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UNITED STATES OF AMERICA. 



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JUST PUBLISHED— Twelfth Edition 

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Locomotive Catechism 

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A CATECHISM 



Combustion of Coal 



AND THE 



PREVENTION OF SMOKE 



A PRACTICAL TREATISE 

FOR ENGINEERS, FIREMEN, AND OTHERS INTERESTED 

IN FUEL ECONOMY AND THE SUPPRESSION OF 

SMOKE FROM STATIONARY STEAM-BOILER 

FURNACES, AND FROM LOCOMOTIVES 



WILLIAM M. BARR, M.E. 

Author of " Boilers and Furnaces," etc. 



WITH EIGHTY-FIVE ILLUSTRATIONS 



NEW YORK 

NORMAN W. HENLEY & COMPANY 

132 Nassau Street 

1900 



72555 



jl-iOi%J7oi Ctmjj^J ^f^>^ 



I NOV 3 1900 

C^yf^ht entry 

S£C(>ND copy. 

0<rfHmr«rf to 



Copyrighted, 1900, 

BY 

WILLIAM M. BARR 



0-6777 r-tV. 



PREFACE. 



This edition of combustion of coal is so entirely differ- 
ent from my former treatise that it is to all intents a new 
book. Much of the original material has been retained, 
but worked over and presented in new form. The aim of 
the writer is sufficiently indicated by the title page, in 
which it will be seen that the subject has special refer- 
ence to the economical and smokeless combustion of or- 
dinary fuels in the generation of steam. 

The best book for practical and busy men is the one 
which is nearest complete in itself. In view of this fact, 
the writer has included in these pages much collateral 
information and useful data, not always bearing directly 
upon furnace combustion, in the belief that such informa- 
tion would be helpful and gladly received by those wishing 
to acquire a broader knowledge, including all the facts 
relating to the subject of combustion in general. 

Unavoidable repetitions occur in this book, as it was 
thought improbable that it would in all cases be studied 
systematically from end to end, in which case the subject- 
matter might have been shortened by means of cross refer- 
ences. In view of the probability that this book will be 
commonly used as its contained information is required, 
which will then be sought out by means of the index, 
it was thought best to make each answer as complete as 
possible, and without reference to the fact that the same 
data occurred elsewhere in this volume. 

There has been a somewhat unlooked-for demand for 



6 PREFACE. 

such a book as this, mainly from locomotive engineers and 
firemen, by reason of the insistance on the part of the man- 
agement of the more important railway lines that their 
locomotive engineers and firemen shall, among other re- 
quirements, undergo a satisfactory examination in the prin- 
ciples of the combustion of coal and of the laws governing 
the prevention of smoke ; this, with a view to securing a 
better or more rational method of firing, as well as leading 
up to the abatement of the smoke nuisance, which in many 
localities has become almost unbearable. For this pur- 
pose my former treatise was wanting in practical detail, 
and is a reason for a new presentation and restatement of 
this important subject. 

The publishers have had marked success in the several 
catechisms issued from their press, and it was their desire 
that this book should conform in size and method of pres- 
entation with their other publications. But aside from 
this, no apology is needed, for no form of presentation is 
so popular with practical and busy men as the simple one 
of question and answer. 

The questions are intended to cover every detail relating 
to the economic combustion of such fuels as are employed 
in steam engineering. The answers are, so far as the 
writer is able to prepare them, scientifically accurate. 
The authorities quoted in my former treatise have been 
used in this, and in addition thereto free use has been made 
of the several excellent papers by Professor Thorpe, on 
fuels, heat, combustion, etc. Acknowledgment is also 
made of materials selected from the writings of such 
authorities as Hoadley, Snow, Kent, Bell, Thurston, Sin- 
clair, Barrus, Carpenter, and others. 

William M. Barr. 

New York, November, 1900. 



CONTENTS. 



7—8 



I.— Fuels, . . . . 

II. — Some Elementary Data, . 
III.— The Atmosphere, 
IV. — Combustion, .... 
V. — Products of Combustion, . 
VI. — Heat Developed by Combustion, 
VII.— Fuel Analysis, .... 
VIII. — Heating Power of Fuels, . 
IX. — Steam Generation, . 
X. — Stationary Furnace Details, 
XI. — Locomotive Furnace Details, . 
XII. — Chimneys and Mechanical Draft, 
XIII. — Spontaneous Combustion, 



PA«K. 

9 

48 
68 

83 
103 
140 
160 
178 
201 

215 
249 

309 
330 



COMBUSTION OF COAL. 



CHAPTER I. 

FUEL. 

Q. What is meant by term fuel ? 

Fuel expresses in a word and in general terms any sub- 
stance which may be burned by means of atmospheric air, 
with sufficient rapidity to evolve heat capable of being 
applied to economic purposes. The economic value of any 
fuel will depend upon its heating power. The two ele- 
ments contributing this property to fuel are carbon and 
hydrogen. The more important varieties of fuel include 
wood, peat, lignite, coal, natural and producer gas, and 
petroleum. 

Q. Of what does fuel consist? 

All fuel consists of vegetable matter or the products 
of its alteration. The elementary constitution of fuel is 
consequently much the same, carbon, hydrogen, oxygen, 
nitrogen, and inorganic matter that constitutes the ash. 
The gradual process of woody tissue into anthracite is 
shown in the following analytical results in which the 
hydrogen and oxygen percentages are based on that of 
carbon : 



IO 



COMBUSTION OF COAL. 
Table i. — Composition of Fuel. 



Fuels. 



Wood 

Peat 

Lignite 

Bituminous coal 
Anthracite 



Carbon. 


Hydrogen. 


IOO 


I2.I8 


IOO 


9.85 


IOO 


8.37 


IOO 


6.12 


IOO 


2.84 



Oxygen. 



83.07 
55.67 
42.42 
21.23 
1.74 



The following table shows the chemical alterations in 
approximate percentages of carbon, hydrogen, and oxygen 
as occurring in the different fuels : 



Table 2. — Composition of Fuel. 



Fuels. 



Wood ......... 

Peat 

Lignite 

Bituminous 

Semi-anthracite 
Anthracite 



Carbon. 


Hydrogen. 


52.65 
60.44 
66.96 
76.18 


5.25 
5.96 

5-27 
5.64 


90.50 
92.85 


5.05 
3-96 



Oxygen. 

42.IO 
33-60 
27.76 
18.07 
4.40 

3-19 



Q. What is coal? 

Coal, as denned by Dr. Percy, is a solid stratified mineral 
substance, black or brown in color, and of such a nature 
that it can be economically burnt in furnaces or grates. 

Our acquaintance with the chemistry of coal is almost 
entirely confined to a knowledge of its ultimate composi- 
tion. We know it to be made up of variable proportions 
of carbon, hydrogen, oxygen, and nitrogen ; but there are 
reasons for believing that in bituminous coals there exist 
ready formed definite compounds, at all events, of hydro- 
gen and carbon. 

Besides these strictly organic ingredients coals contain 
varying amounts of what must be regarded as impurities 
in the shape of mineral matters, which constitute the ash, 



CLASSIFICATION OF COAL. I I 

and pyrites or bisulphide of iron. Sulphur in the free 
state is sometimes present in coal. 

Q. What is the commercial classification of coals ? 

The coals of the United States range in hardness from 
the dense anthracite through all gradations to the soft, 
easily crumbled lignite. The commercial classification 
separates them broadly into hard and soft coals, or into 
anthracite and bituminous coals. This classification in- 
cludes among the anthracite coals the semi or gaseous an- 
thracites. The bituminous coals include semi-bituminous, 
caking, non-caking, cannel, block, and other varieties, as 
well as all the gradations of lignite, a faulty classification, 
but one which works little or no inconvenience, because 
orders for bituminous coals are usually placed in open 
market designating whether intended for coke-making, 
gas-making, blacksmith and forge work, boiler furnaces, or 
other need of the customer ; large orders not infrequently 
specifying the locality if not the particular mines from 
which the coals are to be shipped. 

