine, and iodine form with the metals com- pounds which possess the appearance and certain properties of salts. Indeed, common salt, or sodium chloride, has given the name to the entire class of saline compounds. Hence Berze- lius named chlorine, bromine, and iodine the halogen bodies, and called their combinations with the metals the haloid salts. Thus he admitted the relation between these compounds and the true salts, while at the same time distinguishing them by a particular name, for while they resemble the salts in their prop- erties, they differ from them in composition. This subject will be more fully considered farther on. Composition. — The metals, as a rule, combine directly with chlorine, but the different metals do not combine with CHLORIDES. 259 it in the same atomic proportions, and often the same metal forms several distinct combinations with this element. Hence the differences in the composition of the chlorides. They are formed by the union of an atom of metal with one, two, three, four, five, or six atoms of chlorine. KCl CaCP SbCP SnCP SbCP MoCP Potassium chloride. Calcium chloride. Antimony trichloride. Tin tetrachloride. Antimony pentachloride. Molybdenum hexachloride. NaCl FeCP BiCP TiCP WCP WCP Sodium chloride. Ferrous chloride. Bismuth trichloride. Titanium tetrachloride. Tungsten pentachloride. Tungsten hexachloride. AgCl ZnCP AuCP PtCP Silver chloride. Zinc chloride. Gold trichloride. Platinum tetrachloride. CuCl CuCP AlCP Cuprous chloride. Cupric chloride. Aluminium chloride. HgCl Mercurous chloride. HgCP Mercuric chloride. CrCP Chromic chloride. It is seen that the same metal may form several combina- tions with chlorine. Mercury and copper combine with one or two atoms of chlorine. Iron combines with two or three atoms of chlorine. Tin and platinum combine with two or four atoms of chlorine. Tungsten combines with four, five, or six atoms of chlorine. Owing partly to faulty determinations, and partly to anom- alies in their vapor densities, some of the chlorides of the first and the third of the above series were for a long time regarded as consisting of two atoms of metal combined with two and with six atoms respectively of chlorine. Thus mer- curous chloride was represented by the formula Hg^CP, and that of aluminium chloride was written APCP. In these, as well as in analogous cases, it has been shown that the vapor densities and other physical constants, when determined under the proper conditions, accord perfectly with the simpler for- mulae given above. Physical Properties of the Chlorides. — Most of the chlo- rides are solid and possess the aspect, color, and physical prop- erties of the salts of the same metal. Nearly all are crystalline and soluble in water. Only the chloride of silver, mercurous 260 ELEMENTS OP MODERN CHEMISTRY. and cuprous chlorides are insoluble ; lead chloride and thal- lous chloride are but slightly soluble in water. Certain metallic chlorides are liquid at ordinary tempera- tures. Such are the tetrachlorides of tin and titanium. Some, like the chlorides of zinc and bismuth, are solid, but fusible at low temperatures. These latter were formerly designated as metallic butters. Most of the chlorides are fusible at high temperatures, and many of them are volatile and can be distilled without altera- tion. It is thus with the liquid chlorides, with the chlorides of zinc, bismuth, mercury, etc. Chemical Properties. — As a rule, the chlorides are very stable. Only the chlorides of certain of the precious metals, as those of gold and platinum, are entirely decomposed by a high temperature. Some of the higher chlorides lose chlorine when calcined, and are converted into lower chlorides. Thus, cupric chloride is converted into cuprous chloride when heated out of contact with. air. A great number of the chlorides are reduced when they are heated in a current of hydrogen. In this case, hydrochloric acid is disengaged, and the metal remains. Thus, hydrogen removes the chlorine from the chlorides of silver and iron. These decompositions are determined by the powerful affinity of chlorine for hydrogen. The action of the metals upon the chlorides gives rise to interesting phenomena which are worthy of study. If corrosive sublimate, which is mercuric chloride, be mixed with powdered tin and the mixture be heated in a small glass retort provided with a receiver, a liquid will soon collect in the latter which diffuses thick vapors in the air. It is the tetra- chloride of tin, which was formerly known as " fuming liquor of Libavius." It is formed by the decomposition of the mer- curic chloride, which gives its chlorine to the tin, metallic mercury being at the same time set free. Bismuth decomposes mercuric chloride in the same manner when the two substances are heated together. These experi- ments are conducted in the dry way. They may be modified by operating in the presence of water, in which we have re- marked that most of the chlorides are soluble ; it is thus with mercuric chloride. If a plate of copper be plunged into a solution of this body, it at once becomes covered with a layer of metallic mercury. CHLORIDES. 261 That metal is displaced from its combination by the copper, wbicb combines with tbe chlorine : cupric chloride is formed, and after the lapse of some time, the liquid will contain only that compound. It becomes green, and if a plate of zinc be plunged into it, the copper will be precipitated in its turn, and the zinc will combine with the chlorine and enter the solution ; the liquid then contains zinc chloride. Thus, the metals mutually displace each other from their solutions, according to the energy of their affinities. In this case it is the possession of the chlorine for which they antago- nize each other, the stronger driving out the weaker. It must be remarked that in this respect the chlorides behave in the same manner as the oxygen salts. This analogy is continued in innumerable reactions. Solu- tions of the chlorides enter into double decompositions like solutions of the true salts. If potassium hydroxide be added to a solution of either cupric sulphate or cupric chloride, in each case a light-blue precipitate of cupric hydroxide is obtained. CuSO* + 2K0H = K^SO* + Cu(OH)*^ Cupric sulphate. Potassium liydroxide. Potassium sulphate. Cupric hydroxide. CuCP + 2K0H = 2KC1 + Cu(0H)2 Cupric chloride. Potassium chloride. But cupric chloride resembles the sulphate in still another property. When perfectly pure it is yellowish. If it be moist- ened with water, it becomes heated and assumes a green color. It has combined with water, and will dissolve if enough of that liquid be added. A green liquor is thus obtained, which de- posits, by spontaneous evaporation, magnificent green prisms. These crystals are hydrated cupric chloride. They contain water of crystallization, and can only exist on that condition. It is the same with the crystals of cupric sulphate. Thus, certain chlorides are capable of taking water of crys- tallization like the true salts. We may complete the analogy by one more characteristic. 1. If a solution of aluminium sulphate be added to a con- centrated solution of potassium sulphate, and the mixture be agitated, an abundant crystalline deposit is obtained. This is a double salt, — potassium and aluminium sulphate, or alum. 2. If a solution of platinic chloride be added to a concen- trated solution of potassium chloride, a yellow precipitate is 262 ELEMENTS OF MODERN CHEMISTRY. formed at once. It is the double chloride of potassium and platinum, which contains all of the elements of two molecules of potassium chloride and one molecule of platinic chloride. This example shows that the chlorides can combine together, forming double chlorides, just as the true salts may combine together to form double salts. SALTS. Definition. — The salts are formed by the substitution of metal for the hydrogen of the acids, and they result from the action of the acids upon the metallic oxides or hydroxides. The name acid applies to two classes of compounds : the first are formed by the union of hydrogen with a strongly electro-nega- tive element, such as chlorine or bromine ; these are the hy- dr acids. Such are hydrochloric acid, HCl, and hydrobromic acid, HBr. The acids of the other class are more complicated, contain- ing hydrogen united with a strongly electro-negative oxidized group, that is, a group of atoms formed by oxygen and another element ; these are the oxyacids. Such are nitric acid^ HNO^, and sulphuric acid, H^SO*. These two classes of acids behave in the same manner in contact with basep, that is, with metallic oxides or hydroxides. 1. If hydrochloric acid be gradually added to a concentrated solution of potassium hydroxide, the liquid becomes heated, and, as it is neutralized by the acid, a white crystalline de- posit separates and augments on cooling : it is potassium chloride. 2. If sulphuric acid diluted with its volume of water be cautiously and gradually added to a concentrated solution of potassium hydroxide, the liquid becomes heated, and, as it is neutralized by the acid, a white crystalline deposit separates and increases on cooling : it is potassium sulphate. The analogy between the two reactions is marked. In each case a powerful base, potassium hydrate, has been neutralized by an energetic acid; the reaction has been accompanied by the production of heat, and has given rise to the formation of a saline matter which has been deposited. The part of the reaction which is invisible is the formation of water. This formation of waterj which always accompanies the generation SALTS. 263 of a salt in the ordinary manner, is expressed in the following equations : . ' KOH -f HCl = KCl + WO Potassium hydroxide. Potassium chloride. 2K0H + H^SO* = K^SO* + 2H^0 Potassium sulphate. These reactions, it will be seen, consist in an interchange of elements, a double decomposition. The hydrogen of the acid is exchanged for the metal of the potassium hydroxide and by the exchange the potassium hydroxide is converted into water, while the acid, that is, the salt of hydrogen, is converted into a salt of potassium. All hydrogen compounds capable of thus exchanging their hydrogen for an equivalent quantity of metal, fill the functions of acids, and these acids become salts when their hydrogen is thus replaced by a metal. It may then be seen what an important part hydrogen plays in the formation of salts. Whence comes this property, this capacity for making such exchanges, and for replacement by metals? Without doubt from the element or group with which the hydrogen is united in the acids ; and in this respect chlorine and sulphur play the same parts in hydrochloric and hydrosulphuric acid's that the oxidized groups play in nitric, sulphuric, and phos- phoric acids. HCl H^S Hydrochloric acid. Sulphydric acid. H(NO^) H^CSO^) H^^CPO^ Nitric acid. Sulphurous acid. Phosphorous acid. H(CIO^) H\SO*) H\PO*) Chloric acid. Sulphuric acid. Phosphoric acid. This property is characterized by saying that the elements or groups, to which the hydrogen is united, are strongly electro- negative, or acid, in opposition to the hydrogen, which is strongly electro-positive, or basic. When such an acid reacts upon an oxide, or upon a hydroxide, an interchange of elements takes place, and a salt and water are formed ; the latter is a constant product necessary to the reaction. Other examples may be added to those already given. If a current of hydrogen sulphide be passed into a solution of potassium hydroxide until no more is absorbed, potassium hydrosulphide and water are formed, ffS -f KOH = KSH + H^O Potassium hydrosulphide. 264 ELEMENTS OF MODERN CHEMISTRY. If an excess of dilute sulphuric acid be poured into a solu- tion of potassium hydroxide, potassium acid sulphate and water are formed. ff SO* + KOH = KHSO* + ff Potassium acid sulphate. Lastly, if cupric oxide be heated with dilute sulphuric acid, it dissolves, coloring the liquid blue. Cupric sulphate and water are formed. H^SO* _|_ CuO = CuSO* + H^O Cupric oxide. Cupric sulphate. Neutral, Acid, and Basic Salts. — If the salts result from the substitution of the metals for the basic hydrogen of acids, it is evident that their composition must be related to that of the acids from which they are derived. We know that the latter contain one, two, or three atoms of hydrogen, capable of being replaced by an equivalent quantity of metal : they are monobasic, dibasic, and tribasic. It is evident that the salts must present analogous differences in their composition, accord- ing as they are derived from a monobasic, a dibasic, or a tribasic acid. A salt is neutral when the basic hydrogen has been entirely replaced by an equivalent quantity of metal. But the substi- tution may be only partial, for when an acid contains two atoms of basic hydrogen, only one of these atoms may be replaced by one atom of metal ; there will then remain in the salt thus formed one atom of basic hydrogen. When an acid contains three atoms of basic hydrogen, it may happen that only one is replaced by one atom of metal ; there will then remain in the salt two atoms of basic hydrogen ; or it may be that two atoms of hydrogen are replaced by an equivalent quantity of metal, and there will then remain in the salt a single atom of basic hydrogen. Whenever basic hydrogen thus remains in a salt, the satura- tion of the acid is said to be incomplete. The salt formed ordinarily retains the characters of an acid ; it is an acid salt. The following table indicates the possible cases of complete or incomplete saturation which may be presented by a mono- basic, a dibasic, and a tribasic acid : HNO^ H^SO* HTO* J^itric acid. Sulphuric acid. Phosphoric acid. SALTS. 265 KNO^ || SO* ^2 [ PO* Potassium nitrate. Potassium acid sulphate. Monopotassium phosphate. K^SO* g I PO* Potassium sulphate. Dipotassium phosphate. Tripotasslum phosphate. Certain neutral salts possess the property of combining with the hydroxides or the oxides. The compounds so formed con- tain all the elements of the neutral salt plus those of the hydroxide or oxide ; they are called basic salts. Thus, the oxides of lead and copper may combine with the various salts of lead and copper, forming basic salts of those metals. Richter's Laws. — Towards the close of the last century fruitful investigation was made into the phenomena of neu- tralization or saturation of acids by bases. We know that a given weight of acid requires for its neutralization a fixed and absolutely invariable quantity of a given base. Thus, for the conversion of 1000 grammes of sulphuric acid into neutral potassium salt, a quantity of potassium hydrate corresponding to 961 grammes of potassium oxide, K^O, is required. To saturate these 1000 grammes of sulphuric acid, it is necessary to take weights of the oxides which are invariable for each one separately, but which vary among themselves. Thus, 1000 grammes of concentrated sulphuric acid are neu- tralized by the following quantities of the oxides named : Potassium oxide 961 grammes. Sodium oxide 632 " Barium oxide 1561 " Calcium oxide 571 " Zinc oxide 866 " Cupric oxide 811 " Mercuric oxide 2204 " Silver oxide 2367 " Again, to neutralize 1000 grammes of the most concentrated nitric acid, the following quantities of the same oxides are required : Potassium oxide 747 grammes. Sodium oxide 492 " Barium oxide 1214 " Calcium oxide 444 " Zinc oxide 651 " Cupric oxide 631 « Mercuric oxide 1714 "' Silver oxide 1841 ** M 23 266 ELEMENTS OF MODERN CHEMISTRY. Ricliter was the first to remark that these latter quantities are precisely in the same ratio to each other as the quantities of oxides which neutralize 1000 grammes of sulphuric acid. Thus, 961 ^ 747 632 492 961 _ 747 1561 ~1214 'J} =lfL, etc. 571 444 In other words, the quantities of oxides which neutralize a given weight of one acid are proportional to the quantities of the same oxides which neutralize the same weight of another acid. This law of the composition of salts was discovered, towards the close of the last century, by Kichter, a chemist of Berlin. It is the law of relative combining proportions, applied to particular cases and the reactions of compounds, but soon afterwards to be generalized by Daiton and expressed as the fundamental law of chemical combination. Richter also studied the phenomenon of the precipitation of metallic solutions by the metals. It is known that when a piece of iron is plunged into a solution of cupric sulphate, the iron dissolves, displacing a certain quantity of copper, without other change. Since the new salt formed, ferrous sulphate, ex- ists in the solution in the same conditions of neutrality as the cupric sulphate, the quantities of metal which thus displace each other are equivalent. As neither oxygen nor acid is set at liberty, it must be admitted that the respective quantities of the metals, in the salts successively formed, are united to the same quantity of oxygen. It has even been supposed that in the salts which, like the sulphates, contain four atoms of oxygen, the metal is in intimate relation with one of these atoms, which is precisely sufficient to constitute the metal in the state of monoxide. CuSO* = CuO,SO^ FeSO* = FeO,SO' If this were so, it is evident that when cupric sulphate is decomposed by iron, the quantity of metal which enters into solution would combine or enter into relations with precisely the quantity of oxygen abandoned by the copper. This quantity of oxygen being constant, the quantities of the metals which com- SALTS. 267 bine successively with it, differ, but are equivalent to each other, and it is evident that the oxides thus formed would be more rich in oxygen as the weight of metal which enters into solution is less considerable; in other words, the richness of all these oxides in oxygen is inversely proportional to the weights of the metals which successively become dissolved ; it was in this form that Kichter announced the second law of the com- position of salts. It will be seen that this law is implied in the first, and that both are but particular cases and natural con- sequences of the theory of equivalents, as it is understood at present and as it has already been explained (page 33). General Properties of Salts. — The salts present very differ- ent colors. Those which are formed by an acid possessing a color are themselves colored ; such are the chromates, manga- nates, and permanganates. Most of the colored oxides form salts presenting various colors. Ferrous salts are bluish-green. Ferric salts are yellow or yellowish-brown. Manganese salts are pink. Chromium salts are dark green or red. Nickel salts are green. Cobalt salts are currant-red. or blue. Cupric salts are blue or green. Gold salts are yellow. It is to be remarked that these various colors are only devel- oped, as a rule, when the salts are hydrated, that is, combined with water of crystallization. The taste of the salts depends upon their solubility ; it is wanting altogether or but slightly marked in the insoluble salts ; more or less pronounced and very diverse in the soluble salts. The salts of magnesium are bitter ; the aluminium salts are astringent ; those of iron astrin- gent, with a metallic after-taste; the salts of lead are at the same time sweet and astringent ; the salts of copper, antimony, and mercury have an acrid metallic taste, which is nauseous, and is called styptic. The salts generally occur in crystalline form. Some of them may be obtained as amorphous precipitates, but if such salts be formed slowly under circumstances favoring crystallization, they also assume the form of crystals. Isomorphism. — Certain salts which possess similar atomic compositions crystallize in identical or nearly identical forms; they are called isomorphous. It is thus with the double sul- 268 ELEMENTS OF MODERN CHEMISTRY. phates, wHich are called alums, and of whicli ordinary alum or aluminium and potassium sulphate is the type. These alums are formed by the union of a sulphate, R^SO*)^, with a sul- phate, M^SO*, and they all contain 24 molecules of water of crystallization. Thus, ordinary alum, AP(SO^)lK=^SO' + 24H^O Aluminium and potassium double sulphate. is isomorphous with chrome alum and iron alum. Cr^(SO^)lK^SO* + 24ffO Chromium and potassium double sulphate. Fe\SO*)lK^SO* + 24H20 Iron and potassium double sulphate. All of these alums crystallize in regular octahedra. Further, a solution containing two alums, for example, aluminium and potassium sulphate and aluminium and ammonium sulphate, deposits on concentration crystals in which the two salts are mixed. Such is the character of isomorphous bodies ; crystal- lizing in the same form, they may mix together and replace each other in all proportions in the same crystal. Many exam- ples of isomorphism will be cited in the course of this work. It will now be sufficient to add that this idea of isomorphism has rendered valuable service to chemical theory by permitting the grouping together of bodies similar both in crystalline form and atomic constitution, and by furnishing in such cases useful indications for the determination of the atomic weights. It is evident that when two similar combinations, two sulphates, for example, are recognized to be isomorphous, it is necessary to represent their constitutions by analogous formulae, and the latter can only be possible under the condition that the atomic weights of the metals contained in these sulphates have known values. Action of Water upon the Salts. — If water be poured upon and agitated with powdered chalk, a white, cloudy liquid is obtained. The chalk is suspended in the water without being dissolved ; it is simply held up in the form of minute particles, and if the liquid be allowed to stand, the precipitate is de- posited, and clear water again appears above the deposit. However, if saltpetre, or potassium nitrate, be agitated with water, a colorless, transparent liquid is obtained. The saltpetre is dissolved in the water; it has disappeared as a solid body. SALTS. 269 It is melted by tlie water, as is commonly said, and is uniformly diffused through the liquid. It has itself become liquid, and this is the phenomenon of solution. It is accompanied by a production of cold, that is, an absorption of heat ; for in assum- ing the liquid state and becoming diffused throughout the water, the saltpetre must absorb heat. If the introduction of powdered nitre into the solution m continued, the solid still disappears, but a time arrives when\ the salt introduced ceases to dissolve ; for water at a given tem- perature can only dissolve a fixed quantity of a salt, and when this limit is attained, the solvent force of the water upon the salt- petre is exhausted. The water is then said to be saturated with the salt, and any excess of the latter remains in the solid state. But if now the solution be heated, this excess is in its turn dissolved, for the solubility augments with the temperature, and as the latter is raised, a larger quantity of the salt is dis- solved. When the liquid begins to boil, the temperature and the solubility of the salt have reached their extreme limit. If the boiling saturated solution be allowed to cool, it depos- its a large portion of the salt in the form of crystals. In this manner voluminous, colorless, and transparent prisms are ob- tained which fill the vessel, and which are surrounded by a solution of saltpetre, saturated at the temperature to which the liquid has been cooled. This liquid is called the mother-liquor of the crystals. It is thus that soluble salts are crystallized by cooling their hot saturated solutions. G-enerally the same facts are observed for other soluble salts. Their solubility increases with the temperature; there are, however, some exceptions to this rule. Sodium chloride is but slightly more soluble in hot than in cold water, and gypsum, or calcium sulphate, is sensibly more soluble in cold than in hot water; for, while 500 parts of boiling water are requisite to dissolve one part of gypsum, only 460 parts of cold water are necessary to dissolve the same quantity. The maximum solu- bility of sodium sulphate is between 32 and 33°. Crystals of nitre may be obtained by another process. We may expose the cold saturated solution to the air at the ordi- nary temperature, or, better still, place it in a bell-jar over a vessel containing sulphuric acid. The water of the solution slowly disappears, and, as it is dissipated in vapor, a portion of the dissolved salt separates in the solid form. The crystals thus formed by spontaneous evaporation are generally very regular. 23* 270 ELEMENTS OP MODERN CHEMISTRY. But water exerts another and a different action upon the sahs. Perfectly dry cupric sulphate, CuSO*, is a white powder. If water be poured upon it, it becomes blue and dissolves, com- municating to the liquid a blue color and notably raising its temperature. On evaporation, this liquid deposits crystals of blue vitriol, and if these be compared with the dry white pow- der with which we started, they will be found to differ from it by the water they contain. We have employed the anhydrous salt, and have hydrated it. In fact, the sulphate, CuSO*, has absorbed five molecules of water, with which it has combined, and this combination, like all others, has taken place with the production of heat. The water which is thus absorbed by cer- tain salts, and which combines with them in definite propor- tions, is necessary to the formation of their crystals ; it is called water of crystallization. It is not necessary to the constitution of the salts them- selves ; they can exist without it, and generally lose it when they are heated to a temperature more or less elevated, without undergoing any other decomposition. Certain salts abandon their water of crystallization with such facility that they give it up to the surrounding air when the latter is not saturated with moisture. They then become opaque and lose their forms, for crystals cease to exist when their water of crystalli- zation is disengaged. These salts become covered with a dry powder in the air and are called efflorescent salts. It is seen by the example just cited that the phenomenon of solution of salts in water, which depends upon a physical action, upon a change of state, is often complicated with a true combination of the salt with water, that is, a chemical action which disengages heat. The latter is generally more energetic than the physical action, and the difference between the two effects is then manifested by an elevation of temperature. But the physical phenomenon is produced alone when the salt which dissolves is incapable of combining with water of crystallization. A depression of temperature is then observed, as we have seen in the case of nitre, the crystals of which are anhydrous; but another example will more clearly illustrate this important phenomenon. If water be poured upon recently fused and powdered calcium chloride, the salt dissolves with production of heat. It changes not only its state but its composition ; it combines energetically SALTS. 271 with the water, and this combination produces more heat than is absorbed by the change of state. Hence there is an eleva- tion of temperature. If calcium chloride, combined with its water of crystalliza- tion, be rapidly mixed with snow, the salt is so soluble in water that it causes the snow to melt at the same time that it becomes liquid itself Here there is no combination, no chemical action, and no heat is disengaged. It is a double physical phenome- non, — fusion of the snow and fusion of the calcium chloride, — and neither of these bodies can undergo a change of state with- out absorbing heat. Hence there is a depression of tempera- ture which may reach — 40°. A mixture of snow and calcium chloride is a freezing mix- ture. A mixture of equal parts of common salt and broken ice or snow is frequently used for the production of cold. The phenomenon of the solution of salts in water presents none of the characteristics of a chemical action; it does not take place in definite proportions. In fact, a soluble salt requires for its complete solution a quantity of water, which is always the same for a certain weight of the salt at a given temperature ; but there exists no atomic relation between this quantity of water and the weight of the salt which is dissolved. Further, although the solubility of a salt presents for each temperature a maximum limit, that is, although a given weight of a salt requires for its solution a quantity of water which is invariable and which cannot be diminished, when the solution has been accomplished an indefinite quantity of water may be added, and the liquid will still remain perfectly homogeneous. Super saturation. — We have seen that a saturated solution of a salt at a given temperature generally deposits a part of that salt on cooling. This is not always the case ; it sometimes happens, if the cooling take place under certain conditions, that a portion of the salt, which the difference in temperature should reduce to the solid state, still remains in solution. The solu- tion is then said to be supersaturated. Sodium sulphate and alum have a great tendency to form such solutions. A hot, saturated solution of sodium sulphate is contained in the tube A (Fig. 95). It is heated to boiling, so that the vapor escapes by the drawn-out extremity. By the aid of a blow- pipe, the tube is then sealed at C, before the vapor can con- dense, and is then allowed to cool. A vacuum is formed above 272 ELEMENTS OF MODERN CHEMISTRY. the solution, for the air has been driven out by the vapor. The cold liquid remains limpid ; it deposits no crystals. But the instant the drawn-out point of the tube is broken off, the air enters and crystallization at once commences at the surface and Fig. 95. proceeds throughout the entire mass, which becomes solid ; at the same time an elevation of temperature may be observed. 100 grammes of water and 200 grammes of crystallized so- dium sulphate may be heated to ebullition in a narrow-necked flask, and as soon as vapor begins to issue from the mouth, the latter may be covered with a watch-glass and the whole allowed to cool tranquilly. The salt remains dissolved, and the solution contained in the flask is supersaturated; but as soon as the watch-glass is removed the liquid becomes a solid mass of crys- tals (Loewel). In the first experiment it is the sudden entry of the air which determines the crystallization; in the second, it is the free access of air, and it may be admitted that in each case the air acts by the corpuscles which it holds in suspension, and which, falling into the solution, determine the crystallization. Indeed, Loewel has shown that air which has been filtered SALTS. 273 through cotton-wool has lost the property of causing supersat- urated solutions to crystallize. But what is the nature of these particles which by falling upon the surface of supersaturated solutions occasion crystalli- zation ? The researches of Gernez have thrown great light upon this question. According to him, they are saline particles simi- lar to the salt dissolved. The sodium sulphate is deposited in the preceding experiments because the entry of the air has allowed an imperceptible particle of sodium sulphate to fall upon the surface of the liquid, and around this particle the crystallization begins immediately and is propagated through- out the entire mass of the supersaturated liquid. The air then contains a trace of sodium sulphate, as it contains a trace of common salt and of carbonate and sulphate of calcium. These particles are suspended in the air in a state of extreme division, and are carried from great distances by the winds. A boiling saturated solution of sodium hyposulphite may be allowed to cool in a carefully-corked flask. When cold, it is so concentrated that it possesses an oily consistency. The flask may be carefully uncorked and the surface of the liquid touched with a rod to the end of which a small particle of sodium hy- posulphite has been made to adhere. Crystallization at once commences at the spot where the rod touches the liquid, and in a few seconds the whole mass becomes solid. There is at the same time a notable disengagement of heat (Grernez). The crystallization will also take place if a particle of sodium sulphate be allowed to fall into the solution, for the latter salt possesses the same crystalline form as sodium hyposulphite, and an analogous constitution. Ebullition of Saline Solutions. — Aqueous solutions of the salts generally possess a boiling-point higher than that of water. Thus, a saturated solution of common salt boils at 108.4° ; a saturated solution of potassium nitrate boils at 115.9°; and a saturated solution of calcium chloride boils only at 179.5°. Action of Heat upon the Salts. — The hydrated salts lose their water when they are heated. Ordinarily, a temperature of 100° is sufficient to expel the water of crystallization. Cer- tain salts melt in this water before losing it ; they are so soluble in hot water that they dissolve in the water which at a lower tem- perature constitutes them in the crystalline state. This is called aqueous fusion. A great number of anhydrous salts melt when they are exposed to intense heat ; this is called igneous fusion. 274 ELEMENTS OF MODERN CHEMISTRY. Heat exerts a decomposing action upon many salts. Upon this point it is difficult to give general laws. It can only be said that the stability of a salt depends upon three conditions, namely, the fixedness of the corresponding acid, the stability of the corresponding oxide, and the energy of the affinity with which the two react together to form the salt. Thus the salts of acids decomposable by heat are themselves decomposed at an elevated temperature. It is thus with the chlorates, the perchlorates, and the nitrates. Among the sul- phates, some are decomposable, others are fixed. The latter are those of potassium, sodium, barium, strontium, calcium, mag- nesium, lead, etc. The corresponding oxides of potassium, sodium, barium, etc., are fixed bases, and possess a powerful affinity for sulphuric acid. Hence their sulphates are stable. Most of the carbonates are decomposable by heat; indeed, the affinity of carbonic acid for the bases is as a rule feeble. It is exceptionally strong for the alkaline bases ; hence the alkaline carbonates resist the action of heat. Action of Electricity upon the Salts. — When an electric current traverses the aque- ous solution of a salt, the latter is decomposed. The metal separates at the neg- ative pole, and the other element of the salt at the positive pole. This other element may be an elec- tro-negative element, such as chlorine, or an oxidized group, that is, a group of atoms, one or more of which is oxygen. The electrolysis of a salt may be eff'ected as follows: An U tube (Fig. 96) contains a solution of cupric chloride. In each branch a plate of platinum dips into the liquid, and Fig. 96. these plates, connected by conducting wires with the two poles of a battery, constitute the positive and negative electrodes As soon as the current SALTS. 275 passes, the electro-positive element of tlie salt, the copper, is deposited upon the electro-negative electrode, and the chlorine, which, is electro-negative, is disengaged at the positive electrode. A part of this chlorine combines with the platinum electrode by a secondary reaction, forming platinum chloride, but the principal action, that is, the decomposition of cupric chloride by electrolysis, is represented by the following equation: CuCP = Cu -f ci^ Cupric chloride. Copper. Chlorine. If the cupric chloride be replaced by cupric sulphate, the current will decompose this salt into copper, which deposits upon the negative electrode, and into SO*, which possesses no stability, and consequently breaks up at the positive electrode into SO^, which combines with the water to form sulphuric acid, and 0, which is disengaged at the positive electrode. The decomposition of the SO* is a secondary action. The principal action accomplished by the work of the current is expressed by the following equation : CuSO* = Cu + SO* Cupric sulphate. Copper. Oxidized group. The secondary reactions are as follows : SO* == SO^ + SO^ -f H^O = H^SO* The experiment may be repeated upon potassium sulphate, and a solution of this salt colored by the syrup of violets is in- troduced in the U tube. As soon as the current passes, bub- bles of gas are seen to arise from each electrode. Free oxygen appears at the positive electrode, as in the preceding case, and at the same time the liquid filling this branch of the tube as- sumes a red color. This is the evidence of the presence of sulphuric acid formed at the positive electrode. The gas disengaged at the negative electrode is hydrogen, which is produced by a secondary action of the water upon the potassium which is removed from the salt at the negative pole. Potassium hydroxide is thus formed, and the syrup of violets in this branch of the tube is colored green. The principal ac- tion accomplished by the current is expressed, as in the pre- ceding cases, by the equation K'SO* = 2K + SO* Potassium sulphate. Potassium. Oxidized group. 276 ELEMENTS OP MODERN CHEMISTRY. The appearance of hydrogen and potassium hydroxide at one pole, and the disengagement of oxygen and formation of sulphuric acid at the other, are due to secondary reactions inde- pendent of the current, as has been explained. The positive pole is called the anode, and the negative pole the cathode, and the elements or groups which separate are distinguished as anions and cathions, according to the poles at which they are set free. The groups into which a compound is separated by the electric current are called the ions. According to a theory proposed by Arrhenius, a salt in dilute solution exists as such only in small proportion, the larger pro- portion being dissociated into the ions. Although it would at first seem improbable that a compound like sodium chloride would thus exist in solution as free chlorine atoms and free sodium atoms, it can be conceived that neither of them would manifest active properties in presence of the other. We have analogous cases in the vapors of certain substances : that of ammonium chloride, for instance, is dissociated into free am- monia and hydrochloric acid, each of which masks the reactions of the other. Phosphorus pentachloride vapor is in like man- ner dissociated into phosphorus trichloride and chlorine. The theory is supported by many facts which cannot be given here. The conduction of the current is effected by the ions, which are thus continually united and dissociated through the mass of the liquid while those at the poles are set free. Faraday discovered the law expressing the relative quantities of the ions of different electrolytes that would be set free by a given current : it is, that a current of the same strength will set free quantities of the ions that are exactly proportional to their chemical equivalents. Referred to the elements, these quantities will be in the ratio of the atomic weights divided by the quantivalence. Action of the Metals upon the Salts. — The metals may displace each other in their saline solutions. If a plate of copper be plunged into a solution of silver nitrate, the copper enters into solution in the form of cupric nitrate, displacing and precipitating the silver. Cu + 2AgN0^ = Cu(N0^)2 + 2Ag Silver nitrate. Cupric nitrate. If a piece of iron be introduced into a solution of cupric sulphate, the iron instantly becomes covered with a layer of berthollet's laws. 277 metallic copper, precipitated by a portion of the iron which enters the solution. Fe + CuSO* = Cu + FeSO* Cupric sulphate. Ferrous sulphate. If a strip of zinc around which some brass wires have been twisted be suspended in a dilute solution of plumbic acetate, the zinc will slowly displace the lead, which will be deposited in brilliant scales upon the brass wires. The latter gradually assume the appearance of fern-leaves, and the experiment constitutes the formation of the lead-tree. Richter, of Berlin, was the first to remark (1792) that the metals displace each other in their saline solutions without the neutrality of the latter being disturbed. When a neutral salt is precipitated by a metal, a new neutral salt results. The ferrous sulphate formed by the action of iron upon cupric sul- phate is neutral like the latter. It may be further stated that in this respect the chlorides behave like the oxygen salts. Iron displaces copper from cu- pric chloride as from the sulphate. In the first case it com- bines with CP, in the second with SO*, and in this circumstance again the latter group acts in the same manner as chlorine. CuCP + Fe =^ FeCP + Cu Cupric chloride. Ferrous chloride. Cu(SO^) + Fe = Fe(SO*) + Cu Cupric sulphate. Ferrous sulphate. BERTHOLLET'S LAWS. To conclude this general study of the salts, it only remains to indicate the actions exerted upon them by the acids and the bases, and the reciprocal actions of the salts themselves. These facts have been established and discussed principally by Ber- thollet, who demonstrated the influence of physical conditions, such as insolubility and volatility, upon the direction of chem- ical decompositions. Action of Acids upon the Salts. — When an acid, that is, a salt of hydrogen, is added to a metallic salt, the former tends to exchange elements with the latter, in such a manner as to form a new salt and a new acid. If sulphuric acid be added to powdered potassium nitrate, 24 278 ELEMENTS OF MODERN CHEMISTRY. the latter partially dissolves without the aid of heat, and potassium acid sulphate and nitric acid are formed. KNO^ -h ffSO* = HNO^ + KHSO* Potassium nitrate. Sulphuric acid. Nitric acid. Potassium acid sulphate. But this reaction is by no means complete. Powerful as are its affinities, the sulphuric acid cannot decompose the whole of the potassium nitrate unaided by heat ; a portion of the latter salt remains unaltered in presence of the excess of sulphuric acid, so that the resulting thick and fuming liquid really con- tains two acids and two salts, namely : Sulphuric acid. Nitric acid. Potassium acid sulphate. Potassium nitrate. The reaction takes place as if two acids were in presence of a single base. There is a conflict between the acids, and they tend to divide the base, which is potassium, in such a manner that each acid may saturate a portion. Hence the decomposition of potassium nitrate is not com- plete, and it is arrested as soon as the nitric acid set free can dispute with the sulphuric acid the possession of the base. There is then established a state of equilibrium between the two acids, both remaining in presence of the two salts. But this equilibrium is unstable and may be deranged by various circumstances. If the acid mixture be heated, abundant white vapors are disengaged. It is the nitric acid which volatilizes. But the sulphuric acid becomes thus preponderant in the liquid and decomposes another portion of potassium nitrate, and, if the volatilization of the nitric acid set free be not arrested by the removal of the heat, it is evident that nothing can prevent the complete decomposition of the potassium nitrate by the sul- phuric acid. The nitric acid, which by its presence alone prevented this total decomposition, is rendered powerless. Such is the influence of volatility or the gaseous state upon the progress of decompositions ; it is manifested in the highest degree in acids more volatile than nitric acid, such as carbonic and sulphurous acids. We have already seen that the carbon- ates and sulphites are easily and entirely decomposed by the energetic acids. While the volatility of acids favors the decomposition of their salts, insoluhility may play an analogous part. berthollet's laws. 279 If hydrochloric acid be added to a solution of potassium sili- cate, a gelatinous precipitate of silicic acid is at once produced, and at the same time potassium chloride is formed. The de- composition is complete, for the silicic acid is insoluble. If sulphuric acid be poured into a solution of barium nitrate, a precipitate of barium sulphate is immediately formed, while at the same time nitric acid is set free. Ba(NO^)^ + ffSO* = 2HN0^ + BaSO* Barium nitrate. Sulphuric acid. Nitric acid. Barium sulphate. In this case also the decomposition is complete, for the ba- rium sulphate is insoluble. In these two reactions, the division of the base between the two acids cannot take place, since one of the products is imme- diately removed from the sphere of action by its insolubility. In the first case, it is the newly-formed acid which is precipi- tated ; in the second, it is the newly-formed salt which is de- posited in the insoluble state. Influence of Mass. — One other circumstance can influence the extent of these decompositions : it is the relative masses of the bodies which are in presence of each other. In the first experiment, it was supposed that an amount of sulphuric acid had been added to potassium nitrate sufficient to produce the double decomposition. If a large excess had been employed, it is evident that it would have become preponderant in the mixture, and that it would have displaced a more con- siderable portion of nitric acid. The influence of mass is manifested in the case of very feeble acids, and permits them to displace stronger acids. If a small quantity of tricalcic phosphate be introduced into water charged with carbonic acid, the latter, compensating by its mass for its deficiency in energy, will remove from the phosphate a portion of its base. Calcium dicarbonate and calcium acid phosphate are formed, both of which are soluble. Such, according to Berthollet, is the influence of insolubility and volatility upon the phenomena of double decomposition ; such, on the other hand, is the influence of mass. The same conditions intervene, and in the same manner, in the reactions which we are about to study. Action of Bases upon the Salts. — We will here consider only the action of the soluble bases, that is, the alkaline hy- droxides. 280 ELEMENTS OF MODERN CHEMISTRY. If a solution of potassium hydroxide be poured into a solu- tion of sodium sulphate, no apparent change takes place ; but, according to the principle which has just been announced, it is probable that the potassium hydroxide has liberated a portion of sodium hydroxide. Na^SO* + 2K0H = K^SO* + 2NaOH Sodium sulphate. Potassium hydroxide. Potassium sulphate. Sodium hydroxide. But this decomposition cannot be complete, and the liquid must contain four bodies, namely : Sodium sulphate. Potassium sulphate. Sodium hydroxide. Potassium hydroxide. If potassium hydroxide be added to a solution of cupric sul- phate, a light-blue precipitate of cupric hydroxide is obtained. In this case the decomposition is complete, owing to the insol- ubility of the cupric hydroxide, which cannot dispute with the potassium hydroxide the possession of the acid. CuSO^ + 2K0H = K^SO* + CuCOH)^ Cupric sulphate. Potassium hydroxide. Potassium sulphate. Cupric hydroxide. If a solution of barium hydroxide be poured into a solution of potassium sulphate, a precipitate of barium sulphate is pro- duced, and potassium hydroxide remains in solution. In this case again, the decomposition is complete, by reason of the in- solubility of the barium sulphate. The potassium cannot di- vide the acid with the barium, for the latter escapes with all of it in the form of insoluble sulphate. K^SO* + Ba(OH)^ = BaSO* + 2K0H Potassium sulphate. Barium hydroxide. Barium sulphate. Potassium hydroxide. Action of the Salts upon each other. — The action of salts upon each other is what would naturally follow from the prin- ciples exposed in treating of the action of acids upon salts. Indeed, the latter possess the same constitution as the acids, and in their reactions upon salts should give rise to phenomena of the same order. These are exchanges of elements, double decompositions, which take place and are more or less complete, according to the physical conditions of the bodies which are produced, and also according to the relative masses of the re- acting bodies. In the first place, we must consider the reciprocal actions of the soluble salts, berthollet's laws. 281 If a solution of cupric sulphate be treated with a solution ©f sodium chloride, no precipitate is formed, but the blue color of the liquid is changed to green. This color is that of cupric chloride, and it may be supposed that the latter salt is formed by the reciprocal action of the sodium chloride and cupric sulphate. CuSO^ + 2NaCl = Na^SO* + CuCP Cupric sulphate. Sodium chloride. Sodium sulphate. Cupric chloride. But this interchange of elements between the cupric sulphate and the sodium chloride is arrested before the decomposition of the two salts is complete. A part of each remains unaltered in the presence of the other and of the two new salts which are formed. Consequently, the gi'een liquor obtained in this experiment contains four salts, namely : Cupric sulphate. Sodium chloride. Sodium sulphate. Cupric chloride. The respective proportions in which these salts exist in the mixture depend upon several circumstances. Malaguti has shown that in cases of this kind it is the energy of the affinity of the acids for the bases which governs the decomposition. The most energetic acid tends to combine with the most power- ful base, and the proportion of the salt thus formed predomi- nates in the mixture. Thus there is set up, as it were, between the elements in presence a sort of conflict, in which the stronger are victorious, while the weaker are not altogether annihilated. The result is a state of equilibrium which is only disturbed in case one of the products is by reason of its insolubility removed from the sphere of action of the other. The latter condition is realized in the following experiments. When barium chloride is added to the blue solution of cupric sulphate, a precipitate of barium sulphate is immediately formed, and cupric chloride remains in solution, coloring the liquid green. CuSO* + BaCF = BaSO* -f CuCP Cupric sulphate. Barium chloride. Barium sulphate. Cupric chloride. In this case the decomposition is complete, owing to the in- solubility of the barium sulphate. That salt is removed by cohesion from the sphere of action of the compounds which remain in solution. The portions first formed, and thus with- 24* 282 ELEMENTS OF MODERN CHEMISTRY. drawn, are replaced by others, and tlie reaction once commenced is finished in the same manner, so that the whole of the cnpric sulphate is converted into barium sulphate. A concentrated solution of common salt produces no precipi- tate in a concentrated solution of magnesium sulphate. How- ever, we must admit that there is an interchange of elements, and that the liquid contains four salts, namely : Magnesium sulphate. Sodium chloride. Sodium sulphate. Magnesium chloride. If this solution be exposed to an intense cold, it deposits crystals of sodium sulphate, while magnesium chloride remains in solution (Balard). Of the four salts which are in presence of each other, the sodium sulphate is the least soluble ; it is therefore deposited, and the double decomposition continues in the same manner until the greater part of the magnesium sulphate has been decomposed. The subject could be further developed by other examples. Those which have been given are sufficient to expose the true principle of double decomposition. We may add that if the operations be conducted in the dry way and at a high temperature, the volatility of the products which may be formed exerts an influence upon the reactions analogous to that which has been established for insolubility. If an intimate mixture of mercuric sulphate and sodium chloride be heated in a glass matrass, a sublimate of mercuric chloride is formed. HgSO* + 2NaCl = Na^SO* + HgCP Mercuric sulphate. Sodium cliloride. Sodium sulphate. Mercuric chloride. Action of Soluble Salts upon Insoluble Salts. — The study of double decomposition may be concluded by a summary ex- position of the action of soluble salts upon insoluble salts. It is analogous to that which has just been studied, that is, it is characterized by a tendency to an interchange of elements. A single example will be sufficient. If a solution of sodium carbonate be boiled for a long time with barium sulphate, it is found that the latter salt has under- gone a partial decomposition. It is partially converted into barium carbonate, insoluble like the sulphate, and the liquid becomes charged with a certain quantity of sodium sulphate. BaSO* -f Na^CO' = Na'^'SO* + BaCO^ Barium sulphate. Sodium carbonate. Sodium sulphate. Sarlum carbonate. NITRATES. 283 This decomposition is more complete as the proportion of sodium carbonate which reacts upon the barium sulphate is increased. Here, as in some of the preceding experiments, the influence exerted by the greater mass is very appreciable. This study may be aptly terminated by summary indications upon the composition and properties of the more important classes of salts, which are the nitrates, sulphates, and carbonates. NITRATES. Composition. — Nitric acid containing HNO^, the nitrates contain the group NO^ combined with a metal which replaces the hydrogen of the acid. Consequently they contain one or more groups, NO^, according to the nature of the metal which has neutralized the nitric acid. Thus, 1. KOH -f HNO^ = KNO^ + WO Potassium hydroxide. Nitric acid. Potassium nitrate. 2. PbO + 2HN0^ = Pb(N0^)2 -}- H^O Plumbic oxide. Plumbic nitrate. 3. gijo^ + 3HN0^ = Bi(N0^7 + 3H20 Bismuth hydroxide. Bismuth trinitrate. With these few examples, we may conclude : 1. That potassium, which unites with one atom of chlorine to form potassium chloride, KCl, unites also with one group, NO^, to form potassium nitrate. 2. That lead, which unites with two atoms of chlorine to form plumbic chloride, PbCP, unites also with two groups, NO'^, to form plumbic nitrate. 3. That bismuth, which unites with three atoms of chlorine to form bismuth trichloride, BiCP, unites also with three groups, NO^ to form bismuth trinitrate. In the chloride K'Cl potassium is monatomic. In the chloride Pb"C12 lead is diatomic. In the chloride Bi"'Cl3 bismuth is triatomic. In the nitrates, these three metals play the same parts as in the chlorides ; and we may say, in a general manner, that tbe metallic nitrates contain a metal united with as many times NO^ as the metal possesses atomicities. In K'(N03) monatomic potassium is united with NO^ In Pb"(]Sr03)2 diatomic lead is united to 2N03 In Bi'"(N03)3 triatomic bismuth is united to SNO^ Such is the law of the composition of the nitrates. 284 ELEMENTS OF MODERN CHEMISTRY. Properties. — All of the nitrates are soluble in water. Some of them are deposited from their solutions in the form of hy- drated crystals. Such is cupric nitrate, which crystallizes with six molecules of water at a low temperature. Others separate in anhydrous crystals. Such are the nitrates of potassium, sodium, silver, barium, and lead. All of the nitrates are decomposable by heat, and the pro- ducts of the decomposition vary with the nature of the nitrate and with the temperature. Thus, potassium nitrate is first converted into nitrite, and this is finally decomposed into nitrogen, oxygen, and potassium oxide. The nitrates of barium and lead yield nitrogen peroxide, oxygen, and a residue of oxide. Silver nitrate yields nitrogen peroxide, oxygen, and a residue of metal. 2AgN0^ = 2N0' + 0' + 2Ag All of the nitrates liberate oxygen when they are heated; rich in oxygen, they constitute an abundant source of that element, and they are also easily reduced by bodies possessing a strong affinity for it. Sulphur, charcoal, phosphorus, and certain metals are ener- getically oxidized when heated with the nitrates. If sulphur be heated with potassium nitrate, potassium sulphate is formed, and sulphurous oxide and nitrogen are disengaged. 2KN0^ -f S^ = K^SO* + SO^ + N^ Potassium nitrate. Potassium sulphate. When powdered potassium nitrate is thrown upon burning charcoal, the salt melts and increases the combustion of the charcoal, producing a vivid deflagration. Potassium carbonate is formed and carbon dioxide and nitrogen are disengaged. 4KN0^ + 50 = 2K^C0=' + 3C0'^ + 2^^ Potassium nitrate. Potassium carbonate. Distinctive Characters. — All of the nitrates deflagrate when thrown upon incandescent charcoal. With concentrated sulphuric acid they evolve white vapors of nitric acid in the cold, and more abundantly when the reaction is aided by heat. When mixed with copper-filings and treated with concentrated sulphuric acid, they disengage red vapors. When the solution of a nitrate is mixed with its own volume of concentrated sulphuric acid, and a crystal of ferrous sulphate is introduced into the liquid, the crystal very soon assumes a StTLPHATES. 285 brown color, which is communicated to the liquid. In this very delicate reaction the nitric acid is reduced by the ferrous sulphate to nitric oxide, which colors the excess of ferrous sulphate brown (page 164). The solution of a nitrate, when treated with sulphuric acid, will decolorize solution of sulphate of indigo when the liquid is heated to boiling. SULPHATES. Composition. — Sulphuric acid, H^SO*, contains two atoms of hydrogen capable of being replaced by a metal. When both are replaced by an equivalent quantity of metal, a neutral sul- phate is formed. An acid sulphate is formed when a single one of these atoms of hydrogen is replaced by a single atom of metal. The hydrogen of the acid is removed by the oxygen of the metallic oxide or hydroxide which more or less com- pletely saturates the sulphuric acid. Several cases may be presented. 1. K'OH -f- H^SO* = g I SO* + H^O Potassium hydrate. Potassium acid sulphate. 2. 2K'0H + ffSO* = K'^SO* 4- Potassium sulphate. 2H=^0 3. Pb"0 + H^SO* =: Pb"SO* + H^O Plumbic oxide. Plumbic sulphate. r H^so* (SO* 4. (AP)-03 + ] ffSO* = (AP)- } SO* + 3ffO (H^SO* (_S0* Aluminium oxide. 3 molecules. Aluminium sulphate. These examples show that all of the sulphates contain the group SO*, which in sulphuric acid is united with two atoms of hydrogen. This group is diatomic; it is necessary, then, that in the sulphates it shall be united with a quantity of metal equivalent to two atoms of hydrogen. 1. In the acid sulphates it is united with an atom of hydro- gen and an atom of a monatomic metal, tt I SO*. 2. It is united with two atoms of a monatomic metal in the neutral sulphates R'^SO*. 3. With one atom of a diatomic metal in the neutral sul- phates M"SO*. These cases are very simple. It is not so, however, with 286 ELEMENTS OF MODERN CHEMISTRY. the fourth, in which we consider the saturation of sulphuric acid by an oxide E^O^, such as ferric oxide or aluminic oxide. Each of the three atoms of oxygen of the oxide WO^ removes H^ from a molecule of H^SO*, and it results that the metal which was combined with 30", combines with 3(S0*)". The two atoms of metal which are substituted for 3H'^ in three mol- ecules of H^SO* are then equivalent to 6 atoms of hydrogen. They are hexatomic, as is marked by the index ^'. Properties. — The sulphates are nearly all soluble in water. Those of barium, strontium, and lead are insoluble. The sul- phates of calcium and silver, and mercurous sulphate are but slightly soluble. The alkaline sulphates, and those of calcium, barium, stron- tium, magnesium, and lead, are undecomposable by heat. The others are decomposed at a high temperature. A residue of oxide generally remains, while sulphur dioxide and oxygen are disengaged. The sulphates of zinc and copper are thus decomposed at a high red heat. CuSO'^ ^ SO^ + O + CuO Cupric sulphate. Cupric oxide. In case the oxide is reducible by heat, the residue consists of metal. HgSO* = Hg + SO^ + 0^ Mercuric sulphate. Mercury. The sulphates R\SO*/ are decomposed at a comparatively low temperature, disengaging vapor of sulphur trioxide and leaving a residue of sesquioxide. Fe\SO*)^ = Fe^O^ -j- 3S0=^ Ferric sulphate. Ferric oxide. Sulphuric oxide. The sulphates are readily deoxidized by carbon and other reducing agents. If an intimate mixture of potassium sulphate with an excess of charcoal be heated to bright redness, and allowed to cool out of contact with the air, a black powder is obtained, which pro- duces a shower of sparks when projected into the air. It is the pyrophorus of Gay-Lussac. It owes its spontaneous in- flammability on contact with the air to finely-divided potassium sulphide which it contains, and which attracts oxygen with great avidity. The sulphide is formed according to the following reaction : K^SO* + 4C = 4C0 + K^S Potassium sulphate. Potassium sulphide. CARBONATES. 287 In the same manner barium sulphate and calcium sulphate are converted into sulphides by the action of charcoal at a high temperature. The other sulphates are also reduced under the same circum- stances, but the products vary; carbon dioxide or carbon mon- oxide and sulphurous oxide are disengaged, and the residue consists of either oxide or metal. Distinctive Characters. — When treated with sulphuric acid, the sulphates do not evolve any gas. They do not deflagrate when thrown upon burning charcoal. Their solutions give a white precipitate of barium sulphate with barium nitrate, which is insoluble in nitric acid. When this precipitate is washed, dried, and calcined with an excess of charcoal, it leaves a resi- due of barium sulphide, and when this is moistened with hy- drochloric acid, it evolves hydrogen sulphide, which is easily recognized by its odor, CARBONATES. Composition. — Carbonic acid is dibasic, like sulphuric acid. It is not known in the state of hydrate, and the carbonates are formed by the direct union of carbon dioxide with the metallic oxides or hydroxides. When freshly-burnt lime is exposed to the air, it attracts at the same time the moisture and the carbonic acid gas of the air, and is converted into carbonate. CO^ + CaO = CaCO^ Calcium oxide. Calcium carbonate. The carbonates then contain the group CO^ combined with a metal. In carbonic acid, this group would be united with two atoms of hydrogen. The composition of the more simple car- bonates is expressed by the following formulae : H^CO^ carbonic acid (unknown). R' ) TT [ C03 acid carbonates (dicarbonates). R'2C03 neutral carbonates. M"C03 neutral carbonates. In these formulae, R' represents a monatomic metal, such as potassium, which is equivalent to one atom of hydrogen. M" represents a diatomic metal, such as calcium, which is equiva- lent to two atoms of hydrogen. Properties. — Only the alkaline carbonates are soluble in pure 288 ELEMENTS OE MODERN CHEMISTRY. water. The others are insoluble, but they dissolve in water charged with carbonic acid. The soluble carbonates possess an alkaline reaction. It is the same with the acid carbonates of the alkaline metals, which are ordinarily called bicarbonates, such as potassium acid car- bonate or bicarbonate of potassium. All of the carbonates except the alkaline carbonates are de- composable by heat. In this decomposition carbon dioxide is disengaged, and there remains a residue of oxide, or of metal in case the oxide be reducible by heat. Thus, the carbonates of magnesium, calcium, zinc, lead, and copper leave a residue of oxide after calcination ; silver carbonate leaves a residue of metal. Barium and strontium carbonates are but slowly decom- posed at a white heat ; their decomposition is facilitated by a current of steam, and easily effected in the electric furnace. Reducing agents, such as carbon and metallic magnesium, act upon the carbonates as upon the corresponding oxides : if the base be reducible, the metal is formed. If cupric carbonate be heated with charcoal, carbon dioxide is disengaged, and metallic copper remains. 2CuC0^ + C = 3C0^ + 2Cu Cupric carbonate. Copper. In this experiment carbon dioxide is disengaged, for cupric oxide is easily reducible by charcoal. It is not the same with potassium oxide ; hence potassium carbonate is only reduced by charcoal at a very high temperature with disengagement of carbon monoxide. K^CO^ -f 2C = SCO + K^ When magnesium is substituted for the charcoal in this experiment, less heat is required to bring about the reaction, and the carbon as well as the potassium of the carbonate is reduced to the elementary state. K^^CO^ -f 3Mg = C + 2K + 3MgO All the carbonates are decomposed by phosphorus. A small piece of phosphorus may be placed at the bottom of a small test-tube, and the latter then nearly filled with well- dried sodium carbonate. The part of the tube containing the carbonate being heated to redness, the phosphorus may be heated so that its vapor will pass over the incandescent car- CLASSiriCATION OF THE METALS. 289 bonate. The latter will be decomposed witli the formation of sodium phosphate and a deposition of carbon. After cooling, the contents of the tube will be black. The experiment may be repeated upon calcium carbonate. The phosphorus is placed in a small crucible, which is then introduced into a larger one. The calcium carbonate (chalk) is then placed upon the lid of the smaller crucible, which is pierced with holes. The arrangement is heated upon a double grate, so that when the chalk has been brought to incandes- cence, the vapor of phosphorus may be caused to pass through it by placing some hot coals upon the lower grate. The chalk is rapidly decomposed, carbon monoxide is disengaged, and a mixture of calcium phosphate and phosphide is formed. This mixture serves for the preparation of hydrogen phosphide. Distinctive Characters. — When treated with sulphuric acid, the carbonates disengage a colorless, incombustible gas, which extinguishes burning bodies and produces a milkiness when agitated with lime-water. CLASSIFICATION OF THE METALS. In the preceding pages we have studied the composition and the general properties of metallic compounds. This study has revealed the fact that the metals possess very different aptitudes to form compounds, and various capacities of combination, which are manifested by the greater or less number of other atoms which the atoms of these metals can attract. In this respect, the differences existing between the metals are analogous to those which we have already remarked between the non-metals. On comparing the metals among themselves, some are discov- ered which resemble each other in the general structure. of the compounds which they are capable of forming, and such can naturally be classed in the same group. On this plan the metals are divided into several families analogous to those first proposed by Dumas for the non-metals, and it will be seen that the general composition of the metallic compounds furnishes the elements for a natural classification of the metals. While this principle is excellent, its application is attended with some difficulties which chemistry has not yet been able to solve. Consequently, this chapter must be limited to summary indi- cations upon the subject. Some of the metals are incapable of combining with more N t 25 290 ELEMENTS OF MODERN CHEMtSTft"?. than a single atom of chlorine, bromine, or iodine. The com- pounds thus formed correspond in their atomic constitution to hydrochloric, hydriodic, and hydrobromic acids. On comparing potassium chloride or silver chloride to hydrochloric acid, it will be seen that an atom of potassium or an atom of silver occupies in them the place occupied by the hydrogen of the acid. The atoms of potassium and of silver are therefore equivalent to the atoms of hydrogen as far as their capacity of combination is concerned. The other alkaline metals, such as sodium and lithium, are similar and belong to the same group. Their chlorides, bromides, and iodides, which are arranged in the following table, present analogous compositions : MoNATOMic Metals. monatomic Chlorides. monatomic Bromides. monatomic Iodides. Potassium K' H'Cl EBr HI KCl KBr KI Sodium Na' NaCl NaBr Nal Lithium Li' LiCl LiBr Lil Silver Ag' ...... . AgCl AgBr Agl These metals form hydroxides or oxides whose atomic con- stitutions correspond to that of water, one or both of the hydrogen atoms of the latter being replaced by an equivalent amount of metal. In the same manner the hydrosulphides and monosulphides of these metals are derived from hydrogen sulphide. Type H20. Oxides. Hydroxides. K20?« KOH Na20 ?* NaOH Li20 LiOH Ag20 Type H2S. Monosulphides. Hydrosulphides. K2S KSH Na2S NaSH Li2S LiSH Ag2S The same analogy is continued among tne salts of these * The existence of these monoxides of potassium and sodium is rather doubtful. They are not obtainable from the hydroxides, carbonates, or nitrates by the action of heat, and the products resulting from the direct combination of the metals with oxygen appear to be very stable per- oxides of the types RO2 and BO. CLASSIFICATION OF THE METALS. 291 metals, as will be seen from the nitrates and sulphates which we take as examples. Nitric Acid, HNQS. Sulphueic Acid, HSSO*. Nitrates. Sulphates. Acid Sulphates. KNOS K^SO* KHSO* NaN03 Na2S04 NaHSO* AgN03 Ag2S04 It is seen that in all of these compounds the metals under consideration replace hydrogen atom for atom ; each of them possesses the same capacity of combination as that gas. They are said to be monatomic. Certain other metals manifest a double capacity of combina- tion; one atom of any of these is capable of replacing two atoms of hydrogen, consequently it can combine with two atoms of chlorine, bromine, or iodine, or with one atom of oxygen or sulphur. In the chlorides of these metals, the two atomicities of the metal are satisfied by the two atomicities of two atoms of chlorine. In their oxides, the two atomicities of the metal are satisfied by the two atomicities or bonds of affinity which reside in one atom of oxygen. These metals are then diatomic. They are quite numerous and can be divided into several groups, one of the most natural of which com- prises barium, strontium, calcium, and lead. The following table shows the constitution of the principal compounds of these metals : Diatomic Metals. Chlorides. Oxides. Nitrates. Sulphates. Barium Ba" . Strontium Sr" . Calcium Ca" . Lead Pb" . . 2HC1 H20 2HN03 H2S0* BaC12 SrC12 CaC12 PbC12 BaO SrO CaO PbO Ba(N03)2 Sr(N03)2 Ca(N03)2 Pb(N03)2 BaSO* SrSO^ CaSO* PbSO* The metals of this group combine with oxygen in two pro- portions, forming not only the monoxides, RO, but also the dioxides, ROl They thus form two oxides, while they are capable of forming but one chloride, RCP. Thus, barium forms a monoxide, BaO, a dioxide, BaO^, and a dichloride, 292 ELEMENTS OF MODERN CHEMISTRY. BaCP ; but no tetrachloride of barium is known, and it is not probable that barium can act as a tetratomic element. How is it, then, that in the dioxide this metal can combine with two atoms of oxygen, while it cannot combine with four atoms of chlorine, which are equivalent to two atoms of oxygen ? In other words, what is the atomicity of barium in the dioxide which would seem to correspond to a tetrachloride? It is undoubtedly diatomic in the dioxide as it is in the monoxide, and the constitution of barium dioxide is analogous to that of hydrogen dioxide, which has already been indicated. The two atoms of oxygen mutually satisfy two of their atomicities by combining together, and they retain two which are neutral- ized in combining with the diatomic atom of barium. Thus, in barium monoxide one atom of oxygen is joined to one atom of barium by both of its atomicities ; in the dioxide two atoms of oxygen are united to one atom of barium, each by one atom- icity. If we represent the saturation of two atomicities by a straight line, as has before been explained, we will have the following formulae : Ba=:0 Ba Barium monoxide. /\ 0-0 Barium dioxide. In this manner, theory enables us to fix the relations existing between the atoms in a given body. The comparison may be continued between the other diatomic metals. Magnesium, the radical of magnesia, somewhat resem- bles calcium in its relations, and forms, as it were, the centre of a group including magnesium, zinc, cobalt, and nickel, and which is called the magnesium group. Manganese and iron, on one hand, and copper, on the other, seem to join this group by certain of their characteristics. In their most stable and gen- erally their most important compounds, these metals act as diatomic elements. All form the dichlorides RCP and the oxides BO. But in other compounds, manganese and iron seem removed from the metals of this group, and resemble chromium and aluminium. Copper, which resembles magne- sium in the series of cupric compounds, approaches mercury and silver in the cuprous series. Bismuth, which might be classed with antimony, and gold are triatomic in their most important combinations. They form the chlorides BiCP and AuCP. CLASSIFICATION OF THE METALS. 293 A certain number of the metals may be grouped together as tetratomic^ since they manifest four atomicities in their principal combinations. They are tin, titanium, and zirconium. They form the chlorides RCP and the oxides K0^ In stannic chlo- ride, SnCl*, the tin is saturated with chlorine, of which it cannot combine with more than four atoms ; it is tetratomic in this saturated compound. But it may combine with only two atoms of chlorine, thus forming the chloride SnCP, which is not saturated, for it can still fix two more atoms of chlorine. Tin only manifests two atomicities in the dichloride. In the same manner, ferrous chloride, FeCP, can absorb chlorine, becoming ferric chloride. Above 700° the latter con- tains one atom of iron and three of chlorine, but just above its temperature of volatilization it appears to contain two atoms of iron united with six of chlorine. The two iron atoms would constitute a hexatomic couple ; the same peculiarity is presented by chromium and aluminium. Compounds. Chlorides. Oxides. Sulphates. Ferric Manganic Chromic Aluminic JFeCF or [ Fe2Cl6 f MnCl3 or 1 Mn2Ci6 fCrCl3 or 1 Cr2Cl6 fAlCl3 or 1 A12C1« Fe203 Mn203 Cr203 A1203 Fe2(SO*)3 Mn2(SO*)3 Cr2(S0*)3 A]2(S04)3 The following table gives a resume of the constitution of the principal metallic combinations. The metals there chosen as examples have different atomicities. Metals. Chlorides. Oxides. Nitrates. Sulphates. Monatomic metal— Potassium K' . KCl K20 KN03 K2S04 Diatomic metal— Barium Ba" . . . BaC12 BaO Ba(N03)2 BaSQi Triatomic metal— Bismuth Bi"' . . BiC13 Bi203 Bi(N03)3 Bi2(S04)3 Tetratomic metal— Tin Sniv . . , SnC14 Sn02 Hexatomic group— (Fe2)Ti .... Fe2C16 re203 Fe2(N03)6 Fe2(S04)3 -.._. . ... J 25* 294 ELEMENTS OF MODERN CHEMISTRY. Such are the principles furnished by the theory of atomicity for a rational classification of the metals. Mendelejeff's Theory. Within recent years the labors of a Russian chemist, Men- delejeff, have developed interesting relations between the atomic weights and properties of the elements. He has shown that the properties are functions of the atomic weights, and that the functions are periodic. This relation is not applicable to a limited group of elements, but extends throughout the whole series, and consists not in certain analogies, but in the general physical and chemical properties taken together. If the elements be arranged in the order of their atomic weights, it will be noticed that these latter increase gradually by only a few units, and also that the properties of the elements are gradually modified with the increase in atomic weights. The modifications are not, however, continuously progressive, but are developed in several series. The difi'erences between the atomic weights of neighboring elements are not equal, but are nearly so, and where these differences are excessive it is probably owing to the existence of undiscovered elements. Mendelejeff predicted the existence of several such elements, and at least three of the gaps have since been filled by the discovery of gallium, scandium, and germanium. The hypothesis is then certainly worthy of seri- ous consideration in all attempts to classify the elements. The theory may be best explained by considering an example of the periodicity on which it rests. Let us study the first fourteen elements after hydrogen in the order of their atomic weights. Li = 7. Gl = 9. B = ll. C = 12. N = 14. = 16. F = 19. Na=23. Mg = 24. Al = 27. Si = 28. P = 31. S = 32. CI =35.5. We have here two groups, in each of which the change in physical and chemical properties is markedly progressive with the increase in atomic weight. The densities gradually increase to the middle of each series, and then decrease to the end. The atomic volumes, which are the quotients of the atomic weights by the densities, gradually decrease to the middle of the series, and then augment. The volatility also diminishes from sodium to silicon^ and again increases to the end of the series, CLASSIFICATION OF THE METALS. 295 Na. . 0.97 Mg. 1.75 14 AL 2.67 10 Si." 2.49 11 P. 1.84 16 S. 2.06 16 01. 1.8R Atomic volumes . . 24 27 The atomicity, or combining capacity, as indicated by the number of atoms of hydrogen or chlorine with which one atom of the elements combines, displays a similar periodicity. LiCl GICP BCP CH* NH^ OH^ FH NaCl MgCP AlCP SiCP PH^ SH^ CIH The oxygen compounds show a similar progression. Li^O GPO' B^O^ C^O* N^O^ ^ Na^O Mg^O' APO^ SPO^ P^O^ S'O' CPO^ The number of oxygen atoms with which a constant number of atoms of elements of these series can combine, regularly increases, and the properties of the oxides undergo a gradual modification. Those at the beginning of the series form pow- erful bases ; the intermediate oxides are indifferent, while the latter members form strong acids. That which characterizes these variations is that they occur in the same manner in the two groups, so that the first member of the first series (Li) corresponds to the first member of the second. These two series form the first two periods of Men- delejeff, who has shown that these series or periods can be ex- tended throughout the whole list of elements, and that the properties of the ele7nents are in periodic relations with their atomic weights. The arrangement of the elements in the periodic system is shown in the table on the following page. The horizontal rows, consisting when complete of seven elements, are called periods, while the vertical columns constitute the natural groups. The series are sub-classified according to the number of the line, as odd and even. The members of each group are related by their atomicities, as well as by the isomorphism and some other properties of their compounds, but differ very materially in other respects. The fourth, the sixth, and the tenth periods are each followed by three elements having nearly equal atomic weights, and these nine elements constitute the eighth or transi- tional group. Hydrogen stands alone. The empty spaces in the table are probably the positions of elements yet to be dis- covered. The positions of argon and helium are unknown. 296 ELEMENTS OF 3I0DERN CHEMISTRY. i f 1 SI'S 03 9? 3 M II S II 0) o'd to s ^ a.So3 88§ 4 fH t- O II II II II' II II OJ o rs-o f^O «Ph OPM Hi S II II 00 g s gi 1 II : : i : : of the othe ivalence fo the first gr e together. i|-5l CO i> i> . ^ • 2 00 i> : ^<^rd" o §8 IT o II CO 00 g II II ^ (-1 O ! « II 0) o H '• to II 00 "ll t3 like the mem roup, but the ; most marke ghts are very g 05 s « II M i S J2i o 1— 1 Eh > o II II Pi -1 II II ^ s . 0^ o3 o < ^ > ;^ s H O 00 CO 00 : <35 1— 1 1— 1 o > II g2 S j 1 ^. ilar properti^ increases up The metalli ements who ill s o ^ 1 11 ^ § II 11 ^ II CC g J ^ ?2 ^ g ■rf o> '^^ : i> p possess Sim for oxygen i 3 to the 8th. ree similar el pi 05 II o II II o CO eo II 5 II 1-1 • S II t>.CU.d Hi l_J CO ^ s i> 05 : 1 '"' SS (M II N CO "-I CO o II O II S5 II II 3 CO CC 1 bo W II 85 OJ II CD g II II t* CO tn : «o 3 o II o a '^ 1 00 Ol O iH (M j^^S'SJ p3 tH r-l i-i H O 3 02 m POTASSIUM. 297 POTASSIUM. K = 38.82 Potassium was discovered by Sir Humphry Davy in 1807. It ordinarily occurs in commerce in gray, globular masses, readily indented by tlie finger-nail. It has a dull, tarnished appearance, but when freshly cut it exposes a brilliant surface. Preparation and Properties. — Potassium is prepared by decomposing potassium carbonate by carbon at a high tem- perature. K^CO^ + 2C = SCO + K=^ Potassium carbonate. Carbon monoxide. The mixture is heated to whiteness in an iron retort and the vapors are passed into a copper receiver. The potassium dis- tils and condenses in globules or irregular masses, still contain- ing charcoal. It is purified by redistillation in an iron retort, and is condensed in a copper receiver filled with naphtha. The manufacture of potassium is a dangerous operation, owing to the formation of a very explosive compound of potas- sium and carbon monoxide, C^O^K^ (see page 697). Winkler has proposed a method of preparing the metal which consists in heating a mixture of potassium hydroxide and magnesium. 2K0H -f Mg = MgO -f ff + 2K The hydrogen disengaged in this reaction facilitates the distillation of the potassium. Potassium melts at 62.5° (Bunsen). It boils at a red heat, and its vapor is green. When exposed to the air, it rapidly absorbs oxygen and at the same time decomposes the atmos- pheric moisture. It inflames at a temperature but slightly elevated and becomes converted into oxide. If a fragment of this metal be thrown into water, it at once takes fire and rushes about on the surface of the liquid, burn- ing with a violet flame. Finally, it disappears with a little explosion. This brilliant phenomenon is due to the energy with which potassium decomposes water. 2W0 + K2 z= 2K0H + H^ The hydrogen which is disengaged is inflamed by the incan- descent metal. The potassium hydrate formed ultimately dis- solves in the water, but its temperature being very high at the moment of its solution, and its combination with the water also producing heat, there results a sudden formation of gteam, which gives rise to the little explosion, 298 ELEMENTS OF MODERN CHEMISTRY. POTASSIUM OXIDES. Potassium peroxide^ KO^ or K^O*, is formed when the metal is gently heated in a current of dry oxygen or air. It is an orange-colored substance which becomes darker on heating, and melts at about 280°, forming a dark-brown liquid. With water and with acids this peroxide reacts with violence, oxygen being disengaged, while hydrogen peroxide and potassium hydroxide or potassium salts are also formed. Potassium monoxide^ K2O, is not known in the pure state. The product resulting from the combustion of the metal in air appears to be a mixture of this oxide and the peroxide. POTASSIUM HYDROXIDE, OR CAUSTIC POTASH. This important compound is prepared by boiling 1 part of potassium carbonate with 12 parts of water, and gradually add- ing milk of lime to the boiling liquid. The lime combines with the carbonic acid, forming an insoluble carbonate, while the potassium hydroxide remains in solution. K^CO^ + Ca(OH)^ = CaCO^ + 2K0H Calcium hydroxide. Calcium carbonate. When the decomposition is finished the liquid is allowed to settle, and the clear solution decanted and rapidly evaporated. The residue is melted in a silver dish and poured out upon flat stone slabs or cast in cylindrical metallic moulds (Fig. 97). This product is known as potash by lime. It is impure. By treating it with alcohol, which dissolves only the potassium SULPHIDES OF POTASSIUM. 299 hydrate, it may be purified from lime, and the salts of potas- sium it may contain, and especially the carbonate, which is formed by the absorption of carbonic acid gas from the air during the evaporation. The clear alcoholic solution is decanted, and after the alcohol has been expelled by distillation, the resi- due is evaporated to dryness and fused in a silver dish. It is known B,fi potash hy alcohol. Perfectly pure potassium hydroxide, such as is frequently required in the laboratory, is prepared by double decomposi- tion between potassium sulphate and barium hydroxide, the potassium hydroxide solution being separated by decantation from the insoluble barium sulphate. K^SO* + Ba(OH)^ = BaSO* + 2K0H Recently-fused potassium hydroxide occurs as opaque, white fragments having a short fibrous fracture and a density of 2.1. It melts at a red heat and volatilizes at whiteness ; it is not decomposed by heat. When exposed to the air, it absorbs moist- ure and carbonic acid gas, and deliquesces. It is very soluble in water, and produces heat in dissolving. A hydrate, KOH -|- 2H^0, is deposited from its hot and very concentrated solu- tion in acute rhombohedra. Potassium hydroxide is very caustic. It softens and destroys the skin, and for this purpose is employed in surgery as a caustic. It manifests the properties of an alkali in the highest degree ; these are its solubility in water, its power to neutralize the acids and decompose a great number of metallic solutions, and its corrosive action on the tissues. This alkalinity may be shown by the energy with which the most feeble solutions of potash restore the blue color to reddened litmus, and change to green the tincture of violets. SULPHIDES OF POTASSIUM. Potassium will burn in vapor of sulphur. It unites with the latter body in five difierent proportions, forming the sul- phides K^S, K'^S^ K^S^ K^SS and K^S^ Potassium monosvlphide is formed when potassium sulphate is heated to redness in a current of hydrogen, or in a brasqued^ and covered crucible with charcoal. 1 A brasqued crucible is a clay crucible into whicb powdered charcoal moistened with gum-water has been strongly pressed, and afterwards cal- cined. The substance to be reduced is placed in a cavity hollowed out in the charcoal, 300 ELEMENTS OF MODERN CHEMISTRY. K^SO* + 4C = 4C0 + K^S Potassium sulphate. Potassium monosulphide. A reddish, deliquescent, and caustic mass is thus obtained. When a mixture of sulphur and potassium carbonate is fused, carbon dioxide is disengaged, and a brown mass is obtained on cooling, which is known as liver of sulphur. It is a mixture of potassium polysulpliide with undecomposed carbonate and potassium sulphate or hyposulphite, according to the tempera- ture and the proportions of sulphur which have been employed. With an excess of sulphur, potassium pentasulphide is obtained. Liver of sulphur dissolves in water with a brown-yellow color. Potassium pentasulphide and hyposulphite are also formed when potassium hydrate is boiled with an excess of flowers of sulphur. The filtered solution is brown. When treated with hydrochloric acid, it evolves hydrogen sulphide, and finely- divided, yellowish, pulverulent sulphur is deposited. K^S^ + 2HC1 = 2KC1 + H^S -f S* POTASSIUM CHLORIDE. KCl This salt is found crystallized in cubes in the neighborhood of certain fissures of Vesuvius, and in thin layers in the saline deposits at Stassfurt, Prussia, and in other localities. At Stassfurt there is found a double chloride of potassium and magnesium, carnallite, KCl,MgCr^ -f- 6H^0. When this is dissolved in hot water, the greater part of the potassium chloride is deposited on cooling while the magnesium chloride remains in solution. Potassium chloride crystallizes in cubes, but it sometimes separates in octahedra from solutions containing free alkali. It is unaltered by the air. Its taste is more bitter than that of sodium chloride ; it is more soluble in water than the latter, and produces a greater depression of temperature in dissolving. 1 part of chloride of potassium dissolves in 3 parts of water at 17.5°. 100 parts of water at 0° dissolve 29.23 parts of potassium chloride and 0.2738 additional for each degree of temperature. POTASSIUM IODIDE AND POTASSIUM BROMIDE. KI and KBr These compounds are important on account of their use in medicine and photography. Potassium iodide is obtained b^ POTASSIUM NITRATE. 301 adding powdered iodine to a solution of potassium hydroxide until the latter is completely neutralized. Potassium iodide and iodate are formed, the latter being precipitated. The whole is evaporated to dryness, and the residue heated to red- ness, by which the iodate is converted into iodide. The mass is dissolved in hot water ; on cooling the solution deposits the iodide in fine colorless and transparent crystals. These crys- tals are opaque if the solution contains any free alkali. They are cubic and anhydrous. They melt at a red heat without decomposition ; their taste is salty and somewhat bitter. 100 parts of water at 18° dissolve 143 parts of potassium iodide. A solution of potassium iodide dissolves iodine abundantly, assuming a dark-brown color. If nitric acid be added to a solution of potassium iodide, iodine is at once deposited and red vapors are disengaged if the solution be concentrated (page 141). This decomposition of potassium iodide takes place even in very dilute solutions. It may serve for the detection of the smallest trace of this salt if a solution of starch be previously added to the liquid ; in this case a blue color will be produced. Potassium bromide is prepared by a process similar to that which yields potassium iodide. It crystallizes in cubes which are soluble in about 1.5 parts of cold water. POTASSIUM NITRATE. KN03 This important salt, long known as nitre and saltpetre, im- pregnates the soil and sometimes effloresces upon its surface in certain regions of India, Egypt, Persia, Hungary, and Spain. In the United States, it is found in many localities, generally in caverns in limestone rock, called saltpetre caves. It is obtained by lixiviating the earthy matters containing it and evaporating the solution. It is less abundant in northern climates. It is formed wherever nitrogenized organic substances decompose in pres- ence of potash. Thus, it exists in small quantities in the soil of cellars, in moist walls, and in old crumbling mortar. In these cases it is mixed with a certain quantity of sodium nitrate and a large excess of calcium and magnesium nitrates. Formerly such materials were lixiviated to obtain the nitrates, all of which were then converted into potassium nitrate. Nitre is also manufactured artificially by exposing to the air mixtures 2t) 302 ELEMENTS OP MODERN CHEMISTRY. of animal matters witli wood-ashes and lime which are fre- quently moistened with stale urine or stahle-drainings. By far the greater part of the saltpetre of commerce is now ob- tained from sodium nitrate, of which vast deposits occur in Chili and Peru. The conversion of this Chili saltpeter^ as it is called, into potassium nitrate is effected as follows. The recrystallized sodium nitrate is dissolved in water, and an equivalent molecular quantity of potassium chloride (obtained from Stassfurt salt) is added. The solution is boiled down until it attains a density of 1.5, when the hot liquid deposits sodium chloride, which is separated, and potassium nitrate crystallizes on cooling. Properties. — This salt crystallizes from its aqueous solution in. long, six-sided prisms, terminated by six-sided pyramids. Gen- erally these crystals are grooved or striated. They belong to the orthorhombic system. Their taste is cooling and slightly bitter. Potassium nitrate melts at about 350° ; at a higher tem- perature it disengages oxygen and is converted into potassium nitrite, KNO^, which is in its turn decomposed at a red heat, leaving a mixture of oxide and peroxide of potassium. Potassium nitrate is very soluble in hot water : 100 parts of water at 0° dissolve only 13.32 parts of the salt, but at 18° they dissolve 29 parts ; at 97°, 236 parts ; and at 100°, 246 parts. The facility with which potassium nitrate parts with its oxy- gen, of which it contains nearly half its weight, renders it an energetic oxidizer of many bodies. If a small quantity of pulverized saltpetre be thrown upon glowing coals, the salt melts and decomposes, increasing the combustion at the point of contact with the fuel : it is said to deflagrate. The nitrate becomes converted into carbonate. Ordinary black gunpowder is an intimate mixture of nitre, charcoal, and sulphur. Its average composition is 75 per cent, of nitre, 15 of charcoal, and 10 of sulphur. The com- bustion of this mixture is instantaneous, and gives rise to the sudden formation of gaseous products. The decomposi- tion may be expressed generally by stating that the char- coal combines with the oxygen of the nitre to form carbon dioxide and carbon monoxide ; the nitrogen is liberated, and the sulphur combines with the potassium, forming potassium sulphide. As the mixture contains all the oxygen necessary for its complete combustion, the latter can be efl"ected in a POTASSIUM SULPHATE — POTASSIUM CHLORATE. 303 limited and closed space. It can readily be understood that the explosive energy of the powder is due to a sudden evo- lution of gas occupying many times the volume of the pow- der, and of which the volume is still further augmented by the high temperature. POTASSIUM SULPHATE. K2S0* This salt is obtained as a by-product in various industrial operations. It deposits from the mother-liquors of the soda from sea-weed when these are exposed to low temperatures. It may be made by saturating with potassium carbonate the potas- sium acid sulphate which is formed in the preparation of nitric acid by the decomposition of potassium nitrate with sulphuric acid, a process which is now but little employed. It crystallizes in four-sided prisms or in double, six-sided pyramids belonging to the orthorhombic system. These crys- tals are hard, anhydrous, unaltered by the air, and melt at a red heat without decomposition. They are but slightly soluble in water and insoluble in absolute alcohol. 100 parts of water at 0° dissolve 8.36 parts, and 0.1741 part for each additional degree of heat. POTASSIUM ACID SULPHATE. This salt may be obtained by fusing 13 parts of the neutral sulphate with 8 parts of concentrated sulphuric acid. The saline mass is dissolved in boiling water, and the solution when properly concentrated deposits rhombic octahedra or tabular crystals belonging to the orthorhombic system. Potassium acid sulphate is much more soluble in water than the neutral salt ; its solution is acid. When strongly heated, it first gives up water and then sulphuric oxide, leaving a resi- due of neutral sulphate. POTASSIUM CHLORATE. KC103 This salt is formed, together with potassium chloride, by the action of chlorine upon a concentrated solution of potassium hydrate or carbonate : 6C1 + 6K0H = KCIO^ -f 5KC1 -f 3H=^0 304 ELEMENTS OF MODERN CHEMISTRY. It is less soluble than the chloride, and is consequently de- posited in great part as the solution becomes saturated with chlorine. It is purified by several recrystallizations. On a large scale it is obtained by the action of chlorine on milk of lime, and decomposing the resulting calcium chlorate with potas- sium chloride. ; 6Ca(OH)2 -f 6CP = Ca(C103)2 + 5CaCP + GH^O and Ca(C103)2 + 2KC1 =: CaCP + 2KC103. Another process, recently introduced, depends upon the fact that an aqueous solution of potassium chloride is decomposed by the electric current into chlorine and potassium hydroxide which, under suitable conditions, will react and form the chlorate. Potassium chlorate crystallizes in colorless, monoclinic tables. When very thin they present an iridescent reflection. It melts at 360°, and at a higher temperature is decomposed into oxygen and chloride and perchlorate of potassium, the latter of which is also decomposed when the temperature is raised still further. 2KC10^ = KCl + KCIO* + 0^ KCIO* = KCl -^ 0* Potassium chlorate deflagrates when thrown upon hot coals ; when mixed with sulphur, it explodes by friction or percussion ; the detonation becomes dangerous if the sulphur be replaced by phosphorus. It is not very soluble in cold water. 100 parts of water at 0° dissolve 3.3 parts, and at 24°, 8.44 parts. It is much more soluble in boiling water. POTASSIUM PERCHLORATE. KC104 This salt is formed by the action of either heat or sulphuric acid upon potassium chlorate (page 134). It is but slightly soluble in water, requiring 65 parts at 15° for its solution. It crystallizes in anhydrous and transparent right rhombic prisms. Above 400° it decomposes into potassium chloride and oxygen. POTASSIUM CARBONATES. Potassium Neutral Carbonate, K^COl — This carbonate is found in commerce under the simple name potash, and is known according to its source as Russian or American potash. POTASSIUM CARBONATES. 305 It is obtained by lixiviating wood ashes; tbat is, exhausting them with water, evaporating the solution to dryness, and cal- cining the residue in the air. The potash thus obtained is impure carbonate mixed with other salts of potassium, princi- pally the chloride and sulphate, and small quantities of silicate. It contains from 60 to 80 per cent, of carbonate. Potassium carbonate is now manufactured from the native chloride, Stassfurt salt, by a process similar to that which will be described for the manufacture of sodium carbonate from common salt. Pure potassium carbonate may be prepared by calcining potas- sium acid tartrate, or cream of tartar, at a red heat. A black mass is thus obtained from which water dissolves pure potas- sium carbonate, and the solution is evaporated to dryness. Neutral potassium carbonate is very soluble in water, and absorbs moisture from the air. 1 part of the anhydrous salt dissolves in 1.05 parts of water at 3°, and in 0.49 parts at 70° (Osann). The solution has a decided alkaline reaction. A very concentrated hot solution deposits rhombic octahedra containing K^CO^ -|- 2H^0 on coohng. Potassium Acid Carbonate, KHCOl — When a current of carbonic acid gas is passed into a concentrated solution of potas- sium neutral carbonate, the gas is absorbed, and crystals of potassium acid carbonate, ordinarily known as bicarbonate of potash, are formed. It represents carbonic acid in which a single atom of hydro- gen is replaced by an atom of potassium. C02 + H20 == H2C03 carbonic acid (hypothetical). C02 + KHO = -n- [ CO^ potassium acid carbonate. . v€02 + K20 = K2C03 potassium carbonate. Potassium acid carbonate readily crystallizes in monoclinic prisms. It is much less soluble in water than the neutral carbonate, and its solution disengages carbonic acid gas on boiling. Its reaction is alkaline. Characters of Potassium Salts. — The salts of potassium communicate a violet tint to flame. Their solutions are not precipitated either by hydrogen sulphide, ammonium sulphide, or sodium carbonate. Perchloric acid occasions a white precipitate of potassium perchlorate. 26* 306 ELEMENTS OF MODERN CHEMISTRY. Platinum tetracliloride produces a yellow, crystalline precip- itate of platinum and potassium double chloride, 2KCl.PtCf*. Hydrofluosilicic acid forms a white, gelatinous precipitate consisting of potassium fluosilicate. SODIUM. Na = 22.88 Sodium was discovered by Sir Humphry Davy in 1807. It was formerly obtained by a process analogous to that described for the preparation of potassium. An intimate mixture of sodium carbonate and charcoal was heated to whiteness in cast- iron cylinders, and the sodium vapor condensed in suitable vessels, carbon monoxide being disengaged. Na^CO^ +-2C r= 2Na + SCO For a number of years also the metal of commerce was manufactured by the more economical processes of Castner and Netto, in both of which it is extracted from sodium hydroxide. In Castner's process the reduction is effected by strongly heat- ing a mixture of the hydroxide and carbide of iron, CFe^ 6NaOH + 2C = 2Na^C0^ -f SH^ + 2Na That of Netto consists in allowing fused caustic soda to trickle over incandescent charcoal contained in an iron retort. The sodium carbonate, formed as in the preceding equation, is drawn off at the bottom of the retort, while the metal is dis- tilled. At the present time the bulk of the sodium of commerce is produced by electrolysis of fused sodium chloride. 2NaCl = 2Na + CP The salt used for this purpose is mixed with other chlorides — those of potassium and strontium are generally employed — in order to lower its melting point sufficiently to prevent the formation of a subchloride of sodium, and thus to increase the yield of metal. Sodium is soft at the ordinary temperature. It has a silvery lustre, melts at 96°, and boils at 742°. Its affinity for oxygen is less powerful than that of potassium ; it can be melted in the air without taking fire. When thrown upon water, it SODIUM. 307 melts and runs around on the surface, producing a hissing noise. The water is decomposed with disengagement of hydrogen and the formation of sodium hydroxide. The re- action is analogous to that of potassium upon water, but is less energetic ; frequently, however, it terminates by an ex- plosion. When sodium is heated in a current of hydrogen, and the temperature maintained at 300°, the gas is absorbed, sodium hydride^ Na^H, being formed. This compound has the ap- pearance of silver, and a density of 0.96 ; at 240° it breaks up into its elements. OXIDES AND HYDROXIDE OF SODIUM Two oxides of sodium are known, a monoxide, Na^O, and a dioxide, NaO or Na^Ol The former has not been obtained in the pure state, but is probably one of the products of the action of metallic sodium upon the hydroxide. 2Na -f. 2NaOH = 2Na^0 -f H^ Sodium hydroxide, NaOH, is frequently employed in the laboratory and in the arts under the name caustic soda. It is prepared by decomposing a rather dilute, boiling solution of so- dium carbonate by milk of lime, in the manner described for the preparation of potassium hydroxide (page 298). It occurs as a white solid, which attracts moisture and carbonic acid from the air, and finally becomes transformed into a dry mass of carbonate. Sodium hydroxide is freely soluble in water, and is very caustic. It is known in commerce as concentrated lye. Commercial caustic soda contains many impurities. The chemically pure hydroxide is best obtained by the action of metallic sodium upon water. For this purpose very small quantities of water and sodium are alternately introduced in a well-cooled and capacious silver dish. The resulting solu- tion is evaporated by heating, and the fused residue cast into moulds. Sodium dioxide, Na^O^ (sodium peroxide), is now produced on a commercial scale by heating the metal to 300° in a mixture of nitrogen and oxygen gases in which the propor- tion of the latter is gradually increased. It is a yellowish substance, and acts as a powerful oxidizing agent. Water decomposes it into hydrogen dioxide and sodium hydroxide. Its chief use is for bleaching silk and wool. 308 ELEMENTS OF MODERN CHEMISTRY. SODIUM SULPHIDE AND HYDROSULPHIDE. Sodium sulphide^ Na^S, is prepared by the following proc- ess : A concentrated solution of sodium hydroxide is divided into two equal parts; one part is then saturated with hydrogen sulphide, sodium hydrosulphide being formed. NaOH + H^S = NaSH + H^O Sodium hydroxide. Sodium hydrosulphide. To this hydrosulphide the other portion of sodium hydroxide is added, and the solution is concentrated out of contact with the air. Hydrated crystals of sodium sulphide are deposited. NaSH + NaOH = WO -f Na^S These crystals are rectangular prisms terminated by four- faced points. When pure, they are colorless; they are very soluble in water. SODIUM CHLORIDE. NaCl This body is common salt, or sea-salt. It is widely diffused in nature. It is found in the solid state, as rock-salt, in large deposits in many countries. Sea-water contains a large proportion of sodium chloride, and this salt also exists in a number of mineral waters, of which it forms the most abundant constituent. Much of the salt of commerce is obtained by the evapora- tion of sea-water along the Mediterranean. The water is led into basins, where it forms a shallow layer, which is continu- ally swept by the summer winds. It thus becomes concen- trated, and is kept in motion from one basin to another, until it arrives in the areas where the salt is deposited. In many localities salt is obtained by direct mining operations ; more frequently, however, the crude salt is first dissolved in water, and after the insoluble residue has been separated the brine is evaporated. Thus, in Cheshire, England, bore-holes are sunk down to the salt bed, water is turned into these holes, and after it has become saturated with salt is pumped up and evaporated. Sodium chloride is also obtained by the evaporation of the waters of brine springs. The operation is conducted in large sheet-iron boilers ; the salt crystallizes from the hot liquid, SODIUM SULPHATE. 309 and a double sulphate of calcium and sodium, which is but slightly soluble, incrusts the basins in the course of time. Sodium chloride crystallizes from its aqueous solution in cubes. The crystals are generally small, and a great number of them frequently become agglomer- ated in symmetrical hopper-like masses (Fig. 99). These crystals are anhy- drous, but contain a small quantity of interposed water ; when heated they decrepitate, because this water is vola- tilized and suddenly separates the crys- Fig. 99. tals. Sodium chloride fuses at a red heat and solidifies to a crystalline mass on cooling. It vola- tilizes at a white heat. It is very soluble in water, and its solubility increases only slightly with the temperature. Ac- cording to Gray-Lussac, 1 part of common salt dissolves in 2.78 parts of water at 14° a u u 2.7 " " 60° a u (( 2.48 " " 109.7° The saturated solution boils at 109.7° ; its density at 8° is 1.205. Sodium chloride is insoluble in absolute alcohol. SODIUM SULPHATE (Glauber's Salt). Na2S0* This salt is obtained in the arts by decomposing common salt with sulphuric acid (page 127). This operation, which constitutes the first step in the manu- facture of sodium carbonate, is conducted in a reverberatory furnace, connected with a suitable apparatus for the condensa- tion of the hydrochloric acid which is disengaged. Sodium acid sulphate is first formed, and at a higher temperature this reacts upon another molecule of sodium chloride. Na| HJ SO* + NaCl = Na^SO* + HCl Sodium acid sulphate. Sodium sulpliate. Sodium sulphate is now extensively produced by subjecting the mother-liquors from the manufacture of salt from sea-water to intense cold. It crystallizes from water in four-sided, oblique rhombic prisms, containing 10 molecules of water of crystallization j 310 ELEMENTS OF MODERN CHEMISTRY. these crystals effloresce in the air. They possess a bitter, salty, and disagreeable taste. They are very soluble in water, and the temperature of their maximum solubility is 33°. Accord- ing to Gay-Lussac, 100 parts of water at 0° dissolve 12 parts of sodium sulphate. « « 18° " 48 " " u (( 25° " 100 " " « .< 330 « 332.6 « (( (( « 500 (( 263 " " When the solution saturated at 33° is heated, it deposits an- hydrous sodium sulphate in orthorhombic octahedra, analogous to the anhydrous sodium sulphate found in nature {thenardite). Sodium Acid Sulphate, -^ \ SO*.— This salt may be ob- tained by dissolving in water the requisite proportions of so- dium neutral sulphate and sulphuric acid. On cooling the saturated solution, oblique rhombic prisms are obtained, which, according to Mitscherlich, contain two molecules of water of crystallization. These crystals are very soluble in water, and have an acid taste. Alcohol decomposes them into sulphuric acid, which dissolves, and neutral sulphate, which precipitates. SODIUM CAEBONATE. This important salt, known also as soda and soda ash, is manufactured on an immense scale in the arts. It is used in the manufacture of soap and glass, for washing, and many other purposes. It was formerly obtained from the ashes of fuci, algae, and other sea-plants which furnished Alicant soda. It is now most generally prepared from sodium chloride. One process, which is due to Le Blanc, consists of three distinct operations: 1st, the transformation of the sodium chloride into sulphate by sulphuric acid ; 2d, the conversion of the sul- phate into carbonate by calcination with a mixture of chalk and coal; 3d, lixiviation of the calcined mass and evaporation of the solution. Only the latter two operations need be de- scribed here : they are conducted in reverberatory furnaces, of which the doubly-arched roofs are licked by the flame of the combustible (Fig. 100). A mixture of 1000 parts of sodium sulphate, 1040 parts of chalk, and 580 parts of coal is first introduced into compart- SODIUM CAEBONATE. 311 ment B of the furnace, where it is dried. It is then transferred to compartment A, where the temperature is very elevated, and where the sodium sulphate is reduced to sulphide by the Fig. 100. coal. The sodium sulphide and chalk react upon each other, forming sodium carbonate and calcium sulphide (Kolb). The results of the reaction may be expressed by the follow- ing equation : Na^SO* + CaCO^ + C^ = XaTO^ + CaS + 4C0 There are, however, certain secondary reactions which talie place at the same time ; thus, a certain quantity of sodium oxide is formed by the action of the coal upon the carbonate. Na^CO^ -{- C == 2C0 + Na^O When the incandescent mass has become pasty, it is removed from the farnace. reduced to powder, and thoroughly lixiviated. The water dissolves the sodium carbonate, and leaves the in- soluble calcium sulphide, which remains mixed with the lime produced by the decomposition of the excess of chalk employed (Grossage, Scheurer-Kestner). The solutions are concentrated in the boiler D, heated by the waste heat from the soda fur- nace. Finally, they are drawn off into the compartment C, where they are evaporated to dryness. The soda ash of commerce is thus obtained. When the properly-concentrated solution is allowed to cool, the crystallized soda (washing soda) of commerce is deposited. Another process, known as the ammoiiia-soda process, has not only entered into successful competition with that of Leblanc, but appears to gradually supersede it. It is also known as Solvay's process. 312 ELEMENTS OF MODERN CHEMISTRY. It depends upon the double decomposition whicli takes place between ammonium acid carbonate and sodium chloride in concentrated aqueous solution. NaCl + (NH*)HCO^ = NH*C1 + NaHCO^ The sodium acid carbonate, which is but slightly soluble, is precipitated ; it is collected and converted into the neutral car- bonate by the action of heat. 2NaHC0^ = Na^CO^ + CO^ + H^O It thus loses half of its carbonic acid, which is utilized for the preparation of a new quantity of ammonium acid carbonate. The other portion of the carbonic acid necessary for this oper- ation is produced by the calcination of lime-stone (calcium car- bonate), which at the same time yields the lime necessary for the liberation of the ammonia contained in the mother-liquor in the form of ammonium chloride. A considerable quantity of sodium carbonate is also manufac- tured from cryolite^ which is a double fluoride of sodium and aluminium, and of which large deposits exist in Greenland. The mineral is calcined with lime, calcium fluoride and alumi- nate of soda being formed. 2AlFl3NaF -f 6CaO = 6CaF^ -f AP0^3Na^0 Cryolite. Calcium fluoride. Aluminate of soda. The latter compound is dissolved out by water and decom- posed by carbonic acid gas, aluminium hydroxide being pre- cipitated and sodium carbonate remaining in solution. Sodium carbonate crystallizes in monoclinic prisms, con- taining 10 molecules of water of crystallization. When heated, they fuse in this water of crystallization, which they then abandon ; they also lose it by efflorescence when exposed to the air. Sodium carbonate is very soluble in water, and the solution has a strongly alkaline reaction. According to Poggiale, 100 parts of water at 0° dissolve 7.08 parts of sodium carbonate. " " 10° " 16.06 " « " " 20° " 25.93 « " « " 25° " 30.83 " « " " 30° " 35.90 " " " " 104.6° " 48.5 " " The saturated solution boils at 104.6°. Sodium carbonatQ is insoluble in alcohol, SODIUM BORATE. 313 Sodium Acid Carbonate, NaHCO^— When carbonic acid gas is passed into a solution of sodium carbonate or over crystals of that salt, the gas is absorbed and sodium acid car- bonate, commonly called bicarbonate of soda, is formed. This salt crystallizes in oblique, four-sided prisms, shortened into the form of tables. Its taste is salty and slightly alkaline. It is less soluble in water than the neutral carbonate. It restores the blue color to reddened litmus ; its solution does not pre- cipitate that of magnesium sulphate, and when boiled loses carbonic acid, neutral carbonate being formed. PHOSPHATES OF SODIUM. There are three phosphates of sodium derived from ordinary or otho-phosphoric acid. H) Na") Na^ Na") H ^ PC* H ^ PC* + 2H20 Na )■ PC* + 12H20 Nsi } PO* + 12H20 hJ hJ hJ NaJ Phosphoric Monosodium Disodium phosphate. Trisodium phosphate, acid. phosphate. Monosodium phosphate reddens blue litmus ; the disodium and trisodium salts have an alkaline reaction. The most important in the arts and in commerce is disodium phosphate, or common phosphate of soda. It is prepared by neutral- izing the calcium acid phosphate, obtained by digesting bone-dust with dilute sulphuric acid and filtering, with so- dium carbonate. Tricalcium phosphate is precipitated, and disodium phosphate remains in solution.- By evaporation of the filtered liquid, the salt may be obtained in voluminous, transparent, monoclinic prisms, containing 12 molecules of water of crystallization. Monosodium phosphate exists in urine, and is the cause of the normal acidity of that excretion. SODIUM BORATE, OB BOBAX. This salt corresponds to tetraboric acid, containing 2B^0^ -f- H^O = H'^B^O^ It results from the action of one molecule of sodium oxide upon two molecules of boric oxide. 2(B'0') -f Na^O = Na^B^O^ It crystallizes with either 10 or 5 molecules of water. Borax was formerly obtained from Asia, where it exists in solution in the waters of certain lakes. By the evaporation o 27 314 ELEMENTS OF MODERN CHEMISTRY, of these waters a product known as tinkal was obtained ; this is natural borax. Part of the borax of commerce is obtained by saturating the boric acid of Tuscany with sodium carbo- nate, and evaporating the solution below 56°. Borax is found in abundance in certain lakes in California, and large quanti- ties are now derived from the naturally occurring borates of calcium (colemanite and horocalcite) and magnesium (bora- cite). These yield borax by double decomposition with sodium carbonate. When a concentrated boiling solution of borax is allowed to cool, it deposits between 79° and 56° regular octahedral crystals containing 5 molecules of water of crystallization ; below 56° the crystals deposited are rhombic prisms and contain 10 molecules of water. The latter form is that found in commerce. Borax solution is faintly, alkaline. When borax is heated, it melts in its own water, swells up and becomes dry, and then undergoes igneous fusion. Melted borax dissolves a large number of oxides, forming borates. On solidifying, the color and appearance of a number of these are highly characteristic. For this reason borax is a valuable agent in analysis. Anhydrous borax dissolves in 12 parts of cold and 2 parts of boiling water. Borax possesses antiseptic properties and is used as a preservative. Characters of Sodium Salts. — Sodium salts are not pre- cipitated from their solutions by either hydrogen sulphide, ammonium sulphide, sodium carbonate, or platinic chloride. Hydrofluosilicic acid forms with them a white precipitate. A solution of potassium antimonate produces a white precipitate of sodium antimonate (Fremy). Sodium salts impart a yellow color to non-luminous flames. A small quantity of alcohol may be ignited in a saucer and will burn with an almost colorless flame, but the introduction of a small quantity of sodium hydrate, chloride, or any other sodium compound, at once colors the flame bright yellow. This character is very sensitive, and the smallest trace of sodium may thus be recognized by introducing a platinum wire, dipped into the substance to be tested, into the colorless flame of the blow-pipe or of a Bunsen burner. LITHIUM — CESIUM AND RUBIDIUM. 315 LITHIUM. Li = 6.97 In 1817, Arfvedson, a Swedish chemist, discovered a new alkali, lithia, which is the hydroxide of lithium, LiOH, anal- ogous to potassium hydroxide, KOH. To this hydroxide cor- responds an oxide, Li^O, and a chloride, LiCl. Bunsen was the first to obtain the metal lithium, which he prepared by electrol- ysis of the fused chloride. It is a silvery-white metal, but its surface rapidly tarnishes in the air. It is the lightest of the solid elements, its density being between 0.578 and 0.589. It melts at 180°. It is less oxidizable than either sodium or potassium. When heated above its point of fusion in the air or in oxygen, it burns with a brilliant white flame. It decomposes water at ordinary temperatures, but without melting like sodium. The salts of lithium are soluble in water, but the carbonate and phosphate only slightly so. There exists also a double phosphate of sodium and lithium, which is but slightly soluble. The salts of lithium communicate a red color to the flame of alcohol or of the Bunsen burner. The compounds of lithium are generally prepared from lepidolite^ tripJiyline^ aniblygonite^ or spodumene^ minerals of complex composition containing small amounts of the ele- ment in the form of silicate or phosphate. CESIUM AND RUBIDIUM. SPECTRUM ANALYSIS. Cesium and rubidium are two alkaline metals discovered by Kirchhoff" and Bunsen in 1860-61, by the aid of a new method of analysis. This method consists in the examination of spectra ; hence the name spectrum analysis. The solar spectrum formed upon a screen which intercepts a beam of solar light refracted by passage through a prism, con- sists of a series of colored bands. The different simple rays of which white light is composed are unequally refracted by the prism, and separate from each other on their emergence. The violet rays, which are farthest turned from their original direction, form the most deviated extremity of the spectrum. 316 ELEMENTS OF MODERN CHEMISTRY. The red rays, which are the least refracted, form the least de- viated extremity. The visible spectrum of solar light presents not only a succession of variously-colored bands ; when it is closely examined by the aid of magnifying instruments, it is found that the succession is not continuous, but that the lumi- nous bands are traversed by dark lines. These lines, which were discovered by Wollaston. and studied by Fraunhofer, are very numerous, and are irregularly distributed throughout the spectrum, from the red to the violet, but each one of them occupies a definite position, and for the principal lines that position has been determined by exact measurements. Fraun- hofer designated them by the letters A, B, C, D, E, F, Gr, H. The D line is the most distinct of all : its place is in the yel- low. Other lights, the stars, for example, give similar discon- tinuous spectra. On the contrary, an incandescent platinum wire, or any other luminous source which contains no volatile matter, gives a continuous spectrum. Very interesting facts are observed when the sources of light are flames into which the vapors of volatile substances, par- ticularly the metallic salts, are introduced. The spectra of such flames are formed exclusively of brilliant lines (see plate). If a platinum wire which has been dipped into a solution of sodium chloride be introduced into the colorless flame of a Bunsen burner, the flame will assume a yellow color, and will give a visible spectrum, but one which is very incomplete, since it consists of a single yellow line. It has been found that this line exactly coincides with the dark line D, existing in the yellow of the solar spectrum. This line characterizes sodium in all of its compounds : it is the spectrum of sodium. In the same manner, a flame into which a compound of potas- sium, lithium, barium, calcium, or other volatile metal is intro- duced, will give for each metal a particular spectrum formed of variously-colored lines. Each is perfectly characterized by the number, color, and position of the lines. Barium gives the most numerous and the widest lines ; other metals give more compli- cated spectra. That of iron is composed of 70 brilliant lines. Kirchhofi* and Bunsen, who discovered these facts, made a happy application of them to analysis. To detect the presence of a metal in a compound or even in a mixture, a small portion of the substance is introduced into a colorless gas flame, and the spectrum then given by the flame is observed by the aid of an instrument called a spectroscope. The light to be examined SILVER. 317 is caused to pass through a narrow rectangular slit before falling on the prism. The image of the slit is then refracted to its own peculiar place in the spectrum. The method is so sensitive that -g-.-ooT.Too- ^f a milligramme of sodium chloride will render the yellow sodium line distinctly visible. The discovery of two new metals, caesium and rubi- dium, crowned the brilliant researches of Kirchhoff and Bunsen. Since then, a number of new metals have been discovered by the aid of spectrum analysis : thallium, which gives a green line, indium, which gives an indigo-blue line, gallium, which gives two violet lines very close together, and several others which will be mentioned farther on. Spectrum analy- sis has been useful also in the discovery and characterization of the new gaseous elements, argon, helium, and krypton. SILVER. Ag (Argentum) = 107.11 Natural State. — Silver is found native and in combination in many minerals. Among these are the sulphide, the sulph- antimonides and sulpharsenides, the antimonide, chloride, bromide, iodide, selenide, telluride, and lastly an amalgam of silver. It is found in small proportions in many galenas and copper pyrites. Treatment of Silver Ores. — According to the nature of the ores the extraction of the silver is effected in the dry way or the wet way. Argentiferous galena is reduced as described under lead, and the metal which contains all the silver is remelted and subjected to the process of cupellation (page 345), whereby the lead is removed as oxide, and the silver remains in the metallic state. In case the lead contains but a very small proportion of silver, a process devised by Parkes is employed ; it depends on the fact that when melted lead containing silver is agitated with a small proportion of zinc, the latter metal dissolves out all the silver, and the resulting alloy rises to the surface in the form of a scum. This is readily collected and the zinc and lead are removed, the first by distillation, the last by cupellation. 27* 318 ELEMENTS OF MODERN CHEMISTRY, When the silver ore is free from lead, the extraction of the silver may be accomplished by means of mercury ; an amalgam of silver is formed from which the mercury is sepa- rated by distillation. Mexican Amalgamation or Patio Process. — American silver ore consists of sulpharsenide and sulphantimonide of silver, mixed with silver chloride and native silver, the whole being disseminated in silica, calcium carbonate, and ferric oxide. In Mexico, the following primitive process is still used. The finely-pulverized ore is mixed with two per cent, of common salt and thrown into circular areas paved with flag-stones, where it is rendered homogeneous by being trodden for several hours by mules. About one per cent, of copper pyrites which has been roasted in the air and contains cupric sulphate is then added. The latter salt reacts with the sodium chloride, forming sodium sulphate and cupric chloride, which latter decomposes the silver sulphide, forming silver chloride and cupric sulphide. Mercury is then added and reduces the silver chloride, with formation of chloride of mercury and metallic silver. During the whole time the mass is continually trodden by the mules, and the mercury comes in contact with the disseminated silver : the amalgam formed solidifies in about a fortnight. A second and finally a third addition of mercury is then made until 7 or 8 parts of that metal have been employed for one part of silver to be extracted. After a few months, the operation is terminated, and the mass is washed with large quantities of water to remove the earthy and salty matters. The amalgam remains, and is heated in order to extract the silver. American or Washoe Process. — The above method of ex- traction is too slow to be employed for the vast quantities of silver ore that are mined on the Pacific Slope. The ore is there crushed and roasted with sodium chloride and a small proportion of cupric sulphate, in furnaces of a peculiar con- struction. By this means all of the silver is converted into chloride. The mass is made into a pulp with water and agi- tated with mercury in large tanks or " pans." The silver chloride is reduced as before, and the amalgam obtained is first squeezed out and afterwards heated to expel the mercury. To this end it is placed in horizontal iron retorts (Fig. 102), which are heated to cherry redness. The mercury distils and is collected under water, while an impure silver remains. SILVER. 319 Fig. 102. Silver may also be extracted in the wet way. The Patera process, which is applicable to sulphide ores, consists in trans- forming the silver into chloride by roasting the ore with salt, and lixivi- ating the product with so- dium thiosulphate. Sul- phide of silver is then precipitated by adding an alkaline sulphide to the solution. Ziervogel's process de- pends on the conversion of sulphide of silver into sul- phate by roasting the ore in the air. Upon treating the mass with hot water, the silver sulphate passes into solution, from which the metal may be precipitated by metallic copper. Properties. — Silver is the whitest and most brilliant of all the ordinary metals. Next to gold, it is the most malleable and the most ductile. Its density is 10.5. It is the best conductor of heat and electricity. It melts towards 1000°, and when fused has the curious property of dissolving oxygen, of which it absorbs 22 times its volume. On solidifying, it again disengages the gas ; this phenomenon, which occasionally causes the projection of por- tions of silver, is called spitting. Silver volatilizes at the high temperatures of the oxyhydrogen blow-pipe and the electric furnace. Its vapor is green. It is unaltered by the air. In the presence of moisture, it is acted upon by ozone, being converted into the peroxide, AgO or Ag^Ol It decomposes concentrated solution of hydriodic acid, dis- engaging hydrogen and forming silver iodide (Deville). Hy- drochloric acid only attacks it superficially. Hydrogen sulphide blackens it, forming a pellicle of silver sulphide. Its best sol- vent is nitric acid which attacks it in the cold, yielding silver nitrate and disengaging red vapors. The alkalies have no action upon silver; for this reason, silver vessels are used for fusing potassium hydroxide and concen- trating its solution. 320 Elements of modern chemistry. By precipitating silver solutions witli various reducing agents, under peculiar circumstances, Carey Lea has obtained interest- ing allotropic forms of silver, red, blue, and gold in color, and having a high degree of lustre. They are readily reconverted into ordinary silver. SILVER OXIDE. Ag^O The only important oxide of silver is the monoxide, which is precipitated in the anhydrous state when potassium hydrate, free from chloride, is added to a solution of silver nitrate. It forms an olive-brown, flocculent deposit which yields a brown powder on drying. Silver oxide is readily decomposed by heat into silver and oxygen. It is reduced by hydrogen at a temperature below 100°. When recently precipitated, it is slightly soluble in water. It is an energetic base, perfectly neutralizing the acids, and displacing cupric oxide from the cupric salts. When oxide of silver is digested with ammonia it is con- verted into a very explosive, black powder, known as fulmi- nating silver. It appears to be the nitride Ag^N. SILVER SULPHIDE. To the oxide of silver corresponds the sulphide Ag^S, which occurs native, as argentite, crystallized in regular octahedra, ordinarily modified by facettes. It is soft and can be scratched by the finger-nail. Silver and sulphur combine readily by the aid of heat. SILVER CHLORIDE. AgCl^ This body is found native and is known to mineralogists as horn-silver. It is sometimes found crystallized in cubes and octahedra. It is formed directly when silver is heated in chlo- rine gas, and is prepared by double decomposition by adding hydrochloric acid or a solution of sodium chloride to solution of nitrate of silver. A white, curdy precipitate is thus obtained, which assumes a violet tint when exposed to the action of light. The change of color is due to partial decomposition. Silver chloride melts at about 260°, and solidifies on cooling to a gray, horn-like mass that can be cut with a knife. If recently precipitated and moist silver chloride be placed upon a sheet of zinc, in a short time a dark color will appear SILVER IODIDE — SILVER NITRATE. 321 on tlie borders of the chloride, and the whole of that body will soon be converted into a dark-gray powder of finely-divided silver. Zinc chloride is at the same time formed. This reaction takes place much more rapidly if the silver chloride be moistened with hydrochloric acid. In this case the reduction is eifected by nascent hydrogen produced by the action of the hydrochloric acid on the zinc. When silver chloride is fused with the alkaline hydrates or carbonates, it is reduced to metallic silver : oxygen is disen- gaged, and an alkaline chloride is formed. Recently-precipitated silver chloride dissolves readily in aque- ous ammonia. When dry, it absorbs ammonia gas abundantly, and Faraday employed this compound for the preparation of liquid ammonia. Silver chloride dissolves also in alkaline hyposulphites. SILVER IODIDE. Agl Silver iodide is obtained as a yellow precipitate by adding potassium iodide to a solution of silver nitrate. It blackens on exposure to light. It is but very slightly soluble in ammo- nia, a property which distinguishes it from silver chloride. SILVER NITRATE. AgNQs This salt is prepared by dissolving silver in nitric acid. If the metal be pure, a colorless solution is obtained which after concentration and cooling deposits large, colorless tables of an- hydrous silver nitrate. If silver coin be employed, the solution will be blue, containing, independently of silver nitrate, cupric nitrate. The latter may be removed by evaporating the residue to dr3mess and carefully heating it, so that the salt may remain fused for some time. The cupric nitrate is decomposed, while the silver nitrate remains mixed with cupric oxide, from which it may be freed by solution and filtration. This salt dissolves in its own weight of cold, and in half its weight of boiling water. The solution is neutral to test- paper. When exposed to the air, it blackens, as do also the crystals and the fused salt, a partial reduction being produced by organic matters in the air. It blackens the skin from a similar cause. 322 ELEMENTS OF MODERN CHEMISTRY. Hydrogen slowly reduces the solution of silver nitrate with deposition of metallic silver (Beketoff). Silver nitrate is extensively used in photography ; it is also used in medicine, and when fused constitutes lunar caustic. Characters of Silver Salts. — Solutions of silver are precipi- tated black by hydrogen sulphide and by ammonium sulphide. Caustic alkalies give an olive-green precipitate of silver oxide, insoluble in excess. Ammonia does not precipitate them. Hydrochloric acid and the soluble chlorides form a white precipitate of silver chloride, insoluble in either cold or boiling nitric acid, but soluble in ammonia. Potassium iodide gives a yellow precipitate, almost insoluble in ammonia. Silvering. — This operation consists in covering the common metals or glass with a coating of silver more or less thick. The metals are silvered by either amalgamation or galvanic deposition. In the latter and preferable operation, a solution of the double cyanide of silver and potassium is generally used. Mirrors and glass articles in general are silvered by the re- duction of a silver salt by aldehyde, glucose, or tartaric acid. The following receipt is given by Liebig: a solution of 10 grammes of silver "nitrate is supersaturated with ammonia and rendered strongly alkaline by caustic soda. The volume of the liquid should be 1450 c.c. Another solution is prepared by dissolving 1 part of milk sugar in 10 parts of water. The latter solution is mixed with its own volume of the first solu- tion, and the glass to be silvered is washed with alcohol and immersed in the liquid. The reduction of the silver salt begins immediately, and does not require the aid of heat. The experiment may easily be made in a glass flask, the interior of which will be uniformly silvered. Assaying of Silver. — This name is applied to the methods which serve for the analysis of alloys of silver and copper, such as coin, medals, silverware, and jewelry. The assay may be conducted by the dry way or by the wet way. The dry assay consists in the operation called cupellation (Fig. 103). A certain quantity of metallic lead is melted in a cupel of bone-ash in a reverberatory furnace, and a weighed quantity of the alloy of silver and copper, carefully wrapped in a small piece of paper, is placed upon the fused metal. The silver dissolves in the melted lead, and a ternary alloy is thus obtained which is exposed to the action of air at a red heat. ASSAYING OF SILVER. 323 Under these conditions, the lead and copper become oxidized ; the oxide of lead fuses, and the melted litharge, which should be in great excess in proportion to the oxide of copper, dis- solves the latter, and with it is absorbed by the porous cupel. The phenomenon of brightening (page 346) indicates the ter- mination of the process. Fig. 103. The wet assay ^ invented by G-ay-Lussac, consists in. adding to a solution in nitric acid of a known weight of the alloy of silver and copper, a titrated solution of sodium chloride, that is, a solution containing an exactly known weight of salt in one litre of water. This solution is cautiously added until it no longer precipitates silver chloride, and the quantity of silver present is calculated from the volume of the titrated solution that has been required to completely precipitate the silver in the form of chloride. As the latter readily deposits from a liquid that is carefully agitated, it is easy to ascertain the end of the operation, that is, the precise moment when all of the silver is precipitated and the addition of the titrated liquid mast be arrested. 324 ELEMENTS OF MODERN CHEMISTRY. Process. — Two titrated solutions are used to precipitate the silver : 1st, a normal solution, containing 0.5417 gramme of sodium chloride per decilitre, a quantity sufficient to precipitate one gramme of silver ; 2d, a decinorinal solution, that is, one containing the same quantity of sodium chloride per litre, so that 1 c.c. of this liquid will precipitate one milligramme of silver. To analyze an alloy of silver, a coin, for example, such a quantity is weighed as would contain one gramme of silver, if the proportion of silver were a little less than the extreme limit allowed. If the alloy ought to contain 900 thousandths pure silver, with an allowance of 3 thousandths, it would be rejected should it contain less than 897 thousandths. We suppose, however, that the latter is its quality, and weigh a quantity of the alloy which would then contain one gramme of pure silver, that is, 1.1148 grammes. This alloy is dissolved in nitric acid, and one decilitre of the normal solu- tion is added. All of the silver should not be precipitated, for the standard of the alloy should be above 897. This is deter- mined by adding to the clarified liquid one or more cubic cen- timetres of the decinormal solution, until the liquid ceases to become cloudy on a fresh addition. As each cubic centimetre of this solution corresponds to one milligramme of silver, we must add to the gramme of silver at first precipitated as many milligrammes as we have added cubic centimetres of the deci- normal solution, the last cubic centimetre added counting for only half a milligramme. Knowing the quantity of pure silver contained in 1.1148 grammes of the alloy analyzed, the standard of the latter is determined by a simple calculation. CALCIUM. Ca = 39.8 Lime, which is universally known, is the oxide of a metal called calcium. The latter was discovered by Davy in 1808, and isolated in 1854 by Matthiessen, who obtained it by decomposing fused calcium chloride by the voltaic current. According to Lies-Bodard and Jobin, calcium may be obtained by decomposing calcium iodide with sodium in an iron crucible. Calcium has a yellow color when freshly filed, but it tar- nishes rapidly in moist air and becomes covered with a grayish OXIDE AND HYDROXIDE OF CALCIUM. 325 layer of hydroxide. When heated upon platinum-foil it takes fire and burns with a dazzling flame. It decomposes water at ordinary temperatures. OXIDE AND HYDROXIDE OF CALCIUM. Lime^ or calcium oxide^ CaO, is obtained by calcining the carbonate in special furnaces, which are called lime-kilns. As quick-lime, it forms large, compact, and hard grayish masses. It is infusible. When exposed to the air, it attracts moist- ure and carbonic acid, augments in volume, and is finally con- verted into a white powder, a mixture of calcium hydroxide and carbonate. When lime is sprinkled with water, it absorbs the liquid without giving rise to any particular phenomenon; but in a little while, the pieces saturated with water become hot, give ofi" steam, and then they split and increase in volume. If enough water be used, the quick-lime will be converted into a white powder, which is called slaked lime; it is calcium hydroxide. CaO -f WO = CaO^H'^ = Ca(0H)2 When slaked lime is suspended in water, a white, creamy liquid is obtained that is called milk of lime. If this be fil- tered or allowed to settle, the clear, limpid liquid resulting will have an alkaline reaction, for it contains a small quantity of calcium hydroxide in solution : it is lime-iuater. Calcium hydroxide is more soluble in cold than in hot water. Employment of Lime in Constructions. — Lime is largely employed for building purposes in both ordinary and submarine constructions. The limestone which is used for the preparation of lime is rarely pure, and consequently the product of its calcination presents differ- ent qualities, according to the proportions of foreign matters which remain in the lime, and which consist of a small quantity of mag- nesia, oxide of iron, and especiallj^ clay. Fat limes are those pro- duced by the calcination of almost pure limestone ; they develop much heat, and swell up very much on slaking. Such lime forms an unctuous and binding paste with water, and makes ordinary mortar when mixed with sand. Impure limestones yield lean lime, containing magnesia, oxide of iron, and clay. It is gray, and de- velops but little heat and increases but slightly in volume on slaking. The calcination of limestone containing from 10 to 30 per cent, of clay produces hydraulic lime. Such lime sets under water, that is, the mortar solidifies after a few days, and becomes very hard, even when immersed in water. On account of this curious property it is used in submarine constructions. Such lime is yellow ; slaking it produces but little heat, and scarcely any increase in volume. The 28 326 ELEMENTS OF MODERN CHEMISTRY. hydraulic mortar formed by its mixture with sand will harden under water. Mortars possessing this property may also be prepared by mixing lime with baked argillaceous materials, such as powdered tiles, pottery, bricks, etc. Certain argillaceous rocks of volcanic origin, the pozzolana so abundant near Vesuvius, for example, yield an excellent hydraulic lime when mixed with fat lime. Cement is a variety of lime resulting from the calcination of lime- stones containing from 40 to 50 .per cent, of slate. When mixed with water, such cement sets in a few minutes in a solid mass like plaster. Vicat has shown that the diiferent varieties of hydraulic lime and cement can be prepared by properly calcining carbonate of lime, or chalk, with various proportions of clay. According to him, ordinary mortar sets because the lime gradually absorbs car- bonic acid gas from the air, forming a carbonate which hardens and binds together the grains of sand. The hardening of hydraulic lime and mortar is due to another cause : on contact with water, the clay which they contain in the anhydrous state becomes hydrated and forms a double silicate of calcium and aluminium, or a silicate and aluminate of calcium, which are insoluble and very coherent. CALCIUM CHLORIDE. CaCP This salt is prepared by dissolving white marble or chalk in hydrochloric acid. On evaporation, the solution deposits large, six-sided prisms, containing 6 molecules of water of crystal- lization. They are very deliquescent and lower the tempera- ture when they are dissolved in water. If they be mixed with their own weight of snow, a cold of — 45° may be produced. When they are heated, they melt in their water of crystal- lization, of which they lose 4 molecules at 200°, and the re- mainder at a red heat. At the latter point the mass enters into igneous fusion, and on cooling solidifies to a white, crys- talline mass, in which form it is ordinarily employed for the desiccation of gases. Calcium chloride dissolves readily in alcohol. CALCIUM CARBIDE. CaC2 At the high temperature of the electrical furnace lime is promptly reduced by carbon, but metallic calcium is not ob- tained. The reduced metal combines with part of the carbon, forming a black, homogeneous, crystalline mass, which is the carbide CaC^ (H. Moissan). It has a density of 2.2, and is fusible at the high temperature at which it is formed. When heated in air, it burns into calcium carbonate. Water in- stantly reacts with it, forming calcium hydroxide and acety- lene, Qm\ CALCIUM NITRATE — CALCIUM CARBONATE. 327 CALCIUM NITRATE. Ca(N03)2 + 4H20 This salt is formed naturally in the neighborhood of dwell- ings, in the soils of cellars, and in damp walls. It is con- tained in what are known as saltpetre materials, and exists in certain spring and well waters. It may be made by satu- rating nitric acid with calcium carbonate. It is very soluble in water and in alcohol. It crystallizes with difficulty in six- sided, oblique rhombic prisms, which contain 4 molecules of water of crystallization : they are deliquescent. CALCIUM CARBONATE. CaC03 Calcium carbonate, commonly known as carbonate of lime, is found in great abundance in nature and under different forms. It is dimorphous, being found as calcite crystallized in rhombohedra and as arragonite in right rhombic prisms. Iceland spar is calcite which is colorless and perfectly trans- parent ; the crystals are doubly refracting. The various limestones and marbles constitute natural cal- cium carbonate in which crystalline structure is more or less apparent, and many varieties are colored by foreign matters. All the varieties of marble are susceptible of a high polish. Statuary marhle is the whitest, and is made up of brilliant crystalline grains ; lithographic-stone is exceedingly fine- grained, very compact, and has a yellowish-white color. Chalk is a soft and amorphous calcium carbonate, made up of the mineral remains of marine animalcules. Pure water dissolves but feeble traces of this salt ; water charged with carbonic acid dissolves a larger quantity, con- verting it into dicarbonate. It is in this state that it is contained in hard waters. When the carbonic acid slowly evaporates, the calcium carbonate is deposited from such waters in compact form having crystalline structure, and when the water drips from the dome of a cave, large and fantastically shaped stalactites and stalagmites are frequently formed, consisting of almost pure calcium carbonate. Calcium carbonate may be prepared by double decomposi- tion between solutions of sodium carbonate and calcium chloride. When heated to bright redness, it is completely decomposed into lime and carbonic anhydride, 328 ELEMENTS OF MODERN CHEMISTRY. CALCIUM SULPHATE. CaSO* This salt exists in two states in nature : anhydrous, it con- stitutes the anhydrite of mineralogists ; combined with two molecules of water of crystallization, it forms gypsum or plas- ter stone. G-ypsum sometimes occurs in lance-head-shaped crystals, grouped together ; they are divisible into thin, trans- parent layers, easily scratched by the finger-nail. Alabaster and satin-spar are varieties of gypsum. All the forms of hydrated calcium sulphate contain 21 per cent, of water. When heated to 80° in the air, or to 115° in closed vessels, the sulphate, CaSO* -|- 2H^0, abandons its water of crystalli- zation and is converted into the anhydrous sulphate. Between 120 and 130°, this dehydration is rapid and complete. It is operated on the large scale in plaster furnaces. In this state calcium sulphate will readily recombine with its water of crystallization. If the plaster be calcined at too high a tem- perature it will not again become hydrated. If powdered plaster of Paris be mixed with enough water to form a creamy liquid, it may be poured into a mould, and in a few minutes will harden to a compact mass, completely filling every cavity of the mould. In becoming hydrated, the particles of calcium sulphate assume the crystalline form and increase in volume. These properties render plaster of Paris valuable in building operations, for ornamental work, and for making casts. It is also employed to a large extent in agriculture. Calcium sulphate is but slightly soluble in water. 1000 parts of boiling water dissolve a little more than 2 parts of the salt; at 35° they dissolve 2.64 parts; at 20°, 2.05 parts. CHLORINATED LIME. (bleaching-powder.) This substance is largely employed in the arts under the name chloride of lime^ and is obtained by exposing well-slaked lime to the action of chlorine. Its constitution is not perfectly understood; it was long regarded as a mixture of calciunj CHLORINATED LIME. 329 chloride and calcium hypochlorite, CaCP + Ca(ClO)^ but re- cent researches have shown that it does not contain calcium hypochlorite already formed. The formation of the alkaline hypochlorites by the action of chlorine on a solution of an alkaline hydrate is explained on page 133. With the hydrates of diatomic metals like calcium the action is more complicated, and is probably expressed by the equation Ca(0H)2 -I- CP = Ca(OCl)Cl + H^O Its manufacture is conducted by passing a current of chlorine over slaked lime placed in layers upon shelves arranged in the walls of masonry chambers (Fig. 104). The product always contains a certain proportion of lime which cannot possibly be chlorinated. Fig. 104. Chlorinated lime is an energetic bleaching agent ; under the influence of acids it is decomposed, chlorine being set free. A solution of the compound is decomposed by the more feeble acids, even by carbonic acid gas, and decomposes spontaneously in a short time into calcium chloride and calcium hypochlorite. 2a* 330 ELEMENTS OF MODERN CHEMISTRY. Inasmuch as the substance is a mixture, and not a definite compound, its reactions may be interpreted in several different manners. It always contains water, calcium hydroxide, and a proportion of calcium chloride, and its active principle is probably expressed by one, or perhaps both, of the following formulae : Ca<^^^ = CaOCP ; ^^<0E =" ^^^^^-^^ The reactions might then be written as follows: The spontaneous decomposition of the solution, 2CaOCP = Ca(ClO)^ -f CaCP Calcium hypochlorite. Calcium chloride. 2CaOC1.0H = Ca(ClO)^ + Ca(0H)2 ; its decomposition by hydrochloric acid, CaOCP + 2HC1 = CaCP + H^O + CP CaOClOH + 3HC1 = CaCP + 2H20 + CP When a solution of chlorinated lime is boiled, it is at once decomposed, yielding calcium chloride and calcium chlorate : eCaOCP = 5CaCP + Ca(C10^)2 Calcium chloride. Calcium chlorate. Characters of Calcium Salts. — Calcium salts are not pre- cipitated either by hydrogen sulphide or ammonium sulphide. Sodium carbonate forms in them a white gelatinous precipitate. Sulphuric acid and the soluble sulphates produce a white pre- cipitate, if the calcium solutions be concentrated or only mod- erately dilute. Oxalic acid, or better, ammonium oxalate, produces a white precipitate of calcium oxalate, even in the most dilute solutions of calcium salts. Calcium compounds impart an orange-red color to non-luminous flames. STRONTIUM. Sr = 86.95 Strontium was discovered by Davy in 1808, but the pure metal was first obtained by Bunsen and Matthiessen by a pro- Qes3 similar to that which serves for the preparation of barium, BARIUM. 331 Matthiessen describes it as a yellow metal, having a density of 2.50-2.58, harder than lead, and decomposing cold water. Strontium forms two oxides, a monoxide^ SrO, and a dioxide^ SrOl Strontium chloride, SrCP, crystallizes in deliquescent needles which contain six molecules of water of crystallization. It is very soluble in water and fairly soluble in alcohol; the alcoholic solution burns with a red flame. Strontium nitrate, Sr(NO^)^, which is prepared like barium nitrate, is deposited from its hot aqueous solution in anhydrous octahedra, and crystallizes at low temperatures in oblique rhom- bic tables containing 5 molecules of water of crystallization (Laurent). The carbonate of strontium, SrCO' (strontianite^, and the sulphate, SrSO* (celestite), are found native. These two salts are insoluble in water, and are deposited as white precipitates on adding a soluble carbonate or sulphate to the solution of a strontium salt. Strontium sulphate is less insoluble, however, than barium sulphate. Strontium salts color flames red, and the nitrate is used in red fire. BARIUM. Ba = 136.4 Bunsen obtained barium by the electrolysis of fused barium chloride ; this metal is very avid of oxygen, and tarnishes rapidly. It decomposes cold water. Barium Oxide, or Baryta, BaO. — Barium oxide is obtained by calcining barium nitrate. Its nature was first recognized in 1808, by Davy, who decomposed it by the voltaic current. It is a gray, porous substance, which unites energetically with water, producing a hissing noise and a great disengagement of steam, due to the elevation of temperature. The product of the reaction is a white hydrate, ordinarily known as caustic baryta. BaO + WO = Ba(0H)2 Barium oxide. Barium hydroxide. Barium hydroxide is soluble in two parts of boiling water, and on cooling is in great part deposited in large tabular crys- tals, containing 8 molecules of water. The solution of barium hydroxide in water is called baryta water, 332 ELEMENTS OF MODERN CHEMISTRY. Barium Dioxide, BaO^ — When dry oxygen is passed over barium oxide heated to dull redness, the gas is absorbed and a dioxide, BaO^ is formed. It is a gray, porous mass, some- times greenish. It loses one atom of oxygen at a bright-red heat (see page 66). When brought in contact with water, it combines with the latter quietly and without disengagement of heat, forming a pulverulent hydrate. This hydroxide is readily prepared pure by adding an excess of baryta water to a solution of hydrogen dioxide ; it separates in beautiful scales. It reacts with cold dilute hydro- chloric acid, forming barium chloride and hydrogen dioxide. Barium Sulphide, BaS. — This is obtained by reducing barium sulphate with charcoal. BaSO* + C* = BaS + 4C0 The sulphate is reduced to fine powder, and is mixed with a certain quantity of flour or rosin. The mixture is then made into a paste with linseed oil, and shaped into little balls. These are calcined at a bright-red heat in a covered crucible, and a porous, gray mass is thus obtained which, when treated with boiling water, yields a solution which deposits hexagonal tables after filtration and cooling. These crystals do not present a very constant composition, being a mixture of sulphide, hydro- sulphide, and hydroxide of barium. Their solution has a light- yellow color. BARIUM SALTS. Barium Chloride, BaCP + 2H'0.— This salt is obtained by saturating the solution of barium sulphide with hydrochloric acid. Hydrogen sulphide is disengaged ; the solution is boiled, filtered, and evaporated to crystallization. Barium chloride separates in quadrangular tables belonging to the type of the right rhombic prism. These crystals are inalterable in the air. 100 parts of water at 18° dissolve 43.5 parts of barium chlo- ride, and 78 parts at 105.5°, the temperature of ebullition of the saturated solution (Gray-Lussac). Absolute alcohol dis- solves -jl-Q- of its weight of barium chloride. Barium Nitrate, Ba(NO^)^ — Barium nitrate is prepared by decomposing barium sulphide or carbonate with dilute nitric acid, and filtering and evaporating the solution. It crystallizes in regular octahedra, or in cubo-octahedra. The crystals are transparent and unaltered in the air. One GLUCINUM, OR BERYLLIUM. 333 part of this salt requires for its solution 20 parts of water at 0.12° ; 5 parts of water at 15° ; 2.8 parts at 106°, the tem- perature of ebullition (Gay-Lussac). When heated to redness, barium nitrate gives off oxygen, nitrogen, and red vapors, leav- ing a residue of oxide, BaO. Barium Sulphate, BaSO*. — This salt is found abundantly in nature as lieavy spar, and sometimes occurs in right rhom- bic crystals. It is entirely insoluble in water and acids, with the exception of concentrated sulphuric acid. It is precipi- tated as a finely-divided, amorphous powder when sulphuric acid or a soluble sulphate is added to a solution, even very di- lute, of a salt of barium. Barium Carbonate, BaCO^. — Barium carbonate constitutes an amorphous, white powder, which is obtained by double de- composition on adding solution of sodium carbonate to a solu- tion of barium sulphide. Natural barium carbonate is an abundant mineral, and is found crystallized in right rhombic prisms; it is called loitlierite. Characters of Barium Salts. — Barium salts are precipi- tated neither by hydrogen sulphide nor by ammonium sulphide. Sodium carbonate produces in them a white precipitate. Even when very dilute, the barium salts produce a white precipitate with sulphuric acid, which is insoluble in either cold or boiling nitric acid. The salts of barium communicate a green color to flames ; the nitrate is used in green fire. Grlucinum, magnesium, zinc, and cadmium form a group in which the chemical analogies of the members are well marked. They are diatomic, forming oxides BO, and chlorides RCP. GLUCINUM OR BERYLLIUM. Gl, or Be = 9.01 The varieties of beryl, including the green precious stone emerald and aqua-marine, contain a double silicate of aluminium and glucinum. The latter metal was first isolated by Woehler in 1827. Glucinum is prepared by the reduction of its chloride by po- tassium or sodium. It is white and brilliant, has a density of 1.6, and melts at a temperature below the fusing-point of silver. It does not decompose water, even by the aid of heat, but is 334 ELEMENTS OF MODERN CHEMISTRY. readily attacked by hydrochloric and sulphuric acids, hydrogen being evolved and a chloride or sulphate formed. Glucinum Oxide, GIO, is prepared from beryl, or by pre- cipitating by ammonia a solution of glucinum chloride. In the latter case a hydrate Gl(OH)^ is obtained, which is converted into oxide by heat. The oxide is a light, white, infusible powder, soluble in acids and alkalies. When heated in the oxyhydrogen flame, it vola- tilizes like magnesium and zinc oxides. Glucinum Chloride, GICP. — This salt may be prepared by passing chlorine over an intimate mixture of the oxide and charcoal at a high temperature. Glucinum chloride forms white, deliquescent crystals that fume in the air, condensing atmospheric moisture. It is fusible, and volatilizes at a low red heat. It is very soluble in water, and forms a hydrate which is decomposed by heat, yielding glucinum oxide and hydrochloric acid. Glucinum forms a nitrate, and a sulphate which is isomor- phous with magnesium sulphate. The salts of glucinum possess a sweet taste, to which the metal owes its name. MAGNESIUM. Mg = 24.18 Magnesium was discovered by Bussy. Matthiessen obtained it by decomposing fused magnesium chloride by electricity. Preparation. — Deville and Caron recommend the following process for the preparation of considerable quantities of mag- nesium. A mixture of 600 grammes of anhydrous magnesium chloride, 100 grammes of sodium chloride, 100 grammes of calcium fluoride, and 100 grammes of sodium cut into small pieces is heated to redness in a covered crucible. The mag- nesium chloride is reduced by the sodium, and the magnesium set free collects in little globules disseminated in the fused mass, which must be stirred with an iron rod. These little globules are removed from the scoriae when cold, introduced into a charcoal boat, and heated to bright redness in a cur- rent of hydrogen. The magnesium volatilizes and condenses farther on in the tube ; it may then be fused with a flux con- sisting of magnesium chloride, sodium chloride, and calcium fluoride. The metal collects at the bottom of the crucible. MAGNESIUM OXIDE, OR MAGNESIA. 335 Within recent years magnesium lias acquired considerable commercial importance. It is manufactured by electrolyzing carnallite, the double chloride of magnesium and potassium. This salt is fused in an iron crucible (A, Fig. 105), which serves as a negative electrode. A carbon rod forms the anode, which is enclosed by a porcelain cylinder perforated at the bottom to permit free passage of the fused carnallite, and con- nected at the top with a pipe to carry off the evolved chlorine. In this manner the metal liberated at the cathode cannot come in [ T ^ _ 7 contact with the chlorine, Pjq 1Q5 with which it would at once recombine, and it is protected from oxidation by the passage of an inert gas, such as nitrogen or hydrogen, through the space in the iron retort. Properties. — Magnesium has a density of 1.74 or 1.75. It fases at 500°. It decomposes water at ordinary temperatures but slowly. It may readily be rolled into ribbon or drawn into wire. The wire is grayish and not very brilliant. The end of a bundle of these wires may be heated in an alcohol lamp until they take fire, and the whole may then be plunged into a jar of oxygen. They burn with an incomparable splendor that the eye cannot support; at the same time the jar becomes filled with a white smoke, which condenses into a white powder, the product of the combustion ; it is magnesia, the oxide of mag- nesium. Magnesium also combines directly with nitrogen. In the form of powder, magnesium is employed in the flash-lights used in photography and in pyrotechnics. MAGNESIUM OXIDE, OH MAGNESIA. MgO This body is obtained by calcining white magnesia, or mag- nesium hydrocarbonate. It is a white, voluminous powder, less fusible even than lime. It does not dissolve in water, but combines with that liquid forming a hydrate, Mg(OH)''* = MgO.H^O. This hydrate slowly restores the blue color to reddened litmus-paper. 336 ELEMENTS OF MODERN CHEMISTRY. Magnesium hydroxide is precipitated when a solution of caustic potash is added to the solution of a magnesium salt. Calcined magnesia is frequently employed in medicine. On account of its great infusibility (it melts only at the temperature of the electric arc), crude magnesia is employed for lining furnaces and crucibles. MAGNESIUM CHLORIDE. MgCP This salt is known in the anhydrous state and crystallized. Anhydrous magnesium chloride is prepared by dissolving the carbonate in hydrochloric acid, adding ammonium chloride to the solution and evaporating to dryness. A double chloride of magnesium and ammonium is thus obtained which may be per- fectly dried ; the dry mass is introduced into a clay crucible and heated ; the ammonium chloride volatilizes, while the magne- sium chloride remains, and solidifies on cooling to a colorless, pearly mass. It is very soluble in water, and when properly concentrated, the solution deposits deliquescent, prismatic crystals containing six molecules of water of crystallization. These crystals can- not be dehydrated, nor can their solution be evaporated to dryness, without decomposing the chloride by the action of the water; under these circumstances the magnesium chloride is converted into hydrochloric acid and magnesia. MgCP + H^O = 2HC1 + MgO MAGINESIUM CARBONATE. MgCO^ The anhydrous carbonate MgCO^, known as magnesite, is found native, crystallized in rhombohedra, similar to those of calcium carbonate. Considerable deposits are also found of a double carbonate of magnesium and calcium, known as dolomite. When a boiling solution of magnesium sulphate is precipi- tated by an excess of sodium carbonate, carbonic acid gas is disengaged, and a precipitate is formed containing at the same time magnesium carbonate and magnesium hydrate (magnesium hydrocarbonate). When this is dried, it constitutes the white magnesia of the pharmacies. ZINC. 337 MAGNESIUM SULPHATE. MgSO* + 7H20 This salt exists in solution in sea-water and in certain pur- gative mineral waters, such as those of Epsom, in England. Its common name is Epsom salts. At Stassfurt, it is found crystallized with one molecule of water (Ideserite) and mixed with the anhydrous sulphate. When it separates at ordinary temperatures from an aqueous solution that has been tolerably concentrated by heat, it crystal- lizes in transparent and colorless right rhombic prisms. At 0°, it crystallizes with 12 molecules of water ; at 30°, with 6 molecules. Its taste is disagreeable, at the same time salty and bitter. When magnesium sulphate crystallized with 7 molecules of water is heated, it first melts in its water of crystallization, of which it loses 6 molecules. At 132°, it still retains one molecule, which it loses only at 210°. It is very soluble in water ; 100 parts of water at 0° dissolve 25.76 parts of the anhydrous sulphate, and 0.4781 6 part for every additional degree (Gay-Lussac). It forms a double sulphate with potassium sulphate, K^SO^MgSO^ -f GH^O. Characters of Magnesium Salts. — They are precipitated by neither hydrogen sulphide nor ammonium sulphide. Sodium, carbonate produces a white, flocculent precipitate. Caustic potash and ammonia form white precipitates, but ammonia will not precipitate magnesia from an acid solution or from one containing ammonium chloride. Sodium phosphate and ammonia together produce a crystalline precipitate of ammonio-magne- sium phosphate. This is the most delicate test for magnesium. ZINC. Zn = 64.91 Treatment of Zinc Ores. — The most important ores of zinc are zinc spar (smifhsonife) , ZnCO* ; blende or sphalerite, ZnS; calamine, Zn^SiO' -f H^O ; willemite, Zn^SiO*; red zinc ore, ZnO, ?ind franJdimte, (Zn,Fe)O.Fe^O^ Zinc ores are abundant in England, Silesia, Belgium, and throughout the United States. They are generally accom- panied by other minerals ; thus, blende is often mixed with pyrites and galena (lead sulphide). The ore is then first submitted to an ingenious system of washing, by which the T w 2e. 338 ELEMENTS OF MODERN CHEMISTRY. various sulphides separate from eacli other by reason of their different densities. In order to extract the zinc from blende separated by this method, or from zinc spar, the minerals are first roasted. By the action of heat zinc spar loses carbonic acid gas and water, and the blende disengages sulphur dioxide and is converted into zinc oxide. Thus converted into oxide, and rendered more friable by the heat, the zinc ores are pulverized and calcined with charcoal. Carbon monoxide is disengaged, and the zinc set at liberty volatilizes, and is condensed in suitable receivers. The operation is conducted in cylinders of refractory clay, a number of which are arranged in a furnace, and their open extremities connected with conical recipients of galvanized iron (Fig. 106). In Silesia, these cylindrical retorts are re- placed by muffles, which are heated in a furnace and com- municate with recipients placed outside (Fig. 107). Fig. 106. Fig. 107. The zinc of commerce is impure. It contains small quan- tities of iron, copper, lead, cadmium, carbon, and arsenic. It may be purified by repeated meltings with small quantities of nitre. The last traces of impurities can be removed only by fractional distillation in vacuo (Morse). Properties. — Zinc has a bluish-white color ; its density varies from 6.86 to 7.2, according as it has been melted or rolled ; its fracture is laminated and brilliant. Commercial ZINC OXIDE. 339 zinc is brittle at ordinary temperatures ; it becomes malleable at a few degrees above 100°, but when heated to 200° it again becomes brittle. It melts at 410°, and distils at about 1000°. Its vapor density compared to hydrogen indicates that the molecule contains but one atom. Its surface soon tarnishes in moist air, but the tarnish is only superficial. It is due to the formation of an impermeable layer of hydro- carbonate of zinc, which protects the metal from further oxidation. When heated to redness in air, zinc volatilizes and burns with a greenish flame into a smoke of oxide, which falls in light, white flakes, formerly called flowers of zinc or philoso- pher's wool. Zinc dissolves with evolution of hydrogen in hydrochloric and sulphuric acids, and in boiling solutions of potassium and sodium hydroxides. When perfectly pure, it is dissolved with difficulty by dilute sulphuric acid at ordinary temperatures, and the easy solubility of the metal of commerce must be attrib- uted to the presence of small quantities of foreign metals. The latter being electro-negative in contact with zinc, form voltaic couples, in which the zinc is the more oxidizable metal. Galvanized iron is iron covered with a thin layer of zinc ; it is prepared by plunging carefully-cleaned iron objects into a bath of molten zinc. Brass is an alloy of copper and zinc, obtained by melting the two metals together in crucibles. ZINC OXIDE. ZnO This oxide is prepared in the arts by heating zinc in large muffles ; the product is separated from traces of metallic zinc by suspending it in water and rapidly decanting the white liquid. The zinc sinks to the bottom of the A^essel before the lighter white powder has time to deposit ; the latter is therefore carried by the water into a second vessel, where it is allowed to settle. The process is called elutriation. This oxide is now manufactured on an enormous scale by drawing an excess of air through a burning mixture of zinc ore and coal. The zinc is reduced and oxidized at one operation, and the oxide is drawn through the blower and collects in can- vas bags through which the waste gases are forced. 340 ELEMENTS OF MODERN CHEMISTRY. Oxide of zinc is white ; it turns yellow wlien heated, is infusible and is irreducible by beat and insoluble in water. The corresponding hydroxide is precipitated when caustic alkalies are added to the solution of a zinc salt, ZnSO^ + 2K0H = K^SO* + Zn(OHy Zinc sulphate. Zinc hydroxide. An excess of alkali will redissolve the precipitate. Zinc oxide is largely used in the arts as a substitute for white lead as a pigment. ZINC SULPHIDE. ZnS The blende which occurs in nature is sulphide of zinc. It crystallizes in the isometric system, often in hemihedral forms. Sometimes it occurs as lourtzite in hexagonal prisms (Friedel). On adding an alkaline sulphide to a neutral solution of a zinc salt a white precipitate is obtained, which is hydrated zinc sulphide. This precipitate is soluble in mineral acids. When moderately heated in contact with the air, zinc sul- phide absorbs four atoms of oxygen and is converted into sul- phate. At a very high temperature it is converted into oxide, with formation of sulphurous oxide. ZINC CHLORIDE. ZnC12 Zinc reduced to thin sheets will burn in chlorine. Zinc chloride is prepared in the laboratory by dissolving zinc in hydrochloric acid. The aqueous solution, evaporated to a syrupy consistence, deposits a hydrated chloride, ZnCP -|- H^O, crystallizing in deliquescent octahedra. This salt loses its water when strongly heated, and melts at about 250°. On cooling, a solid white mass is obtained, which is the anhydrous chloride ; in this state it is very avid of water and deliquesces when exposed to the air. It volatilizes without decomposition at a red heat. It is very soluble in water, and dissolves also in alcohol. ZINC SULPHATE. ZnSO^ + 7H20 This salt was formerly known as white vitriol. It is ob- tained by moderately roasting blende. The latter being often CHARACTERS OP ZINC SALTS. 341 mixed with pyrites, zinc sulphate and ferrous sulphate are formed, and when the product of the roasting is lixiviated a solution of the two salts is obtained. The solution is evapo- rated, and the dry residue moderately calcined. The ferrous sulphate decomposes, yielding sulphuric acid, which distils, and ferric oxide, which remains mixed with the zinc sulphate. The residue being exhausted with water, the zinc sulphate dissolves and is deposited in crystals on the cooling of the concentrated solution. The salt may be prepared in the laboratory by dissolving zinc in dilute sulphuric acid : it is the residue in the prepara- tion of hydrogen. Sulphate of zinc crystallizes with 7 molecules of water. In this state it occurs as orthorhombic prisms, isomorphous with magnesium sulphate. When heated, it melts in its water of crystallization, of which it loses 6 molecules ; the seventh it abandons only at 238°. At a high red heat it is decomposed into zinc oxide, sul- phurous oxide, and oxygen. Zinc sulphate is very soluble in water, of which 100 parts dissolve 48.36 parts of the anhydrous salt at 10°, and 95.6 parts at 100°. The solution has a styptic taste. Zinc sulphate forms crystallizable double salts with the alka- line sulphates ; thus, there is a double sulphate of zinc and potassium, containing ZnSOMPSO* + QWO Characters of Zinc Salts. — The zinc salts are colorless unless the corresponding acid be colored. Their neutral solu- tions are partially decomposed by hydrogen sulphide, which precipitates white sulphide of zinc ; the addition of a mineral acid prevents the precipitation ; the zinc salts of organic acids, such as the acetate and lactate, are completely decomposed by hydrogen sulphide. Ammonium sulphide produces a white precipitate of sul- phide; this reaction is characteristic. The alkaline hydroxides, and ammonia-water, form white precipitates, soluble in an excess of the reagent. Potassium ferrocyanide gives a white precipitate. 29* 342 ELEMENTS OF MODERN CHEMISTRY. CADMIUM. Cd = 111.08 Natural State arid Extraction. — Cadmium is generally found associated with zinc, either as oxide in calamine, or as sulphide in zinc blende. As it is more volatile than zinc, it becomes concentrated in the first products of distillation. It is found especially, in the state of oxide, in the brown powder called cadmies^ which condenses during the first hours of the distillation in the sheet-iron receivers adapted to the re- torts (Fig. 106). When mixed with powdered charcoal and calcined, this powder yields an alloy of zinc and cadmium which distils. The cadmium is extracted by dissolving the alloy in dilute sulphuric acid and passing a current of hydrogen sulphide through the acid liquid. The cadmium is precipitated as a yellow sulphide. This sulphide is dissolved in hydrochloric acid and the solution of cadmium chloride precipitated by am- monium carbonate. The cadmium carbonate thus obtained is calcined, and so converted into oxide, which is mixed with one-tenth its weight of powdered charcoal and heated in a clay retort. The cadmium distils. Properties. — Pure cadmium has a white lustre, but soon tarnishes in the air. Its density is 8.60-8.69. It melts at 320°, and boils at 860°. Its vapor density is 56. It may be obtained crystallized in octahedra. It dissolves in dilute sulphuric and hydrochloric acids with evolution of hydrogen. Cadmium Oxide, CdO. — The oxide of cadmium may be ob- tained by calcining either the carbonate or nitrate. It has a yellowish-brown color, or a brown more or less deep. It is re- duced at high temperatures by carbon and by hydrogen, its reduction taking place more readily than that of zinc oxide. Cadmium Sulphide, CdS. — This sulphide occurs in nature as greenockite in the form of bright yellow, hexagonal prisms, terminated by six-sided pyramids. It may be prepared in the laboratory by precipitating a solu- tion of a cadmium salt by hydrogen sulphide or a soluble sul- phide. An amorphous precipitate of a fine yellow color is thus obtained. In this form it is employed in oil painting. Cadmium Iodide, CdP. — This salt is prepared, by digesting LEAD. 343 finely-divided cadmium with iodine in presence of water. It crystallizes from its aqueous solution in transparent and color- less, hexagonal prisms having a brilliant lustre. It is soluble in water and alcohol. Cadmium Sulphate, 3CdS0* + 8H='0.— Cadmium Sul- phate is obtained by dissolving the metal, or its oxide or carbonate, in dilute sulphuric acid. The neutral and con- centrated solution deposits the salt in beautiful monoclinic prisms. These crystals are efflorescent. LEAD. Pb (Plumbum) = 205.4. Lead is related to the diatomic metals by a series of normal salts, the chloride PbCP, sulphide PbS, oxide PbO, etc., but it is undoubtedly tetratomic in other compounds, among which are a tetrachloride PbCl*, and a dioxide PbO^ It is probable, however, that lead is tetratomic in all of its compounds, in which case the dichloride must be represented by the formula C{>Pb=Pb.sss..sv..s..s.. .;^s^ vapor and rich in carbonic acid gas. The leaden sheets are introduced into glazed earthen pots, A (Fig. 110), containing a small quantity of vinegar. The lead rests upon short projecting arms, B, below which is placed the crude vinegar. The pots are covered by a disk of lead, D, which incompletely closes them. They are then arranged in rows in large chambers ; a row of pots is placed on a bed of spent tan or horse-manure ; these are cov- ered with planks, upon which more spent tan or horse-mantire is placed, and then another layer of pots, and so on. The fer- FiG. 110. LEAD CHROMATE. 353 mentation of the tan or manure raises the temperature to 30 or 40°, and produces carbonic acid gas. On the other hand, the oxygen of the air intervenes, causing the lead to be attacked by the acetic acid, so that basic acetate of lead is formed upon the surface of the metal ; but this salt is con- tinually decomposed by the carbonic acid gas, so that the lead gradually becomes covered with a layer of carbonate. Thenard suggested another process by which litharge is dis- solved in a solution of lead acetate, and a current of carbon dioxide passed through the solution of subacetate so formed. Lead carbonate is precipitated and neutral acetate regenerated ; the latter is then again transformed into basic acetate. The product so obtained is known as Clichy white lead. LEAD CHROMATE. PbCrO* This salt exists crystallized in nature, constituting the crocoite of Siberia. It is prepared by double decomposition between solutions of potassium chromate and lead acetate ; a yellow precipitate is thus obtained, and is employed in painting under the name chrome yellow. Lead chromate melts at a red heat ; at a white heat it loses 4 per cent, of oxygen. It is easily reduced by charcoal and hydrogen. Insoluble in water, it dissolves readily in solutions of potassium hydroxide. Characters of Lead Salts. — The soluble lead salts have a sweetish taste. Black precipitates are formed in their solutions by both hydrogen sulphide and ammonium sulphide. The caustic alkalies give white precipitates, soluble in a large excess of the reagent. Ammonia gives a white pre- cipitate, insoluble in excess. Sulphuric acid forms a white precipitate even in the most dilute solutions of lead. Hydrochloric acid forms a white precipitate of lead chloride, but this precipitate is not produced in dilute solutions. Potassium chromate throws down a yellow precipitate, soluble in potassium hydroxide. When heated with sodium carbonate upon a piece of charcoal in the reducing flame of the blow-pipe, the lead salts yield a metallic globule which when cold can readily be flattened out by hammering. X 3d* 354 ELEMENTS OF MODERN CHEMISTHY. THALLIUM. Tl = 202.6 The spectroscopic green line given by this metal was first observed by William Crookes, who regarded it as characteris- tic of a new element. The honor of having isolated the latter and of establishing its true character belongs to Lamy. Thallium is widely distributed in nature, but constitutes only a very small proportion of the minerals in which it occurs, excepting the very rare crookesite, which contains 16 to 18 per cent. It is a heavy metal, rather whiter than lead ; it is soft and sectile. Its density is 11.9, and it melts at 285°. It is sol- uble in dilute sulphuric and nitric acids. Thallium forms two oxides, to which correspond two series of salts. Thallous oxide^ TPO, is a black powder ; the corresponding hydroxide, TIOH, is soluble and caustic like the alkalies, and crystallizes in yellowish prisms. Thallous chloride, TlCl, is sparingly soluble in water. The carbonate, TPCO^ is quite soluble in water. Thallic oxide^ TPO^ is obtained as a dark powder, when thallium burns in oxygen or when the hydroxide is heated. The compounds derived from this oxide are less stable than the thallous compounds : the chloride TICP, sulphate TP(SO*)^, and other thallic salts have been prepared. COPPER. Cu(Cuprum) = 63.12 Natural State. — Copper is found in the native state, some- times crystallized in isometric forms, sometimes in masses. It is also found as cuprous oxide, Cu^O, cupric oxide, CuO, and cupric carbonate, CuCO^ ; but its most abundant minerals are cuprous sulphide, Cu^S {clialcocite), and a, double sulphide of copper and iron, Cu'^S.Fe^S^ designated as copper pyrites. Under the name gray copper are also worked various minerals containing cuprous sulphide combined with the sulphides of antimony and arsenic, and in which the copper is sometimes replaced by iron, zinc, silver, and mercury. Treatment of Copper Ores. — Copper is easily extracted from cuprous oxide and cupric carbonate. These ores are COPPER. 355 melted with charcoal in suitable furnaces, and the metal is at once obtained. Copper pyrites, which is often mixed with cuprous sulphide, requires a more complicated treatment. The iron and sulphur must be eliminated, and for this reason the ore is subjected to an incomplete roasting. This operation is conducted in a reverberator j furnace (Fig. 111). The flame Fig. 111. of the fire sweeps the arched vault of the furnace w. The opening of the chimney is at C, and the ore is fed in from iron troughs placed above the furnace. The first roasting drives out part of the sulphur, and the sulphides of iron and copper are partially converted into oxides and sulphates. An excess of sulphide remains, and the im- perfectly-roasted ore is fused in presence of silicious materials. The scoriae formed in roasting the matte (see farther on) are generally added, and sometimes fluor spar, to render the slag more fusible. This operation is conducted either in cupola-fur- naces or in reverberatory furnaces of peculiar construction. In presence of the unattacked sulphide of iron, the cupric oxide formed during the roasting is converted into cuprous sulphide, and oxide of iron is formed. The latter unites with the silica, as does also the oxide produced by the roasting, both being reduced to ferrous oxide by the redticing gases of the fire. Ferrous sili- cate is thus formed, and constitutes a very fusible slag, below which accumulates the sulphide of copper containing much less sulphide of iron than the original pyrites. This product is the matte. 356 ELEMENTS OP MODERN CHEMISTRY. The sulphur, which was thus far necessary to expel the iron, must now be removed, and the matte is broken up and repeat- edly roasted, by which the remainder of the iron is oxidized and nearly all of the sulphur expelled. The mineral is now again melted with silicious materials and the scoriae produced in refining black copper, and rich in cupric oxide, are added. Ferrous silicate separates as a slag, and a metallic mass contain- ing from 90 to 94 per cent, of copper, still alloyed with iron, lead, arsenic, sulphur, etc., is obtained. This is black copper. Instead of reducing matte by successive roasting and melt- ing as above, the sulphur is often removed by blowing air through the melted material in a vessel resembling a Bessemer converter (page 395) and lined with quartz : iron and copper are rapidly oxidized, while sulphur dioxide is given ofi". The resulting metal is much purer than that obtained by the older process. Refining of Black Copper. — The impure metal is melted in a reverberatory furnace ; the air-holes are then opened, and the impurities are partly volatilized, partly oxidized. The sulphur is driven off as sulphur dioxide, and iron and other metallic impurities, as well as copper, become oxidized and pass into the slag. This is skimmed off so that the metal may absorb more oxygen, which it transmits to the remaining sulphur. Finally the oxygen is eliminated by covering the surface of the metal with coal and plunging poles of green wood into it. The hydrocarbons and carbon monoxide so produced reduce the cuprous oxide to the metal. Large quantities of copper are now refined by electrolysis. The crude metal is cast in plates which serve as anodes in an acid bath of copper sulphate solution, the cathodes being thin copper plates. Under the influence of the current the anodes are dissolved, and an equivalent quantity of pure copper is deposited on the cathodes. The precious metals remain un- dissolved, and accumulate in the anode mud at the bottom of the tanks, while other impurities, such as arsenic and anti- mony, are held in solution. The electrolytic process yields a product which is practically free from impurities, and it effects the extraction of the gold and silver from crude copper. In the Lake Superior region, the native copper is separated mechanically from the rock and then subjected to refining operations analogous to those first described. The product is known as Lake Copper ^ and is of the highest grade. COPPER. 