Q. What are the physical properties of the coals in 
Gruner's classification ? 

In Gruner's classification of coals the following physical 
properties predominate : 

1. Anthracite, or lean coals; burning with a short 
flame; having a black color, and a specific gravity of 1.33 
to 1.4. These coals form the transition to true anthracite. 
On coking they yield 82 to 90 per cent fritted or pulveru- 
lent coke, and 12 to 18 per cent of gas. Evaporative 
factor, 9 to 9.5. 

This coal adapted for domestic use. 

2. Caking coals (fat coals) burning with a short flame; 



12 COMBUSTION OF COAL. 

color, black, shining, often with lamellar structure. Spe- 
cific gravity, 1.30 to 1.35. Yields 74 to 82 per cent fairly 
hard coke, caked together very densely, and 12 to 15 per 
cent gases. Evaporative factor, 9.2 to 10. 

Adapted for coking and for heating steam boilers. 

3. Caking coals proper, or furnace coals. Burning with 
longer flame ; color, black, shining, lustre more marked ; 
these coals swell under the action of heat more than those 
of classes 1 and 2. Specific gravity, 1.30. Yields 68 to 
74 per cent caked fairly dense coke, and 13 to 16 per 
cent gases. Evaporative power, 8.4 to 9.2. 

Adapted for coking and smithy use. 

4. Caking coals, long flaming (gas coal). These coals 
burn with a long flame. Color, dark, high lustre. Coals 
hard and tough. Specific gravity, 1.28 to 1.30. Yields 
60 to 68 per cent caked but very friable coke and 17 to 
20 per cent gases. Evaporative factor, J .6 to 8.3. 

Adapted for gas manufacture and for reverbatory fur- 
naces. 

5. Dry coals, burning with a long flame. Color, in- 
tense black. Coals hard, break with conchoidal fracture 
(splint coal). Specific gravity, 1.25. Yields 50 to 60 per 
cent pulverulent coke and 20 per cent gas. Evaporative 
factor, 6.J to 7.5. 

Adapted for reverbatory furnaces. 

The ash-forming constituents of coal vary from 0.5 to 
30 per cent, averaging from 4 to 7 per cent in the best 
coals; 8 to 14 in medium; and upward of 14, with 0.5 to 
2 per cent of sulphur in the worst. 

Q. What is meant by evaporative factor as employed 
by Gruner in his classification of coals ? 

The evaporative factor, as employed by Gruner, means 



ANTHRACITE COAL. I 3 

the number of times its weight of water is evaporated by 
a unit weight of coal starting at ioo° C, or 21 2° F. 

Q. What is anthracite coal? 

Anthracite is the most rich in carbon, greatest in dens- 
ity, and hardest of all varieties of coal. Typical anthracite 
coals contain : 

Carbon 90 to 95 per cent. 

Hydrogen ... 1 to 3 

Oxygen and nitrogen 1 to 3 " 

Moisture 1 to 2 " 

Ashes 3 to 5 " 

The best varieties of anthracite coal are slow to ignite, 
conduct heat badly, burn at a high temperature, radiate an 
intense warmth, and once ignited are difficult to quench. 
Generating almost no water during its combustion, anthra- 
cite coal powerfully desiccates the atmosphere of an apart- 
ment in which it is burning. Anthracite coals occur 
principally in Pennsylvania. 

J. P. Lesley states that anthracite is not an original 
variety of coal, but a modification of the same beds which 
remain bituminous in other parts of the region. Anthra- 
cite beds, therefore, are not separate deposits in another 
sea, nor coal measures in another area, nor interpolations 
among bituminous coal, but the bituminous beds them- 
selves altered into a natural coke, from which the volatile 
bituminous oils and gases have been driven off. 

Q. What is the commercial classification of anthracite 
coal ? 

The larger sizes are known as lump, steamboat, egg } and 
stove coals, the latter in two or three sizes. For steam- 
making, the commerce is confined almost exclusively to pea 
and smaller sizes. 



H 



COMBUSTION OF COAL. 



Table 3. — Coxe Bros. & Co.'s Standards for Small Anthracite 

Coals. 



Size. 

Chestnut 

Pea 

Buckwheat 

Rice 

Barley 



Made through. 



1-^ inches. 
•§• inch 

A " 
I " 

a " 

IS - 



Made over. 



$ inch. 



T6 



Approximate 
price at mines. 



$2-75 

1.25 

•75 

•25 

.IO 



The above meshes are all round-punched. 

Q. What is the composition of Pennsylvania anthracite 
coal? 

In physical appearance anthracite coal differs sufficiently 
from other coals that once known it may be ever after 
distinguished at sight. The fracture presents a con- 
choidal appearance and is quite homogeneous in structure. 

Anthracite coal from Tamaqua, Pa., is compact, slaty, 
conchoidal, grayish black, splendant (Geol. Sur. Pa.). 
Specific gravity, 1.57 = 98.13 pounds per cubic foot. 

Fixed carbon 92.07 per cent. 

Volatile matter 5.03 " 

Ash, white 2.90 " 

100.00 " 

Heat units in one pound of coal= 14,221, equal to an 
equivalent evaporation of 14.72 pounds of water from and 
at 212 F. per pound of coal. 

Lehigh County, Pa., Anthracite Coal — Proximate Analysis. 

Fixed carbon 88. 1 5 per cent. 

Volatile combustible 5- 2 8 " 

Moisture : 1.01 " 

Ash 5.56 

100.00 " 



ANTHRACITE COAL. I 5 

Heat units in one pound of coal— 13,648, equal to an 
equivalent evaporation of 14.13 pounds of water from and 
at 212 F. per pound of coal. 

The Buck Mountain, Carbon County, Pa., anthracite coal, 
in the smaller sizes, such as pea or buckwheat, is largely 
employed as a steam coal. Such coals, by reason of the 
small sizes, contain an excess of slaty matter, which re- 
mains on the grate as ash. In average composition they 
run about as follows : 

Carbon 82. 66 per cent. 

Volatile combustible 3.95 

Moisture 3. 04 

Ash 10.35 

100.00 " 

Heat units in one pound of coal =12,634, equal to an 
equivalent evaporation of 13.08 pounds of water from and 
at 212 F. per pound of coal. 

Semi-anthracite coal from Wilkesbarre, Pa., in the 
smaller sizes, such as buckwheat, shows an excess of ash 
due to the impracticability of picking the slate out of the 
coal, as is done in stove and larger sizes. The average 
composition of fine coals from this locality is as follows : 

Carbon 76. 94 per cent. 

Volatile combustible 6.42 " 

Moisture 1.34 " 

Ash 15.30 " 

100.00 " 

Heat units in one pound of coal = 12,209, equal to an 
equivalent evaporation of 12.64 pounds of water from and 
at 212 F. per pound of coal. 



l6 COMBUSTION OF COAL. 

Q. What is culm ? 

Culm is fine anthracite coal. Formerly this was waste 
product and had no commercial value. Culm heaps 
abound in the anthracite regions of Pennsylvania, and 
much attention has been given to various processes for its 
employment as fuel. The late Eckley B. Coxe, an expert 
in all matters relating to the subject of coal, devoted much 
time to the utilization of culm in steam-making, but with- 
out satisfactory commercial results ; that is, no demand for 
culm has been created outside the mining regions. An- 
thracite differs from bituminous or coking coals in that it 
burns only at the surface. Hence it is absolutely essen- 
tial to provide for the necessary air spaces around the 
pieces on the grate. This can be accomplished only by 
careful sizing. With coal not carefully sized the inter- 
stices between the larger particles are filled by the 
smaller ; and, the air being unable to find a free enough 
passage, combustion is imperfect. Culm banks are mixed 
fine coal, of many sizes, with a considerable proportion of 
slate and pyrites ; requiring careful attention as to draft, 
firing, and details of grate, upon which it is to be burned. 

Q. What is semi-anthracite coal ? 

The semi-anthracite coals are restricted, with few ex- 
ceptions, to those coals which possess on an average from 
seven to eight per cent of volatile combustible matter. In 
consequence of this combustible matter, part of which at 
least resides probably in a free or gaseous state in the cells 
of the coal, this variety kindles more promptly ; and when 
sufficiently supplied with air, burns more rapidly than the 
hard anthracites. 

This coal occurs principally in Pennsylvania. Samples 



SEMI-BITUMINOUS COAL. 1 7 

from Wilkesbarre average as below : The semi-anthracites 
of this locality are compact, conchoidal, iron-black, splend- 
ant. Specific gravity, 1.40 = 87.5 pounds per cubic foot. 

Fixed carbon 88.86 per cent. 

Volatile matter 7. 66 " 

Earthy matter 3. 46 " 

100.00 " 

The calorific power of this coal is 14,199 heat units per 
pound; this is equal to an equivalent evaporation of 14. 59 
pounds of water from and at 21 2° F. per pound of coal. 

This coal is held in high estimation for domestic use, 
and for the generation of steam. 

Q. What is semi-bituminous coal ? 

Semi-bituminous coal is not so hard, and contains more 
volatile matter than the anthracite coals proper. In this 
as in all other classifications of coals its limits must be 
fixed somewhat arbitrarily. In appearance it more closely 
resembles the anthracite than the bituminous coals, differ- 
ing from anthracite in fracture, as being less conchoidal ; 
it is not so hard; it is of less specific gravity; and when 
thrown upon the fire it kindles much more readily and 
burns faster than anthracite. 

Cumberland, Md., semi-bituminous coal. Specific grav- 
ity, 1. 41 = 88. 13 pounds per cubic foot. 

Fixed carbon 68. 19 per cent. 

Volatile matter 17.12 " 

Sulphur .71 " 

Ash 13.98 " 

100.00 " 

This coal takes high rank as a fuel. Although contain- 
ing less carbon than anthracite, it is quite as desirable on 
2 



1 8 COMBUSTION OF COAL. 

account of the readiness with which it kindles and the 
quantity of heat it is capable of giving off when burned in 
steam-boiler furnaces. 

Blossburg, Pa., semi-bituminous coal. Specific gravity, 
1.32 = 82.50 pounds per cubic foot. 

Fixed carbon 73. n per cent. 

Volatile matter 15.27 " 

Sulphur 85 " 

Ash 10.77 " 

100.00 " 

Semi-bituminous coals are much more easily regulated 
in the furnace when burning than in the case of anthra- 
cites. It is characteristic of these coals that they burn 
almost entirely smokeless. 

Q. What are the properties of bituminous coal ? 

Bituminous coal is the product of the decomposition of 
vegetable matter, and was formed previously to or in the 
Cretaceous period. Chemically it occupies a place between 
lignite and anthracite coal, but the transition of lignite 
into bituminous coal is as gradual as the latter is into an- 
thracite, so there is no precise line of demarcation between 
these classes of coal." The use of the term bituminous is 
a misleading one, because none of the so-called bituminous 
coals in this country contain any bitumen in their composi- 
tion. The true bitumens are destitute of organic structure ; 
they appear to have arisen from coal or lignite by the action 
of subterranean heat, and very closely resemble some of 
the products yielded by the destructive distillation of those 
bodies. It is possible that its name has been applied to 
certain varieties of coal on account of a similarity between 
the burning of a coal rich in hydrocarbon and bitumen. 



BITUMINOUS COAL. 19 

The latter is very inflammable, and burns with a red 
smoky flame. 

All coals which contain as much or more than 18 or 20 
per cent of volatile combustible matter are quite indiscrimi- 
nately classed among bituminous coals. Some coals con- 
tain as much as 50 per cent of volatile combustible. 

In external properties the common bituminous coals 
range in color from a pitch black to a dark brown. Their 
lustre is vitreous, resinous, or in the more fibrous varieties 
silky; their structure is compact and cuboidal, slaty, 
columnar, and even fibrous ; their fracture, irrespective of 
structural joints and cleavage, is conchoidal, and often 
flat and rectangular, and sometimes fibrous. 

It is distinctive of these coals to burn with a more or 
less smoky yellow flame, and to emit when burning a bi- 
tuminous odor. 

Q. What is the composition of bituminous coal? 

In proximate composition — namely, in fixed carbon or 
coke, volatile matter or combustible gases, and earthy 
sedimentary residue or ashes — they may be regarded as 
ranging between the following general limits : 

Proximate Composition. 

Fixed carbon 52 to 84 per cent. 

Volatile matter 12 to 48 " 

Earthy matter 2 to 10 " 

Sulphur , 1 to 3 " 

Dried at a temperature of 212 F., from 1 to 5 per cent 
of moisture may be driven off, with occasionally higher 
percentages. 

. The proportion of earthy matter, or ash, is too variable 
to fix a maximum limit, as all bituminous coals may, by 
impurities, graduate into carbonaceous shales. 



20 



COMBUSTION OF COAL. 



Bituminous coals may be regarded as ranging : 

Ultimate Composition. 

Carbon 60 to 80 per cent. 

Hydrogen 5 to 6 

Nitrogen , 1 to 2 

Oxygen 4 to 10 

Sulphur o. 5 to 4 

Ash 3 to 12 

The proximate composition of coals as given in Table 4 
is intended to give a general survey of the principal bitu- 
minous coal fields of the United States, and is not at all 
complete as to localities. 



Table 4. — Selected American Bituminous Coals. 
W= Water. G — Gas. C — Carbon. A = Ash. 



Locality. 



Alabama 

Jefferson Co. . . . 
Arkansas 

Johnson Co 
California 

Alameda Co. . . . 
Colorado 

Tremont Co ... . 
Georgia 

Dade Co 

Illinois 

Mercer Co 

Vermilion Co 

Indiana 

Block Coal 

Cannel Coal 

Vermilion Co. . , , 
Indian Territory. . . 

Choctaw Nation 
Iowa 

Monroe Co 



Volatile 
matter. 



w. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 



3.01 

42.76 

1.52 
14-73 
18.08 
39-3o 

3-93 
42.43 

1.20 
23.05 

8.40 
31.20 

5.7S 
43-70 
13-05 
32.34 

3- 50 
48.00 

5-50 
44.00 

6.66 
35.42 

5.16 
40.21 



Coke. 



c. 

A. 
C. 
A. 
C. 
A. 
C. 
A. 
C. 
A. 
C. 
A. 
C. 
A. 
C. 
A. 
C. 
A. 
C. 
A. 
C. 
A. 
C. 
A. 



48.30 

5.93 
74-49 

9.26 
35-6i 

7.01 
47.16 

6.48 
60.50 
15.25 
54-8o 

5.60 
45-37 

5.15 
48.78 

5.83 
42.00 

6.50 
46.00 

4.50 
51-32 

6.60 
45-88 

8.75 



Heat 

units per 

pound. 



14,017 
13,217 
II,6o8 

13,797 

12,553 
J 3,o63 

13,746 
12,377 
13,962 
13,886 
13,248 
13,247 



Evaporation 
from 



14.51 
13.68 
I2.0I 
14.28 
12.99 
13.52 
14.23 
I2.8I 
14.45 
14.37 
13-71 
13.71 



BITUMINOUS COAL. 



21 



Locality. 



Kansas 

Cherokee Co 

Kentucky 

Muhlenberg Co 

Maryland 

Cumberland 

George's Creek 

Missouri 

Putnam Co 

Montana 

Cascade Co 

Nebraska 

Adams Co 

New Mexico 

Colfax Co 

North Carolina 

Guilford Co 

Ohio 

Hocking Valley 

Mahoning Co 

Oregon 

Tillamook Co 

Pennsylvania 

Pittsburg 

Connellsville 

Youghiogheny 

Tennessee 

Marion Co 

Texas 

Palo Pinto 

Utah 

Iron Co 

Virginia 

Rockingham Co 

West Virginia 

Mineral Co 

Pocahontas (semi-bit.) 
Washington 

Pierce Co 

Wyoming 

Weston Co 



Volatile 
matter. 



w. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 

W. 