357 Cement copper is copper precipitated from a solution of cupric sulphate by metallic iron. It is very pure. Properties of Copper. — This metal has a characteristic red color that is universally known. When rubbed with the hand it exhales a peculiar, disagreeable odor. By fusion it crystal- lizes in cubes, but it may be deposited by electrolysis in reg- ular octahedra. It melts towards 1100°, and maybe volatilized by the heat of the oxyhydrogen blow-pipe or in the electric furnace. Its density varies from 8.85 to 8.95. It is very malleable, ductile, and tenacious. In dry air it is unaltered at ordinary temperatures, but it absorbs oxygen in presence of moisture and carbonic acid gas. Grreen spots are then formed upon the surface of the metal, constituting a hydrocarbonate of copper; this is the product ordinarily called verdigris. At a high temperature copper absorbs oxygen with avidity, being converted into black, cupric oxide if the oxygen be in excess ; but in the contrary case, red, cuprous oxide is formed. The oxidation is favored by division of the metal. If some pulverulent copper, produced by the decomposition of copper acetate, be thrown upon a moderately hot tile and an incandescent coal be approached so as to heat one point, a black spot instantly forms there and rapidly extends throughout the mass, showing the progress of the oxidation. In presence of acids or ammonia, copper rapidly absorbs oxygen at ordinary temperatures. If some ammonia and copper-turnings be shaken up with air in a glass-stoppered bottle, the ammoniacal liquid becomes blue; if now the bottle be turned upside-down and opened under water, the latter will rise in the bottle, replacing the. oxygen which was absorbed. The blue liquid contains in solution am- moniacal oxide of copper and nitrite of copper (Schonbein, Peligot). This liquid is capable of dissolving cotton and lint, which are almost pure cellulose (Schweizer). "When heated with concentrated sulphuric acid, copper is converted into sulphate with disengagement of sulphurous acid gas. Nitric acid, even dilute, dissolves it readily, forming cupric nitrate and evolving nitric oxide. Boiling hydrochloric acid attacks it slowly, disengaging hydrogen and forming cuprous chloride. Uses of Copper. — Copper is much employed for the con- 358 ELEMENTS OP MODERN CHEMISTRY. struction of boilers, alembics, stills and worms, and for kitchen utensils. Owing to its high electric conductivity, enormous quantities are used in electric constructions for cables, dyna- mos, etc. Sheet-copper is used for coating the bottoms of ships and sometimes for roofing houses. This metal enters into the composition of many important alloys, such as brass, varioufe bronzes, and Grerman silver. CUPROUS OXIDE. Cu^O This oxide is found native as cuprite^ sometimes in vitreous masses, sometimes in beautiful, red, regular octahedra. It is ordinarily prepared in the wet way by boiling a solution of acetate of copper with glucose ; a bright-red, crystalline pow- der is precipitated, which is anhydrous cuprous oxide. When heated in contact with air, it absorbs oxygen and is converted into cupric oxide. When caustic potash is added to a solution of cuprous chloride, a yellow precipitate of cuprous hydroxide is thrown down. Cuprous oxide is used to communicate a red color to glass. CUPRIC OXIDE. CuO Two processes are used for the preparation of this important body : calcination of copper in the air ; calcination of cupric nitrate. The first method furnishes a granular, compact, black oxide ; the second, a fine, deep-black powder. Cupric oxide is easily reduced by both hydrogen and char- coal, with formation of either water or carbon dioxide. Cupric hydroxide^ Cu(OH)^, is obtained as a voluminous, light-blue precipitate when caustic potash is added to the solu- tion of a cupric salt. This hydroxide is converted into brown, anhydrous oxide by boiling with water. Cupric oxide is largely used in the laboratory in the analysis of organic sub- stances. It is used in the arts to color glass, to which it im- parts a green color. SULPHIDES OF COPPER. Copper forms two sulphides, corresponding to the oxides. Cuprous sulphide, Cu^S, occurs in nature as chalcocite in fusible, steel-gray crystals, which may be scratched with a knife. CHLORIDES or COPPER— OUPRIC SULPHATE. 359 Cupric sulphide CuS, is formed in tlie wet way when a solution of a copper salt is precipitated by hydrogen sulphide. When strongly calcined, it loses sulphur and is reduced to cuprous sulphide. If copper filings or turnings be thrown into a flask containing boiling sulphur, a brilliant incandescence takes place from the union of the two elements. CHLORIDES OF COPPER. Cuprous chloride, CuCl, is prepared by boiling copper- turnings in hydrochloric acid and adding small quantities of nitric acid from time to time. The nitro-muriatic acid formed converts the copper into cupric chloride, which is reduced by the excess of copper present. A brown liquid is thus obtained which, by continued boiling, becomes almost colorless. On adding water to this liquid, a white, crystalline precipitate of cuprous chloride is deposited. It is insoluble in water, but dis- solves in aqueous ammonia, forming a liquid which remains colorless when kept in closed vessels in presence of an excess of copper, but becomes blue on exposure to the air, from which it absorbs oxygen. Carbon monoxide is perfectly absorbed by a solution of cuprous chloride in hydrochloric acid or in ammonia. Cupric chloride, CuCP, is obtained by dissolving cupric oxide in hydrochloric acid or copper in aqua regia. A green solu- tion is formed, which, after concentration, deposits beautiful rhombic prisms of a bluish-green color, containing 2 mole- cules of water of crystallization. CUPRIC SULPHATE. CuSO* + 5H20 Preparation. — This salt is commonly called blue vitriol. It is a product of many industrial operations, such as roasting sulphurous copper ores, and the decomposition by copper of the silver sulphate resulting from the refining of gold, — that is, the treatment of silver coin containing gold with sulphuric acid. Cupric sulphate produced by roasting copper ore contains more or less ferrous sulphate. The two salts crystallize together in monoclinic prisms, containing 7 molecules of water of crystallization. The mixture is called Salzburg vitriol. 360 ELEMENTS OF MODERN CHEMISTRY. Instead of copper pyrites, artificial cupric sulphide may be oxidized. Old copper plates are moistened and sprinkled with flowers of sulphur; they are then heated in a furnace, and the sulphide of copper first formed is converted into sulphate by the oxygen of the air drawn into the furnace. The still hot plates are plunged into water, which dissolves the layer of cupric sulphate, and the same operation is repeated until all of the metal is transformed into sulphate. The simplest process consists in boiling copper turnings and clippings with sulphuric acid : sulphurous acid gas is disen- gaged, and cupric sulphate formed. In the arts, the operation is conducted in wooden tanks lined with lead and heated by steam. Properties. — Cupric sulphate crystallizes in large tabular forms belonging to the triclinic system. These crystals have a fine blue color, and contain 5 molecules of water. When exposed to dry air they effloresce superficially : heated to 100°, they lose 4 molecules of water, disengaging the fifth only at 243°. The anhydrous salt is white. At a high heat, cupric sulphate is decomposed into cupric oxide, sulphurous oxide, and oxygen. Cupric sulphate dissolves in 4 parts of cold, and in 2 parts of boiling water, and the concentrated solution has a pure blue color. It is insoluble in alcohol. When an excess of ammonia is added to a solution of cupric sulphate, a beautiful, dark-blue liquid is obtained. It contains ammoniacal cupric sulphate, CuSO* -|- 4NH^ -\- H^O, which separates in dark-blue crystals when alcohol is added to the aqueous solution. There are several basic sulphates of copper representing compounds of cupric sulphate and cupric hydroxide. One of tbem is obtained as a green powder when a solution of cupric sulphate is digested with cupric hydroxide. The bluish pre- cipitates obtained by incompletely precipitating solutions of cupric sulphate with potassium hydroxide are basic sulphates. Uses. — Cupric sulphate is employed as a caustic applicable to diseases of the eye. In the arts, it is used in the prepara- tion of blue ashes, a mixture of calcium sulphate and cupric hydrate, made by decomposing cupric sulphate with milk of lime. It is much used in dyeing, particularly in dyeing black on wool and cotton. It is also employed for preserving wood. CARBONATES OF COPPER — ALLOYS OF COPPER. 361 Large quantities of sulphate of copper are employed for elec- trotyping, and for electric batteries. CARBONATES OF COPPER. When cold solutions of sodium carbonate and cupric sul- phate are mixed, a bluish-green precipitate is obtained, and at the same time carbonic acid gas is disengaged. The precipi- tate becomes gTeen when washed with warm water. It is known as mineral green, and can be regarded as a combina- tion of one molecule of cupric carbonate with one molecule of cupric hydroxide. It contains CuCO^ + Cu(0H)2 A similar compound exists in nature, constituting malachite. This mineral occurs in green masses. When cut and polished, it presents veins of various tints, and is fashioned into orna- mental objects, such as vases, cups, etc. AzuTite or mountain blue, which crystallizes in beautiful, blue, oblique rhombic prisms, can be regarded as a compound of two molecules of cupric carbonate with one of the hydrate. 2CuC0^ + Cu(OH)^ Debray has reproduced azurite artificially by leaving calcium carbonate for a long time in contact with cupric nitrate in sealed tubes. ALLOYS OF COPPER. Brass is an alloy of copper and zinc, ordinarily containing ^ zinc and f copper. It often contains a small proportion of tin and even of lead. Bronze is an alloy of copper and tin (see table of alloys, page 249). While brass is malleable and ductile, bronze is brittle when it has been slowly cooled, but it becomes malleable after tempering, — that is, when it is heated to redness and then plunged into cold water. Grerman silver contains 25 per cent, of zinc, 25 of nickel, and 50 of copper. Aluminium-bronze, phosphor-bronze, manganese-bronze, and silicon-bronze are very tenacious and valuable alloys of copper with the elements indicated by the names. Silicon- bronze is used for telegraph-wires, and manganese-bronze for Q 31 S62 ELEMENTS OF MODERN CHEMISTRY. the propellers of ships, as it resists the corroding action of salt water and is remarkably tenacious. Characters of Copper Salts. — These salts are blue or green. Their solutions are precipitated brown by hydrogen sulphide and ammonium sulphide ; an excess of the latter reagent will not dissolve the precipitate. Potassium hydroxide forms a dense, light-blue precipitate, insoluble in excess. Ammonia-water first forms a pale-blue precipitate, which is then dissolved by an excess of the reagent with a rich sky-blue color. Potassium ferrocyanide gives a reddish-brown precipitate even in very dilute cupric solutions. An apple-green precipitate of cupric arsenite (Scheele's green) is formed when potassium arsenite is added to cupric sulphate. A bright piece of iron plunged into a cupric solution in- stantly becomes covered with a deposit of metallic copper. MERCURY. Hg (Hydrargyrum) = 200 Natural State and Extraction. — Mercury occurs native, and especially combined with sulphur, mercuric sulphide or natural cinnabar being its principal ore. It is found in differ- ent localities in Europe and America, principally at Almad'en, Spain ; Idria, in Carniola ; and in California. The treatment of the ore is very simple. The sulphide is roasted in a current of air in furnaces of peculiar construction : the sulphur is oxidized, and passes off as sulphur dioxide, the mercury being set free. The metal volatilizes and is led, to- gether with the gases from the combustion, either into con- densation-chambers, or through long rows of little cylindrical vessels, where the mercury condenses. Fig. 113 represents the furnaces employed at Almaden, with the fireplace, and the body, AB, charged with ore. The mercury-vapor passes by o, and condenses in a series of aludels entering one in the other, and arranged upon two inclined planes, ah^ he. The condensed metal runs into a channel, 6, from which it is conducted into a reservoir. The sulphurous acid gas, still charged with vapor of mercury, passes into a chamber, C, descending to the floor, where it is cooled by conta.ct with a MERCURY. 363 trougli filled with water, d. In this chamber the condensa- tion of the mercury- vapor is completed. Fig. 113. Fig. 114 represents the several-storied furnaces aa, hh, cc, and the condensation-chambers CC, used at Idria. Cinnabar may also be reduced by iron or by lime. The metal thus extracted is purified by filtration through ticking-cloth or chamois-skin. It is ordinarily transported in forged iron bottles. Fig. 114. The mercury of commerce is nearly always alloyed with small quantities of other metals, such as lead, tin, copper, and 364 ELEMENTS OF MODERN CHEMISTRY. bismuth. In this state its surface is not as brilliant as when pure, it does not run as readily, and the drops are drawn out to a point. They are said to form tails. It may be purified by distillation, an operation which requires certain precautions on account of the violent bumping of boiling mercury. This distillation is best effected under diminished pressure. Mer- cury may also be purified by digesting it for several days with one-thirtieth its weight of commercial nitric acid diluted with its own weight of water ; the aqueous liquid is then decanted and the mercury washed, first with warm water acidulated with nitric acid, then with pure water, after which it can be dried. In this operation, the nitric acid removes the foreign metals, more oxidizable than the mercury, which displace the latter metal from its solution in the nitric acid. Properties. — Mercury is liquid, but solidifies at — 40°. The solid metal at this low temperature is malleable, and has a density of 14.4. The density of liquid mercury is 13.595. It boils at 350° of an air thermometer. Its vapor is colorless, and has a density of 6.976. It is unaltered by contact with the air at ordinary tempera- tures, but at 300° it slowly absorbs oxygen, and its surface becomes covered with a red powder, which is mercuric oxide, called by the ancients red precipitate. Mercury combines with chlorine, bromine, and iodine at ordi- nary temperatures, and with sulphur by the aid of a gentle heat. Hydrochloric acid does not attack it. Dilute nitric acid dis- solves it in the cold, forming mercurous nitrate. Hot nitric acid dissolves it, forming mercuric nitrate and evolving red vapors. OXIDES OF MERCURY. Two oxides of mercury are known, mercurous oxide, Hg^O, and mercuric oxide, HgO. The first is prepared by digesting mercurous chloride with potassium hydroxide; a black powder is obtained which is very unstable. By the action of light, or by a temperature above 100°, it decomposes into mercuric oxide and mercury. Mercuric Oxide, HgO, can be obtained by either the dry or wet method. The first consists in decomposing mercuric nitrate by heat; the salt is gradually heated in a flask on a sand- bath until red vapors cease to be disengaged. MERCtmiC SULPHIDE. 365 The oxide thus prepared is an orange-red, granular, and crystalline powder. Mercuric oxide is prepared in the wet way by decomposing a solution of mercuric chloride by caustic potash. A yellow precipitate of anhydrous mercuric oxide is obtained. When mercuric oxide is heated, it assumes a dark-red color and decomposes, if the temperature be above 400°, into oxygen and mercury. It yields its oxygen to many bodies, such as charcoal, sulphur, and phosphorus, which it oxidizes energet- ically. When heated with sulphur, it produces an explosion. In these reactions the finely-divided yellow oxide is more active than the red oxide. MEECURIC SULPHIDE. HgS This is the cinnabar generally found in nature in compact masses, sometimes in transparent, red, hexagonal prisms or rhombohedra. It is manufactured by directly combining sul- phur and mercury. The combination takes place when the bodies are triturated together in the cold, in the proportion of 100 parts of mercury and 18 parts of sulphur. A black mass is thus obtained which is sublimed in iron vessels. Cinnabar prepared by sublimation occurs in dark-red masses, having a fibrous and crystalline structure. Its density is 8.124. At a high temperature, it volatilizes without melting. When heated in the air, it burns with a blue flame, yielding sulphur- ous acid gas and metallic mercury. It is decomposed by hydro- gen, charcoal, and most of the metals. Boiling sulphuric acid decomposes it with formation of sulphurous acid gas and sul- phate of mercury. Nitric acid scarcely attacks it, even when boiling. Vermilion is a finely-divided mercuric sulphide having a rich scarlet color. It is prepared by triturating for several hours in a mortar, 300 parts of mercury and 114 parts of flowers of sulphur, and adding to the black sulphide thus ob- tained 75 parts of caustic potash and 400 parts of water. The mixture is maintained at a temperature of about 45°, being continually triturated with a pestle. As soon as the powder has acquired a fine scarlet color, it is rapidly washed with hot water and dried. It is employed in painting and also to color sealing-wax. 31* 366 ELEMENTS OP MODERN CHEMISTRY. MERCUROUS CHLORIDE, OR CALOMEL. HgCl Mercurous chloride is largely used in medicine under the name calomel or mild chloride of mercury. Preparation. — An intimate mixture of mercurous sulphate and sodium chloride is heated in a capacious glass matrass on a sand-bath. The mercurous chloride, formed by double decom- position, sublimes. Hg^SO^ + 2NaCl == 2HgCl + Na^SO* It is thus obtained in compact, crystalline masses. When it is strongly heated and its vapor passed into large stoneware vessels filled with steam, it condenses in an impalpable powder, in which form it is used by preference in medicine. Calomel may also be prepared in the wet way by adding hydrochloric acid, or a solution of sodium chloride, to a solu- tion of mercurous nitrate. A white, curdy precipitate is obtained which is washed and dried. Properties. — Prepared in the dry way calomel occurs as dense, fibrous, crystalline and slightly transparent masses, one side of which is smooth, the other presenting the sharp points of the crystals. When exposed to light, it becomes yellow and even gray in time, being partially decomposed. Its density is 7.17. It melts and volatilizes at the same temperature : the density of the vapor is 8.12, and corresponds to the formula HgCl, which is analogous to that of silver chloride. When slowly sublimed, calomel crystallizes in tetragonal prisms. It is insoluble in water. A solution of potassium iodide agitated with calomel con- verts it into a green powder of mercurous iodide. If an excess of potassium iodide be employed, the green powder disappears and is replaced by a gray precipitate of metallic mercury, the mercurous iodide at first formed being decomposed into mercury and mercuric iodide, which dissolves in the potassium iodide. An analogous reaction takes place with the alkaline chlorides by the aid of heat, the mercurous chloride breaking up into mercuric chloride which dissolves, and metallic mercury which is deposited. MERCURIC CHLORIDE, OR CORROSIVE SIJBLIMATE. 367 MERCURIC CHLORIDE, OR CORROSIVE SUBLI- MATE. HgCP Preparation. — This body is obtained by double decomposi- tion, by heating a mixture of mercuric sulphate and sodium chloride on a sand-bath. The mercuric chloride condenses in the upper part of the matrasses which are imbedded up to the neck in the sand. HgSO^ + 2NaCl = Na^SO^ + HgCP Towards the close of the operation the heat is increased in order to agglomerate the sublimate by a partial fusion. Another process consists in passing chlorine into heated mercury ; the combination takes place with the production of luminous heat. Properties. — IMercuric chloride prepared by the dry method occurs in compact, white, crystalline and friable masses, having a density of 6.5. It is an energetic poison. It melts at about 265°, and boils towards 295°. The density of its vapor is 9.42. By sublimation it may be obtained crystallized in rec- tangular octahedra. It is soluble in 19 parts of cold water, also in alcohol and ether. It is deposited from its hot, saturated, aqueous solution in long prisms, belonging to the type of the right rhombic prism. The crystals are anhydrous. The aqueous solution of mercuric chloride produces a white precipitate in a solution of albumen of white of egg. This precipitate is a combination of mercuric chloride and albumen. Albumen is thus the antidote to corrosive sublimate. Corro- sive sublimate is one of the most powerful antiseptics : it is used in surgery, medicine, taxidermy, preserving wood, etc. When a slight excess of ammonia is added to a solution of corrosive sublimate, a white deposit is formed, known as ichite precipitate, of which the composition is HgH^NCl. HgCP + 2XH^ = XH^Cl -L HgH^NCl It may be regarded as the chloride of mercury-ammonium, that is, ammonium chloride in which 2 atoms of hydrogen are replaced by one atom of the diatomic metal mercury. Ho^' HgH^NCl = H ^ NCI H 368 ELEMENTS OE MODERN CHEMISTRY. Corrosive sublimate forms crystallizable double combina- tions with the alkaline chlorides and with ammonium chloride. MERCUROUS IODIDE. Hgl This compound is ordinarily prepared by directly combining mercury and iodine. 100 parts of mercury and 63.5 parts of iodine are triturated with a small quantity of alcohol, until the whole is converted into a green powder, which is then washed with boiling alcohol and dried. It may also be prepared by double decomposition by precipi- tating a solution of mercurous nitrate with potassium iodide, or by the reaction of the latter body upon calomel. Mercurous iodide is not a stable compound. It is decom- posed by light. Heat breaks it up into mercury and mercuric iodide, and the same decomposition is effected by potassium iodide and the alkaline chlorides. MERCURIC IODIDE. HgP Mercuric iodide is prepared by pouring a solution of 100 parts of potassium iodide into a solution of 80 parts of corro> sive sublimate. A beautiful scarlet-red precipitate of mercuric iodide is thrown down. It is necessary that the bodies be employed in the propor- tions indicated ; an excess of potassium iodide would dissolve the mercuric iodide first precipitated. Mercuric iodide is almost insoluble in water ; it is slightly soluble in boiling alcohol, which deposits it on cooling in small red octahedral crystals. If mercuric iodide be heated in a small glass retort, it melts to a dark-yellow liquid which solidifies on cooling to a yellow mass. At a higher temperature the liquid boils and its vapor condenses in a dark-yellow liquid which solidifies to a yellow mass ; at the same time, right rhombic prisms of a yellow color sublime. If these be rubbed with a glass rod or other hard body they instantly become red, first at the point of contact, then throughout the entire mass. These two forms of mercuric iodide constitute one of the most curious examples of dimorphism. Mercuric iodide forms a combination with potassium iodide NITRATES OF MERCURY SULPHATES OF MERCURY. 369 which is soluble in water. A solution of this potassium-mer- curic iodide is not precipitated by potassium hydroxide, but the liquid rendered alkaline by the latter reagent is a very sensi- tive test for ammonia (JSfesslers test), with which it gives a pre- cipitate or a brown cloud more or less intense, according to the quantity of ammonia present. NITRATES OF MERCURY. Neutral mercurous nitrate, HgNO'^ -f H'^0, is obtained by the action of an excess of cold, dilute nitric acid upon metallic mercury. After some time, short colorless prisms are formed in the liquid, constituting the neutral salt. The latter is readily soluble in water charged with nitric acid. When mercury is attacked by an excess of boiling nitric acid and the solution is evaporated, voluminous crystals of a basic mercuric nitrate separate, Hg(NO^)^.HgO -f- 2H^0. The syrupy liquid from which these crystals are deposited, contains neutral mercuric nitrate. Hg(N0=')^+4PP0 This salt is deposited in large, colorless, rhombic tables when the syrupy solution is cooled to — 15°. A large quantity of cold water decomposes this nitrate into nitric acid which dissolves, and a basic salt, Hg(NO^)^2HgO -f- H^O, forming a yellow powder. SULPHATES OF MERCURY. There is a mercurous sulphate, Hg^SO*, and a mercuric sulphate, Hg"SO*. The first is obtained by heating equal parts of mercury and sulphuric acid, arresting the operation when two-thirds of the mercury are converted into a white, crystalline powder. Mer- curous sulphate is but slightly soluble in cold water. To prepare mercuric sulphate, 1 part of mercury and IJ parts of sulphuric acid are heated to dryness on a sand-bath. Hg + 2ff SO* ^ 2W0 + HgSO* + SO^ It is well to add a small quantity of nitric acid before drying. Mercuric sulphate is an anhydrous, white powder. It decom- poses at a red heat into metallic mercury, sulphurous acid gas, and oxygen. Charcoal reduces it readily, equal volumes of carbon dioxide and sulphur dioxide being disengaged. y 3'rO ELEMENTS OP MODERN CHEMtSTRt^. Mercuric sulphate is slightly soluble in water : a large quan- tity of cold water converts it into a yellow, basic salt, HgSO*. 2HgO, known as tiirpeth mineral. Characters of Mercuroiis Salts. — Their solutions are pre- cipitated black by hydrogen sulphide, and also by potassium hydroxide and ammonia. Hydrochloric acid gives a white precipitate which is blackened by ammonia. Potassium iodide forms a green precipitate of mercurous iodide, converted by an excess of the reagent into mercuric iodide which dissolves, and gray metallic mercury. Characters of Mercuric Salts. — Solutions of mercuric salts are precipitated black by an excess of hydrogen sulphide, and by ammonium sulphide. Potassium hydroxide forms a yellow precipitate, insoluble in excess. Ammonia yields a white precipitate in solutions of corrosive sublimate. Hydrochloric acid does not precipitate the mercuric salts. Iron, zinc, and copper precipitate metallic mercury from both mercurous and mercuric solutions. A strip of copper dipped into such solutions becomes covered with a gray coating which acquires brilliancy by rubbing. Heated with lime in a glass tube, all of the mercury com- pounds yield metallic mercury which sublimes in small globules, easy to recognize under the microscope, and which can be char- acterized by the addition of iodine, the vapor of which converts the metallic globules into yellow or red mercuric iodide. Atomicity of Copper and Mercury.— Copper and mer- cury form two series of compounds. In the cuprous and mer- curous compounds they resemble silver, playing the part of monatomic elements. In other compounds, constituting the cupric and mercuric series, these metals are distinctly diatomic, like those of the magnesium group. VANADIUM. V = 51 Vanadium, niobium, tantalum, thallium, gold, and bismuth constitute a class of triatomic or pentatomic elements. The NIOBIUM AND TANTALUM. 371 first three are more closely related to the non-metallic bodies than to the metals, and might properly be considered as mem- bers of the group of which nitrogen and phosphorus are types. Vanadium is widely disseminated, occurring as vanadates of lead, copper, bismuth, zinc, calcium, etc., and in many argillaceous iron ores, but always in small quantity. The compounds of the metal may be prepared most readily from the native vanadates vanadhiite or mottramite. The powdered mineral is dissolved in hydrochloric acid, the solu- tion concentrated, and ammonium chloride added; ammonium metavanadate separates. This is repeatedly recrystallized and converted into vanadic oxide, V^O^, by gentle ignition. By heating vanadic oxide in hydrogen, it is converted into the trioxide Y^O^ and with carbon it may be reduced to the dioxide Y'^O^ The metal has been obtained by the long- continued action of perfectly pure hydrogen upon the dichlo- ride YCP at a red heat (Roscoe), and also by heating the oxides with charcoal in the electric furnace (Moissan). Its chemical relations place vanadium in the nitrogen group : the vanadates are isomorphous with the phosphates and arsenates. The oxides known are Y^O, Y^O^ Y^O^ Y==0*, and Y^0^ and the chlorides YCP, YCP, and YCP have been obtained ; there are also oxychlorides. Although vanadium is not very abundant, vanadic acid is employed in certain dyeing operations, by reason of the facility with which it passes to a lower stage of oxidation and again becomes oxidized, thus transferring oxygen from the air to the dye stuff. Metavanadic acid, HYO*, is a brilliant yellow, metal-like substance, and has been proposed as a substitute for gold bronze. NIOBIUM AND TANTALUM. Nb = 94 Ta = 182 These elements are associated in several minerals, and ^rere regarded as identical until 1846. Their principal sources are cdumhite, a niobate of iron and manganese, (NbO^)^FeMn, in which more or less of the niobium is usually replaced by tan- talum ; tantalite^ a ferrous tantalite, Fe(TaO^J^ in which in like manner a portion of the tantalum is replaced by niobium ; pyro- chlorite^ fergusonite^ yttrotantalite, and euxeriite, in which these elements are associated with yttrium, cerium, etc. 372 ELEMENTS OP MODERN CHEMISTRY. Niobium was obtained as steel-gray crusts by Roscoe, who passed through a red-hot tube the vapor of niobium chloride mixed with hydrogen. Its specific gravity is 7.06 ; it oxidizes with incandescence when heated in the air, and burns also in chlorine. There are three oxides of niobium, Nb'O^ Nb'O*, and Nb'O^ A mixture of the latter with the corresponding tantalic oxide may be obtained by fusing niobiferous minerals with potassium acid sulphate, and boiling the fused mass with water. The res- idue is digested with ammonium sulphide, and the remaining powder boiled with hydrochloric acid. The two oxides, which are unaffected by this treatment, are then separated by convert- ing them into fluotantalate and fluoniobate of potassium ; the latter is much more soluble than the former. The potassium salts are then decomposed by boiling with sulphuric acid. Niohic oxide, Nb^O^, is a white, insoluble, infusible powder, which is yellow while hot. When strongly heated in hydrogen it is reduced to the tetroxide, a bluish-black powder, which burns into the pentoxide when heated to redness in the air. Niobium pentoxide is the anhydride of niobic acid, HNbO^ which is obtained as a white powder by the reaction of niobium pentachloride, NbCl^, with water. The normal niobates have the general composition R'NbO^, and there is also a series of highly complicated niobates, derived from an unknown hydrate, H^Nb^O^^ -f nH^O. Niobium forms two chlorides, NbCP and NbCP, and an oxy- chloride, NbOCP. Tantalum has probably not been obtained in a pure state. Berzelius obtained it as a black powder by heating potassium fluotantalate with potassium. There are two oxides, Ta'O* and Ta^O^ Tantalic oxide is separated from the niobic acid, with which it is associated in its minerals, by the process already indicated. It is a white, infu- sible powder, and becomes crystalline when heated. By strong ignition with charcoal it is converted into the tetroxide. Tantalic acid, HTaO^ is analogous to niobic acid, and forms corresponding series of salts. Tantalum chloride, TaCP, is formed by heating an intimate mixture of tantalic oxide and charcoal in a current of chlorine. Niobic chloride is formed in a similar manner. Both are fusi- ble, volatile solids, crystallizing in yellow needles. There is no tantalum chloride corresponding to the niobous chloride NbCP. GOLD. 373 GOLD. Au (Aurum) = 195.74 Natural State. — Gold is one of the most anciently known metals. It is generally found in the native state, either in streaks or veins, or in sand. It ordinarily occurs in scales or rounded grains disseminated in alluvial sands, or in the rocks whose disintegration produces such sands. It is well known that gold-dust is suspended in the waters of certain rivers. It is often found associated with ores of silver, lead, and copper; sometimes in combination with tellurium. Extraction. — Gold is extracted from auriferous sand by washings, which remove the particles lighter than the gold. The sand, pebbles, and gold, and a strong stream of water are thrown into long wooden sluices arranged in zig-zag and provided with pockets ; in the latter the gold sinks, while the lighter earthy material is carried on by the force of the stream. When the gold is in particles too minute to be separated mechanically from the sand, which still remains in small quantity, the whole is agitated with mercury ; the gold Fig. 115. dissolves. The amalgam thus obtained is compressed in a chamois-skin, which allows the passage of the excess of mer- cury. When the solid residue is distilled the gold remains. Auriferous quartz rocks are crushed to powder, which is then subjected to washings. Mercury is sometimes employed to ex- tract the gold from the pulverized rock. The following process has been employed for some years in California and Australia. The crushed rock, with mercury, water, and two cast-iron balls, is introduced into basins, to wnich a rotating motion is given 32 374 ELEMENTS OF MODERN CHEMISTRY. (Fig. 115). By the friction of the balls it is soon reduced to an impalpable powder, wbicb remains suspended in the water, and is carried out with the latter through openings in the upper part of the basins, while the gold amalgamates with the mercury. Another process, known as the cyanide process^ depends upon the solubility of finely divided gold in solution of potas- sium cyanide. A double cyanide of gold and potassium is formed, from which the gold is precipitated by metallic zinc. 4Au + 8KCN + 2H-^0 -f 0^ == 4KAu(CN7 + 4K0H 2KAu(CN)'^ + Zn = K^ZnCCN)* -f 2Au From sulphide ores (pyrites) gold may be extracted by means of chlorine. The roasted ore is moistened and treated with chlorine gas. The mass is exhausted with water, when auric chloride goes into solution and the gold is precipitated by means of ferrous sulphate. Native gold, as well as that extracted from difi'erent minerals, is nearly always alloyed with silver. The two metals are sep- arated by the wet way, by attacking the alloy with either nitric or sulphuric acid. Nitrate or sulphate of silver is formed, the latter being soluble in hot water. The gold remains in a pul- verulent state. It is to be remarked that the alloy of gold and silver must be rich in silver in order that this process, called refining, can be applied. Hence it is sometimes necessary to increase the proportion of silver by melting the alloy with that metal. An alloy of gold and silver rich in gold may also be treated with aqua regia. Both metals are converted into chlorides; that of silver is insoluble, while that of gold dissolves. When ferrous sulphate is added to the yellow solution of chloride of gold, a precipitate of metallic gold is obtained, the chlorine acting upon the iron of the ferrous sulphate which is thus transformed into ferric salt. Properties of Gold. — Pure gold has a beautiful yellow color. In thin leaves it is translucent, allowing the passage of a green- ish light. Its density is 19.5. It is quite soft, and is the most malleable and most ductile of the metals. It melts at 1075°, and volatilizes at a higher temperature. Its vapor is green. It is unaltered by the air at all temperatures. Sulphuric, hydrochloric, nitric, and phosphoric acids have no action on it OXIDES OF GOLD — CHLORIDES OF GOLD. 375 either in the cold or when aided by heat. It is dissolved by nitro-hydrochloric acid. Some gold leaf may be boiled with hydrochloric acid in a test-tube ; the gold will resist the action of the acid, and will retain its lustre. Some more gold leaf may be boiled with pure nitric acid in another tube, and again the metal will not be attacked. But on mixing the two liquids, the gold will be dis- solved with disengagement of red vapors. Grold trichloride will be formed, and will color the liquid yellow. OXIDES OF GOLD. There are two compounds of gold and oxygen, a monoxide, Au^O, and a trioxide, Au^Ol The latter forms compounds with the bases. When magnesia is added to solution of auric chloride, an insoluble yellow precipitate of magnesium aurate is formed ; when this is decomposed by nitric acid it leaves auric hydroxide. This hydroxide is yellow ; it easily parts with its water, and is eonverted into a brown-black powder of auric oxide. The latter is not stable, being decomposed by light and by a temperature of about 250°. CHLORIDES OF GOLD. Aurous chloride, AuCl, is obtained as an insoluble yellow powder by heating auric chloride to 230°. Auric chloride or trichloride of gold, AuCP, is prepared by dissolving the metal in aqua regia. After concentration the liquid solidifies, on cooling, to a dark-red, crystalline and deli- quescent mass. The solution of auric chloride is yellowish-brown when con- centrated, pure yellow when dilute. It is decomposed by light. It colors the skin violet, and is reduced by a great number of bodies. Phosphorus, and hypophosphorous, phosphorous and sulphurous acids precipitate from it metallic gold. It is the same with most of the metals, which combine with the chlorine, setting free the gold. A brown precipitate of metallic ^Id is immediately obtained on adding a solution of ferrous sulphate to a solution of auric chloride. Auric chloride dissolves in ether, which removes it from its aqueous solution when the two liquids are agitated together. If a solution of auric chloride be added to a mixture of stannous and stannic chlorides in solution, a flocculent precipi- 376 ELEMENTS OF MODERN CHEMISTRY. tate of a purple color, more or less pure according to the con- centration of the solutions and the proportions of the mixture, will be formed. It is purple of Oassius, a compound employed in painting on glass and porcelain. It contains tin, gold, oxy- . gen, and hydrogen, but its constitution is not well known. Auric chloride forms crystalline compounds with the alkaline chlorides. When a mixture of chloride of gold and sodium chloride is evaporated until a pellicle forms on its surface, yellow crystals containing NaCl. AuCP -|- 2H^0, are formed on cooling. Gilding'. — Several processes are used for gilding metals, such as silver and copper. The objects may be gilded by amalga- mation, or by galvanic deposition. Gilding hy Amalgamation. — Grold readily alloys with mer- cury, and the amalgam is used for gilding objects of silver and copper. The pieces are heated to destroy greasy matters, and are then cleaned by dipping them into dilute sulphuric acid, after which they are washed and dried with saw-dust. They are then rubbed with a brush of brass wires dipped into a solu- tion of mercurous nitrate, and then with a brush impregnated with an amalgam of one part of gold and eight parts of mer- cury. They are afterwards heated to volatilize the mercury, an operation dangerous to the health of the workmen, and which should be conducted in a furnace having a good draught. The pieces thus gilded are dull; they become lustrous after suitable washings and polishings. Electro- Gilding. — The copper objects, previously heated and cleaned by dilute sulphuric acid, are plunged for a few seconds into dilute nitric acid and then wiped dry. They are then connected with the negative pole of a battery and dipped into a bath composed of 1 part of cyanide of gold, 10 parts of potas- sium cyanide, and 100 parts of water. A plate of gold plunged into the same bath constitutes the positive pole. When the current passes, the objects become covered with a uniform and adherent coating of gold. As the metal is precipitated from the solution, it is replaced by an equivalent quantity from that whic]^ constitutes the positive pole, and which dissolves. The bath thus retains a constant composition. The same process is applicable to electro-silvering. Assaying of Gold Alloys. — Gold i-s assayed by cupellation. The alloy is first melted with silver, so that the quantity of the latter metal present may be at least triple that of the gold. This alloy is submitted to cupellation, an operation which BISMUTH. 377 presents no difficulty, for silver rich in gold does not spit. The button is hammered out to a thin sheet, reheated and formed into a little cornet, which is introduced into a small flask and heated with nitric acid of 22° Baume. After several minutes' boiling the greater part of the silver is dissolved ; the liquid is then decanted and replaced by more concentrated nitric acid. All of the silver dissolves and the gold remains in the form of a but slightly coherent cornet. It is washed, heated to redness in a crucible to give it coherence, and finally weighed. BISMUTH. Bi = 206.54 Extraction. — This metal is found native in a quartzy gangue. It is extracted by simply heating the mineral in cast or sheet iron tubes, which are arranged in an inclined position in a fur- nace. The bismuth melts and runs out at an opening in the lower end of the tubes. The bismuth of commerce is never pure ; it contains traces of other metals, nearly always of arsenic and sometimes of sulphur. It is purified by pulverizing it, mixing it with 2V its weight of potassium nitrate, and heating the mixture to redness in a clay crucible. The foreign metals more oxidiza- ble than the bismuth are thus converted into oxides, the ar- senic into arsenate of potassium, and the sulphur into potassium sulphate. This treatment may be repeated a second time if necessary. Properties. — Bismuth is a whitish-gray metal, having a reddish tinge. Its fracture is crystalline and laminated. Its density is 9.83, and it melts at 264°. On cooling, it crystal- lizes in rhombohedra, of which the surfaces become covered with a thin film of oxide, causing a beautiful iridescent play of colors like that on a soap-bubble. Bismuth increases in volume on solidifying. It volatilizes at a white heat. It is unaltered by the air at ordinary tempera- tures, but at a red heat it absorbs oxygen and burns, formiag bismuth oxide. Its best solvent is nitric acid, which converts it into nitrate. The various compounds of bismuth present great analogy to those of antimony, next to which this metal might be placed in the group including nitrogen, phosphorus, arsenic, antimony, and bismuth. 32* 378 ELEMENTS OF MODERN CHEMISTRY. This analogy is shown in the following synoptic table : BiCP SbCP Bismuth trichloride. Antimony trichloride. Bismuth trioxide. • Antimony trioxide. Bi^O^ Sb^O^ Bismuthic anhydride. Antimonic anhydride. I Bi^O* Sb^O* II Bismuth bismuthate. Antimony antimonate. ■' Bi^S^ Sb^S^ Bismuth trisulphide. Antimony trisulphide. Otherwise, bismuth is related to the metals proper, not only by its properties, but by the facility with which it forms defi- nite salts. It is triatomic in its more important combinations, the oxide, chloride, and nitrate. BISMUTH TRIOXIDE. Bi203 This body is obtained by decomposing the nitrate by heat. It is a straw-yellow powder, fusible at a red heat, and yielding on cooling a dark-yellow, vitreous mass. It attacks clay cruci- bles even more rapidly than litharge. A hydroxide of bismuth is formed when the nitrate or sub- nitrate is treated with potassium hydroxide or ammonia. It is a white powder, insoluble in an excess of alkali, and when boiled with caustic potash it is converted into the crystalline anhydrous oxide. BISMUTH TRICHLOmDE. BiC13 Finely-divided bismuth will burn in chlorine, being con- verted into chloride. The latter is prepared by directing a current of chlorine upon melted bismuth contained in a retort. The chloride distils and solidifies in the receiver to a fusible, crystalline, and deliquescent mass, formerly known as butter of bismuth. A crystallized, hydrated chloride of bismuth may also be obtained by evaporating a solution of bismuth in nitro- hydrochloric acid. Bismuth chloride dissolves in water charged with hydro- chloric acid, but is decomposed when treated with pure water j BISMUTH NITRATE. 379 in the latter case an oxychloride is formed and precipitated as a fine, white powder, hydrochloric acid being at the same time formed. 2BiCP + 2H^0 = 2BiOCl + 4HC1 Bismuth oxychloride is known as pearl-white. It contains BiOCl. BISMUTH NITBATB. Bi(N03)3 Bismuth dissolves readily in nitric acid, and the concentrated solution deposits large, four-sided prisms, which are colorless and deliquescent. They contain Bi(N0'7 -j- 3H^0. They are very soluble in water acidulated with nitric acid, but if this solution be poured into a large excess of water, a pulverulent, white precipitate is formed, and increases in volume if very dilute ammonia be gradually added to the liquid in order to partly neutralize the free acid. This precipitate is much employed in medicine in cases of chronic diarrhoea under the name of subnitrate of bismuth. Its composition is generally expressed by the formula BiNO* 4- H^O = (BiO)'NO^ -f WO. It may be regarded as bismuthyl nitrate, that is, nitric acid, HNO^ in which the monobasic atom of hydrogen is re- placed by the monatomic group BiO. Or it may be considered as a derivative of orthonitric acid, H^NO*, corresponding to orthophosphoric acid, H^PO* (page 191). Boiling water removes still more nitric acid from this sub- nitrate, leaving a residue, which is used as a cosmetic, known as hlanc de fard. Characters of Solutions of Bismuth. — When mixed with k large quantity of water, bismuth solutions give white pre- cipitates of sub-salts. Hydrogen sulphide, and the soluble sulphides form a brown precipitate of bismuth sulphide, insolu- ble in an excess of ammonium sulphide. The alkaline hydrox- ides and carbonates give white precipitates, insoluble in an excess of the reagent. Bismuth solutions are not precipitated by either sulphuric or hydrochloric acid. When heated with sodium carbonate in the reducing flame of the blow-pipe, compounds of bismuth yield a metallic globule, very brittle after cooling. 380 ELEMENTS OF MODERN CHEMISTRY. The following elements, from aluminium to manganese, form series of compounds in which they must be regarded as tri- atomic. In these compounds a single atom of the metal is united with three monatomic atoms or radicals, or two such atoms act as a hexatomic couple (R^)""'. The chlorides may consequently present either the general formula RCP or E.^CP, while the oxides are represented by R^O^ In addition, iron, nickel, cobalt, and manganese form compounds in which the metal appears to be diatomic ; as, for example, iron in ferrous oxide, FeO, and ferrous sulphate, FeSO*. The oxides of this latter class are strongly basic ; the sesquioxides are also basic, but in the presence of more energetic bases may act as weak acids. Iron and manganese also form oxides of the composi- tion FeO^ and MnO'^, which act as the anhydrides of acids. ALUMmiUM. Al = 26.91 This metal long remained a chemical curiosity, and has only become common within a few years. It was discovered in 1827 by Wohler, and in 1854, H. Saint-Claire Deville suc- ceeded in producing it on a large scale by decomposing alu- minium and sodium double chloride by sodium. 2AlCP,NaCl + 6Na = 8NaCl + 2A1 Aluminium is now produced most cheaply by the processes of Hall and Heroult. They consist in the electrolytic de- composition of alumina, APO'^ dissolved in a bath of fused cryolite, AlFlSNaF. The latter is melted by the heat of the electric arc, and alumina constantly added while a powerful current is passing through the mass. The oxygen disen- gaged combines with the carbon forming the anode, and the aluminium collects upon the hearth, which serves as the cathode. The process is continuous : fresh alumina is con- stantly added to keep the bath saturated with it, and the furnace is tapped periodically. Aluminium of a high degree of purity is obtained in this manner. Aluminium is a white metal, with a somewhat bluish lustre when polished. It is ductile, malleable, very sonorous, and a good conductor of heat and electricity. It is as light as glass ALUMINIUM OXIDE — ALUMINIUM CHLORIDE. 381 and porcelain, its density being only 2.56. It melts at 700°, and is not volatile. Aluminium is unaltered by the air, even by moist air. Wben heated in tliin sheets in a current of oxygen, it burns and is converted into alumina. Nitric and sulphuric acids scarcely attack it. Hydrochloric acid dissolves it rapidly, disengaging hydrogen. It is immediately attacked by boiling solutions of potassium or sodium hydroxide ; hydrogen is disengaged and alkaline aluminates are formed. ALUMINIUM OXIDE, OR ALUMINA. AP03 Corundum^ a very hard precious stone, consists of anhydrous alumina. It is named oriental ruby when it has a red color ; sapphire when it is blue, and oriental topaz when it has a yellow tint. Emery is a sort of opaque corundum ; it is gran- ular and colored by a small quantity of oxide of iron. When ammonium carbonate is added to a solution of alum, carbon dioxide is evolved, and a gelatinous precipitate of hy- drated alumina is formed. The precipitate dissolves readily in caustic potash. When heated, it loses water and is converted into anhydrous alu- mina; the latter is fusible only in the flame of the oxyhydro- gen blow-pipe and in the electric furnace. It assumes crys- talline structure upon solidifying. Some of the precious stones above mentioned have been produced artificially by melting alumina with various fluxes and minute quantities of coloring matters (Gaudin, Fremy). Alumina is reduced by carbon only at the high tempera- ture of the electric furnace, but it readily yields to the joint action of carbon and chlorine, and is converted into aluminium chloride. ALUMINIUM CHLORIDE. AlCF or AFCP When a current of chlorine is passed over an incandescent mixture of alumina and charcoal, aluminium chloride and carbon monoxide are formed (Oersted). APO' + 3C -f 3CP = SCO + 2A1CP Aluminium chloride thus formed is a white, crystalline sub- stance, sometimes having a light-yellow color. It is fusible, and 382 ELEMENTS OF MODERN CHEMISTRY. volatilizes in tlie air at a temperature little above 100°. When exposed to the air it gives oiF white fumes and attracts moist- ure. It dissolves in water with production of heat. A solution of aluminium chloride may be obtained by dis- solving gelatinous alumina in hydrochloric acid. When this solution is evaporated, it decomposes as soon as it attains a certain degree of concentration, disengaging hydrochloric acid, and leaving alumina. Aluminium chloride readily combines with sodium chloride, forming a double chloride, AlCP.NaCl, fusible towards 200°. ALUMINIUM SULPHATE. A12(SO*)3 -f 18H20 This is obtained in the arts by decomposing non-ferruginous clays with sulphuric acid. It crystallizes with difficulty in needles and in thin, pearly scales. In this state it contains 18 molecules of water of crystallization. It dissolves in 2 parts of cold water. When heated, it first loses its water, and at a higher temperature it gives off sulphuric anhydride, leaving a residue of alumina. AP(SO*)^ = 3S0^ + APO^ It is seen that aluminium sulphate represents 3 molecules of sulphuric acid, in which the 6 atoms of hydrogen have been replaced by the hexatomic couple AP. H^SO*^ (SO* H^SO* [ + APO^ = BH^O + (AP)-^ ] SO* H^SO*) (so* ALUMINIUM AND POTASSIUM DOUBLE SUL- PHATE, OR ALUM. A12(S04)3.K2S04 -f 24H20 If a concentrated solution of aluminium sulphate be added to a concentrated solution of potassium sulphate, and the mix- ture be stirred with a glass rod, a crystalline deposit soon forms from the union of the two salts to form a double sulphate which is alum. This salt is not very soluble in cold water, but dissolves abundantly in boiling water, and is deposited on cooling in ALUM. 383 voluminous, transparent octaliedra. When heated, these crys- tals melt in their water of crystallization (24 molecules), and in losing this water, the melted mass swells up considerably. Alum may be obtained crystallized in cubes, and it is prepared in this form in the neighborhood of Civita-Yecchia by working a mineral which contains the elements of alum with a large excess of alumina. The mineral is known as alumimte, and the cubical alum is called Roman alum. This cubical variety may be prepared in the laboratory by adding a small quantity of potassium carbonate to a hot solu- tion of ordinary alum, so that the precipitate first formed will be redissolved on agitating the liquid. On cooling, cubical crystals are deposited which are ordinarily opaque. These are formed under the influence of a small quantity of basic sul- phate (aluminium sulphate combined with an excess of alu- mina) contained in the liquid, and which probably enters into the constitution of the crystals. With this slight difference, octahedral alum and cubical alum present the same composi- tion, which is expressed by the formula AP(SO*)lK'SO* + 24H^O. Ammonia alum is obtained by adding ammonium sulphate to solution of aluminium sulphate. It possesses a constitution analogous to that of ordinary alum, with which it is isomor- phous. It contains AP(SO^)l(NH0'SO* + 24H^O It is often substituted in the arts for potassium alum, being cheaper than the latter. When strongly calcined, it leaves a residue of pure alumina. Other alums are known in which iron, manganese, and chro- mium play the part taken by aluminium in ordinary alum.. These alums are all isomorphous (Mitscherlich). By the ac- tion of sulphuric acid on the sesquioxides of the above metals, sulphates are formed analogous to aluminium sulphate, and of which the composition is expressed by the general formula (R')^'(SOO'. With the sulphates W^0\ they form alums, all of which crystallize in regular octahedra, and which can be mixed in one and the same crystal without the form of the latter being affected by the mixture. The following are the most important of these compounds : Manganese alum .... Mn2(SO*)3.K2SO^ + 24H20 Iron alum Fe2(SO*)3.K2S04 + 24H20 Chromium alum .... Cr2(S0*)3.K2S0* + 24H20 384 ELEMENTS OP MODERN CHEMISTRY. It is seen that eacli of tliese presents an atomic composition similar to that of ordinary alum. The aluminium compounds are widely disseminated in nature. Feldspar^ or orthodase, is a double silicate of aluminium and potassium. The latter metal is replaced by sodium in alhite, and by calcium in anortliite and lahradorite. Many other minerals contain aluminium silicate combined with alkaline or earthy silicates : such are leucite, garnet, idocrase, mica, etc. The zeolites are silicates of aluminium containing water of crystallization. Clay is a hydrated silicate of aluminium ; it results from the disintegration of feldspar by the action of water and air, the alkaline silicate being gradually dissolved and eliminated. The purest clay is kaolin, or porcelain clay ; it contains alumina, silica, and water in the proportions indicated by the formula 2SiO^AP0^2H•^0. Plastic clays are those which form a binding paste when mixed with water, and acquire great hardness after being baked, without fusing. They are used for the manufacture of pottery, refractory fire-bricks, and crucibles. Fuller s earth is a clay which forms with water a paste that is but slightly adhe- rent ; it is employed in scouring and fulling cloth. Marls are intimate mixtures of clay and chalk ; they are employed in agriculture. Pottery. — Clay is the basis of all pottery. Other matters, such as sand, powdered feldspar or quartz, etc., are generally added, for while they diminish the plasticity of the clay, they also diminish its shrinkage on baking. Pottery is classified as semivitrified pottery, such as porcelain and stoneware ; porous pottery, such as faience and bisque; and common pottery or terra-cotta. Porcelains. — These are manufactured from kaolin, to which sand is added to prevent shrinkage, and feldspar, which causes the ware to undergo a partial fusion, and renders it translucent. These materials are finely pulverized, mixed with water, and the paste is kneaded for a long time in order to render it homo- geneous. Pieces fashioned in this paste are submitted to a pre- liminary baking, which gives them a certain degree of coherence. The porous porcelain thus obtained must be coated with a var- nish which will melt and spread upon its surface : this glaze is CERIUM, LANTHANUM, AND DIDYMIUM. 385 formed of a mixture of quartz and kaolin reduced to an impal- pable powder ; the latter is suspended in water, into whicli tlie pieces are dipped. They are then subjected to a second baking in ovens where the temperature is sufficiently elevated to fuse the glaze and partially vitrify the paste. Ceramic Stonewares. — These are manufactured from the same materials as porcelain, but less pure ; they are therefore slightly colored. They are baked at a high temperature, and are glazed by throwing common salt upon the incandescent, objects in the furnace ; hydrochloric acid is disengaged, and a double silicate of aluminium and sodium is formed, which fuses and spreads upon the surface of the ware. Faiences are made from plastic clay mixed with quartz re- duced to an impalpable powder. Articles formed of this paste are submitted to a preliminary baking, and are then coated with a fusible glaze, composed of quartz, potassium carbonate, and oxide of lead. A second baking causes the pieces to become covered with an impermeable, vitreous layer of silicate of lead and potassium. This glaze is transparent ; for ordinary ware it is rendered opaque by the addition of oxide of tin. It is a true enamel. Common pottery^ which serves for culinary purposes, is made from ferruginous clay, mixed with sand and marl. The glazing is composed of a double silicate of aluminium and lead. CEEIUM, LANTHANUM, AND DIDY- MIUM. These rare metals are found associated as silicates in the mineral cerite^ and as phosphates in monazite. Their separa- tion is a matter of some difficulty. The mineral is treated with sulphuric acid, by the aid of heat, and the solution ob- tained after filtering from the separated silica is precipitated by ammonium oxalate. A mixture of the oxides is obtained when the oxalates are calcined : these oxides are converted into nitrates and these again into double nitrates with am- monium nitrate. By repeated and systematic fractional crys- tallization a clean separation of the elements is effected. The same process also serves to break up didymium, long supposed to be an element, into its components, neodymium 2jidi praseo- dymium (Auer V. Welsbach). ■R z 33 386 ELEMENTS OP MODERN CHEMISTRY. The metals have been isolated by decomposing their chlorides by electricity. They possess about the hardness of lead, and a color and lustre resembling iron : didymium is rather more yellow. Their den- sity is comprised between 6.05, that of lanthanum, and 6.7, of cerium. They are readily oxidised, and burn brilliantly when heated in the air. The cerium metals are triatomic, cerium itself also tetra- tomic. It forms the oxides Ce'^O^ and CeO^ Lanthanum oxide has the composition La'^0^ ; neodymium oxide is Nd'^0^, while praseodymium forms two oxides, Pr^O^ and Pr*0^ The chlorides correspond to the formula RCP. The cerous com- pounds are mostly colorless ; eerie compounds are yellow. Lanthanum salts are colorless, while the pink color of didy- mium salts is the resultant of a mixture of reddish-violet (neodymium) and apple-green (praseodymium). The oxides of lanthanum and cerium, as well as several other oxides (zirconia, thoria), are employed in the Welsbach burner, in which a fine gauze cylinder of such oxides is ren- dered incandescent by the heat of a non-luminous gas-flame. GALLIUM. Ga = 69.9 In 1869, Mendelejeff predicted the existence of an unknown metal whose chemical relations should resemble those of alumin- ium, and whose atomic weight should be about 70. In 1876, Lecoq de Boisbaudran, while pursuing spectroscopic investiga- tions, and in a line of research very different from that of Men- delejeff, discovered the missing element in a zinc blende. Since then it has been found in small quantity in many blendes : one of the richest, found in Westphalia, contains only one sixty- thousandth of its weight. In order to extract the gallium, the ore is roasted, and the product dissolved in sulphuric acid. An acid liquor is thus obtained, containing principally sulphate of zinc, with sulphates of iron, aluminium, indium, etc., and a trace of gallium sul- phate. The following reactions are employed by Lecoq de Bois- baudran and Jungfleisch for the separation of the gallium : INDIUM. 387 1. When the liquid is neutralized, the ferric oxide, alumina, and gallium oxide, which is a sesquioxide, are precipitated. The precipitate is redissolved in sulphuric acid, and the same operation repeated after converting the ferric oxide into ferrous oxide, which remains dissolved in the neutral liquid. By this means the greater part of the iron is removed. 2. Gallium oxide dissolves, like alumina and zinc oxide, in an excess of potassium hydrate ; when this solution is saturated with hydrogen sulphide, the zinc is precipitated as sulphide, while tne gallium and aluminium remain in solution. The gTeater part of the zinc is thus separated. 3. When water is added to a boiling solution of gallium sulphate, the latter is precipitated as subsulphate, while alumi- nium sulphate remains in solution. 4. Gallium oxide dissolves in an excess of ammonia ; alumina does not. 5. Gallium separates in the metallic state when a voltaic current is passed through an alkaline solution of gallium oxide. Physical Properties. — Gallium has a metallic lustre recalling that of nickel. It readily crystallizes in forms derived from a right rhombic octahedron, generally in magnificent laminae. Its density is 5.96. It melts at 29.5°, and has a tendency to re- main in a state of superfusion. It is not volatile. This collection of properties gives to gallium a special place among the metals. Chemical Properties. — These are but little known at present. Gallium is oxidized but little, if at all, when heated in the air or in oxygen. It forms a sesquioxide, Ga^O^, which resembles alumina in that it forms alums. Gallium alum was obtained by Lecoq de Boisbaudran. Gallium combines directly with chlorine, forming a solid, crystalline, and very volatile chloride. i:^DIUM. In = 113.4 This metal was discovered in 1863 by Reich and Richter in the zinc blendes of Freiberg (Saxony). It appears to exist in the majority of zinc blendes, and accompanies the zinc which 388 ELEMENTS OF MODERN CHEMISTRY. is extracted from those minerals. It is ordinarily obtained from commercial zinc, which, however, contains only very small quantities of it. Indium is a brilliant metal, possessing almost the lustre of silver. It is soft and ductile. It melts at 176°, and is vola- tile, but less so than zinc and cadmium. It approaches these metals in its general chemical properties, but is more electro- negative, both of the latter metals precipitating it from its solutions. Its position in the periodic system relates it to gal- lium and aluminium on the one hand, and to zinc and cad- mium on the other. Indium is characterized by several spectroscopic lines, among which are a very brilliant blue and a less marked vio- let line. Two oxides of indium have been described, a sesquioxide, ln'^0^, and a suboxide, InO. The first is obtained by cal- cining the nitrate ; it is yellow. When heated to 300° in a current of hydrogen, it is partially reduced, yielding a black suboxide. Indium chloride, InCP, is formed when indium is heated in a current of chlorine. It is a snow-white, volatile solid. Like aluminium and gallium, indium forms double sul- phates, or alums ; the ammonium double sulphate has the composition InXS0*)l(NH^)2S0* + 24:WO. RAEE EAETHS. In 1794, Gadolin, a Finn, discovered in the mineral gado- linite, which bears his name, an oxide, which was named yttria. In 1843, Mosander concluded from researches on this earth that it contained at least three oxides, the metallic radicals of which were introduced into the list of elements under the names erbium, terbium, and ytterbium or yttrium. Until recently little was known concerning these oxides, but the investigations of Crookes, Delafontaine. Lawrence Smith, Marignac, Cleve, and Nilson have shown that the earths formerly known as erbia and yttria are much more complex than was supposed. The oxides of at least six metals have been isolated, and it is possible that the series may be com- pleted by the separation of others. IRON. 389 These elements exist in gadoUnite, euxenite, orthite, thorite, and particularly in the samarsJcite of North Carolina, in which they occur as niobates and tantalates. Their quantity is so small, and the separation of their oxides is attended with such difficulties, that, excepting yttrium, the elements have not yet been isolated. Their oxides, and in some cases a number of salts, have been examined, and spectroscopic analysis has aided in setting aside all doubt as to the existence of the elements. The following atomic weights of these elements are calcu- lated to agree with the formula B.^0^ for the oxides : Scandium, discovered by Nilson and studied by Clave, bas an atomic weight of about 44; the oxide is white. The existence of scandium was predicted by Mendelejeff under the name ekaboron. Samarium. — Atomic weight = 149. This element was named by Lecoq de Boisboudran, and appears to be identical with decipium, of which Dela- fontaine announced the existence in 1878; its oxide is white. Holmium. — Atomic weight about 162 (Cleve). Erbium. — Atomic weight = 166 ; forms a pink oxide and rose-colored salts (Cleve). Thulium. — Atomic weight = 170.4 ; a white oxide. Yttrium. — Atomic weight = 89.6. The metal has been prepared by electrolysis of the chloride, and also by reduction of the latter by sodium and magnesium. It is a gray powder. Yttria is a white oxide. Ytterbium. — Atomic weight = 172.6. IROK Fe (Ferrum) = 55.60 Natural State and Metallurgy. — Iron is the most impor- tant of the metals. Its preparation and working are- difficult, therefore it was not the first metal used by civilized man. The bronze age preceded the iron age, and those who first employed the latter metal probably extracted it from the masses which fall from time to time upon the surface of the earth, and are known as meteorites. Their principal constituent is metallic iron, which is alloyed with nickel, cobalt, and chromium. Iron is employed in three principal forms : soft or malleable iron, cast iron, and steel. Soft iron is almost pure iron ; cast iron is a combination of iron with carbon and silicon ; steel also contains carbon, but in smaller proportion than cast iron. The principal ores of iron are the magnetic, or black oxide, 33* 390 ELEMENTS OF MODERN CHEMISTRY. Fe^O*, red hematite, Fe^O^, and spathic iron or ferrous carbon- ate, FeCO^. The various hydrates of the sesquioxide {^oolitic iron, brown hematite, etc.) and ferrous carbonate mixed with clay (bog-iron ore), are more abundant than the preceding, but are not as rich and are less valuable. All of these minerals are oxidized. If the ore contain sul- phur, that element is first driven out by roasting. The metal- lurgy of iron then consists in reducing the oxide with carbon, and separating the reduced iron from the earthy matter, which is generally silicious. Two methods are employed for this purpose. The first consists in heating the rich ores with charcoal alone ; part of the oxide of iron then combines with the gangue, forming a very fusible slag (double silicate of aluminium and iron). This is the Catalan method. The other consists in mixing the ore with coal and calcium carbon- ate ; the gangue then com- bines with the lime, forming a double silicate of lime and aluminium, which fuses only at a very high temperature. Under these conditions the iron unites with a portion of the carbon, forming cast iron. This is the blast-fur- nace method. Catalan Method. — This is only applicable to very rich ores and in countries where combustibles are expensive, as in Spain, the Pyrenees, and in Corsica. Fig. 116 represents a sec- tion of a Catalan furnace ; it is a trough-shaped masonry furnace with a hearth. The materials are jDlaced in two piles, side by side, upon a layer of well-ignited charcoal ; one pile consists of charcoal and is next the tuyere ; the other is the ore, equal to half the quantity of charcoal, and is placed oppo- site. The combustion is sustained by the blast from a tuyere, D, which reaches the border of the hearth. The carbon dioxide here formed is converted into carbon monoxide by the Fig. 116. IRON, 391 mass of incandescent charcoal, and the latter gas reduces the ore, again passing into the state of dioxide. Metallic iron is thus formed, and at the same time a portion of the ferric oxide is reduced to ferrous oxide, and combines with the gangue, forming a double, alumino-ferrous silicate, which is very fiisible and constitutes the slag. The reduced iron collects in the bottom of the hearth in the form of a spongy mass, which is agglutinated and forged under the hammer. Fig. 117. Blast-furnace Process. — All iron ores may be treated by this method. They are crushed and introduced with alternate layers of limestone and coal into the blast-furnace (Fig. 117). The latter has the form of two cones, the bases of which axe 392 ELEMENTS OF MODERN CHEMISTRY. joined together. It is closed at the bottom, and hot air is in- jected through tuyeres to sustain the combustion. It is open at the top, where it is continually charged with fresh materials, as the incandescent mass sinks in the furnace and the molten mate- rials are drawn off below. The latter first collect in a cavity placed below the vent of the tuyere, and separate on this hearth into metal, which sinks to the bottom, and slag, which floats and is drawn off periodically through an opening called the slag-hole. When the crucible is full of molten metal, the latter is run off into channels made in sand upon the floor of the casting-room. In these rough moulds it solidifies in bars having a semicircular section, which are called pz^s. The reactions which take place in the blast-furnace are of great interest. At the lower part, where the temperature is the highest, carbon dioxide is produced by the combustion of the coal ; farther up, in the widest portion, this gas is reduced to carbon monoxide by the incandescent coal ; still higher, where the furnace begins again to contract, and where the temperature is dull red, the carbon monoxide reduces the oxide of iron, and a spongy mass of metallic iron is there formed. In descending, this iron unites with part of the carbon, and at the same time the silica of the gangue combines with the lime, forming a silicate which fuses and constitutes the slag. A small quantity of silica is reduced in the hottest part of the furnace, and the silicon formed combines with the cast iron. Cast iron is converted into soft iron by refining ; this opera- tion consists in removing from the cast iron the greater part of its carbon. For this purpose it is melted in contact with the air ; the carbon, silicon, and a small proportion of iron are oxidized, forming a basic silicate, of which the excess of oxide is finally reduced by the carbon of the cast iron. The latter thus becomes less fusible, and is converted into a spongy mass of soft iron. Several of these masses are united and the scoriae expressed from them by the blows of a steam-hammer. Or the metal is melted on the hearth of a reverberatory furnace under a layer of ferruginous scoriae and scales of oxide of iron ; the oxygen of these materials burns the carbon out of the cast iron, the whole mass being vigorously stirred. The latter operation is called puddling. Preparation of Pure Iron. — Pure iron may be obtained by reducing ferric oxide by hydrogen at a temperature near red- ness, or by passing hydrogen over anhydrous ferrous chloride IRON. 393 contained in an incandescent porcelain tube. Hydrochloric acid is formed and evolved, and the iron remains as a gray, spongy mass, having a metallic lustre where it has been in contact with the porcelain (Peligot). Properties of Soft Iron. — Forged or bar iron is not pure. It contains a small quantity of carbon, and traces of silicon, sul- phur, phosphorus, and even nitrogen. The purest soft iron is that used for the teeth of carding-machines and for piano-strings. The density of forged iron varies from 7.4 to 7.9. It is very tenacious, ductile, and malleable. When rolled out, it is called sheet iron. Tin plate is sheet iron covered with a layer of tin. Galvanized iron is coated with a surface of zinc. Iron melts only at the highest heats of a wind-furnace. When softened by a white heat, it may be soldered to itself, or welded, a very important property for the working of the metal. 0.05 per cent, of aluminium greatly lowers the melting point of iron, so that the presence of this quantity of aluminium per- mits iron castings to be made that otherwise would be impos- sible. They are called mitis castings. Iron is attracted by tho, magnet ; it is magnetic ; but it is not, like steel, capable of retaining magnetism when removed from the magnetic influence. It is not altered by dry air at ordinary temperatures, but at a red heat it absorbs oxygen and is converted into scales of black oxide of iron. Iron may be obtained as an impalpable powder by reducing finely-divided ferric oxide in a current of hydrogen at as low a temperature as possible. In this state it takes fire when exposed to air at ordinary temperatures : it is pyrophoric. Iron rapidly becomes oxidized in moist air ; it becomes cov- ered with a layer of rust, which is ferric hydroxide. It is con- sidered that the oxidation of iron moistened with water is first set up by the oxygen dissolved in the water ; it continues with greater energy as soon as a light coat of ferric hydroxide has been formed on the metal. The hydroxide forms a voltaic couple with the iron itself, by which the water is decomposed ; part of the hydrogen displaced by the iron combines with the nitrogen of the air, forming ammonia; indeed, rust always contains a small proportion of ammonia. Iron decomposes water at a red heat, setting free the hydro- gen. It dissolves readily in hydrochloric acid, liberating impure and fetid hydrogen. If dilute nitric acid be poured upon iron tacks, the metal is at once attacked, with an abundant disen- gagement of red vapors. 394 ELEMENTS OF MODERN CHEMISTRY. On the other hand, the metal is not attacked by concen- trated nitric acid (sp. g. 1.45). After having been immersed in the strong acid, it may be put into dilute acid, and the latter will have no effect upon it. By the action of the con- centrated acid (other oxidizing agents act in a similar manner) the iron has become passive : its surface is covered with a thin film of oxide which protects it. If now it be touched with a copper wire while in the dilute acid, the protecting film is ruptured and chemical action promptly re-established. Cast Iron and Steel. — The properties and appearance of cast iron differ with the proportions of carbon and silicon which it contains. These elements appear to exist in the iron in a number of forms ; they are partly in combination with the metal and partly only dissolved by it when it is liquid. When cast iron containing much carbon is quickly cooled, it becomes hard, brittle, whiter than soft iron, and seems homogeneous. This is white iron. When slowly cooled, a large proportion of the carbon is deposited as laminae of graphite, and the less homogeneous iron then possesses a certain degree of mallea- bility : it is gray iron. Some cast irons contain sulphur and phosphorus, and re- main white even after very slow cooling. Others are lamellar and glittering ; they contain manganese and are rich in carbon (spiegeleisen and ferromanganese). The proportion of carbon contained in cast iron varies from 2 to 5.5 per cent. Steel contains less carbon, from 0.7 to 2 per cent. The quantities of carbon contained in steel and even in cast iron render it difficult to suppose that these products are veritable carbides of iron. Steel may be obtained by a partial decarbonization of cast iron, Manganiferous iron is especially applicable for this prep- aration. It is submitted to a partial refining, being maintained in the liquid state for some hours under a layer of scoriae rich in oxide of iron. A part of the carbon is burned out by the oxygen of this oxide : natural steel is thus obtained. Soft iron may be converted into steel. The operation is con- ducted in cases of refractory fire-clay, into which bars of iron, and charcoal-powder, mixed with a small quantity of ashes and common salt, are introduced in alternate layers. The bars being thus isolated in a bed of charcoal, the cases are closed and heated to redness in a furnace. The incandescent metal absorbs carbon, and at the termination of the operation is found con- verted into steel by cementation. IRON. 395 The most homogeneous and most valuable steel is cast steel. It is obtained by fusing crude steel in crucibles in a wind-fur. nace. Bessemer has introduced an important improvement in the manufacture of steel. His process, which bears his name, con- sists in adding variable quantities of a properly-constituted cast iron to molten and perfectly refined soft iron. In this process, the iron to be converted into steel is decar- bonized by a current of air which is forced through the molten metal by strong press- ure. The operation is conducted in an appa- ratus represented in Fig. 118, which is called the converter. It has an ovoid form, is constructed of strong plate iron, and is well- lined with refractory fire-bricks. It is ar- ranged on trunnions, so that an oscillating move- ment may be given to it. The air arrives under pressure by the tuyeres which open into the bot- tom of the converter. The latter is first filled with incandescent coke, which is brought into active combustion by the blast. When the interior of the converter is heated to whiteness, the coke is emptied out and replaced by the molten cast iron, the con- verter being inclined to prevent the entrance of the metal into the tuyeres. The blast is then again turned on, and the com- pressed air bubbling through the molten metal burns out all of the carbon. A flame of great brilliancy rushes from the orifice of the apparatus, and the aspect of this flame indicates precisely the progress of the operation and its termination. At this moment the apparatus is inclined, the blast arrested^ and a sufiicient quantity of melted spiegeleisen, a crystalline cast iron rich in carbon, is added to the now refined iron to convert the whole into steel. The steel is then run out into suitable moulds. Fig. 118. 396 ELEMENTS OF MODERN CHEMISTRY. A lining of lime or magnesia is substituted for the fire-bricks when the iron to be converted into steel is rich in phosphorus. The latter is then carried into the slag as a phosphate. Steel is susceptible of a high polish, and, like malleable iron, it can be forged. At the temperature at which malleable iron becomes soft, steel melts. It becomes hard and brittle when it is suddenly cooled after having been heated to redness. This operation, which is called tempering, develops new quali- ties in the steel, — elasticity and hardness. It assumes these properties in different degrees, according to the rapidity of the cooling, and the difference between the temperature to which it has been heated and that to whi^h it is cooled. The greater this difference, and the more rapid th'^, cooling, the harder will the steel become. Slow cooling makes it soft and malleable. When tempered steel is heated, and allowed to cool slowly, it partly or entirely loses its hardness. It loses it entirely if it be heated to the temperature to which it was exposed before tempering. Its temper is drawn incompletely, that is, it re- tains a certain amount of hardness and elasticity, if it be re- heated to inferior temperatures. The qualities which it will assume after cooling may be predicted from the various tints developed on its surface during the heating. Each of these tints corresponds to a determined temperature. Straw-yellow corresponds to 220° Brown " 255° Light blue " 285-290° Indigo-blue " 295° Sea-green « 331° OXIDES OF lEON. Three oxides of iron are known: Ferrous oxide FeO Ferric oxide Fe^O^ Ferroso-ferric oxide Fe^O* Fremy discovered the existence of a ferric acid, of which the composition is not certainly established. Ferrous Oxide, FeO. — Debray obtained this oxide by heat- ing ferric oxide in a current of gas formed of equal volumes of carbon monoxide and carbon dioxide. Ferrous oxide re- mains as a black powder. Fe^O^ + CO =: 2FeO + CO' Ferrous hydroxide^ Fe(OH)^, is formed as a white precipi- tate when an alkaline hydroxide is added to the solution of OXIDES OF IRON. 397 a ferrous salt. In presence of air it absorbs oxygen rapidly and becomes dark in color. Ferric Oxide, Fe^Ol — This is found anhydrous in nature in red hematite and specular iron. It may be prepared by calcining ferrous sulphate, or green vitriol. This salt first loses its water, and then at a red heat decomposes into sul- phuric anhydride, sulphurous oxide, and ferric oxide. 2FeS0* = SO^ + SO^ + ¥e'0' A red powder is thus obtained, which is known as colcothar, or jeweller's rouge. This oxide is amorphous, while red hematite is crystallized in acute rhombohedra. H. Deville has succeeded in converting the amorphous oxide into the crystallized by heating the former to redness in a very slow current of hydrochloric acid. Kust is ferric hydroxide, a combination of ferric oxide with water, and ordinarily presents the composition 2Fe^O"-J-3H^O. This hydroxide occurs native as hrown hematite. Another mineral, known 2iB goetldte^ contains Fe^O^+H^O. Ammonia or potassium hydroxide will at once produce a voluminous and flocculent, rust-colored precipitate in a solu- tion of ferric chloride. This precipitate constitutes a ferric hydroxide. But if an excess of tartaric acid be added to the solution of a ferric salt, the liquid may be saturated with potassium hy- droxide and will still remain clear, no precipitate of ferric hydroxide being formed. Advantage is taken of this property in analysis for the sepa- ration of ferric oxide from other oxides which tartaric acid does not retain in solution in an alkaline liquid. If a solution of ferric acetate be poured into a dialyser (page 209), and the water in the exterior vessel be frequently changed, the salt will finally be entirely decomposed. Acetic acid will pass through the membrane, while ferric hydrate will remain dissolved in the water in the dialyser (Grraham). Ferroso-ferric Oxide, Fe^O*. — This compound, also called magnetic oxide of iron, occurs native as magnetite, and con- stitutes the black scales which form on the surface of iron when it is heated to redness in the air ; it may be regarded ag a compound of ferrous and ferric oxides. FeO + Fe^O^ = Fe^O* 34 398 ELEMENTS OF MODERN CHEMISTRY. SULPHIDES OF IRON. Several sulphides of iron are known. The disulphide, or pyrites, FeS^, a largely-diffused mineral, is the most important of these sulphides. It occurs in two distinct forms : Pyrite, which crystallizes in brilliant cubes, or pentag- onal dodecahedra, having a yellow color and a metallic lustre. Marcasite, which forms rhombic prisms, variously modi- fied, and presents a dull, greenish-yellow color. This variety is much more alterable than the other, and possesses a great tendency to attract oxygen from the air and become converted into sulphate. When heated in closed vessels, pyrites loses a part of its sulphur. A combination of monosulphide and sesquisulphide of iron is encountered in nature ; it crystallizes in regular hexagonal prisms and is called magnetic pyrites. Monosulphide of Iron, FeS, is found in small quantity in many meteorites. It is ordinarily obtained by heating to red- ness in a covered crucible a mixture of three parts of iron- filings and two parts of sulphur. When the mixture has fused, it is poured out and solidifies to a brittle, blackish mass, having a metallic reflection. In this state, it is used for the preparation of hydrogen sulphide. CHLORIDES OF IRON. Ferrous Chloride, FeCP, is obtained anhydrous by the action of dry hydrochloric acid gas upon metallic iron. It forms white pearly scales. When iron is treated with aqueous hydrochloric acid, it dissolves, and hydrogen is disengaged. The green, filtered liquid deposits, when sufficiently concentrated, bluish- green, oblique rhombic prisms. This is hydrated ferrous chlo- ride, FeCP + 4H^0. Ferric Chloride, FeCP, is formed when a current of chlo. rine is passed over iron-turnings heated in a glass or porcelaiii tube. The two bodies combine with incandescence, and if the chlorine be in excess, ferric chloride will be obtained as a brilliant black, crystalline sublimate. The vapor density of ferric chloride above 700° corresponds to FeCP, but at lower temperatures its composition is probably Fe'^CP. FERROUS SULPHATE. 399 This body is very soluble in water and forms a yellow-brown solution. The latter may be obtained by dissolving ferric oxide, such as powdered hematite, in hot hydrochloric acid, or by passing chlorine into a solution of ferrous chloride. Ferric KOCrO^ COMPOUNDS OF CHROMIUM AND CHLORINE. Several combinations of chromium and chlorine are known. The most important is the violet chloride, CrCP, correspond- ing to aluminium chloride and ferric chloride. It is prepared by passing chlorine gas over an intimate and perfectly dry mixture of chromium oxide and charcoal, heated to redness in a porcelain tube ; carbon monoxide is disengaged, and chromic chloride sublimes into the cooler portion of the tube in brilliant peach-blossom-colored scales. These crystals are almost insoluble in cold water, and dis- solve but slowly in boiling water. Hydrogen reduces them at a red heat, with formation of hydrochloric acid, and a chloride, CrCP, which crystallizes in white scales (Peligot). 2CrCP -f H^ = 2HC1 -f- 2CrCP If a small quantity of the chloride CrCP, be added to hot water, holding in suspension the violet chloride CrCP, the latter will be instantly dissolved, forming a green solution. Chromyl chloride, CrO^CP, is obtained by heating a pre- viously fused mixture of common salt and potassium di- chromate with sulphuric acid ; abundant red vapors are disen- gaged, and condense to a blood-red liquid. This body boils at 116.8°. Its density at 25° is 1.920 (Thorpe). On contact with water it decomposes into hydrochloric acid and chromic anhydride. CrO^CP -f WO = CrO' + 2HC1 35^ 414 ELEMENTS OF MODERN CHEMISTRY. MOLYBDENUM. Mo = 96 This metal is prepared by reducing molybdic oxide, MoO', by a current of hydrogen at a high temperature. It is a white, very hard, and almost infusible metal, having a density of 9.01. It forms five oxides, MoO, Mo^O^ MoO^ Mo^O^ and MoO^ and the chlorides MoCP, MoCP, MoCl*, and MoCP. Molybdic Oxide, MoO^ is obtained by roasting the native sulphide, molybdenite, MoS^, which occurs in black foliated masses closely resembling graphite, and capable of marking paper in the same manner. The roasting is conducted at a temperature not above redness, and the resulting oxide is dis- solved in ammonia, and the solution filtered. On evaporation and cooling, crystals of ammonium molybdate are obtained which yield molybdic oxide when calcined in the air. Molybdic oxide is a white, fusible, and volatile powder ; it is but slightly soluble in water ; the solution, however, being acid. It is the anhydride of an acid which forms a somewhat complicated series of salts, one of the most important being a molybdate of ammonium having the composition Mo^O^*(NH0'+4H2O = 3(NH*)2MoO*4-4H2MoO^ This is the compound which is formed when a solution of mo- lybdic oxide in ammonia is evaporated. It is employed in the laboratory as a test for phosphorus. When its solution in nitric acid is added to a warm solution containing phosphoric acid, a yellow precipitate containing molybdic acid, ammonia, and phos- phoric acid, is thrown down. This precipitate is insoluble in nitric acid, but soluble in ammonia. TUNGSTEN. W (Wolframium) = 184 Tungsten occurs in a number of minerals, associated princi- pally with tin ores. Wolfram is tungstate of iron and manga- nese. Scheelite is calcium tungstate ; stolzite or scheelitine is tungstate of lead. The metal may be obtained by reducing tungstic oxide, WO^, by means of either carbon or hydrogen at very high temperatures. It is of a steel-gray color, very hard and brittle. TUNGSTEN. 415 and extremely refractory. Its density is 19.1. It is not tar- nished by air under ordinary conditions, but when heated in the form of powder it takes fire, forming tungstic oxide. Another oxide, WO''', and four different chlorides of tungsten — WCP, WCP, WCP, and WCP— are known to exist. Tungstic Oxide, WO^ occurs native in a yellow powder called wolfram oclire. It may be prepared from scheelite or from wolfram. The mineral is treated with nitro-muriatic acid, and the undissolved residue, consisting of tungstic oxide, is dissolved in ammonia. The filtered solution is evaporated to dryness, and on calcination the ammonium tungstate leaves tungstic oxide as pale yellow scales. It is fusible at a high temperature, insoluble in water and acids, soluble in alkaline solutions with formation of tungstates. Tungstic oxide is the anhydride of several acids forming well-marked salts. Normal tungstic acid, H^WO*, is precipitated as an insolu- ble yellow powder when the solution of a tungstate is decom- posed by an excess of hot acid. The alkaline normal tungstates have the general formula K^WO"*. Besides these, there are highly complicated salts derived from the condensation of several molecules of the normal salts. One of these, known as sodium paratungstate, is prepared on a large scale by roasting wolfram with sodium hydrate and exhausting the mass with water. Its composition is Na^°W"0*^ : it is used as a mordant in dyeing, and has been recommended for rendering fabrics of vegetable origin non- inflammable. The goods are treated with a solution containing twenty per cent, of sodium tungstate and three per cent, of sooium phosphate. The remaining elements are tetratomic, some of them at the same time forming unsaturated compounds in which the me- tallic atom may be diatomic, as in the oxides of tin, Sn'^0^ and Sn"0. Or two atoms of the metal may form a hexatomic couple, as in titanium sesquioxide, Ti^O^ Tin, titanium, zirconium, and thorium form a group of which the chemical analogies become evident in a comparison of the composition and relations of similar compounds, while platinum is the most important member of another group of metals which are associated together in nature, and which are related by certain chemical and physical properties. 