G. 



i. 9 4 

36.77 
3.60 

30.60 
1.23 

15-47 
•59 

18.52 

9-03 
37-48 

3.01 
30.23 

0.21 
27.82 

3.10 
35-oo 

1.79 
29.56 

8.25 
35-88 

2.47 
31.83 

8.00 
37.83 

1.80 
35-34 

1-93 
28.71 

1. 00 
35.oo 

3.16 

31-94 
6.67 

40.20 
3-5o 

43-66 
1-34 

30.98 
.76 

19-39 

•50 

19.83 

1. 10 
35-IO 

4.20 
40.60 



Coke. 



c. 52. 

A. 8. 

C. 5S. 

A. 7. 

C 73- 

A. 9. 

C. 74. 

A. 6. 

C. 46. 

A. 7. 

C. 59- 

A. 7. 

C. 60. 

A. 11. 

C. 51. 

A. 10. 

C. 58. 

A. 10. 
C. 
A. 
C. 
A. 
C, 
A. 



53- 

2. 

64. 

1. 

45- 

9- 

C. 54- 
A. 7- 
C. 63. 



A. 

C. 
A. 
C. 
A. 
C. 
A. 
C. 
A. 



C 43 
A. 9 
C 43 



C. 41 

A. 13. 



Heat 

units per 
pound. 



Evaporation 

from 
and at 212 . 



13,585 
13,544 
13,205 
I3,8l2 
12,852 
I3,6l6 
13,390 
13,208 
13,302 
I3.59 1 
14,537 

12,754 
13,762 
13,881 
14,208 
13,185 
12,906 

I3,4H 
13.321 
13,764 
14,218 

13,659 
12,676 



14.06 
14.02 

13.67 
14.30 
13.30 
14.10 
13.86 
13.67 
13-77 
14.07 
15.05 
13.20 
14.25 
14.37 
14.71 
13.65 
13.36 
13.88 
13.79 
14.25 
T4.72 
14.14 
13.12 



22 COMBUSTION OF COAL. 

Q. How are bituminous coals classified ? 

Gruner's classification is given on page.n, and in addi- 
tion thereto the classification for economic purposes, by 
Percy, is also given : 

i . Non-caking or free-burning coals rich in oxygen. 

2. Caking coals. 

3. Non-caking coals rich in carbon. 

This classification of coals is based on their chemical 
composition, and therefore on their calorific powers. 

Q. What are the distinguishing properties of a caking 
coal? 

Caking coal is the name given to any coal which, when 
heated, the lumps seem to fuse together and swell in size, 
having a pasty appearance and emitting a gummy or sticky 
substance over the surface, liberating meanwhile small 
streams of gas, which appear to escape as from a consider- 
able pressure from within the coal ; this escaping gas burn- 
ing with a yellow and sometimes a reddish flame terminat- 
ing in smoke. A characteristic of caking coal is that 
lumps, either large or small, being rendered pasty by the 
action of the heat, will cohere in the fire and form a spongy 
looking mass, which not unfrequently covers almost the 
whole surface of the grate ; this is the property called cak- 
ing. 

Q. For what purposes are caking coals especially de- 
sirable ? 

Caking coals are employed in forges where a hollow fire 
is wanted for heating iron or steel. Caking coals rich in 
hydrocarbons are highly esteemed by gas manufacturers, 
because after driving off the gas the remaining coke is a 
valuable by-product which commands a ready sale. Cak- 



COKE. 23 

ing coals which will yield a hard strong coke are valuable, 
inasmuch as coke having these properties is greatly in de- 
mand in the manufacture of iron and steel. 

Q. What is coke ? 

Coke is the solid product left after the expulsion of the 
volatile matter from coal by the action of heat. The only 
coke of any commercial value is that made from caking 
coals. The fine coal, screenings, or small lumps of caking 
coals, when heated sufficiently high and protected from the 
atmospheric air, as in a coke oven, gas retort, or in a closed 
furnace, will have the volatile portions of the coal driven 
off, and a coherent mass of fixed carbon, containing usually 
5 to 10 per cent of earthy matter, alone remains; this 
final product is called coke. 

A very excellent quality of coke is made in the Con- 
nellsville region, Pennsylvania. It is there produced in 
enormous quantities for the manufacture of iron and steel 
in and near Pittsburg, and for the remelting of pig iron in 
cupola furnaces in other localities. The coal from which 
this coke is made is mined in Fayette County, Pa. ; it is 
of columnar structure, inclined to be granular, and easily 
broken into small fragments. In appearance this coal 
displays prismatic colors on every side ; its specific grav- 
ity is 1.28 = 80 pounds per cubic foot. By proximate 
analysis it contains : 

Fixed carbon 65.00 per cent. 

Volatile combustible 24.00 " 

Moisture 4. 50 " 

Ash, white 6. 50 " 

100.00 " 

Coke 71.50 per cent, of steel-gray color, having a me- 
tallic lustre, columnar, very strong, dense, slightly puffed 



24 COMBUSTION OF COAL. 

on the surface — this coke occurs in long pieces, not un- 
like ordinary cord wood sawed in half. It is an excellent 
fuel for melting iron. It requires a strong draft, about 
the same as hard anthracite coal. It yields an intense 
heat, burns free under a strong blast, and will support a 
considerable weight of iron above it in the cupola without 
crushing. 

Q. What is the object in coking coals? 

i. The coking of bituminous coal is intended to drive off 
the volatile combustible gases and thereby to concentrate 
the carbon which the coal contains, so that the coke may 
be capable of producing a higher temperature. 

2. To remove the volatile substances which on burning, 
chiefly for domestic purposes, have an unpleasant smell. 

3. To deprive the coal of the property of becoming 
pasty at a high temperature, in iron blast furnaces for 
instance, in consequence of which the blast cannot pene- 
trate sufficiently, and the process of the furnace becomes 
disordered. 

4. To remove part of the sulphur, which coal frequently 
contains in the form of sulphide of iron. 

The production of good coke requires a combination of 
qualities not very frequently met with in coal, and hence 
first-rate coking coals can be procured only from certain 
districts. 

Q. What are the general properties of coke ? 

The properties of coke must in some degree be influ- 
enced by the properties of the coal from which it is made. 
In external features it will depend whether the coke is the 
product of a gas retort or that of an oven, the general ap- 
pearance being wholly unlike. As an article of commerce 
cokes contain : Carbon, 80 to 96 per cent ; ash, 2 to 15; 



CANNEL COAL. 25 

hygroscopic moisture, 1 to 5 ; and is capable of absorbing 
from 5 to 10 per cent additional water if exposed to the 
weather. 

Coke weighs 40 to 60 pounds per cubic foot and the 
denser varieties more. About 60 cubic feet of space are 
required for storage per ton. 

Q. What properties in the coal are required for making 
the best coke? 

To make a homogeneous good coke the fixed carbon of 
the coal must be of a kind that will melt at the lowest pos- 
sible temperature; for if the process of coking produces 
the least pressure on the volatile hydrocarbons whereby 
there is an increase of heat, such pressure causes so com- 
plete a liquefaction and expansion of the fixed carbon that 
the coke is left cellular instead of being compact. 

Q. For what purposes is coke chiefly employed ? 

Coke may be employed in all kinds of firing which do 
not require a large flame, but it is most effective in those 
instances in which great heat is required in a small space, 
as, for instance, in crucible meltings, in smelting of iron 
ores in blast furnaces, in remelting of pig iron in cupola 
furnaces, etc. When a sufficient quantity of air is ad- 
mitted, coke produces a far greater heat than charcoal. 
As it remains longer in the furnace than charcoal before 
being ignited, it undergoes a better preparatory heating 
before ignition, and by this means its effect is increased. 

Q. What is cannel coal ? 

Cannel coal is a variety of bituminous coal very rich in 
hydrogen. In appearance this coal differs from all other 
bituminous coals. Its structure is more nearly homoge- 
neous than others, being a compact mass, varying from 



26 COMBUSTION OF COAL. 

brown to black in color, and having usually a dull resinous 
lustre. When broken it does not usually preserve any 
distinct order of fracture, and is liable to split in any 
direction. On account of its being excessively rich in 
hydrocarbons it is highly esteemed as a gas coal, prefer- 
ence being given to those coals in which hydrogen bears 
the greatest proportion to the contained oxygen. 