416 ELEMENTS OP MODERN CHEMISTRY. Tnsr. Sn (Stannum) = 118.15 Natural State and Extraction. — The only mineral of tin wliich is worked is the dioxide (cassiterite). It is found in veins in the oldest formations, or disseminated in sand produced by their disaggregation. The principal tin mines are in India, in Malacca and the island of Banca, in Wales and in Saxony. Tin ore generally occurs mixed with various other minerals, such as sulphide and sulph-arsenide of iron, sulphides of copper and tin, etc. It is crushed and washed in order to remove light, earthy matters, and then roasted. The sulphides and sulph-arsenides are thus oxidized and disintegrated, and the product is submitted to a sec- ond washing which removes the lighter oxides, leaving the cassiterite. The latter is then heated with charcoal in a cupola-furnace, represented in Fig. 119 ; it is a sort of pris- matic furnace, having a hearth at the bottom where the melted metal collects. Air is blown in through the tuyere D. Car- bon monoxide is formed, and this reduces the stannic oxide ; || the tin collects on the hearth, ^j| from which it is drawn into ^ : the basin I, where it is stirred with rods of green wood. The steam and gases produced by the carbonization of the wood, agitate the melted mass and bring to the surface the foreign matter or dross, which is removed. The tin is then run into moulds. Thus obtained, tin generally contains small quantities of copper, iron, lead, antimony, and arsenic. It is purified by slowly heating it on the hearth of a reverberatory furnace; the pure tin melts first and runs out of the furnace, while the less fusible alloys remain upon the hearth. This method of purification is called liquation. Properties. — Pure tin is a white metal, resembling silver in Fig. 119. TIN. 417 its color and lustre. It melts at 228°, and crystallizes when slowly cooled. Crystals of tin, belonging to the type of the right square prism, may also be obtained by galvanic precipi- tation of the metal. Their density is 7.178. That of the fused and slowly-cooled metal is 7.373 (H. Deville). Tin is ductile and malleable. When a bar of tin is bent, it produces a peculiar noise called the cry of tin. The metal is unaltered by the air, but when fused, rapidly becomes covered with a grayish pellicle of oxide. Tin dis- solves in concentrated hydrochloric acid, disengaging hydrogen. The action is rapid when heat is applied. If ordinary nitric acid be poured upon granulated tin, an energetic action takes place immediately. The tin is converted into a white powder of dioxide, and torrents of red vapors are evolved. Very dilute nitric acid attacks tin almost without disengage- ment of gas. After some time the liquid will be found to con- tain a small quantity of tin nitrate and ammonium nitrate. The ammonia is formed by the simultaneous reduction of water and nitric acid by the tin. HNO^ + H^O = 20^ + NH^ When tin is heated with a concentrated solution of either potassium or sodium hydroxide, hydrogen is disengaged, and an alkaline stannate is formed. Uses of Tin. — Tin enters into the composition of bronzes ; it is made into dishes and covers, and the thin foil in which various substances, such as chocolate and tobacco, are enveloped. Tinning of kitchen vessels consists in covering them with a thin coating of tin. This protects the copper or iron from the action of the acids which enter into the composition of various articles of food. The objects to be tinned are first well cleaned by rubbing them with sand, and are then dipped into melted tin. After separating the excess of metal, they are polished by rubbing with cloths dipped in sal ammoniac. Tin-plate is sheet-iron covered with a thin layer of tin. The iron is first dipped into dilute sulphuric acid to remove the oxide; it is then rubbed with sand, and afterwards plunged successively into a bath of melted tallow and a bath of tin covered with tallow. On contact with the iron, the tin enters into com- bination, forming a true alloy, which becomes covered with a coating of pure tin. ib 418 ELEMENTS OF MODERN CHEMISTRY. When the surface of tin-plate is washed with a mixture of hydrochloric and nitric acids, the superficial coat of tin is dis- solved, and the crystallized alloy of tin and iron is exposed. This is called crystallized tin-plate. COMPOUNDS OF TIN AND OXYGEN. Tin forms two compounds with oxygen, stannous oxide, SnO, and stannic oxide, SnO^. The first is of but little importance. It is obtained by precipitating a solution of stannous chloride by potassium hydroxide, and boiling the precipitate, by which the white, stannous hydroxide first formed loses water and is converted into black stannous oxide. When the latter is moderately heated in contact with the air, it becomes incan- descent and is converted into stannic oxide. STANNIC OXIDE. Sn02 This body is found in nature as cassiterite, in the form of beautiful, hard, transparent crystals of a yellowish-brown color, belonging to the tetragonal system. From this mineral the tin of commerce is extracted. The white powder obtained when the metal is treated with nitric acid is a stannic hydrate, which plays the part of an acid, and was named by Fremy metastannic acid. He attributes to it the composition 5(H*SnO*). It would be a polymer of normal stannic acid. ^^J 0* = (onysn^' When heated to 100°, this hydrate loses half of its water; at a red heat, it loses the remainder and is converted into stannic oxide. When ammonia is added to an aqueous solution of stannic chloride, a white, gelatinous precipitate is formed, constituting a hydrate. This is the stannic acid of Fremy. It dissolves readily in hydrochloric acid, and the solution behaves as would an aqueous solution of stannic chloride. H^SnO^ + 4HC1 = SnCl* + 3H^0 SULPHIDES OF TIN — STANNOUS CHLORIDE. 419 It reacts with tlie bases, forming stannates of whicli the general composition is expressed by the formula: E^SnO^ _ Sn ) ^3 — E^ 1^ When heated to 140°, or even when dried for a long time in a vacuum, it becomes insoluble in acids. SULPHIDES OF TIN. Two sulphides of tin are known : a monosulphide, SnS, and a disulphide, SnSl The first is obtained by heating tin-filings with flowers of sulphur : the product still contains an excess of tin, and it is necessary to again heat it with a fresh quantity of sulphur. It is a crystalline, lead-colored mass. Tin disulphide or stannic sulphide is prepared by first making an amalgam of 12 parts of tin and 6 parts of mercury ; this is pulverized and the powder is mixed with 7 parts of flowers of sulphur and 6 parts of sal-ammoniac. The mixture is intro- duced into a matrass of hard glass and gradually heated to dull redness on a sand-bath. Sulphur, sal-ammoniac, sulphide of mercury, and stannous sulphide are condensed in the upper part of the matrass, of which the interior becomes covered with a yellow crystalline mass of stannic sulphide. The presence of sal-ammoniac and mercury, which volatilize in this opera- tion, prevents an elevation of temperature, which would decom- pose the stannic sulphide. The latter is carried with their vapors, and condenses in brilliant, gold-like scales, which are greasy to the touch. This body is known as mosaic gold. It is decomposed by a red heat into stannous sulphide and sul- phur. It is used for coating the cushions of electric machines, to imitate gilding, and very extensively as a pigment; STANNOUS CHLORIDE. SnCP This compound may be prepared anhydrous by heating tin in hydrochloric acid gas. Hydrogen is evolved, and a white or grayish mass remains, which has a greasy appearance, and is almost transparent. It fuses at 250°, and boils at about 600°. This is stannous chloride. When tin is dissolved in hot, concentrated hydrochloric acid and the limpid solution is evaporated and allowed to cool, beautifal transparent crystals are obtained, which contain 420 ELEMENTS OF MODERN CHEMISTRY. SnCP -f- 2H^0. This is known in commerce as tin salt or tin crystals. The crystals of stannous chloride dissolve in a small quan- tity of water, forming a limpid liquid, but when treated with a large quantity of water, they yield a cloudy liquid, which holds in suspension a small quantity of white oxychloride. The atmospheric oxygen dissolved in the water takes part in this decomposition of stannous chloride, from which it removes part of the metal, a corresponding quantity of stannic chloride (tetrachloride) being formed. Stannous chloride reduces many oxygenized and chlorinated compounds. It decomposes the salts of silver and mercury, setting free the metal. It instantly decolorizes the purple solution of potassium permanganate. If a solution of stannous chloride be added to a solution of corrosive sublimate (mercuric chloride), a white precipitate of calomel (mercurous chloride) is instantly formed. By adding an excess of stannous chloride, all of the chlorine may be re- moved from the mercuric chloride, and a gray precipitate of metallic mercury will be formed. Stannous chloride is employed as a mordant in dyeing. STANNIC CHLORIDE (TETRACHLORIDE OF TIN). SnCl* If thin tin-foil be thrown into a jar of chlorine gas, the metal will take fire, and in presence of an excess of chlorine will be converted into anhydrous stannic chloride. This is liquid, and gives off white fumes in the air. It was formerly known as fuming liquor of Lihavius. It is prepared by passing dry chlorine upon tin contained in a small retort. The anhydrous chloride condenses in the re- ceiver in the form of a yellow liquid. It may be decolorized by rectification with a small quantity of mercury, which removes the excess of chlorine. Tin tetrachloride boils at 120°. Its density is 2.28. A small quantity of water added to it is absorbed with a hissing noise, and the formation of a crystalline deposit of a hydrate, SnCl* + 5H^0. These crystals may also be obtained by dissolving tin in aqua regia and evaporating the solution, or, again, by passing chlo- TITANIUM. 421 rine into a solution of stannous chloride and concentrating the solution. The crystals of hydrated stannic chloride dissolve in water, forming a clear solution. Characters of Stannous Solutions. — Brown precipitates are formed by both hydrogen sulphide and ammonium sulphide ; the precipitate dissolves in yellow ammonium sulphide. Potassium hydroxide forms a white precipitate, soluble in an excess of reagent; ammonia yields a white precipitate, in- soluble in excess. An excess of stannous chloride produces a gray precipitate of metallic mercury in a solution of mercuric chloride. Chloride of gold gives a purple precipitate (purple of Cas- sius) in dilute stannous solutions. Characters of Stannic Solutions. — Hydrogen sulphide and ammonium sulphide form yellow precipitates, soluble in a large excess of the latter reagent. Potassium and sodium hydroxides, and ammonia water all form white precipitates, disappearing in an excess of the reagent. Chloride of gold does not precipitate stannic solutions. A sheet of iron or zinc will precipitate the tin from either stannous or stannic solutions in gray scales, which assume the metallic lustre when burnished. TITANIUM. Ti = 47.79 Titanium occurs as the dioxide, TiO^ in rutile, anatase, and brooJcite, and with iron in ilmenite (Fe,Ti)'^0^, and in many iron ores. Cubical copper-colored crystals of a nitro- cyanide of titanium are frequently found in the cinders of blast-furnaces in which titaniferous ores are reduced. The metal has been obtained by reduction of the oxide by carbon in the electric furnace (Moissan). It manifests a remarkable affinity for nitrogen. Titanium forms three chlorides, TiCP, Ti^CP, and TiCl*; there are two well-defined oxides, Ti^O^ and TiO^ and possibly a third, TiO. These compounds sufficiently characterize the element as a chemical analogue of tin. Titanium Dioxide, TiO^ as before mentioned, occurs in three different crystalline forms in nature j as square prisms in 36 422 ELEMENTS OP MODERN CHEMISTRY. rutile, square octahedra in anatase, and orthorhombic prisms in brookite. When prepared in a pure form from either of these minerals, it is a white, infusible, insoluble powder. Like stannic oxide, it is the anhydride of an acid forming a well- marked series of titanates. GERMANIUM. Ge = 72.3 In 1886, Winkler discovered in a rare silver ore argyrodite^ found near Freiberg, a new element corresponding in proper- ties with one whose existence had been predicted by Mendele- jeff under the name ehasilicon. This metal constitutes about 7 per cent, of argyrodite, and has also been found in euxenite. It may be isolated by the reduction of its oxide by hydrogen or carbon, or of potassium-germanium fluoride by hydrogen or sodium. Germanium crystallizes in brilliant regular octahedra, having a density of 5.469, and melting at about 900°. It forms two oxides, GeO and GeO^, a sulphide GreS, a chloride GeCl*, and probably also a chloride G-eCP. Its properties as well as most of those of its compounds agree remarkably with the predictions of Mendelejeff. ZIRCONIUM. Zr = 89.9 This metal also resembles tin in its chemical relations. Its principal mineral is a silicate known as zircon. It may be obtained crystallized, amorphous, and in a condition resembling graphite. Crystallized zirconium may be made by fusing in a carbon crucible potassium zirconium double fluoride with aluminium. On cooling, the excess of aluminium is dissolved in dilute hydrochloric acid, and zirconium remains as crystalline plates containing small proportions of silicon and of aluminium. Its density is 4.15, and it is less fusible than silicon. Zirconium forms but one chloride, ZrCP, which may be formed by the action of chlorine on a highly-heated mixture of zirco- nium oxide and charcoal. It is a white solid, which dissolves in water with the formation of a hydrated oxychloride. THORIUM. 423 Zirconium Oxide, ZrO^, the only known oxide, may be obtained from the native silicate zircon. The pulverized min- eral is fused with potassium hydroxide, then exhausted with hydrochloric acid, and the solution evaporated to dryness to separate the silica. The residue is dissolved in water, and the solution treated with ammonia, which precipitates hydrates of iron and zirconium. The precipitate is treated with oxalic acid, and ferric oxalate dissolves, while insoluble zirconium oxalate remains and yields zirconium oxide when calcined. Zirconium oxide is a white powder, of a density between 4 and 5, according to the temperature of calcination. It is insoluble in acids, with the exception of hydrofluoric and sulphuric acids. It is infusible, and becomes highly incan- descent when heated. It is an excellent substitute for lime in the oyxhydrogen light, and is extensively used for the Welsbach light. Zirconium oxide acts both as a base and as the anhydride of an acid forming salts analogous to the silicates. THORIUM. Th = 231.5 Thorium was discovered by Berzelius, in 1828, in the min- eral thorite, from Norway, in which it exists as an impure silicate. It occurs in the same form in orangeite, and associ- ated with cerium and lanthanum as phosphate in monazite. The metal has been obtained only as a gray powder by heat- ing its chloride with potassium or sodium. It does not decom- pose water, but burns when heated in the air. Thorium Oxide, ThO^, may be prepared from thorite by boiling the powdered mineral with hydrochloric acid, evapor- ating to dryness, and exhausting the residue with boiling water. After passing hydrogen sulphide through the filtrate, the clear liquid is precipitated with ammonia. The precipitate is dis- solved in hydrochloric acid and treated with potassium sul- phate ; a double sulphate crystallizes out, and this is redissolved in water and thorium hydroxide, Th(OH)*, precipitated by the addition of ammonia. 424 ELEMENTS OP MODERN CHEMISTRY. The oxide obtained by igniting the hydroxide is hard, gray- ish, and translucent. It is infusible, and is not reduced by charcoal or attacked by fused alkalies. It is dissolved only by boiling sulphuric acid. When heated to incandescence it emits a more brilliant light than zirconia, and is the most valued earth for the Welsbach light. Thorium Chloride, ThCP, is prepared by passing chlorine over a heated mixture of the oxide with charcoal. It then volatilizes in short, white prisms. It is deliquescent, and a solution of its hydrate may be obtained by dissolving thorium hydrate in hydrochloric acid. This hydrate contains ThCl* -{- 8H^0, and, when heated, is decomposed with formation of hydrochloric acid. Thorium forms oxysalts replacing four atoms of hydrogen in the acids. PLATINUM. Pt = 193.41 Natural State and Treatment of Platinum Ores. — The only compound of platinum found in nature is the arsenide PtAs'^ known as sperrylite^ which is isomorphous with pyrite and is found in the nickel-mines of Sudbury, Ontario. Com- mercial platinum is derived from the native metal, which is generally found in alluvial sands. Its principal deposits are in the Ural Mountains, Brazil, and California. The plati- num ore, extracted from the sand by washing, contains, in- dependently of 73 to 86 per cent, of platinum, various other metals, such as iridium, palladium, rhodium, osmium, ruthenium, gold, iron, and copper ; an alloy of osmium and iridium, and various minerals, such as titaniferous iron, chrome iron, pyrites, etc. The ore is well washed to remove the sand, and treated with dilute aqua regia which dissolves the gold, iron, and cop- per ; it is then heated with concentrated hydrochloric acid and nitric acid is gradually added. The aqua regia dissolves the platinum and certain of its accompanying metals, leaving the osmium and iridium. A solution of ammonium chloride is added to the filtered liquid ; it produces an abundant pre- cipitate of ammonium and platinum double chloride, which PLATINUM. 425 generally contains a small quantity of ammonium and iridium double chloride. This precipitate is calcined at a dull-red heat, and leaves a dull-gray, spongy residue. It is spongy To give coherence to this sponge and convert it into a mal- leable and ductile metal, it is reduced to powder in a wooden mortar and triturated with enough water to convert it into a perfectly homogeneous paste. This paste is introduced into a slightly-conical cylinder of brass or iron, and compressed first with a wooden piston, then by a steel rod. The compression is finished by the aid of a hydraulic press, and the slightly- conical cylinders so formed are heated to whiteness and forged under the hammer, as iron is forged. To obtain perfectly pure platinum, the metal is dissolved in aqua regia, the excess of acid evaporated, and the residue heated to 150° ; the iridium is thus converted into Ir^CP which remains in solution when the platinum is precipitated with ammonium chloride. H. Sainte- Claire Deville and Debray extracted the metal by simple fusion of the ore. The fusion is effected in a len- ticular cavity cut in two large masses of quick-lime, placed one above the other. A current of illuminating gas is di- rected into this furnace, and the combustion is supported by a continual supply of oxygen. Properties of Platinum. — Platinum has a grayish-white lustre. It melts only at the highest attainable temperatures. The density of the cast metal is 21.1 ; that of the forged metal 21.5. It softens at a white heat, and can then be forged and welded like iron. The experiments of H. Deville and Troost have shown that a red-hot platinum tube allows hydrogen to pass through its pores. Platinum has the curious property of condensing gases on its surface, and this property is the cause of certain chemical phe- nomena that were formerly attributed to mere contact of the metal. If a morsel of platinum-sponge be introduced into a small jar filled with an explosive mixture of oxygen and hydrogen, the gases will combine instantly, with explosion. This property is most highly developed in platinum-blach, for in this form the metal exists in an extreme state of division. It may be prepared by reducing a solution of platinic chloride by zinc ; or platinum dichloride may be boiled 36* 426 ELEMENTS OF MODERN CHEMISTRY. with potassium hydroxide, and alcohol or a solution of sugar gradually added to the liquid, which must be continually stirred. The platinum is precipitated as a black powder. Platinum is unaltered by the air. It is not attacked by either nitric, hydrochloric, or sulphuric acid, even boiling. It dissolves in aqua regia. The alkaline hydroxides attack it at high temperatures on contact with the air. It is the same with the alkaline nitrates. There are two oxides of platinum, a monoxide, PtO, and a dioxide, PtOl CHLOKIDES OF PLATINUM. These are the more important compounds of platinum. There are two, a dichloride, PtCP, and a tetrachloride, PtCl*. Platinum dichloride is obtained by cautiously heating the tetrachloride to 200"^. Chlorine is disengaged, and after cool- ing, the residue is exhausted with boiling water, which leaves an olive-green powder, constituting the dichloride. When ammonia is added to a solution of platinum dichloride in hydrochloric acid, a green, crystalline powder separates after some time. It is called green salt of Magnus, and contains PtCP-f 2NH^ It may be regarded as the dichloride of platinoso-diammonium. Pt" It is derived from two molecules of ammonium chloride by the substitution of an atom of diatomic platinum for two atoms of hydrogen. Platiniim tetrachloride, or platinic chloride, PtCl*, is formed when platinum is dissolved in aqua-regia. A red- brown solution is obtained, which, after concentration and cool- ing, deposits red-brown needles of hydrated platinic chloride. The crystals lose their water when heated, and are converted into a dark, red-brown mass, which constitutes the anhydrous chloride PtCl*. This body absorbs moisture when exposed to the air. It is very soluble in water, alcohol, and ether. If a solution of ammonium chloride be added to a solution of platinic chloride, a yellow, crystalline precipitate of plati- num and ammonium double chloride is immediately formed. r2 r NICP OTHER METALS OF THE PLATINUM GROUP. 427 This body is but little soluble in cold water, but more soluble in boiling water, from which it is deposited in microscopic, regular octahedra. It is almost insoluble in alcohol. It contains PtCP.2NH^Cl A yellow, crystalline precipitate of double chloride of plati- num and potassium is obtained, in the same manner, on adding a solution of platinic chloride to a solution of a potassium salt, if the liquids be not too dilute. PtCl*.2KCl OTHER METALS OF THE PLATINUM GROUP. Rhodium, ruthenium, palladium, iridium, and osmium are associated with native platinum, and are usually extracted from platinum residues. They are fusible with great difficulty, and not readily attacked by acids. Their separation from each other is accomplished by tedious and complicated reactions, but, with the exception of ruthenium and rhodium, they possess certain valuable properties which have found for them applications in the arts. They combine with oxygen, forming a series of feeble bases, and a series of acid oxides. With the exception of the volatile oxides of ruthenium and osmium, these compounds are decomposed by heat into metal and oxygen. Rhodium is less fusible than platinum, and almost insoluble in aqua-regia, which, however, dissolves it if it be alloyed with the baser metals. Its specific gravity is 12.1. It forms oxides RhO, Rh20^ and RhO^ and a chloride Rh^CP. Ruthenium is a hard metal, having a density of 12.26 at 0°, and is more infusible than iridium. It is hardly attacked by boiling aqua-regia. One of its most interesting compounds is a volatile oxide RuO*. Its chloride has the composition Ru^CP. Palladium has the lowest melting-point of the group of platinum metals, fusing at about the same temperature as wrought iron. Its specific gravity at ordinary temperatures is 11.4. When a bright piece of* the metal is heated in the air, its surface becomes tarnished from the formation of a film of oxide, but at a higher temperature this oxide is again reduced 428 ELEMENTS OF MODERN CHEMISTRY. to metal. The remarkable facility with whicli palladium ab- sorbs hydrogen has already been mentioned (page 61). Pal- ladium forms three oxides, Pd^O, PdO, and PdO^ and two chlorides, PdCP and PdCl*. Iridium occurs with the platinum ores in grains of platin- iridium and osmiridium. Its fusing-point is the highest after osmium and ruthenium. It is very hard, and next to osmium it has the highest specific gravity of any substance known, its density being 22.38. An alloy of platinum and iridium con- taining ten per cent, of the latter metal is as hard and elastic as steel, unalterable in the air, and less fusible than platinum. It is used for the points of gold pens. Iridium forms two oxides, Ir^O^ and IrO^, and two chlorides, Ir^CP and IrCh Osmium has been obtained in cubical or rhombohedral crystals having a density of 22.48. Its melting-point is about 2500°. When strongly heated in the air it burns into a vola- tile oxide, OsO'^, which is dangerously poisonous. The native alloy, osmiridium, is used for the points of gold pens. Two chlorides are known, OsCP and OsCl*. ORGANIC CHEMISTRY. GENERAL IDEAS UPON THE CONSTITUTION OF OEGANIC COMPOUNDS. Organic chemistry studies the history of the compounds of carbon. The most simple of these are the gases carbon monoxide and carbon dioxide ; each contains but a single atom of carbon. In this respect they resemble the inflammable gas which is disengaged from the mud of marshes ; it contains one atom of carbon combined with four atoms of hydrogen. The gas hydrogen dicarbide or ethylene, which has already been mentioned, contains two atoms of carbon united with four atoms of hydrogen. A great number of compounds are known which contain only carbon and hydrogen, and they are called hydrocarbons or carburetted hydrogens. The atoms of carbon are aggregated in them, together with the atoms of hydrogen. Other elements are often added to the preceding, forming molecules more or less complex. The carbon atoms form as it were the framework, and the carbon compounds possess pecu- liar properties precisely on account of the great facility with which the atoms of carbon accumulate in one and the same molecule, and link themselves in some manner one to another. The following developments will give some idea of the mode of formation and the structure of organic molecules. The most Simple Organic Compounds. — Their Composi- tion proves Carbon to be a Tetratomic Element. — The most simple of the hydrocarbons is marsh gas. When this gas is submitted to the action of chlorine, one or more atoms of hydrogen may be removed from it ; they com- bine with the chlorine and are disengaged in the form of hy- drochloric acid gas. The curious fact, first noticed by Dumas, is then observed, that each atom of hydrogen which is removed is replaced by an atom of chlorine. This substitution gives 429 430 ELEMENTS OF MODERN CHEMISTRY. rise to a series of chlorinated compounds, wliicli present tlie most simple relations with marsh gas. The latter contains only carbon and hydrogen. The chlorine compounds derived from it by substitution, form with it the following series : CH* marsh gas, or methane. CH^Cl monochloromethane (methyl chloride). CH2C12 dichloromethane (methylene chloride). CHC13 trichloromethane (chloroform). CCl* tetrachloromethane (carbon tetrachloride). In each of these compounds a single atom of carbon is united with four monatomic atoms. We have seen that the atoms of chlorine and hydrogen are equivalent as regards their power of combination. In the preceding compounds, the sum of the atoms of hydrogen and chlorine which are combined with one atom of carbon is invariably four, and this number cannot be exceeded. But two atoms of a monatomic element may be re- placed by one atom of a diatomic element. One atom of car- bon, which unites with four atoms of hydrogen or chlorine, may unite with two atoms of oxygen to form carbon dioxide CO"' and this compound is saturated like those preceding, for one atom of oxygen is equivalent to two atoms of hydrogen or chlorine. In carbon monoxide, CO'', the affinity of carbon is not satisfied ; hence this gas will unite directly with an atom of oxygen to form carbon dioxide, or with two atoms of chlo- rine to form carbonyl chloride. CO'^CP In ammonia, one atom of nitrogen is combined with three atoms of hydrogen ; nitrogen is triatomic ; hence it may replace three atoms of hydrogen. A body is known which represents marsh gas, in which three atoms of hydrogen are replaced by one atom of nitrogen. This is the dangerous poison known as prussic or hydrocyanic acid, and the composition of which is represented by the formula CN'"H In all of the compounds which have just been mentioned a single atom of carbon is invariably united to a number of ele- ments of which the sum of the atomicities is four, and never more nor less than that number. It is then reasonable to conclude that in them carbon plays the part of a tetratomic INTRODUCTION TO ORGANIC CHEMISTRY. 431 element. This important fact, first exposed by Kekule, can be clearly understood if we represent tbe preceding atomic formulae in a graphic manner, that is, by symbols so arranged as to show the reciprocal relations of the atoms and their mutual satura- tion. In these formulas a saturated atomicity is indicated by a line of union, two atomicities by two lines, etc. H H H CI H-C-H H-C-Cl Cl-C-Cl Cl-C-Cl I I I H H CI h Marsh gas. Monocliloro- Tnchloroiiietliane. Carbon methane. (Chloroform.) tetrachloride. CI 0=C-0 Cl-C-0 H-CEN Carbon dioxide. Carbonyl chloride. Hydrocyanic acid. There exists a very volatile, ethereal liquid, which represents marsh gas, in which one atom of hydrogen is replaced by iodine. It is the body known as methyl iodide, CH^I. If this body be heated for a long time in a sealed tube with a solution of potassium hydroxide, potassium iodide will be grad- ually formed, and the solution will contain a volatile, spirituous liquid which can easily be separated by distillation, for it boils at 66°. It is the same body which constitutes the most vola- tile of the liquids which are formed in the destructive distilla- tion of wood ; it is called wood spirit, and its chemical name is methyl alcohol. The reaction by which it is formed is very simple. The iodine of the methyl iodide combines with the potassium ; but when this iodine is removed, the carbon remains united to but three atoms of hydrogen. It is no longer saturated, and it therefore combines with the oxygen and hydrogen which were united with the potassium in the potassium hydroxide. CH^I -f KOH = CHIOH + KI It will be seen that the atom of oxygen alone does not com- bine with the group CH^, which is called methyl. It is accom- panied by an atom of hydrogen, with which it remains united in the new compound, which is called methyl hydroxide or methyl alcohol. As has been said, this oxygen replaces the iodine in the iodide of methyl, but as it possesses two atomici- ties, and the carbon already united with H^ has only one free atomicity, the atom of oxygen can only fix upon the carbon by 432 ELEMENTS OF MODERN CHEMISTRY. one of its atomicities ; the other remains saturated by the atom of hydrogen. The latter is then drawn into the combination, and is united, not to the carbon, but to the oxygen. The reaction takes place as if the atom of iodine were replaced by the group hy- droxyl (OH) which is monatomic. Hence the relations between the atoms in methyl hydroxide are represented by the formula H H-CJ-COH)' H If we compare the constitution of the three bodies CH^Cl, CH^I, CH^(OH), we notice that they contain a common ele- ment, namely, the group CH^, which is united to chlorine, to iodine, or to hydroxyl. Besides this, experiment has shown that methyl iodide can be transformed into the hydroxide. The group methyl hence presents a certain stability and can pass from one combination to another. This is expressed by saying that it is a radical. If methyl iodide be heated with an aqueous solution of ammonia, among the products formed will be found the hydri- odide of a base which represents ammonia in which one atom of hydrogen is replaced by the group methyl. Potassium hydroxide sets this base at liberty. At ordinary temperatures and pressures, it constitutes a gas, very soluble in water and possessing a strong ammoniacal odor. It is methylamine. The reaction by which it is formed is as follows : the iodine with- draws one atom of hydrogen from the ammonia, which atom of hydrogen is replaced by the group CH^. QWl + NH=^ = CH\NH^).HI. Methylamine hydriodide. In methylamine then, the fourth atomicity of the carbon atom is saturated by nitrogen, but as this element is triatomic it brings into the combination two atoms of hydrogen which saturate its two other atomicities. It may then be said that in methylamine the fourth atomicity of carbon is saturated by the group NH^ This is expressed in the following formulae. H H H-C-N=H^ = H-C1-(NH7 H Methylamine. i INTRODUCTION TO ORGANIC CHEMISTRY. 433 Formation of Hydrocarbons containing Several Atoms of Carbon. — The preceding compounds contain but a single atom of carbon, but starting with one of these compounds we may produce more complicated organic molecules containing several carbon atoms. If methyl iodide be heated with sodium in sealed tubes, sodium iodide is formed, and a gas, a hydrocarbon, is confined under great pressure in the tubes. This gas escapes, and may be collected, when the drawn-out points of the tubes are opened in the blow-pipe flame. It is dimethyl, and has been formed according to the following reaction : 2CH3I -f Na^ = C^H« + 2NaI Methyl iodide. Dimethyl, or ethane. Two molecules of methyl iodide have entered into the reac- tion, and the whole of the carbon of these two molecules is found in one molecule of the hydrocarbon, C^H^ = (CH^)^, which results. On losing their iodine the two methyl groups combine to- gether. One of the carbon atoms attracts the other, exchanging with it the fourth atomicity set free by the loss of the iodine. Hence the iodine of one of the molecules of methyl iodide has been replaced by the carbon of the other, which fixes upon the group CH^ by a single one of its atomicities, and at the same time brings into the combination the three atoms of hydrogen which saturate the other three atomicities. This is expressed in the following formulae : H H H H H-C-H H-C-I H-C-C^H I I II H H HH Methane (methyl hydride). Methyl iodide. Dimethyl (ethyl hydride or ethane). The mode of generation of this new hydrocarbon, which contains two atoms of carbon, is worthy of consideration. It results from the substitution of a methyl group for one atom of hydrogen in methyl hydride. One atom of carbon, accompa- nied by three atoms of hydrogen, fixes upon another atom of carbon of which it completes the saturation. By this exchange of atomicities each of the carbon atoms retains only three afiin- ities which are satisfied by three atoms of hydrogen. The two methyl groups, CH^ -f- CH^ = C^H*, are then united by their carbon atoms, and are held together by the affinity of T cc 37 434 ELEMENTS OP MODERN CHEMISTRY. carbon for carbon. In methyl hydroxide the group hydroxy! is bound to the group CH^ by the affinity of carbon for oxygen. In methylamine, the group NH^ is united to the group CH^ by the affinity of carbon for nitrogen. In dimethyl, it is carbon which is united to carbon. This has before been expressed by saying that the atoms of this element possess a faculty to accu- mulate in one and the same molecule. It is in this curious property that must be sought the reason for the existence of those innumerable compounds, more or less rich in atoms of carbon, which constitute the immense field of organic chemistry. But it is important to study by new examples this mode of formation of organic compounds. Dimethyl, which we have seen is produced by the action of sodium upon methyl iodide, is also known as ethyl hydride. If one of its atoms of hydrogen be replaced by an atom of chlo- rine, ethyl chloride, C'H^Cl, is obtained. Ethyl iodide, C'H^I, represents ethyl hydride, in which one atom of hydrogen has been replaced by iodine. If a mixture of methyl iodide and ethyl iodide be heated with sodium, among the products of the reaction will be found a gas containing C^H® ; this gas is methyl-ethyl, and it results from the combination of methyl, CH^, with the group ethyl, C^H^ It represents ethyl iodide in which the atom of iodine has been replaced by a methyl group, the carbon of the latter group being fixed by one of its atomicities to one of the carbon atoms of the group C^H^. In the same manner, by heating a mixture of propyl iodide, C^H^I, and methyl iodide with sodium, we may add to the propyl group, C^H^, a new atom of carbon escorted by its three atoms of hydrogen. HH HHH HHHH H-C-C-I H-C-C-C-H H-C-C-C-C-H, etc. 1 1 HH Ethyl iodide. i 1 1 HHH Methyl-ethyl (propane). 1 1 1 1 HHHH Methyl-propyl (butane). Nothing prevents the continuation of these additions of car- bon to incomplete hydrocarbons, that is, to the residues of the subtraction of iodine from the saturated iodides, of which the following are the names and formulae : CffI C^H^I C^H^I C*H«I C^H^^I, etc. Methyl iodide. Ethyl iodide. Propyl iodide. Butyl iodide. Amyl iodide. INTRODUCTION TO ORGANIC CHEMISTRY. 435 The following hydrocarbons would then be formed succes- sively : CH3-CH3 C2H5_CH3 C5H7-CH3 C*H9-CH» CSHH-CHs, etc. Methyl-metliyl Methyl-ethyl Methyl-propyl Methyl-butyl Methyl-amyl (Ethane). (Propane). (Butane). (Pentane). (Hexane). In all of these cases, the atoms of carbon united together form, as it were, a continued chain, and the atoms of hydrogen are grouped around them as satellites. Homologous Bodies. — Very simple relations exist between the hydrocarbons of which we have just studied the mode of formation. They form a series of which each member differs from the preceding by the addition of CH^ These relations will appear clearly if the formulse already given be replaced by the crude formulse : C H* methane. C'W ethane. C^H^ propane. C'W^ butane. C^H^^ pentane. This group of hydrocarbons constitutes what is called the homologous series of marsh gas, or the series C"H^"+l Many other series are known, the terms of which are related to each other in the same manner, and the bodies which form part of them may present the greatest differences in composition. Sometimes they contain only carbon and hydrogen. Again, they may contain oxygen or nitrogen in addition to these ele- ments ; in this case the former elements are united to carbon by one or more of their atomicities, as has already been indicated. In any organic body whatever, if an atom of hydrogen united with carbon be replaced by a methyl group, CH^, the superior hoTYiologue of that body is obtained, that is, the compound which differs from the original body by the addition of CH^. There is a great resemblance in physical and chemical properties between such homologues. Some of these homologous series will be indicated farther on. Composition and Classification of Organic Compounds. — The elements carbon, hydrogen, oxygen, and nitrogen are the most common constituents of organic compounds. Those which occur in the vegetable kingdom consist, for the most part, of the three first named, although there are also many nitrogenous bodies of vegetable origin. Animal matter, as a 436 ELEMENTS OF MODERN CHEMISTRY. rule, contains all four of tlie elements mentioned and not in- frequently sulphur and phosphorus in addition. But nearly all of the other elements can be introduced artificially into organic compounds ; it is thus with chlorine, bromine, iodine, arsenic, boron, silicon, and a great number of the metals. In uniting with carbon, in different manners and in various proportions, these elements form an innumerable multitude of compounds, each of which has a fixed composition and definite properties. These bodies constitute the chemical species, so to say. When submitted to the action of reagents, all may be modified in a thousand manners, and transformed into each other. Sometimes their composition is simplified, one or more carbon atoms being removed from the chain. Sometimes it is complicated by synthesis ; that is, the addition of new atoms of carbon. All these bodies contain carbon, and are distinguished : 1. By the number of carbon atoms contained in the molecule. 2. By the nature and arrangement of the other atoms com- bined with the carbon. 3. By the arrangement of all the atoms in the molecule. The facts relative to the atomic composition of organic com- pounds are obtained by elementary analysis and by the deter- mination of the molecular weight. ELEMENTARY ANALYSIS. The object of elementary analysis is the determination of the nature and proportion of the elements contained in any given organic body. We can give here but a summary descrip- tion of the processes employed, considering only those which have for object the determination of carbon, hydrogen, and ni- trogen. Oxygen is almost invariably estimated by difference. The percentages of carbon and hydrogen are determined in one operation. In case nitrogen or other elements are present, the relative quantity of each of these must be ascertained by separate operations. Determination of Carbon and Hydrogen. — To determine the proportion of carbon and hydrogen contained in 100 parts of any given organic substance, the carbon is converted into carbon dioxide, which is collected and weighed, and the hydro- gen into water, which is condensed and weighed. These opera- tions are conducted according to a method devised by Liebig. ELEMENTARY ANALYSIS. 437 For this end, tlie organic matter, previously dried with care, is burned with an excess of cupric oxide. The operation is exe- cuted in a combustion-tube of hard glass, which is wrapped with a spiral of metallic foil to prevent it from bending and swell- ing under the influence of the heat. Well-dried cupric oxide is introduced into the tube, then an intimate mixture of the substance to be analyzed with a large excess of the same oxide, and the remainder of the tube is filled with pure cupric oxide. The tube is then placed in a combustion furnace, and its open extremity is put in communication with (1) an U tuhe,jg (Fig. 120), containing fragments of calcium chloride in the first branch, and pumice-stone impregnated with sulphuric acid in the second; (2) a tube with five bulbs, h, called Liebig's potash bulbs, containing a concentrated solution of potassium hydroxide, and followed by a small U tube, i, containing pumice-stone im- pregnated with potassium hydroxide in the first branch, and frag- ments of potassium hydroxide in the second. These different tubes have first been accurately weighed. When the appa- ratus is arranged, the combustion-tube is slowly heated, com- mencing at the extremity B, and gradually extending the heat so that each part of the tube is successively heated to redness. The water formed by the combustion is collected in the first U tube, the carbon dioxide is absorbed by the potassium hy- droxide in the bulbs. When the operation is terminated, a rub- ber tube connected with an oxygen reservoir is slipped over the drawn-out end of the combustion tube which is then crushed within the rubber tube. An excess of oxygen is then passed through the combustion-tube, in order to drive out the traces of carbon dioxide and aqueous vapor which it contains at the end of the combustion. It is then only necessary to weigh the water tube and the carbon dioxide tubes. The increase in weight which is found indicates, on one hand, the quantity of water, and on the other the quantity of carbon dioxide, pro- duced by the combustion of the organic matter. The compo- sition of water and of carbon dioxide being known, it is easy to deduce from the weight of these two bodies the quantities of hydrogen and carbon contained in the analyzed substance, and consequently the proportion of these two elements con- tained in 100 parts of that substance. Fig. 120 represents the operation towards its close : the combustion-tube is in the gas-furnace, B, and communicates, on the right with the tubes g, h, i, destined to receive the pro- 37* 438 ELEMENTS OF MODERN CHEMISTRY. ELEMENTARY ANALYSIS. 439 ducts of the combustion, on the left with two large U tubes, the first of which is filled with pumice-stone impregnated with potassium hydroxide to absorb traces of carbon dioxide, the second with pumice-stone saturated with sulphuric acid to absorb moisture. Through these tubes is passed the oxygen, at the close of the operation, to expel the last portions of carbon dioxide and vapor of water. When the substance contains carbon, hydrogen, and oxygen, the proportion of oxygen is the difference between the total percentage of carbon and hydrogen found and 100. EiG. 121. Determination of Nitrogen. — Nitrogen may be determined by several methods. One of these is to burn a given weight of the nitrogenous substance with an excess of cupric oxide. The carbon of the substance is converted into carbon dioxide ; the hydrogen is converted into water ; the nitrogen is disen- gaged. The gases, nitrogen and carbon dioxide, are received in a graduated jar standing on the mercury-trough and con- taining potassium hydroxide. The carbon dioxide is absorbed, the nitrogen remains. At the close of the operation, the last traces of nitrogen are expelled by a current of carbon dioxide. The volume of nitrogen is then measured, and its weight de- duced from its volume (Dumas). Another process (Fig. 121) consists in decomposing the nitrogenous organic matter with an alkali at a high tempera- ture. By this means all of the nitrogen is converted into ammonia. The substance is intimately mixed with soda lime, that is, lime impregnated with caustic soda. The mixture is heated to redness in a tube of hard glass, and the ammonia is 440 ELEMENTS OF MODERN CHEMISTRY. received in a tube with three bulbs containing dilute hydro- chloric acid. Ammonium chloride is formed ; when the opera- tion is terminated, the liquid containing the salt is mixed with a solution of platinic chloride. It is then evaporated and exhausted with alcohol, which leaves the platinum and ammo- nium double chloride, 2(NH*C1) + PtCl*. The latter is col- lected upon a tared filter, then washed and dried. From its weight is calculated that of the nitrogen contained in the organic substance (Will and Varrentrapp). The ammonia disengaged may also be received in 10 cubic centimetres of a normal solution of sulphuric acid, that is, an acid liquor containing a known quantity of sulphuric acid in a determined volume. The strength of this acid is determined by neutralizing 10 c.c. of it with a dilute alkaline solution of known strength and noting the volume of the latter required. The same operation is repeated with the 10 c.c. of which the acid has been par- tially neutralized by the ammonia. The quantity of ammonia corresponds to the difference between the volumes of the alka- line liquid employed in these two operations, and can easily be calculated by simple proportion (Peligot). Still another mode of estimating nitrogen, devised by Kjel- dahl, depends upon the fact that the nitrogen of organic bodies is quantitatively converted into ammonia, when such bodies are heated with strong sulphuric acid. After an excess of caus- tic soda has been added to neutralize the acid, the ammonia liberated is distilled off and estimated as above described. Determination of the Molecular Weight of Organic Sub- stances. — Elementary analysis permits the determination of the centesimal composition of organic substances. This is indispensable, but it is insufficient for the establishment of their atomic composition, that is, the number of atoms of car- bon, hydrogen, oxygen, and nitrogen which are contained in a single molecule of a given organic compound. But if the weight of the molecule be known (hydrogen being taken as unity), it is easy to deduce the atomic composition from the figures given by elementary analysis, as will be seen by the following example. By elementary analysis it is found that 100 parts of acetic acid contain Carbon 40. Hydrogen 6.67 Oxygen 53.33 100.00 ELEMENTARY ANALYSIS. 441 On the other hand, methods which will be described have shown that the molecular weight of acetic acid is 60 ; that is to say, the total weight of the atoms of carbon, hydrogen, and oxygen contained in a molecule of acetic acid, is 60. Hence by the following proportions : If 100 parts acetic acid contain 40 of carbon, 60 parts contain x. " " " 6.67 of hydrogen, '' " y. " " " 53.33 of oxygen " « z. From which, x = 24; y = 4 ; 2 = 32. Hence 24 represents the weight of the atoms of C contained in a molecule of acetic acid. 4 represents the weight of the atoms of H contained in a molecule of acetic acid. 32 represents the weight of the atoms of contained in a molecule of acetic acid. By dividing these numbers by the weights of the respective atoms, the number of atoms of C, H, and contained in a molecule of acetic acid is readily determined. 24 -=- 12 = 2 atoms of carbon. 4 -i- 1 = 4 " hydrogen. 32 -^ 16 = 2 " oxygen. Hence the formula of acetic acid is C^H*0^. After the analysis of an organic substance has been made, it is only necessary to determine the molecular weight in order to establish the atomic composition. Several processes are em- ployed for this determination, of which the most convenient, when applicable, is the determination of the vapor density. The vapor density is most conveniently determined by measuring the volume occupied by the vapor of a known weight of the substance and dividing this weight by that of an equal volume of hydrogen at the same temperature and pressure. An apparatus devised by Victor Meyer and shown in Fig. 122 is generally employed for this purpose. The inner vessel b is heated by the vapor of some liquid whose boiling-point is considerably higher than that of the given substance. When the temperature becomes constant, which is indicated by air ceasing to escape through /, a graduated tube filled with water is inverted over the mouth of /. A small stoppered tube filled with a weighed quantity of the substance has been supported by the glass rod c h, and is caused to fall by slightly withdrawing the rod. On reaching the bottom the substance instantly volatilizes, and the vapor displaces an equal volume of air of the same temperature 442 ELEMENTS OP MODERN CHEMISTRY. and pressure ; this escapes througli /, and is collected and measured in the graduated tube, and its volume under normal conditions calculated by aid of the formula -^ (1 + .003665 i) 760' in which v is the measured volume, P the pressure under which the air is measured, li the tension of aqueous vapor at the temperature, ^, at which the air is measured. The weight of an equal volume of hydrogen is then divided into the weight of substance taken, and the quotient is the required density. The vapor density of acetic acid com- pared to hydrogen is thus found to be 30 ; the molecular weight corresponding would be 60. Other methods must be em- ployed for determining the molecular weights of sub- stances that cannot be vapor- ized without decomposition, and advantage has been taken of the fact that in dilute solu- tions substances behave in many respects like gases or vapors. The most accurate and most convenient of the methods based on this prin- ciple is the cryoscopic method, devised by E-aoult. When a dilute solution of a com- pound is cooled to its freezing- point, the latter is found to be lower than the freezing-point of the pure solvent. Within certain limits of concentration this depression of the freezing- point is directly proportional to the weight of the substance -b Fig. 122. ELEMENTARY ANALYSIS. 443 dissolved, and has been shown by Raoult to be proportional to the number of molecules of the substance dissolved in a certain weight of the solvent, and independent of the nature of the substance. Hence, if several substances in equimo- lecular proportions be dissolved in like quantities of the same solvent, each will produce the same depression of the freezing-point. The depression produced by the number of grammes corresponding to the molecular weight of the sub- stance in 100 grammes of the solvent is called the molecular depression of the solvent ; different solvents have different molecular depressions. If this constant be known for any solvent, the molecular weight of a substance may be de- duced by determining the depression pro- duced by a known proportion of the substance. If c be the depression ob- served when p grammes of the sub- stances are dissolved in I grammes of the solvent, then ^ I grammes of the sub- stance must be dissolved in 100 grammes of solvent to produce the same depression. If T represent the molecular depression of the solvent and Jif the required molec- 100 p j^^^lOOpT ular weight, 31 = c : T, and „_ Ic Fig. 123 represents an apparatus, de- scribed by Beckmann, for accurate meas- urements of the depression of the freezing- point, e is a wide tube having a capacity of about 25 c. c. up to the lateral tube, and closed by a cork carrying a stout platinum stirring-rod and a thermometer graduated to .01°. e is surrounded by a wider tube, d, which is fixed in the metal lid of the vessel cr, which contains a liquid cooled to about 5° below the freezing-point of the solvent. The annular space between e and d contains air, which pre- vents too rapid cooling. A weighed quantity, about 15 grammes, of the solvent is introduced into e, and constantly stirred with the rod until it Fig. 123. 444 ELEMENTS OF MODERN CHEMISTRY. begins to freeze ; as soon as the temperature becomes con- stant the freezing-point is noted. The tube e is now with- drawn and the solvent allowed to melt, when the tube is replaced, and a weighed quantity of the substance is dropped in through the lateral tube. The freezing-point of the solu- tion is noted, and the difference between the two readings is the depression. When for any reason neither of the methods already de- scribed can be applied to determine the molecular weight, a chemical method may be employed. We will again con- sider acetic acid. Salts may be formed with this acid, and we know that these salts contain one atom of metal. We may then analyze silver acetate. 100 parts of that salt contain 64.67 parts of silver. This fact being known, it is easy to deter- mine the molecular weight of silver acetate. Since the latter contains one atom of silver, we can conclude, if 64.67 parts of silver are contained in 100 parts of silver acetate, 108 parts of silver, that is, one atom, are contained in x parts of silver acetate ; whence x = 167. This number represents the molec- ular weight of silver acetate. That of acetic acid may be de- duced by substituting the atomic weight of hydrogen for that of silver, which gives for the molecular weight of acetic acid 60. Analogous operations and reasoning permit the determina- tion of the molecular weights of bodies playing the part of bases. They are combined with an acid, the molecular weight of which is known, and the composition of the combination furnishes the data for the calculation of the molecular weight of the base. This method can be applied in a large number of analogous cases, and presents a great generality. Determination of Meltings-Points and Boiling-Points. — A knowledge of the color, density, crystalline form, tempera- tures of freezing and boiling, and other physical constants of carbon compounds, is of importance not only as means of identification, but in the development of the theory which shall throw light on the influence of composition on proper- ties. Many carbon compounds are fusible and volatile with- out decomposition, and the exact temperatures at which these changes of state occur are highly characteristic, and are determined with great care. For the determination of the melting-point, a small quan- tity of the substance in fine powder is introduced into a capillary tube closed at one end, which is then attached by ISOMERISM, METAMERISM, POLYMERISM. 445 tlie side of a chemical thermometer so that the substance shall be on the same level as the bulb ; a caoutchouc band or a fine platinum wire keeps the capillary tube in position. The thermometer is then supported over a beaker, h (Fig. 124), in which the thermometer bulb and substance are just immersed in a liquid of high boiling-point, such as sulphuric acid or paraffin oil. The whole is cautiously heated while agi- tating by the stirrer s, and the temperature of fusion is noted. Fig. 124. Fig. 125. Boiling-points are determined by distilling a small quantity of the substance in a " Wurtz distilling tube" (Fig. 125), which is a small, long-necked flask, /, with a side tube, s, through the cork of which passes the thermometer t. It is advisable that the neck of the flask should be so long that the whole mercurial column at the given boiling-point is surrounded by the vapor. ISOMERISM, METAMERISM, POLYMERISM. Elementary analysis demonstrates that many bodies which differ in their physical and chemical properties, possess ex- actly the same centesimal composition. Such bodies are said to be isomeric. Two kinds of isomerism exist. Sometimes the isomeric bodies contain the same number of similar atoms in molecules of the same size, and diff"er only by the arrange- ment of these atoms ; sometimes they contain similar atoms 38 446 ELEMENTS OF MODERN CHEMISTRY. united in the same proportion, but not in tlie same number, in molecules of unequal magnitude. In both cases the centesimal composition is the same, for it depends only on the relative number of the atoms. The first kind of isomerism constitutes metamerism; the second, polymerism. Acetic acid and methyl formate are an example of two metameric bodies. Each contains 2 atoms of carbon, 4 of hydrogen, and 2 of oxygen ; their molecules are equal in size, but different in atomic structure. The latter fact may be expressed by the following formulae : C'^HSQ.OH acetic acid CH30.0CH methyl formate The first expresses that acetic acid contains a group of atoms, C^ffO, acetyl, which is united with hydroxyl, OH ; the second, that methyl formate contains a group, CHO, formyl, which is united with oxymethyl, CH^O. The difference in the atomic arrangement becomes evident, if the preceding formulae be developed in the graphic manner. 0-H 0-CH^ I I c=o c=o 1 I CH« H Acetic acid. Methyl formate. The theory of atomicity has thus enabled to discover the atomic structure of a great number of combinations, and to explain numerous isomerisms. Acetic acid and glucose or grape-sugar present an example of^ polymerism. Both contain the atoms of carbon, hydrogen, and oxygen, united together in the same proportions, but the molecule of the second contains three times as many of each a^ that of the first. C2H402 acetic acid. 3 X C2H402 = C6H1206 glucose. Among the more important and better known cases of po- lymerism, may be mentioned the numerous hydrocarbons which present the centesimal composition of ethylene or olefiant gas, and which differ from it by the regularly increasing number of their atoms of carbon and hydrogen. These bodies form the following homologous series : C2H* ethylene. C^Iie propylene. C*H8 butylene. C^Hio amylene. FUNCTIONS OF ORGANIC COMPOUNDS. 447 Within recent years chemists have been called upon to ex- plain still another kind of isomerism ; the atoms constituting the molecules of different substances may be not only the same in kind and number, they may be even similarly grouped. Thus there are three acids known to have the formula COOH. CH(OH).CH(OH).COOH, but they differ markedly in cer- tain physical properties. In such cases it is now generally held that the differences are caused by different arrangement of the atoms in space. (See page 614.) FUNCTIONS OF OKGANIC COMPOUNDS. In the study of mineral chemistry it has been seen that bodies present great differences in properties, according to their composition. Some are simple and apt to enter into combina- tion ; others are compound and indifferent ; the first are more or less energetic in their affinities, the others saturated and satisfied. In one case, we have examined either more or less powerful acids or bases, some of which are hydroxides, as potassa and soda, others are oxides, as those of lead and silver. In the other case we have studied the salts result- ing from the union of the former bodies. In organic chemistry we again encounter various kinds of bodies which have different functions, according to their com- position. It may be said, in a general manner, that the properties of compound bodies depend upon the nature of the atoms and their arrangement in the molecule. In treating of isomerism, the influence of the latter condition has been indicated ; that of the former is still more powerful. Water and potassium hydroxide are both constituted, and in an analogous manner, of three elementary atoms. Each con- tains one atom of oxygen united to two monatomic atoms. HOH KOH Water. Potassium hydroxide But what a difference in their properties ! But may not this be expected when it is considered that one contains the energetic metal potassium, in the place occupied in the other by the light gas hydrogen ? Is the difference between potash and water greater than that between potassium and hydrogen ? 448 ELEMENTS OP MODERN CHEMISTRY. And if for tlie two atoms of hydrogen we substitute two atoms of chlorine, is it not to be expected that hypochlorous oxide Cl-O-Cl the molecule of which is similar in structure to that of water. shall differ from the latter in its properties as much as chlo- rine differs from hydrogen ? It is thus that the nature of the elements contained in compound bodies is the dominant condi- tion in the manifestation of their properties. The following considerations are of a nature to demonstrate the truth of this proposition inasmuch as concerns organic compounds : MONATOMIC RADICALS. Saturated Hydrocarbons. — The hydrocarbons belonging to the series of marsh gas are all saturated. Consider, for example, C^H® ; all of the atomicities of two atoms of carbon are satisfied by the union of the latter together and with six atoms of hydrogen. HH H-C-C-H I I HH Ethane, or ethyl hydride. It is the same with all of its homologues ; the hydrides of propyl, butyl, amyl, etc., are all saturated hydrocarbons, as will be seen by developing the formula of any one of them, pentane, for example : HHHHH I I I I I H-C-C-C-C-C-H I I I I I HHHHH Pentane, or amyl hydride. All of these bodies are incapable of fixing other elements by direct addition, but they may be modified by substitution, that is, one or several of their atoms of hydrogen may be replaced by other elements. Monatomic Chlorides, Bromides, and Iodides. — By the reaction of bromine upon any of the hydrocarbons, we may MONATOMIC RADICALS. 449 obtain compounds containing an atom of bromine in the place of an atom of hydrogen. C'H« + Br^ = C'WBr + HBr Ethane. Ethyl bromide. A saturated and indifferent hydrocarbon is thus converted into a bromide. The corresponding chloride and iodide exist, possessing the same constitution as the primitive hydrocarbon, and forming with it the following series : C2H6 ethane, C2H5C1 ethyl chloride. C2H5Br ethyl bromide. C2H5I ethyl iodide. To the other hydrocarbons correspond chlorides, bromides, and iodides analogous to the preceding. Thus, the following groups are known : CH* methane. C^Hi^ pentane. CH301 methyl chloride. C^HUCl amyl chloride. CH^Br methyl bromide, C^HiiBr amyl bromide. CH3I methyl iodide, C^HUI amyl iodide. All of these bodies may be made to undergo the most varied transformations. They may be attacked by a number of re- agents, to which they present a hold, as it were, since the chlo- rine, bromine, and iodine which they contain are gifted with powerful affinities. The residues resulting from the subtraction of the chlorine, bromine, or iodine then enter into other combinations. It will be remarked that these residues represent the saturated hydro- carbons from which one atom of hydrogen has been removed. CH^ = CH^Br — Br, or CH* — H C^H^ = C^ffBr — Br, or C'W — H C^H^i = C^H"Br — Br, or C^H^^ — H The atoms of carbon contained in these residues, CH^, C^H^, and C^H", are no longer entirely saturated, since CI, Br, I, or H has been removed, elements which satisfied one atomicity. Therefore, these residues are capable of entering other com- binations, but as they possess only one free atomicity, they can only saturate one when they combine. This is expressed by saying that they play the part of monatomic or univalent radicals. The chlorides, bromides, and iodides from which they are derived contain but one atom of the halogen. dd 38* 450 ELEMENTS OE MODERN CHEMISTRY. Alcohols. — The neutral hydroxides corresponding to the preceding chlorides, bromides, and iodides, are called alcohols. If ethyl iodide be heated for a sufficiently long time with potassium hydroxide, potassium iodide will be formed, and the alkaline liquid will contain alcohol which may be separated. This body is ethyl hydroxide, and is formed according to the following reaction : C^H^I + KOH == KI 4- C^HIOH Ethyl iodide. Ethyl hydroxide. It is formed, as is seen, by double decomposition. The potassium having removed the iodine from the ethyl iodide, the monatomic residue C^H^ combines with the monatomic residue OH. Alcohol is then the hydroxide which corresponds to the iodide, C^H^I, and to the hydrocarbon, C^H^ Analo- gous hydroxides correspond to the other hydrocarbons of the same series ; they constitute the series of monohydric alcohols, and may be defined as derived from the saturated hydrocarbons by the substitution of the group hydroxyl for one atom of hydrogen. The alcohols now known are numerous : the follow- ing are some of them : CH3.0H methyl hydroxide, or methyl alcohol. C^H^.OH ethyl hydroxide, or ethyl alcohol. C^H'^.OH propyl hydroxide, or propyl alcohol. C*H9.0H butyl hydroxide, or butyl alcohol. C^Hii.OH amyl hydroxide, or amyl alcohol. C^H^^.OH hexyl hydroxide, or hexyl alcohol. C^H^s^OH heptyl hydroxide, or heptyl alcohol. C^Hi'^.OH octyl hydroxide, or oetyl alcohol. Each member of this series differs from that which follows by — CHI All are allied by analogous properties. These two conditions characterize homologous bodies. The alcohols of which the general formula is C"H^''"*"^OH, form one of the most important series of homologues. If one of these alcohols be heated with hydrochloric, hydro- bromic, or hydriodic acid, water will be formed and the alcohol will be converted into a monatomic chloride, bromide, or iodide. In this reaction the hydroxyl, OH, is replaced by chlorine, bromine, or iodine. C^H^OH -f HCl = WO H- C^H^Cl Ethyl hydroxide. Ethyl chloride. The bodies thus formed are the monatomic chlorides, bro- MONATOMIC RADICALS. 451 mides, or iodides before considered. These experiments show the relations which exist between the latter compounds and the corresponding hydroxides, which are the alcohols. Monobasic Acids. — Acetic acid, which exists in vinegar, is a derivative of alcohol, of which it is one of the products of oxidation. It is formed under many conditions, one of which is the oxidation of alcohol vapor on contact with platinum black and the air. C'ff.OH -{. 0' = C'H^O.OH + H^O Alcohol. Acetic acid. In this reaction an atom of oxygen removes two atoms of hydrogen to form water, and the place of these two atoms of hydrogen is filled by another atom of oxygen. The group ethyl, C^H^, thus becomes the group acetyl, C^H'''0, and if alcohol be the hydroxide of ethyl, acetic acid is the hydroxide of acetyl. We can account for this reaction by developing the formulae of alcohol and acetic acid according to the principles before explained. HH HO H-C-C-OH + 0^ =:= H-C-C-OH + H^O I I I HH H Alcohol. Acetic acid. In alcohol, the second carbon atom is combined with two atoms of hydrogen and with one group hydroxyl, while in acetic acid it is combined with an atom of oxygen and a group hydroxyl. Acetic acid contains two atoms of carbon united together, and combined, the one with H^, the second with and OH. It is thus formed of a group CH^ united to a group CO-OH = CO^H. There exist many other acids analogous to acetic acid, and derived, like it, by oxidation of the monatomic alco- hols of the series C"H"^"+^OH. All of these acids contain a hydrocarbon group analogous to methyl, combined with the group CO^H :=: CO-OH. The hydrogen of the latter group can be readily replaced by an equivalent quantity of metal. This hydrogen is said to be strongly basic, and all of the organic acids which contain a single group, CO^H, united to a hydro- carbon group, are monobasic like acetic acid. The homologues of the latter form the followino; series : 452 ELEMENTS OF MODERN CHEMISTRY. C H2 02 = H -C02H formic acid. C2 H* 02 = C H3 -C02H acetic acid. C3 H6 02 = C2H5 -C02H propionic acid. C4 H8 02 = C3H7 -C02H butyric acid. C5 H10O2 ^ C*H9 -C02H valeric acid. C6 H1202 = C5H11-C02H caproie acid. 07 H1402 = C6H13-C02H cenanthic acid. C8 H1602 = Cmi5-C02H caprylic acid. C9 H1802 _ C8H17-C02H pelargonic acid. C10H2002 = C9H19-C02H capric acid, etc. The first series of formulae indicates simply the nature and number of atoms contained in the acids of the series CH^'^O^. They are empirical formulae. The second series gives certain indications upon the relations existing between these atoms. They are rational formulae, and when developed so as to ex- press the relations between all of the atoms, they become constitutional formulae. Compound Ethers. — The compound ethers are combina- tions which represent acids of which the hydrogen has been replaced by a hydrocarbon group. If one of the alcohols of the preceding series, ordinary alco- hol, for example, be heated for a long time with acetic acid, water will be formed, and a volatile, neutral liquid possessing an agreeable odor may be separated from the product ; this sub- stance is ethyl acetate, or acetic ether. It is formed according to the following reaction : Alcohol. Acetic acid. Ethyl acetate. On comparing this compound with alcohol, we find that it is formed by substitution of the group C^H^O, the existence of which is admitted in acetic acid, and which is called acetyl, for one atom of hydrogen in alcohol ; and this atom of hydro- gen which is replaceable by acetyl is that which is united to the oxygen in alcohol, — that which forms a part of the hydroxyl group. The other atoms of hydrogen, those which constitute part of the group C^H^, cannot be replaced by acetyl. All of the acids can form with alcohol, and indeed with all of the alcohols, compounds analogous to ethyl acetate, and these combinations are called compound etheo-s, or ethereal salts. The property possessed by the alcohols of etherifying acids is general and characteristic of this class of compounds. Alco- hols which require for etherification but a single molecule of KETONES. 453 an acid analogous to acetic acid are called monohydric. Many exist which are not included in the preceding series. Aldehydes. — Acetic acid is not the only product of the oxidation of alcohol. There is another compound interme- diate between these two ; it results from the action of a single atom of oxygen upon the molecule of alcohol, which thus loses two atoms of hydrogen without other change. The new com- pound is aldehyde. CWO + = H^O + C^H^O Alcohol. Aldehyde. It is a very volatile liquid having a great tendency to become oxidized and converted into acetic acid. It forms crystalline combinations with the alkaline acid-sulphites. To the other alcohols of the series C"H^"+^0, and other acids of the series Qnjj2nQ2^ corrcspoud compounds analogous to aldehyde by their composition and by their properties. They form the following series : C^H^O aldehyde or acetaldehyde. C^H^O propionic aldehyde. C^HSQ butyric aldehyde. C5H10O valeric aldehyde, etc. Ketones. — When calcium acetate is submitted to dry distil- lation a neutral, volatile liquid is obtained, having a peculiar aromatic odor, and known by the name acetone. Q2JJ3Q2 Calcium acetate. Acetone. Calcium carbonate. To the other acids of the acetic acid series correspond bodies analogous to acetone, and forming with it a homologous series. These ketones are related by properties and composition to the aldehydes. Like the latter, they form crystalline combinations with the alkaline acid-sulphites. It may be considered that while aldehyde is the hydride of acetyl, acetone is the methyl- ide of acetyl, and that in general the ketones are derived by the substitution of a hydrocarbon group, analogous to methyl, for an atom of hydrogen in the aldehydes considered as hy- drides. CH^-CO-H CH^-CO-CH^ Aldehyde (acetyl hydride). Acetone (acetyl methylide). Hence, acetone contains two methyl groups united to a group, CO (carbonyl). Its mode of formation justifies this conclusion, 454 ELEMENTS OF MODERN CHEMISTRY. as shown in the following equation, in which the constitu- tional formula of acetic acid is employed : CH3-C0 0>^^ = CaCO^ + CH3-CO-CH3 Calcium acetate. Calcium carbonate. Acetone. Diketones. — Free acid radicals. — Like the methyl group, the radicals of the monobasic acids cannot exist alone, but only in combination with other atoms or groups. Just as two methyl groups unite to form dimethyl or ethane, so two acetyl groups are combined in diacetyl. Such compounds contain- ing two carbonyl groups are called diketones. CH3CO.COCH3 diacetyl CH3CO.COC2H5 acetyl propionyl, etc. Chlorides of Acid Radicals. — A compound is known in which the acetyl group is united with chlorine. Acetyl chlo- ride, C^H'O.Cl, is a monatomic chloride, like ethyl chloride C'^H^Cl, from which it is distinguished by the strongly electro- negative nature of its radical. If acetyl chloride be poured into water, it disappears in a short time with development of heat and the formation of acetic and hydrochloric acids. C2H30.C1 -f H20 = C^H^O.OH + HCl Acetyl chloride. Acetic acid. To acetyl chloride correspond other chlorides which contain radicals of acids analogous to acetic acid. When they are treated with water they yield hydrochloric acid and the acids corresponding to their radicals. C3H50.C1 C3H50.0H Propionyl chloride. Propionic acid. C^H^O.Cl C*H70.0H Butyryl chloride. Butyric acid. Amides. — If acetyl chloride be treated with ammonia, am- monium chloride will be formed, together with a solid, neu- tral, nitrogenized body called acetamide. C^HSCCI + 2NH3 = NH*C1 + C^HSQ.NH^ Acetyl chloride. Acetamide. There are many other compounds similar to acetamide, and known by the name amides. They are formed by the action of ammonia upon organic halides analogous to acetyl chloride. They are also formed by the action of heat upon the ammonia- cal salts of the monobasic acids. The latter compounds then lose one molecule of water, and are converted into amides. C^H^O.ONH* = C5H90.NH2 + H^O Ammonium valerate. Valeramide. COMPOUND AMMONIAS. 455 Acetamide may be regarded as ammonia in wliieli an atom of hydrogen lias been replaced by the radical acetyl. ( H ( C^H^O r C^H^O Ammonia. Acetamide. Valeramide. Compound Ammonias, or Amines. — If ethyl iodide be heated with ammonia, one of the products of the reaction will be the hydriodide of a base derived from ammonia by the sub- stitution of an ethyl group for an atom of hydrogen. C^H^I + NIP = (C^H5)NHIHI Ethyl iodide. Ethylamine hydriodide. In this reaction, other ethylated bases are formed, independ- ently of ethylamine, among which must be mentioned diethyl- amine and triethylamine. All present the most striking anal- ogy to ammonia. They may be regarded as ammonia in which one, two, or three atoms of hydrogen have been replaced by one, two, or three ethyl groups. Ammonia. The other alkyl groups, C°H^''+^, can in the same manner replace one or more atoms of hydrogen in ammonia. The products are bases having constitutions analogous to those of the ethyl bases. They are called amines, or compound ammonias. It is necessary that the signification of the formulae above given and those that are to follow shall be clearly understood. They are examples of typical notation, and indicate the rela- tions of the compounds with the type ammonia. N"' ] H (H The brace joining the three hydrogen atoms signifies that the whole three are united to a single atom of triatomic nitro- gen, with which each exchanges one atomicity; this may be expressed by writing the formula for ammonia thus : C^H^) C'W) C^H^) H y-N C'W [ N C'W Y N Hj H) C'W) Ethylamine. Diethylamine. Triethylamine. 456 ELEMENTS OF MODERN CHEMISTRY. What, then, takes place when one or more atoms of hydro- gen are replaced by a group like ethyl ? The latter exchanges one atomicity with the nitrogen atom, precisely as the hydro- gen atom did, and combines with the nitrogen by one of the atoms of carbon of the group ethyl, CH^-CH^, which requires the satisfaction of one atomicity. This is clearly expressed in the following graphic formulae : H H N-CH^- I H CH^ N-CH^-Cff CH^-CH^ Ethylamine. Diethylamine, However, such formulae would be too cumbrous for ordinary use, and our formulae must be more condensed. /C^H^ /C^m N^H N^C'H^ NCC^'Hsy ^H ^H Ethylamine. Diethylamine. Triethylamine. Phosphines. — Arsines. — Stibines. — There exist several se- ries of combinations belonging to the same type as the com- pound ammonias, but in which the nitrogen is replaced by phosphorus, arsenic, or antimony. These compounds are de- rived from the hydrogen compounds of phosphorus, arsenic, and antimony by the substitution of one or more alkyl' groups for one or more atoms of hydrogen. H^ cm'-) C^H^-) C'H^") H VP H fP C'H^ [ P C^H^ [ P HJ H ) H) cw) Hydrogen phosphide. Ethylphosphiue. Diethylphosphine. Triethylpliosphine H) CH^) CW) cnn CH^' [ As CH^' j H V As H V As CW [ As HJ HJ CI j Hydrogen arsenide. Methylarsine. Dimethylarsine Trimethylarsine. H) chloride. C^H^^ XT ( Ol. C^H^ [ Sb C'H^) Hydrogen antimonide. Triethylstibine. Organo-metallic Compounds. — Ethyl and its congeneric radicals, methyl, amyl, etc., can enter into combination not only with nitrogen, phosphorus, arsenic, etc., of which they saturate one or more atomicities, but with a large number of ORGANO-METALLIC COMPOUNDS. 457 metals. Thus, zinc, wliicli is diatomic, can combine with two ethyl groups to form zinc ethyl. Mercury, also diatomic, can unite with one or two ethyl or methyl groups, etc. In the second case, the new combination is saturated ; in the first, it is monatomic, (Hg"C^H^)', and re- quires for saturation an atom of a monatomic element, or a monatomic group, iodine, for example. Hg |(..H^ Hg I J Mercur-ethyl. Mercur-monethyl iodide. Bismuth, which is triatomic, can fix three ethyl groups. Bi'" \ cm' (cm' Bismuth-ethyl. Stanno-tetrethyl is formed by the union of four ethyl groups with one atom of tetratomic tin. If the four atomicities of tin be not all satisfied, non-satu- rated compounds may be formed. Sn'' ] y,,^, -Sn-^ C'^H^ or -Sn-^C^H^ Stanno-diethyl. Stanno-triethyl. Stanno-diethyl is known in the free state, but stanno-triethyl doubles its molecule as soon as it is set at liberty, combining with itself, as it can combine with iodine. ISn'-(C^H^)^ (C^H5)"^Sn^^-Sn'-(C'H5)3 = Sn^CC^IF)^ stanno-triethyl iodide. Sesquistannethyl. Non-saturated compounds are apt to combine with other elements or radicals. Stanno-tetrethyl, which is saturated, does not possess this faculty. The bodies just mentioned belong to the class of organo- metalUc compounds. Their study is of great importance in the history of the atomicity of the metals, that is, their power of saturation. The theoretical considerations concerning them have been discussed by Frankland, Baeyer, and Cahours. u 39 458 ELEMENTS OF MODERN CHEMISTRY. Monatomic Radicals. — From the preceding summary may be understood the position occupied in organic chemistry by certain groups containing carbon, groups that are distinguished as monatomic because they can manifest but a single atomicity. Only a single monatomic atom or group is wanting that all of the carbon atoms contained in these groups may be entirely saturated. These groups of atoms or radicals cannot exist in the state of liberty, but they can pass from one compound to another, replacing a single atom of hydrogen or other mon- atomic element^ and consequently pla^dng the part of that ele- ment in the new combination. This is expressed by saying that these groups act as monatomic radicals. To indicate the constitution of the combinations containing such groups, and especially the metamorphoses that they may undergo by exchanging these radicals by double decomposition, it is convenient to designate the latter by expressions written separately in the formula and distinct from those for the other elements. The composition of all of the bodies which have just been reviewed may be represented by very simple formula3, by comparing them to hydrogen compounds, such as free hydrogen, or hydrochloric acid, water, and ammonia. The notation then assumes a typical form, exceedingly clear for the interpretation of the majority of reactions. The following are the typical formulae for the combinations that have been considered : Type HH, Type g jo. Type H ^N. (eff)Cl (c-h;.)„ H fN Ethyl chloride. Ethyl hydrate. Ethylamine. (C^H^O)Cl Acetyl chloride. Ethyl hydroxide. Diethylamine. (C^H30)H (C^^jo {(JW) ) Aldehyde. Acetic acid. Triethylamine. (C^H^O)(CH0 H fN H) Acetone. Ethyl acetate. ■ Acetamide. POLYATOMIC RADICALS. 459 POLYATOMIC RADICALS. If chlorine and defiant gas, or ethylene, be mixed in equal volumes, both gases disappear and are converted into an oily substance, which was formerly called Dutch liquid. This body results from the combination of a molecule of ethylene with a molecule (two atoms) of chlorine. It is ethylene chloride. C^H^ + CP = C^H^CP Ethylene. Ethylene chloride. If the constitution of ethylene gas, C^H*, be compared with that of the saturated hydrocarbon ethane, C^H®, which like the former contains two atoms of carbon, it will be noticed that it contains two atoms of hydrogen less. C'H^ — H^ = C'H* In ethylene the six atomicities of the pair of carbon atoms are not saturated. Hence that gas can absorb directly two atoms of chlorine or bromine to form a saturated compound. HH H H HH H-C-C-H -C-C- Cl-C-C-Cl II II II HH HH HH Ethane. Ethylene. Ethylene chloride. It is a diatomic radical, or alkylene, and it can exist in the free state because until other atoms are presented to satisfy the atomicities of the two atoms of carbon those two atoms are bound together by a double affinity. Thus, H^C=CH'. One of these bonds is loosed when the ethylene manifests its affini- ties and enters directly into combination, because the affinity of carbcr for chlorine or "uch an element is greater than its affinity for carbon Ethylene is the first of a numerous class. The following bodies form with it the homologous series CH^"" •. C2H4 ethylene. C^H^ propylene. C^HS butylene. C5H10 amylene. C6H12 hexylene. C^i* heptylene. C8H16 octylene. C9H18 nonylene. C10H20 decylene, etc. 460 ELEMENTS OF MODERN CHEMISTRY. All of these bodies are able to fix directly two atoms of chlorine or bromine. When they enter into combination, they take the place of two atoms of hydrogen. They can pass by double decomposition from one compound to another, and their combinations may undergo various metamorphoses analogous to those already indicated. Dihydric Alcohols, or Glycols. — The glycols are compounds in which the two atomicities of the alkylenes are saturated by two hydroxyl groups. The two atoms of bromine in ethy- lene bromide, C^H^Br^, may be replaced by two hydroxyl groups (OH), and the resulting combination is ethylene hydroxide. The two atoms of hydrogen united to the oxygen in the hydroxyl groups in glycol may both be replaced by acid radi- cals analogous to acetyl, just as the single atom of hydrogen in the single hydroxyl group of a monatomic alcohol may be replaced by an acid radical. This is characteristic of a dihydric alcohol. To ethylene hydroxide, or ordinary glycol, correspond the hydroxides of the other hydrocarbons homologous with ethy- lene. The following glycols are known : C^H^jol glycol. r OTT C^HS j Qjj propyleneglycol. C4H8 I ^ butyleneglycol. C5H10 I Qg amyleneglycol. C6H12 1 ^ hexyleneglycol, etc. Around each of these bodies are grouped a great number of derivatives, among which we can only consider the ethers^ acids, and compound ammonias. Ethers of the Glycols. — The ethers of the glycols result from the substitution of alcoholic or acid radicals for the hydro- gen of the groups OH. One or both of these hydrogens may be thus replaced, and the following examples will illustrate the constitution of the compounds so formed : ^ ^ 1 OH ^^ 1 O.C2H5 ^^ I OH ^^ 1 O.C2H30 Monethylic glycol. Diethylic glycol. Glycol monacetate. Glycol diacetate. POLYATOMIC RADICALS. 461 Hydroxy-acids and dibasic acids result from the oxida- tion of the glycols. Their formation and constitution may be understood by developing the formulae of the hydrocarbons which constitute the radicals of these glycols. Ordinary glycol may yield two acids by oxidation, the first resulting from the substitution of an atom of oxygen for two atoms of hydrogen, the second from the substitution of two atoms of oxygen for four atoms of hydrogen. The following for- mulae express the constitution and derivation of these com- pounds : CH^ CH^Br Cff.OH CHIOH CO.OH CH^ bwBr CHIOH CO.OH C!O.OH Ethylene. Ethylene bromide. Glycol. Glycolllc acid. Oxalic acid. Grlycollic acid and oxalic acid are, therefore, both derived from the same dihydric alcohol ; but the former is monobasic because it contains but a single atom of hydrogen that can be replaced by a metal. The second is dibasic, for it contains two atoms of hydrogen that are replaceable by an equivalent quantity of metal. This basic hydrogen is that which forms part of the group CO'^H. Oxalic acid is composed simply of two groups -CO'^H ; it is dibasic. Glycollic acid contains but one, and it is consequently monobasic. The hydrogen united to the oxygen in the group -CH^OH is called alcoholic hydro- gen ; it may be replaced by an acid radical, but it cannot be easily replaced by a metal. All bodies containing a group CHI OH are alcohols, and all bodies containing a group CO.OH are acids. The alcohols and acid are thus defined by their constitution. Grlycollic acid is at the same time an alco- hol and an acid, — an hydroxy-aeid, — for it contains both a group CH'^.OH and a group CO.OH. There exists a series of acids homologous with glycollic acid, and another series homologous with oxalic acid. Both series are derived from the higher dihydric alcohols. Diatomic Ammonias, or Diamines. — Compounds exist which hold the same relation to the dihydric alcohols as ethyl- amine and its homologues to the monohydric alcohols. Such a compound is ethylene-diamine. Its relations with ethylene chloride and glycol are expressed by the following formulae : C^H*<^} G"^'NH It is, then, possible that there may be two isomeric modifica- tions of cyanuric acid. There are certainly two isomerides of its ethers : the trimethylic ether of the true cyanuric acid, C^N^(OCH^)^, is formed by the action of cyanogen chloride on sodium methylate ; and, on the other hand, there are ethers of tricarbimide or isocyanuric acid, which will be described farther on. CARBAMIC ACID — UREA. 477 CARBAMIC ACID. OTT This acid is not known in the free state. Its ammonium salt is commonly known as anhydrous ammonium carbonate ; its ether, urethane, or ethyl carbamate, is described on page 515. Ammonium carbamate. Urethane. When two volumes of ammonia gas and one volume of carbon dioxide are mixed over the mercury trough, a white mass is obtained ; this exists in the ammonium carbonate of commerce, and constitutes ammonium carbamate. At 60°, it is dissociated and resolved into its constituent gases, one molecule of ammonium carbamate yielding four volumes of ammonia and two volumes of carbon dioxide. Water converts it into ammonium carbonate. CO^ Methyl chloride. Methyl oxide. CHOP ^ CW>^ Chloroform. Methyl acetate. These compounds will be but briefly described. METHANE. (marsh gas.) The inflammable gas which is disengaged from the mud of marshes is impure methane. The same gas is frequently evolved in the galleries of coal mines, and constitutes the fire-damp of miners. It is produced artificially by the action of an excess of alkali upon acetic acid (Persoz, Dumas). Preparation. — Methane is most conveniently prepared in the pure state by strongly heating in a glass flask or retort a mixture of 1 part of sodium acetate, 1 part of potassium hy- droxide, and 1 1 parts of lime ) the lime is added to prevent the action of the potassium hydroxide upon the glass. The gas may be collected over water. NaC^H^O^ + NaOH = CH* + Na^CO^ Sodium acetate. Methane. Properties. — Methane is a colorless, odorless gas. Its den- sity is 0.559 ; it is but slightly soluble in water, somewhat more so in alcohol. It burns in the air with a pale, almost non- luminous flame. A mixture of methane and oxygen explodes violently on the application of flame or the passage of an electric spark. If two volumes of methane and four volumes of oxygen be introduced into an eudiometer and the spark be passed, a bright flash is visible. After the combustion, the mercury rises in the tube, and it is found that the volume of gas is reduced to one- METHYL HYDROXIDE. 485 third of the original volume (to 2 volumes); if a solution of caustic potash be introduced, the whole of the remaining gas will be absorbed. 2 volumes of methane produce in burn- ing 2 volumes of carbon dioxide, and require 4 volumes of oxygen. This experiment establishes the molecular com- position of methane. 2 volumes of carbon dioxide contain 2 volumes of oxygen combined with 1 volume (1 atom) of carbon ; consequently one molecule of marsh gas contains one atom of carbon. The other 2 volumes of oxygen consumed have combined with 4 volumes of hydrogen, contained in 2 volumes of methane ; that is, the molecule of methane contains 4 atoms (=2 molecules) of hydrogen. Hence it follows that a molecule of methane contains 1 atom of carbon and 4 atoms of hydrogen. A mixture of chlorine and methane explodes when exposed to direct sunlight. In diffused daylight, the action is less violent, especially if an inert gas, such as carbon dioxide, be added. In this case, methyl chloride is formed, and in pres- ence of an excess of chlorine, methylene chloride, chloroformj and jfinally carbon tetrachloride. CH* + CP = HCl + CH^Cl methyl chloride. CH* + 2CP = 2HC1 + CH^CP methylene chloride. CH* + 3CP = 3HC1 + CHCP chloroform. CH* + 4CP = 4HC1 + CCP carbon tetrachloride. It is seen that in these reactions the chlorine is substituted for hydrogen, atom for atom. Inversely, when these substitution products are submitted to the action of nascent hydrogen, an inverse substitution is effected : they are reconverted into methane. This may be accomplished by putting the chlorine compounds in contact with sodium amalgam and water. The latter is decomposed by the sodium, and constitutes a source of hydrogen (Melsens). CHCP + 3H2 = 3HC1 + CH* METHYL HYDROXIDE, OR METHYL ALCOHOL. (wood-spirit.) CH*0 = CH3-0H The products of the dry distillation of wood contain about one per cent, of a spirituous liquid, which was discovered in 41* 486 ELEMENTS OF MODERN CHEMISTRY. 