The amount of combustible matter which it contains, 
and the readiness with which this is given off in com- 
bustion, account for the name given it by the miners 
as "cannel," a corruption of candle coal. This coal 
kindles readily and burns without melting, emitting a 
bright flame like that of a candle. When thrown in the 
fire the piece splits up into fragments, producing a crack- 
ling noise, which, from a fancied resemblance, has also 
received the name of " parrot " coal. It is highly es- 
teemed for domestic use, being especially bright and 
cheerful when burned in an open grate. Cannel coals are 
used for enriching gas made from coals containing a large 
amount of volatile combustible, but somewhat deficient in 
illuminating power. 

Q. What is the composition of cannel coal ? 

Cannel coal occurs in so few localities that the variations 
in composition are less noticeable than is the case with 
other varieties of bituminous coal. Cannel coal from 
Breckenridge, Ky., analyzed by Dr. Peters, resulted in: 

Proximate Analysis. 

Carbon 32.00 per cent. 

Volatile combustible 54-4° 

Moisture 1 . 30 " 

Ash 12.30 

100.00 " 



CANNEL COAL. 



27 



Elementary Analysis. 

Carbon 68. 128 per cent. 

Hydrogen 6. 489 

Nitrogen 2.274 

Oxygen and loss 5. 833 

Sulphur 2. 476 

Ash 14. 800 



Cannel coal from Davis County, Ind. Analysis by E. 
T. Cox. Specific gravity, 1.229 = 76.81 pounds per cubic 
foot. 

Proximate Analysis. 

Carbon 42. 00 per cent. 

Volatile combustible 48. 50 " 

Moisture 3. 50 " 

Ash, white 6.00 " 



100.00 

Coke, 48 per cent, laminated, not swollen, lustreless. 



Elementary Analysis. 

Carbon 71.10 per cent. 

Hydrogen 6. 06 

Oxygen 12. 74 

Nitrogen 1. 45 

Sulphur 1. 00 

Ash 7.65 



Q. What is the calorific value of cannel coal? 

The calorific power of cannel coal from Davis County, 
Ind., analysis of which is given on this page, is 13,131 heat 
units per pound of coal. This is equal to an equivalent 
evaporation of 13.58 pounds of water from and at 21 2° F. 
per pound of coal. 



28 COMBUSTION OF COAL. 

Q. What properties do non-caking coals exhibit in the 
fire? 

Non -caking coals have the property of burning free in 
the fire much the same as wood charcoal burns ; that is, 
heat does not cause them to fuse or run together in the 
fire. Perhaps the representative non-caking bituminous 
coal is the block coal of the Western States, and notice- 
ably that of Indiana. 

Q. What is block coal ? 

Block coal is a non-caking bituminous coal occurring in 
large quantities in Indiana. It may be described as lami- 
nated in structure, consisting of successive layers of coal, 
easily separated into thin horizontal slices, not unlike 
slate. Between these slices of coal is a layer of fibrous 
carbon resembling charcoal. In appearance it has a dull, 
lustreless face on the line of separation, and glistening or 
resinous black when broken at right angles to its horizon- 
tal face. A peculiarity of this formation, and that which 
gives it its name, is the presence of fractures occurring 
in the coal bed at right angles, or nearly so, and extending 
from top to bottom of the seam, enabling the miner to get 
it out in rectangular blocks, as these lines of fracture indi- 
cate or permit. It is a very strong coal, and will burn 
well under a heavy load without crushing. The blocks 
are very compact, and will endure rough handling and 
stocking without suffering material loss from abrasion. 

A sample of typical block coal from near Brazil, Clay 
County, Ind., has the following characteristics : The coal 
of a dull lustreless black, in thin laminae, separated by 
fibrous charcoal partings, very strong across the bedding 
lines, free from pyrites and calcite. A sample fresh 



BLOCK COAL. 29 

from the mine, and holding an excess of moisture, analysis 
by E. T. Cox. Specific gravity, 1. 285 = 80. 3 1 pounds per 
cubic foot. 

Fixed carbon 56. 50 per cent. 

Volatile combustible 32. 50 " 

Moisture 8.50 

Ash, white 2. 50 " 

100.00 " 
Coke = 59 per cent, laminated, not swollen, lustreless. 

The 8.50 per cent of moisture was reduced by exposure 
to the air to about 3. 50 per cent. The heat units in the 
wet coal= 13,588, and that of the dry coal = 14,400. 

This coal is used as fuel in blast furnaces for smelting 
iron, and in puddling furnaces. It is largely used for 
steam-making and for domestic stoves, grates, etc. 

A test of Indiana block coal by A. F. Nagle in steam- 
making yielded as follows : 

Ratio of heating to grate surface = 50 to 1 

Ash, per cent = 7.25 
Rate of combustion, pounds per square foot of 

grate = 15 

Temperature of escaping gases = 557° F. 
Evaporation per pound of combustible from and 

at 212 = 10.05 pounds. 

Q. What is brown coal? 

Brown coal is an imperfect coal. The term is often 
used interchangeably with lignite. The brown coal of the 
Germans is distinguished from true coals by the large pro- 
portion of oxygen in its composition. The chemical dif- 
ference between brown coal and lignite may be determined 
by dry distillation, in which the lignite yields acetic acid 
and acetate of ammonia, whereas the brown coal produces 
only ammoniacal liquor. Woody fibre gives rise to acetic 



30 COMBUSTION OF COAL. 

acid. Lignite must therefore still contain undecomposed 
woody fibre. It, together with brown coal, belongs chiefly 
to the Cretaceous and Tertiary periods (Cox). According 
to their geological age brown coals have either a distinct 
texture (true lignite, fibrous brown coal), or are without 
organic structure and earthy in fracture (earthy brown 
coal), or black, shining, with conchoidal fracture. 

Thorpe's analysis of organic substance consists of : Car- 
bon, 60; hydrogen, 5 ; oxygen, 35 — 100 in fibrous brown 
coal; and carbon, 75; hydrogen, 5; oxygen, 20 = 100 in 
conchoidal brown coal. 

The analysis of brown coal from Ballard County, Ky., 
shows it to contain 20 to 30 per cent less fixed carbon 
than coals of the Carboniferous epoch, and a larger quan- 
tity of hygrometric moisture. The specific gravity of this 
coal is 1. 173. 

Fixed carbon 31.0 per cent. 

Volatile combustible . 48. o " 

Moisture 11. 5 " 

Ash, white 9.5 " 

100. o " 

The large quantity of hygrometric moisture in this coal 
lessens its evaporative power as compared with any aver- 
age bituminous coal for steam-making. It is quite im- 
probable that any considerable quantity of available heat is 
given off by the volatile combustible in this coal ; and that 
its heating power is limited, almost if not entirely, to the 
fixed carbon, yielding 4,495 heat units, or an equivalent 
evaporation of 4.66 pounds of water from and at 21 2° F. 
per pound of coal. 

Q. What is lignite? 

Lignite is classed among mineral coals, and includes 



LIGNITE. 3 1 

those varieties which form the intermediate stage between 
peat and true coals of the Carboniferous age. It is believed 
to be of later origin than bituminous coal, and is in a less 
advanced stage of decomposition. The woody fibre and 
vegetable texture of lignite are almost entirely wanting in 
coal, though there is little doubt that they are of one com- 
mon origin. 

Lignite varies considerably in appearance and structure, 
usually, however, preserving a wood-like appearance when 
broken. The fracture is uneven, presenting a brown to a 
very dark brown-black color, with a dull and frequently a 
fatty lustre. Lignites break easily and crumble in han- 
dling ; they will not bear rough transportation to great dis- 
tance ; neither will they bear long-continued exposure to 
weather, crumbling rapidly. As a fuel lignite must be used 
in its natural state, and near where it is mined, to get the 
best results. It is non-coking in the fire, and yields but 
moderate heat as compared with the best bituminous 
coals. 

In specific gravity lignites vary from 1. 10 to 1.35, cor- 
responding to 68.75 t0 84.38 pounds per cubic foot. 