1812 by Taylor, and named wood- spirit. It is separated by several distillations and rectifications over lime ; for, being more volatile tlian the other products, it passes over first. The methyl alcohol of commerce is always impure, and cannot be purified by fractional distillation, as it contains a considerable proportion of acetone, of which the boiling-point (56°) is very near that of niethyl alcohol. The impurities may be removed by treating the impure alcohol with cal- cium chloride, with which it forms a crystalline compound, CaCP -j- 4CH^.0H. The crystals are drained, dried between folds of blotting-paper, and distilled with water, when they yield dilute methyl alcohol. This is rectified by repeated distillation, and finally dehydrated over quick-lime. To obtain the alcohol perfectly pure, an ether of methyl is prepared and freed from all impurities by either crystal- lization or distillation. The ether is then decomposed with an alkaline hydroxide, and the methyl alcohol formed is dis- tilled ofi" and dehydrated over lime. Thus, methyl oxalate is prepared by treating the still impure methyl alcohol with oxalic acid, and is purified by crystallization. 2CH10H -I- eO^ff == (CH^.C^O* + 2H20 Methyl hydroxide. Oxalic acid. Methyl oxalate. The methyl oxalate is boiled with potassium hydroxide, and the methyl alcohol which distils is rectified over quick- lime. (CWy.C'O' + 2K0H = 2CH10H -f C^^O^K^ It is a mobile, colorless liquid, having an alcoholic odor. It boils at 66.5°. Its density at 0° is 0.8142. It is inflammable and burns with an almost colorless flame. It is miscible with water, alcohol, and ether in all proportions. It dissolves caustic baryta, forming a definite combination. Potassium and sodium react energetically upon methyl hy- droxide ; the metal dissolves with disengagement of hydrogen and formation of an alkaline methylate or methoxide. CH'-OH CH'-OK Methyl hydroxide. Potassium methylate. If methyl alcohol be placed under a bell-jar containing also some watch-glasses filled with platinum black, so that the vapor of the wood-spirit mixed with air may come in contact with the finely-divided metal, it is found that the liquid soon becomes CHLORIDE, BROMIDE, AND IODIDE OF METHYL. 487 strongly acid. By the slow oxidation of the wood-spirit under these conditions, formic acid and formaldehyde are produced. Cff-OH + 0^ = CHO-OH + H^O Methyl hydroxide. Formic acid. 2CH3-OH + 0' = 2H-CH0 + 2H^0 Formaldehyde. METHYL OXIDE, OK METHYL ETHER. (CH3)20 When methyl alcohol is heated with twice its weight of concentrated sulphuric acid, a colorless gas is disengaged, which is methyl oxide. 2CH3.0H = (Cff)^O + WO Methyl hydroxide. Methyl oxide. This gas is formed by the dehydration of methyl alcohol and the linking together of two methyl groups by an atom of oxygen. Methyl ether is readily absorbed by water, and is even more soluble in alcohol and ether. It liquefies at — 23°. CHLORIDE, BROMIDE, AND IODIDE OF METHYL. These compounds may be regarded as marsh gas in which one atom of hydrogen is replaced by an atom of chlorine, bro- mine, or iodine. They are formed by the action of hydrochloric, hydrobromic, and hydriodic acids upon methyl alcohol. Cff.OH + HCl = CH^Cl + ffO Hence they are considered as derived from the hydracids by the substitution of the group methyl for the atom of hydrogen. HCl (CH3)C1 Hydrochloric acid. Methyl chloride. Methyl chloride is a colorless gas, having an agreeable odor. When exposed to intense cold, it condenses to a liquid which boils at — 22°. When heated for a considerable time with a concentrated solution of potassium hydroxide, it is converted into methyl alcohol. Liquid methyl chloride is employed in- dustrially in the production of cold, and large quantities are consumed in the manufacture of dye-stuffs. 3Iethi/l iodide, CH^I, boils at 43° ; its density at 0° is 2.1992. 488 ELEMENTS OF MODERN CHEMISTRY. It is made by gradually adding iodine to a mixture of methyl alcohol and amorphous phosphorus, and distilling. The dis- tilled liquid is mixed with water, which precipitates the iodide ; the dense liquid is separated, dried with calcium chloride, and distilled. METHYLENE CHLOEIDE. CH^CP This compound may be prepared by the action of chlorine on methane, or on methyl chloride, or by the reduction of chloroform by nascent hydrogen. The latter method is the more convenient. An alcoholic solution of chloroform is treated with zinc in a flask connected with a condenser, and hydrochlo- ric acid is introduced in small portions. Methylene chloride and unaltered chloroform distil over, and towards the close of the operation the distillation is continued by the aid of heat. The distillate is then washed, dried, and submitted to fractional distillation. Methylene chloride is a mobile liquid, having an odor resem- bhng that of chloroform, and boiling at 40°. Its density at 0° is 1.36. METHYLENE IODIDE, CH^P, is made by the action of hydriodic acid on chloroform or iodo- form in sealed tubes at a temperature of 150°. CHOP + 4HI = CH^r H- 3HC1 + P It is also formed by the action of sodium ethylate on iodo- form. It is a yellow, highly refracting liquid, having a density of 3.342 at 5°, and soHdifying at 2°. It boils at 182°, with partial decomposition. OCH' Methylal, or the dimethylic ether of methylene, CH^<^QpTj3, is obtained by the action of sulphuric acid and manganese di- oxide on methyl alcohol. It is a limpid liquid, boiling at 42°. Its reactions are identical with those of formaldehyde (p. 545). QQ2JJ5 Methylene diethylate, CH^W0 Nitromethane. Methylamine. METHYLNITROLIC ACID. CH2N203==CH<:^^'2 This remarkable combination has been obtained by Y. Meyer by the action of nitrous acid upon nitromethane. CH^NO^) + NO.OH = CH(x^^^jj + H^O It is seen that in this compound two atoms of hydrogen of the methyl group CH^, are removed by an atom of oxygen of the nitrous acid, and replaced by the residue (N.OH). Methylnitrolic acid is prepared by dissolving 5 grammes of nitromethane in water, and adding first a dilute solution of potassium nitrite cooled to 0°, then dilute sulphuric acid also cooled to 0°, and finally dilute solution of potassium hydrate as long as the red color persists. At this moment, sulphuric acid is again added until the liquid is decolorized ; the solution is then saturated with calcium carbonate, and agitated with ether, which dissolves the methylnitrolic acid. FULMINATES OF MERCURY AND SILVER. 495 After tlie evaporation of the ether, the acid remains as large, transparent, colorless prisms, fusible at 54°, but decomposing at the same time into formic acid and nitrogen. Dilute sul- phuric acid decomposes methylnitrolic acid into formic acid and nitrogen monoxide. CHWO^ = CH^O^ + N^O Formic acid. Nitrogen monoxide. The crystals decompose spontaneously in a few days. FULMINATES OF MEKCURY AND SILVER. Among the important compounds related to the more simple organic combinations are those explosive salts known as fulmi- nates of mercury and silver. They are obtained by dissolving mercury or silver in nitric acid and adding alcohol to the still hot solution. In a few minutes a brisk effervescence takes place, and fulminate of mercury or of silver is deposited as a white, crystalline precip- itate. When dry, these bodies explode violently by either heat or percussion. Fulminate of mercury is the basis of percus- sion-caps. The composition of these salts is interesting. They are derived from fulminic acid^ a body which is isomeric with cyanic acid (Liebig, Gay-Lussac). According to Kekule, ful- minic acid is nitro-acetonitrile, CH^(NO^).CN, that is methane in which one hydrogen atom is replaced by the monatomic group NO^ and a second one by the cyanogen group (CN). More recent investigations by Nef and others make it appear probable, however, that it is carbj/loxime, C = NOH, in which a diatomic carbon atom is united with the group N = OH, which characterizes a large and important class of carbon compounds known as the oximes (page 554). In fulminate of mercury one atom of metal replaces two atoms of hydrogen in two molecules of the acid, while in the silver salt the metal replaces hydrogen atom for atom : the formula of mercury fulminate is 2C^N^0^Hg -f- H^O, and that of the silver salt C'N^O'Ag^ Free fulminic acid results when these compounds are decom- posed by strong acids. Its odor resembles that of hydrocyanic acid, and, like the latter, it is very poisonous. Upon heating with hydrochloric acid, it yields formic acid and hydroxylamine. 496 ELEMENTS OF MODERN CHEMISTRY. CACODYL, OR DIMETHYLARSINE. As2(CH3)4 This interesting compound has long been known in an im- pure state, having been first obtained in 1760 by Cadet as a product of the distillation of a mixture of potassium acetate and white arsenic (arsenious oxide). He collected in the re- ceiver an oily liquid, having an extremely offensive odor, and producing dense white fumes in the air. Hence the name fuming liquor of Cadet. Bunsen's investigation into the chemistry of this body and its combinations has become classic. According to his re- searches, the fuming liquor of Cadet is a mixture of two bodies, one of which, containing only carbon, hydrogen, and arsenic, plays the part of a radical : it is cacodyl ; the other body is the oxide of this radical. To obtain cacodyl in the pure state, the crude product is treated with hydrochloric acid, which converts the oxide of cacodyl into chloride. As^CCH^yO -f 2HC1 =z 2As(CH^)'Cl + WO Dimethylarsine oxide. Dimethylarsine chloride. This chloride, separated by distillation, and treated with zinc at 100° in sealed tubes, furnishes free cacodyl. The latter is a dense liquid boiling at 170°, and having a penetrating arsenical odor. It is very poisonous. It produces dense white fumes in the air, even taking fire spontaneously. Its vapor density is 7.101. According to this vapor density, free cacodyl is diarsenic tetramethyl, As^CH^)* = (CH=^)'As-As(Cff )^ Arsenic being either triatomic or pentatomic it is seen that cacodyl is not saturated; hence it can directly fix chlorine, oxygen, etc., yielding two series of compounds. Thus, one molecule of cacodyl, As^(CH^)*, can fix 1 or 3 molecules of chlorine, forming the two chlorides : As2(CH3)4 + C12 = 2As(CH3)2Cl As2(CH3)4 + 3C12 = 2As(CH3)2Cl3 To the two chlorides correspond the bromides, iodides, oxides, sulphides, etc. The oxides are Cacodyl oxide [As(CH3)2]'20 Cacodylic acid As(CH3)20.0H ETHYL COMBINATIONS. 497 Independently of the cacodyl compounds, other combinations of arsenic and methyl are known, — the metliylarsines and the compounds of methylarsonium. These bodies form two series, which were discovered and studied by Baeyer, and which belong to the type AsX^ and AsX^. The compounds of the first kind are not saturated, and can combine with CP, or the equivalent of CP, passing into the state of the saturated compounds of the series AsX^. Series AsX^ Series AsX^ As(CH3)3 Triraethylarsine. As(CH3)4Cl Tetramethylarsonium chloride. As(CH3)2Cl Dimethylarsine monochloride. As(CH3)3C12 Triraethylarsine dichloride. As(CH3)Cr-^ Mouomethylarsine dichloride. As(CH3)2Cl3 Dimethylarsine trichloride. AsCls Arsenic trichloride. As(CH3)Cl* Monomethylarsine tetrachloride. [AsCl5] It is worthy of remark that the trichloride of arsenic is incapable of fixing CP, and passing into the state of penta- chloride, although the corresponding fluoride, AsF^, is known. These compounds need not be described. It may only be mentioned that trimethylarsine, As(CH^)^, is formed, together with cacodyl, by the action of methyl iodide on sodium arsenide. It is a liquid boiling below 100°. ETHYL COMBESTATIONS. The monatomic residue (C'H^)' = C'H« — H, which is the radical of ordinary alcohol, is called ethyl. Numerous com- pounds are known into which the radical enters. When combined with hydrogen, it forms a gas, C^H®, which is ethyl hydride or ethane. The chloride, bromide, iodide, and cyanide of ethyl were formerly designated as simple ethers. C2H5C1 ethyl chloride. C2H5Br ethyl bromide. C2H5I ethyl iodide. C3H5.cn ethyl cyanide. Ordinary alcohol is the hydroxide, ether is the oxide of ethyl. C2H5-OH ethyl hydroxide (alcohol). C2H5-0-C2H5 = (C2H5)20 ethyl oxide (ether). 99 42* ,_ 498 ELEMENTS OF MODERN CHEMISTRY. The neutral compound ethers are derived from the corre- sponding acids by the substitution of the radical C'^H^ for their basic hydrogen. C2H30-OH C2H30-OC2H5 Acetic acid. Ethyl acetate. I OH ^ "" 1 O.C2H5 Oxalic acid. Ethyl oxalate. roH ro.c^Hs PO^^OH PO^O.C2H5 (OH i0.C2H5 Phosphoric acid. Phosphoric ether (triethyl phosphate). Free Ethyl, or Butane, C*H^''. — When it is sought to obtain free ethyl by heating ethyl iodide to 150° with zinc in sealed tubes, the radical combines with itself, its molecule being doubled (Frankland). 2C2H5I + Zn =: ZnP + (C^H^)^ A gas is thus formed which liquefies at -|-1°- It was formerly named free ethyl, but is the hydride of butyl, or butane. Indeed, it is incapable of regenerating ethyl compounds containing the simple radical (C^H^). When treated with bro- mine, it yields hydrobromic acid and a bromide C*H^Br^, which, according to Carius, is identical with butylene bromide. Ethyl Hydride, Ethane, or Dimethyl, C^H« = CH^-CH^ — Frankland obtained this gas by treating zinc-ethyl with water. ZniQ'Wy + 2W0 = 2.Q'W + Zn(0H)2 Zinc ethyl. Ethane. Zinc hydrate. It is likewise formed when methyl iodide is heated with sodium in closed tubes. 2QW1 + 2Na = C^H^ + 2NaI It is a colorless gas, burning with a slightly blue, luminous flame. When treated with chlorine, it yields ethyl chloride and hydrochloric acid. ETHYL HYDROXIDE, OR ALCOHOL. C2H60 = CH3-CH2.0H Alcohol is the product of the fermentation of solutions which contain glucose, or a substance capable of transformation into glucose. It may be formed synthetically in various manners : 1. By passing ethylene gas into sulphuric acid (Hennell and ETHYL HYDROXIDE. 499 Faraday) and boiling the ethylsulphuric acid so formed (Ber- thelot). Ethylene. Ethylsulphuric acid. Ethylsulphuric acid. Alcohol. 2. By heating ethylene gas with hydriodic acid and decom- posing the ethyl iodide so formed with potassium hydroxide (Berthelot). C^H* + HI = C'Wl C^ffl + KOH = en^OH + KI 3. By bringing aldehyde in contact with sodium amalgam in presence of water. The nascent hydrogen formed in this case fixes upon the aldehyde, converting it into alcohol (A. Wurtz). C^H^O -f H^ = C^H^O Aldehyde. Alcohol. Preparation and Purification of Alcohol. — Alcohol is manufactured by distilling fermented liquors, such as wine, fermented juice of beet-roots, and the product obtained from the fermentation of malt, which is saccharified barley, corn, or other grain. The apparatus now used for this operation has reached such a degree of excellence that alcohol of 95 per cent, may be obtained immediately by one distillation. Absolutely pure alcohol is obtained by rectifying the alcohol of commerce over hygroscopic substances, such as anhydrous potassium carbonate, quick-lime, or caustic baryta. The last portions of water are removed, and absolute alcohol obtained by redistilling the rectified alcohol with caustic baryta. Or some sodium may be dissolved in the alcohol, which may then be rectified on a water-bath. Properties. — Alcohol is a colorless, mobile liquid, having an agreeable, spirituous odor. Density at 0°, 0.8095. BoiHng- point, 78.4° at the normal pressure. It freezes at — 130°. Alcohol mixes with water and ether in all proportions. Its mixture with water takes place with elevation of temperature and contraction of volume. The maximum contraction takes place when the two bodies are mixed in the proportion of one molecule of alcohol (46 parts) to three molecules of water (54 parts). 500 ELEMENTS OF MODERN CHEMISTRY. Alcohol absorbs moisture wben exposed to tbe air. It dis- solves many gases, liquids, and solids. Tinctures are solutions of various medicinal substances in alcohol. Among the simple bodies which are soluble in alcohol may- be mentioned iodine. Potassium and sodium hydroxides dis- solve in it readily, and the same is true of many of the mineral acids. Many of the chlorides are soluble in alcohol ; such are those of calcium, strontium, zinc, and cadmium, ferric, cupric, mercuric, and auric chlorides. Alcohol dissolves the natural alkaloids, the essential oils, resins, and fatty bodies, the latter, however, less readily than ether. Decompositions. — When vapor of alcohol is passed through a red-hot porcelain tube, it is decomposed into water, carbon monoxide, hydrogen, methane, and ethylene. Besides this, carbon is deposited in the porcelain tube, and a small quantity of naphthalene is produced (Th. de Saussure), as well as benzene and phenol (Berthelot). The principal products of the decomposition of alcohol at a dull-red heat are methane, hydrogen, and carbon monoxide. (JWO = CO + CH^ + H^ On the application of a burning body, alcohol takes fire and burns with a slightly luminous, bluish flame. On contact with platinum black, alcohol vapor mixed with air undergoes a slow combustion, which produces successively aldehyde and acetic acid. C^H^O + = C^H*0 -f H^O Alcohol. Aldehyde. Q'WO + = C'H^O' Aldehyde. Acetic Acid. Acetic ether and a small quantity of a volatile, neutral body, called acetal, are at the same time formed as accessory products (Stas). The lamp without flame of Dobereiner depends upon the slow combustion of alcohol. The wick of an ordinary spirit- lamp is surmounted by a spiral of platinum wire, so that when the lamp is lighted the spiral is heated to incandescence. If then the flame be extinguished, by covering it for an instant with a test-tube, the alcohol vapor continues to rise with the air around the still hot spiral, and undergoes a slow combustion. But the latter develops heat, and the spiral rapidly becomes ETHYL HYDRATE. 501 heated to incandescence, and if the current of air be regulated by a small glass chimney, the experiment may continue as long as the wick emits vapor of alcohol in sufficient quantity. Bodies rich in oxygen oxidize alcohol at ordinary tempera- tures ; such are chloric and chromic acids. If a little alcohol be poured upon some chromic acid placed upon a brick, the liquid is immediately inflamed and the chromic acid reduced to chromium oxide. Chlorine attacks alcohol with great energy, the final product of the reaction being a body which has received the name chloral (Liebig, Dumas). If a small piece of potassium or sodium be thrown into pure alcohol, the metal soon melts, and then dissolves with disen- gagement of hydrogen. The product of the reaction is a crys- talline, solid matter which is ethylate of potassium or sodium, that is, a body derived from alcohol by the substitution of an atom of an alkaline metal for an atom of hydrogen. C2H5^ C2H5^ C2H5^ H>^ K-^^ Na>^ Alcohol. Potassium ethylate. Sodium ethylate. Uses of Alcohol. — Alcohol is used as a combustible in spirit- lamps. In the arts, it is employed in the manufacture of ether, chloroform, perfumeries, and many other products. It is largely used in the laboratory, and in pharmacy, as a solvent ; it serves for the preservation of anatomical specimens. In France and England, alcohol employed for certain industrial uses is exempted from part of the tax, when it has previously been mixed with about one-tenth of wood-spirit and a few per cent, of mineral oils and resin. Such a mixture is unfit for the manufacture of brandy and liquors, but its usefulness as a solvent is in most cases unimpaired. Alcohol exists in fermented liquors, such as wine, cider, and beer. It is contained in much larger quantities in brandies, whiskeys, and spirits. These are products of the distillation of various alcoholic liquids. They are more or less rich in alco- hol. Brandy is prepared by the distillation of wine, cider, or the products of fermentation of cherry-juice (cherry-brandy), sugar-cane (rum), beet-root molasses (beet-brandy). Whiskey is distilled from fermented starchy materials, such as corn, rye, potatoes, etc., the starch being first saccharified. The richness of these materials in alcohol is indicated by the degrees of an 502 ELEMENTS OF MODERN CHEMISTRY. alcoholometer. The following table gives the strength of some of these liquors. (For wine, beer, etc., see page 648). BATTM^'S SPECIFIC ^"^^^^^'hOL "" HYDROMETER. GRAVITY. ^y VOLUME. Weak brandy 16° 0.9605 37.9 Proof spirits 19° 0.9420 60.1 Strong brandy 22° 0.9241 59.2 Ordinary alcohol .34° 0.8688 86.1 Rectified alcohol (strongest commercial) 40° 0.8296 95. Absolute alcohol 46° 0.8095 100. ETHYL OXIDE, OR ETHEE. (C2H5)20 = OH3-CH2-0-CH2-CH3 If ethyl iodide be added to an alcoholic solution of ethylate of sodium and a gentle heat be applied, a deposit of sodium iodide is formed and vapors are disengaged which may be con- densed in a cooled receiver into an ethereal liquid. It is oxide of ethyl. Cm^I + <''§l>0 = Nal + gHJ>o Ethyl iodide. Sodium ethylate. Ethyl oxide. If, in the preceding experiment, the ethyl iodide be replaced by methyl iodide, an extremely volatile liquid will be formed, which is the double oxide of methyl and ethyl. CH3I + <^§l>0 = Nal + %^l>0 Methyl iodide. Oxide of methyl and ethyl. These classic experiments, due to Williamson, show that the oxide of ethyl contains two ethyl groups. It may be regarded as alcohol in which the hydrogen atom of the group hydroxyl is replaced by ethyl. H-O-H C2H5-0-H C2H5-0-C2H5 Water. Alcohol. Ethyl oxide. Ether may also be obtained by the action of ethyl iodide on silver oxide. Preparation. — Ether is prepared in the arts by the action of sulphuric acid on alcohol. A mixture of 9 parts of con- centrated sulphuric acid and 5 parts of alcohol of 90 per cent, is heated in a flask, A (Fig. 126), and a small, continuous stream of alcohol is allowed to flow into this mixture through the funnel-tube a. The temperature of the liquid, indicated by the thermometer t, should not exceed 140 or 145°. The vapor disengaged is condensed in a Liebig's condenser, B, through ETHYL OXIDE. 503 which a stream of cold water flows continually. Under these conditions, a mixture of ether and water collects in the re- ceiver D, together with a little alcohol, and towards the close of the operation, a small quantity of sulphurous acid gas is disengaged. The product is purified by washing with milk of lime, and then with pure water, after which it is rectified over calcium chloride on a water-bath. Fig. 126 represents the apparatus used for public demonstration ; in the arts, the opera- tion is conducted on a large scale in apparatus of an analogous construction. Fig. 126. Theory of Etherification. —The transformation of alcohol into ether is a true dehydration, brought about by the sul- phuric acid. 2(C^ff .OH) = (C^H^yO + H^O Williamson clearly proved that it is effected in two distinct phases ; in the first, ethylsulphuric acid and water are formed. Ethylsulphuric acid. C^H^>0 Alcohol. In the second, another molecule of alcohol reacts with the ethylsulphuric acid; ether is formed and sulphuric acid is yegenerated. 504 ELEMENTS OF MODERN CHEMISTRY. jj>bO* + jj>0 = C2H5>^ + H-^^^ Ethylsulphuric acid. Alcohol. Ether. Sulphuric acid. Hence the ether and water collected in the receiver are pro- ducts of two distinct phases of the reaction. Ethylsulphuric acid is continually formed and as continually decomposed, regenerating sulphuric acid ready to act upon new por- tions of alcohol. However, although the operation is con- tinuous, it cannot go on indefinitely : the mixture blackens ; while the acid is being diluted continually with water formed in the first phase of the reaction, it is also in part reduced by the alcohol, sulphur dioxide being formed. Properties of Ether. — Ether is a colorless, very mobile liquid ; its taste is at first burning, then cooling ; its odor is suave and agreeable, and is called ethereal. Density at 0°, 0.7366. Boiling-point under the normal pressure, 34.5°. It is but slightly miscible with water, on the surface of which it forms a separate layer. 9 parts of water dissolve 1 part of ether ; 36 parts of ether dissolve 1 part of water. Ether dis- solves in all proportions in alcohol and in methyl alcohol. It slightly dissolves sulphur and phosphorus, and notable quantities of bromine, iodine, ferric, mercuric, and auric chlo- rides, and many organic bodies, such as the oils, fats, resins, alkaloids, etc. In 1846, Dr. William T. G. Morton, of Boston, discovered the fact that ether vapor when inhaled produces unconscious- ness and anaesthesia. This discovery has been of inestimable value in surgery, and while other anaesthetics, such as chloro- form, have been introduced, ether still seems to have the general preference. It is very inflammable and burns with a quite luminous flame. Its vapor explodes violently when mixed with air or oxygen and ignited. If a heated spiral of platinum wire be suspended in a glass jar containing a little ether, in such a manner that the lower extremity of the wire is but a little distance from the surface of the liquid, the wire will soon become brightly incandescent and will ignite the ether. This eff'ect is due to the ether vapor, which, coming in contact with the platinum, and being mixed with air, undergoes a slow combustion. Heat is thus developed, and the wire becomes incandescent. Ohlorine acts on ether with extreme energy. If the a-ctiou HYDROSULPHIDE AND SULPHIDE OF ETHYL. 505 be moderated, various products of substitution are obtained, among which the following have been well studied : Monochloretlier ^^^^^^'^0 liquid boiling at 98-99°. DicMorether ^^%%'>0 liquid boiling at 140-147°. Tetrachlorether q2jjzcI'^^^ liquid, density 1.5. r;2r;i5 PercMorether 02015-^^ colorless crystals, fusible at 69°. The last is a solid body, crystallizing in octahedra. By the action of heat it is decomposed into carbon sesquichloride and perchloraldehyde (Malaguti). C2C15>^ = C2C16 + C2C1*0 Perchlorether. Carbon sesquichloride. Perchloraldehyde. When two parts of bromine are added to one part of ether, and the mixture is cooled, a garnet-colored compound of bro- mine and ether, (C^H^)^O.Br'^, separates. It crystallizes in thin plates, fusible at 22°, and is easily decomposed (Schtitzen- berger). HYDROSULPHIDE AND SULPHIDE OF ETHYL. Two bodies are known which are intimately related, as re- gards their constitutions, with alcohol and ether. They are the hi/ dro sulphide and the sulphide of etliyl. The first, formerly known as mercaptan^ represents alcohol containing an atom of sulphur instead of an atom of oxygen ; the second represents ether in which the oxygen atom is replaced by sulphur. C^ff.OH (C^H^)^O Ethyl hydroxide. Ethyl oxide. C^H^SH (C^ff)^S Ethyl hydrosulphide. Ethyl sulphide. Ethyl hydrosulphide is obtained by distilling a concentrated aqueous solution of potassium hydrosulphide with a solution of potassium ethyl sulphate. It may also be prepared by passing vapor of ethyl chloride into an alcoholic solution of potassium hydrosulphide. The liquid is distilled as soon as it is saturated with ethyl chloride, and water is added to the distillate. Ethyl hydrosulphide separates. KSH -h C^H^Cl -= KCl + C'^H^SH Potassium hydrosulphide. Ethyl chloride. Ethyl hydrosulphide. W 43 506 ELEMENTS OP MODERN CHEMISTRY. Ethyl hydrosulphide is a transparent, colorless liquid, very mobile, and having a fetid odor. Density at 21°, 0.835. Boiling-point, 36.2° (Liebig). It reacts energetically with mercuric oxide, forming water and a white, crystalline body which represents ethyl hydros sulphide in which the hydrogen is replaced by mercury. Hence the name mercaptan (niercurium captans) given to the hydrosulphide of ethyl by Zeise. This mercuric compound is insoluble in water j it contains (C^H^S)^Hg". Ethyl sulphide is obtained, like the hydrosulphide, by double decomposition. Vapor of ethyl chloride is passed into an alco- holic solution of potassium monosulphide. K^S -f 2C^ffCl = 2KC1 + (C'H^)2S Potassium sulphide. Ethyl chloride. Ethyl sulphide. Ethyl sulphide is a colorless liquid, having a garlicky odor. It boils at 91°. It is insoluble in water. ETHYL CHLORIDE. C2H5C1 This body is prepared by saturating alcohol with hydrochloric acid gas and distilling on a water-bath. Ethyl chloride is dis- engaged, and should be passed first through a wash-bottle and then through a tube containing calcium chloride, after which it may be condensed in a receiver placed in a freezing mixture. Below 12.5°, its boiling-point, ethyl chloride is a mobile, colorless liquid, having a penetrating and agreeable odor. It is inflammable, and burns with a flame tinged with green. If some solution of silver nitrate be agitated in a jar con- taining vapor of ethyl chloride, no precipitate will be formed; but if the agitation be continued after the vapor has been ignited, an abundant precipitate of silver chloride will be formed, owing to decomposition of the silver nitrate by the hy- drochloric acid produced by combustion of the ethyl chloride. Ethyl chloride produces a precipitate of silver chloride when passed into an alcoholic solution of silver nitrate. Chlorinated Derivatives of Ethyl Chloride. — When ethyl chloride is submitted to the action of chlorine, various com- pounds are successively formed by the substitution of chlorine for hydrogen, atom for atom. The following is the nomencla- ETHYL BROMIDE. 507 ture and composition of these chlorinated compounds, which were discovered by V. Regnault. C2H5C1 ethyl chloride. C2H*C12 dichlorethane (ethylidene chloride)— boils at 57.5°. C2H3CP trichlorethane— boils at 75°. C'^H2C14 tetrachlorethane— boils at 127.5°. C2HC15 pentachlorethane— boils at 158°. C^Cl^ hexachlorethane (sesquichloride of carbon). It will be noticed that the second of these compounds is isomeric with ethylene chloride, or Dutch liquid, of which the description will be found farther on. It may be obtained by treating aldehyde with phosphorus pentachloride. CH^-CHO -\~ POP = CH^-CHCP + POCP Aldehyde, Dichlorethane. Phosphorus oxychloride. This mode of formation indicates its constitution, which is expressed by the formula C!HCP To distinguish it from its isomeride ethylene chloride, CffCl CH^Cl it is named dichlorethane or ethylidene chloride. In the sesquichloride of carbon, C^CP, the hydrogen atoms are all replaced by chlorine. Carbon sesquichloride is a crys- talline solid, melting at 187°, and boiling at 200°-210° ETHYL BROMIDE. C2H5Br Ethyl bromide is prepared by distilling a mixture of alcohol, bromine, and amorphous phosphorus, or a mixture of potassium bromide, alcohol, and sulphuric acid diluted with its own volume of water. In either case the distillate is washed with water, and the oily ethyl bromide separated and dried with potassium carbonate. It is a colorless, refracting liquid, having an odor resembling that of chloroform, and a burning taste. It mixes in all pro- portions with alcohol and ether, but is insoluble in water. Its density at 15° is 1.4189, and it boils at 40.7°. It has been employed to a limited extent as an anaesthetic. 508 ELEMENTS OF MODERN CHEMISTRY. ETHYL IODIDE. C^Hsi This important compound is prepared by the action of alco hoi on iodine in presence of amorphous phosphorus. Phos- phorus iodide is formed, and reacts upon the alcohol, yielding ethyl iodide and an acid of phosphorus. The former distils into the receiver, together with the alcohol which escapes the reaction. AVater is added, and the lower layer of liquid is separated, dried with calcium chloride, and rectified on a water- bath. Ethyl iodide is a colorless liquid, but becomes brown when long kept, especially when exposed to light. Density at 0°, 1.9753. Boiling-point, 72.2°. It can exchange its iodine by double decomposition, as can potassium iodide. If ethyl iodide be added to an alcoholic solution of silver nitrate, a yellow precipitate of silver iodide is at once formed, while ethyl nitrate remains in solution. C'H^I + AgNO^ = Agl + (C^H^)NO^ Ethyl iodide. Silver nitrate. Ethyl nitrate. ETHYL CYANIDE. C3H5N = CH3-CH2-CN This compound is formed when ammonium propionate is distilled with phosphoric anhydride. (NH*)C3H50^ = C^H^N + 2W0 Ammonium propionate. Ethyl cyanide. From this mode of formation, ethyl cyanide is sometimes called propionitrile. The same body exists in the product of the distillation of a mixture of potassium cyanide and potassium ethylsulphate. KCN -h ^^^^>S04 = K^SG* -f C2H5.cn Potassium Potassium Potassium Ethyl cyanide, cyanide. ethylsulphate. sulphate. But this product, which is liquid and has a variable boiling- point, contains, independently of the true cyanide of ethyl, an isomeride of that body, whose existence was foreseen by Meyer, and discovered by Gautier in the product of the action of ethyl iodide on silver cyanide. NITROETHANE AND ITS DERIVATIVES. 509 Ethjl cyanide is a colorless liquid, having a penetrating and pleasant odor. It boils at 96.7°. When it is boiled with potassium hydroxide, potassium pro- pionate is formed and ammonia is disengaged (Dumas, Mala- guti, and Le Blanc). effN + KOH + H^O = KC^H^O^ + NH^ Ethyl cyanide. Potassium propionate. When ethyl cyanide is brought into contact with dilute sul- phuric acid and zinc, it fixes 4 atoms of hydrogen and is converted into propylamine (Mendius). C^H^N -I- H* = en^N Ethyl cyanide. Propylamine. Ethylcarbylamine. — This name was given by Gautier to the isomeride of ethyl cyanide already mentioned. It is a color- less liquid, having a very penetrating and intensely offensive odor. It boils at 79°. With potassium hydroxide it yields potassium formate and ethylamine. C2H5-^ + K0H + H20= H-^N + KCHO2 H -^ Ethylcarbylamiae. Ethylamine. Potassium formate. ETHYL NITRITE, OR NITROUS ETHER. C2H5.0-NO This compound is obtained by the action of nitric acid on alcohol. The reaction is very violent, and abundant red vapors are evolved. After passing through a wash-bottle, they are conducted into a well- cooled receiver, where the ethyl nitrite condenses. It is a yellowish, very volatile liquid, whose odor recalls that of apples. It boils at 18°. It is but slightly soluble in water. Hot water immediately decomposes it into alcohol and nitrous acid, the latter being itself decomposed into nitric acid and nitric oxide. NITROETHANE AND ITS DERIVATIVES. C2H5-N02 This isomeride of ethyl nitrite represents ethane, C^H^, in which one atom of hydrogen is replaced by the group (NO^)'. It is the higher homologue of nitromethane. 43* 510 ELEMENTS OP MODERN CHEMISTRY. It is obtained, together with a certain quantity of etliyl nitrite, when ethyl iodide is treated with silver nitrite. C^H^I + AgNO^ = C^H^CNO^) + Agl Ethyl iodide. Silver nitrite. Nitrethane. It is a liquid having a peculiar, ethereal odor and boiling at 113-114°. Density at 13°, 1.0582 (V. Meyer). With nascent hydrogen, it furnishes pure ethylamine. All of the homologues of nitroethane thus yield the corre- sponding amines. It is a general character of the nitro com- pounds, and one which is not possessed by their isomerides, the nitrous ethers. In constitution and properties, nitroethane approaches nitrobenzene, as will be seen by the following comparison of their formulae : Ethane. Benzene. Nitroethane. Nitrobenzene. Ethylamine. Phenylamine (aniline). The presence of the group (NC^) confers acid properties upon nitroethane. Its sodium compound, C^H*<^^ , is formed either by the action of an alcoholic solution of sodium hydrate on nitroethane, or by the direct action of sodium on the same body ; in the latter case hydrogen is disengaged. Sodium- nitroethane is very explosive (Y. Meyer and Stuber). When it is sought to prepare potassium-nitroethane by the action of alcoholic potassium hydrate on nitroethane, the latter body is decomposed, yielding, among other products, potassium nitrite. Now, the latter salt exerts a remarkable action on nitroethane, giving rise to a new body of complex composition, potassium ethylnitrolate. Ethylnitrolic acid may be obtained by a process analogous to that which has been described for the preparation of methyl- nitrolic acid. Ethylnitrolic acid contains C=N.OH ETHYL NITRATE— ETHYL StJLPHATE. 511 It crystallizes in light-yellow, transparent prisms, possessing a feeble bluish fluorescence and a very sweet taste. It decom- poses without violence at 81-82° into nitrogen, nitrous vapors, and acetic acid. When boiled with dilute sulphuric acid, it decomposes into acetic acid and nitrogen monoxide. Ethylnitrolic acid. Acetic acid. ETHYL NITRATE, OR NITRIC ETHER. (C2H5)N03 This is obtained by the action of nitric acid upon alcohol in presence of a small quantity of urea. The latter body prevents the reduction of the nitric acid to nitrous acid. Nitric ether condenses in the receiver. It is washed with water, dehydrated with calcium chloride, and rectified. It is a liquid, having an agreeable, ethereal odor. It boils at 86°. Density at 0°, 1.1322. Potassium hydroxide decomposes it, like all compound ethers, forming potassium nitrate and alcohol. (C^H5)N0^ + KOH = C^H^OH + KNO^ It dissolves in ammonia, especially if the latter be warm, yielding ammonium nitrate and ethylamine. The reaction is analogous to that of ammonia upon methyl nitrate. ETHYL SULPHATES. Ethylsulplmric or Sulphovinic Acid. — tj [ SO* = Q2JJ5Q Jtl j TT^^-SO^. This body is an example of an acid ether. It results from the substitution of a single ethyl group for one atom of hydrogen in sulphuric acid, which is dibasic. I j sov ^' H>^^* It is formed by the action of sulphuric acid upon alcohol. The mixture of the two bodies becomes hot, and if after cool- ing the liquid be diluted and saturated with barium carbonate, an abundant precipitate of barium sulphate will be formed, and a soluble salt of barium, the ethylsulphate, will remain in solu- tion. A solution of ethylsulphuric acid may be obtained by exactly decomposing this salt with dilute sulphuric acid. 512 ELEMENTS OF MODERN CHEMISTRY. By boiling, ethylsulphuric acid is decomposed into sulphuric acid and alcohol. The ethylsulphates are beautiful salts ; they are crystalliz- able and soluble in water. p2TT5 ^ r2TT5 n Ethyl Sulphate.— ^2^5 1 SO^ = q'2^^'^>^0\ This body, which represents sulphuric acid in which the two atoms of hydrogen are replaced by two ethyl groups, is formed when silver sulphate is warmed with ethyl iodide ; double decom- position takes place, thus : Ag^SO* + 2C^H^I = (C^ff)^SO* 4- 2AgI It is an oily liquid having an acrid taste. Its density is 1.184. It boils at 208°, with partial decomposition. ETHYLSULPHONIC ACID AND ETHYL SULPHITE. When mercaptan, C^H^SH, is oxidized by nitric acid, a thick, very acid liquid is obtained, which in a vacuum solidifies to a crystalline mass. It is ethylsulphonic acid, which con- centrated nitric acid oxidizes and converts into ethylsulphuric acid. Unlike the latter, ethylsulphonic acid is very stable. It is not decomposed by boiling with potassium hydrate : when fused with the latter, it yields potassium sulphite and alcohol. C^ff .SO'K + KOH = C^H^OH + K^SO^ Phosphorus pentachloride converts it into ethylsulphonic chloride, C^H^-SOICI, a Hquid boiling at 173°. Ethylsulphonic acid is analogous in its properties and con- stitution to phenylsulphonic acid, and its analogues, which will be described farther on. Ethylsulphonic acid is the sul- phonic derivative of ethane. C2H6 ethane. C^B.^ benzene. C2H5.S03H ethylsulphonic acid. C6H5.S03H phenylsulphonic acid. The sulphonic acids may be considered as derivatives of a hypothetical acid, H.SO^OH, to which the name unsym- metrical sulphurous acid has been given. The hydrogen atom in direct combination with the sulphur is replaceable by ethyl, ETHYL SULPHITES. 513 phenyl, etc., and the sulphonates result from the replacement of the remaining hydrogen by metals or alcohol radicals. There is possible another sulphurous acid, symmetrical sul- phurous acid HO.SO.OH, and derivatives of this acid are also known : they are the sulphites of the alcohol radicals, and present the structure SO(OE,)^. 1. If silver sulphite and ethyl iodide be heated together, a double decomposition takes place, yielding silver iodide and ethyl sulphonate. AgS02.0Ag + 2C2H5I = 2AgI + C2H5.S02.0C2H5 Silver sulphite. Ethyl iodide. Ethyl sulphonate. This is the ether of the ethylsulphonic acid which has been described. It may be obtained by the action of ethyl- sulphonic chloride on sodium ethylate. C2H5.S02.C1 + C2H5.0Na = NaCl + C2H5.S02.0C2H5 It is a liquid, boiling at 208°, and having at 0° a density of 1.47. 2. By the action of thionyl (sulphuryl) chloride on absolute alcohol, ethyl sulphite is obtained isomeric with the preceding. SOCO + NH3 = c2h5)>CO + C'HS.OH Ethyl carbonate. Ethyl carbamate. 516 ELEMENTS OP MODERN CHEMISTRY. It yields urea and alcohol when heated to 100° with am- monia. C2H5:o>^^ + 2NH3 = C0<™ + 2C2H5.0H Ethyl carbonate. Urea. ETHYL CHLOROCARBONATE. CL C2H50 >co Dumas obtained this ether by passing carbonyl chloride into alcohol. Water is added to the product of the reaction, and the insoluble liquid is separated, dried, and distilled. ^J>CO + C2H5.0H ^ HCl + C2H50>^^ Carbonyl chloride. Ethyl chlorocarbonate. It is a liquid having a pungent, ethereal odor. It boils at 94°. Hot water decomposes it. Ammonia converts it into ethyl carbamate, or urethane. C2H5S>CO + 2NH3 = NH^Cl + C2HH)>C0 ETHYL ISOCYANATE. C2H5-N:=CO This compound is prepared by distilling on an oil-bath a mixture of 2 parts of potassium ethylsulphate and 1 part of recently-prepared and well-dried potassium isocyanate. The product which condenses in the receiver is rectified on a water- bath (Wurtz). Ethyl isocyanate is a colorless liquid, having a very irritating odor. It boils at 60°. Potassium hydrate de- composes it into carbonic acid gas and ethylamine. It com- bines with ammonia, developing heat and producing ethylurea (page 481). The bodies which were formerly known as cyanic acid and ethyl cyanate, are only isomerides of the oxygen compounds of cyanogen. They have been described as isocyanic acid and isocyanate of ethyl. The true cyanic ether, (C^H^O)CN, or rather a polymeride of that body, has been obtained by Cloez. It is formed by the action of cyanogen chloride on ethylate of sodium. CNCl -f Na.OC^H^ = CN.OC^H^ + NaCl Cyanogen chloride. Sodium ethylate. Ethyl <>yauate. Potassium hydroxide decomposes the true ethyl cyanate, like SATURATED HYDROCARBONS. 517 all other compound ethers, into alcohol and the corresponding potassium salt (cyanate), or into the decomposition products of that body, — carbon dioxide and ammonia. CYANURIC ETHEKS. When potassium isocyanate is distilled with ethyl sulphate, besides the ethyl isocyanate which has just been described, there is formed also the isocyanurate. C'OW (C'H^)=^ = (CO)^=(N.C2H0' The latter condenses in a solid white mass which may be purified by recrystallizatioa from boiling alcohol. It crystallizes in brilliant prisms, fusible at 95° ; it boils at 276° (A. Wurtz). Boiling potassium hydroxide decomposes it, like the isocyanate, with disengagement of carbon dioxide, a reaction which justi- fies the constitution indicated by the preceding formula. Its isomeride C^N^(OC^H^)^, which corresponds to the nor- mal cyanuric acid (page 474), melts at 29° and boils at 275°. The mother liquor from which triethyl isocyanurate has deposited, contains diethyl isocyanurate, C^O^N^H(C'^II^)^, which crystallizes in six-sided prisms, fusible at 173°. Normal methyl cyanur ate is formed by the action of cyanogen chloride on sodium methylate. 3CNC1 + SCHlONa = 3NaCl + C^N^(OCH^)' It crystallizes in needles fusible at 132°. It boils between 160 and 170°, and at this temperature is converted into its isomeride methyl isocyanurate, fusible at 175°, and boiling at 296°. By the action of boiling potassium hydroxide, it is decomposed into potassium cyanurate and methyl alcohol. SERIES OF SATURATED HYDROCARBONS. To methane and ethane, which have already been described, are related numerous hydrocarbons belonging to the same series, CH^''"^^. They are called saturated because no hydro- carbons are known in which the number of hydrogen atoms exceeds that indicated by the preceding formula. Again, the hydrocarbons in question can fix directly no other atoms. For example, in order that chlorine can enter into one of their molecules, hydrogen must first be removed, and this displace- 44 518 ELEMENTS OP MODERN CHEMISTRY. ment is known to take place, atom for atom, according to the law of substitution. Thus, if chlorine be made to act upon the hydrocarbon C^H^* (hexane), the compounds C^H^^Cl, C^H^^CP, C*^H^^CP, may be obtained successively. Let us con-< sider the first of these compounds, C^H^^Cl. The CI may be replaced by the group OH, and the chloride is thus converted into an alcohol. For this purpose the chloride is caused to react with a silver salt, the acetate, for example, and hexyl acetate is formed by double decomposition. C'Hi^Cl + AgC^ffO^ = C^H^lC^ffO^ + AgCl Hexlyl chloride. Silver acetate. Hexyl acetate. Boiling potassium hydroxide will transform this ether into hexyl hydroxide. C^H^^C^H^O^ + KOH = KO^H^O'^ + C^H^IOH Hexyl acetate. Potassium acetate. Hexyl hydroxide. This series of reactions permits of the successive transforma- tion of any hydrocarbon of the saturated series into a chloride, an acetate, and a hydroxide, and the latter is the alcohol corre- sponding to the hydrocarbon. The following is the series of saturated hydrocarbons : CH4 methane. C2H6 ethane. C3H8 propane. C4H10 butanes. C5H12 pentanes. C6H14 hexanes. Cmi6 heptanes. C8H18 octanes. C9H20 nonanes. C101P2 decanes, etc. All of these hydrocarbons, after the fourth of the series, up to the term C^'^H^*, have been obtained from petroleum and the products of distillation of bitumen and peat. Towards the close of the distillation, when the temperature passes above 300°, the products which distil condense to a solid mass on cooling. When properly purified, this solid forms a colorless, translucent mass, which has received the name paraffin. It is probably a mixture of several hydrocarbons of the series Qnjj2ii+2_ j^g point of fusion varies between 45 and 65°. All of the compounds belonging to this series cannot be described here, but we may briefly consider their constitution. The third member of the series, propane, C^H^, has the con- stitution indicated by the formula CH^-CH^-CHl It is a gas which liquefies at — 1*7°. PETROLEUM. 519 Its higher homologue, butane, C*H^°, has the constitution CH'-CH'-CH'-CH^ and can be obtained by the action of zinc or sodium on ethyl iodide. 2C'^H^I + Na^ = 2NaI + C'W It is a colorless gas, condensable at +1°. But we have here a remarkable instance of isomerism. There is another butane, isomeric with the preceding, and having the consti- QJJ3 tution expressed by the formula CH^-CH<CH-CH2-CH^OH, but contains also a variable quantity of active amyl alcohol. AMYL ALCOHOLS. 525 It may be obtained by fractional distillation of the fusel oil from beet-root and potatoes, as well as of that from the marc of grapes, whiskey, etc. These products are only the residues of the distillation of alcohol from various sources. The inactive amy! alcohol or isobutylcarbinol may be separated by the following process, indicated by Pasteur. By treatment with sulphuric acid the crude amyl alcohol is converted into amylsulphuric acid. The liquid is diluted with water, neutralized with barium carbonate, and filtered. Two barium amylsulphates are thus obtained, of which the one is less soluble than the other, and crystallizes first when the solu- tion is evaporated, while the other remains in the mother liquid. The former is derived from the inactive alcohol, the latter from the active alcohol ; these alcohols are obtained by decomposing the corresponding barium salts with sulphuric acid, filtering, and distilling with water the free amylsulphuric acids. SO^<^g + H^O = S0X0H)2 + C^H".OH Amylsulphuric acids. Sulphuric acid. Amyl alcohols. Isobutylcarbinol has been obtained by synthesis, and the process clearly proves its constitution (Balbiano). The con- stitution of butyl alcohol of fermentation has been established with certainty by Erlenmeyer. This alcohol may be converted successively into iodide and cyanide, and this, by decomposition with potassium hydrate, into inactive valeric acid. The barium salt of the latter acid when distilled with calcium formate yields the corresponding aldehyde, valeraldehyde (Piria), and this is converted into inactive amyl alcohol by the action of nascent hydrogen. QH3>CH-CH^-CH0 + H^ == ^g3>CH-CH^-CH2.0H Valeraldehyde. Isobutylcarbinol. Properties. — Pure isobutylcarbinol is a colorless, somewhat oily liquid, soluble in fifty parts of water at 13°. Its density at 0° is 0.823, and it boils at 131.4°. When oxidized it yields inactive valeraldehyde and acid. C^Hi^O 4- = H^O + c^ir°o Amyl alcohol. Valeric aldehyde (valeral). C^H^^O + 0' = H^O + C^H^oQ^ Valeric acid. The crude alcohol of fermentation is an oily liquid, of a dis- agreeable odor. It boils at 129-132°. It turns the plane of 526 ELEMENTS OF MODERN CHEMISTRY. polarized light to the left, but its rotatory power is variable, for it contains variable proportions of active amyl alcohol. When distilled with zinc chloride, it yields ordinary amylene, which is a mixture of several isomeric amylenes, trimethyl- ethylene being the most abundant. Amyl alcohol. Amylenes. Many amyl derivatives have been studied. They resemble the ethyl compounds, but contain, of course, the group C^H^^ instead of C'H^ Amyl oxide, r(5oii!>0, is formed, together with amylene, by the action of sulphuric acid on crude amyl alcohol (William- son). It is a colorless liquid, of an aromatic odor, boiling at 176°. Amyl chloride, C^H"C1, is a colorless liquid, boiling at 101.4°. Amyl bromide, C^H"Br, boils at 120.4°. Amyl iodide, C^H^^I, is prepared by a process similar to that which yields ethyl iodide. It is a colorless liquid, boiling at 148°. It turns brown on exposure to the light. Amyl nitrite, C^H^NO^ is prepared by passing nitrous vapors, made by the action of nitric acid on starch, into amyl alcohol, and distilling the carefully washed product. It is a pale yellow liquid, boiling at 96°, and having a peculiar odor somewhat like that of apples. Its vapor when inhaled pro- duces dilatation of the capillary system, and violent but tran- sitory headache. Its inhalation has been recommended as a remedy for sea-sickness, in certain heart-affections, and as an antidote in cases of poisoning by chloroform vapor. Active Amyl Alcohol is contained to the extent of about thirteen per cent, in crude amyl alcohol. One method of separation has already been indicated, but Le Bel has proposed a better method when it is desired to prepare only the active alcohol. If hydrochloric acid gas be passed through the crude alcohol, the inactive alcohol is first attacked and converted into chloride ; the active alcohol then remains after the separation of the inactive chloride. It boils at 127°. It rotates the plane of polarized light to the left [a]D = —4.4°. Its chloride boils at 97-99° ; its iodide at 144-145°. Oxidation converts it into active valeric acid ; hence its constitution is probably p2tr6>C!H-CH^OH. HIGHER ALCOHOLS. 527 Tertiary Amyl Alcohol, or Hydrate of Amylene. This alcohol is prepared by treating with hydriodic acid trimethyl- ethylene, described on page 574, which forms the greater part of crude amylene. ^^3>C=:CH-CH3 + HI = ^|3>CI-CH^-Cff Trimethylethylene. Trimethylethyl iodide. The iodide so formed, when acted on by water and silver oxide, yields the corresponding hydrate, which is tertiary amyl alcohol or dimethylethylcarbinol. It is a mobile, colorless liquid, having an odor somewhat like camphor. At — 12° it forms a crystalline mass ; it boils at 102.5°, and at 200° is decomposed into amylene and water. By reason of the latter reaction, Wurtz, who discovered th-e alcohol, named it hydrate of amylene. Its chloride boils at 86°, its bromide at 108-109°, and its iodide at 127-128°. Oxidation converts it into acetic acid and acetone. HIGHER ALCOHOLS. Of th.e rapidly increasing number of members of this series which are becoming well known, we can consider but a few. Hexyl and Heptyl Alcohols. — Faget announced that the residues from the distillation of fusel-oil from fermented grape-juice contained a small quantity of liexyl (C^H^^O) and liepyl (C^H^^O) alcohols, but the existence of such alcohols in that product has not been corroborated. Normal hexyl alcohol has been obtained from the volatile oil of the seeds of Heracleum gigantenm^ an oil which contains butyrate of hexyl, C^H^lC^H^Ol The normal alcohol boils at 157-158°. K'ormal heptyl alcohol, C^H^^O, has been prepared by the action of nascent hydrogen on oenanthic aldehyde C^H^^O. It boils at 175-177°, and has an aromatic odor. Octyl Alcohols, C^H^^O.- -Normal octyl alcohol may be ex- tracted from the seeds of Heracleum spondylium and Hera- cleum giganteum^ in which octyl acetate, C^H^^C^H^O^, exists. This ether is separated and decomposed by boiling potassium hydroxide. Its boiling-point is 199°. Bouis discovered secondary octyl alcohol. By boiling one 528 ELEMENTS OF MODERN CHEMISTRY. of the acids produced by the saponification of castor-oil, rici- nolic acid, with potassium hydroxide, he succeeded in obtaining sebacic acid and a new secondary alcohol. This is octyl alco- hol, C^H^^O, a colorless liquid having a pleasant, aromatic odor, and boiling at 178°. The following equation explains its formation : Qi8H3*0^ + 2K0H = WC'WO' + C^H^^O -f H^ Kicinolic acid. Potassium sebacate. Octyl hydroxide. Cetyl Alcohol. — The solid portion of an oil which fills the cranial sinuses of the sperm-whale is called spermaceti. When properly purified it occurs in beautiful pearly plates, fusible at 49°. It is a compound ether of which the nature was recognized by Chevreul in 1823. By submitting it to the action of potassium hydroxide, that chemist decomposed it into palmitic acid and a new alcohol which he called ethal, to denote its relations with alcohol and ether. It is now called cefi/l alcohol, or ceti/l hydroxide. ^cSh33>^ + ^^^ = C16H33.0H + KC16H3102 Cetyl palmitate. Cetyl hydroxide. Potassium palmitate. It belongs to the same homologous series as the preceding alcohols. Alcohols from Wax. — The most complex alcohols of the series under consideration were obtained from wax by Brodie. Ordinary beeswax is a mixture of a fatty acid, C^^H^^O^ called cerotic acid (cerin), and a compound ether, the pahyittate of rtiyricyl (myricin). The two bodies are separated by alcohol, which readily dissolves the first, but in which the second is but slightly soluble. By boiling the palmitate of myricyl with potassium hydroxide, it breaks up into palmitic acid and hydroxide of myricyl, or myricyl alcohol, C^°H^'^0. Chinese wax is a compound ether; it is cerotate of ceryl, and may be decomposed by caustic potash into cerotic acid and ceryl hydroxide, or ceryl alcohol, C"H^^O. The hydroxides of cetyl and ceryl are solid bodies. ALLYL ALCOHOL. C^H^.OH = CH2^CH-CH2.0H All the alcohols thus far considered belong to the series (^njj2n+2Q There are other monohydric alcohols which belong to different series, that is, in which there are different relations ALLYL ALCOHOL. 529 between the number of hydrogen atoms and the number of carbon atoms. Among these other alcohols, the most impor- tant is allyl alcohol^ or hydroxide of allyl^ so named because it is closely related to the essential oil of garlic, which is allyl sulphide. Another natural oil, that of mustard, is sulpho- cyanate of allyl. C^^H^.OH (C^H5)2S C^H^CNS Allyl hydroxide. Allyl sulphide. Allyl sulphocyanate. Hofmann and Cahours prepared allyl hydroxide and a great number of its derivatives artificially by the aid of allyliodide^ C^HP, which is formed when glycerol is acted upon by iodide of phosphorus, P"''!* (Bertheiot and de Luca). This iodide, whose relations to allyl alcohol are the same as those of ethyl iodide to ordinary alcohol, is a colorless liquid, having a slightly pungent, garlicky odor, and boiling at 101°. When heated with mercury and concentrated hydrochloric acid, it yields pure propylene gas (Bertheiot). 2C^H^I -f 2HC1 + 4Hg = 2C^H*' + HgT + Hg^CP Allyl iodide. Propylene. ToUens and Henninger discovered a very simple process for the preparation of allyl alcohol. It consists in heating formic acid, or oxalic acid, from which the former acid is produced, with glycerol to 220°. The allyl alcohol which distils is washed with a concentrated solution of potassium carbonate, and rectified over lime. In this reaction, a monoformine of glycerol is first produced, and this decomposes at 220° into carbon dioxide, water, and allyl alcohol. fO.CHO C3H5 \ OH = C02 + H20 + C3H5.0H (OH Monoformine of glycerol. Allyl alcohol. It will be seen that the reaction is really a reduction. Allyl alcohol is a colorless liquid, boiling at 97°, and having a pungent, alcoholic odor. It dissolves in all proportions of water. Density at 0°, 0.858. Allyl alcohol is an unsaturated compound ; it can fix directly two atoms of hydrogen, so form- ing normal propyl alcohol. It combines directly with bromine, forming dibromopropylalcohol. CH^Br-CHBr-CH^OH. Acrolein^ or acraldehyde, CH^ = CH-CHO, a volatile liquid that is formed in the distillation of fatty bodies, is the alde- hyde of allyl alcohol. Acrylic acid is the corresponding acid. X a 45 530 ELEMENTS OF MODERN CHEMISTRY. COMPOUND AMMONIAS, OK AMINES. Wurtz gave these names to the basic combinations resulting from the substitution of alcoholic radicals, such as methyl, ethyl, etc., for the hydrogen of ammonia. This substitution may be more or less complete; 1, 2, or 3 atoms of hydrogen may be replaced by as many alkyl groups. Hence there are various classes of amines ; they are designated by the names primary, secondary, and tertiary. PRIMARY AMINES. SECONDARY AMINES. TERTIARY AMINEg. 1^1 CH3) cm) CH3) H VN hIn chsIn ch^In HJ hJ HJ CH3J mmonia. Methylamine. Dimetliylamine. Trimethylamine. C2H5) C2H5^ C2H5) H^N C2H5 [ N C2H5 I N hJ HJ C2H5J Ethylamine. Dlethylamine. Triethylamine. Lastly, bases are known which are the most energetic of all, and may be considered as derived from the hypothetical hydroxide of ammonium by the substitution of alcoholic radi- cals for 4 atoms of hydrogen. N.OH C2H5- C2H5 C2H5 C2H5J Hydroxide of tetrethylammonium. :U OH Ammonium hydroxide. The latter ammoniated bases, as well as the secondary and tertiary amines, were discovered by Hofmann. The compound ammonias, or amines, are formed in the fol- lowing reactions : 1. By the decomposition of an isocyanic or isocyanuric ether by potassium hydroxide. In this case primary amines are obtained (A. Wurtz). CO = N-C2H5 + 2K0H - NH2(C2H5) + K2C03 Ethyl isocyanate. Ethylamine. 2. By the action of alkyl bromides or iodides on ammonia (A. W. Hofmann). C2H5I + Ethyl iodide. 2C2H5I + NH3 zcmn NH3 = NH2(C2H5)HI Ethylamine hydriodide. = NH(C2H5j2HI + HI Dlethylamine hydriodide. NH3 = NH(C2H5)3HI + 2HI Triethylamine hydriodide. COMPOUND AMMONIAS. 531 3. By decomposing carbylamines by dilute acids (Gautier). 4. By the reduction of nitromethane and its homologues by nascent hydrogen (V. Meyer, see p. 494). 5. By the action of nascent hydrogen on the alkyl cyanides, also called nitriles (Mendius). CH3.CN + H* = CH3-CH2-NH2 Methyl cyanide, or acetonitrile. Ethylamine. 6. By reducing oximes (p. 554) or hydrazones (p. 554) in alcoholic solution by means of nascent hydrogen (E. Fischer). General Properties. — The amines are energetic bases, pre- senting great analogies with ammonia, having a similar odor, a like solubility in water, and the same pronounced alkaline reaction. The more simple are combustible gases or volatile liquids. The basic energy increases with progressive substitu- tions : thus triethylamine is a stronger base than either ethyl- amine or ammonia, both of which it displaces from their com- binations. The hydroxides of the quaternary bases, or com- pound ammoniums, are almost as caustic as potassium hydrox- ide. All the compound ammonias form with platinic chloride crystallizable double salts comparable to ammonium chloro- platinate. They can replace ammonia in ammonia alum. When the hydrochlorides of the amines are subjected to de- structive distillation, they decompose into an alkyl chloride and a lower amine, a reaction which allows the molecules to be simplified by a sort of inverse substitution. N(CH3)4C1 = N(CH3)3 + CH3C1 Tetramethylammonium chloride. Trimethylamine. N(CH3)3.HC1 = NH(CH3)2 + CH3C1 Trimethylamine hydrochloride. Dimethylamine. NH(CH3)2.HC1 = NH2(CH3) + CH3C1 Dimethylamine hydrochloride. Methylamine. Action of Nitrous Acid. — This acid converts primary amines into alcohols, water being formed and nitrogen disengaged. NH^CC^HO + HO.NO = C^mOH + H^O + N^ With the same acid the secondary amines undergo a remark- able reaction, giving rise to nitroso-hsises, or nitroso-Simines, formed by the substitution of the group nitrosyl^ NO, for the single atom of hydrogen in the ammonia residue NH (imidogen). /H /NO N^CH^ + NO.OH = N^CH^ + H^O Dimethylamine. Nitrosodimethylamine, 532 ELEMENTS OF MODERN CHEMISTRY. The nitrosamines are oleaginous liquids, insoluble in water ; they can be distilled without decomposition, and, generally, are unalterable by either acids or alkalies. On the addition of phenol and sulphuric acid they produce intense colors. When their alcoholic solutions are treated with zinc and acetic acid, the nascent hydrogen evolved converts them into disubstituted hydrazines (see below). In the amines, nitrogen acts as a triatomic element or tri- valent; but it may assume two other atomicities. In sal- ammoniac, it is pentatomic, and it may play precisely the same part in the amines. H C2H5 1 CI H H N (OH)' (C2H5)' (C2H5)' N /\ H H Ammonia. C2H5 C2H5 Triethylamine. H H Ammonium chloride. (C2H5)' (C2H5)' Tetrethylammonium hydroxide. Helated to the amines are various organic combinations which have the same constitution, but in which the nitrogen is replaced by an analogous element, such as phosphorus, arsenic, or antimony. A great number of these bodies have been discovered, of which the more important are C2H5) C2H5^ C2Hn C2H5 \ P'" C2H5 \ As'" C2H5 \ Sb C2H5J C2H5J C2H5J Triethylphosphine. Triethylarsine. Triethylstibine. Hydrazines. — The nitrogenized bases that have just been considered belong either to the type NX^ or to the type NX^. A new class of compounds has recently been discovered, be- longing to the type N^X^. It is evident that the group NH^ (amidogen) cannot exist in the free state. Hydrazine, discovered and described by Curtius, consists of two such groups, Nff-NH^ It is dia- mide (page 160). Derivatives of hydrazine, in which one or two atoms of hydrogen are replaced by organic radicals, had previously been obtained by Fischer, who described ethylhydrazine^ NH2-NH(C'H^), and diethylhydrazine N(C^H5)'-NIP Dimethyl- and diethylhydrazine are formed by the action of nascent hydrogen on the corresponding nitroso compounds (page 531). METHYLAMINE. 533 ^53>N-NO + H* = H^O + ^(C^')' These hydrazines are closely related to the amines by their chemical and physical properties. They are very volatile liquids, having an ammoniacal odor, and soluble in water, alcohol, and ether. METHYLAMINE. CH3) CH5N = H ^ N hJ This body may be prepared by boiling together potassium hydrate and methyl cyanate or cyanurate, and passing the vapors which are disengaged into dilute hydrochloric acid; methylamine hydrochloride is thus formed. on CH3) (,^^N + 2K0H = K2C03 + hIn Methyl cyanate. Methylamine, The solution is evaporated to dryness, and the residue fused and allowed to cool ; it is then mixed with double its weight of powdered quick-lime, and the mixture gently heated. The methylamine disengaged may be collected over mercury. It is a colorless gas, which condenses to a light liquid at a temperature a few degrees below 0°. It is inflammable, and burns with a pale flame. Its odor is strongly ammoniacal and, at the same time, recalls that of the sea. It is the most solu- ble of all gases. 1 volume of water at 12.5° absorbs 1153 volumes of methylamine. The aqueous solution possesses the odor of the gas, a caustic taste, and a strong, alkaline reaction. Like ammonia, it precipitates the oxides from solutions of the metallic salts. If a solution of methylamine be added to a solution of cupric sulphate, a light-blue precipitate is first formed, but disappears if an excess of methylamine be added, yielding a beautiful blue solution. Methylamine Hydrochloride, CH^N.HCl, difi'ers from am- monium chloride by its solubility in boiling alcohol, from which it is deposited on cooling in large, colorless, deliquescent plates. With platinic chloride it forms a yellow precipitate, soluble in boiling water, from which it crystallizes in golden-yellow scales. It is a chhroplatinafe, (CH^N.HCniPtCh 45* 534 ELEMENTS OP MODERN CHEMISTRY. DIMETHYLAMINE, TRIMETHYLAMINE, TETRA- METHYLAMMONIUM HYDRATE. These compounds were discovered by Hofmann. Dimethylamine^ (CH^)^NII, is a combustible gas wliicli lique- fies at 8°. Trimethylamine^ (CH^)^N, exists ready formed in the Cheno- podium vidvaria, in the flowers of Cratse^us oxyacantha, in herring-brine, in cod-liver oil, and in coal-gas tar. Vincent extracts large quatities of it from the residues of the distilla- tion of fermented beet-juice. At ordinary temperatures it is a gas ; it liquefies at 9°. It is very soluble in water and in alcohol. It has a strong, ammoniacal odor, and an intense, alkaline reaction. It unites directly with methyl iodide, forming the iodide of tetramethylammonium. (CH3)^N + CH^i = (cwym This iodide possesses all the appearances of a salt. It is soluble in water, and the solution treated with silver oxide yields silver iodide and tetramethylammonium hydroxide. 2(CH=^)^NI + Ag^O + H^O = 2AgI + 2(CH3)^N.OH The latter body is very soluble in water, and the solution is caustic. When submitted to dry distillation, it decomposes into trimethylamine and methyl alcohol. (CHO'N.OH = CHIOH -f (CH^)^N ETHYLAMINE. cm ) hJ Ethylamine is prepared by a process analogous to that which yields methylamine ; cyanate or cyanurate of ethyl is decom- posed with boiling potassium hydroxide, and the vapors are con- densed in very dilute hydrochloric acid. The dry ethylamine hydrochloride is then treated with quick-lime (A. Wurtz). Another process has been indicated by Hofmann. It consists in causing ammonia to react upon the bromide or iodide of ethyl. H) C2H5) C2H5Br + H I N = H ^ N.HBr hJ hJ Ethylamine hydrq bromide. DIETHYLAMINE. 535 Ethylamine is a ligbt, mobile, colorless liquid ; it boils at 18.7°. Its odor is strong and exactly resembles that of am- monia. Ethylamine is inflammable. It mixes with water, alcohol, and ether in all proportions. Its aqueous solution is caustic, and precipitates most of the metallic salts like solution of am- monia, and, like the latter, redissolves cupric hydrate, forming a blue liquid. Ethylamine Hydrochloride, C^H^N.HCl.— This salt crys- tallizes in large, deliquescent plates, soluble in absolute alcohol. Its aqueous solution yields with platinic chloride a precipitate composed of yellow scales, soluble in boiling water, and consti- tuting a chloro-platinate, (C'H^N.HCl)lPtCP. DIETHYLAMINE, TRIETHYLAMINE, TETKETHYL- AMMONIUM HYDROXIDE. Diethylamine, C^H^ I N, was obtained by Hofinann by heat- ing ethylamine with ethylbromide, and decomposing the die- thylamine hydrobromide formed by an alkali, cmn C2H5- .HBr H5) C2H5) H I N + C2H5Br = C2H5 I N.] Hj hJ Ethylamine. Diethylamine hydrobromide. The free base is a liquid having an ammoniacal odor and boiling at 57.5° Triethylamine may be formed by the action of ethyl bro- mide on diethylamine ; triethylamine hydrobromide is formed, (J2JJ5 f ]v^ jj;Bj.^ from which alkalies cause the disengagement of triethylamine, a colorless liquid, boiling at 91° ; its odor is ammoniacal and its reaction strongly alkaline. Tetrethylammonium Hydroxide. — When a mixture of ethyl iodide and triethylamine is heated on a water-bath, the two bodies combine, forming the compound which Hofinann has named tetrethylammonium iodide. Q'Wl -f (C^H^)^N = (C^H5)*N.I Ethyl iodide. Triethylamine. Tetrethylammonium iodide. When this is treated with silver oxide and water, it yields silver iodide and tetrethylammonium hydroxide, (C^H^)*N.OH, 536 ELEMENTS OF MODERN CHEMISTRY. a powerful base, which is crystallizable and soluble in water. Its alkalinity is comparable to that of potassium hydroxide. ETHYLPHOSPHINES. Primary, secondary, and tertiary ethylphosphines are known, as well as the compounds of tetrethylphosphonium. cms] cm^-) cm^) g|n , Ethylphosphine. Diethylphosplaine. Triethylphospbine. Tetrethylphosphonium. The first two were discovered by Hofmann. The third by Hofmann and Cahours, who obtained it by the action of phosphorus trichloride on zinc ethyl. 2PCP + 3[Zn(C^H^)^] = 2[P(C^H5y] + 3ZnCP Zinc ethyl. Triethylphosphine. The operation must be conducted out of contact with the air, and the zinc ethyl must be diluted with anhydrous ether. Monethylphosphine and diethylphosphine are produced when ethyl iodide is made to react upon phosphonium iodide, PH'^I, hydriodide of hydrogen phosphide (page 177), in presence of an excess of zinc oxide. 2C2H5I + 2PH*I + ZnO = 2[(C2H5)H2P.HI] + ZnP + H20 2C2H5I + PH^I + ZnO = (C2H5)2HP.HI + ZnF + H20 As both reactions are accomplished simultaneously, both phosphines are obtained at the same time. They are separated by the action of water upon the two hydriodides which are formed. That of monethylphosphine is decomposed by water, while that of diethylphosphine is only decomposed by the alka- lies. It is sufficient then to add water to the product of the reaction in order to set free the monethylphosphine ; when the latter has been completely expelled by heat, potassium hy- drate added to the residue will cause the disengagement of the diethylphosphine. These operations should be conducted in a current of hydrogen. Monethylphosphine, (C^H^)HT. — This is a colorless liquid, lighter than water, in which it is insoluble, and boiling at 25°. It has a most disagreeable odor. It takes fire on contact with chlorine or nitric acid. Its hydriodide crystallizes in beautiful, white, quadrangular tables. diethylphosphine, (C^H^)'HP. — A colorless liquid, lighter PRODUCTS OF OXIDATION OF ETHYLPHOSPHINES. 537 than water, and boiling at 85°. It is very avid of oxygen, and sometimes takes fire spontaneously on contact with the air. TriethyiphospMne, (C^H^)^P. — This is a colorless liquid, boiling at 127.5°. Density at 15°, 0.812. It combines di- rectly with oxygen, forming triethylphosphine oxide, (C^H^)^PO. The latter is a crystalline solid, very soluble in water and in alcohol. It distils at 240°. When treated with ethyl iodide, triethylphosphine yields tetrethylphosphonium iodide, (C^H^)*PI, a compound which may be obtained in beautiful crystals. When this iodide is acted upon by moist silver oxide, it furnishes the corresponding hydrate, which is an energetic base. 2[(C'^H^)TI] + Ag^O + H^O = 2AgI + 2[(C^H^)T.0H] Tetrethylphosphonium Tetrethylphosphonium iodide. hydrate. PRODUCTS OF OXIDATION OF ETHYLPHOS- PHINES. When the ethylphosphines are treated with fuming nitric acid under suitable conditions, they act in a characteristic man- ner. Monethylphosphine is transformed into a dibasic acid, monethylpliosphinic ^ diethylphosphine yields a monobasic acid, dietJiylphospliinic. Triethylphosphine yields an indifferent oxide, which has already been mentioned. Now, if it be remem- bered that under the same circumstances hydrogen phosphide furnishes phosphoric acid, it will be seen that the preceding oxidation compounds may be regarded as phosphoric acid, in which 1, , 2, or 3 groups OH are replaced by as n groups. (■H rOH P^ H PQ^ OH 1h [on Hydrogen phosphide. Phosphoric acid. rC2H5 rc2H5 P^ H PO^ OH U (OH Monethylphosphine. Monethylphosphinic acid. ('C2H5 rC2H5 P^C2H5 PO \ C2H5 1h (oh Diethylphosphine. Diethylphosphinic acid. rc2H5 fC2H5 P \ C2H5 PO \ C2H5 (C2H5 iC2H5 Triethylphosphine. Triethylphosphine oxide. 538 ELEMENTS OF MODERN CHEMISTRY. The compounds of arsenic and ethyl are entirely analogous to the phosphines ; they have already been alluded to. Besides these, there are ethylic combinations corresponding to cacodyl and its derivatives. SILICON-ETHYL. Si(C2H5)4 This compound is obtained by treating silicon chloride with zinc ethyl. SiCl* + 2Zn(C2H5)2 = 2ZnCP + Si(C^HS)* Silicon- tetrethyl is a colorless, mobile liquid, not decomposed by water, combustible, burning with a brilliant white flame and production of white fumes of silicic acid. It is indifferent to the action of reagents, and acts in all points like a hydrocarbon, C(C^H^)* = C^H^°, in which one atom of carbon is replaced by an atom of silicon. Its analogue, silicon-methyl, a liquid boil- ing at 30°, corresponds to tetramethylmethane, C'^H^^, a hydro- carbon boilin": at 10°. 'o Si(C^H5)* Si(CH^)* C(CH^)* Silicon-ethyl. Silicon-methyl. Tetramethylmethane. The following facts, discovered by Friedel, show the analogy between these compounds of silicon and the corresponding hydro- carbons : When silicon-ethyl is submitted to the action of chlorine, an atom of hydrogen is exchanged for an atom of chlorine, and the chloride Si(C'H*Cl)(C'H5)^ is formed. The latter is a liquid boiling at 185°, and can have its chlorine atom replaced by other atoms or groups, like the alcoholic chlorides. When dis- tilled with potassium acetate, it yields the corresponding acetate, (C'H5)3Si-eH^O.C'H^O, which may be saponified by potas- sium hydroxide, like an alcoholic acetate, the oxyacetyl group, OC^H^O, being replaced by a hydroxyl group. The alcohol so formed, (CH^lSi-C^H^OH, has been named by Friedel silico- nonyl hydroxide, on account of its analogy with nonyl hj^droxide. SiC^H^^OH C^H^IOH Silicononyl hydroxide. Nonyl hydroxide. It is a colorless liquid, insoluble in water, and boiling at 190°. ORGANO-METALLIC COMPOUNDS. 539 OEQANO-METALLIC COMPOUNDS. ZINC-ETHYL. Zn^^(C2H5)2 One of the more important of the compounds formed by the Unftn of the metals with alcoholic radicals is zinc-ethyl, dis- covered by Frankland. It is prepared by heating ethyl iodide with zinc-turnings and a small quantity of sodium on a water-bath. Zinc iodide and zinc-ethyl are formed. When the reaction is terminated, the product is distilled and that portion collected which passes above 115^. All these operations are conducted in an at- mosphere of carbon dioxide. Zinc-ethyl is a colorless, mobile, and highly-refractive liquid. It has a peculiar, penetrating, and very disagreeable odor. It boils at 118°. It takes fire spontaneously on contact with the air, burning with a green flame, and producing white fumes of zinc oxide. If water be added to a small quantity of zinc-ethyl contained in a tube, a brisk eflervescence at once takes place, and a white deposit is formed. The gas is ethane, and the deposit is zinc hydrate. Zn(C'H5)2 -f 2W0 = Zn(OH)^ + 2C'H« Zinc-ethyl will enter into double decompositions, and is much used in the synthesis of organic substances. By the action of phosphorus trichloride on this body, Hof- mann and Cahours obtained triethylphosphine and zinc chloride. There is a zinc-methyl^ Zn(CH^)^, corresponding to zinc- ethyl. MERCUE-METHYL AND MERCUR-ETHYL. These compounds were obtained by Frankland and Duppa, by the action of methyl and ethyl iodides on sodium amal- gam, in presence of a small quantity of acetic ether. Mercur-etJiyl is a colorless, inflammable liquid, insoluble in water. Density, 2.44. Boiling-point, 158-160°. It is one of the most dangerous poisons known. The inhalation of its vapor, even in small quantity, will produce fatal poisoning. 540 ELEMENTS OF MODERN CHEMISTRY. Chlorine, bromine, and iodine instantly decompose mercur- ethyl with formation of a compound of mercur-monethyl. Hgjgl' + r = cm + HgjfH^ Mercui-ethyl. Ethyl iodide. Mercur-monethyl iodide. STANNETHYLS. The discovery of the numerous compounds of tin and efhjl is due to Lowig. Their history has been completed by Frank- land, Cahours, and Riche. As the nomenclature and constitution of the stannethyls have already been indicated (page 457), we need only consider a few of these interesting compounds. Stanno diethyl, Sn(C^H^)l — The iodide of this compound is obtained when ethyl iodide is heated with tin-filings to about 180°. This iodide, Sn(CTI^)'r, purified by crystallization in alcohol, furnishes free stannodiethyl when its solution is treated with zinc, which removes the iodine. Stannodiethyl is an oily, yellow liquid, which does not vola- tilize without decomposition. When heated to 150° it begins to boil, but the greater part of it is decomposed into stanno- tetrethyl and tin. 2[Sn(C^H^)2] = SniC'Wy + Sn The iodide of stannodiethyl crystallizes in pale yellow needles. In its solution, the alkalies precipitate the oxide Sn(C^H^)^0, which forms an amorphous, white precipitate, insoluble in water and alcohol, but soluble in the alkalies and acids with which it forms salts. Stannotriethyl or Sesquistaimethyl, SnXC'HS)^ = (C'H^)' Sn-Sn(C'^H^)l — This is formed, together with the preceding compound, by the reaction of ethyl iodide on an alloy of tin and sodium. It is separated by fractional distillation ; it boils between 265 and 270°. It plays the part of a radical and combines directly with oxygen. The oxide contains Sn^(C^H^)^0 = [Sn(C^H^)^]^0. It combines with the elements of water, form- ing a hydrate, Sn(C^H^)lOH, crystallizable in prisms. These crystals are fusible at 44°. The oxide distils at 272°. It reacts with the acids to form crystallizable salts. [Sn(C^H0^]2O H- 2HN0^ = 2[Sn(C^H^)lN0T + H^O stannotriethyl oxide. Stannotriethyl nitrate. VOLATILE FATTY ACIDS. 541 The iodide, Sn(C^H^)^I, is a liquid having a mustard-like odor, and distilling without decomposition towards 235-238°. Density at 15°, 1.833. Stannotetrethyl, Sn(C^H^)*. — Colorless liquid, almost odor- less, and boiling at 181°. Density, 1.187. It is formed by the action of zinc ethyl on stannodiethyl iodide. Sn(C^H5)^P + Zn(C^H^)2 = Sn(C^H^)* + ZnP Stannnodiethyl iodide. Zinc-ethyl. Stannotetrethyl. It is a saturated compound, and does not enter into combi- nation, but by the action of energetic reagents it yields com- pounds of stannodiethyl or stannotriethyl. Thus, with iodine, the following reaction takes place : SnCC^H^)^ + r = Sn(C'HO'I + C'Wl VOLATILE FATTY ACIDS DERIVED FROM. THE ALCOHOLS. Modes of Formation and Constitution. — These acids result from the oxidation of the alcohols of which the principal com- pounds have been described. They are formed in a great num- ber of reactions, and many of them exist already formed in nature, either in the free state or in combination in neutral fatty compounds, that is, the oils and fats. Their composition is expressed by the general formula C"H^" 0^ ; they contain one more atom of oxygen and two atoms of hydrogen less than their corresponding alcohols. Their principal modes of formation are as follows : 1. By oxidation of an alcohol : CH^O -i- 0' = CH^O^ -I- H^O Methyl alcohol. Formic acid. 2. By oxidation of an aldehyde : Aldehyde. Acetic acid. 3. By the decomposition of an organic cyanide with boiling potassium hydroxide : Methyl cyanide. Potassium acetate. 46 542 ELEMENTS OP MODERN CHEMISTRY. The acetic acid is formed in this last reaction, by the union of the carbon of the cyanogen group with the oxygen of both the potassium hydroxide and the water, the hydrogen of these two bodies combining with the nitrogen of the cyanogen to form ammonia. It may then be admitted that acetic acid con- tains a radical carbonyl, CO, united on the one hand with a methyl group (that of the methyl cyanide), and on the other with a hydroxyl group, OH. The other acids of the series possess an analogous constitu- tion. CH3 C2H5 C3H7 C4H9 CO.OH CO.OH CO.OH CO.OH etc. Acetic acid. Propionic acid. Butyric acid. Valeric acid. 4. A method of synthesis, discovered by Wanklyn, furnishes a direct support to this theory of the constitution of the fatty acids. That chemist realized the synthesis of acetic and pro- pionic acids by passing a current of carbonic acid gas over sodium-methyl and sodium-ethyl, organo-metallic compounds which result from the action of sodium upon zinc-methyl and zinc-ethyl. NaCHS + CO.O = ?^^ CO.ONa Sodium-methyl. Sodium acetate. C2H& ]S[aC2H5 + CO.O = I CO.ONa Sodium-ethyl. Sodium propionate. General Properties. — 1. The volatile fatty acids of the series Qnjj2nQ2 ^j.g niouobasic ; each contains one atom of hydrogen which may be replaced by an equivalent quantity of a metal. 2. When submitted to dry distillation, many of their salts yield a ketone and a carbonate. CH3-C0.0^(. ,, _ CH3-C0.0^^^ Calcium acetate, 3. The same reaction may produce an aldehyde and a hydro- carbon of the series CH^" (Chancel). C3H7 (C3H7-CO.O)2Ca = ,4- C3H6 -f- CaCOS CHO Calcium butyrate. Butaldehyde. Propylene. CH3 CO + CaC03 CH3 cetone Calcium carbonate. FORMIC ACID. 543 4. When a mixture of a salt of a fatty acid and a formate is subjected to dry distillation, the principal product of the reaction is an aldehyde (Piria). CH3 CH3-C0.0K + H-CO.OK = i + K'^GO^ CHO Potassium acetate. Potassium formate. Aldehyde. 5. The fatty acids are converted into chlorides by the action of phosphorus pentachloride, or oxy chloride (G-erhardt). C2H30.0K + PC15 = C2H30.C1 + P0C13 + KCl Potassium acetate. Acetj'l chloride. Phosphorus oxychloride. 6. By the action of these chlorides upon the salts of the fatty acids, the anhydrides of the acids are formed (G-erhardt). C^H^^JO + C2H3.0C1 = KCl + g™}0 Potassium acetate. Acetyl chloride. Acetic anhydi-ide. 7. When subjected to the action of phosphoric anhydride, the ammonium salts of these acids lose 2H^0 and are con- verted into nitriles or cyanogen ethers (Dumas, Malaguti and Le Blanc, Frankland and Kolbe). CH3 CH3 I = 2H20 + I C0.0(NH4) ^ CN Ammonium acetate. Acetonitrile. (Methyl cyanide.) FORMIC ACID. CH202 This acid, which was discovered by S. Fischer in 1760, in red ants, is formed in a great number of reactions, particularly in the oxidation of methyl alcohol, in the decomposition of hydrocyanic acid by acids or alkalies, in the distillation of oxalic acid, and in the oxidation of many organic matters, such as starch, sugar, etc. Berthelot achieved its direct synthesis by heating carbon monoxide for a long time to 100° in sealed flasks containing a concentrated solution of potassium hydrate. CO + KOH = HCO.OK Potassium formate. Preparation. — Formic acid is best prepared by heating oxalic acid with glycerol ; the latter is found unchanged after the reaction, but the oxalic acid is decomposed according to the equation C^O^H^ = H.COOH -f COl 544 ELEMENTS OF MODERN CHEMISTRY. Equal weights of the two substances are heated to about 110° in a retort connected with a condenser; carbon dioxide is disengaged and dilute formic acid distils over. When the action has ceased, a fresh quantity of oxalic acid is added and the heating continued ; the same decomposition takes place, but a more concentrated formic acid (56 per cent.) collects in the receiver. As the glycerol does not suffer a permanent change, the operation may be made continuous by adding fresh quantities of oxalic acid to the retort. Anhydrous formic acid is prepared by decomposing the dry lead salt in a current of hydrogen sulphide. (HCOO)Tb + H^S = 2HC00H + PbS Properties. — Formic acid is a colorless liquid, having a pungent odor and a very acid taste. It boils at 101°, and solid- ifies to a crystalline mass at 8.5°. It mixes with water in all proportions. If an excess of sulphuric acid be added to a small quantity of formic acid contained in a test-tube, and a gentle heat be applied, a regular disengagement of gas will take place ; it may be ignited at the mouth of the tube, and will burn with a blue flame. It is carbon monoxide, formed according to the equa- tion CH^O^ == CO -h H^O. If formic acid be added to solution of silver nitrate, and the liquid heated, it soon becomes clouded ; silver is pre- cipitated, and carbon dioxide disengaged. The formic acid becomes oxidized in reducing the silver nitrate. CH^O^ + = CO^ + H^O Chlorine determines an analogous decomposition. CH^O^ + CP = CO' + 2HC1 Formates. — Formic acid is an energetic acid, perfectly neu- tralizing the bases. It is monobasic; one of its hydrogen atoms can be replaced by an equivalent quantity of metal. The formates are soluble ; the most characteristic are cnpric for- mate^ Cu(CHO')' -j- 4H^0, which crystalHzes in magnificent, obHque rhombic prisms, and lead formate, Pb(CHO'/, which forms long, colorless needles, slightly soluble in cold water. Ammonium formate, which is obtained by saturating formic acid with ammonia, crystallizes in prisms which are very solu- ble in water. When quickly heated to about 200°, it breaks up into hydrocyanic acid (formonitrilc) and water (Pelouze). (NH*)CHO' = 2H^0 + CNH ACETIC COMBINATIONS. 545 FORMALDEHYDE. CH20 = H-CHO Hofmann obtained this body by the slow combustion of methyl alcohol, brought about by a spiral of platinum wire. CH^O + = H^O + CH^O It is also formed in the distillation of barium and calcium formates. Formaldehyde is known only as a vapor at high temperatures, and in aqueous solution. The latter has a pungent odor and powerful antiseptic properties ; " formalin" is a 40 per cent, solution of it used as an antiputrescent and caustic. On evaporation of its aqueous solution, formalde- hyde becomes polymerized, an amorphous solid called para- formaldehyde being produced. Dilute solutions of alkaline hydroxides convert the aldehyde into formose^ a mixture of polymers containing acrose, (CH^O)®, related to the sugars. ACETIC COMBINATIONS. It may be assumed that these compounds contain the mon- atomic radical acetyl (C'H^O)' = (CH'-CO)', which may be regarded as oxidized ethyl. (C2H5)' = I (C2H30)' = I ^ -CH2 ^ -co Ethyl. Acetyl. Diacetyl contains twice this radical, aldehyde is the hy- dride, and acetic acid the hydroxide. Besides these, there are known the oxide and chloride of acetyl, methyl acetyl (acetone), acetyl ammonia or acetamide, etc. The following formulae indicate the relations of these bodies : C2H30.C^H30 C2H30.0H Diacetyl. Acetyl hydrate (acetic acid). C2II30.H (C2H30)20 Acetyl hydride (aldehyde). Acetyl oxide (acetic anhydride). C2H30.CI C2H30 ) Acetyl chloride. H i- N C2H30.CH3 hJ Acetyl methylide (acetone). Acetamide. ACETIC ACID. C2H<02 Acetic acid is the acid of vinegar. It is the product of the oxidation of alcohol. It is formed in a number of other reac- tions, among which we may mention the oxidation of aldehyde, kk 46* 546 ELEMENTS OF MODERN CHEMISTRY. the decomposition of metliyl cyanide by potassium hydrate, the action of carbon dioxide on sodium-methyl, and the dry distil- lation of a great number of organic substances, such as wood, starch, gum, sugar, etc. Preparation. — The large quantities of acetic acid employed in the arts are obtained by the destructive distillation of wood. The operation is conducted in large iron cylinders, heated directly by a fire (Fig. 123). The products of the distillation consist of liquids and gases. The liquids are condensed in a large worm, tt, cooled by a continual circulation of cold water through surrounding pipes mm ; the gases are conducted back to the fire-grate by the pipe h. The condensed product consists of an aqueous portion and of tar. The greater part of the latter is separated by a new distillation ; the first portions which pass contain wood-spirit, after which acetic acid distils. Tlie acid liquid is neutralized by lime, and the calcium ace- tate formed is converted into sodium acetate by adding a solu- tion of sodium sulphate. The liquid, separated by filtration from the calcium sulphate, yields on evaporation sodium ace- tate, still colored brown by tarry matters. The latter are destroyed by frying the salt, that is, by heating it for some time to 250°, a temperature which carbonizes the tar but does not a.ff"ect the sodium acetate. The mass is then exhausted with water, the solution filtered, concentrated, and crystallized. Crystals of pure sodium acetate are thus obtained, a salt which was formerly called ]pyrolignite of soda. Acetic acid is pre- ACETIC ACID. 547 pared by drjdng this salt and distilling it with -| its weight of concentrated sulphuric acid. Or the dry salt may be decomposed by an exact quantity of sulphuric acid. The acetic acid which separates from the sodium sulphate may then be decanted, and cooled in a freez- ing mixture. The portion remaining liquid is separated and the solid mass constitutes pure acetic acid. Vinegar. — Vinegar is the product of the acid fermentation of wine and other alcoholic liquids. The following process is largely employed for the conversion of wine into vinegar. It is the Orleans process. A small quantity of warm vinegar is first introduced into large vats, which have already been used for the operation and are impregnated with the peculiar fer- ment formed ; quantities of wine are then added at intervals of several days, the vats being maintained at a temperature between 24 and 27°. In a fortnight, the acetification is com- plete, and a portion of the vinegar is withdrawn and replaced by a new quantity of wine which also becomes converted into vinegar. The process is thus continuous. Under these cir- cumstances, the alcohol is converted into acetic acid by the influence of a peculiar ferment that is called mother of vinegar. It is a vegetable product, , | amycoderm(J[^co6?er??ia \ ™ aceti), which appears on the surface of the liquid, where it absorbs oxygen from the air and subse- quently cedes it to the alcohol (Pasteur). Its action may be compared to that of platinum black. By another process, a mixture of weak alcohol, water, and albuminoid matter (the juice of pota- toes, beets, etc.), contain- ing the elements neces- sary for the production of the ferment, is allowed to trickle over beech-wood shavings. The latter, which have been previously steeped in strong vinegar, are contained in a large cask, A (Fig. 124), Fig. 128. 548 ELEMENTS OP MODERN CHEMISTRY. where tliey rest upon a double bottom perforated with holes. Tubes, tt^ pass through the upper portion, maintaining a current of air which enters at the lower portion of the cask. Under these conditions, the liquid, which spreads over the shavings and exposes a considerable surface to the air, becomes oxidized with such energy that the temperature soon rises to 30° ; a second passage of the liquid through the casks completes the acetification. Properties of Acetic Acid. — Acetic acid is solid below 1*7°, and crystallizes in large plates. It boils at 118°. Its density at 0° is 1.0801. Its odor is pungent and acid. It is very corrosive. It mixes with water and alcohol in all proportions, and when it is added to water there is a contraction in volume. The maximum contraction, and consequently the maximum density of aqueous acetic acid, corresponds to a mixture con- taining C^H^O^ -f H'^0. Vapor of acetic acid passed through an incandescent porce- lain tube yields gases and deposits carbon, at the same time forming small quantities of acetone, benzene, phenol, and naphthalene (Berth el ot). Phosphorus pentachloride converts acetic acid into acetyl chloride, with formation of hydrochloric acid and phosphorus oxy chloride. en^O.OH -f PCP = C^H^O.Cl + HCl + POCP Acetic acid. Acetyl chloride. If a mixture of small quantities of potassium acetate and arsenious oxide be heated in a test-tube, dense white vapors having an intense and disagreeable odor of garlic will be dis- engaged. This experiment permits the detection of minute traces of acetic acid ; if the latter exist in the free state in the liquid, its potassium compound must first be formed. The white vapor disengaged is due to a body formerly known as fuming liquor of Cadet (see page 496). ACETATES. The more important neutral acetates have the composition R'(C'H^O0 or K"(C'H^02)^ according as the metal which replaces the basic hydrogen of the acetic acid is univalent or bivalent. There are many basic acetates. Potassium Acetate, KC^H^O^ — This is prepared by satu- ACETATES. 