Q. Where are lignites principally found? 

Lignites and " brown coal " occur plentifully on the 
continent of Europe. In the United States very extensive 
deposits occur in Colorado, Nevada, Utah, Wyoming, New 
Mexico, California, Oregon, and Alaska, and in lesser 
quantity in some other States. As the States and Terri- 
tories west of the Mississippi are developed, lignite will 
become a matter of growing importance, as it must be- 
come their chief fuel after the disappearance of the for- 
ests. 



32 COMBUSTION OF COAL. 

Q. What is the composition of lignite? 

The lignites of the United States vary greatly in their 
chemical composition, consisting of : 

Fixed carbon 40 to 70 per cent. 

Volatile combustible 23 to 48 " 

Moisture 4 to 40 " 

Ash 3 to 20 " 

Colorado lignite, Canon City: Color, jet black; specific 
gravity, 1.279. 

Fixed carbon 56. 80 per cent. 

Volatile combustible 34. 20 " 

Moisture 4.50 * ' 

Ash, ochre yellow 4. 50 " 

100.00 " 
Coke = 61.30 percent, slightly swollen, unchanged, semi-lustrous (Cox). 

Washington lignite, Billingham Bay: Color, glossy 
black ; fracture slaty and parallel to stratification. In the 
opposite direction the fracture is irregular and brittle. 

Proximate Analysis. 

Fixed carbon 58.25 per cent. 

Volatile combustible 31-75 " 

Moisture 7.00 " 

Ash, reddish brown 3.00 " 

100.00 " 
Coke = 61.25 per cent, slightly shrunken, dull black. 

Ultimate Analysis. 

First Second 

sample. sample. 

Carbon Per cent 68. 454 67. 090 

Hydrogen " 6.666 4-555 

Sulphur " 1. 000 1. 000 

Water at 212 F " 7.000 7.000 

Ashes " 3-4QO 3. 100 

Oxygen, nitrogen and loss " 13.480 17.255 

100.000 100.000 



LIGNITE. 33 

Samples contained a large amount of oxygen and were 
deficient in the amount of hydrocarbons, and therefore 
more difficult of ignition than most of the Western varie- 
ties of bituminous coals ; but it is rich in fixed carbon in 
the coke and will therefore be durable. It is intermediate 
in composition of its ultimate elements to cannel coal and 
lignites (Cox). 

Kentucky lignite, Ballard County : Sample had much 
the appearance of coal, hence apt to be mistaken for it ; 
but it is of much more recent origin. Specific gravity, 
1.201. 

Fixed carbon 40 per cent. 

Volatile combustible 23 " 

Moisture 30 " 

Ash, reddish yellow 7 " 

100 " 
Coke = 47 per cent. Reduced in bulk and nearly the same shape as orig- 
inal specimen (Cox). 

Arkansas lignite, Ouachita County : This lignite has a 
rhomboidal cleavage. Can be cut with a knife, and re- 
ceives a good polish, which gives it a much blacker ap- 
pearance. It is solid, heavy, compact, of a bluish-brown 
color, disintegrating, however, by exposure to the atmos- 
phere. 

Fixed carbon 34. 50 per cent. 

Volatile combustible 28.50 " 

Moisture at 260 F 32. 00 

Ash 5.00 " 

100.00 " 
Coke = 39,5 per cent. 

Vancouver's Island lignite : Color, dull black, submetal- 
lic. Fracture, foliated and slaty, numerous partings filled 
with scales cf carbonate of lime. 
3 



34 COMBUSTION OF COAL. 

Fixed carbon 62 per cent. 

Volatile combustible 31 " 

Moisture 4 " 

Ash, reddish brown 3 

100 " 

Coke = 65 per cent. This lignite shrinks slightly in coking, and is dull 
black in color (Cox). 

Texas lignite, Robertson County : Sample taken from 
seam ten feet thick. Color, lustreless, dull brown, with 
irregular fracture and much inclined to shrink, crack, and 
fall to pieces on exposure to air. Specific gravity, 1.232. 

Fixed carbon 45. 00 per cent. 

Volatile combustible 39. 50 " 

Moisture \.. 11.00 " 

Ash, white 4. 50 

100.00 " 
Coke, slightly shrunken, lustreless, and bears a close resemblance to 
wood charcoal. Heat units, 13,068. 

The ash of lignites is extremely variable as to quality 
as well as to quantity. In composition it is similar to 
that of bituminous coal. It differs from the ash of peat 
in the low percentage of phosphoric acid. Usually it is 
rich in sulphur, as gypsum, iron pyrites, and sometimes as 
free sulphur. 

Q. What is the quality of coke obtained from lignite ? 

Lignites are in general non-caking in an open fire. The 
coke obtained by distillation from the best lignites is not 
of good quality and takes rank much below the inferior 
grades of coke made from gas coals. 

Q. How are woods classified? 

Wood as a fuel is commonly divided into two classes — 
hard and soft. Hard woods include the heavy compact 



WOOD. 



35 



varieties, such as oak, hickory, beech, elm, ash, walnut, etc. 
The soft woods include pine, birch, poplar, willow, etc. 

The specific gravity of wood varies considerably. Air- 
dried woods, with 20 per cent hygroscopic moisture, hav- 
ing a specific gravity of more than o. 5 5 are classed as hard 
woods; with a lower specific gravity they are classed as 
soft woods. After complete expulsion of air from the 
pores the specific gravity is the same in all woods, viz., 1.5. 

Q. What is the composition of wood ? 

Wood consists of about 96 per cent of organic tissue 
and 4 per cent of sap, containing a small proportion of 
inorganic matter. Freshly cut green wood contains on an 
average about 45 per cent of moisture; and after long 
exposure to the atmosphere under favorable conditions it 
still retains from 1 8 to 20 per cent of moisture, a matter 
of practical importance in the direct application of wood 
as fuel. The accompanying table, by M. Eugene Chevan- 
dier, shows the composition of several well-known varie- 
ties of wood : 

Table 5. — Composition of Wood (Chevandier) . 



Woods. 


Composition in Per Cent. 


Carbon. 


Hydrogen. 


Oxygen. 


Nitrogen. 


Ash. 


Beech 

Oak 


49-36 
49.64 
50.20 
49-37 
49-9D 


6.0I 
5.92 
6.20 
6.21 

5.96 


42.69 
41.16 
41.62 
41.60 
39-56 


O.9I 

I.29 

I- 15 

.96 

.96 


I. OO 
1.97 

.81 
1.86 
3-37 


Birch 

Poplar 

Willow 


Average .... 


49.70 


6.06 


4I.3O 


I.05 


1.80 



Q. What quantity of moisture is contained in wood ? 

Wood contains about 45 per cent of moisture when 
freshly cut. Some of this is lost by subsequent evapora- 



36 



COMBUSTION OF COAL. 



tion in the atmosphere, but there still remains about 20 
per cent of moisture which cannot be expelled except by. 
means of artificial heat. The following table, prepared by 
M. Violette, shows the proportion of water expelled from 
wood at gradually increasing temperatures. The samples 
of wood operated upon had been kept in store during two 
years. In each experiment the specimens were exposed 
during two hours to desiccation in a current of superheated 
steam, of which the temperature was gradually raised from 
257 to 437 F. When wood, which has been strongly 
dried by means of artificial heat, is left exposed to the at- 
mosphere, it reabsorbs about as much water as it contains 
in its air-dried state. 



Table 6. — Water Expelled from 100 Parts of Wood (Violette). 



Temperatures 

257°F 

302 F 

347°F 

392° F 

437° F 



Oak. 



15.26 
17-93 
32.13 

35.80 

44- 3 1 



Ash. 



14.78 
16.19 
21.22 
27.51 

33-38 



Elm. 



15.32 

I7.02 

36.94? 

33.38 

40.56 



Walnut. 



15-55 
17-43 
21.00 

41.77? 

36.56 



Q. What is a distinguishing property of wood as a 
fuel ? 

Though the calorific intensity of wood is small as com- 
pared with coal, its combustibility is greater than that of 
any other solid fuel, and it gives more flame. 

Q. What is bagasse? 

Bagasse is the woody fibre of sugar-cane after the 
saccharine juices have been expelled for sugar-making. 
Special furnaces have been contrived for burning it, and 
with fair results. The contained water is about 50 per 
cent of the gross weight. The remaining fibre is not un- 



TAN. 37 

like wood in its heat-giving power. On an average six 
pounds of bagasse are equivalent to one pound good bitu- 
minous coal. 

Q. What is tan ? 

Tan is the spent bark from which the tannic acid has 
been extracted in the process of tanning leather. The 
barks commonly used are oak and hemlock. The princi- 
pal drawback to tan as a fuel is its contained moisture, 
and for this reason special furnaces are made for burning 
it. Tan bark, as commonly used for fuel, will yield about 
3,600 heat units per pound, which is one-half the value of 
ordinary dry wood, and about one-fourth the value of good 
bituminous coal. 

If it were not for the contained moisture in tan very 
much higher calorific results could be obtained. Accord- 
ing to M. Peclet 5 parts of oak bark produce 4 parts of 
dry tan, and the heating power of perfectly dry tan, con- 
taining 15 per cent of ash, is 6,100 heat units, while that 
of tan in an ordinary state of dryness, containing 30 per 
cent of water, is only 4,284 heat units. The equivalent 
evaporation from and at 21 2° F. would be: 

Perfectly dry tan , J ~TZ~ = 6. 3 1 pounds of water. 

4,284 
\\ et tan, 30 per cent water, — — - = 4.44 pounds of water. 
900 

Results which are much higher than obtain in average 
practice. 

Q. What is peat? 

Peat is the product of the decay of plants which are un- 
dergoing a gradual transformation by a process of slow 
burning or carbonization, in which the oxygen of the 



38 COMBUSTION OF COAL. 

plants is being liberated under special conditions of air 
and moisture, leaving a spongy, carbonaceous mass, in 
which the remains of the plants are often so well preserved 
that species may easily be distinguished. 

In color peat varies from a yellowish brown through all 
gradations to a very dark brown, almost black. The struc- 
ture of the former is light, spongy, and fibrous ; the latter 
is more compact and pitchy in appearance, the fibrous tex- 
ture being almost entirely obliterated. In advanced stages 
of decomposition it is compact and dense, presenting an 
earthy fracture when broken ; in general the darker the 
peat the richer it is in carbon. 

Q. What is the composition of peat ? 

In its natural and more advanced state peat contains 
about 75 per cent of its entire weight of water. In the 
earlier stages of decomposition the quantity of water more 
nearly approaches 90 per cent, the peat being of the con- 
sistency of mire, and is of course totally unfit for any of 
the purposes for which fuel is employed. 

Peat shrinks very much in drying, yet 20 to 30 per 
cent of moisture still remain in ordinary air-dried samples. 
The remaining product is decomposed vegetable matter 
and contains the elements common to plants. The chemi- 
cal composition of peat varies according to its stage of 
decomposition. The following analysis of Irish peat is 
upon the authority of Sir Robert Kane : 

Light fibrous. Compact 
and dense. 

Carbon 58. 53 56. 34 

Hydrogen 5.73 4.81 

Oxygen 32. 32 30. 20 

Nitrogen 93 .74 

Ash 2.47 7.90 



PEAT. 39 

These samples yielded by distillation : 

Light fibrous. Compact 
and dense. 

Water 38. 1 38.1 

Crude tar 4. 4 2. 8 

Charcoal 21.8 32.6 

Gas 35.7 26.5 

The tar when redistilled yielded water, paraffine oils, char- 
coal, and gas. The water yielded chloride of ammonium, 
acetic acid, and wood spirit. 

The inorganic constituents of peat vary from 0.5 to 20, 
or even 50 per cent, according to the elevation at which 
the peat was formed. The average ash-giving constitu- 
ent is from 6 to 12 per cent, and, unlike that of wood, 
the ash is poor in alkalies, and consists chiefly of a mix- 
ture of : 

Argillaceous sand up to 35 per cent. 

Magnesia-bearing gypsum « " 40 " 

Ferric oxide ' ' 30 

Alkalies " 3 " 

With traces of phosphoric acid and chlorine. 

Q. What is the density of peat? 

The density of peat varies according to its occurrence 
with reference to the surface of the ground, that belong- 
ing to the upper stratum being lightest. The specific grav- 
ity of the light fibrous peat in the preceding question is but 
0.280, while the compact and dense peat in the same para- 
graph is 0.65 5. Thus the light fibrous peat =17.5 pounds 
per cubic foot, or 114 cubic feet per ton of 2,000 pounds. 
The compact and dense peat = 40.94 pounds per cubic foot, 
or 48.85 cubic feet per ton of 2,000 pounds. Compressed 
peat will weigh from 70 to 85 pounds per cubic foot, or 
from 24 to 30 cubic feet per ton of 2,000 pounds. The 
dense peat found in the lower strata of peat beds, and 



40 COMBUSTION OF COAL. 

which is in a more advanced state of decomposition, is not 
easily compressible. Its specific gravity is seldom greater 
than that of water or unity ; therefore the densest varie- 
ties will seldom weigh more than 62.5 pounds per cubic 
foot, or 32 cubic feet per ton. 

Q. How is peat prepared for use as fuel? 

The machinery used for making peat fuel is not expen- 
sive, and requires but little attention when in operation. 
If the fibre of the upper formation of peat is crushed or 
milled while it is still wet, the contraction in drying is 
much increased; and as surface peat is always fibrous and 
spongy, it is the lightest. This breaking up of its fibres 
facilitates its subsequent compression for use as fuel, the 
degree of compression varying with the density of the 
peat, which grows more dense in the lower strata, where 
the fibrous texture is nearly or wholly obliterated. 

In Canada the peat is cut and air-dried, after which it is 
pulverized by being passed through a picker and auto- 
matically deposited in a hopper, which feeds a steel tube 
about two inches in diameter and fifteen inches long. 

The pulverized peat is forced through this tube by press- 
ure, and formed into cylindrical blocks three inches in 
length and almost equal in density to anthracite coal. 
The fuel is non-friable and weather-proof by reason of its 
solidity and the glaze imparted to it by frictional contact 
with forming dies. The inherent moisture of the peat is 
reduced to 12 per cent of the mass. It is claimed that 
peat can be thus prepared at a cost of 60 cents per ton. 

Q. What are the properties of peat charcoal? 

The charcoal produced by the carbonization of ordinary 
air-dried peat is very friable and porous; it takes fire 



PEAT. 41 

readily, and when ignited continues to burn until its car- 
bonaceous matter is wholly consumed; it scintillates in a 
remarkable degree when burnt in a smith's fire; its ex- 
tinction when in mass is difficult, and hence this is the 
troublesome part of its manufacture by the usual method 
of carbonization in piles ; and it is so little coherent that 
it cannot be conveyed without much of it being crushed to 
dust. 

When sufficiently coherent, and when the percentage of 
phosphoric acid is low, it may be used in low, small fur- 
naces. Peat charcoal is easily kindled, and has a calorific 
power of 11,700 to 12,600 heat units. It is not adapted 
for iron-making, but may advantageously be used for gas 
furnaces on account of the large size of the lumps, absence 
of clinkers, and the fact that the ash readily falls through 
the bars. 

Q. Where is peat principally found ? 

Peat formations are confined to cold and temperate 
countries and swampy ground. It occurs in the United 
States, Canada, Ireland, Sweden, Germany, France, and 
other countries. In Europe peat is used not only for do- 
mestic purposes, but for metallurgical purposes as well. 
One of the most extensive peat beds known is in the Kan- 
kakee valley, Indiana, the bed being some three miles wide 
and sixty miles long, varying from five to fifty feet in 
thickness. 

Q. How may peat be classified ? 

Peat may be classified : (1) according to the localities 
where it has been formed, as lowland and mountain peat ; 
(2) according to its age, as recent peat with distinct vege- 
table structure, and old peat of a dark brown or black 
color, with more traces of organic texture ; (3) according to 



42 COMBUSTION OF COAL. 

the mode in which it has been extracted, as cut peat or 
dredge peat (Thorpe). 