549 rating acetic acid witli potassium carbonate and evaporating to dryness. It is thus obtained in crystalline, very deliquescent laminae. It melts at 292°, and is very soluble in water. Sodium Acetate, NaC'H^O' + 3H^0.— This salt is obtained on a large scale in the arts in the manufacture of acetic acid. It was formerly called pyroUgiiite of soda. It crystallizes in large, oblique rhombic prisms, which are very soluble in water, and effloresce in dry air. Acetates of Lead.— Neutral lead acetate, PbCC^H^O')' + 3H^0, known also as sugar of lead, is made by neutralizing acetic acid with litharge. It crystallizes in transparent, efflor- escent, oblique rhombic prisms, having a sweet and astringent taste. It dissolves in half its weight of cold water, and in 8 parts of alcohol. It melts in its water of crystallization at 75.5°. The neutral solution of lead acetate dissolves oxide of lead, forming different basic salts, according to the proportion of oxide dissolved. The more important of these are a dibasic acetate, Pb(C'H^O')' + PbO + 4H^0, and a tribasic acetate, PbCC'H^'O')' -I- 2PbO + nH^O. These two salts are gener- ally formed simultaneously when a solution of lead acetate is boiled with litharge. The solution thus obtained is used in medicine as Goulard's solution. If a few drops of it be added to ordinary river or well water, a cloud is produced, owing to the formation of lead sulphate and carbonate. If carbonic acid gas be passed into a solution of the sub- acetate of lead, a deposit of lead carbonate is formed. In this reaction, which serves for the preparation of white lead by the Clichy method, the excess of lead is removed from the subace- tate by the carbonic acid, neutral acetate being formed and remaining in solution. Acetates of Copper. — The neutral acetate Cu(C^H^O^)^ -j- H^O, is prepared by double decomposition by mixing hot solu- tions of sodium acetate and cupric sulphate. The cupric acetate is deposited on cooling in beautiful, oblique rhombic prisms of a deep bluish-green color. They dissolve in 5 times their weight of boiling water. The dilute aqueous solution is de- composed by boiling, a tribasic acetate being formed, while acetic acid is set free. When cupric acetate is heated, it first loses its water of crys- tallization, and decomposes when the temperature reaches 240 or 250°, disengaging acetic acid, acetone, and carbon dioxide^ 550 ELEMENTS OF MODERN CHEMISTRY. The residue is finely-divided copper. The product of the dis- tillation is a blue liquid, which, when rectified, yields colorless acetic acid mixed with a small quantity of acetone. It was formerly called radical vinegar. The name verdigris is applied to a basic acetate of copper consisting mostly of a dibasic acetate, Cu(C^H^O^)^ -f- CuO -|- 6H^0. Verdigris is prepared by exposing to the air copper sheets piled up in layers with the pulp of grapes. In a few weeks the metal becomes covered with bluish crusts of verdi- gris, which are scraped off" and delivered to commerce in the form of light-blue balls. The alcohol, formed by the fermenta- tion of the sugar contained in the grape-pulp, becomes oxidized by the air and is converted into acetic acid, and under the in- fluence of the latter, the copper itself absorbs oxygen. Water and copper basic acetate are thus formed. Ferric Acetate, Fe(C^H^O^)l — The aqueous solution of this salt possesses a blood-red color. Boiling decomposes it, precipitating ferric hydroxide and liberating acetic acid. The salt is largely used as a mordant in dyeing. Silver Acetate, AgC^H^Ol — This salt, which is but slightly soluble in water, is precipitated when concentrated solutions of sodium acetate and silver nitrate are mixed. It is deposited from boiling water in brilliant, pearly, flexible plates, which darken on exposure to light. Ammonium Acetate, (NH*)C^IFOl — When acetic acid is saturated by a current of ammonia gas, this salt is obtained as a deliquescent, crystalline mass. It is very soluble in water and in alcohol. When heated, it first loses ammonia, then acetic acid, and acetamide finally distils. Nm.C^'ffO^ = WO + C^H^^O.NH^ Ammonium acetate. Acetamide. When distilled with phosphoric anhydride, ammonium acetate yields methyl cyanide, or acetonitrile. Ethyl Acetate, C^H^.C^ffO^, ordinarily known as acetic ether, is prepared by distilling a mixture of alcohol, sulphuric acid, and potassium or sodium acetate : ethyl acetate passes over, together with a certain quantity of alcohol which escapes the reaction. It is purified by agitation with a solution of calcium chloride, and the ether which floats is decanted, dried over calcium chloride, and rectified on the water bath. SUBSTITUTION PRODUCTS OP ACETIC ACID. 551 It is a colorless liquid having a very agreeable, ethereal odor. It boils at 77°. Density at 0°, 0.9105. It is but slightly soluble in water, but dissolves in all proportions in alcohol and ether. Like all compound ethers, it is readily decomposed by potassium hydroxide. C^Hs.C^H^O^ + KOH = KC^H^O^ + C^H^.OH Ammonia converts it into acetamide and alcohol. C2H30.0C2H5 + NH3 = C^Hs.OH + C^HSQ.NHz It undergoes a remarkable reaction with sodium, which dissolves in it, forming sodium ethylate and the compound C^H^NaOl 2[C2H30.0C2H5] + ITa^ = NaO-C^H^ + C^H^NaO' + H^ The body C^H^NaO' is the sodium compound of acetoacetic ether, Q'W'O' = CmXCm'0)0-OC'B.', which is derived from acetic ether, C^H^O-OC^H^, by the substitution of an acetyl group, C^H^O, for one atom of hydrogen in the radical acetyl. Free acetoacetic ether may be obtained by the action of dilute hydrochloric acid upon the sodium compound C^H^NaO^ It is a colorless liquid having an agreeable odor, and boiling at 182°. Density at 15°, 1.03. Sodium acetoacetic ether is extensively used in organic synthesis : it reacts readily with many halogen compounds, such as ethyl iodide, thus : CH'^-CO-CHNa-COO.C^Hs + C'Wl= Sodium acetoacetic ether. CH=*-CO-CH(C2H5)-COO.C^H5 + Nal Ethyl acetoacetic ether. The hydrogen of the CH group in the latter compound can be successively replaced by sodium and an alkyl group, thus : CH3-CO-CNa(C2H5)-COO. C^Hs and CH^-CO-C {Cm^y-COO. Cm^ Sodium ethyl acetoacetic ether. Diethyl acetoacetic ether, SUBSTITUTION PRODUCTS OF ACETIC ACID. Three chlorinated acids are derived from acetic acid : Monochloracetic acid C^HSCIG^ Dichloracetic acid C2H2C1202 Trichloracetic acid C2HC1302 Monochloracetic acid is formed when a current of chlorine is passed into acetic acid heated to 100°, and containing a small quantity of iodine. 552 ELEMENTS OF MODERN CHEMISTRY. Monochloracetic acid is solid, and crystallizes in deliques- cent, rhomboidal tables or in prisms. It boils between 185 and 187.8°. It is very corrosive. It is converted into glycollic acid when heated with an excess of potassium hydrate. KC^H^CIO' + KOH = KC'HXOH)0^ + KCl Potassium Potassium glycoUate. monochloracetate. Ammonia converts it into amidoacetic acid, C^HYNH^) O.OH. V^^^l + NH3 = HCl + ?^^-^^^ CO.OH CO.OH Monochloracetic acid. Glycocoll. Trichloracetic acid, C^HCPO^, a very important compound in the history of the science, was discovered by Dumas in 1840. It was then one of the most remarkable examples of a body formed by substitution, and a comparison of its properties with those of acetic acid led Dumas to announce the first idea of chemical types. It is obtained by exposing acetic acid to the action of a large excess of chlorine in direct sunlight ; more conveniently by oxidizing chloral with concentrated nitric acid (page 556). It forms transparent and deliquescent crystals, fusible at 52.3°, and boiling between 195 and 200°. Its aqueous solution regenerates acetic acid by the action of sodium amalgam, an interesting reaction, since it furnished one of the first examples of inverse substitution (Melsens), as the replacement of chlorine by hydrogen is called. When boiled with potassium hydrate, trichloracetic acid fur- nishes potassium carbonate and chloroform. C^HCPO^ = CHCP + CO^ ACETIC ANHYDRIDE. (C2H30)20 This important body, discovered by Grerhardt in 1852, is prepared by the action of one part of phosphorus oxychloride on three parts of dry sodium acetate. In this operation, acetyl chloride is first formed, and this reacts upon an excess of so- dium acetate, producing sodium chloride and acetyl acetate, or acetic anhydride. CWO.Cl + ^'^N°}0 = Na^' + c'ffo}*^ Acetyl chloride. Sodium acetate. Acetic anhydride. ALDEHYDE. 553 Acetic anhydride is a colorless, mobile liquid, having a strong odor of acetic acid. It boils at 138°. When thrown into water, it sinks to the bottom, and, absorbing one molecule of water, is converted into acetic acid, which dissolves. It acts upon many other substances containing the hydroxyl group, forming acetyl derivatives. For example : 2eH50H + (C'H^O)'O == H'O + 2C^H5.C='H^O^ ALDEHYDE, OR HYDRIDE OF ACETYL. C^H^O = CH3-CH0 This body was discovered by Dobereiner in 1821 ; its com- position and principal properties were studied by Liebig. Preparation. — Aldehyde is prepared by oxidizing alcohol by heating it with manganese dioxide and dilute sulphuric acid, or better, with potassium dichromate and sulphuric acid. The vapors disengaged are condensed in a well-cooled receiver. The distilled liquid is rectified over calcium chloride, only the more volatile portion being collected. This is mixed with twice its volume of ether, and the ethereal solution saturated with ammonia gas. Crystals are deposited which constitute a com- bination of aldehyde with ammonia, and the aldehyde is ob- tained from them by adding a quantity of sulphuric acid exactly sufiicient to form ammonium sulphate with the ammonia; a gentle heat is applied, and the aldehyde vapor is passed through a tube filled with calcium chloride, and finally condensed in a well-cooled receiver (Liebig). Properties. — Aldehyde is a colorless, very mobile Hquid, hav- ing a penetrating and somewhat suffocating odor. It boils at 21°. It mixes in all proportions with water, alcohol, and ether. It combines with ammonia, forming aldehyde-ammonia (Liebig). C^H^O.NH^ = C^H^O.NH* It unites with the alkaline acid- sulphites, forming crystal- lizable combinations. It is readily oxidized, being transformed into acetic acid. C^H^O -f O = C^H^O' If some aldehyde and a few drops of ammonia be added to a solution of silver nitrate, and a gentle heat be applied, the liquid soon becomes clouded, and the sides of the vessel con- taining it are covered with a brilliant deposit of metallic silver. T 47 554 ELEMENTS OF MODERN CHEMISTRY. By tte action of sodium amalgam and water, aldehyde fixes two atoms of hydrogen, and is converted into alcohol (A. Wurtz). C^H^O + H^ =: C^H^O. When hydrochloric gas is passed into a mixture of aldehyde and absolute alcohol, monochlorether is formed. Cm^O + C2H5.0H + HCl = H20 + ^^^2H5>^ Monochlorether. Chlorine converts aldehyde into acetyl chloride and then into butyl chloral. C2H30.H + C12 = C2H30.C1 + HCl Acetyl chloride. Phosphorus pentachloride converts aldehyde into ethi/l- idene chloride, C^H*CP, thus : CH3 CH3 I + PC15 = I + P0C13 CHO CHC12 ^ Aldehyde. Ethylidene chloride. By the action of hydrochloric acid diluted with twice its volume of water, aldehyde doubles its molecule and is converted into a thick, colorless, neutral body, boiling at 95° in a vacuum ; it is soluble in water and reduces ammoniacal silver nitrate. This body is aldol, Q'WO'' (A. Wurtz). When heated with ordinary hydrochloric acid, aldehyde gives crotonic aldehyde (Kekule). Aldehyde. Crotonic aldehyde. The same transformation takes place when aldehyde is heated to 100° with a small quantity of zinc chloride and a trace of water. An important derivative of aldehyde, known as acetaldox- ime, results from the action of hydroxylamine upon aldehyde. CH3CH0 + H^NOH = CH3CHN0H + H20 Hydroxylamine. Acetaldoxime. This body represents a numerous class, the oximes, which are formed by the reaction of hydroxylamine with bodies containing the carbonyl group. Phenylhydrazine, H^N-NH.C'ff (page 676), is another important reagent for compounds containing the carbonyl group. It forms with them condensation products known as phenyJliydrazones, water being eliminated. With aldehyde the reaction is expressed as follows : CH3.CH0 + H2N.NH.C6H5 = CH3.CH=N-NH.C6H5 + H20 ACETYL CHLORIDE. 555 Like all of its analogues, aldehyde can unite with hydro- cyanic acid, forming the compound CH^-CH(OH)(CN), a liquid soluble in water and alcohol, boiling at 183°, and con- verted by acids and alkalies into lactic acid, with disengage- ment of ammonia (see page 598). If sulphur dioxide be added to a dilute magenta solution until the latter is decolorized, the addition of a trace of alde- hyde will immediately restore the pink color. Nearly all the aldehydes respond to this test. When aldehyde is heated to 100° with alcohol, acetal is formed ; this is also found in small quantities among the products of the oxidation of alcohol. CHICHO + C^mOH ^ H^O -f- CH3CH<^^'[^5 Aldehyde. Alcohol. Acetal. Polymerides of Aldehyde, — Aldehyde has a great ten- dency to become converted into polymeric modifications. Among these are paraldehyde^ which is liquid, and metalde- hyde, which is solid (Liebig). Paraldehyde, C^H^^O'^, is formed by the action of a trace of sulphuric acid or of zinc chloride on aldehyde. It is a color- less liquid, having a density of 0.998 at 15°, and boiling at 124°. At a low temperature it solidifies to a leaf-like, crys- talline mass, fusible at 10.5°. It dissolves in eight times its volume of water. When distilled with a small quantity of sulphuric acid, it is again converted into aldehyde. ACETYL CHLORIDE. C2H30.C1=V COCl This body was obtained by Grerhardt in 1852, by treating sodium acetate with pentachloride, or oxychloride of phos- phorus. NaC^ffO^ H- PCP = C^H^OCl + NaCl + POCP Sodium acetate. Acetyl chloride. Phosphorus oxychloride. It is also formed by the action of chlorine on aldehyde. It is a colorless, mobile liquid, having a pungent odor. It boils at 55°. If it be poured into water, it sinks to the bottom, but rapidly decomposes into hydrochloric and acetic acids. CTFO.Cl f H^O = HCl + C^H^O.OH 556 ELEMENTS OF MODERN CHEMISTRY. It undergoes a similar decomposition witli alcohol, forming ethyl acetate and hydrochloric acid. C^H^O.Cl + C^H^OH .:= HCl + C^HlC^ffO^ With ammonia, it forms acetamide and ammonium chloride. C'ff O.Cl + 2NH3 = NH*C1 + C'H^O.NH^ It reacts with acetates, forming acetic anhydride. CHLORAL, OR TRICHLORALDEHYDE. CCF C2C13HO = 7 CHO This important body was discovered by Liebig and Dumas. It is formed by the prolonged action of chlorine on alcohol. It is a colorless, mobile liquid, having a peculiar, penetrating odor. It boils at 97.7°. Grerhardt regarded it as aldehyde in which the three atoms of hydrogen of the radical are replaced by three atoms of chlorine. C^H^O.H C^CPO.H Aldehyde. Chloral. (Acetyl hydride.) (Trichloracetyl hydride.) Its reactions resemble those of aldehyde. It forms crystal- lizable compounds with the disulphites. Its ammoniacal solu- tion reduces silver nitrate. These facts indicate that chloral contains the group CHO, characteristic of the aldehydes. It regenerates aldehyde by the action of nascent hydrogen (Personne). The caustic alkalies decompose it into chloroform and a formate (Dumas). C^HCPO 4- KOH = KCHO' + CHCP Chlox-al. Potassium formate. Nitric acid converts it into trichloracetic acid, in the same manner that aldehyde is converted into acetic acid. C'HCPO + == C^HCPO^ Chloral forms a crystallizable compound with water, C^HCPO CCP -1- H^O = I ' called chloral hydrate. The latter CH(0H)2 -^ melts at 57°, and boils at 98° (Personne), being at the same time decomposed into anhydrous chloral and water. It is very soluble in water. ACETONE. SST In contact with concentrated sulphuric acid, chloral is rapidly converted into a white, solid substance which is insol- uble in water ; it has the same composition as ordinary chloral, and is called insoluble chloral. Chloral also combines with alcohol, forming alcoTiolate of chloral (Personne). Chloral hydrate has for some time been successfully employed in medicine as a soporific and anodyne (Liebreich). DIACETYL. (CH3.CO)2 Two acetyl radicals which cannot exist alone unite together forming the interesting compound diacetyl. This has been obtained in various ways by reactions too intricate to describe here. It is a yellow liquid having a characteristic odor. It boils at 87°, and mixes readily with water and alcohol. Like other ketones, it will combine with hydroxylamine, and since it contains two carbonyl groups it is capable of forming a monoxime and a dioxime. The latter is highly characteristic, being a white crystalline body, insoluble in water. Its melt- ing-point is 234°. Diacetyl also combines with phenylhydra- zine and hydrocyanic acid. ACETONE. C3H60 Acetone is the methylide of acetyl, C^H^O.CH^, and since acetyl itself is carbonyl (carbon monoxide) methylide, CH^-CO, acetone can be regarded as carbonyl dimethylide, CH^-CO-CH^. CO" IS . C0"fCH3 Carbonyl chloride. Carbonyl dimethylide (acetone). Indeed, the synthesis of acetone has been made both by treat- ing acetyl chloride with zinc methyl (Pebal and Freund), and by treating sodium methyl with carbonyl chloride. Zn(CH3)2 + 2(C^H30.C1) = 2(C^H3O.CH0 + ZnCP Zinc methyl. Acetyl chloride. Acetone. 2(CHlNa) + CO I ^} = 2NaCl + CO | ^^3 Sodium methyl. Carbonyl chloride. Acetone. Preparation. — Acetone is prepared by distilling dry calcium acetate in a clay retort. The vapors given oiF are condensed 47* 558 ELEMENTS OF MODERN CHEMISTRY. in a well-cooled receiver, and the liquid obtained is distilled on a water-bath with an excess of calcium chloride. CaCC^H^O^)^ = C'WO + CaCO^ Properties. — Acetone is a colorless liquid, having a slightly empyreumatic, ethereal odor. It boils at 56°. It dissolves in all proportions in water, alcohol, ether, and wood-spirit. Like aldehyde, it forms crystallizable combinations with the alkaline acid-sulphites. Acetone and its homologues are not susceptible of direct oxidation. If it be heated with a mixture of sulphuric acid and potassium dichromate, it breaks up into acetic acid and formic acid, a portion of the latter being oxidized to carbon dioxide. CHICO.CH^ + 0^ =:= CH^-CO.OH + HCO.OH Nascent hydrogen, produced by sodium amalgam and water, converts it into secondary propyl alcohol (page 521). Besides isopropyl alcohol, the action of nascent hydrogen on acetone gives rise to a product of condensation of IP with two molecules of acetone, which is named pinacone. Pinacone. It is a tertiary glycol (see page 578). It constitutes a colorless, crystallizable mass, fusible at 42°, and boiling at 172°. When acetone is added in small portions to phosphorus pontachloride, a very energetic reaction takes place and two chlorides are formed. One of them, C^H'^CP (methylchlor- acetol), boils at 70°. The other, C^H^Cl (monochloropropy- lene), boils at 23° (Friedel). C3H60 -I- POP = C^H'^CP + POCP C^H«CP = C^H^Cl + HCl Like aldehyde, acetone will unite with hydrocyanic acid, forming a cyanide (or cyanhydrin), which is decomposed by both acids and alkalies, with disengagement of ammonia and formation of an acid; the group CN is then converted in carboxyl CO.OH. ^|3>C0 + HON = CH3>C<^^ Acetone. Acetone cyanhydrin. ACIDS OF THE SERIES C°h'^°0^. 559 Acetone unites with hydroxylamine, forming a highly characteristic, colorless crystalline compound, acetoxime, which melts at 59°. CH3>C0 + H2N0H = ^g3>CN0H + H20 With phenylhydrazine it condenses to acetone phenylhy- drazone, (CH^)^=N-NH.C^H^ a reaction which is likewise characteristic of bodies containing the carbonyl group. ACETAMIDE. C2H30.NH2 This amide may be obtained by heating ethyl acetate to 100° in sealed tubes with aqueous ammonia. Alcohol and acetamide are formed according to the equation When the resulting liquid is evaporated in a vacuum, the acetamide remains. It may be purified by distillation, collecting that which passes above 200°. Acetamide is also formed by the action of ammonia on acetyl chloride ; one of the readiest methods of preparing it consists in simply distilling ammonium acetate. It is a solid, crystallizable body, soluble in water in all pro- portions. Its odor resembles that of mice. Boiling potassium hydrate reacts with it, forming potassium acetate and ammonia. Phosphoric anhydride removes from it the elements of water, converting it into acetonitrile or methyl cyanide. ACIDS OF THE SERIES C"H^"0^ Formic and acetic acids, of which the principal derivatives have just been described, are the first terms of a very extensive homologous series. It is the series of volatile fatty acids, so named because it includes a great number of compounds which were at first obtained from the natural fatty bodies, and which are the fatty acids proper. Among the bodies congeneric with acetic acid, those of which the molecules are less complicated are liquid at ordinary temperatures ; the others are solid. The following table gives the nomenclature, composition, and prin- cipal physical properties of these acids : 560 ELEMENTS OF MODERN CHEMISTRY. NAMES OF ACIDS. CETJDE EATIONAI, MELTING- BOILING^ FORMULA. FOEMUL^. POINTS. POINTS. Formic acid . . . . CH202 H-CO.OH 8° 101° Acetic acid . . . . . C2H402 CH3-C0.0H 17° 118° Propionic acid . C3H602 C2H5-CO.OH —36.5° 140.7° Butyric acid . . . C*H802 C3H7-CO.OH 0° 163° Valeric acid (isovaleric) C5Ili0O2 C4H9-C0.0H —51° 175° Caproic acid (isocaproic) C6H1202 C5H11-C0.0H 8° 205° (Enanthylic acid . . . C7Hi*02 C6Hi3_CO.OH —10.5° 212° Caprylic acid . . . C8H1602 C7H15-CO.OH 16.5° 236° Pelargonic acid . . C9H1802 C8Hn-C0.0H 12.6° 260° Capric acid . . . . C10H20O2 C9H19-CO.OH 31.4° Laurie acid . . . . C12H2402 C11H23-CO.OH 43.6° Myristic acid . . . C1*H2802 C13H27-CO.OH 53.8° Palmitic acid . . . C16H3202 C15H31-CO.OH 62° Margaric acid . . . 01^3*02 C16H33-CO.OH 60° Stearic acid . . . . C18H3602 C17H35-CO.OH 69.2° Arachnic acid . . . C20H40O2 C19H39-CO.OH 75° Benic acid . . . . C22H4402 C21H43-CO.OH 96° Cerotic acid . . . C27H5402 C26H53-CO.OH 78° Melissic acid . . . C30H6002 C29H59-CO.OH 88° We have already noticed the existence of numerous isomeric alcohols, and in their study the principles of isomerism have been explained. Such isomerides exist also in the series of acids, and are caused by the different atomic structure of the radicals, C"H'^"+\ which figure in the preceding formulae. We will consider two examples. 1. When normal butyl alcohol, CH^-CH^-CH^-CHIOH, is oxidized, normal butyric acid, or the butyric acid of fermentation, is obtained, CH^-CH^-CH^- CO.OH. The acid obtained by oxidation of the butyl alcohol of fermentation is different from this, and the difference is caused by the difference in structure of the radicals (C^H^)'. Isobutyric acid, derived from the alcohol of fermentation, whose constitution is pTT3^CH-CH^0H, contains prrs^ CH-CO.OH. The acid is derived from the alcohol by the substitution of for H^ in the group (CHIOH)'. 2. As we have already seen, the constitution of amyl alcohol of fermentation is expressed by the formula The valeric acid produced by its oxidation is then Qg3>CH-CH2-CO.OH PROPIONIC ACID. 561 Normal valeric acid results from the oxidation of normal amyl alcohol, and contains CH3-Cff-CH^-CH=^-C0.0H QJJ3 Methylethylacetic acid, pjrrs^CH-CO.OH, or optically active valeric acid, is derived from active amyl alcohol. The trimethylacetic acid, which was discovered by Butlerow, contains (CH^)^C-CO.OH ; it is derived from the alcohol (CH^yC-CHlOH, which is not known. If we compare the three isomeric acids, C^H^°0^ with acetic acid itself, we will find that their isomeric relations can be ex- pressed in a very simple manner, by saying that normal valeric acid is propylacetic acid, the acid derived from the alcohol of fermentation is isopropylacetic acid, and that the last two are methylethylacetic and trimethylacetic acids. CH3 CH2(C3H7) CH2(CH<^23) CO.OH CO.OH CO.OH Acetic acid. Propylacetic acid. Isopropylacetic acid. CH<^2H5 C(CH3)3 CO.OH CO.OH Methylethylacetic acid. Trimethylacetic acid. The foregoing facts are sufficient to elucidate the isomerism of acids of the series C^B.'^'OK PEOPIONIC ACID. C3H602 = CH3-CH2-CO.OH This acid is formed by the action of potassium hydrate on ethyl cyanide. It is also a product of fermentation ; thus, it has been obtained by allowing a solution of sugar, mixed with chalk and cheese, to ferment during a year. It is also formed in small quantity in the distillation of wood. Wanklyn made its synthesis by passing carbon dioxide over sodium ethyl. CO.O + C'Wm = C^H^-CO.ONa Sodium propionate. It is most conveniently prepared by oxidizing normal propyl alcohol by means of chromic acid (Pierre and Puchot). CH^-Cff-CH^.OH + 0^ = CH^CH^COOH + H=^0 II 562 ELEMENTS OP MODERN CHEMISTRY, Properties. — It is a colorless, mobile liquid, having an odor like that of acetic acid. It solidifies at — 36.5°, and boils at 140.7°. Density at 21°, 0.996. It is miscible with water in all proportions. Calcium chloTide separates it from its aqueous solution. There are a great number of substitution products directly related to propionic acid. Among these are the chlorine, bro- mine, and iodine derivatives, and the amides. Two of these derivatives are known of each particular species, presenting curious isomeric relations. The following examples will serve as illustrations : CH3 CH3 CH2C1 CH3 CH2(NH2) CH2 CHCl CH2 CH(NH2) CH2 C02H C02H C02H C02H C02H Propionic a-Chloropro- jS-Chloropro- a-Amidopropi- /3-Amidopropi- acid. pionic acid. pionic acid. onic acid. onic acid. Only the iodo-derivatives will be described here, and farther on we will mention the amides. a-iodopropionic acid^ C^H^IO^, is prepared by the action of concentrated hydriodic acid or phosphorus iodide on lactic acid. CWO^ + HI = C^H^IO^ -f H^O Lactic acid. It is a thick, oily body, almost insoluble in water. 13-todopropwmc acid is formed by the action of concentrated hydriodic acid or phosphorus iodide and water on glyceric acid. C^H«0* + SHI = C^H^IO^ -f 2H20 +r Glyceric acid. It is also formed by the direct combination of hydriodic acid and acrylic acid, C^H*0^. (;i3JJ4Q2 _|_ HI ^ C^H^IO^ It is a solid, occurring in crystalline laminae, fusible at 82°. It is very soluble in boiling water. When heated to 180° with hydriodic acid, it is converted into propionic acid. C^H^IO' + HI r= r + C^H^O' BUTYRIC ACIDS. C4H802 Normal Butyric Acid, CH^-CH^-CH^-CO.OH, was dis- covered by Chevreul in butter, where it exists in combination BUTYRIC ACIDS. 563 with glycerol in butyrin. Pelouze and G-elis have shown that it is formed in abundance when a solution of sugar, glucose, or even starch is abandoned for several weeks with the addition of chalk and old cheese. In about ten days a mass of calcium lactate is formed, but this soon disappears, gases being at the same time disengaged. The mass again becomes liquid, and the solution contains calcium butyrate. This is converted into sodium butyrate, which is finally decomposed by sulphuric acid ; the butyric acid separates in the form of an oily liquid, which is decanted and distilled. Properties. — Butyric acid is a colorless liquid, having a pun- gent and disagreeable odor which recalls that of rancid butter. It is quite soluble in water. Density at 14°, 0.958. Boiling- point, 163°. It perfectly neutralizes the bases, forming butyrates. These salts, which are mostly soluble in water, have a fatty aspect. Calcium butyrate, Ca(C*H^O^),^ is more soluble in cold water than in hot water, so that its cold saturated solution becomes a solid mass when heated to 70°. Butyrone, or Dipropyl Ketone. — When calcium butyrate is subjected to dry distillation, it yields, as principal product, butyrone, one of the homologues of acetone (Chancel). Ca(C*H^O'0' = (C3H^)^C0 -f CaCO^ Calcium butyrate. Butyrone. Butyrone is a colorless liquid, lighter than water, and having a peculiar, ethereal odor. It boils at 144°. Butaldehyde, C*H^O, is the principal product of the dis- tillation of a mixture of butyrate and formate of calcium. Ca(C*H^O0^ H- Ca(CHO^)^ = 2CaC0^ + 2C*H«0 This important reaction, discovered by Piria, permits of the conversion of butyric acid into its aldehyde ; it can also l)e ap- plied to the transformation of other acids into aldehydes. Butaldehyde, which was discovered by Chancel, is a liquid, boiling at 74°. Like aldehyde, it forms a crystallizable com- pound with ammonia, unites with the alkaline acid-sulphites, and reacts with hydroxylamine and phenylhydrazine, as do the other aldehydes and the ketones. Isohutyric Acid, ^g3>CH-C0.0H, isomeric with bu- tyric acid, was discovered by Markownikow. It is formed by the oxidation of butyl alcohol of fermenta- 564 ELEMENTS OF MODERN CHEMISTRY. tion, and exists naturally in the fruit of the Ceratonia siliqua (carob locust, St. John's bread). It is also obtained by decom- posing isopropyl cyanide with potassium hydroxide. (C^H^yCN + 2W0 = NH^ + (C^HO'-CO^H It is a liquid having a disagreeable odor, like that of the acid of fermentation. Density at 20°, 0.9503. It boils at 154°. Its calcium salt differs from that of the normal acid in being more soluble in hot than in cold water. YALEKIC ACIDS. C5H10O2 Isovaleric Acid,QTT3>CH-CH2-CO.OH, was discovered by Chevreul, who obtained it from dolphin oil. It may be prepared by distillation of valerian root with water ; hence its name. It occurs also in angelica root and in Viburnum opulus. The same acid is formed when amyl alcohol is oxidized by a mixture of potassium dichromate and sulphuric acid. It is also formed when potassium hydrate is boiled with isobutyl cyanide, a reaction similar to that which has been indicated for the formation of isobutyric acid. ^^3>CH-CH2-CN + 2H20 ^ NH^ + ^]|^3>CH-CH2-C0.0H Isobutyl cyanide. Isovaleric acid. Valeric acid is a colorless liquid, having a pungent, disagree- able odor. Density at 0°, 0.947. It boils at 175°. It dissolves in 30 parts of water, from which it is precipitated by the addi- tion of neutral salts. Its ammonium salt is used in medicine. Normal Valeric Acid, which has already been mentioned (page 561), is a colorless liquid, smelling like butyric acid. It boils at 184-185°, and its density at 0° is 0.9577. Methylethylaeetic Acid, ^2H5>CH-C0.0H, or optically active valeric acid, has been obtained by the oxidation of active amyl alcohol. It boils at 173°. Trimethylacetic Acid is formed when potassium hydrate is boiled with the cyanide derived from trimethylcarbinol. (CH3)^C-CN + 2H20 = (CH^)'C-CO.OH + NH^ It is a crystalline mass, fusible at 35°, and boiling at 163.8°. It dissolves in 40 parts of water at 20°. HIGHER FATTY ACIDS. 565 CAPEOIC ACIDS. C6H1202 There are at present known seven isomeric acids having the composition C^H^^O^ One of them was discovered in butter by Chevreul. Normal caproic acid is formed by the oxidation of normal hexyl alcohol, and in the decomposition of normal amyl cyanide by boiling potassium hydrate. It is an oily liquid, having but a faint odor ; its density at 0° is 0.945, and it boils at 205°. Leucine^ C^H^^NO^ an important nitrogenized body which exists in the animal economy, is an amide, C^II"(NII^)0^, of normal caproic acid. The caproic acid mentioned on page 560 is an isomeride of the preceding acid. It is obtained by decomposing, by potas- sium hydrate, amyl cyanide derived from the alcohol of fer- mentation. HIGHEH FATTY ACIDS. Our limited space will not permit of a description of all of the acids of this series ; we can only briefly consider the last members. Palmitic Acid, C^*^H^^Ol — This exists in palm-oil in com- bination with glycerol. It is prepared on a large scale by distilling palm-oil by means of superheated steam, which de- composes the oil into fatty acid and glycerol. The fatty acids solidify on cooling. The mass is expressed to remove the liquid oleic acid with which it is impregnated, and so obtained in dry, white cakes, which are used for the manufacture of candles. The pure acid melts at 62°. Margaric Acid, C^^H^*0^ — This acid was supposed by Chevreul to exist in most solid fats, but Heintz has shown that the so-called margaric acid derived from fats consists of a mixture of palmitic and stearic acids. Normal margaric acid was prepared synthetically by Kraff"t by decomposing cetyl cyanide by potassium hydroxide. C^«H3^CN -f 2H^0 = C^^H^^COOH -f NH^ It is said to exist in adipocere^ a waxy substance formed by the prolonged action of air and moisture on certain animal substances. Margaric acid crystallizes in white scales fusible at 60°, and soluble in alcohol and ether. 48 666 ELEMENTS OF MODERN CHEMISTRY. Stearic Acid, C^^H^^O^ was obtained from tallow by Chev- reul. It is a solid, melting at 69.2°. After cooling, tlie fused acid becomes a laminated, white mass. It is insoluble in water, but dissolves in alcoliol and ether. The alcoholic solu- tion deposits it in small pearly scales, which are not greasy to the touch. Stearic acid is used for the manufacture of stearin candles. The alkaline stearates are soluble in water. If a large excess of water be added to the solution of a neutral stearate, a crystal- line precipitate is formed which, according to Chevreul, is an acid stearate. On this reaction he has founded a method for the preparation of stearic acid. The stearates of calcium, barium, and lead are insoluble in water, and can be obtained by double decomposition. Cerotic and Melissic Acids. — These acids have been ob- tained from wax by Brodie (page 528). OLEIC ACID AND ITS HOMOLOaUES. Oleic acid, which has just been mentioned and which Chev- reul obtained from olein, is the principal constituent of a great number of oils and fats ; it does not belong to the series of volatile fatty acids. Its formula, C^^H'^^O^, shows that it differs from stearic acid by containing two atoms of hydrogen less than the latter acid. It belongs to the series CH^'^'^Ol AcryHc Acid, CH^^CH-CO.OH.— This is the first term of the series CIP^'^O^ It receives its name from the fact that it results from the oxidation of acrolein^ or acraldeliyde, C^H*0, which is formed in the destructive distillation of neutral fatty substances and glycerol and its compounds ; it is a product of the dehydration of glycerol. C3JJ8Q3 ^ Q3H4Q _|_ ^WO Glycerol. Acrolein. Acrolein reduces silver oxide, like the other aldehydes, being converted into acrylic acid. This acid is liquid, and boils at 140°. Like other unsaturated acids, it combines directly with nascent hydrogen, bromine, and the halogen acids. Fusion with potassium hydrate decomposes it into formic and acetic acids. A similar decomposition occurs with the other unsaturated acids. By fusion with alkaline hydroxides all are decomposed, yielding salts of two acids, but the split does not always take place at the double bond. OLEIC ACID. 567 Crotonic Aldehyde and Acid. — These two bodies are homologues of acrylic aldehyde and acid. Cm^O acraldehyde. Cm'^0^ acrylic acid. C*H60 crotonaldehyde C^H^O^ crotonic acid. Crotonaldehyde is one of the numerous transformation products of ordinary aldehyde. When the latter body is sub- jected to the action of certain salts, it loses the elements of water and is converted into crotonaldehyde. This aldehyde is a liquid having a very irritating odor and an acrid taste. It boils at 103°. When submitted to the action of oxidizing agents, such as silver oxide in presence of water, it is converted into crotonic acid. This acid crystallizes in large plates, fusible at 72°. It boils at 182°. Nascent hydrogen, produced by the action of sul- phuric acid and zinc, converts it into normal butyric acid, CH^-CH^-CH^-CO.OH. It combines directly with bromine, producing heat, and is changed into dibromobutyric acid, CH^-CHBr-CHBr-CO.OH. Fusion with potassium hydrate decomposes it into two molecules of acetic acid. There is an isocrotonic acid^ CH^=:CH-CH^-CO.OH, a liquid boiling at 172°. When heated to 170-180° in sealed tubes, it is converted into crotonic acid. Oleic Acid, C^^H^^O^ — This acid, of which the preparation has been indicated (page 565), is an oily hquid, which solidifies to a crystalline mass at 4°. Its concentrated alcoholic solution deposits it, when cooled, in small needles fusible at 14°. Under a pressure of 10 m.m. it distils without decomposi- tion at 223°. When pure it is odorless, and does not redden litmus paper. On exposure to the air it absorbs oxygen, and becomes rancid and acid. Fusion with potassium hydrate converts it into acetic and palmitic acids. When boiled with nitric acid, it is oxidized, losing carbon dioxide, and there are formed volatile fatty acids from acetic to capric acid, and homologues of oxalic acid, including suberic (C^H^*0*) and succinic (C*H^O*) acids ; nitrogen peroxide con- verts oleic acid into an isomeride, elaidic acid, a solid body, crystallizing in brilliant plates, fusible at 44-45° (Boudet). C^Hio C6H14 Butane. Hexane. C*H6(0H)* C6H8(OH) Erythritol. Mannitol. 568 ELEMENTS OF MODERN CHEMISTRY. POLYATOMIC COMPOUNDS. After the description of the comparatively simple compounds which are naturally grouped with the monohydric alcohols, we proceed to the more complex compounds constituting the poly- hydric alcohols and their derivatives. The latter alcohols are neutral hydroxides, capable of reacting with the acids to form neutral combinations analogous to the compound ethers. Those better known are related to the saturated hydrocarbons, from which they are derived by the substitution of several hydroxyl groups for as many atoms of hydrogen. C2H6 C3H8 Ethane. Propane. C2H*(OH)2 C3H5(OH)3 Dihydroxyethane Trihydroxypropane (glycol). (glycerol). By oxidation of these polyhydric alcohols, acids are pro- duced which bear the same relation to the former that acetic acid bears to ordinary alcohol. It will be noticed that the radicals of these alcohols are un- saturated hydrocarbons, that is, they contain less hydrogen than the saturated hydrocarbons, C''H^"+^. Of these radicals, only those can exist in a free state which contain an even number of atoms of hydrogen. We will briefly consider the more important of them. ETHYLENE. C2H4 = CH2=CH2 This gas, formerly known as olefiant gas or heavy carbu- retted hydrogen, is formed in a great number of reactions. It is produced, together with other hydrocarbons, when substances rich in carbon and hydrogen, such as fats and resins, are de- composed by dry distillation, that is, by the destructive action of heat. Preparation. — A mixture of 25 grammes of alcohol with 150 grammes of sulphuric acid is heated in a 2-litre flask provided with a delivery-tube and a funnel-tube. When the evolution of gas begins, a mixture of 1 part alcohol and 2 parts sulphuric acid is allowed to drop in slowly through tlie funnel-tube, and the gas is washed first through sulphuric acid and afterwards through potassium hydroxide solution. It may be collected over water. ETHYLENE. 569 Towards the close of the operation the liquid blackens, and much sulphurous and carbonic acid gases are disengaged. These are absorbed by the caustic potash in the wash-bottle. The following equation expresses the reaction by which ethylene is formed : Composition and Properties. — Ethylene is a colorless gas, having a feeble, ethereal odor. Its density is 0.9784 compared to air, or 14 compared to hydrogen. It is liquefied by a press- ure of 60 atmospheres at 13° (its critical temperature), and the evaporation of the liquid under reduced pressures affords a valuable means of attaining low temperatures. Its composition may be deduced from the following experiment : 2 volumes of ethylene (2 cubic centimetres, for example) and 6 volumes of oxygen are introduced into an eudiometer over mercury. After the passage of the spark, the 8 volumes will be found to be reduced to 4 volumes, all of which will be entirely absorbed if a solution of potassium hydrate be passed into the tube. The 4 volumes are therefore carbon dioxide. 4 volumes of carbon dioxide represent 200^. 2 volumes of ethylene therefore contain C^. 4 volumes of carbon dioxide contain but 4 of the 6 volumes of oxygen employed ; the other two have therefore been used in the formation of water and have burned 4 volumes of hydrogen. 2 volumes of ethylene then contain 4 volumes of hydrogen. Eudiometric analysis therefore indicates the composition of ethylene to be C'''H* = 2 volumes. This gas is inflammable and burns in the air with a brill- iant flame. When mixed with three volumes of oxygen and ignited, it produces a violent explosion. It is slowly absorbed by concentrated sulphuric acid, ethyl- sulphuric acid being formed. When ethylene is heated with hydriodic acid, the two bodies combine directly to form ethyl iodide. If one volume of ethylene and two volumes of chlorine be- rapidly mixed in a tall jar, and a lighted match be applied, the mixture takes fire and burns with a red flame extending to the bottom of the jar, which becomes covered with a black deposit of carbon. C'H* + 2CP =: 4HC1 + C' If equal volumes of ethylene and chlorine be mixed and ex- posed to diffused light on the pneumatic trough, the water will 4:8* 570 ELEMENTS OF MODERN CHEMISTRY. soon rise in the jar, and the two gases will disappear. At the same time, oily drops will appear on the sides of the jar and upon the surface of the liquid. The body so formed is a liquid insoluble in water, and results from the direct combination of ethylene and chlorine. It was formerly called Dutch liquid, or Dutch oil (hence the old name defiant gas) ; it is now called ethylene chloride. Its composition is expressed by the formula C'H^CP. It boils at 82.5°. If a small quantity of bromine be poured into a large flask filled with ethylene, and manipulated so that the bromine may form a thin layer on the sides of the flask, an elevation of tem- perature will be observed, and the liquid will rapidly become colorless. The bromine has combined with the ethylene to form a colorless liquid, ethylene bromide^ boiling at 131°. Ethylene iodide^ C^H*P, may be obtained by introducing iodine into large jars filled with ethylene, and exposing to dif- fused light during several days. The iodine gradually dis- appears and a white solid is formed which may be purified by crystallization in alcohol ; it is ethylene iodide. Chloro-Derivatives of Ethylene and Ethylene Chloride. — If ethylene chloride be heated with an alcoholic solution of caustic potash, a brisk reaction soon takes place. A gas is disengaged and may be collected over water ; on contact with a lighted taper, it burns with a flame tinged with green. This gas is chlor ethylene. It is formed according to the fol- lowing equation : C^H^CP + KOH = H^O + KCl + C'H^Cl Like ethylene itself, chlorethylene will combine directly with two atoms of chlorine, forming chlorethylene chloride, C^H^Cl. CP, which may also be obtained by the action of chlorine on ethylene chloride. Chlorethylene chloride is decomposed by alcoholic potash, like ethylene chloride. Water, potassium chloride, and dichlor- ethylene are formed. Q2H3QP _|_ g;QH ^ JJ2Q _|_ J^Ql _|_ C^H^CP Chlorethylene chloride. Dichlorethylene. In its turn, dichlorethylene can fix two atoms of chlorine, forming dichlorethylene chloride. These reactions have permitted the preparation of two classes of chloro-compounds, — one derived from ethylene chlo- ride, the other from ethylene itself. DENSITIES. BOILING-POINTS. 1.256 at 12° 82.5° 1.422 at 17° 115° 1.576 at 19° 137° 158° 182° —18 to —15° 1.250 at 14° 55° 87 to 88° 2.619 at 20° 121° HOMOLOGOUS SERIES, C^H^'^. 571 C2H4C13 ethylene chloride. C^H^CF chlorethylene chloride. C2H^C14 dichlorethylene chloride. C2HC15 trichlorethylene chloride. C^Cl^ carbon sesquichloride. C^H-i ethylene. C2H3C1 chlorethylene. C2H2C12 dichlorethylene. C2HC13 trichlorethylene. C2C1* tetrachlorethylene. Regnault, who carefully studied these bodies, has shown that the terms of the first series are isomeric with the chloro- derivatives of ethyl chloride, with the exception of the last two, which are the same in both series. That we may more thoroughly understand this isomerism, we will consider ethylene chloride, C'^H^Cl'^, and its isomeride dichlorethane, called also ethylidene chloride. In the first, two atoms of chlorine are united, each to a different atom of carbon ; in the second, both are united to the same carbon atom. CH2C1 CHC12 CH2C1 CH3 Ethylene chloride. Ethylidene chloride. TetracMor ethylene was discovered by Faraday in 1821. It is formed by the action of alcoholic potassium hydrate on tri- chlorethylene chloride. C^HCP = C^CP + HCl It is also formed by the action of a red heat on carbon sesquichloride. It is a very mobile liquid, which does not solidify at — 18°. It absorbs chlorine under the influence of direct sunlight, being transformed into carbon sesquichloride, C^CP. HOMOLOGOUS SERIES, C^H^"^ Ethylene is the first member of a long series of homologues, of which we will summarily describe a few of the others. Since ethylene is (CH^)^, the constitution of the higher members of the series, properly speaking, should be represented by the formula {QWy. 572 ELEMENTS OF MODERN CHEMISTRY. Such bodies have been prepared, but they cannot be re- garded as the true homologues of ethylene. Their molecules do not contain any doubly-linked carbon atoms, and conse- quently they do not readily combine with the halogens. The superior homologue of ethylene is propylene, CH^-CH=CH^, and isomeric with this is trimethylene, which is represented by the formula CH2 / \ CH2-CH2 Above the fourth member of this series, butylene, the number of isomerides increases rapidly. Thus, the butylene derived by dehydration from butyl alcohol of fermentation is gg3>C=CH2 It is formed according to the following reaction : ^^3>CH-CH2.0H — H20 ^ ^g3>C=CH2 Independently of this butylene, there are two others, the formation and principal properties of which will be indicated farther on. Their constitutions are expressed by the formulae CH3-CH=CH-CH3 CH3-CH2-CH^CH2 The isomeric relations of these three butylenes may be repre- sented in a very simple manner if we consider them to be derived from ethylene, H^C=CH^, the hydrogen of which is partly replaced by methyl or ethyl. The following compounds are thus obtained : Dimethylettiylene a (CH3)2C=CH2, boils at —6°. Dimethylethylene ^ (normal) (CH3)HC=CH(CH3), boils at +3°. Ethylethylene (C2H5)HC=CH2, boils at —5°. The fifth member of the series, amylene or pentene^ C^H^'', presents still more numerous isomerides, but they can all be explained by the principles already exposed : they may be re- garded as derivatives of ethylene by the substitution of a pro- pylic or isopropylic group for one atom of hydrogen, or by the substitution of an ethyl group and a methyl group for two atoms of hydrogen, or lastly, by the substitution of three methyl groups for three atoms of hydrogen. PROPYLENES — BUTYLENES. 573 PROPYLENES. C3H6 Ordinary Propylene, CH^-CH=CH^ — To prepare this gas in a pure state Berthelot and de Luca heat allyl iodide with mercury and concentrated hydrochloric acid. 2C=^H^I + 4Hg + 2HC1 = Hg^CF + Hg^P + 2C'H« It may also be made by allowing propyl alcohol to fall drop by drop on highly heated zinc chloride (Le Bel). Propylene is a colorless gas, having a feeble, alliaceous odor. It is rapidly absorbed by sulphuric acid, with formation of isopropylsulphuric acid (Berthelot). C3H6 + H2S0* =- (^^^^^^'>S0* It unites directly with hydriodic acid, forming an iodide which is isomeric with propyl iodide. C^H^ -\- HI = (C^H'^)'I Propylene unites directly with chlorine and bromine, forming propylene chloride, C^H*^CP, and propylene bromide, C^II^Br^ The latter is a colorless liquid, boiling at 145°. Trimethylene, / \ . — This remarkable body was first CW-CW described by Freund, who prepared it by heating with sodium the bromide, CH^Br-CH^-CH^Br. It is a gas which is absorbed by bromine more slowly than ordinary propylene, the normal bromide, boiling at 164-165°, being regenerated. It combines with hydriodic acid forming the iodide of normal propyl, CH^-CH^-CH^I. Normal propylene bromide is obtained by heating allyl bromide, C^H^Br, with hydrobromic acid. CH^^CH-CH^Br + HBr = CH^Br-CH^-CffBr Allyl bromide. Normal propylene bromide. It is a colorless liquid, boiling at 165°. BUTYLENES, C'W. 1. Dimethylethylene «, (CH3)^C=CHl — This body is formed when isobutyl alcohol is dehydrated by zinc chloride, or by the action of alcoholic potassium hydrate on butyl iodide, C*H^I. It boils at — 6 ° . It unites directly with hydriodic acid, forming tertiary butyl iodide, (CH^)^CI-CII^, and combines 574 ELEMENTS OF MODERN CHEMISTRY. witt bromine, forming the bromide (CH^)^CBr-CH'^Br, wMcli boils at 149°. 2. Dimethylethylene /5 (normal or symmetric), (CH^)HC= CH(CH^). — Is formed by the action of alcoholic potash on secondary butyl iodide, CH^-CH^-CHI-CHl Boils at -f 3° and solidifies to a crystalline mass at 0°. Unites with HI, regenerating secondary bntyl iodide, and with bromine, forming the bromide (CH3)HBrC-CHBr(CH=^), which boils at 159°. Le Bel and Greene have obtained normal dimethylethylene by dropping ordinary isobutyl alcohol on highly heated zinc chloride ; the disengaged gases are passed through bromine, and the bromides of ^ dimethylethylene and ethylethylene — both gases are produced in the decomposition — separated by fractional distillation. De Luynes obtained secondary butyl iodide by reducing erythritol with a large excess of hydriodic acid (page 634). 3. Ethylethylene (ethyl-vinyl), (C^HS)HC=CH^— Is ob- tained by the action of sodium on a mixture of ethyl iodide and bromethylene. C2H5I + BrHC=CH2 + Na2 = Nal + NaBr + (C2H5)HC=CH2 Boiling-point, — 5°. It unites with HI, forming secondary butyl iodide, and with bromine, forming the bromide CH^- CH^-CHBr-CH^Br, boiling at 166°. AMYLENES, OB PENTENES, C^H^^. Several isomeric hydrocarbons are known of the composition Q5jjio_ They exist in unequal proportions in the product of the reaction of zinc chloride on amyl alcohol, a product gener- ally designated as amylene. It is prepared by heating amyl alcohol with zinc chloride, and passing the vapors given off into a well-cooled receiver. The product is rectified, that portion being retained which passes below 40°. It is a mixture of isomeric amylenes, whose boiling-points vary from 22 to 40°, and which result from the dehydration of amyl alcohol. Trimethylethylene or ordinary Amylene may be obtained in a pure state by dehydrating tertiary amyl alcohol (the hydrate of amylene of Wurtz), which may be accomplished by simply heating it. (CH3)2:=C(OH)-CH2-CII3 — H20 = (CH3)2C=CH(CH3) Tertiary amyl alcohol. TrimetUyletliylene. It boils at 36°, and unites directly with hydriodic acid, form- ing tertiary amyliodide, (Cff)''CI-CH^-CH^ boiling at 129°. HYDROCARBONS OF THE SERIES, C''h'^''~^ 575 When bromine is poured into cooled amylene, the addition of each drop produces a hissing noise, indicating a violent reac- tion, and the product is a liquid amylene bromide, boiling be- tween 170 and 180°. If the operation be performed upon crude amylene, a mixture of several bromides will result. Trimethyl- ethylene yields a bromide containing (CH^)'=CBr-CHBr-CHl Isopropylethylene is formed by the action of alcoholic potassium hydrate on amyl iodide (Flavitzky). ^g3>CH-CH2-CH2I — HI = g^3>CH-CH=CH2 Amyl iodide. Isopropylethylene. This body also exists in small quantity in the mixture of hydrocarbons formed by the action of zinc chloride on amyl, alcohol. Boiling-point, 25°. It unites with hydriodic acid, forming a secondary iodide, (CH^)'=CH-CHI-CH^ which boils at 137-139°. It combines with bromine, forming the bromide (CH^)2=CH-CHBr-CH^Br, which boils between 180 and 190°. Propylethylene or Ethylallyl may be obtained by heating with sodium a mixture of allyl iodide and ethyl iodide. CH3-CH2I + CH2=CH-CH2I + Na2 = 2NaI + CH3-CH2-CH2-CH-CH2 Ethyl iodide. Allyl iodide. Ethylallyl. It is also formed by the action of zinc ethyl on ethyl iodide. It boils at 37°, and combines with hydriodic acid, forming the iodide C^H^-CHI-CH^ boiling at 144°. It combines ener- getically with bromine, forming a bromide C^H^-CHBr-CH^Br, boiling at 175°. Polymerides of Amylene. — By the action of zinc chloride on amyl alcohol, there are formed, independently of amylene, other hydrocarbons, among which are the polymeric modifica- tions known as diamylene, C^^H^" ; triamylene, C^^H^" ; tetra- mylene, C^°H*° (Balard, Bauer). These bodies are formed by the union of two, three, or four molecules of amylene. HYDROCARBONS OF THE SERIES C^W^-\ Among the more simple hydrocarbons is one which was dis- covered by E. Davy, and which Berthelot has succeeded in preparing by various processes. It is acetylene, and is the first member of a series which includes, among others, the following hydrocarbons : Acetylene C2H2 (E. Davy, Berthelot). Allylene C^H* (Sawitsch). Crotonylene C*H^ (E. Caventou). Valerylene C^^ (Reboul). 576 ELEMENTS OF MODERN CHEMISTRY. Acetylene, C^ff or CHeeCH. — This hydrocarbon is a prod- uct of the incomplete combustion of many organic substances, and is the only compound of hydrogen and carbon that has been obtained by direct union of these elements. According to Berthelot, it is formed when the electric arc is passed between carbon electrodes in an atmosphere of hydrogen. It may be obtained by heating ethylene bromide with an alcoholic solution of potassium hydroxide, thus : Cm'Br' + 2K0H = 2KBr + C^H'^ + 2ffO The most convenient mode of preparing acetylene is by the action of water upon calcium carbide, which is readily produced in the electrical furnace (Moissan) (page 327). C^Ca + 2H^0 = C^H^ + Ca(0H)2 The reaction takes place at ordinary temperatures. Acetylene is a colorless gas, having a peculiar odor, sug- gesting that of garlic. At ordinary temperatures it dissolves in about its own volume of water. Its critical temperature is 37°. At 19.5° it is liquefied by a pressure of 39.8 atmos- pheres ; the resulting liquid boils at — 83°, and in evaporating absorbs enough heat to freeze a portion to a snow-like mass. Acetylene burns with a highly luminous and smoky flame. With 2.5 times its volume of oxygen, acetylene constitutes one of the most explosive gaseous mixtures. It combines directly with bromine, with which it yields a dibromide, C^H^Br^ and a tetrabromide, C^'H^Br*. When conducted into an ammoniacal solution of cuprous chloride, it produces a brownish red precipitate of cuprous acetylide. This reaction afi'ords a delicate test for acetylene, and an excellent means of removing it from gaseous mixtures. An analogous silver compound is similarly obtained. Both acetylides are highly explosive in the dry state ; with hydro- chloric acid they yield acetylene and the metallic chlorides. C^H^Cu^O -J- 2HC1 = Cu^CP + C^H'^ + H^O On account of its superior illuminating power, acetylene is now manufactured as a substitute for the ordinary gas from bituminous coal. Allylene, C^H*, the second member of the acetylene series, exists in two isomeric forms, methylacetylene^ CH^-C^H, a gas which resembles acetylene in its general properties and forms a precipitate when passed into solution of silver nitrate, GLYCOLS. ST*? and symmetrical allylene, CH^-C=CH2, whicli forms no pre- cipitate with silver nitrate. The number of isomers increases rapidly in this series as the molecules contain a greater number of carbon atoms. DIHYDRIC ALCOHOLS, OR GLYCOLS. The name glycols was given by Wurtz to the hydroxides of the series of hydrocarbons, C"H^'^. If ordinary alcohol be ethyl hydroxide, ordinary glycol is ethylene hydroxide. Ethyl hydroxide. Ethylene hydroxide. While alcohol reacts with a single molecule of a monobasic acid to form a neutral ether, glycol can react with either one or two molecules of a monobasic acid, thus forming two ethers. In other words, while the monohydric alcohols contain but one atom of hydrogen which is replaceable by a single radical of a monobasic acid, glycol contains in the two groups OH two such atoms of hydrogen, capable of being replaced by two radicals of a monobasic acid, or one radical of a dibasic acid. Ethyl acetate. Ethylene;diacetate. Ethylene succinate. The glycols yield diatomic acids by oxidation. There are isomeric glycols, or isoglycols, corresponding to the isoalcohols which have already been defined (page 521). A number of glycols of the series CH^'^+^O^ are now known. DENSITY AT 0°. BOILING-POINTS. Ethylene glycol, or glycol . . . C^WO"^ 1.125 197.5° Propylene glycol, or propylglycol . C^n^O"^ 1.051 188-189° Butylene glycol, or butylglycol . C^HiOQ'-^ 1.048 183-184° Amylene glycol, or amylglycol . . Q^W^O"^ 0.987 177° It is to be remarked that all of the members of the above series are not, strictly speaking, homologous. The isomerism of the glycols, like that of the alcohols, is due to the constitutions of their molecules, which can contain, like the molecules of the alcohols, the following groups : The primary group -CH^.OH The secondary group =CH.OH The tertiary group =C.OH z mm 49 578 ELEMENTS OF MODERN CHEMISTRTf. Thus, ethylene glycol is primary, since it contains two groups, CHIOH. The amylene glycol derived from trimethylethylene is at the same time secondary and tertiary. Pinacone, which has already been mentioned (page 558), is a tertiary glycol; it contains two groups =(C.OH). CH2.0H r^l> C.OH CHS^ 9'^^ CH2.0H CH3-CH.0H CH3^ ^'^^ Glycol. Amylene glycol. Pinacone. (Secondary and tertiary.) (Tertiary.) Among the mixed glycols, that is, those containing at the same time two different alcoholic groups, is ordinary propylene glycol, which is primary and secondary. CIP.OH CH3 CH2 CH.OH CH2.0H CH2.0H Normal propylene glycol. Ordinary propylene glycol. (Primary.) (Primary and secondary.) GLYCOL, OR ETHYLENE ALCOHOL. C2H602 = C2H4(OH)2 Wurtz first obtained glycol by causing either iodide or bro- mide of ethylene to react with silver acetate Silver acetate. Ethylene diacetate. and saponifying the resulting ethylene diacetate by potassium hydroxide. ^2^3^-^|(C2H4)" + 2K0H ==: 2(C2H30.0K) + (C2H*)" | ^j[J Ethylene diacetate. Potassium acetate. Glycol. It is best prepared by Hiifner and Zoller's process, which consists in heating ethylene bromide with an aqueous solution of potassium carbonate, thus : C2H*Br2 + K2C03 + H20 = C2n4(OH)2 + 2KBr + C02 188 grammes of ethylene bromide, 138 grammes of po- tassium carbonate, and 1 litre of water are introduced into a large flask connected with a reversed condenser, and the mix- GLYCOL. 579 ture is boiled until all of the ethylene bromide has disappeared. The aqueous liquid is then concentrated on a water-bath, and alcohol is added to precipitate the potassium bromide ; the alcoholic liquid is then distilled. Alcohol and water first pass, and when the temperature rises above 150°, the liquid which condenses is nearly pure glycol. Properties. — G-lycol is a somewhat syrupy, colorless, and odorless liquid, having a sweet taste. It mixes with water and alcohol in all proportions, but is scarcely soluble in ether. It boils at 197.5°, and distils without alteration. Its analogy to alcohol, from which it differs bv containing one more atom of oxygen, is demonstrated by the following experiments : 1. If platinum black be moistened with glycol and then rapidly plunged into a jar of oxygen, a brilliant incandes- cence is manifested immediately, due to the energetic absorp- tion of oxygen. With dilute glycol, the oxidation is slower, and glycollic acid is formed. CH2.0H CH2.0H CH2.0H + 02 = i^Q^Qjj + H20 Glycol. Glycollic acid. 2. If glycol be heated with ordinary nitric acid, torrents of red vapor are disengaged, and the liquid deposits crystals of oxalic acid on cooling. CH2.0H CO.OH iH2.0H +'^'= bo.On +2H20 Glycol. Oxalic acid. 3. When glycol is heated with potassium hydrate to 250°, pure hydrogen is disengaged and potassium oxalate is formed. C2JJ6Q2 _|_ 2K0H = C^O^K^ + 4.W Glycol. Potassium oxalate. These experiments establish between glycol and glycollic and oxalic acids, relations analogous to those which exist between alcohol and acetic acid. Ethylene Chlorhydrate, or Glycol Chlorhydrin. — When hydrochloric acid gas is passed into glycol, a neutral com- pound is formed which constitutes the monocMorhydrin of glycol, or ethylene chlorhydrate. C2H4S03 = C2H40 ^ HCl CH.OH CH''^ CH2.0H Monochlorliydrin. cn2.0H Glycide. 50 590 ELEMENTS OF MODERN CHEMISTRY. Glycide is a mobile liquid, boiling at 157°. Its density at 0^ is 1.165. Water dissolves it, regenerating glycerol. C^H^O.OH + H^O = C^H^OH)^ Trinitroglycerol, or Propenyl Trinitrate. — When glyce- rol is poured drop by drop into a mixture of concentrated nitric and sulphuric acids, cooled in a vessel of cold water, oily drops of trmitroglycerol^ C"H^(0-NO^)^, are precipitated. It is a colorless oil, insoluble in water, and explodes with great vio- lence by percussion, by heat, or, when impure, even sponta- neously. On account of this property, nitroglycerin is employed as an explosive ; but it is generally incorporated with inert matter, such as finely-divided silica. Such mixtures are called dyna- mites. The manufacture of nitroglycerin is usually conducted in wooden structures which are partly underground, and removed from exposure to influences which might cause the explosion of the product. The explosive force of the compound is more than six times as great as that of an equal quantity of gun- powder, and nitroglycerin produces effects equal to those of powder with an economy of about thirty per cent. Its explosion is too violent to permit its use in fire-arms, but it is well adapted to blasting operations. Curiously enough, while a drop of nitro- glycerin placed on an anvil and struck with a hammer explodes with a loud report, the same drop would burn quietly if brought into a flame. Other Glycerol Ethers. — Berthelot has obtained a number of glycerol ethers by directly heating glycerol with acids. When the reaction is terminated (it is often very slow), he sat- urates the excess of acid with calcium hydrate, and extracts the neutral fatty body, that is, the ether of glycerol, with ether. In this manner he has formed a certain number of natural fatty bodies by combining their acids with glycerol. NATURAL FATTY BODIES. The fats encountered in nature are glycerides, that is, ethers of glycerol. The memorable researches of Chevreul have shown that when these fats are methodically treated with different solvents, various immediate principles are separated, of which the most common are stearin, palmitin, and olein. NATURAL FATTY BODIES. 591 They are the tristearic^ tripalmitic^ and trioleic ethers of glycerol. r O.C18H350 r O.C16H310 r o.cishsso C3H5 J O.C18H350 C3H5i O.C16H310 C3H5J O.C18H330 [ O.C18H350 { O.C16H310 ( O.C18H330 stearin. Palmitin. Olein. When these glycerol ethers are subjected to the action of alkalies, lime, or oxide of lead, in presence of boiling water, they are decomposed, absorbing at the same time the elements of water : glycerol and the acid are set free, and the latter combines with the base forming a soap (see page 593). Thus, when stearin is boiled with milk of lime, calcium stearate and glycerol are formed. When olein is heated with water and litharge, it yields lead oleate and glycerol. Most of the fats and oils occurring in nature consist of such glycerides mixed in various proportions, and may be resolved into the respective acids and glycerol. Stearin and palmitin are solids, olein is liquid. In the fats, the solid principles predominate ; the oils contain a larger proportion of olein. Steariyi is extracted from tallow. That substance is dissolved in boiling ether and made to crystallize. The crystals are pressed, and the operation is repeated with them many times until a substance is obtained which crystallizes in brilliant little scales, fusible at 66.5°. They are but slightly soluble in alco- hol and in cold ether, but freely soluble in boiling ether. Palmitin has been extracted, by the aid of boiling alcohol, from palm-oil which has previously been submitted to heavy pressure between sheets of porous paper. It melts at 60° (Heintz). Olein is the predominating principle of olive-oil and almond- oil, from which it is difficult to obtain it in a pure state. Ber- thelot has prepared triolein artificially by heating glycerol to a temperature between 200 and 240° with an excess of oleic acid. The mass thus obtained is treated with lime and ether ; the latter dissolves the triolein and leaves calcium oleate. The ethereal solution is decolorized with animal charcoal and mixed with eight times its volume of alcohol, which precip- itates the triolein. When dried in a vacuum, triolein is an oil which solidifies at — 6°. Its density* is between 0.90 and 0.92. It is insoluble in water, and very slightly soluble in alcohol. In contact with mercuric nitrate or with peroxide of nitrogen (red vapors), olein is converted into a crystalline, solid, fatty 592 ELEMENTS OF MODERN CHEMISTRY. body, fusible at 36°, to wbicb Boudet has given the name elaidin. Fat Oils and Drying Oils. — The oils of olives, sweet almonds, rape-seed, beech-nuts, etc., acquire an acrid taste and a disagreeable odor when they are long exposed to the air, but they do not solidify. They are called fat^ or non-siccative oils. Olive-oil is the type of this class. It is extracted by press- ure from crushed olives, and has a greenish-yellow color ; its taste is sweet and agreeable ; it is odorless. At a temperature a few degrees above 0°, it becomes a solid mass. When agitated with mercurous nitrate, it becomes solid, the olein which it contains being transformed into elaidin. It becomes rancid by exposure to the air. When other oils, such as linseed, walnut, hemp-seed, poppy and castor oils are exposed to the air, they thicken and finally are converted into somewhat elastic, yellow, transparent masses, species of soft varnishes. They are, therefore, called drying oils, and are employed in the preparation of paints and varnishes. The changes which oils undergo on contact with the air are caused by an absorption of oxygen, and are accompanied by a disengagement of more or less carbon dioxide. Every one is familiar with the uses of the natural fatty bodies in the arts and in domestic economy. Among the industrial applications, we can only mention the employment of tallow and palm-oil in the manufacture of candles, and of these as well as other oils and fats in soap-making. Stearin Candles. — To convert tallow into stearin candles, it is saponified by lime, that is, it is first converted into a lime soap, which is then decomposed by sulphuric acid. The latter acid causes the fatty acids to separate, and they solidify on cooling. They are strongly compressed, first between warm, and finally between hot plates, so that the oleic acid is ex- pressed, while the fatty acids proper remain. This process, which was invented by de Milly and Motard in 1829, consists, as may be seen, in entirely saponifying the tallow by lime. In 1854, de Milly modified it by considerably reducing the amount of lime, and consequently the proportion of sulphuric acid required. But it is then .necessary to operate at higher tem- peratures by the aid of superheated steam. The operation is conducted in closed vessels, and with 2.5 parts of lime, 100 parts of tallow may be saponified at a temperature of 170 or 180°.. SOAP. 593 Palm-oil may be converted into candles by a still more simple process, whicb consists in subjecting it to tbe action of superheated steam at 300°. It is thus directly decom- posed into fatty acids and glycerol, for the vapor of water, at the high temperature employed, acts precisely as would an alkali. Soaps. — In the south of Europe, and principally at Mar- seilles, oils of inferior quality are used for the manufacture of soap, and the oils of sesame and earth-nut have been employed for this purpose for some years. These oils are saponified by boiling them in large boilers with a weak solution of caustic soda. The oil thus becomes pasty, the excess of oil making an emulsion with the solution of soap which is first formed. More concentrated soda lye containing common salt is then added, and the saponification is finished by boiling ; the soap, which is insoluble in the concentrated lye, comes to the surface of the liquid, and the lye is then drawn off. When the soap is well made, the paste hardens on cooling ; it has a bluish-gTay color, due to a ferruginous soap mixed with sulphide of iron. The iron and sulphur are derived from the materials employed, crude caustic soda containing a small quantity of iron. If this paste be heated with about one-twelfth its weight of water, or a very weak solution of caustic soda, it melts, and if the mass be allowed to stand undisturbed, it wiU separate into two por- tions, the lower and strongly-colored layer containing the more dense ferruginous soap ; the upper layer constitutes white soap. When the latter is completely clarified by the deposit of the ferruginous soap, it is di-awn off into large moulds, where it solid- ifies. White soap is thus obtained. If, on the contrary, mar- bled soap be desired, the paste is frequently agitated during the cooling. The colored part, that is, the ferruginous soap, thus be- comes diffused throughout the whole mass, forming bluish veins. For some years, large quantities of soap have been prepared by combining with caustic soda the oleic acid obtained as an accessory product in the manufacture of stearin candles. Soft soaps have potash for their base. They are manufact- ured from various oils, such as hemp, poppy, and linseed oils, which are saponified by caustic potash lye. Saponification. — It will have been noticed that all of these industrial operations have for their object the decomposition of neutral fats into fatty acids, either free or combined with a base. This decomposition has received the name saponifi- nn 50* 594 ELEMENTS OP MODERN CHEMISTRY. cation. It may be effected by tbe action of water and heat alone, by the action of a base, or by the action of a powerful acid, such as sulphuric acid (sulphuric saponification). In the latter case, the acid acts upon the glycerol, forming a sulpho- glyceric acid. Whatever process be employed to effect this decomposition, the presence of water is always necessary, for the elements of that liquid combine directly with the fatty body which is decomposed, as Chevreul has very well shown. In this respect, the decomposition of palmitin by superheated steam may serve as a type for all reactions of this class. ro.ci6H3io roH Cm^\ O.C16H310 + 3H20 = Cm^\ OH + 3Ci6H3iO.OH ( O.C16H310 I OH Palmitia. Glycerol. Palmitic acid. POLYATOMIC AND POLYBASIC ACIDS. These acids are related to the polyhydric alcohols, just as the acids containing two atoms of oxygen, and which we have already studied, are related to the monohydric alcohols. The polyatomic acids are classed in several series, among which we must consider in a special manner those which in- clude glycollic and oxalic acids. As we have already seen, these two acids are products of the direct oxidation of glycol. Their homologues are related to the higher glycols. Glycols. Acids, CnH2n03. Acids, CnH2ci-'-!0 CH2.0H CH2.0H CO.OH CH2.0H CO.OH CO.OH Glycol. Glycollic acid. Oxalic acid. CH2.0H CH2.0H CO.OH CH2 CH2 CH2 CH2.0H CO.OH CO.OH Normal propylglycol. Hydracrylic acid. Malonic acid. CH3 CH3 CH.OH CH.OH CH2.0H CO.OH Isopropylglycol. Lactic acid ot fermentation. CH2.0H CO.OH CH2 CH2 CH2 CH^ CH2.0H CO.OH Normal butylglycol. Succinic acid. GLYCOLLIC ACID, GLYOXYLIC ACID, AND GLYOXAL. 595 The first of tlie above series is that of glycol and the higher glycols. Among the latter, the true homologues of glycol would be those which differ from the latter by nCH^, and of which the formulas would consequently be analogous to that of normal propylglycol. Ordinary propylglycol, which yields lactic acid by oxidation, is an isomeride of normal propylglycol. The second series is that of glycollic acid and its homologues. They are derived from the corresponding glycols by the sub- stitution of for H^ in one group, CHI OH They conse- quently contain but one carboxyl group, CO. OH ; they are monobasic, for the hydrogen atom of the last group can be replaced by a metal. It will also be noticed that they are at the same time acids and alcohols, — acids by virtue of the carb- oxyl, CO.OH, primary alcohols by virtue of the group CH^OH, or secondary alcohols by virtue of the group CH.OH. The third series is that of oxalic acid and its homologues. They are derived from the glycols by substitution of 0^ for 2W in two groups, CH^OH. They consequently contain two carboxyl groups, CO.OH, and they are dibasic because the H of each of these groups may be replaced by an equivalent quantity of metal. Between glycollic and oxalic acids there exists a remarkable acid, because it is at the same time a monobasic acid and an aldehyde : it is glyoxylic acid. It contains C^H^O*, one more atom of oxygen than oxalic aldehyde, which is called glyoxal, C^H^O^ and two atoms of hydrogen less than glycollic acid. These relations of composition will be clearly seen from the fol- lowing formulas : CH2.0H CHO CHO CO.OH CO.OH CO.OH CHO CO.OH Glycollic acid. Glyoxylic acid. Glyoxal. Oxalic acid. GLYCOLLIC ACID, GLYOXYLIC ACID, AND GLYOXAL. Glycollic Acid, CHXOH)-COOH.— This acid is formed by the oxidation of glycol, but is best prepared by heating potassium monochloracetate with dilute potassium hydroxide. KC^H^CIO^ + KOH = KCl + KC^ffO^ Potassium monochloracetate. Potassium glycollate. 596 ELEMENTS OF MODERN CHEMISTRY. The acid forms deliquescent crystals, very soluble in water, alcohol, and ether. It has a strong acid reaction. When heated, it loses the elements of water, and is converted into glycollide^ or glycolUc anhydride, C^H^O^, or C*H*0*. Glyoxylic Acid, CHO-COOH. — When fuming nitric acid, water, and 80 per cent, alcohol are carefully superposed in layers in a tall jar, and left for some days at ordinary tem- peratures, mixture takes place by diffusion, and the products of this slow oxidation of the alcohol are glycollic acid, gly- oxylic acid, and glyoxal. When the carefully evaporated liquid is neutralized with chalk, calcium salts of the two acids are formed and may be precipitated by the addition of alco- hol, in which they are insoluble. From an aqueous solution of the two salts the glyoxylate deposits first on spontaneous evaporation. The free acids may be obtained by decomposing the calcium salts with oxalic acid. Glyoxylic acid is also formed by the careful oxidation of glycol. Grlyoxylic acid is a syrupy and very acid liquid. It has the properties of an acid and those of an aldehyde, as is indicated by its formula. Its solution reduces ammoniacal silver nitrate. When heated with sulphuric acid it disen- gages carbon monoxide. 02JJ2O3 ^ 2C0 + H^O Nascent hydrogen converts it into glycollic acid. Glyoxal, CHO-CHO, may be obtained from the alcoholic liquid above mentioned, from which calcium glycoUate and glyoxylate have been precipitated. It is a deliquescent, amorphous solid, slightly colored, and very soluble in water and alcohol. Its aqueous solution energetically reduces ammonio-nitrate of silver. Like other aldehydes, glyoxal combines with sodium acid-sulphite, with phenylhydrazine, and with hydroxylamine. With the latter it forms the compound HO.N=CH-CH=N.OH, gJyoxime, which is the type of a dioxime. Glyoxal is the aldehyde corresponding to oxalic acid. CHO CO.OH CHO CO.OH Glyoxal. Oxalic acid. LACTIC AND PARALACTIC ACIDS. 597 LACTIC AND PARALACTIC ACIDS. [a-OXYPROPIONIO ACID.] C3H«03 = CH3-CH(0H)-C0.0H Formation and Constitution. — Lactic acid was discovered by Scheele in sour milk. Berzelius discovered the existence in various liquids of the animal economy of an acid which was at first believed to be identical with that which results from the acid fermentation of milk. Later, an acid identical with the latter was found in various vegetable juices, and was recog- nized to be the product of a peculiar fermentation of glucose, called the lactic fermentation (see page 647). It was also discovered that the lactic acid of fermentation is not identical with that which exists in the animal liquids, especially that liquid which impregnates the muscular fibres. The latter acid is called paralactic or dextrolactic acid. It rotates the plane of polarized light to the right, and its salts differ in cer- tain properties from those of ordinary lactic acid. Wislicenus, who has most carefully investigated this isomerism, believes it to be caused by a different arrangement of the atoms in space, and the results of many researches tend to confirm this view. Such cases of isomerism which cannot be represented by the ordinary structural formula are classed as stereoisomer- ism^ and will be more fully explained farther on (see Tartaric Acid). An acid of the same chemical properties, but turning the plane of polarization to the left, has recently been discov- ered by Schardinger. It is distinguished as levolactic acid. Independently of these stereoisomeric lactic acids, there is another isomer which was at first named ethyleue-lactic acid, and which results from the oxidation of normal propylglycol ; its constitution is expressed by the formula CH2.0H CH2 io.OH It is Tiydracrylic add; it is also formed when /9-iodopropi- onic acid is treated with water and silver oxide. Its character- istic property is its easy decomposition into water and acrylic acid, hence the name hydracrylic (Wislicenus). Its isomeride, lactic acid of fermentation, is formed by the oxidation of ordinary propylglycol (A. Wurtz). This fact 598 ELEMENTS OF MODERN CHEMISTRY. determines its constitution, whicli can also be deduced from a very interesting mode of formation discovered by Strecker. When a mixture of aldehyde, hydrocyanic acid, and hydro- chloric acid is allowed to stand for some time, ammonium chlo- ride and lactic acid are formed. CH3 V + CNH + HCl + 2H20 = NH4C1 -1- CH.OH ™0 fco.OH Aldehyde. Hydrocyanic Lactic acid, acid. The isomerism of lactic and hydracrylic acids may be readily understood by the aid of the following formulae : CH2.0H CH3 CH2 CH.OH CO.OH CO.OH Hydracrylic acid. Lactic acid. Both acids are monobasic ; each contains the group CO.OH, which is characteristic of organic acids. The third oxygen atom exists in alcoholic hydroxyl, either in the primary group CHI OH, or in the secondary group CH.OH. The preceding formulae show that lactic acid has a mixed function ; it is at the same time an alcohol and an acid. This is made evident in all of its compounds, and it will be sufficient to mention that one molecule of lactic acid in its function as an acid^ can react with and etherify another molecule in its function of an alcohol, the hydroxyl of the group CO.OH forming a molecule of water with the hydrogen of the alco- holic hydroxyl in the second molecule of the acid. The dilactic acid, lactic anhydride, and lactide which are formed by the more or less complete dehydration of two molecules of lactic acid, are veritable dilactic ethers. This point has been developed by Grimaux. Preparation of Lactic Acid. — A mixture of 3 kilo- grammes of glucose dissolved in 13 litres of water, 4 kilo- grammes of sour milk, 100 grammes of old cheese, and 1.5 kilogrammes of pulverized chalk, is exposed to a temperature of 30 or 35°. At the end of a week, the whole solidifies to a mass of calcium lactate. The salt is purified by crystal- lization, and is exactly decomposed by dilute sulphuric acid. The calcium sulphate is separated by filtration, and the acid liquid is boiled and saturated with hydrocarbonate of zinc; LACTIC AND PARALAOTIC ACIDS. 599 It is then filtered and allowed to cool. The zinc lactate crys- tallizes, and its solution being decomposed by hydrogen sul- phide, zinc sulphide and lactic acid are obtained. The filtered solution is evaporated on a water-bath. For the preparation of lactic acid on a smaller scale, advan- tage is taken of the fact that some sugars (glucose, fructose) upon heating with alkalies yield considerable quantities of the acid. Properties. — Lactic acid is generally obtained as a color- less, syrupy liquid, having a decided acid taste. In the pure state it forms hard crystals, which melt at 18°. When heated, it begins to lose water at 130°, and is converted, little by little, into a yellow, amorphous mass, insoluble in water, but soluble in alcohol and ether. This body is dilactic acid, C^H^°0^. At 230°, it disengages a small quantity of carbon monoxide and carbon dioxide, and a product distils which often solidifies on cooling. It is lactide, or dilactic anhydride, and is derived directly from dilactic acid. Dilactic acid. Lactide. Lactide has been represented by the more simple formula Q3jj4Q2^ but its vapor density as well as the depression it produces in the freezing points of its solvents show that the double formula represents the true constitution of this body. Lactide occurs in colorless crystals, soluble in water and alcohol. It possesses the property of combining directly with the elements of water, lactic acid being re-formed ; it also combines with ammonia, forming lactamide. Paralactic Acid. — This is the lactic acid which may be extracted from meat. It is also called sarcolactic acid. It may be prepared from commercial extract of meat ; this is dissolved in 4 parts of water, and the solution precipitated by 8 parts of 90 per cent, alcohol. The alcoholic solution is decanted, and the residue, which is insoluble in alcohol, is exhausted with 2 parts of lukewarm water, the solution again being precip- itated by alcohol. The alcoholic solutions are united and dis- tilled on a water-bath. The residue is rendered strongly acid by sulphuric acid, and agitated with ether which dissolves the 600 ELEMENTS OF MODERN CHEMISTRY. paralactic acid set free. The ethereal solution is evaporated, and the acid is converted into the salt of zinc, which is subse- quently decomposed by hydrogen sulphide, as has been indicated for the preparation of ordinary lactic acid. Paralactic acid is syrupy like its isomeride. It turns the plane of polarized light to the right (Wislicenus). When heated, it becomes dehy- drated, yielding lactide. Levolactic Acid. — An acid which rotates the plane of polarization to the left, but otherwise identical with para- lactic acid, has been obtained by a peculiar fermentation of sugar (Schardinger). Ordinary lactic acid can be resolved into the two active modifications. Lactates and Paralactates. — Lactic acid is a monobasic acid ; the neutral lactates contain R'C^H50•^ or W'{C'WOy. The most characteristic is zinc lactate, Zn(C^H^O^)'^ -f- 3H^0, which is but slightly soluble in cold water, and separates from its boiling solution in brilliant needles or laminae. Zinc paralactate crystallizes with two molecules of water, and is much more soluble than the ordinary lactate. Calcium lactate, Ca(C^H^O'^)^ -|- 5H^0, crystallizes in rounded masses, formed of little needles grouped around a common centre. Like all the lactates, it is very soluble in water and alcohol. Ferrous lactate, Fe(C^H^O^)^ prepared by double decompo- sition of calcium lactate and ferrous sulphate, forms greenish, crystalline crusts, soluble in water. It is employed in medicine. Lactamide, C^H'^NOl — When an alcoholic solution of lac- tide is treated with ammonia and the liquid is evaporated, crystals are obtained which are soluble in water and alcohol. They constitute lactamide. C^H«0* + 2NW = 2C^H^N0^ Potassium hydrate decomposes lactamide into lactic acid and ammonia. Lactamide represents ammonium lactate less the elements of water. cm cm CH.OH — H20 = CH.OH C0.0(NH4) C0.NH2 Ammonium lactate. Lactamide. HYDRACRYLIC ACID. 601 HYDRACRYLIC ACID. (ethylenelactic, or /J-hydroxypropionic acid.) C3H603 = CH2(OH)-CH2-CO.OH This acid is formed by the oxidation of normal propjlglycol. It is also formed by the action of water and silver oxide on ^-J-iodopropionic acid. CH2I-CH2-C02H 4- AgOH* = CH2.0H-CH''^-C0.0H -f Agl /3-Iodopropionic acid. Hydracrylic acid. The silver salt formed in the latter reaction is converted into the zinc salt, and the latter is decomposed by hydrogen sul- phide. Hydracrylic acid is syrupy. When heated, it breaks up into acrylic acid and water. Q3g603 ^ Q3H402 _(_ H^O When heated with hydriodic acid, it is again converted into /9~iodopropionic acid. Its sodium salt, NaC^H^O^ deposits from alcohol in crystals fusible at 142-143°. Between 180 and 200°, it loses water, and is partly converted into sodium acrylate. Zinc hydracrylate, Zn(C^H^O^)^ + 4H^0, is characteristic. It forms large, very brilliant crystals, soluble in about one part of water. GLYCERIC (DIHYDROXYPROPIONIC) ACID. C3H601 = CH2(0H)-CH(0H)— CO.OH This acid is obtained by oxidizing glycerol with nitric acid, or by treating it with bromine and water. It is also formed by the spontaneous decomposition of nitroglycerin. It is prepared by introducing into a tall jar one part of nitric acid of specific gravity 1.5, and 1 part of glycerol diluted with its own volume of water. Care is taken that the two liquids may not mix, and the whole is left to itself for five or six days. The two bodies gradually mingle and react upon each other. The liquid is evaporated on a water-bath, and the residue is boiled with well-washed hydrate of lead suspended in water, after which the solution of lead-salt is filtered hot. Crystals of lead ^ Instead of Ag20 + H20. 2a 51 602 ELEMENTS OF MODERN CHEMISTRY. glycerate separate on cooling; they are purified, and their aqueous solution when decomposed by hydrogen sulphide, fur- nishes glyceric acid. Properties. — Grlyceric acid is a thick, light-yellow syrup, soluble in water and alcohol. Its reaction is acid ; it is mono- basic. Hydriodic acid, by the aid of heat, converts it into /S-iodopropionic acid. Its relations with glycerol may be seen in the following formulas: CH2.0H CO.OH CH.OH CH.OH CH2.0H CH2.0H Glycerol. Glyceric acid. Closely related to glycollic and lactic acids are two important nitrogenized bodies, glycocoU and alanine. They form part of a series which includes among other bodies leucine, a nitro- genized compound which plays a part in the animal economy. When a current of nitrous anhydride is passed into solutions of glycocoll, alanine, and leucine, nitrogen is disengaged, and these bodies are converted into glycollic, lactic, and leucic acids. We then have the following series : C2H4Q3 C^H^NO^ Glycollic acid. Glycocoll. C3H6Q3 C^H^NO^ Lactic acid. Alanine. 06^120* C^^H^^NO^ Leucic acid. Leucine. GLYCOCOLL, OE GLYCINE. C2H5N02 = CH2(NH2)-CO.OH This body is related to glycollic acid. It was discovered by Braconnot, who obtained it by boiling gelatin with dilute sul- phuric acid for a long time, saturating the solution with barium carbonate and evaporating the filtered liquid. Hence the name sugar of gelatin or glycocoll. Cahours obtained it by the action of ammonia on mono- chloracetic acid. ?-0H + 2NH3 = NH^C. + f°-0« CH2C1 CH2.NH2 Monochloracetic acid. Glycocoll. It is therefore amidacetic acid. GLYCOCOLL. 603 It may also be formed by passing cyanogen gas into boiling hydriodic acid, which is reduced with separation of iodine, the hydrogen effecting the change. Z ^ -- - - = 6™ - - It is a solid body, crystallizing in oblique rhombic prisms, fusible at 235°. Its taste is sweet. It is soluble in 4 parts of water, slightly soluble in alcohol, insoluble in ether. Its solu- tion has a feeble acid reaction. Indeed, glycocoll can react with the bases, forming compounds ; when it is digested for several hours at a temperature between 80 and 104° with silver oxide, the latter is dissolved, and the compound C^H^AgNO^ is formed. The cupric compound, (C'H^^^O'O'Cu -f H'^0, crystallizes in beautiful, dark-blue needles. On the other hand, glycocoll will combine with the acids ; there is a nitrate of glycocoll crystal- lizable in large prisms containing C^H^NOIHNO^. With ferric chloride, glycocoll gives an intense red color de- colorized by acids and reappearing on the addition of ammonia. When nitrous anhydride is passed into a solution of glycocoll, the latter is converted into gly collie acid, nitrogen being at the same time disengaged. Glycocoll. Glycollic acid. MethylglycocoU or Sarcosine, C^H^NO^ — This compound is obtained by the reaction of methylamine and monochloracetic acid, by an interchange analogous to that which yields glycocoll. T^f? + 2NH2(CH3) = NH2(CH3)HC1 + ?^-^^ CH2C1 ^ ^ \ ) -r CH2.NH(CH3) Monochloracetic Methylamine. Methylamine Sarcosine. acid. hydrochloride. It is also formed in the decomposition of creatine and caffeine by baryta water (Liebig). It crystallizes in rhomboidal prisms, very soluble in water, slightly soluble in alcohol. It melts and decomposes at 210°-220°, yielding dimethylamine and carbon dioxide. Like glycocoll, it forms compounds with acids. When distilled with soda-lime, it yields methylamine. It may be distinguished from glycocoll by the action of nitrous acid, which converts it and all compounds which contain the group NH into nitroso-derivatives. CO.OH ^„ ^_ CO.OH I + OH. NO = I -I-H20 CH2.NH(CH3) ^ CH2.N(N0)(CH3) ^ "^ Sarcosine. Nitrous acid. Nitrososarcosine. 604 ELEMENTS OP MODERN CHEMISTRY. ALANINE. C3H7N02 = CH3-CH(NH2)-CO.OH Strecker made the synthesis of alanine by passing hydro- chloric acid gas into a mixture of aldehyde-ammonia and hydro- cyanic acid. Cm'O 4- CNH + IFO = C^H^NO^ The brown liquid resulting from this reaction is evaporated. Alanine crystallizes in hard needles, grouped in stars or tufts. It is soluble in water, only slightly soluble in alcohol, insoluble in ether. The aqueous solution is neutral, and is converted by nitrous anhydride into lactic acid, with evolution of nitrogen. 2C^H^N0' + N^O^ = 2C^H60^ + H^O + 2N^ Alanine. Lactic acid. Alanine may be sublimed by cautiously heating it. By dry distillation, it breaks up into carbon dioxide and ethylamine. C^H^NO^ = CO' + C'HINH^ It is isomeric with lactamide and with an acid amide which is obtained by the action of ammonia on /9-iodopropionic acid. The following formulae account for these isomerides : GIF CH2.NH2 CH3 CH.OH CH2 CH.NH2 C0.NH2 CO.OH CO.OH Lactamide. j8-amidopropionic acid. Alanine. ^-amidopropionic acid^ which is formed in the reaction just indicated, crystallizes in transparent and colorless oblique rhombic prisms. It is very soluble in water and but slightly soluble in alcohol. It melts at 196°, partly subliming in needles, and partly decomposing into ammonia and acrylic acid. LEUCINE. C6H13N02 This body was discovered by Proust, in 1818, in old cheese. It seems to be identical with a substance obtained from cadav- eric fat, and named by Fourcroy aposepedine. It is a product of the putrefaction of animal matters. It is also formed when horn, gelatinous tissues, or albuminous matters are boiled with dilute sulphuric acid, or fused with caustic alkalies. In OXALfC ACID. 605 these reactions, tyrosine, and sometimes glycocoll, is formed at the same time. Leucine exists already formed in the economy. It is met with in the tissues of the liver, spleen, lungs, pancreas, salivary glands, etc., and may be formed artificially, by a pro- cess analogous to that described for the synthesis of alanine. Properties. — Leucine crystallizes in white plates. It dis- solves in 27 parts of cold water and much more abundantly in boiling water. It melts at 270°, and decomposes at a higher temperature into carbon dioxide and amylamine. DIAZO-ACIDS. A series of interesting and important acids has recently been discovered by Curtius as products of the action of po- tassium nitrite on hydrochloric acid solutions of the amido- acid ethers. While it has not been possible to isolate the free acids on account of their tendency to decompose with liberation of nitrogen, their ethers are formed quite readily. Thus, the action of potassium nitrite on ethyl amido-acetate in presence of hydrochloric acid yields ethi/l diazoacetate. KN02 + HCl + NH'^CIP-CO.OC2H5= KCl + n >CH-CO.OC2H5 + 2H20 N This ether is a lemon-yellow oil, which may be distilled in vacuum, but is decomposed with explosive violence when heated under ordinary pressures or on contact with sulphuric acid. Nascent hydrogen converts the diazoethers into hy- drazine derivatives. Diamide and hydrazoic acid (page 160) were first obtained with the aid of these ethers. OXALIC ACID. C2H204 = CO(OH)-CO(OH) Natural State and Modes of Formation. — This important acid exists in many vegetables. Wiegleb and Scheele extracted it from salt of sorrel, which is an acid oxalate of potassium. The process of Scheele has become classic. It consists in precipitating a solution of salt of sorrel with acetate of lead, and decomposing the precipitated lead oxalate by hydrogen sulphide. The great Swedish chemist demonstrated the iden- 51* 606 ELEMENTS OF MOf>ERN CHEMISTRY. tity of the acid tlius formed and that which Bergman had previously obtained by treating sugar with nitric acid. Oxalic acid is met with in the animal economy. Urine often deposits little crystals of calcium oxalate, which salt is some- times deposited in the bladder and there forms rough concre- tions known as mulberry calculi. Oxalic acid is formed by the action of nitric acid or fused caustic potash on a great number of organic matters. Cyanogen yields oxalic acid by its decomposition in contact with water (page 464). We have already studied the relations which exist between oxalic acid and glycol (page 579). Drechsel has made a synthesis of oxalic acid by passing carbon dioxide over metallic sodium disseminated in very dry sand and heated to 350°. The product was sodium oxalate. 2C0^ + Na^ =: Na^C^O* Sodium oxalate. An oxalate also results when sodium or potassium formate is rapidly heated to 440°. 2NaCH0^ = P°-°f + H^O CO.ONa Preparation. — Oxalic acid is prepared in the arts by two processes. One consists in the oxidation of molasses of an inferior quality by nitric acid. The operation gives rise to an abundant disengagement of nitrous vapors and carbon dioxide. It is conducted in leaden boilers that are not attacked in pres- ence of a great excess of oxidizable organic matter. Another process consists in the reaction of potassium hy- drate on saw-dust at a high temperature. The mass is ex- hausted with water which dissolves out potassium oxalate, and the solution is treated with milk of lime. Calcium oxalate is precipitated and potassium hydrate regenerated. The precip- itated calcium oxalate is decomposed by sulphuric acid, calcium sulphate, which is almost insoluble, being formed, and oxalic acid remaining in solution in the water. When the latter is sufficiently concentrated, the acid is deposited in crystals. The potassium hydrate which remains in the first solution is evapo- rated, and serves for new operations. Properties. — Oxalic acid crystallizes from its aqueous solu- tion in large, transparent prisms, containing 2 molecules of water. When exposed to the air, these crystals effloresce, and OXAMC ACID. 607 they completely lose their water at 100° or in a vacuum over sulphuric acid. One part of oxalic acid dissolves in 15.5 parts of water at 10°. It is also very soluble in alcohol. It melts in its water of crystallization at 98°, begins to dis- engage gases at 132°, and between 155 and 160° breaks up into water, carbon monoxide, carbon dioxide, and formic acid. C'H^O* == CO^ + CO + WO At the same time, a portion of the dry acid escapes decompo- sition and sublimes. When oxalic acid is heated with sulphuric acid, it is de- composed into carbon monoxide, carbon dioxide, and water, according to the equation given above. Certain chlorides are reduced by ebullition with a solution of oxalic acid : hydrochloric acid is formed, and carbon dioxide disengaged. Under such circumstances, auric chloride deposits metallic gold ; mercuric chloride is reduced to mercurous chlo- ride. Oxalic acid is a violent poison. In doses of 8, 12, to 20 grammes, it produces poisonous effects which may prove fatal. It acts upon the heart, retarding its movements, and upon the nerve centres, of which it rapidly depresses the functions. Its antidote is chalk or precipitated calcium carbonate. If a solution of oxalic acid, or better, ammonium oxalate, be added to a solution of calcium chloride, a white precipitate of calcium oxalate is formed. This precipitate is formed even in very dilute solutions, and is insoluble in acetic acid. If a small quantity of silver oxalate be heated in a small test-tube, the salt decomposes with explosive violence into carbon dioxide and metallic silver : a portion of the latter is projected from the tube, while the remainder is left as a gray powder. These reactions characterize oxalic acid. Oxalates. — Oxalic acid is dibasic. Its two atoms of hydro- gen may be replaced by two atoms of a univalent metal, or by one atom of a bivalent. Acid oxalates and neutral oxalates are known. Potassium Acid Oxalate, KHC^O* -{- H^O.— This salt con« stitutes the greater part of the salt of sorrel of commerce. It is extracted from the juice of various kinds of Rumex and Oxalis^ the juice of which is clarified with clay and then evap- orated to crystallization. It is but slightly soluble in water. 608 ELEMENTS OF MODERN CHEMISTRY. If a concentrated solution of oxalic acid be agitated with a solution of potassium neutral oxalate, a precipitate of potassium acid oxalate will be formed. If a concentrated solution of oxalic acid be agitated with a solution of potassium acid oxalate, a white precipitate of potassium quadroxalate, a combination of the acid salt and oxalic acid, will be deposited. It contains C^ffO* -j- KHC^O* + 2W0. Neutral Potassium Oxalate, K^C^O* -|- H^O, is obtained by neutralizing a solution of the acid salt with potassium car- bonate and evaporating. It crystallizes in oblique rhombic prisms, very soluble in water. Ammonium Oxalate, (NH^^C^O* + H^O, which is fre- quently used as a reagent, is prepared by neutralizing oxalic acid with ammonia. The concentrated solution deposits color- less crystals belonging to the type of the right rhombic prism. There is also an acid oxalate of ammonium, (NH*)HC^O*. Methyl Oxalate, (Cff)^C^O*, forms colorless crystals melt- ing at 54°. It is prepared by heating anhydrous oxalic acid with methyl alcohol. Ethyl Oxalate, or Oxalic Ether, (C='H5)^C=^0^— This ether may be prepared by distilling a mixture of potassium acid oxalate, alcohol, and concentrated sulphuric acid. It is a colorless oily liquid, heavier than water, and having an aro- matic odor. It boils at 186°. OXAMIDE. If solution of ammonia be added to ethyl oxalate, the latter immediately solidifies to a white mass formed of a crystalline powder. This is oxamide. ^2^5;q>C202 + 2NH3 = C202<^^2 _^ 2(C2H5.0H) Ethyl oxalate. Oxamide. Oxamide is also formed by the dry distillation of ammonium oxalate. NHto>^'^' = C202<^H2 ^ 2H20 The latter reaction, studied in 1830 by Dumas, led to the discovery of the amides. Oxamide is a white, crystalline powder, very slightly soluble MALONIC ACID. 609 in cold water, insoluble in alcohol, somewhat soluble in boiling water, from which it is deposited on cooling. Like all of the amides, it is decomposed by boiling caustic alkalies, ammonia being disengaged and potassium oxalate formed. Oxamic Acid. — This body is formed when ammonium acid oxalate is heated to between 220 and 238° (Balard). Ammonium acid oxalate. Oxamic acid. It is a yellowish, granular powder which boiling water con- verts into ammonium acid oxalate by the direct addition of one molecule of water. The following formulae express clearly the relations existing between oxalic acid, oxamic acid, and oxamide : C^OKoi C202o -I- PC15 = pocp + Y CH2-C0^ CH2-C0C1 Succinic anhydride. Succinyl chloride. Kekule has obtained monohromo-succinic and dibromo-suc- cinic acids by heating moistened succinic acid with bromine in sealed tubes. Monobromo-succinic acid is converted into malic acid when treated with water and silver oxide. C2H3Br<^22§ + AgOH = C2H3(OH)C0 NH C-NH^ This body is related to the complex organic acids which have just been studied. Among the numerous products do- COOH rived from its oxidation, we may mention oxalic acid, i , ^ ' COOH' and an acid, CO(COOH0 + H^O or C(0H)XC00H)2, which has been called mesoxalic. Uric acid was discovered by Scheele, and its numerous meta- morphoses were the subject of a classic research by Liebig and Wohler, and have been more recently studied by Baeyer and other chemists. Preparation. — Uric acid may be extracted from the excre- ments of serpents, from guano, and from certain urinary cal- culi, which are almost entirely composed of it. These sub- stances are reduced to a fine powder, boiled with potassium carbonate and lime, and the solution filtered. The colored solution of potassium urate is mixed with a solution of ammo- nium chloride, which produces a white precipitate of ammonium URIC ACID. 625 urate. This salt is well washed, and treated with hydro- chloric acid, which sets free uric acid. J. Horbaczewski has made the synthesis of uric acid by heating a mixture of urea and glycocoU to 200-230°. Urea. GlycocoU. Uric acid. According to Behrend and Roosen, it is also obtained, and in much larger quantity, by heating a mixture of isodialuric acid, urea, and sulphuric acid. NH-CO-C-OH NH2 NH-CO-C-NH^ C0< II +C0< =C0< II >CO + 2H20 NH C-OH NH2 NH C-NH Isodialuric acid. Urea. Uric acid. Properties. — Pure uric acid is a light, white powder, which has a crystalline aspect under the microscope. When slowly separated from dilute solutions, it sometimes forms larger crys- tals, containing 2 molecules of water of crystallization. It is often deposited from urine in small rhomboidal tables of a brownish-yellow color. Uric acid is insoluble in alcohol and in ether. It requires 15,000 parts of cold water, or 1800 parts of boiling water, for its solution. It dissolves in solutions of the alkalies, form- ing neutral urates containing two atoms of the alkaline metal. It is therefore a dibasic acid. When carbonic acid gas is passed into a solution of a neutral urate, an acid urate, which is almost insoluble, is precipitated. Hydrochloric acid forms ^ a thick, white, gelatinous precip- itate of uric acid when added to the solution of a urate. When uric acid is heated to 160 or 170° with an excess of hydriodic acid, it absorbs water, and is decomposed into glyco- coU, carbonic acid gas, and ammonia (Strecker). C^H^N^O^ -f 5H^0 = C^H^NO^ + 3C0^ -f 3NH' Uric acid. GlycocoU. If a small quantity of uric acid be gently heated with nitric acid in a porcelain capsule, it is dissolved with a disengagement of red vapors, and the solution, evaporated at a gentle heat, leaves a residue which assumes a purple color on the addition of a drop of ammonia. This test is characteristic of uric acid, and permits the de- tection of the least traces of that substance. The purple body formed is called murexide. 2b pp 53 626 ELEMENTS OP MODERN CHEMISTRY. DERIVATIVES OF URIC ACID. Among the numerous compounds which may be derived from uric acid, some are closely related to oxalic acid, or other acid containing two carbon atoms ; others are derived from mesoxalic acid (see farther on), which contains three carbon atoms. All of these derivatives are more or less closely related to urea ; they are substituted ureas, and are more specially designated by the name ureides. Those related to mesoxalic acid are the more direct derivatives. Alloxan, C'H^N^O*.— This body is one of the products of the oxidation of uric acid by nitric acid ; urea is formed at the same time. C^HWO^ + H^O + O =: C^H^N^O* + CH^N^O Uric acid. Alloxan. Urea. It may be prepared by introducing uric acid, in successive small quantities, into nitric acid of a density of 1.41-1.42, as long as it dissolves producing red vapors. The alloxan finally separates in a mass of delicate needles ; in about twenty-four hours they are drained and dissolved in water at 60 or 65°. On cooling, the alloxan separates in voluminous crystals con- taining 4 molecules of water of crystallization. They efilo- resce in dry air. When crystallized from a hot solution, alloxan forms rhombic octahedra, containing but a single molecule of water. It is very soluble in water, and the solution is acid. By the action of alkalies, baryta-water for example, alloxan is con- verted into alloxanic acid^ which is formed by the direct com- bination of the elements of one molecule of water with alloxan. C^H^N^O* -f H^O = C^HWO^ Alloxan. Alloxanic acid. The alloxanates are decomposed by boiling into mesoxalic acid and urea. Thus if a solution of alloxanic acid, or even alloxan, be added to a boiling solution of lead acetate, a precipi- tate of lead mesoxalate is formed. Q4JJ4N205 _|_ H^O = Q'O'W + CH^N^O Alloxanic acid. Mesoxalic acid. Urea. Mesoxalic acid, C=^0\OH)'^ = CO.OH-CO-CO.OH, is a dibasic acid. According to Baeyer, its diatomic radical, mes- oxalyl, exists in alloxan itself, which is mesoxalylurea, that is, urea in which two atoms of hydrogen are replaced by the diatomic radical [(CO)^-C(OH)^]''. DERIVATIVES OF URIC ACID. 627 p^^NH2 p^^NH-C0^p.^TTX2 p^^NH-C202-CO.OH Urea. Mesoxalyl-urea Alloxanic or (alloxan). mesoxaluric acid. Dialuric Acid, C*H*N^O*, is the product of the prolonged action of hydrogen sulphide on a hot solution of alloxan or alloxantin. Alloxan. Dialuric acid. It is also formed by the action of sodium amalgam on the same solutions. It crystallizes in long needles, quite soluble in water ; these crystals assume a red color in the air, and are gradually trans- formed into alloxantin. When a solution of alloxan is added to a solution of dialuric acid, alloxantin is formed. Dialuric acid. Alloxan. Alloxantin. Baeyer regards dialuric acid as tartronyl-urea, that is, urea in which two atoms of hydrogen are replaced by the diatomic radical of tartronic acid. CO.OH ^^■^^ co<^^' co<'^H-^^-^ro ro<'NH-co^p„^„ CO.OH ^^^NH2 ^^^NH-CO>^^ CO<^j^jj_(,q>CH.OH Tartronic acid. Urea. Alloxan. Dialuric acid (tartronyl-urea). Barbituric Acid, C*H*N^Ol— This acid, which is malonyl- urea, is formed by the action of nascent hydrogen on dibrom- alloxan. CO '^^'^ + 2H' = 2HBr + CO<^|:^g>CH' Dibromalloxan. Barbituric acid. It crystallizes in large prisms, slightly soluble in cold and more soluble in boiling water. Ebullition with alkalies converts it into malonic acid and urea. Malonyl-urea. Malonic acid. Urea. Alloxan, dialuric and barbituric acids, which have been de- scribed, are ureides derived from a single molecule of urea by the substitution of the radical of a dibasic acid for two atoms of hydrogen. The groups C^O^[(CO•^-C(OH)'^],C^O^-CH.OH, 628 ELEMENTS OF MODERN CHEMISTRY. C^O^-CH^, wliich in oxalic, mesoxalic, tartronic, and malonic acids are united to two hydroxyls, are diatomic. CO.OH CO.OH CO.OH C(0H)2 CH(OH) CH2 CO.OH CO.OH CO.OH Mesoxalic acid. Tartronic acid. Malonic acid. ^^^(^I^)' CO<^g:g^>CH.OH CO<^H-CO^(.jj, Mesoxalyl-urea Tartronyl-urea Malonyl-urea (alloxan). (dialuric acid). (barbituric acid). The following compounds are diureides; they are derived from two molecules of urea in which four atoms of hydrogen are replaced by two dibasic acid radicals, each of which contains three atoms of carbon and is related to mesoxalyl : Alloxantin, C^H^N^O^ — This body is produced by the re- duction of alloxan. When a current of hydrogen sulphide is passed through a cold solution of alloxan, sulphur separates, and a crystalline precipitate of alloxantin soon forms. 2C*H2N20* + H^S = C«HWO^ + H'^'O + S Alloxan. Alloxantin. Alloxantin is also formed directly, at the same time as alloxan, by the action of weak nitric acid on uric acid. It crystallizes in small, colorless prisms containing 3 molecules of water of crystallization. It is but slightly soluble in cold water. Nitric acid converts it into alloxan, and reducing agents transform it into dialuric acid. Purpuric Acid and Murexide. — Scheele had already ob- served murexide, which Prout studied and described as pur- purate of ammonia. It is, indeed, the ammonium salt of a nitrogenized acid, C^H^N^O^, for which it is convenient to pre- serve the name purpuric acid (Beilstein). Murexide is formed by the action of ammonia on dry allox- antin heated to 100°, or again, when ammonia or ammonium carbonate is added to a hot solution of alloxantin or alloxan. C^HWO^ _|_ 2NH3 = C^H*(NIP)N^O« + H^O Alloxantin. Murexide (ammonium purpurate). Murexide crystallizes in quadrangular prisms, or in tables which are green by reflected and red by transmitted light. These crystals, which contain one molecule of water, present the magnificent metallic reflections shown by the wings of can- tharides. They dissolve in water with a rich purple color. Allantoin, C*H«N*Ol— This body was discovered in 1800, DERIVATIVES OF URIC ACID. 629 by Vauquelin and Buniva, in the allantoic liquid of the cow, that is, the urine of the foetal calf. It occurs also in the urine of young calves. In 1836, Liebig and Wohler obtained it by oxidizing uric^ acid with lead dioxide. Gorup-Besanez has observed its formation in the action of ozone upon uric acid. Grimaux has made the synthesis of allantoin by heating one part of glyoxylic acid with two parts of urea, for eight or ten hours. Q2H2Q3 ^ 2(CH^N^0) = C^HWO^ + 2H20 Glyoxylic acid. Urea. Allantoiu. From this remarkable synthesis, it appears that allantoin is derived from two molecules of urea ; it is the diureide of gly- oxylic acid. Allantoin may be prepared by boiling uric acid with water, and adding lead dioxide, in small quantities, as long as that oxide continues to be converted into a white powder, which is lead carbonate. The filtered liquid, freed from lead by hydro- gen sulphide, yields crystals of allantoin on evaporation. Uric acid. Allantoin. Allantoin crystallizes in brilliant, colorless prisms. It dis- solves in 30 parts of boiling water and in 160 parts of cold water ; it is also soluble in alcohol, but is insoluble in ether. It forms crystallizable compounds with certain metallic oxides. The following compounds are ureides of oxalic and glycollic acids : Parabanic Acid, C^H^N^Ol— This body is formed by the action of an excess of nitric acid on alloxan, which thus gives up the elements of carbon dioxide. Alloxan. Parabanic acid. Parabanic acid forms thin, transparent prisms, which are very soluble in water. By boiling with acids, it is transformed into oxalic acid and urea. Baeyer regards it as oxalylurea. NH-CO When parabanic acid is heated with ammonia, ammonium oxalurate is formed, and separates in fine needles. In this case the parabanic acid is converted into oxaluric acid by directly combining with the elements of water. 53* 630 ELEMENTS OF MODERN CHEMISTRY. Parabanic acid. Oxaluric acid. It is seen that oxaluric acid is related to parabanic acid, as alloxanic acid is to alloxan. Hydantoin, or Glycolyl Urea. — The relations between this compound and parabanic acid are the same as those between glycollic and oxalic acids. It is glycolyl urea, C^H^N^O'^ and is formed by the action of hydriodic acid on allantoin. MTJ_nTT2 C^HWO^ _|_ 2HI = C0< X + CON^O* 4- P ^NH-CO ^ Allantoin. Hydantoin. Urea. It crystallizes in needles, fusible at 215°, very soluble in hot water. Its solution is neutral. When hydantoin is heated with baryta- water, it is converted into hydantoic acid. Q3JJ4jy^2Q2 _|_ J12Q ^ C^H^N^O^ Hydantoin. Hydantoic acid. Hydantoic Acid, C^H^N^O^ may be obtained synthetically by heating urea with glycocoll ; ammonia is disengaged. ^^< j^jj_(i,Q ^^^NH-CO-CO.OH Parabanic acid. Oxaluric acid. ^^<-^Yl-bo ^^^NH-CH2-C0.0H Hydantoin. Hydantoic acid. We cannot further continue the study of the numerous de- rivatives of uric acid. This study has already thrown much light upon the constitution of the acid, without definitely de- termining it. The syntheses indicated by Horbaczewski (page CREATINE — CREATININE. 631 625), and by Behrend and Roosen, as well as more recent investigations of E. Fischer, afford additional proof for the correctness of the formula of uric acid given above, DERIVATIVES OF GUANIDINE. There are interesting structural relations between urea and guanidine ; the latter is urea in which the oxygen is replaced by the imidogen group NH. CONH, which is a derivative of benzene, and, owing to its intensely sweet taste, is sometimes used as a substitute for sugar. FRUCTOSE, OR LEVULOSE. 639 Grlucose is one of the aldoses, being at the same time a pentahydric alcohol and an aldehyde. Its constitution is represented by the formula CHIOH-CH.OH-CH.OH-CH.OH-CH.OH-CHO This is deduced from the following facts : acetic anhydride converts glucose into a pentacetyl derivative, showing it to contain five hydroxyl groups ; its reducing properties are due to the presence of an aldehyde group, which is shown by its oxidation to gluconic acid, CffOH-(CH.OH)*-COOH, and its reduction by nascent hydrogen to mannitol, a primary alcohol. It is confirmed by the behavior of glucose with hydroxyl- amine and with phenylhydrazine. With one molecule of the latter reagent, it yields the hydrazone CHIOH(CH.OH)*- CH=N^H-C^H^, but upon heating with an excess of phenylhy- drazine, phenylglucosazone, CH^0H(CH.0H)^-C(N2HC''H^)- CH=N•^C^H^ is produced. Galactose, C^H^^O^. — This is one of the products of the action of dilute acids and of certain ferments on lactose (page 644). Galactose crystallizes in little masses, formed by the agglomeration of small needles. It is less soluble in water than glucose, and deviates the plane of polarization to the right. It is fermentable, and readily reduces cupro- potassic solutions. Nascent hydrogen converts it into dul- citol. Nitric acid oxidizes it with formation of mucic acid. FRUCTOSE, OR LEVULOSE. C6H1206 = CH2.0H-CH.OH-CH.OH-CH.OH-CO-CH20H Besides the glucose which effloresces on their surface after desiccation, many fruits contain another sugar, which strongly deviates the plane of polarization to the left. It is fructose, formerly known as levulose. Fructose exists in inverted sugar (page 643). Many sweet fruits contain inverted sugar ; among them are grapes, cher- ries, figs, gooseberries, etc. The extraction of fructose from inverted sugar — of which it constitutes one-half — is a laborious procedure. Dubrunfant recommends the conversion of the sugars into their calcium compounds : the fructosate of calcium is difficultly soluble in water, while the glucosate is readily dissolved. A better 640 ELEMENTS OF MODERN CHEMISTRY. metliod of preparing fructose consists in warming inulin witli dilute acids. For this purpose a few drops of sulphuric acid are added to a solution of inulin in water and the liquid heated gently for some time. The sulphuric acid is then precipitated with barium hydrate and the filtrate evaporated. Upon adding a crystal of fructose, the fruit sugar separates in colorless acicular crystals. It may be purified by recrys- tallization from alcohol. Fructose thus obtained contains no water of crystalliza- tion ; the crystals belong to the orthorhombic system. It melts at 95°, and is readily soluble in water and in alcohol. The fructose contained in inverted sugar rotates the plane of polarization to the left, and rather more strongly than the other component, glucose, turns it to the right ; for this reason inverted sugar is slightly levorotatory. A fructose which is optically inactive, but agrees in all other respects with the natural product, has been artificially obtained by E. Fischer. He has further succeeded in con- verting this into mannose and glucose, and in resolving it into its dextro- and levo-rotatory modifications. Thus the synthesis of the most important monosaccharides has been accomplished. Fructose is directly fermentable. Its reactions closely re- semble those of glucose, except that on oxidation it does not yield an acid with the same number of carbon atoms, but is resolved into tartaric and glycollic acids. This proves that fructose is a ketone. Sorbinose, C^H^^O^, a substance which crystallizes in large, transparent rhomboidal octahedra, has been obtained from the berries of the mountain-ash by Pelouze. It appears to be stereoisomeric with the fructoses. SACCHAROSE, OR CANE-SUGAR. Q12II220n Extraction. — Ordinary sugar, which is widely distributed in the vegetable kingdom, is extracted principally from sugar- cane, sugar-maple, and beet-root. Fresh sugar-cane contains about 18 per cent, of sugar, and beet-roots from 12 to 16 per cent. Certain sweet fruits contain cane-sugar, independently of inverted sugar. According to Buignet, such are apricots, peaches, pine-apples, lemons, plums, and raspberries. SACCHAROSE. 641 We can only briefly indicate the processes wliicli are em- ployed for the extraction of sugar from beet-root. The roots are washed, and reduced to pulp in a machine provided with a cylinder armed with teeth and having a rapid rotary motion. This pulp is then strongly pressed in woollen sacks by means of a hydraulic press, and the juice is imme- diately transferred to large boilers having double bottoms and heated by steam, and milk of lime is added. This operation, which is called clarification^ is intended not only to separate certain substances which form insoluble com- pounds with the lime, but to prevent the juice from becoming altered by reason of its acidity. As the sugar itself dissolves a large quantity of lime, the latter must be got rid of. A cur- rent of carbon dioxide is consequently passed into the solution, and decomposes the saccharate of calcium. Another process for removing the excess of lime depends on the employment of ammonium phosphate. Insoluble calcium phosphate is formed, and the ammonia is disengaged on account of the high temperature at which the operation is conducted. By this process the neutralization is more perfect. The liquid is then heated to about 95°, and filtered through a layer of animal charcoal in grains ; it is then concentrated in evaporating-pans heated by steam. When the syrup marks 25° Baume, it is again filtered through animal charcoal, and the concentration is finished in pans heated by steam, and in which a vacuum is maintained during the evaporation. The cooking of the syrup is thus carried on at a temperature not above 75 or 80°, and these conditions assure a fine quality of product and a good yield by preventing as much as possible the transformation of the sugar into uncrystallizable sugar. When the syrup marks 42 or 43°, it is run into cooling- pans, where it is continually stirred until the sugar is depos- ited in small crystals. These are distributed in moulds, which consist of terra-cotta cones having a hole in the summit, which for the time is closed. These cones are placed in an oven heated to 25°, where the crystallization takes place ; when the syrup has solidified, the holes in the cones are opened and the thick and colored mother-liquor is allowed to drain out ; it con- stitutes molasses. The loaves of sugar, drained and dried, are delivered to commerce as crude or brown sugar. For some years an apparatus has been used for draining and bleaching of crude sugars, which consists of a cylindrical qq 64* 642 ELEMENTS OF MODERN CHEMISTRY. cage having perforated metallic walls. It is put into rapid motion on its axis, and the molasses is expelled through the perforated walls by centrifugal force. The apparatus is called the centrifugal drier. Refining^ of Crude Sugar. — The crude sugar is crushed, sifted, and dissolved in about 30 per cent, its weight of water, the operation being conducted in a boiler heated by steam. 5 per cent, of animal charcoal is then thrown into the hot solu- tion, and, after stirring, i per cent, of beefs blood is added. The latter coagulates in the liquid and envelops all of the sus- pended particles, uniting them in a scum which is easily re- moved. When the liquid becomes clear, it is drawn off and filtered. It is then passed through grained animal charcoal, which completely decolorizes it. It is concentrated in vacuum- pans, from which it is drawn into a large copper vessel having a double bottom. It is continually stirred until crystallization commences, after which it is run into moulds, which are then placed in rooms heated to 20°. After the crystallization is completed, the syrup remaining liquid is allowed to drain out. At the termination of the draining, a creamy mixture of white clay and water is poured on the surface of the sugar in each mould, and the water of this broth slowly penetrates the mass of sugar, liquefies the syrup which remains between the crystals, and carries it to the lower part of the mass. The clay, having lost its water, contracts, dries up, and remains upon the decolorized sugar as a dry cake. It is removed, and a syrup of white sugar is run into the whitened and porous loaf and fills up all of the spaces when it solidifies in the oven. This operation, the object of which is the decolorizing of the sugar-loaves, is called claying. The clay broth may be replaced by syrup of white sugar, an operation which is called decoloring. The sugar solidified in the moulds is a compact, crystalline, white mass, composed of little grains. It may be obtained in voluminous crystals by concentrating the syrup until it marks 3*7° Baume, and then exposing it for some days to a tempera- ture of 30° in copper vessels, across which threads are stretched. The sugar is deposited on the threads in large crystals known as rock-candy. Properties of Sugar. — Sugar crystallizes in large, oblique rhombic prisms, having hemihedral facettes. The crystals are hard, anhydrous, and unalterable in the air. Density, 1.606. SACCHAROSE. 643 It dissolves in one-third its weight of cold water ] the solution is thick, and is known as simple syrup. Sugar is insoluble in ether and in cold absolute alcohol. Boiling absolute alcohol dissolves a little more than one per cent. ; ordinary alcohol will take up more. The aqueous solution of sugar deviates the plane of polarization to the right, ([a]D = -f 66.5°), at 20°. At 160°, sugar melts to a thick, transparent liquid, which solidifies to an amorphous, vitreous mass on cooling. ¥/hen maintained for a long time at a temperature of 160 or 161°, it breaks up into glucose and levulosan (Grelis). (.12^22011 ^ C^H^^O^ + C^H^oQ^ Saccharose. Glucose. Levulosan. Between 190 and 200° it loses the elements of water and is converted into a bitter, brown, amorphous mass, which is desig- nated as caramel. Cane-sugar does not reduce alkaline copper solutions, and does not react with phenylhydrazine. Inverted Sugar. — By the action of dilute acids, sugar is converted, slowly in the cold and rapidly on boiling, into a mixture, in equal proportions, of two isomeric sugars which have opposite rotatory powers : they are glucose and fructose. The mixture is called inverted sugar. Q12H22Q11 _|_ JJ2Q ^ C^H^^O^ + C^H^^O^ Saccharose. Glucose. Fructose. The same transformation is efi"ected by the soluble matter of yeast (Berthelot), and also, according to Buignet, by the action of the peculiar ferments which exist in most fruits. Sugar only ferments after having first undergone this trans- formation into inverted sugar by the action of the ferment. Nitric acid converts sugar into saccharic acid., C^H^^O®, and oxalic acid. Concentrated sulphuric acid carbonizes it. Saccharose resists the action of alkalies better than glucose. It forms with them and with the bases in general, definite com- binations known as saccharates. If a mixture of sugar and slaked lime be triturated with water and the whole be thrown upon a filter, the liquid which passes through will be colorless and strongly alkaline. When it is heated to ebullition, it changes into a solid mass which again becomes liquid on cooling. It is a solution of saccharate of calcium, (C^^H'''^0^^)^3CaO. Alcohol precipitates from it the compound C^^H^^qh (j^^q^ 644 ELEMENTS OF MODERN CHEMISTRY. An excess of strontium hydrate precipitates cane-sugar completely from a hot solution ; the resulting disaccharate, Q12JJ22Q11 2gj.Q^ is readily decomposed by carbon dioxide into sugar and strontium carbonate. Scheibler has founded a process for extracting crystallizable sugar from molasses upon these reactions. When sugar is fused with potassium hydrate, it disengages hydrogen, and carbonate, oxalate, formate, acetate, and pro- pionate of potassium are formed. When distilled with quick-lime, sugar is decomposed with formation of carbon dioxide, water, acetone, and metacefone, C^H'O, a liquid having a pleasant odor and boiling at 84°. Sugar forms a crystalline compound with sodium chloride. LACTOSE, OR MILK-SUaAR. This sugar exists in solution in the milk of mammals, and is extracted from the whey which remains after the manufacture of cheese. It is only necessary to evaporate this liquid to crystallization. Milk-sugar occurs in commerce in cylindrical masses, formed of an agglomeration of crystals around a little stick which serves as a nucleus. The crystals are colorless, hard, and creak when crushed by the teeth. They are right rhombic prisms, terminated by octahedral points. They contain one molecule of water of crystallization which they lose at about 140°. They dissolve in 6 parts of cold, and in 2 parts of boiling water. The solution turns the plane of polarization to the right. The rotatory power of old solutions is [a]D = +52.53°. When heated with nitric acid, lactose yields certain acids, •among which is one which is but slightly soluble in water, and which is called mucic acid. It contains C^H^^O^, and is stereoisomeric with saccharic acid, which is also produced by the oxidation of lactose by nitric acid. Moderate oxidation with bromine water converts lactose into lactobionic acid, Qi2jj22Qi2^ which upon warming with dilute acids yields galactose and gluconic acid. When boiled with dilute sulphuric acid, milk-sugar is con- verted into glucose and galactose. Milk-sugar reduces cupro-alkaline solutions, but more slowly than glucose. MALTOSE. 645 With phenylhydrazine it yields phenyllactosazone, C^*H'^ N*0*, yellow needles melting at 200°. When exposed to the air at summer heat, a solution of lactose in presence of calcium carbonate soon undergoes the lactic fermentation (page 647). MALTOSE. This name is given to the crystallizable sugar produced, together with dextrin, by the action of diastase on starch. It may be prepared by digesting starch paste at 60° with a solution of diastase. The solution is precipitated by alcohol, which separates the dextrin, filtered, the alcoholic liquid evaporated to a syrupy consistence, more alcohol added, and the solution set aside to crystallize over sulphuric acid. Mal- tose is a product of the incomplete hydration of starch. Maltose forms masses composed of hard, white needles. It loses its water at 100°. Its solution turns the plane of polarization to the right, [a]D = -\-137°. It reduces Fehling's solution, and when boiled with dilute acids is con- verted into glucose. Maltose is directly fermentable. Heated with acetic anhydride and sodium acetate, it yields an octo- acetyl derivative, C'^Hi*0^(O.CO.CH=*)^ and with an excess of phenylhydrazine it gives phenylmaltosazone, C^^H^WO^ Isomaltose, C^^H^^O^^, is formed by the action of hydrochloric acid upon glucose, and from starch in presence of diastase. It has an intensely sweet taste, and is dextrorotatory to about the same extent as maltose. It is decomposed upon gentle heating, but does not seem to be directly fermentable. Mycose, or trehalose, Ci^H^^O^^ -\- 2W0, was extracted by Mitsch- erlich from the ergot of rye, and has been obtained by Berthelot from a Turkish manna (trehala). It crystallizes in hard, rectan- gular octahedra, gritty between the teeth, and having a sweet taste. It is strongly dextrogyrate, [a]D = -|-199°. It is distinguished from cane-sugar by its ready solubility in boiling alcohol. Melitose, or raffinose, C^^H^^Qie _|_ 5H^0, was extracted by Berthe- lot from Australian manna, a sweet exudation of the eucalyptus, and is known to exist in sugar-beets. Being more soluble than ordinary sugar, it accumulates in the molasses. It crystallizes in fine needles which lose their water of crystallization at 100°, while the residue melts at 118°. Melitose is powerfully dextrorotatory, [a]D z= 104.4°, a property which interferes with the estimation of ordinary sugar by polarimetry when both are present. It does not react with Fehling's solution, but is completely fermentable. On hydrolysis, it yields fructose, glucose, and galactose. 646 ELEMENTS OF MODERN CHEMISTRY. Melezitose, Ci»H320i6 + 2H20, was obtained by Berthelot from Brian9on manna, exuded by the larch {Pinus larix). It crystallizes in monoclinic prisms, with two molecules of water, which it loses at 108°. It is dextrogyrate, [a]D = -f 94°. It melts at 157°. Its complete hydrolysis yields only glucose. FERMENTATION. , If yeast be introduced into a tolerably concentrated solution of glucose, and the liquid be exposed to a temperature between 20 and 30°, bubbles of an incombustible gas will soon be dis- engaged, and this gas will produce a cloud in lime-water. It is carbon dioxide. After the disengagement of gas has ceased, a small quantity of alcohol may be obtained by distilling the liquid. In this experiment, the glucose disappears ; it is broken up into alcohol and carbon dioxide. The decomposition is effected by yeast, and is called fermentation. The sugar is the fer- mentable substance ; the yeast is \hQ ferment. The ferment is an organized matter which develops and mul- tiplies at the expense of the glucose. The latter, is directly at- tacked by this being which lives at its expense, and undergoes a complete decomposition, of which carbon dioxide and alcohol are the principal products. The ferment plays an active part, which was first suspected by Cagniard-Latour and Schwann, and demonstrated by Pasteur. Alcoholic Fermentation. — The decomposition of glucose under the influence of yeast constitutes the alcoholic fermenta- tion. The principal reaction is expressed in the following equa- tion: Q6JJ1206 ^ 2C^H«0 + 2C0' Glucose. Alcohol. It is shown by the experiments of Pasteur, that only 94 per <;ent. of the quantity of glucose decomposed undergoes the change indicated by the above formula. The remaining 6 per cent, are employed: 1, in the formation of small quantities of higher alcohols, succinic acid, and glycerol ; 2, in the de- velopment of new yeast cells. Yeast is composed of a mass of cells or ovoid corpuscles, having a diameter of y^ of a millimetre, and arranged in clusters (Pig. 129). Their walls are an elastic membrane, and their contents are liquid or granular. They contain cellu- lose, albuminoid matter, and mineral salts. When they are FERMENTATION. 647 introduced into a substance which contains the materials neces- sary for their development, they multiply rapidly. Pasteur has made decisive experiments on this point. He planted some yeast cells in a solution of sugar to which he had added a small quantity of an ammoniacal salt and some phosphates. The solu- tion of sugar fermented, and the ferment developed by budding, the new cells absorbing the ammonia and the phosphates. They obtained from the sugar the matter necessary to form cellulose, and from the ammo- nia the nitrogen required for the elaboration of the albumi- noid matters. However, these artificial conditions are not those which are best adapted for the propagation of the cells. The latter increase with ex- treme energy in liquids which contain, besides the yeast, glu- cose, and a small quantity of Ficf* 129. albuminoid matter ready formed. Lactic Fermentation. — This fermentation, of which the conditions have already been indicated (page 597), is accom- plished by the action of a peculiar ferment of vegetable char- acter. It is formed of small round or elongated cells, very short, and isolated, or in masses. They are much smaller than yeast cells, and constitute the lactic yeast of Pasteur. It only acts upon glucose or lactose in a neutral or alkaline liquid. Hence the necessity of adding sodium carbonate or chalk to the liquid. The reaction consists in a splitting of the glucose molecule. (;J6JJ12Q6 ^ 2C^H«0^ Glucose. Lactic acid. Butyric Fermentation. — This consists in the transforma- tion of calcium lactate into butyrate, — a transformation that is accompanied by a disengagement of hydrogen. According to Pasteur, this fermentation is caused by a low organism which can live and thrive only in situations where its members can- not obtain free oxygen. Such is the energy of their respira- tory functions that free oxygen kills them (Pasteur). They decompose oxidized bodies and assimilate the oxygen. 648 ELEMENTS OF MODERN CHEMISTRY. We have already considered the acetic fermentation. "We may add that by the action of a certain ferment, glucose is converted into mannitol and a gummy matter, very soluble in water, and which gives a viscous consistence to the fer- mented liquid. This is called the viscous fermentation. There are many other kinds of fermentation, an exceed- ingly large number of carbon compounds being capable of decomposition in this manner; the ferments are also very numerous, and the special fermentation undergone by a sub- stance depends upon the peculiar ferment present. Fermented Beverages. — The foregoing summary indi- cations regarding fermentation may be supplemented by some general notions upon the fermented beverages wine and beer. Wine. — It is universally known that wine is the product of the fermentation of grape-juice. This juice contains in solution inverted sugar, small quantities of gummy matters, vegetable albumen, a trace of fatty matters, coloring matters, free tartaric and malic acids, and various tartrates, princi- pally potassium acid-tartrate, or cream of tartar. The clarified wine which results from the fermentation of this juice consists of an aqueous solution of various products, some of which existed in the juice, and others which are the result of the transformation through which it has passed. Among the first are the mineral and vegetable salts of the juice (in smaller proportion, because they are partly deposited with the lees), the gummy matter, a small quantity of fatty and albuminoid substances, the coloring matters, free tartaric and malic acids, and the tannin derived from the grape-stems and from the skins and seeds. Among the substances which result from the fermenta- tion are : 1. Alcohol, which is the principal product. 2. Carbonic acid gas ; still wines retain but a small propor- tion, the fermentation taking place entirely in open vessels, but sparkling wines contain it abundantly under pressure, the final fermentation having taken place in the bottle after corking. 3. Small quantities of aldehyde and acetic acid produced by oxi- dation of the alcohol. The acetic acid reacts upon the alcohol con- tained in the wine, forming acetic ether. 4. Grlycerol and succinic acid, in small quantities (Pasteur). 5. Traces of compound ethers, which contribute to the bouquet of the wine. Besides acetic ether, traces of a compound ether called Knanthic ether have been found in wine ; it appears to be pelargonic FERMENTATION. 64Q ethffr, C9H"02(C2H5). Berthelot states the existence of but slightly volatile acid ethers (malic, tartaric) in wine. The following table indicates the quantities by volume of pure alcohol contained in 100 volumes of various wines : California Port 22.00 Madeira 20,48 Port 20.22 Sherry 18.00 Sauterne (white) 15.00 Catawba 13.00 Rhine Wines 11.11 California Riesling 11.20 Champagnes 11.00 to 18.00 Strong Clarets 8.00 to 12.00 Light Clarets 7.5 to 8.00 Red Burgundy 7.66 Red Macon 7.66 White Burgundy 7.83 Beer. — Beer is a fermented beverage, made from a wort of germinated barley, and ordinarily rendered aromatic by bops. Like all other cereals, barley contains a considerable proportion of starch. During the germination, this starch is partially con- verted into maltose by the action of a nitrogenized matter, which is formed in the sprouting grains, and which is called diastase. In order to saccharify the barley, it is then first necessary to cause it to germinate, and for this purpose it is moistened with water, and kept for some time at a temperature of 14 or 15° ; the object of this operation, called malting, is the development of ^ ^^ the diastase necessary for the saccharification - V^^ of the starchy matter. When the sprout has /T>) MW\)) acquired about the same length as the grain (Fig. 130), the germination is arrested by ex- In posing the malt to the action of a temperature \\|^ of about 50°. The dry malt is then reduced to a coarse powder, placed in a large vat, and Fig. 130. brewed for about three hours with water heated to 50 or 60°. In this operation, the diastase of the malt con- verts the starch into dextrin and maltose, which dissolve, to- gether with the other soluble principles of the grain. The sweet wort thus obtained is heated with hops, which yield to it their essential aromatic oil. It is then properly cooled and allowed to ferment in deep vats, into which a cer- tain quantity of yeast produced in a previous operation is in- troduced at the same time. The alcoholic fermentation soon begins and goes on with great activity during a few days. As 2c 55 650 ELEMENTS OF MODERN CHEMISTRY. soon as it has ceased, the liquid can be delivered for consump- tion. The quality of beer is better when the fermentation takes place at a low temperature. Beer contains much water, free carbonic acid gas, alcohol (2 to 5 per cent.), variable quantities of saccharine matters, dex- trin, nitrogenized matters, extractive, bitter, and coloring mat- ters, essential oil, and various salts. Ale and porter are in nature analogous to beer, but are relatively richer in alcohol and nitrogenous and extractive matters. STARCH. (C^HioOS)" Starch is universally diffused throughout the vegetable king- dom. It is especially abundant in the seeds of leguminous plants and cereals, and in the potato. Extraction. — To extract starch from potatoes, they are re- duced to pulp by means of a rasp, and the pulp is placed in a sieve and washed by a stream of water. The water carries with it the fine granules of starch, while the torn cells of the potato remain in the sieve. The starch gradually deposits from the water, and collects in the bottom of the vessel, where it settles, forming a cake from which the supernatant water may be separated by decantation. Starch may be extracted from wheat by making a paste of flour and kneeding it in a sieve under a jet of water : the starch granules are carried with the water, and a soft, gray, elastic mass remains in the sieve, constituting the nitrogenized matter of the flour, or gluten. Another process, almost abandoned at present on account of its offensiveness, consists in allowing the coarsely-ground grain to putrefy. Putrefaction destroys the gluten, while the starch resists decomposition. Physical Properties. — Starch is a white powder, formed of granules which present an organized structure. Their size and shape are variable (Fig. 131), their diameter being from 2 to 185 thousandths of a millimetre. Those of potato starch are larger than those of starch from grain. These granules are made up of concentric layers, which are more dense as they are nearer the surface. It is easy to make this structure apparent by causing the granules to undergo a partial disintegration by the action of hot water. They swell up, burst open, and separate into thin layers, as shown in Fig. 132. STARCH. 651 Chemical Properties. — Starch is insoluble in water, alcohol, and ether. Contact with water heated to 60 or 70° causes it to swell up considerably, without dissolving. A semi-trans- parent, gelatinous mass results, which is known as starch paste. When starch is boiled with a large quantity of water and the whole is thrown on a filter, the liquid which passes is slightly turbid, and constitutes an emulsion of starch. It contains in suspension flakes of amylaceous matter small enough to pass through the filter. It also contains a small quantity of soluble starch (see farther on). If a few drops of solution of iodine be added to the emul- sion, a deep-blue color is at once produced. This blue color disappears when the liquid is heated to 90°, and reappears on cooling. The compound contains about 18 per cent, of iodine, and is known as " iodide of starch" ; its constitution is unknown. The reaction serves as a delicate test both for starch and iodine. Fig. 131. Fig. 132. Metamorphoses of Starch — Dextrin. — When long heated to 100° starch is converted into soluble starch, which yields a blue color with iodine (Maschke). Between 160 and 200° it is converted into a body which is very soluble in water, and the solution of which is not colored by iodine. This solution strongly turns the plane of polariza- tion to the right ; hence the name dextrin given to this body, which is regarded as isomeric with starch, (C^H^°0^)". A very concentrated solution of dextrin has the appearance of a solu- tion of gum. It is ased as a mucilage for labels and postage- stamps, and for the preparation of immovable surgical dress- ings. 652 ELEMENTS OF MODERN CHEMISTRY. Alcohol added to a solution of dextrin precipitates the latter substance in the form of flakes. Subacetate of lead does not precipitate dextrin, a character which permits the latter body to be distinguished from gum arabic. When starch is boiled with water containing a few per cent, of sulphuric acid, it is first converted into dextrin, then into glucose. It is generally considered that the dextrin is formed by a simple molecular transformation of the elements of thq starch, and that the glucose is then produced by the simple fixation of one molecule of water. starch. Glucose. According to Musculus, this is not the case ; but soluble starch is the result of a metameric transformation of starch, and subsequently is converted into dextrin and glucose by a true decomposition. 3C6H10O5 _[_ H^O = C^^H^oQ'" + C^H^^O^ starch. Dextrin. Glucose. By the prolonged action of the acid, the dextrin itself is converted into glucose. The transformation of starch into dextrin and saccharine matter (maltose) takes place easily under the influence of a peculiar ferment which is developed in grain during germina- tion, and to which the name diastase has been given. It may be obtained by precipitating aqueous extract of malt by alcohol. If starch be triturated with one and a half times its weight of concentrated sulphuric acid, avoiding an elevation of tem- perature, and the mixture be left to itself for half an hour and alcohol then added, a substance is precipitated which is soluble in water and assumes a rich blue tint by the action of iodine. It is soluble starch (Bechamp). Starch dissolves abundantly in monohydrated nitric acid, and water precipitates from this solution a white substance, which, after washing and drying, constitutes xyloldin. It is mononitrate of starch, and is formed by the following reaction : Q6H10O5 _^ HNO^ = H^O -h C^H^(NO^)0* starch. Xyloidin. Xyloidin burns with deflagration when heated to 180°, A dinitrate has also been obtained. INULIN — aLYCOGEN — GUMS. 653 INULIN. This body also is largely diffused tlirougliout the vegetable kingdom. It exists in the roots of the elecampane {Inula helenmm), chicory, and Spanish chamomile, in the bulbs of colchicum, the tubers of the dahlia, in the Jerusalem arti- choke, etc. It may be extracted from the tubers of the dahlia by reducing them to a pulp and washing the latter in a sieve under a stream of water. The milky Hquid which passes through deposits the inulin, which consists of granules analo- gous to those of starch. It swells in cold water, in which it is very slightly soluble. It is very soluble in boiling water, which again deposits it in a pulverulent form on cooling. The aqueous solution turns the plane of polarization to the left. It is not colored blue by iodine, which communicates to it a fugitive, yellow-brown tint. By long boiling with water, or by the action of dilute acids, inulin is converted into fructose, and this reaction affords a convenient mode of preparing fruit-sugar. GLYCOGEN. (C6Hi'>05)'i This body, isomeric with cellulose and starch, exists in the animal economy. Claude Bernard discovered it in the liver, and afterwards in the placenta. It exists also in many organs during the foetal life. Nearly pure glycogen may be obtained by adding a large quantity of crystallizable acetic acid to a cold and concentrated decoction of liver. It is also precipitated when alcohol is added to an aqueous decoction of liver. In a pure state, it is a white, amorphous powder. When dried in the air, it has the composition CW^O^ (E. Pelouze). At 100° it loses one molecule of water. With water it forms an opalescent liquid. Alcohol and ether do not dissolve it. Boiling with dilute acids converts it into glucose. Iodine communicates to it a violet or brown-red color. GUMS. By the names gums and mucilages are understood certain substances existing everywhere in the vegetable kingdom, and which dissolve or swell up in water, giving a mucilaginous 65* 654 ELEMENTS OF MODERN CHEMISTRY. consistence to the liquid. The gums proper are distinguished from the mucilaginous substances, which are not really soluble. Both furnish mucic and oxalic acids when treated with nitric acid. Hydrolysis decomposes them into hexoses and pentoses (galactose, arabinose, xylose). Gum Arabic. — Grum arabic is identical with Senegal gum. It flows naturally from different species of acacia. It dissolves abundantly in cold water and is precipitated from its solution by alcohol. Fremy considers that it is composed essentially of the calcium and potassium salts of an acid which he designates as gummic acid (arahin). When dried at 100°, the latter body has the composition indicated by the formula C^^H^^O^^ It is very soluble in water, and its solution rotates the plane of polarization to the left. When heated to 120-150°, it becomes insoluble in water and is converted into metagummic acid. According to Fremy, the gum of cherry- and plum-trees is a mixture of gummates, which are soluble in cold water, and insoluble metagummates. The metagummates are insoluble in water, but when boiled with that liquid are transformed into soluble gummates. Subacetate of lead forms an abundant white precipitate in solutions of gum arabic. When gum arabic is boiled with dilute sulphuric acid, it is converted into saccharine substances; some varieties of this gum yield considerable quantities of galactose when treated in this manner, while others are largely converted into arabinose. On oxidation with nitric acid, the former give mucic 'acid, and the latter oxalic acid. Gum Tragacanth. — This gum flows from the Astragalus of the Levant and of Persia. Bassora gum is derived from a spe- cies of cactus. Both contain a mucilaginous matter insoluble in water, but which swells up in that liquid, forming a transparent jelly. This matter is hassorin. With nitric acid, it yields much mucic acid. When boiled with dilute sulphuric acid, it is readily converted into crystallizable glucose. CELLULOSES. The frame-work of plant tissues consists of a more or less delicate membrane which is a secretion of protoplasmic ac- CELLULOSES. 655 tivity, and is known as the cell-wall. In the earlier stages of its growth and development this consists of cellulose^ (C^H^^O^)", with a varying amount of water. Gradually, however, it is transformed into bodies of more complex con- stitution, — the compound celluloses^ — and, at the same time, mineral matters are deposited in it. The term cellulose does not denote a chemical individual, but a group of closely related isomers of similar properties. Cotton, hemp, flax, and the pith of certain trees consist essentially of cellulose. Wood, cork, and mucilage are chiefly made up of the compound celluloses produced by the meta- morphosis of cellulose. All these bodies are permeated by foreign substances, such as nitrogenous, coloring, and mineral matters ; the latter are found more or less modified in the ashes. Old linen and cotton serve for the preparation of pure cellulose. Such materials are boiled with a weak solution of potassium hydrate, washed, and successively exhausted with a solution of chlorine, acetic acid, alcohol, ether, dilute hydro- chloric acid, dilute hydrofluoric acid, and, finally, water, and dried at 100°. The undissolved residue is pure cellulose. Properties. — Cellulose is a diaphanous, white solid, of a density of 1.5. It is insoluble in all simple solvents, but in presence of certain metallic compounds it forms gelatinous hydrates which are soluble in water. It dissolves completely upon warming with concentrated aqueous solution of zinc chloride, more rapidly and in the cold when a solution of the salt in strong hydrochloric acid is employed (Cross and Bevan). Another valuable solvent for cellulose is cupram- monium hydroxide dissolved in strong ammonia water (Schweitzer's reagent) ; this rapidly converts cellulose into a hydrate, which is gradually dissolved in the blue liquid. Salts of the alkali metals, acids, alcohol, etc., reprecipitate the hydrate. When submitted to dry distillation, cellulose leaves a resi- due of carbon and yields numerous gaseous and liquid prod- ucts. The gas obtained by the distillation of wood is used for illuminating purposes in some localities. The liquid product ordinarily separates into two layers, one of which is aqueous and contains acetic acid, wood-spirit, acetone, etc. ; the other is insoluble in water and constitutes wood-tar. Cellulose is readily attacked by cencentra*ted sulphuric 656 ELEMENTS OP MODERN CHEMISTRY. acid : the resulting viscous solution probably contains a com- pound of sulphuric acid and cellulose, and also various other products resulting from a rapid disintegration of this sul- phate. When the solution is diluted with water and boiled, glucose is formed and sulphuric acid regenerated. Certain celluloses yield mannose instead of glucose. C6JJ10O6 _^ H^O = C^H^^O^ Cellulose. Glucose. When paper is dipped into a cold mixture of sulphuric acid with half its volume of water, and is then carefully washed and dried, a semi-transparent matter is obtained which has a certain rigidity, and is similar to parchment in aspect and toughness. This parchment paper is extensively used as a substitute for animal parchment. Colloidal cellulose is formed by the action of sulphuric acid of density 1.53 on cellulose, and forms with water a milky liquid which can be filtered. The action of sulphuric acid or zinc chloride on cellulose produces a body analogous to starch and called amyloid. Cellulose moistened with iodine tincture and then treated with strong sulphuric acid becomes blue. By treatment with acetic anhydride, cellulose has been converted into the triacetate CH^O'CC'H^O')^ and the tetracetate C*'H^O(C'^H^O^)*, and there are indications that higher acetates may exist. Gim-Cotton. — When carded cotton is immersed for half a minute in monohydrated nitric acid, and then rapidly washed in a large quantity of water and allowed to dry in the air, a substance is obtained which possesses all the exterior appear- ances of cotton, but is very inflammable and burns suddenly without residue. It is gun-cotton, or pyroxylin^ which was discovered by Schonbein in 1847. In its preparation, the monohydrated nitric acid may be advantageously replaced by a mixture of one volume of nitric acid (sp. gr. 1.5) and three volumes of sulphuric acid. The duration of the action determines the composition of the prod- uct. When the acid is allowed to act upon the cotton for a short time only, the latter is converted into a mixture of the compounds, C^'H^«(NO=*)^0« and C^■'H^XNO0^O^ but upon con- tinued treatment with the acids a gun-cotton of the composi- tion C^'^H^XNO^'O* results. These bodies, like nitroglycerin, are true nitric ethers. Alka- lies decompose them into an alkaline nitrate and cellulose. ELEMENTS OF MODERN CHEMISTRY. 657 Grun-cotton looks like cotton, but is more harsh to the touch. It burns with a flash, leaving no residue, and produces a great volume of gaseous products consisting of carbon monoxide, carbon dioxide, nitric oxide, etc., and vapor of water. The hexanitrate is insoluble in water, alcohol, ether, and the cupro- ammoniacal solution. The lower nitrates, however, are soluble in a mixture of ether and alcohol, and collodion is essentially such a solution : it is used in surgery and photography. Celluloid, a substitute for ivory, bone, and horn, is made by dissolving nitrocellulose in melted camphor, to which resinous substances and coloring matters are sometimes added. Nitro-powders, largely used on account of their smokeless explosion, are prepared by gelatinizing finely divided gun- cotton by means of a solvent such as ethyl acetate or acetone. The solvent is removed by pressure and evaporation, and the gelatinous residue is cut into slices or pressed into suitable form. Other substances are usually added to modify the force of the explosion. GLUCOSIDES. The glucosides are complex compounds, which break up under various conditions, fixing the elements of water and yielding a sugar, generally glucose, and other bodies, just as the compound ethers, in fixing the elements of water, are de- composed into alcohols and acids. Various immediate principles of vegetable origin can be classed as glucosides. We may mention particularly the foh lowing : 6LTJC0SIBES. FORMULAS. ORIGIN. Amygdalin .... C''20H27N011 bitter almonds. Salicin C^3jji807 willow and poplar bark. Populin C20H22O8 bark and leaves of the aspen. Phloridzin .... C2iH240io bark and roots of fruit-trees. Arbutin C^^hi^OT leaves of the Arctostaj^hylos uva utsi. Esculin C21H24013 bark of India chestnut. Quercitrin .... C^^H^soso bark of Quercus tin ctoria (quercitron). Tannin , C'*H28022 oak-bark, nut-gall, etc. Coniferin CI6H22O8 cambium of the Coniferse. Digitalin C'^H^soiz leaves of Bigitah's purpurea. Amygdalin, C'^H^^NO".— This body is extracted from the cake of bitter almonds, and it deposits from its alcoholic solu- tion in crystals containing two molecules of water. Its aqueous solution allows it to crystallize in quite large crystals contain- ing three molecules of water rr 658 ELEMENTS OF MODERN CHEMISTRY. Amygdalin is very soluble in water and in boiling alcohel. Its aqueous solution rotates the plane of polarization to tbe left. By the action of dilute acids amygdalin is decomposed into hydrocyanic acid, benzaldehyde (oil of bitter almonds), and glucose. C20H2^NO" -I- 2H20 =: CWO + CHN + 2C«Hi20^ Amygdalin. Benzaldehyde. Hydrocyanic Glucose. acid. The same decomposition takes place by the action of water and a peculiar ferment which is contained in both bitter and sweet almonds, and which is called emulsin, or synaptase. It is a nitrogenized matter, soluble in water, and only acts on amygdalin in presence of water. It is well known, indeed, that bitter almonds only develop the odor of prussic acid when moistened with water. Salicin, C^^H^^O^ — Salicin exists already formed in the bark of the willow and poplar. Wohler discovered its existence in castoreum. It may be prepared by exhausting willow-bark with boiling water, concentrating the liquid and digesting it with litharge. The solution is then filtered and evaporated to a syrupy consistence ; the salicin deposits in a few days. It occurs in small scales, or brilliant needles, soluble in water and alcohol and insoluble in ether. Its taste is bitter. By the action of a solution of emulsin (the nitrogenous mat- ter of almonds), it breaks up into a neutral body called salige- ninol, and glucose. Q13JJ1807 _|_ H^O = Q'WO' + C^H^^O^ Salicin. Saligeninol. Glucose. Dilute sulphuric and hydrochloric acids decompose it by the aid of heat into saliretin and glucose. By the action of a mixture of potassium dichromate and sulphuric acid, salicin yields carbon dioxide, formic acid, and an oxidized oil, which is salicylaldehyde, C^H^O'^ (Piria), Salicin has been obtained synthetically (Michael). Populin, C'°H^20'-f 2H'''0.— Braconnot discovered this sub- stance in the bark and leaves of the aspen (Popuhts tremula). When properly purified, it occurs in very fine, silky, colorless needles. Its taste is sweet ; it is but slightly soluble in water, more soluble in alcohol. By the action of dilute acids it is decornposed into benzoic acid, saliretin, and glucose ; the latter GLUCOSIDES. 659 two products result from tlie decomposition of salicin, so that populin is a combination of benzoic acid and salicin, from whicb substances it has also been obtained artificially. Q20U22Q8 _J_ JJ^O = C^H«0' + C^^H^^O' Populin. Benzoic acid. Salicin. Phloridzin, C'^^H^^O^" + 2H20.— This substance exists in the bark of apple, pear, plum, and cherry trees, and principally in the roots of fruit-trees. When pure, it forms colorless, silky needles, having a bitter taste, and an after-taste which is sweet. It is scarcely soluble in cold water, but dissolves abundantly in boiling water and in alcohol. The alcoholic solution turns the plane of polariza- tion to the left. Dilute acids decompose it into phloretin and glucose. Q21JJ24O10 _^ H^O = C'^H"0^ -f C^H^^O^ Phloridzin. Phloretin. Glucose. PJdoretin is a white substance which crystallizes in little scales, slightly soluble in water and very soluble in alcohol. When phloretin is heated with potassium hydroxide, it breaks up into phloretic acid and 'phloroglucinol (page 696). Q15HU05 + H^O = (TWO' + Q'WO' Phloretin. Phloretic acid. Phloroglucinol. Coniferin, C^^H^^O^, is a glucoside which occurs in the cambium of the Coniferse. It is a crystalline body which melts at 185°, and effloresces in the air. On treatment with boiling dilute acids or with emulsin, it yields glucose and coniferyl alcoliol^ C^°H^^O"', a substance from which vanillin^ the essen- tial principle of the vanilla bean, can be obtained by oxidation. Digitalin, C^^H^^O^l — This is an amorphous body which may be extracted from the leaves of Digitalis purpurea and lutea. When treated with concentrated hydrochloric acid, it yields glucose and various complex bodies. Owing to the peculiar efi"ect it produces on the contractions of the heart, it is of great medicinal value. Tannin, or Tannic Acid, C^*B[^°0^ — The names tannins and tannic acids are applied to certain slightly acid com- pounds which are largely diffused in the vegetable kingdom, and which have two important properties : they precipitate solutions of gelatin and albuminous matters, and produce a 660 ELEMENTS OF MODERN CHEMISTRY. bluisli or greenisli-black color with the ferric salts. The most important of these compounds is the tannin of oak bark, or quercitannic acid. It was formerly considered a glucoside : according to Strecker, it has the composition C'^H'^^0^^, and yields glucose upon treatment with dilute acids. (.34JJ28022 _^ 4H2Q _ 4C^H«0^ + C«H^^O« Taunin, Gallic acid. Glucose. More recent researches of Schiff render it probable, how- ever, that pure tannin is digallic acid, C^*H^°0^, the anhydride of gallic acid (see page 713). Tannin exists in oak bark, in sumac, and in large quan- tities in nut-galls, which are excrescences developed by the sting of an insect on the leaves and branches of the Quercus infectoria. It is prepared by introducing coarsely-powdered nut-galls into a percolator, and exhausting them with ordinary commercial ether. The ethereal solution which passes through is collected in a flask, and in the course of a day separates into two or sometimes three layers. The lower layer is a very concen- trated, aqueous solution of tannin. It is separated and dried in a hot-air oven. The tannin remains as a light, bulky mass, having a yellowish color. Tannin is a colorless, amorphous solid, having a very astrin- gent taste. It is very soluble in water, less soluble in alcohol, insoluble in pure ether. On contact with the air, the aqueous solution of tannic acid absorbs oxygen, disengages carbon dioxide, and deposits gallic acid. This transformation takes place more rapidly when oak tannin is boiled with dilute sulphuric or hydrochloric acid. A solution of tannic acid produces with ferric salts a bluish- black precipitate, which constitutes ink. Tannin does not color ferrous salts, but the mixture soon blackens on exposure to the air by absorbing oxygen. Tannin is employed in medicine as an astringent. Nut-galls, which are very rich in tannin, are used for the manufacture of ink. A good ink may be prepared by the following receipt: One kilogramme of powdered nut-galls is exhausted with 14 litres of water ; the solution is filtered, and a solution of 500 grammes of gum arable is first added, then a solution of 500 grammes of ferrous sulphate (green vitriol). The mixture is well stirred up, and then exposed to the air until it has acquired a fine black color. ACIDS DERIVED FROM THE SACCHARINE BODIES. 661 ACIDS DERIVED FROM THE SACCHARINE BODIES. By moderate oxidation (careful treatment witli bromine water) the sugars containing the aldehyde group are con- verted into the corresponding monobasic acids. The most important of these are mannonic acid, gluconic acid, and galactonic acid. They are derived from hexoses and have the composition C^H^^O^ When subjected to a more energetic oxidizing action (nitric acid or excess of bromine water), the saccharoses and their corresponding monocarboxylic acids yield dibasic acids. Of these we may mention the four isomers represented by the formula C^H^°0^, — namely, mannosaccharic acid, saccharic acid, mucic acid, and isosaccharic acid. The relations which exist between these acids and the sugars from which they are derived afford valuable indica- tions regarding the constitution of the hydrates of carbon. Mannonic Acid results from the oxidation of mannose. It forms a syrupy liquid which readily passes into a crystal- line anhydride (lactone) by the loss of a molecule of water. Gluconic Acid is obtained from glucose by oxidation with bromine water. It is stereoisomeric with the preceding. Upon evaporation of its solution it remains as a syrup, which gradually deposits crystals of its lactone. Galactonic Acid corresponds to galactose, and may be prepared from milk-sugar. It has been obtained crystallized ; its lactone is also known. Mannosaccharic Acid is the dibasic acid resulting from the oxidation of mannose or mannonic acid. When its aqe- ous solution is evaporated, it loses two molecules of water and is converted into the corresponding lactone. Saccharic Acid is produced together with oxalic acid when cane-sugar is oxidized by nitric acid. It is also formed by the oxidation of sorbitose, glucose, and gluconic acid. Free saccharic acid is a thick liquid, which solidifies upon standing owing to the formation of its lactone, C^H^O^ The acid potassium salt is sparingly soluble in cold water. Mucic Acid was discovered by Scheele in 1780. It is 66 662 ELEMENTS OF MODERN CHEMISTRY. prepared by the oxidation of milk-sugar with nitric acid. It may also be obtained from dulcitol, galactose, and galac- tonic acid. It forms a white crystalline powder which melts at 213°, and is but sparingly soluble in cold water. By boil- ing with water it is converted into a lactonic acid. By dry dis- tillation it is converted into pyromucic acid, C^H*0^ (p. 746). PECTIC MATTERS. These bodies, of which the constitution is still obscure, are largely diffused in the vegetable world, notably in fleshy fruits and in many roots. They remain in a gelatinous condition on evaporation of their aqueous solutions, from which they can be precipitated by alcohol. They are probably related to the hydrates of carbon. AROMATIC COMPOUNDS. The compounds of carbon which we have thus far con- sidered may be regarded as derived from methane, CH*, and the great majority of them may be obtained from this hydro- carbon by substitution or by synthesis. They constitute what is known as the aliphatic ox fatty series, and are sharply dis- tinguished from another important and not less numerous class of organic compounds designated as the aromatic series. These latter are derived from benzene, C^H^, a hydrocarbon occurring in coal-tar, and they bear to this a relation similar to that which exists between methane and its derivatives. The term aromaiic is used because the first studied sub- stances of this series were obtained from aromatic resins and oils. It is now recognized that an aromatic smell or taste is not essential to these compounds, but the old name is still retained : we even speak of their " aromatic character" with reference to their chemical behavior. As a rule the aromatic compounds contain a larger propor- tion of carbon than the members of the fatty series ; never- theless, they generally behave like saturated compounds. They further differ from the aliphatic compounds in the facility with which they are modified by substitution, and the products of substitution exhibit many peculiarities which distinguish them from the marsh-gas derivatives. AROMATIC COMPOUNDS. 663 Since tlie aromatic compounds are all derived from ben- zene, a clear conception of the constitution of this funda- mental body is of the utmost importance. It is thirty-five years since (1865) this problem began to engage the atten- tion of chemists, but in spite of the vast amount of work that has been done in this direction, it cannot be said that an entirely satisfactory and conclusive solution has been reached. We are chiefly indebted to Kekule and Baeyer for the theories which are now generally accepted as accounting for the peculiar character of the aromatic compounds. How- ever, before we can proceed to discuss these theories, it is necessary that we acquaint ourselves with the principal facts on which they are based. 1. The hydrogen of benzene may be readily replaced by chlo- rine, bromine, etc., by which monochlorobenzene, monobromo- benzene, dichlorobenzene, etc., are obtained. C6H6 C^H^Cl C^H^Br Benzene. Monochlorobenzene. Monobromobenzene. Dichlorobenzene. Dibromobenzene. These chlorides and bromides are analogous to the corre- sponding compounds of the fatty series, but the chlorine or bromine is much more strongly combined with the benzene nucleus, and cannot be exchanged by double decomposition, as is the case with ethyl bromide and ethylene bromide, etc. 2. By treatment with strong nitric acid, the hydrogen of benzene may be replaced by one or more groups (NO^), form- ing the following compounds : C6H6 C6H5-N02 C6H4<^Q2 Benzene. Nitrobenzene. Dinitrobenzene.- 3. The substitution of the group (NH^) for one atom of hydrogen produces phenylamine, or aniline ; that of two groups NH^ for two atoms of hydrogen yields phenylene-diamine. C6H6 C6H5-NH2 ^^^*;o-derivatives, and contain likewise the group N=N : one affinity, however, is satisfied by a mona- tomic aromatic group, while the other combines it with some other monatomic radical or element. Such is diazobenzene chloride. C6H5-N ci-isr Only a few diazo-compounds have been obtained in the fatty series, and these are distinguished from the aromatic diazo-compounds by their inability to form salts with the mineral acids. Azo-compounds appear to exist only in the aromatic series. 5. Concentrated sulphuric acid eiFects the displacement of hydrogen in benzene by the group SO'H, sulphonic acids being formed. C6H6 C6H5S03H C6H*(S03H)2 Benzene sulphonic acid. Benzene disulphonic acid. Sulphonic acids exist also in the fatty series, but direct sulphonation is a reaction characteristic of the aromatic compounds. 6. The replacement of one or more atoms of hydrogen by the same number of hydroxyl groups converts benzene into compounds known as pheiioh. They correspond to the alco- hols of the saturated hydrocarbons, but, while the alcohols are perfectly neutral, the phenols have acid characters, although they are neutral to litmus. /OH C^HVOH \0H Phenol. Oxyphenol Dioxyphenol (resorcinol and isomerides). (phloroglucinol and isomerides.) 7. If one or more atoms of hydrogen in benzene be replaced by as many methyl groups, CH^, the higher homologues qf benzene are obtained, C6H5.0H CeH^gH AROMATIC COMPOUNDS. 665 C«H6 = C6H6 benzene. C'H8 = C6H5-CH3 toluene (methylbenzene). pTT3 Q8JJ10 ^ C^H*<\pTT3 xylene and isomerides (dimethylbenzenes). C9JJ12 _ C^H^x— CH^ mesitylene and isomerides (trimetbylbenzenes). Ci2Hi8= C(CH3)6 hexamethylbenzene. One ethyl group can replace one atom of hydrogen in benzene, and ethylbenzene, isomeric with dimethylbenzene, results. C6H5-C2H5 C«H4<^g3 Ethylbenzene. Dimethylbenzene. There are many instances of such isomerism, and they re- ceive the same interpretation. One atom of hydrogen in benzene may be replaced by a propyl group, C^H', and propyl benzene, which i^ isomeric with trimethylbenzene, is the result. One atom of hydrogen may be replaced by an ethyl group and another by a methyl group, and the new compound would be ethyl-methylbenzene, isomeric with propylbenzene and with trimethylbenzene. QJJ3 C6H5-C3H7 C6H*H Benzene.* Innumerable experiments have shown that the chemical value of each of the six hydrogen atoms of benzene is absolutely the same. If by the action of reagents one of these hydrogen atoms be replaced by another atom or group of atoms, it is a matter of indifference which of the hydrogen atoms is so replaced, the product is always identical. This fact indicates that the * In this formula, the connecting lines indicate the saturation of the atomicities; the double lines indicate the exchange of two atomicities between two neighboring atoms of carbon. 668 ELEMENTS OP MODERN CHEMISTRY. arrangement of the hydrogen atoms is perfectly symmetrical in relation to the carbon atoms around which they are grouped. In other words, the molecular constitution of ben- zene must be (CH)^ In consequence, each atom of carbon must be united to one atom of hydrogen, — a requirement met by Kekule's theory, — and each carbon atom must be sym- metrically related to the other carbon atoms with which it is combined. The latter condition is not perfectly satisfied by Kekule's theory, for a carbon atom would exchange a double aflfinity with its neighboring atom on one side, while with that on the other side it would exchange but a single atomicity. It would follow that the combination should be stronger on one side than on the other, and the molecule would not be sym- metrical. This difficulty disappears in the following formula proposed by Armstrong and by Baeyer, known as the centric formula : H-C H-C The 6 carbon atoms are arranged at the angles of a hexa- gon, as in the formula of Kekule, but instead of assuming a double linking of alternate pairs of carbon atoms, we con- ceive the fourth affinity of each carbon atom to be directed towards the centre, but without actually connecting any two carbon atoms with each other. While thus augmenting the stability of the molecule, the fourth affinity of each car- bon atom is rendered latent. Although this arrangement is the most satisfactory that has been proposed, it must be admitted that such a method of disposing of the valences is without analogy in the compounds we have thus far con- sidered. Isomerism of Position. — In the benzene molecule the posi- tion of each atom of hydrogen is of the same value. It will be convenient to represent the formula by a simple AROMATIC COMPOUNDS. 669 hexagon and to number tliese positions as in the following diagram : 1 According to Kekulg and Baeyer. Experiment has shown that if but a single atom of hydrogen in benzene be replaced by another monatomic atom or group, the resulting compound does not vary, and is incapable of isomerism. This is not, however, the case if two hydrogen atoms be re- placed, for theory then predicts, and experiment confirms, the existence of three isomeric compounds in each case. This isomerism results from the different positions of one of the substituted atoms or groups with relation to the other in their attachment to the benzene nucleus. Let X and Y be the two substituted monatomic atoms or groups, such as chlorine, hy- droxy 1, nitryl, etc., then the isomerism would be expressed as follows : CH CH cx CY CH 'CH The position at 1 being always supposed to be occupied by one of the substituted groups, the compounds are named ortho if the other replacement be at 2 or 6, meta if it be at 3 or 5, and para if it be at 4. The relations of 2 and 6 to 1 are the same, as are also those of 3 and 5 to 1. ortho ortho meta para 670 ELEMENTS OF MODERN CHEMISTRY. In tlie preceding compounds formed by X and Y, these positions would be marked as follows : Ortho-derivative. C6H4< X(i) ~Y(3) Meta-derivative. C6H4< X(i -Y(4) Para-derivative. The following examples will further explain this isomerism of position, of which we must study numerous cases. ORTHO-SERIES. META-SERIES. PARA-SERIES. X(, X(i) c X(, , ^ >, ,„ / N y V, HC CY(2) HC CH HC CH HC CH HC CY(3) HC CH •\ / \ / \ / C C C H H Y(4) ^ ^ Orthodiphenol, Metadiphenol. Paradipbenol. (pyrocatechin.) (resorcinol.) (hydroquinone.) ^ ^ 3^ liquid, boiling at 172°. Para-dichlorobenzene, C^H^^pjW, fusible at 56°, and boil- ing at 173°. Among the other chloro-derivatives we will mention only hexachlorobenzene, C^CP, which is formed not only by the complete chlorination of benzene, but also when vapor of chloroform or of carbon tetrachloride, CCP, is passed through a red-hot tube. It is a crystallizable solid, fusible at 222°, and boiling at 332°. Monohromohenzene, C^H^Br, may be made by mixing ben- zene and bromine in the proportion of one molecule of the first to two atoms of the second, adding some thin iron wire, and heating for several hours over a small flame. The prod- uct is washed with caustic potash and distilled. A more convenient method is to warm diazobenzene bromide with cuprous bromide. Monobromobenzene boils at 157°. When heated with sodium, it yields to the latter its bromine, and a hydrocarbon C^^H^** =1 , called diphenyl, is obtained. Dibromo-henzenes, C^H'^Br^ — There are three isomerides-. The para-derivative, C*H*<^ \J, is readily formed by the 2d ss 67 674 ELEMENTS OP MODERN CHEMISTRY. action of an excess of bromine on benzene. It crystallizes in beautiful prisms, fusible at 89°. It boils at 218°. Iodine and fluorine derivatives of benzene are also known. NITRO-DERIVATIVES OF BENZENE. Nitrobenzene, C^H^(NO^). — If benzene be poured in small portions into a mixture of strong nitric and sulphuric acids, and water be added to the mixture, an oily, yellow liquid separates, constituting nitrobenzene. C«H« + HNO' = WO + C«H5(NO0 It is benzene in which one hydrogen atom is replaced by the group (NOO'- Nitrobenzene is a yellowish liquid, having a strong odor of bitter almonds. It boils at 205°, and solidifies at 3°. It is employed in perfumery under the name essence of Mirhane. By the action of reducing agents, such as hydrogen sulphide, ammonium sulphide, tin and hydrochloric acid, or iron-filings and acetic acid, nitrobenzene is converted into aniline or phe- nylamine. C«HS(NO^) + 3H2 = 2W0 + C«H5(NH0 Nitrobenzene. Aniline. Dmitrobenzenes, C^H*(NO^)l—The three isomerides are formed when benzene is treated with a large excess of a mixture of nitric and sulphuric acids. The nitro-compounds separate on the addition of water, and are purified by crystallization in alcohol. Metadinitrobenzene separates first, crystalHzing in long colorless needles, fusible at 89.9°. Reducing agents convert it successively into nitrophenylamine and phenylene-diamine. CeH0 Azoxybenzene. Azoxybenzene crystallizes in long needles, soluble in alcohol and ether, insoluble in water. It melts at 36°, and is decom- posed when distilled. If heated with iron filings, it becomes converted into azobenzene. Hydr azobenzene, C^^H^^N^. — Alkaline reducing agents, such as zinc dust and sodium hydroxide, and ammonium sul- phide, in presence of alcohol, convert azobenzene into hy- drazobenzene. C6H5-I^ C6H5-NH II + H2 = I C6H5-N C6H6-NH Azobenzene. Hydrazobenzene. The latter body crystallizes in tables, fusible at 131°, almost insoluble in water but soluble in alcohol and ether.. When submitted to dry distillation, it breaks up into azobenzene and aniline. I! = II + 2C«H5.NH2 Hydrazobenzene. Azobenzene. Aniline. Acids convert hydrazobenzene into a basic isomeride, ben- zidine, from which a number of valuable dye-stuffs (azo-dyes) are derived. Hydrazobenzene. Benzidine. 676 ELEMENTS OP MODERN CHEMISTRY. Hydrazobenzene may be considered as derived from dia- mide, I , by replacement of two hydrogen atoms by phenyl groups. The aromatic hydrazines proper are the unsymmet- rical derivatives resulting from the substitution of one or two aromatic radicals for hydrogen in one Nff group. Phenylliydrazine. Di-phenylhydrazine. Phenylhydrazine is obtained by reducing diazobenzene chloride with sodium sulphite or stannous chloride. C«mN=NCl + 2W = C^H^-NH.NH^HCl It is a colorless oil, solidifying upon cooling in tabular crystals which melt at 17.5°. It boils at 241° with partial decomposition. The density at 23° is 1.097. Phenylhydra- zine is sparingly soluble in water, but readily in alcohol and ether. It acts as a powerful base, forming salts with the acids. Its property to react with aldehydes and ketones to form hydrazones has made it a most important reagent for the detection and isolation of those bodies, especially the sugars. Antipyrine and a number of dye-stuffs are derived from it. BENZENESULPHONIC ACID. C6H5-S02.0H Aromatic compounds are readily acted upon by concen- trated or fuming sulphuric acid, the sulphonic group (SO'^.OHy replacing one or several atoms of hydrogen. Thus, henzenesulphonic acid is formed in the following re- action : C6H6 + S02<^^ = H20 + C6H5.S02.0H It is prepared by heating for a long time a mixture of equal parts of benzene and concentrated sulphuric acid. The liquid is then diluted with a large quantity of water, and neutralized with barium carbonate. The concentrated solu- tion then yields a barium salt, Ba(C'H^SO0' + H^O, which crystallizes in pearly plates. From this salt the acid can be liberated by the careful addition of sulphuric acid. It crys- PHENOL, OR CARBOLIC ACID. 677 tallizes in small plates, soluble in water and alcoliol. When fused with an excess of potassium hydroxide, it yields phenol. Benzene Sulphone, or Sulphobenzide, (C«H5)^S0l— The hydroxyl group in benzenesulphonic acid may be replaced by a phenyl group, and the compound so formed is called sulpho- benzide. It may be obtained by heatiEg phenylsulphuric acid with phosphoric anhydride to 150° in sealed tubes, treating the product of the reaction with a dilute alkaline hydrate, and crys- tallizing the residue in alcohol. It crystallizes from water in silky needles, and from benzene in large rhombic prisms. It melts at 128°. CYANOBENZENE. (phenyl cyanide, benzonitrile.) C6H5.cn This body is formed in various reactions, particularly in the destructive distillation of hippuric acid, and by the dehydration of benzamide by phosphoric anhydride. C^H^-CO.NH^ — H^O = C^H^-CN Benzamide. Benzonitrile. It is a colorless oil, which boils at 191°. When heated with the alkalies, it yields benzoic acid and ammonia. C^H^-CN -I- 2H20 = C^H^-CO^H + NH^ Benzonitrile. Benzoic acid. PHENOL, OR CARBOLIC ACID. C6H5.0H This body bears the same relation to benzene that wood- spirit does jbo marsh gas : it is hydroxy-benzene. CH* CH3.0H Methane. Methyl hydroxide. C6H6 C6H5.0H Benzene. Phenol. It was discovered in coal-tar by Runge, who named it car- bolic acid. Laurent demonstrated that it plays the part of an alcohol. Indeed, it presents points of resemblance with the monohydric alcohols, but it differs from them by its acid char- acter, on account of which it is sometimes called plienic acid. Preparation. — Large quantities of phenol are obtained from coal-tar, from which it is separated by distillation. That part 57* 678 ELEMENTS OF MODERN CHEMISTRY. which passes between 150° and 200° is collected apart and mixed with a saturated solution of potassium or sodium hy- droxide to which solid caustic alkali is added. A crystalline phenate of potassium or sodium is formed ; it is dissolved in boiling water, the insoluble oil which floats is separated, and the alkaline solution is neutralized with hydrochloric acid. The phenol separates ; it is washed with a small quantity of water, dehydrated with calcium chloride, and rectified. The distilled product is cooled to — 10°, and the crystals which are deposited are allowed to drain out of contact with the air. Phenol may be made artificially from benzene by a process which is applicable to the preparation of all the phenols. It consists in treating benzene with fuming or even ordinary sulphuric acid. Benzenesulphonic acid is formed ; this is diluted with water to separate the excess of hydrocarbon, and the solution is neutralized with chalk ; calcium phenyl- sulphonate, which is soluble, and sulphate, which is insoluble, are formed. The calcium benzenesulphonate is converted into sodium salt by double decomposition with sodium carbonate, and after evaporation and desiccation the product is fused in a silver crucible with an excess of potassium hydroxide. The mass is exhausted with water, and the alkaline solution is decomposed by hydrochloric acid. The phenol separates and is dried and purified by distillation (Dusart, Wurtz, Kekule). The decomposition of sodium or potassium benzenesul- phonate is expressed in the following equation : C^H^SO^K + KOH = C«H^OH -\- K'^SO^ Potassium benzenesulphonate. Phenol. Potassium sulphite. There is another very simple synthesis of phenol. In pres- ence of aluminium chloride, benzene absorbs oxygen directly and phenol is formed. C«H« + = C^H^O This reaction is one of the most unexpected and most in- teresting applications of a general method of synthesis discov- ered by Friedel and Crafts (see page 698). Phenol is also formed by the dry distillation of the oxy- benzoic acids (page 709). Oxybenzoic acid. Phenol. PHENOL, OR CARBOLIC ACID. 679 Properties of Phenol. — Phenol is a solid, crystallizing in long, colorless needles, having at 0° a density of 1.084, It fuses at 42°, and boils at 183°. Its odor is peculiar and characteristic, its taste acrid and burning. It is poisonous and antiseptic. It is very soluble in alcohol, ether, and acetic acid, and dissolves in 15 parts of water at 20°. Its solution is colored dark violet by ferric salts, and bromine water forms, even in very dilute solutions, a yellow precipitate of tribromophenol. A. pine shaving moistened with hydrochloric acid assumes a blue color when dipped in phenol and exposed to the air. Although phenol is neutral to litmus-paper, it forms definite combinations with the alkalies. When it is mixed with a very concentrated solution of potassium hydrate, a crystalline mass is obtained which constitutes potassium phenate, C^H^.OK. The same compound is formed, with disengagement of hydrogen, by the action of potassium on phenol. The solubility of phenol in the alkaline hydrates is applied in the separation of this body from the neutral oils which accom- pany it. The property is common to the phenols, and indicates the slightly acid character of the class. Phosphorus perchloride converts phenol into phenyl chloride, identical with monochlorobenzene. C^H^OH + PCP = C^H^Cl + POCP -f- HCl Phenol. Phenyl chloride. The hydrogen of the radical C^H^ in phenol can be readily replaced by chlorine, bromine, or groups such as NO^ NO, NH*, etc. The compounds so formed may sometimes be obtained directly, as the nitro-phenols, — sometimes by indirect processes. In the presence of sodium, phenol directly combines with carbon dioxide, forming salicylic acid (page 709). C^H^OH -I- CO^ + Na^ = C«H^<^^-^^^^ + H=^0 Sodium-salicylate of sodium. The following remarkable reaction of phenol was first noticed by Reimer and Tiemann. When it is heated with chloroform and an excess of sodium hydrate, in the proportion of one molecule each of phenol and chloroform and four molecules of alkali, it is converted into salicylaldehyde. C'H^ONa+SNaOH+CHCP = C^H50^Na+3NaCl+2H20 Sodium phenate. Sodium salicylite. The compound CH^O^Na is the sodium compound of sali- cylaldehyde, into which it is converted by hydrochloric acid. 680 ELEMENTS OF MODERN CHEMISTRY. ETHERS OF PHENOL. Phenyl Oxide, (C«H^)^0.— This body is formed, together with other products, by the dry distillation of copper benzoate. It crystallizes in long needles, fusible at 28°. It boils at 246°. It is very soluble in alcohol and in water. It cannot be reduced by either zinc or hydriodic acid. Methylphenyl Oxide, or Anisol, nTTs >0. — Anisol was first obtained by distilling anisic acid (page 712) with barium oxide or lime. Anisic acid. Anisol. It may be prepared more readily by synthesis in the reaction of methyl iodide on potassium phenate. C^HIOK + CH^I = KI + C^H^OCH* It is a colorless liquid, having an ethereal odor. Its density at 15° is 0.991 ; it is insoluble in water, and boils at 152°. Ethylphenyl Oxide, or Phenetol, r)2TT5>0, may be ob tained by a process analogous to the last method indicated for preparing anisol. It is an aromatic liquid, boiling at 172°. Phenylsulphuric Acid is analogous to ethylsulphuric acid. Ethylsulphuric acid. Phenylsulphuric acid. The acid is not known in the free state. Its potassium salt is formed when potassium phenate is heated with an aqueous solution of potassium pyrosulphate, K^S^O^ It exists in the urine of herbivorous animals. If phenol be ingested, it appears in the urine as potassium phenylsulphate (Baumann). SUBSTITUTED DERIVATIVES OF PHENOL. Among the numerous compounds derived from phenol by the substitution of various elements or groups for the hydrogen of the group C^H^, we can only describe a few of the nitro- and sulphonic compounds. Mononitrophenols, C^H*2y is so named because it was first obtained by the destructive distillation of catecbu. It is also produced by tbe distillation of gum kino and various tannins which produce a green color with ferric salts. It is generally prepared by conducting hydro- iodic acid gas into guaiacol, C®H*(OH)(OCH^), heated to 195°. Pyrocatechin is a solid body, very soluble in water and alcohol, very slightly soluble in ether ; it crystallizes from its aqueous solution in rectangular prisms, belonging to the orthorhombic system. It melts at 104°, and sublimes below that temperature in brilliant, colorless plates. It boils be- tween 240 and 245°. Its odor is strong and excites sneezing. It has the character of an acid, like phenol itself. It dis- solves in the alkalies and in the alkaline carbonates. When exposed to the air, these solutions become colored, first green, then brown and black. An aqueous solution of pyrocatechin produces a deep-green color with ferric chloride, which changes to dark-red on the addition of an alkali. This re- action characterizes the ortho-dihydric phenols. Resorcinol, C'^H*^0 Phtbalic acid. Phthalic anhydride. Phthalic anhydride crystallizes in long, brilliant prisms, fusible at 127°-128°. It boils at 284°. It possesses a remarka- ble property, which was discovered by A. Baeyer, and which^is now applied practically in the arts. When heated with the phenols, it combines with them directly with elimination of the elements of water, and compounds are obtained which are designated as jjhthaleins. Thus, when phthalic anhydride is heated with ordinary phenol, two molecules of phenol combine with one molecule of phthalic anhydride, with elimination of one molecule of water, and the phthalein of phenol is obtained. CO C6H5 0H /C = C(C6H*.0H)s Phthalic anhydride. 2 mol. phenol. Phenolphthalein. Pheriolphthalein occurs as a yellowish crystalline powder. It melts at 250° and dissolves readily in alcohol. Its solu- tion turns pink with the slightest trace of free alkali ; hence it is used as an indicator in alkalimetry. When resorcinol is heated with phthalic anhydride, two molecules of water are eliminated, and a body is obtained to which Baeyer has given the nsnae fluorescein. Phthalic anhydride. 2 mol. respijcinol. Fluorescein. Fluorescein forms orange-red, crystalline grains, insoluble in cold water, and but slightly soluble in boiling water. It dissolves readily in solutions of the alkalies and alkaline 716 ELEMENTS OF MODERN CHEMISTRY. carbonates. Its dilute solutions are yellow, and have a mag- nificent green fluorescence. Hence tlie name fluorescein. Tetrahromo-fluorescein, C^^H^Br^O^, is employed in dyeing under the name eosin. It communicates to silk a beautiful rose-red tint. Terephthalic Acid. — Cailliot obtained this body by sub- mitting oil of turpentine to a long ebullition with dilute nitric acid. The same acid is formed by the oxidation of paraxylene and its derivatives by potassium dichromate and sulphuric acid. It is a white powder, almost insoluble in water, alcohol, and ether. It sublimes without melting and without decomposition. Isophthalic Acid is formed by the oxidation of metaxy- lene or metatoluic acid. Long, thin, colorless crystals, slightly soluble in water, soluble in alcohol, and fusible above 300°. It may be sublimed without decomposition. TRIMETHYL-BENZENES AND ISOMERIDES. The hydrocarbons C^H^^ may be derived from benzene by the substitution : 1, of three methyl groups for three atoms of hydrogen ; 2, of a methyl and ethyl group for two atoms of hydrogen ; 3, of a propyl or isopropyl group for one atom of hydrogen. Their constitutions are then thus expressed : C^H^CCH^)^ C«H^<^2H5 C^H^-C^H^ TrimethylbenzeneSo Methyl-ethyl benzenes. Propyl and isopropyl benzenes. Trimethylbenzenes. — The methyl groups may be arranged in three difi"crent ways, and three isomers of position are actually known. Mesitylene^ C^H^^CH^(^), the symmetrical trimethylbenzene, is obtained by distilling acetone with an equal measure of sul- phuric acid diluted with half its volume of water : the reaction is moderated by adding sand to the mixture. Mesitylene is a liquid having a pleasant odor, and boiling at 163°. When boiled with dilute nitric acid it is oxidized, and forms successively three acids, in which one, two, or all of the methyl groups are converted into carboxyl. CYMENE AND ITS DERIVATIVES. 717 /CH^C) /CH^ /CW /CO.OH ^GWC) ^CO.OH ^CO.OH ^CO.OH Mesitylene. Mesitylenic acid. Mesidic Trimesic acid. or uvitic acid. With concentrated nitric acid it yields nitro-derivatives. Pseudocumene, or asymmetrical trimethylbenzene, C^H^^CH^(^), exists, together with mesitylene, in coal-tar, \CHXO but cannot be separated by fractional distillation. It is ob- tained synthetically by treating a mixture of bromoparaxy- lene and methyl iodide with sodium. It boils at 169°. Hemimellithene, C^H^^CH^O, has the methyl groups in adjacent positions, and is produced when bromometaxylene, (1) (2) (3) C^H^CH^BrCff, is made to react with methyl iodide and sodium (Jacobsen). It boils at 175°. Cumene, or Isopropylbenzene, C^H^-C^H^', was obtained by Gerhardt and Cahours by distilling cuminic acid with lime. Cuminic acid. Cumene. Its synthesis has been made by the action of isopropyl iodide on benzene, in presence of aluminium chloride. C^H« H- CH^-CHI-CH^ = HI + C^H5-CH<^^3 It is a colorless liquid, boiling at 151°. CYMENE AND ITS DERIVATIVES. Cymene, which is a product of the dehydration of camphor, is methylisopropylbenzene. Its synthesis is made by the ac- tion of sodium on a mixture of parabromisopropyl benzene and methyl iodide (Widman). It exists naturally in the essential oil of Cuminum Cyminum^ which contains also cuminol, or cuminic aldehyde, C^H*>0, which sublimes in brilliant needles, fusible at 221°. CaC^^H^^O^ = CaCO^ + C^ff^O Calcium camphorate. Camphorone. Besides ordinary camphoric acid, which is dextro-rotatory, there are two other modifications, — levo-camphoric acid, ob- tained from matricaria camphor, and meso-campJioric acid, formed by the union of equimolecular quantities of the two active varieties. Camphoric acid is dibasic ; its calcium salt yields by dry distilla- tion the compound camphorone, C^H^^O, a liquid boiling at 208°. Camphoronic acid, CT^'^(COOH)^ is produced by the further oxidation of camphoric acid. It is a crystalline com- pound fusible at 135°. By its synthesis it was recognized as CH-^ C(CH^) C(CH-7 trim^thyl-tricarballylic acid, C00^ COOH COOH UNSATURATED AROMATIC COMPOUNDS. 729 Among the other benzene addition compounds we can mention only the following : Quercite, C^HXOH)^ — This compound is pentahydroxy- hexahydrobenzene, but was formerly considered to be related to the sugars, and was called acorn-sugar^ having been first obtained from acorns. It forms monoclinic crystals, fusible at 222°, and subliming at 235°. It is soluble in water and in dilute alcohol, and its solutions are dextro-rotatory, a fact which is easily explained, as it contains two similar asym- metric carbon atoms. Hydriodic acid converts it into ben- zene, and finally into hexyl iodide. Inosite, C^H^(OH)^ — In 1850, Scherer extracted a sweet substance from the muscles, and the same compound has since been found in the lungs, kidney, spleen, and liver. Under the name inosite it was long classified with the sugars, but Maquenne has shown that it is no other than hexahy- droxyhexahydrobenzene. Inosite forms large rhombic tables or transparent, color- less prisms having a sweet taste. The crystals contain one molecule of water of crystallization, and effloresce in the air. Inosite is soluble in water, but insoluble in absolute alcohol and in ether. It is optically inactive, is not fermentable, and will not reduce alkaline cupric solutions. Dambonite, C^H«(0H)XCH^)2.— This substance is the dimethyl ether of inosite, and was first obtained by A. Girard from Gaboon caoutchouc. It forms colorless needles, fusible at 190° and subliming at 210°. It is soluble in water, only slightly soluble in alcohol. Hydriodic acid reduces it to methyl iodide and inosite. UNSATURATED AROMATIC COM- POUNDS. The benzene derivatives so far considered are formed by the replacement of the hydrogen of benzene by saturated groups. There are, however, compounds which contain un- saturated groups, and which can so combine directly with chlorine, bromine, or hydrogen. Among these we will describe only styrolene and some of its derivatives, 730 ELEMENTS OP MODERN CHEMISTRY. STYEOLENE, OR PHENYLETHYLENE. C8H8 = C6H5-CH=CH2 This compound, which may be considered as ethylene in which one atom of hydrogen is replaced by phenyl (C^H^), exists in storax, the thickened juice of the bark of Liquid- ambar orientate. It is extracted by passing steam through this balsam, fused under boiling water ; the styrolene is carried over with the steam. It is also formed when cinnamic acid is heated with lime ; for this reason it has been sometimes called cinna- mene. It is a colorless, mobile, strongly-refracting liquid, having an agreeable odor. The styrolene obtained from storax is optically active, a property which appears due to some impurity, for the hydrocarbon obtained artificially is inactive. Its density at 0° is 0.925, and it boils at 145°. When long kept, it becomes polymerized, and more rapidly if heated, into metastyrolene^ a transparent, amorphous mass, which is reconverted into styro- lene when distilled. Styrolene, being unsaturated, can combine directly with chlo° rine and bromine. The bromide, C^H^Br^, crystallizes in needles or plates, fusible at 74°. When heated with hydriodic acid, styrolene is converted into ethylbenzene. C^H5-CH=CH2 + 2HI ^ C^H^-CH^-CH^ + P CINNAMIC ALDEHYDE. C9H80 = C6H5-CH=CH-CHO Cinnamic aldehyde exists in the essential oils of cinnamon and cassia. It is formed during the distillation of a mixture of cinnamate and formate of barium, by a reaction similar to that which yields the fatty aldehydes under the same conditions. It is made synthetically by passing hydrochloric acid gas into a mixture of ordinary aldehyde and benzaldehyde. C6H5-CHO + CH3-CH0 = C6H5-CH=CH-CHO + H20 Benzaldehyde. Aldehyde. Cinnamic aldehyde. Cinnamic aldehyde is a colorless oil, heavier than water. It has an aromatic odor. When exposed to the air it becomes oxidized into cinnamic acid. It reacts with hydroxylamine and phenylhydrazine, and forms a crystallizable compound with sodium acid sulphite, a property which permits of its ready separation from oil of cinnamon. CINNAMIC ACID. 731 CINNAMYL ALCOHOL, OR STYEONE. O9H10O = C6H5-CH=CH-CH2.0H Styracin^ which may be extracted from storax, is a cinnamyl cinnamate, a compound of cinnamic acid and cinnamic alcohol, and may be readily saponified by potassium hydroxide. C^H^OIC^H^ + KOH = C^H^O^K + C^mOH Cinnamic alcohol crystallizes in brilliant needles, soluble in alcohol, and slightly soluble in water. It melts at 33°, and distils without change at 250°. CINNAMIC OR PHENYLACRYLIC ACID. C9H802 ^ C6H5-CH=CH-CO.OH This acid exists in Tolu and Peruvian balsams, in storax, and in certain gum benzoins. It is formed by the careful oxidation of cinnamic alcohol or aldehyde, and has also been obtained synthetically by heating benzaldehyde with acetic anhydride and dry sodium acetate. C'H^-CHO + CH^-COOH = H^O + C«H^-CH=CH-CO.OH According to Perkin, who discovered this important re- action, the condensation is caused by the dehydrating action of the sodium salt, but Fittig's researches render it probable that the latter enters into the reaction and the anhydride is the dehydrating agent. " Perkin's reaction" has been extensively applied in the preparation of unsaturated acids, especially of the homo- logues of cinnamic acid. Cinnamic acid is colorless and odorless. It crystallizes from hot water in fine needles, and from alcohol in large prisms. It melts at 133°. When rapidly heated, it distils almost without alteration at 290°. When distilled with lime, or heated to 200° with water, it is decomposed, yielding styrolene and carbon dioxide. C9H802 = C02 + C8H8 By fusion with potassium hydrate it is converted into acetic and benzoic acids. C6H5-CH=CH-CO.OH + 2K0H = CefiS-CO.OK + CH^-CO.OK + H2 Concentrated nitric acid converts it into two isomeric nitro- cinnamic acids^ C^H^(NO^)0^ ; orthonitrocinnamic acid, fusible at 240°, and paranitrocinnamic acid, fusible at 288°, 732 ELEMENTS OF MODERN CHEMISTRY. Cinnamic acid can fix directly two atoms of chlorine, bromine, or hydrogen, so forming saturated compounds. Sodium amal- gam converts it into Tiydrocinnamic or phenylpropionic acid, C^H^-CH^-CH^-CO.OH, a compound crystallizing in fine, colorless needles, fusible at 47.5°, and boiling at 280°. The following formula will show the relations between acrylic and propionic acids, on one hand, and on the other those between cinnamic and hydrocinnamic acids. CH2r=CH-C0.0H CH^-CH^-CO.OH Acrylic acid. Propionic acid. CH(C«H^)=CH-CO.OH CH2(CH15)-CFP-CO.OH Cinnamic acid. Hydrocinnamic acid. (Phenylacrylic.) (Piienylpropionic.) The cinnamates resemble the benzoates. Ferric chloride produces a yellow precipitate in their solutions. Phenylpropiolic Acid, C«H^-CeC-CO.OH, is formed when the dibrom-addition product of cinnamic acid, p/ie^iy?- dibromopropionic acid^ is boiled with alcoholic potash. C^H^-CHBr-CHBr-CO.OH = C^H^-CeC-CO.OH -|- 2HBr It crystallizes in needles which melt at 137°. At higher temperatures the acid is resolved into phenylacetylene and carbon dioxide. C«H^-CEC-CO.OH = C^H^-CeCH + CO^ The ortho-nitro-derivative has been used in the artificial preparation of indigo blue. INDIGO. C16H10N2O2 Indigo is obtained from difi"erent species of the genus Indi- gofera ; it is also found in woad (^Isatis tinctorid), but is no longer extracted from this plant. In India, indigo is prepared by macerating the stems and leaves of the indigofera, collected at the time of flowering, with water, in vats where they are allowed to ferment. In 12 or 15 hours the liquid is drawn off into other vats, where it is agitated so as to bring it in contact with the air, an opera- tion which occasions the formation of a blue precipitate. The brown liquor is then drawn off, and the deposit is boiled in copper vessels ; it is then pressed between cloths and cut into cubical pieces and dried. In this form the indigo is delivered to commerce. INDIGO. 733 Indigo is not contained ready formed in tlie plants wticli serve for its manufacture. Schunck considers that these plants contain a substance analogous to the glucosides, indi- can, which is decomposed by fermentation into indigo, and indogludn, C^H^^O^ The indigo of commerce contains from 50 to 90 per cent, of coloring matter. It generally occurs in irregular masses, of which the shade varies from violet-blue to blackish-blue. The most valued varieties present a brilliant coppery reflection. Pure indigo is called indigotin. It may be obtained by heating the indigo of commerce in a current of hydrogen, or by subliming it in small quantities between two watch-glasses (Chevreul). It then forms right rhombic prisms. Indigotin is insoluble in water, in cold alcohol, and in ether, but dis- solves in hot oil of turpentine and in aniline. When care- fully heated, and in small quantity, it volatilizes, and its vapor density corresponds to the formula C^^H^^N^O^ Concentrated, or, better, fuming sulphuric acid dissolves indigo at 50 or 60°, forming a beautiful blue solution, which contains two acids, indigomonosulphonic acid^ C^^H^N^O^. SO^H, and indigodisidphomc or sidpJimdigotic acid^ C^^H^N^O^ (SO^H)^. The solution of indigo in sulphuric acid is used in dyeing ; it is prepared by dissolving indigo in a hot mix- ture of fuming and ordinary sulphuric acids. The blue solu- tion thus obtained is known as sulphate of indigo, Saxon blue, or composition blue. Indigo carmine is the soluble sodium salt of the disulphonic acid. It is employed in dyeing animal fibres. Boiling dilute nitric acid converts indigo into isatin. The concentrated acid converts it first into nitrosalicylic acid, C^ff (NO')O^ and then into picric acid. When heated with potassium hydrate, indigo is converted into anthranilic (orthamidobenzoic) acid^ C^H^(Nff)0^, or into salicylic acid, which is formed at the expense of the anthranilic acid. C^H5(NH2)0^ -f KOH = KC^H^O^ + Nff Anthranilic acid. Potassium salicylate. When indigo is distilled with potassium hydrate, aniline passes over, being formed at the expense of the anthranilic acid first formed. Anthranilic acid. Aniline. 62 734 ELEMENTS OF MODERN CHEMISTRY. Synthesis of Indigo. — Various reactions liave been discov- ered whicli are applicable to the synthesis of indigo. The most important of these are due to von Baeyer, to whom also belongs the honor of having first (1878) prepared indigo artificially. Only a few syntheses of indigo blue can be considered here. 1. Isatin chloride, which will be described farther on, when dissolved in acetic acid and treated with zinc dust yields a colorless liquid, which, when exposed to the air, assumes a blue color, and deposits crystals of indigotin. Ammonium sulphhydrate effects the reduction more rapidly than zinc and acetic acid (Baeyer and Emmerling). 2. There exists normally in human urine a compound which may also be prepared artificially, indoxylsulpliate of potassium. When it is heated in the air, or treated with feeble oxidizing agents, it is converted into indigo (Baumann and Tiemann). Potassium indoxylsulphate, C^H'^NO.SO^K, is a derivative of indoxyl^ C®H®(OH)N, and the conversion of the latter into indigo is represented in the equation, 2C'H'^(0H)N + 0' = C'^ff^N^O^ + 2>W0 Indoxyl. Indigo. 3. A much better yield of indigo blue is obtained by the action of reducing agents upon orthonitrophenylpropiolic acid (Baeyer, 1880). C«H*(N02)CEC-CO.OH-f2H2 = Ci«ffW0^+2C0'-f 2H20 o-nitrophenylpropiolic acid. For this purpose orthonitrocinnamic acid is converted into its dibromide and the latter boiled with alcoholic potash. The resulting nitro-acid, by careful treatment with glucose and potash, is reduced to indigo. The high price of the re- quired materials has caused this process of manufacture to be abandoned. 4. Baeyer has made an interesting synthesis of indigo from orthonitrobenzaldehyde, C^H*CH By reducing oxindol by zinc powder with the aid of heat, Baeyer obtained indol, the parent substance of the indigo group. C«H^NO + Zn = C«H^N -f- ZnO Oxindol. Indol. ^ He has also made the synthesis of indol by heating ortho- nitrocinnamic acid with potassium hydroxide and iron filings. Orthonitrocinnamic acid. Indol. This^ reaction is a proof of the constitution of indol and its derivatives. Properties. — Indol is a solid, crystallizing in brilliant colorless plates. It melts at 52°, and boils with partial decomposition WW 62^ 738 ELEMENTS OF MODERN CHEMISTRY. at 245°. Its vapor is carried over by vapor of water. Its odor recalls that of naplithylamine. It dissolves readily in boiling water and in alcobol and ether. It has feebly basic properties. Indol is formed normally during the pancreatic digestion by the breaking up of albuminoid matters. It occurs, together with its methyl derivative, skatol^ in human excrements. Skatol, C^H^N, has also been obtained synthetically in shining leaflets, having a strong faecal odor, and melting at 95°. NAPHTHALENE. C10H8 This important compound was discovered by Glarden in 1820, in coal-tar. Its composition was determined by Faraday, and its properties and transformations were principally studied by Laurent. It is a frequent product of the dry distillation of organic matters, and is formed in abundance when these matters, or the products of their decomposition, are heated to high tem- peratures. Thus it is formed in large quantities when tar is passed through red-hot tubes. Naphthalene is extracted from coal-tar, and is purified by crystallization in alcohol, or by sublimation. Properties. — Naphthalene occurs in rhombic tables when it has been sublimed, and is deposited in prisms from its ethereal solution. It melts at 79.2°, and boils at 218°. It is inflam- mable, and burns with a very smoky flame. It is insoluble in water, slightly soluble in cold alcohol, freely soluble in boiling alcohol and in ether. By its general properties naphthalene is closely related to benzene : reagents afi"ect it in a similar manner, and the com- pounds which result from the replacement of its hydrogen atoms, or the addition of hydrogen or chlorine, are analogous to the corresponding benzene derivatives. Nitric acid attacks naphthalene, forming nitro-derivatives, among which is nitro-naphthalene, C^''H'(NO^), which crystal- lizes in sulphur-yellow, rhombic prisms, fusible at 61°. By long boiling with dilute nitric acid, naphthalene is converted into phthalic acid and carbon dioxide. Nitronaphthalene oxidized in the same manner yields nitrophthalic acid. NAPHTHALENE. 739 By the action of reducing agents nitronaphtlialene is con- verted into amidonaphthalene (a-naphthylamine), just as aniline results from tlie reduction of nitrobenzene. This amidonaphthalene, upon oxidation, gives phthalic acid. These facts are readily explained by assuming that the naphthalene molecule is formed by two benzene nuclei joined together, or condensed, in such a manner that two adjacent carbon atoms are common to both (Erlenmeyer), thus, — or Kekule's formula. Centric formula. When phthalic acid is produced by the oxidation of naph- thalene, one of the nuclei is destroyed, and the two carbon atoms which remain attached to the other nucleus become oxidized to carboxyl. In nitronaphthalene, under the same conditions, the nucleus which does not contain the nitro- group is oxidized, while in the case of amidonaphthalene the other nucleus, which contains the amido-group (in ex- actly the same place as the nitro-group of the former acid), is destroyed. This view of the constitution of naphthalene derives sup- port from various syntheses (see a-naphthol), and satisfac- torily accounts for all known cases of isomerism in the naph- thalene group. According to the positions occupied by the substituting atoms or groups, we have two series of mono-derivatives. The a-compounds are those which result from the replacement of one of the four hydrogen atoms which occupy an ortho- position with respect to a carbon atom common to both nuclei ; and in the ^-compounds one of the remaining four positions is taken by the entering atom or group. Numerous isom.ers are known of many of the disubstituted naphthalenes. When the substituting atoms or groups are identical, ten are theoretically possible, and when the sub- stituents are different, as many as fourteen isomers may exist. 740 ELEMENTS OF MODERN CHEMISTRY. Chlorine acts on naphthalene in two ways: it combines directly, forming chlorides of naphthalene, and produces numerous substitution products which generally combine with an excess of chlorine. Bromine yields only substitution compounds. Among all these products, we may mention the following : Cioji8Q\2 naphthalene dichloride. C^^'H'^Cl monoehloronaphthalene. C10H8C14 naphthalene tetrachloride. CIOH6CI2 dichloronaphthalene. C10H6C12C14 dichloronaphthalene tetra- CiORSCls trichloronaphthalene. chloride. C^OCFCP perchloionaphthalene di- Ci^'CF perchloronaphthalene. chloride. Concentrated sulphuric acid dissolves naphthalene, forming o- and /3-Naphthalenesulphonic acids, Ci^H'^.SG^H Naphthalenedisulphonic acids, CioH^ | ^^3^ The formation of the first of these acids is expressed in the following equation : Naphthalene. Naphthalenesulphonic acids. NAPHTHOLS. CioH'.OH These bodies are formed artificially by treating naphtha- lene with sulphuric acid, and fusing the naphthalenesulphonic acids so obtained with potassium hydrate (see page 678). C^'^HISO^K + KOH = K^'SO^ + C^^H^OH Potassium naphthalene- Naphthols. sulphonate. a-Naphthol is formed by heating pheni/lisocrotomc acid * to its boiling-point (Fittig and Erdmann). CH CH CH CH ^\/\ ^\/\ HC C CH HC C CH 1 II 1 = = H20 + 1 11 1 HC CH CH2 HC C CH \/ / \X\^ CH CO.OH CH C(OH) a-Naphthol forms silky needles or laminae, soluble in alco- hol, ether, and benzene, almost insoluble in cold water, slightly soluble in boiling water. It melts at 94°, and boils * This is obtained by the action of benzaldehyde upon succinate of sodium in presence of succinic anhydride. C6H6.CHO + C0.0H-CH2.CH2.C00H = C6H5-CH=CH-CH2CO.OH + CO2 + H^O I ANTHRACENE AND PHENANTHRENE. 741 at 278-280°. Its aqueous solution produces a violet color with chloride of lime. When treated with reagents, it forms derivatives analogous to those of phenol. ^-naphihol is prepared from sodium /?-naphthalenesulpho- nate. It crystallizes in small rhombic tables, fusible at 122°, and boils at 285-290°. The mono- and di-sulphonic acids, obtained by heating the naphthols with sulphuric acid, are used in the preparation of many important coloring matters. Naphthol yellow, for ex- ample, is dinitro-a-naphthol sulphonic acid, and /3-naphthol orange and rocellin (a substitute for cochineal) are complex, derivatives of /S-naphthol. NAPHTHYLAMINES. C10H9N = C10H7.NH2 Zinin obtained amidonaphthalene in 1842 by reducing nitronaphthalene by ammonium sulphydrate, which may be advantageously replaced by iron and acetic acid. Nitronaphthalene. Naphthylamine. This a-najphthylamine forms fine, colorless needles. It sub- limes at a gentle heat, melts at 50°, and boils without alteration at 300°. It has a fetid odor. Its reaction is not alkaline, although it perfectly neutralizes the acids, with which it forms well-defined and crystallizable salts. When exposed to the air, the salts of naphthylamine acquire a violet color, probably due to an absorption of oxygen. ^-naphtJiylamine is prepared by heating /?-naphthol with ammonia in presence of zinc chloride. It crystallizes in pearly needles, fusible at 112°, and boils at 294°. The reactions of the naphthylamines are analogous to those of aniline. Their diazo- and diazoamido-derivatives are applied in the preparation of valuable dyes. ANTHEACENE AND PHENANTHRENE. Anthracene, which is solid, exists in the less volatile products of the distillation of coal-tar. It is obtained from the last products of this operation. The mass, which has a buttery consistence, is squeezed in a filter-press, and the 742 ELEMENTS OF MODERN CHEMISTRY. residue is submitted to repeated distillations ; it is finally purified by compression and several crystallizations in ben- zene. Anthracene may be formed artificially by several processes. 1. By passing the vapor of toluene and various derivatives of that body through a tube heated to bright redness. Under these conditions, two molecules of toluene lose six atoms of hydrogen, and are converted into anthracene. C6H5-CH3 „„ C6H4=CH — 3H2 = I C6H5-CH3 C6H4=CH 2 luol. toluene. Anthracene. 2. By heating phthalic anhydride with benzene in presence of aluminium chloride, orthobenzoylbenzoic acid is obtained ; this, upon treatment with phosphorus pentoxide, is converted into anthraquinone, which, when reduced with zinc dust, yields anthracene. In the pure state, anthracene forms monoclinic tabular crystals which are colorless, and present a magnificent blue fluorescence (Fritzsche). They melt at 213°, and distil with- out alteration at 345°. By the action of oxidizing agents, such as chromic acid, an- thracene is converted into a solid body, which crystallizes in beautiful yellow needles, fusible at 276°, and which can be sublimed without alteration. It is antliraqiiinone^ C^^PPO^ a body which bears the same relations to anthracene as quinone to benzene. Q6JJ6 QUJJIO Benzene. Anthracene. Qninone. Anthraquinone. The constitution of anthraquinone is expressed by the formula By treating anthraquinone with bromine, Graebe and Lieber- mann converted it into dibromanthraquinone, C^^H^Br^O'^ a solid body, which crystallizes in yellow needles. Phenanthrene. — Besides anthracene, there is another hydro- carbon of the same composition, which exists in coal-tar, and may also be formed artificially. It is called phenanthrene, and forms colorless scales, having a bluish fluorescence. It melts at 100°, and boils at 340°. It is soluble in 50 parts of alco- ALIZARIN. 743 hol at 13° ; very soluble in hot alcohol, and in ether and benzene. Its constitution is expressed by the formula C«H*— CH ALIZAEIN. Ci*H804=:Ci*H6(OH)202 Natural State and Synthesis. — Alizarin is the name ap- plied to the coloring matter of madder (Euhia tinctorum) which Eobiquet was the first to extract in a pure state. Graebe and Liebermann made its synthesis in 1868 by heating dibromanthraquinone to 200° with potassium hy- droxide. C^^H^Br^O^ + 2K0H = 2KBr + Q''W(01iyO'' Dibromanthraquinone. Alizarin. Alizarin does not exist ready formed in the madder plant. The latter contains a glucoside to which Bobiquet has given the name ruherythric acid^ and which is decomposed by the action of acids into alizarin and glucose. (.26JJ28QU _|_ 2W0 = C^'H^O* + 2C«Hi20« Euberythric acid. Alizarin. Glucose. Preparation. — Alizarin may be extracted from madder by boiling the latter with a solution of alum. The filtered liquid, left to itself for some days, deposits impure alizarin as a brown- red precipitate, and holds in solution another coloring matter which is called purpurin. The precipitated alizarin is purified by washing with dilute hydrochloric acid, and crystallization in alcohol. The product thus obtained is exhausted with a boiling solution of alum, which removes the purpurin, and is finally dissolved in ether, which deposits it in crystals. Alizarin is now almost exclusively obtained from anthra- cene. This hydrocarbon is oxidized to anthraquinone, and the latter body treated with fuming sulphuric acid to con- vert it into anthraquinonesulphonic acid. The sodium salt of this acid is fused with sodium hydroxide, and a small quantity of potassium chlorate is added to the fused mass. gi6H7(S03Na)02 4- 3NaOH+02 = C"H6(0]S'a)202+ Na2SO*+2H20 744 ELEMENTS OF MODERN CHEMISTRY. The alkaline mass is dissolved in water, precipitated by hydrocliloric acid, and the precipitate purified by crystalliza- tion from toluene and finally by sublimation. The artificial product is delivered to commerce in the form of a paste, but the reaction by which it is formed produces, at the same time, isomerides which remain mixed with the aliza- rin, properly so called. Eight isomeric compounds are known having the composition C^^H^O*. One of them, purpuroxan- thin, is contained in small quantity in madder. Properties of Alizarin — Alizarin forms long, brilliant, orange-yelk w prisms. It is scarcely soluble in cold water, but dissolves better in boiling water, and is soluble in alcohol, ether, and carbon disulphide. It melts at 278°, and sublimes in long, orange-red needles. It dissolves in sulphuric acid with a blood-red color, and water precipitates it without alter- ation from this solution. Boiling dilute nitric acid converts it into oxalic and phthalic acids. When alizarin is heated to redness with zinc powder, it is reduced to anthracene (G-raebe and Liebermann). Alizarin forms combinations with the bases ; it dissolves in ammonia, with a purple color, and in the caustic alkalies, yielding purple solutions which have a blue reflection. Uses. — Alizarin produces a red color (Turkey red) on fabrics that are mordanted with alumina, or with ricinoleic- sulphonic acid,* and a violet on those which are mordanted with ferric oxide, PURPUEIN. Ci*H5(OH)302 This name is given to another coloring matter which may be extracted from madder, and which has already been mentioned. It appears to exist in the plant as a glucoside. It dissolves readily in alcohol and ether, with a red color. It crystallizes from weak alcohol in orange-colored needles, which contain one molecule of water of crystallization. From concentrated alcohol, it deposits in red, anhydrous needles. When heated, it melts at 254°, and sublimes in red needles. With aluminium mordants, it gives scarlet-red shades. Purpurin is an oxyalizarin, or a trioxyanthraquinone, C^*H^(OH)^0^ : indeed, it may be obtained by treating a * This is prepared by treating castor oil with sulphuric acid.. FURPURANE, THIOPHENE, AND PYRROL. 745 solution of alizarin in concentrated sulphuric acid with an oxidizing agent, such as manganese dioxide (de Lalande). Inversely, the reduction of purpurin reproduces alizarin (Rosenstiehl). It undergoes a complete reduction, and is converted into anthracene, when heated with zinc-dust. Anthrapurpurin and JiavopiLrpurin are isomeric with the purpurin just described ; they are contained in commercial alizarin. The hydrocarbons of the aromatic series and the products obtained from them by substitution and addition all contain closed chains consisting of carbon atoms exclusively. There exist, however, very numerous compounds of an " aromatic character" whose nuclei are not made up entirely of carbon atoms, but in which other elementary atoms, such as oxygen, sulphur, and nitrogen, form part of the closed chains. Among these bodies we will consider furfurane, thiophene, pyrrol, pyridine, and quinoline, and some of their more im- portant derivatives. FURFURANE, THIOPHENE, AND PYRROL. When the barium salt of pyromucic acid (page 662) is heated with a little soda-lime, a colorless liquid of peculiar odiOY^ furfurane^ C*H*0, distils. Thiophene^ C*H*S, and pyrro?, C*H^NH, are similar bodies which occur in small quantities in coal-tar. The striking analogies in the chemical behavior of these bodies, as well as their close resemblance to benzene, are best accounted for in the formulae HC — CH HC — CH HC — CH „ll II II II II II HC CH HC CH HC CH Y NH Furfurane. Thiophene. Pyrrol. Furfarane is contained in pine-tar. It boils at 32°, is insoluble in water, but miscible with alcohol and ether. Its most important derivative \b furfural, C*H^O-CHO, an aldehyde. This is formed in the dry distillation of many carbohydrates, and most readily by heating bran or sawdust 2a 63 I 746 ELEMENTS OF MODERN CHEMISTRY. with dilute sulphuric acid. Furfurol is a colorless liquid of peculiar odor. It boils at 162°. When heated with silver ox- ide and water it is oxidized to pyi'omucic acid, C*H^O.COOH, which also results from the dry distillation of mucic acid. Pyromucic acid crystallizes in colorless leaflets, melting at 134°. Treated with bromine and water, it is converted into fumaric acid, carbon dioxide being given off. Thiophene was discovered by Y. Meyer in commercial benzene. Its isolation from this source offers considerable difficulty, but a very pure product may be obtained syntheti- cally by heating a mixture of dry sodium succinate and phos- phorus trisulphide (Volhard and Erdmann). The physical as well as the chemical properties of thio- phene are remarkably like those of benzene. It is a colorless, mobile liquid, which congeals at very low temperatures. Its boiling-point is at 84°. The derivatives of thiophene are made in the same manner as those of benzene, which they closely resemble in their properties. Of the homologues of thiophene, thiotolene, C^H^S.CH^, and thioxene, C*H^S(CH^)^, occur in coal-tar. Having nearly the same boiling-points as the corresponding benzene deriva- tives, they accumulate in the fractions constituting commer- cial toluene and xylene. TMophfene, C^H*S^, may be regarded as the " naphtha- lene" of the thiophene group. Its constitution is expressed by the formula ^ C HCn n nCH HC\ jL /CH s s MtrotMophene, C*H^S.NO^ is one of the products of the action of nitric acid upon thiophene. It is a solid, crystal- lizing in monoclinic prisms, and melting at 44°. It boils at 224°. Upon reduction with tin and alcoholic hydrochloric acid, it yields amidotUophene, C^H^S.NH^ The free base, which is a colorless oil, is very unstable. It is not diazotized by treatment with nitrous acid, but it forms azo-compounds with diazo-derivatives of benzene. TMophenesidplionic add, C'H^S.SO^H, is easily obtained by the direct sulphonation of thiophene : by repeated treat- ment with sulphuric acid, commercial benzene may be de- PYRIDINE AND ITS DERIVATIVES. 747 prived of the admixed tliiopliene. When superheated with water, the sulphonic acid is resolved into thiophene and sul- phuric acid. The very numerous derivatives of thiophene that have been described by V. Meyer and others also include phenols, aldehydes, ketones, carboxylic acids, etc. The " indophenin" reaction, which has already been given (page 736), constitutes the most delicate test for thiophene. Pyrrol was discovered by Runge. It is present in coal- tar and in bone-oil, and is produced in the dry distillation of ammonium mucate. When freshly prepared it is a color- less liquid, which turns brown in the air. It boils at 131°. Although practically insoluble in water, it mixes readily with alcohol and ether. Metallic potassium converts it into potas- sium-pyrrol, C*H*(NK), a crystalline body which is decom- posed by water into pyrrol and potassium hydroxide. When treated with nascent hydrogen, pyrrol is reduced to pyrroline^ C*H^(NH), a strong base, boiling at 91°. By heating this base with hydriodic acid, it takes up more hydrogen and is converted into pyrrolidine, C*H^(NH), an alkaline liquid which boils at 83°. The most characteristic test for pyrrol consists in exposing to its vapor a pine shaving moistened with hydrochloric acid : it assumes a deep-red color. A great variety of substitution products of pyrrol have been obtained. Both the hydrogen of the imido-group and that united with the carbon atoms may be replaced by alkyl groups. lodol (tetraiodopyrrol), C*P(NH), is an odorless substitute for iodoform. It is made by the action of iodine and an alkali upon pyrrol. It crystallizes in yellow leaflets, soluble in alcohol. PYRIDINE AND ITS DEBIVATIYES. From the oil obtained by the dry distillation of animal mat- ters, and which was formerly known as the hone oil of Dip- •pel, Anderson has extracted a series of bases isomeric with the aromatic amines. Among these bases are the following : Pyridine, C^HSN. Picolines, C^H'^N, isomeric with aniline. Lutidines, C^H^N, isomeric with toluidine. Collidines, C^HUN, isomeric with xylidines. Parvolines, C»Hi3N, etc. •748 ELEMENTS OF MODERN CHEMISTRY. These bases also occur in coal-tar ; in fact, they are gen- erally formed when nitrogenous organic matter is subjected to destructive distillation. Some of the bases, as well as many of their derivatives, have been obtained synthetically. The following are the most important modes of formation that have been observed : 1. Pyridine is produced when a mixture of acetylene and hydrocyanic acid is passed through a red-hot porcelain tube. 2C'H2 + HCN =r C^H^N 2. By the action of ammonia upon certain aldehydes, oxi- dized bases are formed, thus : Acrolein. Acrolein-ammonia. 2C^H60 + NH^ = C'H^^NO + H^'O Crotonaldehyde. By dehydration these condensation products yield pyridic Picoline, CoUidine. 3. Baeyer and Ador have also obtained a collidine (alde- iiydine) by heating aldehyde-ammonia in closed vessels. Collidine, 4. Pyridine is formed by the action of methylene iodide and sodium methylate upon potassium pyrrol. 5. Piperidine (hexahydropyridine) results when penta- methylene hydrochloride is rapidly heated. C^Hi«(NHOlHCl = (JWm + NmCl This base yields pyridine when heated with concentrated sulphuric acid. 6. A dihydro-dicarboxylic acid of collidine is obtained when aldehyde-ammonia is heated with acetoacetic ether. 2C6H10O3 + CH3.CH0 + ^W = C5N(H2)(CH3)3(CO.OH)2 -f BWO The two additive hydrogen atoms are removed by treat- ment with nitrous acid. The first term of the series is pyridine. . According to an ingenious hypothesis of Kbrner, this compound has a consti- PYRIDINE. Y49 tution analogous to that of benzene, tlie five carbon atoms and the nitrogen atom forming a closed chain similar to the benzene nucleus. H H c c HC CH HC CH I II I II HC CH HC CH ^^ V C N H Benzene. Pyridine. The higher homologues of pyridine, such as picoline, luti- dine, and collidine, then result from the substitution of one or more methyl or other alkyl groups for the hydrogen of pyridine. According to the position of these groups with relation to the nitrogen atom in the pyridic chain, isomerism will occur, precisely analogous to that which we have con- sidered in the case of the aromatic amines. Pyridine may, indeed, be regarded as a mono-substituted benzene, its nitrogen occupying the place of a CH group. The mono-derivatives of pyridine are therefore analogous to the di-derivatives of benzene. They exist in three isomeric forms, designated as a-, /5-, and ^-derivatives, and correspond- ing to the ortho-, meta-, and para-disubstituted benzenes. We cannot extend these theoretical considerations. How- ever, the pyridic bases and quinoline, which is related to them, appear to take part in the constitution of the natural alkaloids. Indeed, some of the latter, such as cinchonine and brucine, yield by distillation with potassium hydrate a mixture of pyridic bases and quinoline. Pyridine, C^H^N. — This base has been obtained from the animal oil of Dippel by Anderson, and from coal-tar by Greville Williams. It may be prepared from these products, but is best ob- tained in a pure condition by heating nicotinic acid (see page 750) with lime. C^H^N.COOH == C^ffN + CO^ It is a colorless liquid, having a characteristic odor, and at 0° a density 1.003. It boils at 115°, and is soluble in water and alcohol. It is an energetic base, forming deliquescent salts. Sodium converts it into a polymeride, dipyridine^ Q^^W^W. 63* 750 ELEMENTS OF MODERN CHEMISTRY. Piperidine^ or hexahydropyridine, C^H^^N, is formed by the action of sodium upon a hot alcoholic solution of pyridine. It is a colorless liquid, whose odor suggests that of pepper. It boils at 106°, and is miscible with water and alcohol. Piperidine is a powerful base which forms crystalline salts with acids. We cannot describe the other pyridic bases : they all exist in several isomeric modifications. Thus, there are three pico- lines, or methyl-pyridines, C^H*(CH^)N ; nine lutidines, of which six are dimethyl-pyridines and the others ethyl derivatives. The collidines comprise trimethyl-pyridines, methylethyl-pyridines (aldehydine), and propyl-pyridines. Under the action of oxidizing agents, such as potassium permanganate in alkaline solution, the pyridic bases behave like aromatic hydrocarbons. The lateral chains are oxidized and converted into carboxyl, CO. OH. Thus methylpyridine (/5-picoline) and ethylpyridine (/?-lutidine) yield the same pyridine-carhoxylic (nicotinic) acid, C5H*<^^' and C5H*<^'^' yield C5H*<^^-^^ Methylpyridine. Ethylpyridine. Nicotinic acid. Picolinic add and isonicotinic acid are the corresponding a- and ^-derivatives. There are ^\x pyridine-dicarhoxylic acids. /CO.OH C^H^^CO.OH QUINOLINE. Gerhardt obtained this base by distilling certain natural alkaloids, among which are quinine and cinchonine, with potassium hydroxide. It is identical with a base which Runge had extracted, several years previous, from coal-tar, and which he named leacol or leucoline. Considerable quantities of quinoline are found in bone-oil. Being accompanied by isomeric and homologous bases (iso- quinoline, quinaldine, lepidine, etc.), the pure substance can- QTIINOLINE, ETC. 751 not readily be isolated from any of these sources. It may, however, be prepared synthetically by a method which was discovered by Skraup, and which consists in heating aniline with glycerol and sulphuric acid in presence of nitrobenzene. Aniline. Glycerol. Quinoline. The sulphuric acid aids the condensation by its dehy- drating action, and the nitrobenzene plays the part of an oxidizing agent. Quinoline is a mobile, colorless, strongly refracting liquid. Its density at 0° is 1.081, and it boils at 238°. It has a pene- trating odor and a very bitter taste. It is insoluble in water ; with acids it forms well-defined salts, and behaves as a ter- tiary base. With ethyl-iodide it forms quinoline ethiodide. C»H'N<^,jj, Quinoline is related to the true aromatic compounds, and at the same time to the pyridic bases. Its synthetical forma- tion and its reactions have led to the following representation of its constitution, which is that of naphthalene, in which a group CH is replaced by an atom of nitrogen. H H C C ^\/\ HC C CH I II I HC C CH C N H Quinaldine, or a-methylquinoline, C^H^(CH^)N, is present in coal-tar, and is formed when aniline is heated with paral- dehyde and hydrochloric acid (Doebner and Miller). It is a colorless liquid, boiling at 246°. Besides quinaldine, there exist six mono-methylquinolines and many higher homologues. Isoquinoline is very similar to its isomeride, quinoline. It is present in coal-tar, and has been obtained synthetically. It is a solid, melting at 22°. Its boiling-point is the same as that of quinoline. 752 ELEMENTS OF MODERN CHEMISTRY. When oxidized witli potassium permanganate it yields cin- chomeronic and phtlialic acids. The former is one of the pyridine dicarboxylic acids ; its carboxyl groups are in the /?- and /'-positions. Hence the constitution of isoquinoline must be H H C C J /\ 1 II 1 HC C N %/\// C C H H Acridine, C^^H^N, is another solid base contained in coal- tar. It accompanies anthracene, from which it may be sepa- rated by treatment with sulphuric acid. It crystallizes in colorless needles, fusible at 110°, but sub- liming even below this temperature. It boils at 360°. It forms salts, which in dilute solutions exhibit a blue fluores- cence. The constitution of acridine is expressed by the formula H H C C ^\ H /\ HC C— C— C CH I II I II I HC C— N— C CH V Y H H ALKALOIDS. This term has been applied to the nitrogenous organic bases which are derived from plants. Many of these sub- stances are possessed of poisonous or medicinal properties ; they constitute the " active principles" of vegetable drugs. The alkaloids cannot be said to represent a sharply-defined group of compounds. While the constitution of only a small number of these complex bodies is clearly established, it is well known that the great majority are derivatives of pyri- dine, quinoline, and isoquinoline, others are closely related CONINE. 753 to uric acid, and still others belong to different groups of the fatty and aromatic series. It is customary to divide the alkaloids into two classes, the first of which includes the liquid and volatile bases, the second those which are solid. The latter generally contain oxygen, the former do not. With few exceptions the alkaloids are very sparingly solu- ble in water ; most of them, however, dissolve readily in alcohol, ether, chloroform, benzene, etc., and they all form soluble salts with acids. A number of special reagents are used to isolate and identify the alkaloids. Platinic and auric chlorides form well-defined crystalline double salts (chloroplatinates and chloraurates) with their hydrochlorides, and tannic acid, phosphomolybdic acid, potassium mercuric iodide, etc., produce precipitates in their solutions. From these insoluble compounds the alkaloids can be reo;enerated with the aid of alkalies. CONINE. C8H1W This is a liquid and volatile alkaloid which is extracted from the hemlock ( Conhim maculatuin). The seeds of this plant are crushed and distilled with sodium hydrate. The alkaline liquid which collects in the receiver is neutralized by dilute sulphu- ric acid, evaporated to a syrupy consistence, and the residue exhausted with a mixture of alcohol and ether, which dissolves the Conine sulphate, and leaves ammonium sulphate. The alco- hol and ether are driven out by evaporation ; a concentrated solution of sodium hydrate is added to the conine sulphate, and the liquid is distilled. The conine passes with a certain quan- tity of water, on which it floats. It is separated, dried over some fragments of calcium chloride, and rectified in a vacuum. Ladenburg made the synthesis of conine by heating a- picoline with aldehyde and subjecting the resulting a-allyl- pyridine to the action of nascent hydrogen. C5H*(CH^)N -f CH«-CHO = H^O + C^HXCH=CH-CH^)N a-picoline, a-allylpyridine. 754 ELEMENTS OF MODERN CHEMISTRY. Conine is therefore a-propylpiperidine. CH2 H2C CH2 I I H2C CH-CH2-CH2-CH3 NH It contains one asymmetric carbon atom, and exists in three stereoisomeric modifications. Natural conine is dextro- rotatory, and the synthetic conine which is inactive can readily be broken up into the two active varieties of opposite rotatory power. Conine is a limpid, oleaginous liquid, having a penetrating and nauseating odor, recalling that of hemlock. It boils at 168°. It is slightly soluble in water, more so in cold than in hot water, so that a cold, saturated solution becomes clouded when heated. It is very soluble in alcohol and in ether. It has a strongly alkaline reaction, immediately restoring the blue color to reddened litmus-paper. It precipitates many metallic oxides from solutions of their salts. On contact with the air it becomes brown and resinified. The density of conine at 0"^ is 0.886, Conine is often mixed with methylconine, a compound de- rived from conine by the substitution of a methyl group for an atom of hydrogen, and formed artificially by the action of methyl iodide on conine. Wertheim has obtained from the flowers and seeds of the hemlock a solid alkaloid, which he has named conhydrine, C^^H^NO, and which contains the elements of conine plus a molecule of water. NICOTINE. CioHi*N2 This alkaloid exists in tobacco. It may be obtained by ex- hausting tobacco with boiling water and evaporating the liquid to a syrupy consistence on a water-bath ; the still hot extract is then mixed with twice its volume of alcohol, allowed to settle, and the alcoholic liquid separated from the thick lower layer, which contains much calcium malate. The alcohol is distilled ofi", and the residue exhausted with strong alcohol, of which the greater part is then driven off by evaporation. Potassium PIPERINE — ATROPINE. TSS hydrate is added to the alcoholic extract, which is then agitated with ether, which dissolves the nicotine set free. A few grammes of oxalic acid added to the ethereal solution causes the separa- tion of a syrupy deposit which contains oxalate of nicotine. This salt is decomposed by potash and the nicotine set free is dissolved out by ether. After the ether has been expelled on a water-bath, the nicotine is distilled in a current of hydrogen, that part being retained which passes above 180° (Schloesing). Properties. — Nicotine is a colorless liquid, having an offen- sive, penetrating odor. It rotates the plane of polarization to the left. It boils between 240 and 250°, not, however, with- out undergoing partial decomposition. Above 146°, it begins to distil slowly, and at 100° it emits white vapors ; at ordinary temperatures it gives off so much vapor that a rod wet with hydrochloric acid will be enveloped in white fumes if held a little distance above the nicotine. Nicotine dissolves in ail proportions in water, alcohol, and ether. It has a strongly alkaline reaction, and perfectly neu- tralizes the acids, and precipitates the metallic oxides from solutions of their salts. It is one of the most violent poisons known. It is a diatomic base ; its chloroplatinate, which crystallizes in red prisms, has the composition PIPERINE. C"Hi9N03 This alkaloid occurs in various species of pepper, particularly in black pepper, from which it may be extracted by alcohol. It crystallizes in prisms, fusible at 129°, very soluble in alcohol and ether, and insoluble in water. Its reaction is neutral, and its salts are not well defined. Sulphuric acid dissolves it, pro- ducing a dark-red color. When heated with alcoholic potash, it yields piperidine (p. 750) snad piperic acid. Piperidine. Piperic acid. ATROPINE. This alkaloid, which is largely used in the treatment of dis- eases of the eyes, was discovered in 1833 by Geiger and Hesse, and by Mein, in the deadly nightshade (^Atropa Belladonna). 756 ELEMENTS OF MODERN CHEMISTRY. It has been obtained also from the thorn-apple {Datura Stra- mo7num). It appears that atropine does not exist already formed in the deadly nightshade, but that it is formed during ex- traction from an isomeric alkaloid, hyoscyamine, which, together with another alkaloid, hyosdne^ exists naturally in the plant. Preparation. — Belladonna-root is reduced to powder and digested several days with alcohol. The solution is filtered, slaked lime, in quantity equal to one-twentieth of the weight of root employed, is added, the solution again filtered, and rendered slightly acid with sulphuric acid. It is again filtered, and | of the alcohol distilled oiF. The residue is concentrated at a gentle heat, and a concentrated solution of potassium carbonate is added until the liquid, now neutral, begins to be clouded. After a few hours, the precipitate is separated by filtration, and potassium carbonate is added to the filtrate as long as impure atropine is precipitated. The next day, the deposit is collected on a filter, pressed, dried, and exhausted with 96 per cent, alcohol. The solution is decolorized with animal charcoal, the liquid diluted with six times its volume of water and put in a cool, dark place. The atropine is deposited in twenty-four hours in crystalline needles. Properties. — Atropine crystallizes in delicate needles, fusi- ble at 115°. It dissolves in 300 parts of cold water, and in almost all proportions of alcohol. It is less soluble in ether. At 140° it volatilizes, but the greater part of it is decomposed. In burning, atropine diffuses the odor of benzoic acid. When it is treated with potassium dichromate and sulphuric acid, benzyl aldehyde distils and benzoic acid is formed (Pfeifier). Atropine is a virulent poison. The sulphate of atropiue is much used in ophthalmic surgery. A single drop, even of a very dilute solution of this salt, produces dilatation of the pupil. When a small quantity of atropine is moistened with nitric acid, evaporated to dryness, and the residue treated with alcoholic potash, a rich violet color is developed (Vitali). A solution of bromine in aqueous hydrobromic acid throws down from solutions of atropine a yellow amorphous precipi- tate which soon becomes converted into characteristic crystals (Wormley). COCAINE. 757 When heated with baryta water, or with hydrochloric acid, atropine breaks up into tropine and tropic acid (Lossen and Kraut). Atropine. Tropic acid. Tropine. Tropine is an energetic base, soluble in water, alcohol, and ether : from the latter solvent it separates in tables, fusible at 61°, It is a derivative of piperidine. Tropic acid is the phenyl derivative of hydracrylic acid. CH'i.OH CH2.0H CH2.C0.0H ^^CH il II ^CH N — C — NH/ N — C — N-^^^^ MEASUEES OE WEIGHT. 1 MilligramniG 1 Centigramme 1 Decigramme 1 Gramme 1 Decagramme 1 Hectogramme 1 Kilogramme GRAINS. 0.01543 0.15432 1.54323 15.43234 154.32349 1543.23488 15432.34880 OUNCES TROY = 480 GRAINS. 0.000032 0.000321 0.003215 0.032150 0.321507 3.215072 32.150726 POUNDS AVOIRDUPOIS. 0.0000022 0.0000220 0.0002204 0.0022046 0.0220462 0.2204621 2.2046212 1 Grain 1 Oz. Troy 1 Lb. Avoirdupois = 0.064799 grammes. = 31.103496 " 0.453495 kilogrammes. 1 Cubic Centimetre of water at 4° C. weighs 1 gramme. To convert Centigrade degrees into Fahrenheit degrees, multiply by 9 and divide by 5 ; add 32°. To convert Fahrenheit degrees into Centigrade degrees, subtract 32°, then multiply by 5 and divide by 9. 1 Metre = 39.370708 inches. 1 Centimetre = 0.39370 " 1 Millimetre = 0.03937 " llnch 2.539954 centimetres. MOHS'S SCALE OF HARDNESS. 1. Talc. 2. Gypsum. 3. Calcite. 4. Fluor spar. 5. Apatite. 6. Feldspar. 7. Quartz. 8. Topaz. 9. Corundum. 10. Diamond. 789 INDEX. Abstrich, 346. Acetal, 555, 583. Acetaldoxime, 554. Acetamide, 559. Acetanilide, 684. Acetates, 548. Acetic anhyride, 552. Acetoacetic ether, 551. Acetone, 557. Acetonitrile, 492. Acetophenone, 707. Acetyl chloride, 555. Acetylene, 576. Acid, 52. acetic, 545. acetoacetic, 551. aconitic, 623. acrylic, 529, 566. alloxanic, 626. amalic, 769. amidacetic, 602. amidopropionic, 604. amidosuccinic, 613. anisic, 711. anthranilic, 733. antimonic, 197. arsenic, 192. arsenious, 190. aspartic, 614. atropic, 757. barbituric, 627. benzenesulphonic, 676. benzoic, 705. boric, 203. bromic, 140. butyric, 562. campholic, 725. camphoric, 728. camphoronic, 728. caproic, 565. carbamic, 477. carbolic, 677. carbonic, 219. in air, 78. /cerotic, 528^ 566^ Acid, chlorethylsulphonic, 585. chloric, 135. chlorous, 135. cholalic, 785. chromic, 412. cinchomeronie, 752, 762. cinchoninic, 762. cinnamic, 731. citraconic, 624. citric, 621. crotonic, 567. cyanic, 474. cyanuric, 472, 475. dextrotartaric, 616. dialuric, 627. dibromosuccinic, 611. dichloracetic, 553. digallic, 660. dihydroxypropionic, 601, dilactic, 599. dioxysuccinic, 614. ditartaric, 617. dithionic, 106, 119. elaidic, 567. ethylnitrolic, 510. ethylphosphinic, 537. ethylsulphonic, 512. ethylsulphuric, 511. formic, 543. fumaric, 612. fulminic, 495. galactonic, 661. gallic, 713, 660. gluconic, 661. glutamic, 772. glutaric, 621. glyceric, 601. glycocholic, 785. glycollic, 595. glyoxylic, 596. gummic, 654. hippuric, 707. bydantoic, 630. hydracrylic, 597, 601. hydrazoic, 160. 791 792 INDEX. Acid, hydriodic, 142. hydrobromic, 138. hydrochloric, 126. hydrocinnamic, 732. hydrocyanic, 465. hydrofluoric, 147. hydrofluosilicic, 208. hydrosulphurous, 106, 110. hypobromous, 139. hypochlorous, 132. hypophosphorus, 181. hyposulphuric, 106, 119. hyposulphurous, 106, 110. indigodisulphonic, 733. indigomonosulphonic, 733. indigotic, 710. iodic, 144. lodopropionic, 562. isatic, 736. isethionic, 584. isobutyric, 563. isocrotonic, 567. isocyanic, 474. isonicotonic, 750. isophthalic, 916. isosuccinic, 612. isovaleric, 564. itaconic, 624. lactic, 597. lactobionic, 644. lactonic, 661. leucic, 605. levolactic, 600. maleic, 612. malic, 612. malonic, 609. manganic, 406. mannonic, 661. mannosaccharic, 661. margaric, 565. meconic, 763. melissic, 566. mellitic, 665. mesaconic, 624. mesotartaric, 620. mesoxalic, 626. mesoxaluric, 627. metaboric, 204. metagummic, 664. metantimonic, 199. metaphosphoric, 185. metavanadic, 371. methylethylacetic, 564. methylnitrolic, 494. methylparoxy benzoic, 712, Acid, methylsuccinic, 621. metoxybenzoic, 711. molybdic, 414. monobromsuccinic, 611. monochloroacetic, 551. mucic, 644, 661, raphthalenedisulphonic, 740. naphthalenesulphonic, 740. nicotinic, 750. niobic, 362. nitric, 167. in air, 80. nitrocinnamic, 731. nitrohydrochloric, 170, nitrosalicylic, 710. nitrotartaric, 617. nitrous, 164. oleic, 567. opianic, 767. ortharsenic, 192. orthophosphoric, 183. orthoxybenzoic, 709. oxalic, 605. oxamic, 609. oxybenzoic, 709-711. oxymalonic, 610. palmitic, 666. parabanic, 629. paralactic, 597, 699. paratartaric, 619. paroxybenzoic, 711. pentathionic, 107. perbromic, 140. perchloric, 136. perchromic, 97. periodic, 146. permanganic, 407. persulphuric, 106, 120. phenic, 677. phenolsulphonic, 682. phenylacrylic, 731. phenylisocrotonic, 740, phenylpropionic, 732. phenylsulphuric, 680. phloretic, 669. phosphoric, 183. phosphorous, 182. phthalic, 715. picolinic, 750. picramic, 682. picric, 681. propionic, 661. prussic, 466. purpuric, 628. pyrantimonic, 199, INDEX. 793 Acid, pyridine carboxylie, 750. pyridine dicarboxylic, 750. pyrogallic, 713. pyromucic, 662, 746. pyrophosphoric, 184. pyrosulphuric, 118. pyrotartaric, 617, 621. pyruvic, 617, 620. quinic, 758. ricinoleic-sulphonic, 744. rosolic, 692. ruberythric, 743. saccharic, 643, 661. saccharinic, 638. salicylic, 709. silicic, 209. stannic, 418. stearic, 566. succinic, 610. sulphindigotic, 733. sulphocarbonic, 225. sulphovinic, 511. sulphuric, 106, 111. constitution of, 115. fuming, 118. test for, 118. sulphurous, 106. sulphydric, 102. tannic, 659. tantalic, 372. tartaric, 614. inactive, 619. tartronic, 610, 617. taurocholic, 786. terephthalic, 716. tetraboric, 204. tetrathionic, 107. thiocyanic, 482. thiophenesulphonic, 746. thiosulphuric, 106, 119. tricarballylic, 623. trichloracetic, 552. trimethylacetic, 564. trithionic, 607. tropic, 757. tungstic, 415. uric, 624. valeric, 564. Acids, 31, 52. diatomic, 461. fatty, 541, 559. synthesis of, 541. ketonic, 620. metallic, 257. monobasic, 451. 2i Acids, polyatomic, 594. Aconitine, 768. Acraldehyde, 566. Acridine, 752. Acrolein, 529, 566. Adenine, 788. Adipoeere, 565. Affinity, 21. Air, 73. composition of, 73. dew-point, 85. Alabaster, 328. Alanine, 604. Albite, 384. Albumen, 774. Albuminoid matters, 770. Albumoids, 774. Albumoses, 773. Alcohol radicals, 458. Alcohol, allyl, 528. amyl, 524. active, 526. fermentation, 524. normal, 524. tertiary, 527. benzyl, 702. butyl, 522. fermentation, 522. normal, 523. secondary, 523. tertiary, 523. cetyl, 528. cinnamic, 731. ethyl, 498. heptyl, 527. hexyl, 527. isopropyl, 522. methyl, 485. octyl, 527. propyl, 522. Alcohols, dihydric, 462, 577. monohydric, 450, 483, 549. polyhydric, 460, 633. primary, secondary, tertiary, 521. Aldehyde, acetic, 553. polymerides of, 555. anisic, 711. cinnamic, 730. crotonic, 554, 567. formic, 545. salicylic, 708. Aldehydes, 453. Aldehydine, 750. AldoL 554. 67 794 INDEX. Aliphatic series, 662. Alizarin, 743. Alkaloids, 752. Allantoin, 628. Alloxan, 626. Alloxantin, 628. Alloys, 57, 248. table of, 249. AUyl alcohol, 628. bromide, 573. iodide, 529. sulphide, 529. sulphocyanate, 529. tribromide, 529. Allylene, 576. Alum, 382. Aluminite, 383. Aluminium, 380. chloride, 381. oxide, 381. silicates, 384. sulphate, 382. Amalgams, 57. Amblygonite, 315. Amelide, 472. Amides, 454. Amidoazobenzene, 688. Amidobenzene, 683. Amidonaphthalene, 739. Amidothiophene, 746. Amines, 455, 530. nitroso, 531. Ammonia, 149. action of CI and I, 154. action of potassium, 155. alum, 383. combustion of, 153. composition, 151. in air, 79, in gas liquor, 157. liquefaction, 150. -water, 151. Ammonias, compound, 455, 530. Ammonium acetate, 550. amalgam, 155. carbamate, 159. carbonate, 158. chloride, 156. formate, 544. isocyanate, 475. molybdate, 414. nitrate, 158. oxalate, 608. oxalurate, 629. purpurate, 628. Ammonium sulphate, 159. sulphide, 157. sulphocyanate, 482. sulphydrate, 157. theory of, 156. Ampere's theory, 40. Amygdalin, 657. Amyl alcohols, 524. chloride, 526. iodide, 626, nitrite, 526. oxide, 626. Amylenes, 674. bromides, 575. polymerides of, 575. Amyloid, 666, 773. Anatase, 421. Anhydrite, 328. Anil, 695. Anilides, 684. Aniline, 683. colors, 691. hydrochloride, 684. oxalate, 684. salts, 684. Anisic aldehyde, 712. compounds, 711. Anisol, 680. Anorthite, 384. Anthracene, 741. Anthracite, 212. Anthrapurpurin, 745. Anthraquinone, 742. Antifebrin, 684. Antimonio-potassium tartrate, 618. Antimony, 195. antimonate, 198. oxide, 197. pentachloride, 197. pentasulphide, 200. pentoxide, 199. trichloride, 196. trioxide, 198. trisulphide, 199. Antipyrine, 676, 770. Apomorphine, 765. Aposepedine, 604. Aquamarine, 333. ^ Aqua-regia, 170. Arabinose, 636, 654. Arbutin 657. Argentite, 320. Argon, 77. in air, 73* Argyrodite, 422. INDEX. 795 Aromatic compounds, 662. isomerism of, 665. Arragonite, 327. Arrhenius's theory, 276. Arsenic, 186. chloride, 189. disulphide, 193. fluoride, 189. pentasulphide, 194. pentoxide, 192. tests for, 190. trioxide, 189. trisulphide, 193, Arsine, 188. Arsines, 466. Aseptol, 683. Asparagin, 613. Assay, dry, 322. wet, 323. Assimilation, 782. Atmospheric air, 73. Atomic heats, 44. theory, 37. weights, 49. determination of, 41-47. Atomicity, theory of, 232-234, 291. Atoms, 23, 36. Atropine, 755. Auric chloride, 375. Aurin, 692. Aurous chloride, 375. Australene, 720. Avogadro's law, 42. Azobenzene, 663, 675. Azoxybenzene, 675. Azure blue, 401. Azurite, 361. Barium, 331. carbonate, 333. chloride, 332. dioxide, 332. hydrate, 332L nitrate, 332. oxide, 331. sulphate, 333. sulphide, 332. tests, 333. Bassorin, 654. Beer, 649. Benzalchloride, 700. Benzalazine, 704. Benzaldehyde, 703. Benzamide, 705, 707. Benzene, 671. Benzene addition compounds, 672. azoderivatives, 674. azoxy-, 675. constitution of, 667. dibromo-, 673. dichloro-, 673. dinitro-, 674. hexachloro-, 673. hydrazo-, 675. monobromo-, 673. monochloro-, 673. nitro-, 674. substitution compounds, 672. sulphone, 677. Benzidine, 675. Benzil, 705. Benzine, 520. Benzoin, 704. Benzol, 671. Benzonitrile, 677. Benzophenone, 707. Benzoyl chloride, 705. Benzotrichloride, 700. Benzyl alcohol, 702. chloride, 699, 703. Benzylamine, 703. Berthollet's laws, 277. Beryl, 333. Beryllium, 333. Bessemer process, 395. Bilirubin, 786. Biliverdin, 787. Binary compounds, 50. Bismuth, 377. chloride, 378. nitrate, 379. oxide, 378. tests, 379. Bituminous coal, 212. Biuret, 481. Bleaching, chlorine, 125. -liquids, 133. -powder, 123, 328. sulphur dioxide, 110. Blende, 337. Blue vitriol, 359. Boiling-points, determination of, 445. Bone-oil, 747. Borax, 313. Boron, 201. chloride, 202. crystallized, 202. fluoride, 203. oxide, 203. 796 INDEX. Boro-potassium tartrate, 619. Brauite, 405. Bromine, 137. oxides, 139. Bromobenzenes, 673. Bromoform, 490. Bromopicrin, 492. Bronze, 361. Brookite, 421. Brucine, 762. Bunsen burner, 231. Butaldehyde, 563. Butane, 498, 519. Butyl alcohols, 522. Butylenes, 573. Butyrone, 663. Cacodyl, 496. Cadaverine, 584. Cadmics, 342. Cadmium, 342. iodide, 342. oxide, 342. sulphate, 343. sulphide, 342. Caesium, 315. CaflFeidine, 769. Caffeine, 768. Calamine, 337. Calcite, 327. Calcium, 324. butyrate, 563. carbide, 326. carbonate, 327. chloride, 326. -freezing mixture, 271. hydrate, 325. hypochlorite, 329. lactate, 600. nitrate, 327. oxide, 325. saccharate, 643. sulphate, 328. tests, 330. Calomel, 366. Camphenes, 659. Camphor, 724. artificial, 722. Borneo, 726. mint, 726. thyme, 718. Camphorone, 728. Camphoroxime, 725. Camphors, 718. Candles, 592. Caoutchouc, 723. Caramel, 643. Carbamide, 474, 477. Carbimide, 475. Carbinol, 522. Carbon, 210. compounds, 429. classification of, 435. saturated, 430. dioxide, 219. in air, 77, 79. liquefaction, 222. disulphide, 225. estimation of, 436. monoxide, 217. compounds of, 473. oxysulphide, 226. sesquichloride, 571. tetrachloride, 489, 492. Carbonates, 287. tests for, 289. Carbonyl chloride, 219. Carborundum, 216. Carbylamines, 493, 514. Carvacrol, 718. Casein, 781. Cassiterite, 416, 418. Catechol, 693. Cedrene, 723. Celestite, 331. Celluloid, 657. Celluloses, 635, 654. Cement, 326. copper, 355. Cerite, 385. Cerium, 385. Cerusite, 352. Ceryl alcohol, 528. Cetyl alcohol, 528, Chalk, 327. Chalkosine, 354. Charcoal, 212. absorbent properties of, 214. animal, 214. reduction by, 215. wood, 212. Chemical energy, 240, Chloral, 556. Chloranile, 695. Chlorethylene, 570. Chlorhydrins, 587. Chlorides, 258. monatomic, 448. of acid radicals, 454, of sulphur, 136, INDEX. 797 Chlorine, 122. analogies, with Br and I, 145, bleaching by, 125. disinfection by, 125. group, analogies of, 145. liquefaction, 124. manufacture of, 123. oxides, 131. peroxide, 134. Chlorobenzenes, 673. Chloroform, 489. Chloropicrin, 491. Cholesterin, 784. Choline, 784. Chondrin, 782. Chromates, 412. Chrome alum, 412. iron, 410. yellow, 353. Chromium, 410. chlorides, 413. oxides, 411. oxychloride, 413. Cinchona bark, 758. Cinchonicine, 758. Cinchonidine, 758. Cinchonine, 761. Cineol, 726. Cinnabar, 362, 365. Cinnamic alcohol, 731. aldehyde, 730. Clay, 384. Cleveite, 410. Coal, 212. Cobalt, 401. chloride, 402. glance, 401. oxides, 401. sulphate, 402. tests, 402. Cocaine, 757. Codeine, 766. Coefficient of solubility, 67. Cohesion, 21, 25. Coke, 212. Colcothar, 397. Collidines, 750. Collodion, 657. Columbite, 371. Combination, 18, 23. laws of, 33, 37. Combustion, slow, 68. Conhydrine, 754. Coniferin, 659. Conine, 753. Copper, 354. acetates, 549. alloys, 358, 361. atomicity of, 370. carbonates, 361. chlorides, 359. formate, 544. glance, 358. oxides, 358. pyrites, 354. sulphates, 360. sulphides, 358. tests, 362. Coralline red, 692. Corrosive sublimate, 367. Corundum, 381. Cotarnine, 767. Creatine, 632. Creatinine, 632. Cresols, 700. Critical temperature, 61. Crocoite, 410. Crotonaldehyde, 567. Cryolite, 312. Crypton, 80. Crystallization, water of, 270. Cubebene, 723. Cumene, 717. Cuminol, 717. Cupellation, 318, 322. Cyamelide, 474. Cyanamide, 471. Cyanides, 467. Cyanobenzene, 677. Cyanogen, 463. bromide, 471. chlorides, 470. compounds, 462. iodide, 471. Cymene, 717. Dalton's laws, 33, 36. Dambonite, 729. Daturine, 756. Decomposition, 23, 27, 30. Definite proportions, law of, 31. Dew-point, 85. Dextrin, 651. Diacetyl, 557. Diamines, 461. Diamond, 211. combustion of, 220. Diastase, 649, 652. Diazoacids, 605. Diazoamidobenzene, 687. 67* 798 INDEX. Diazobenzene compounds, 686. Diazocompounds, 664. Dibenzoyl, 705. Dichlorethane, 607. Dichlorether, 505. Dichlorethylene, 570. Dichlorhydrins, 688. Didymium, 385. Diethyl, 498. Diethylamine, 535. Diethylphosphine, 536. Digitalin, 659. Dihydrocymene, 723. Diketones, 454. Dimethyl, 498. Dimethylacetal, 583. Dimethylamine, 534. Dimethyl-aniline, 685. Dimethylarsine, 496. Dimethylbenzenes, 714. Dimethylethylenes, 673. Dimorphism, 100. Dinitrobenzenes, 674. Dioxindol, 737. Dioxybenzenes, 692. Diphenyl, 672, 673. Diphenylamine, 685. blue, 686. Diphenylketone, 707. Dipyridine, 749. Disspciation, 86. Disulphones, 582. Dobereiner's lamp, 500. Dolomite, 336. Ductility, 245. Dulcitol, 634. Dutch liquid, 570.. Ecgonine, 758. Edisonite, 421. Efflorescence, 2701, Ekasilicon, 422. Elaidin, 592. Electrolysis, 274. of water, 80. laws of, 276. Elementary analysis, 436. Elements, 20, 23. table of, 49. Emerald, 333. Emery, 381. Emulsin, 658. Endothermic compounds^ 242. Eosin, 716. Epichlorhydrin, 589. Epsom salt, 336. Equivalence, 234. Erbium. 388. Erythritol, 633. Esculin, 657. Ethane, 498. Ether, 602. acetoacetic, 551. Kay's, 489. cenanthylic, 648. pelargonic, 648. Etherification, theory of, 503. Ethers, compound, 452, 498. cyanuric, 517. nitrous, 510. phosphoric, 514. simple, 497. Ethyl acetate, 550. acetoacetate, 551. borate, 514. bromide, 507. carbamate, 515. carbonate, 516. carbylamine, 509. chloride, 506. chlorocarbonate, 516. cyanate, 508. cyanide, 608. cyanurate, 517. diazoacetate, 605. hydroxide, 498. iodide, 506. isocyanate, 516. malonate, 609. nitrate, 511. nitrite, 609. orthocarbonate, 515. oxalate, 608. oxide, 602. phosphates, 514. silicates, 514. sulphates, 512. sulphide, 505. sulphite, 512. sulphurous chloride, 513. sulphydrate, 606. Ethylallyl, 676. Ethylamine, 634. hydrochloride, 534. Ethylates, 601. Ethylene, 668. acetates, 580. bromhydrate, 680. bromide, 670. chlorhydrate, 579. INDEX. 799 Ethylene, chloride, 570. chloro-derivatives, 570. diamines, 584. hydrate, 578. iodide, 570. nitrates, 580. oxide, 581. bases from, 582. Ethylethylene, 574. Ethylhydrazine, 532. Ethylidene chloride, 554. cyanide, 612. glycol, 582. Ethyl-phenyl oxide, 680. Ethylphosphines, 536. Ethylvinyl, 574. Eudiometric synthesis, 82. Euxenite, 371, 389, 409. Exothermic compounds, 242. Faraday's law, 276. Fats, natural, 590. Fatty series, 662. Feldspar, 384. Fenchene, 722. Fenchone, 726. Fenchoneoxime, 726. Fergusonite, 371. Fermentation, 646. acetic, 547. alcoholic, 646. butyric, 647. lactic, 597, 647. viscous, 648. Ferric acetate, 550. chloride, 398. ferrocyanide, 469. oxide, 397. sulphate, 400. Ferricyanides, 469. Ferrocyanides, 468. Ferro-potassium tartrate, 619. Ferrosoferric oxide, 397. Ferrous carbonate, 400. chloride, 398. ferricyanide, 470. lactate, 600. oxide, 396. sulphate, 399. Fibrins, 773, 776. Fire, 68. -damp, 484. Flame, 68, 228. Flavopurpurin, 745. Fluorescein, 715. Fluorine, 146. Formaldehyde, 545. Formates, 544. Formonitrile, 466, 544. Formose, 545. Formula, chemical, 48. Formulae, constitutional, empirical, rational, 452. Freezing mixture, 271. ii^o/ing-points, determination of, 444. Fructose, 639. Fuchsine, 689. Fulminates, 495. Furfurane, 745. Furfurol, 745. Fusel oil, 525. Fusible metal, 248. Gadolinite, 388. Galactose, 639. Galena, 343, 349. Gallium, 386. Galvanized iron, 339. Garnet, 384. Garnierite, 403. Gases, molecular volume of, 42„ Gasoline, 520. Gay-Lussac's laws, 37. Gelatin, 781. Gelatinoids, 774. Germanium, 422. German silver, 361. Gilding, 376. Glass, 210. etching on, 147. soluble, 209. Glauber's salt, 309. Globulins, 773, 776. Glucinum, 333. chloride, 334. oxide, 334. Glucose, 637. tests for, 638. Glucosides, 657. Gluten, 650. Glycerides, 690. Glycerol, 586. ethers of, 587, 590„ Glycide, 689. Glycine, 602. Glycocoll, 602. Glycocyamidine, 631. Glycocyamine, 631. Glycogen, 653. 800 INDEX. Glycol, 678. ethers of, 579. GlycoUide, 595. Glycols, 460, 577. propylene, 586. Glycolyl urea, 630. Glyoxal, 596. Glyoxime, 596. Goethite, 397. Gold, 373. assay, 376. chlorides, 376. oxides, 375. Goulard's solution, 549. Graphite, 211. Guaiacol, 693. Guanidine, 472. derivatives of, 63L Guanine, 788. Gum arabic, 654. tragacanth, 654. Gums, 653. Gun-cotton, 656. Gunpowder, 302. nitro, 657. Gutta-percha, 723. Gypsum, 328. Hardness, scale of, 789. Hausmannite, 405. Heavy spar, 333. Helium, 410. Hematin, 780. Hematite, 390. Hematoidin, 780. Hemimellithene, 717. Hemoglobin, 778. Hexachlorethane, 507. Hexahydrobenzene, 672. Hexamethylbenzene, 664. Holmium, 389. Homologous bodies, 435. Horn silver, 320. Hydantoin, 630. Hydrates, 52, 53. Hydrazine, 160. Hydrazines, 532. aromatic, 676. Hydrazobenzene, 675. Hydrocarbons, C^R^^+'^y 517. C"H2^ 571. C°H2n-2, 575. formation of, 433. structure, 434. Hydrocinchonine, 761. Hydrogen, 58. absorption by palladium, 61, 64, antimonide, 196. arsenide, 188. carbide in air, 80. chemical properties, 61. dioxide, 95. estimation of, 436. liquefaction, 60. occlusion of, 61. persulphide, 105. phosphide, 175. physical properties, 60. preparation, 59. silicide, 205. sulphide, 102. Hydrogenium, 61. Hydroquinone, 693. Hydroxides, 53, 87. Hydroxyethylene amines, 582. Hydroxyl, 116. Hydroxylamine, 159. Hyoscine, 756. Hyoscyamine, 756. Hypnone, 707. Hypochlorous anhydride, 132, Hypoxanthine, 788. Idoerase, 384. Igasurine, 762. Indican, 733. Indiglucin, 733. Indigo, 732. carmine, 733, syntheses of, 734. white, 735. Indium, 387. Indol, 737. Indophenin, 736. Indoxyl, 734. Ink, 401, 660. sympathetic, 402. Inosite, 729. Inulin, 653. Iodine, 140. oxides, 144. test for, 142. Iodoform, 490. lodol, 747. Iridium, 428. Iron, 389. carbonate, 400. cast, 394. chlorides, 398. lactate, 600. INDEX. 801 Iron oxides, 396. passive, 169, 394. soft, 393. sulphates, 399. sulphides, 398. tests, 400, 401. Isatin, 736. Is ethionamide, 585. Isomaltose, 645. Isomerism, 445. of position, 668. of the benzene derivatii Isomorphism, 47, 267. Isoprene, 720, 723. Isopropyl alcohol, 522. iodide, 522. Isopropylbenzene, 717. Isopropylethylene, 575. Isoquinoline, 751. Isuret, 480. Jet, 212. Kairine, 770. Kaolin, 384. Kay's ether, 489. Kerosene, 520. Ketones, 453. Kieserite, 336. Kupfemickel, 403. Labradorite, 384. Lactamide, 600. Lactates, 600. Lactose, 644. Lamp-bla<3k, 213. Lanthanum, 385. Lead, 343. acetates, 549. argentiferous, 345. atomicity of, 343. carbonate, 352. chloride, 350. chromate, 353. dioxide, 348. formate, 544, iodide, 350. monoxide, 347. nitrate, 351. red oxide, 348. sulphate. 351. sulphide, 349. tests, 353. white, 353. Lecithine, 582, 784. 665. Lepidolite, 315. Leucine, 565, 604. Leucite, 384. Leucoline, 750. Leucorosaniline, 690, Levulosan, 640. Levulose, 639. Lignite, 212. Lime, 325. chlorinated, 328. hydraulic, 325. Liquation, 248. Litharge, 346, 347. Lithium, 315. Lithographic stone, 327, Lunar caustic, 322. Lutidines, 750. Lyons blue, 691. Magenta, 689. Magnesite, 336. Magnesium, 334. carbonate, 336. chloride, 336. citrate, 622. oxide, 335, sulphate, 337. tests, 337. Magnetite, 397. Malachite, 361. green, 685, 700. Malamide, 613. Malleability, 245. Malonyl urea, 627. Maltose, 645. Manganese, 405. carbonate, 408. dioxide, 406. oxides. 405. steel, 405. sulphate, 407. tests, 408. Mannitan, 634. Mannitol, 634. Mannose, 686. Marble, 327. Marcasite, 398. Marl, 384. Marsh gas, 484. Marsh's apparatus, 191. Massicot, 347. Matches, 175. Meconine, 767, Melamine, 472. Melezitose. 646. 802 INDEX. Melitose, 645. Melting-points, determination of, 444. Mendelejeff's periodic theory, 294. Menthene, 727. Menthol, 726. Mercaptan, 605. Mercur-ethyl, 539. Mercuric chloride, 367. iodide, 368. Mercur-methyl, 639. Mereurous chloride, 366. iodide, 368. Mercury, 362. atomicity of, 370. cyanide, 467. fulminate, 495. nitrates, 369. oxides, 364. sulphates, 369. sulphide, 364. tests, 370. Mesitylene, 716= Mesoxalyl-urea, 626. Metacetone, 644. Metaldehyde, 555. Metallic carbonates, 287. chlorides, 258. hydrates, 260, 256. nitrates, 283. oxides, 250. chemical properties of, 253. classification of, 251. sulphates, 286. sulphides, 267. Metals, 243. classification of, 289, 296. diatomic, 290. general properties of, 243. monatomic, 290. natural state and extraction, 247. tetratomic, 293. Metamerism, 446. Metastyrolene, 730. Metaxylene, 714. Methane, 484. Methylacetylene, 576. Methylal, 488. Methylamine, 533. hydrochloride, 533. Methylaniline, 685. Methylarsines, 497. Metbylbenzene, 697. Methyl bromide, 487. Methyl carbylamine, 493, chloride, 487. compounds, 483. cyanide, 492. cyanurate, 517. hydroxide, 485. iodide, 487. nitrate, 493o nitrite, 493. oxalate, 486, 608. oxide, 487. salicylate, 710. Methylchloracetol, 558. Methylene chloride, 488. diacetate, 489. diethylate, 488. iodide, 488. Methylethyl oxide, 502. Methylglycocoll, 603. Methylmorphine, 766. Methylphenyl ketone, 707. Methylphenyl oxide, 680. Mica, 384. Millerite, 403. Millon's reagent, 771. Mineral waters, 92. Minium, 348. Molecular structures, 237. weights, determination of, 41 440. Molecules, 21. Molybdenite, 414. Molybdenum, 414. Monazite, 385, 423. Monochlorether, 505, Monochlorhydrin, 587. Morphine, 764. Mortar, 326. Mucilages, 653. Murexide, 625, 628. Mycose, 645. Myosin, 777. Naphtha, 620. Naphthalene, 671, 738 Naphthols, 740. Naphthylamines, 741.. Narceine, 764. Narcotine, 767. Neurine, 582, 784. Neodymium, 385. Nickel, 403. chloride, 404. glance, 40.3. oxides, 403. INDEX. 803 Nickel plating, 403. steel, 403. sulphate, 404. tests, 404. Nicotine, 754. Night green, 691. Niobium, 371. chlorides, 372. oxides, 372. Nitrates, 283. tests for, 284. Nitric anhydride, 167. oxide, 163. Nitrobenzene, 674. Nitroethane, 509. Nitroferrocyanides, 470. Nitroform, 491. Nitrogen, 148. chloride, 154. estimation of, 439. group of elements, 200. hydrogen, compounds of, 149. in air, 73-77. iodide, 155. monoxide, 161. oxides, 160. pentoxide, 167. peroxide, 165. trioxide, 164. Nitroglycerin, 590. Nitromethane, 493. Nitronaphthalene, 738. Nitrophenols, 680. Nitro-powders, 657. Nitroso-amines, 685. Nitrosodimethylaniline, 685. Nitrosomethylaniline, 685. Nitrosophenol, 681. Nitrosyl-chloride, 171. Nitrothiophene, 746. Nitrotoluenes, 700. Nitryl, chloride and bromide, 166. Nomenclature, 47. Nornarcotine, 767. Notation, 47-57. Occlusion, 61. (Enanthic ether, 648. Oils, essentia], 718. fatty and drying, 592. Olein, 591. Oolitic iron, 389. Opium, 763. Orangeite, 423. Orcein, 701. Orcinol, 701. Organo-metallic compounds, 456, 539. Orpiment, 193. Orthite, 389. Orthoxylene, 714. Osmium, 428. Oxalates, 606. Oxalyl-urea, 629. Oxamide, 608. Oxides, 50, 251. acid, 251. antimonic, 199. antimonous, 198. arsenic, 192. arsenious, 189. basic, 251. boric, 204. chlorocarbonic, 219. chlorous, 133. cupric, 358. cuprous, 357. ferric, 397. ferroso-ferric, 397. ferrous, 396. hypochlorous, 132. manganic, 405. man^anoso-manganic, 405. mercuric, 364. mercurous, 364. ■ metallic, 250, classification of, 251. molybdic, 414, niobic, 372. nitric, 163. nitrous, 161. persulphuric, 120. phosphoric, 183. plumbic, 347. plumboso-plumbic, 348. saline, 251. silicic, 208. singular, 251. stannic, 418. stannous, 418. sulphuric, 110. sulphurous, 107. tantalic, 372. vanadic, 370. Oxindol, 737. Oxygen, 64. in air, 73. liquefaction, 67. manufacture, 66. preparation, 65. 804 INDEX. Oxygen properties, 66. Oxyhemoglobin, 779. Oxyhydrogen blowpipe, 69. Oxyphenols, 693. Ozone, 69, composition, 72. formation, 70. in air, 80. properties, 71. tests for, 69. Palladium, 427. Palmitin, 591. Papaverine, 764. Paracetphenetidine, 769. Paraeyanogen, 463. Paraffin, 620. Paraldehyde, 555. Pararosaniline, 690. Paraxylene, 714. Parchment paper, 656. Paris violet, 691. Pectic matters, 662. Pelargonic ether, 648. Pentachlorethane, 507. Pentamethylene diamine, 584. Pentenes, 674. Pepsin, 778. Peptones, 773. Perchloraldehyde, 505. Perchlorether, 506. Perkins's reaction, 731, Perseitol, 635. Petroleum, 520. ether, 520. Phellandrene, 723. Phenacetin, 770. Phenanthrene, 742. Phenetidines, 769. Phenetol, 680. Phenol, 677. ethers of, 680. Phenols, 664. Phenyl cyanide, 677. nitro-, 680. nitroso-, 680. oxide, 680. Phenylacetylene, 732. Phenylamine, 683. Phenylhydrazine, 554, 676. Phenylhydrazones, 554. Phenyllactosazone, 645. Phenylmaltosazone. 645. Phenylmethane, 697. Phloretin, 659. Phloridzin, 659. Phloroglucinol, 696. Phosgene gas, 219. Phosphine, 179. Phosphines, 456. Phosphonium, 177. Phosphoric anhydride, 183. ethers, 514. Phosphorus, 171. amorphous, 173. bromide, 179. iodide, 180. oxides, 180. oxychloride, 179. pentachloride, 178. pentoxide, 183. poisonous properties, 174. sulphides, 186. sulphochloride, 179. trichloride, 178. Phthaleins, 715. Phthalic anhydride, 715. Picolines, 750. Pinacolin, 558. Pinacone, 558, 578. Piperidine, 748, 750. Piperine, 765. Pitchblende, 409, Plaster of Paris, 328. Platinum, 424. black, 62, 425. chlorides, 426. sponge, 425. Plumbago, 211. Polymerism, 445. Populin, 658. Porcelain, 384. Potash, caustic, 288. Potassamide, 155. Potassium, 297. acetate, 548. acid carbonate, 305. acid sulphate, 303. amide, 155. bromide, 301. carbonate, 304. chlorate, 303. chloride, 300. chromate, 412. cyanate, 475. cyanide, 467. dichromate, 412. ethylate, 501. ferricyanide, 469. ferrocyanide, 468. INDEX. 805 Potassium hydroxide, 298. iodide, 300. isocyanate, 474. manganate, 406. methylate, 486. nitrate, .301. oxalates, 607, 608. oxides, 298. perchlorate, 304. permanganate, 407. pierate, 682. sulphate, 303. sulphides, 299. sulphocyanate, 482. tartrates, 618. tests, 305. thiocyanate, 482. Pottery, 384. lead glazing, 349. Praseodymium, 386. Propenyl tribromide, 589. trinitrate, 590. Proprionitrile, 508. Propyl alcohol, 522. iodide, 522. Propylene glycols, 586. Propylenes, 573. Propylethylene, 675. Proteids, 770. Prussian blue, 401, 469. Pseudocumene, 717. Purine, 788. Purple of Cassius, 376. Purpurin, 744. Putrescine, 584. Pyridic bases, 747. Pyridine, 749. Pyrite, 398. Pyrocatechin, 693. Pyrochlorite, 371. Pyrogallol, 713. Pyrolusite, 406. Pyroxylin, 656. Pyrrol, 747. Pyrrolidine, 747. Pyrroline, 747. Quercite, 729. Quercitrin, 657. Quinaidine, 751. Quinhydrone, 694. Quinicine, 768. Quinidine, 768. Quinine, 769. Quinoline, 760. Quinone, 694. dioxime, 696. monoxime, 681, 696. Radicals, diatomic, 460. monatomic, 448, 468. polyatomic, 469. Rare earths, 388. Raffinose, 645. Realgar, 193. Red precipitate, 364. Resorcinol, 693. Respiration, 69, 783. Rhamnose, 636. Rhodium, 427. Richter's laws, 265. Rochelle salt, 618. Rosaniline, 689. colors, 691. Rubidium, 315. Ruby, 381. Ruthenium, 427. Rutile, 421. Saccharin, 638. Saccharose, 640. Safety-lamp, 229. Salicin, 658. Salicyl aldehyde, 708. Saligeninol, 658, 708. Saliretin, 658. Saltpetre, 302. Chili, 302. Salts, 53, 262. action of acids, 277. bases, 279. electricity, 274. heat, 273. metals, 276. salts, 280, 282. water, 268. etflorescent, 270. neutral, acid and basic, 264. Samarium, 389. Samarskite, 389. Sandmeyer's reaction, 687. Saponification, 593. Sapphire, 381. Sarcine, 788. Sarcosine, 603, 632. Satin spar, 328. Saturated hydrocarbons, 517. Scandium, 389. Scheelite, 414. Selenium, 121. Silica, 208. 806 INDEX. I'' Silica, soluble, 210. Silicon, 204. chloride, 206. crystallized, 205. fluoride, 207. oxide, 208. Silicon-ethy], 538. Silver, 317. acetate, 550. assay, 322. chloride, 320. cupellation, 318. fulminate, 495. fulminating, 320. iodide, 321. metallurgy of, 317. nitrate, 321. oxide, 320. Patio process, 318. spitting of, 319. sulphide, 320. tests, 322. AVashoe process, 318. Silvering, 322. Skatol, 738. Slow combustion, 68. Smalt, 401. Smaltite, 401. Smithsonite, 337. Soap, 593. Sodio-potassium tartrate, 616. Sodium, 306. acetate, 549. acid carbonate, 313. acid sulphate, 310. borate, 313. carbonate, 310. chloride, 308. dioxide, 307. ethylate, 501. hydracrylate, 601. hydrate, 307. hydrazoate, 160. hydrosulphite, 110. hyposulphite, 110. manufacture of, 306. Castner's process, 307. Deville's process, 306. Netto's process, 307. nitrofeiTOcyanide, 470. oxides, 307. phosphates, 313. sulphate, 309. sulphide, 308. sulphydrate, 308. Sodium tests, 314. thiosulphate, 119. tungstate, 415. uranate, 409. Solubility, coefficient of, 67. Solution, 89, 268. saturated, 269. •Sorbinose, 640. Sorbitol, 634. Spathic iron, 390, 400. Specific heat, 44. Spectrum analysis, 315. Spermaceti, 528. Sperrylite, 424. Sphalerite, 337. Spiegeleisen, 394. Spodumene, 315. Stannethyls, 540. Stannodiethyl, 540. Stannotetrethyl, 541. Starch, 650. soluble, 652. mononitrate, 652. Starches, 635. Stassfurth salt, 306. Stearin, 591. candles, 592. Stearoptenes, 718. Steel, 394. Stereoisomerism, 614. Stibine, 196. Stibines, 456. Stolzite, 414. Strontianite, 331. Strontium, 330. carbonate, 331. chloride, 331. nitrate, 331. saccharate, 644. Strychnine, 762. Styracin, 731. Styroline, 730. Succinic anhydride, 611o Succinyl chloride, 611. Sugar, cane, 640. fruit, 639. grape, 637. inverted, 643. milk, 644. Sugars, 635. Sugar of lead, 649. Sulphates, 286. tests for, 287. Sulphides, metallic, 257. Sulphobenzide, 677. INDEX. m Sulphocarbamide, 473. Sulphonal, 582. Sulphonic acids, 664. Sulpho-urea, 482, 483. Sulphur, 98. analogies with oxygen, 102. chlorides, 136. dimorphism of, 100. dioxide, 106, 107. oxygen acids, 106. peroxide, 106, 120. sesquioxide, 106, 107. soft, 100. trioxide, 106, 110. Sulphuric anhydi-ide. 111. Sulphurous anhydride, 107. Sulphuryl chloride, 110, 116. Supersaturation, 271. Synaptase, 658. Syntonin, 777. Tannin, 659. Tantalite, 371. Tantalum, 371. chloride, 372. oxide, 372. Tartar-emetic, 618. Tartaric anhydride, 617. Tartrates, 618. Tartronyl-urea, 627. Taurine, 585. Tautomerism, 697. Tellurium, 121. Terebene, 721. Terpenes, 718. Terpin, 721. hydrate, 721. Terpinene, 723. Terpinolene, 723. Tetrachlorethane, 507. Tetrachlorether, 505. Tetrachlorethylene, 571. Tetramethylammonium, 534. Tetramethylene diamine, 584. Tetrethylammonium, 535. Thalline, 770. Thallium, 354. Thebaine, 764. Theine, 768. Theobromine, 768. Thermo-chemistry, 240. Thiophene, 672, 746. Thiophtene, 746. Thiotolene, 746. Thioxene, 746. Thorite, 389. Thorium, 423. Thulium, 389. Thymol, 718. Tin, 416. dichloride, 419. oxides, 418. sulphides, 419. tests, 421. tetrachloride, 420. Tinctures, 500. Tinplate, 417. Titanium, 421. dioxide, 421. Toluene, 697. chloro- 699. nitro- 700. Toluidines, 701. Topaz, 381. Trehalose, 645. Tribenzylamine, 703. Tribromhydrin, 589. Trichloraldehyde, 556. Trichlorethane, 507. Trichlorhydrin, 588. Triethylamine, 535. Triethylphosphine, 537. Trimethylamine, 534. Trimethylbenzenes, 716,, Trimethylcarbinol, 523. Trimethylene, 571. Trimethylethylene, 572. Trimethylrosaniline, 691. Trinitroacetonitrile, 493. Trinitroglycerol, 590. Trinitrophenol, 681. Trioxymethylene, 545. Triphenylrosaniline, 691. Triphyline, 315. Tropaeolines, 689. Trypsin, 778. Tungsten, 415. Tungstic oxide, 415. Turnbull's blue, 470. Turpentine, 720. Turpeth mineral, 370. Type metal, 196. chemical, 88. Tyrosine, 712, 772. Uranite, 409. Uranium, 409. chlorides, 410. oxides, 409. yellow, 409. BOH INDEX. Uranyl nitrate, 410. Urea, 477. Ureas, compound, 481. Ureides, 626. Urethane, 515, 516. Vanadinite, 370. Vanadium, 370. bronze, 371. Vanillin, 659. Verdigris, 550. Vermilion, 365. Vinegar, 545. Vitriol, blue, 360. green, 3'J9. white, 340. Water, 80. analysis, 81. charcoal filter for, 215. dissociation, 86. hard, 00. in air, 78. maximum density, 85. mineral, 92. acidulous or gaseous, 92. alkaline, 93. chalybeate, 93. saline, 94. sulphatic, 94. sulphur, 95. natural state of, 89. of crystallization, 270. properties of, 85, 86. reactions of, 87. soft, 90. solvent properties of, 89. synthesis of, 82. Wax, 528. Welsbach light, 423, 424. White vitriol, 340. lead. 352. precipitate, 367. Willemite, 337. Wine, 648. Witherite, 333. Wolfram, 414. Wood-spirit, 485. Wurtzite, 340. Xanthine, 787. Xylenes, 714. Xyloidin, 652. Xylose, 636, 654. Yeast, 590. Ytterbium, 389. Yttria, 388. Yttrium, 389. Yttrotantalite, 371. Zeolites, 384. Zinc, 337. chloride, 340. hydracrylate, 601. lactate, 600. oxide, 339. sulphate, 340. sulphide, 340. tests, 341. -ethyl, 539. -methyl, 589. Zircon, 422. Zirconium, 422. THE END. OCT 20 1900 I