Q. What are fuel briquettes ? 

Briquette is a name given to a small body of prepared 
fuel, made up chiefly of the culm of bituminous coal held 
together by a bonding material, also combustible, the mix- 
ture being then compressed into a compact mass, of a size 
and shape suitable for use as fuel. 

Briquette-making has become quite an industry in Ger- 
many, Austria, and France, where the fuel question is 
much more important than it is with us. The culm piles 
are being utilized in those countries and made a profitable 
source of income. 

Brown coal has so far been the chief material for bri- 
quettes. Some recent experiments with briquettes made 
of solidified petroleum or residuum have been made, which, 
however, did not result satisfactorily, for the reason that 
the boilers were unable to withstand the intense heat de- 
veloped by this kind of fuel. 

L Industrie describes a process devised by the chemist 
Velna, who uses petroleum or mineral tar only for enrich- 
ing culm and other inferior, formerly worthless combus- 
tibles, and produces briquettes from this material the 
heating power of which is 30 per cent higher than that of 
good coal. He first prepares a mixture consisting of pe- 
troleum or bituminous shale tar, oleine and soda in suit- 
able proportion, and by this means the culm, slack, or coal 
dust is cemented together. Three kinds of briquettes are 
produced in this way, namely, industrial briquettes for 
general firing purposes, gas briquettes for the manufacture 
of illuminating gas, and metallurgical coke. 

The cost of briquettes by this method is said to be as 



PATENT FUEL. 43 

follows : If culm or dust from a good coal, valued at $1.20 
per ton (France = 2, 205 pounds), be taken for their manu- 
facture, six per cent of the mixture would be sufficient. 
The price of a ton of briquettes would be : 

94 per cent coal 2,073 pounds @ 6 cents = $1. 24 

6 " mixture 132 " @, 60 " = 79 

Labor 40 

Total cost per ton = $2.43 

It is claimed that the heating power of these briquettes 
exceeds that of average coal by at least 25 per cent. 

Q. What is patent fuel ? 

Patent fuel is a term much used in Europe to designate 
compressed fuels as a class. Numerous patents have been 
taken out for producing a good fuel by mixing various sub- 
stances with small coal, in proportions sufficient to enable 
the mixture to be pressed into a coherent block. Various 
binding materials have been tried, such as soluble glass, 
asphalt, turpentine. Meal from potatoes was abandoned 
because the blocks were not water-tight. Coal tar (War- 
lick's process) was tried at Swansea, England, the blocks 
being baked after compression, whereby a quantity of tar 
was recovered. On the Continent cellulose (German pat- 
ent) and treacle (crude molasses) have been tried. Pitch 
made from coal tar has been used for many years with 
great success. 

In the dry process small coal is carried by an elevator 
into a large bunker, whence it is lifted by another ele- 
vator to a chute, into which it is tipped with the contents 
of a small elevator containing pitch. The mixture then 
passes into a disintegrator, and the resulting product, con- 
taining 8 to 12 percent of pitch, passes to heaters, and 



44 COMBUSTION OF COAL. 

finally to the presses, which turn out ioo to 200 blocks, 
weighing 10 to 30 pounds, per day of twelve hours. 

In the steam process there is used a large vertical iron 
cylinder with arms revolving inside, constantly kept full 
of a mixture of pitch and coal. High-pressure steam is 
injected near the bottom and allowed to percolate up 
through the mass, while the arms expose every portion to 
its action. 

Attempts have been made to utilize peat by mixing it 
in a state of powder with small coal and sawdust, and 
pressing the mixture into blocks (Thorpe). 

Q. What advantages are claimed for artificial fuels? 

The advantages claimed for patent fuels over ordinary 
coal are stated to consist — 

1. In their efficacy in generating steam. 

2. In occupying less space; that is to say, 500 tons of 
patent fuel may be stowed in an area which will contain 
only 400 tons of coal. 

3. They are used with much greater ease by the firemen 
than coal, and they create little or no dust or dirt, con- 
siderations of some importance where no bulkhead sepa- 
rates the fire-room from the engine-room. 

4. They produce a very small proportion of clinkers, 
and are far less liable to choke and destroy the furnace 
grates than coal. 

5. The combustion is so complete that comparatively 
little smoke and only a small quantity of ashes are pro- 
duced by them. 

6. From the mixture of the patent fuel and the manner 
of its manufacture it is not liable to enter into sponta- 
neous ignition. 



PATENT FUEL. 45 

Q. What is the composition of Grants patent fuel ? 

This fuel is composed of coal dust and coal-tar pitch. 
These materials are mixed together, under the influence of 
heat, in the following proportions : Twenty pounds of 
pitch to 112 pounds of coal dust, by appropriate machin- 
ery, consisting of crushing rollers for breaking the coal in 
the first instance, to pass through a one-fourth inch 
screen ; secondly, of mixing pans or cylinders heated to a 
temperature of 220 F., either by steam or by heated air; 
and thirdly, of moulding machines by which the fuel is 
compressed, under a pressure, equal to five tons, into the 
size of a common brick. The fuel bricks are then white- 
washed, which prevents their sticking together, either in 
the coal bunkers or in hot climates. 

Q. What is the Strong method of making artificial 
fuel? 

The combination of materials and processes of manufac- 
turing artificial fuel or coal briquette by R. S. Strong's 
method is to wash the small coal in order to free the same 
from shale and dirt, and convey it from the drainers to a 
disintegrator by which it is ground, adding about 2 per 
cent of fresh calcined powdered alkaline earth, preferably 
lime, in order to absorb the moisture in the coal. To this 
is added 4 to 10 per cent (according to the nature of the 
coal or the purpose for which the fuel is intended) of 
pyroligneous acid, preferably from a steam-jacketed tank. 
This acid is the whole of the distillate from destructive 
distillation of wood or other ligneous substances and im- 
mediately absorbs the lime and solidifies the mixture, 
which is at once pressed in briquette form in the usual 
way, and on leaving the press may be cooled by a fan or 
blower and shipped or used at once. 



46 COMBUSTION OF COAL. 

In carrying out the process with unwashed coal only one 
per cent or less of the caustic alkaline earth is used to 
give a hook to the pyroligneous acid to act on, all other 
treatment being as before described. 

Fuel manufactured as described is suitable for house- 
hold, steam, or metallurgical purposes, and burns with a 
clear bright flame, and is produced at a reasonable cost. 

Q. What is the Corning method of making artificial 
fuel? 

In the working of the Gardner Corning process the 
binding ingredients employed for uniting the coal dust 
into briquettes are suitable bitumens and quick or fresh- 
burned lime. Of the bitumens natural asphaltum is pre- 
ferred, although the artificial bitumens, such as the by or 
residual products of petroleum, are suitable. The crude 
natural asphaltum, however, is too brittle for the purpose 
and requires tempering by the admixture of some artificial 
bitumen, especially a residuum'oil of petroleum, to impart 
elasticity and tenacity. To properly combine the coal 
dust and bitumen, both are heated to as high temperature 
as practicable without injury by burning or cooking. By 
thorough intermixture while thus heated the thinnest pos- 
sible film or coating of bitumen is given to the dust parti- 
cles to secure their firm adhesion when cooled. The pref- 
erable temperatures employed with natural asphaltum 
have been found to be about 300 F. for the dust and 
320 to 340 for the asphaltum. If other bitumens are 
used, the temperatures may be varied to adapt them to the 
different melting points of the bitumens. To secure the 
most efficient binding action of the lime, it is slaked with 
sufficient water to make a liquid mass of about the consist- 
ency of cream, and which is therefore known as " cream 



PATENT FUEL. 47 

of lime." This is intermixed with the combined dust and 
bitumen while their mass is still hot, and this step of the 
process is the most essential part of the method. 

The proportions of the ingredients are : Coal-dust, about 
1,870 pounds; bitumen, about 80 pounds ; and lime, about 
50 pounds. 

Where natural asphaltum is employed, about 5 pounds 
of the artificial or tempering agent is mixed with about 
75 pounds of the asphaltum. 

Either anthracite, bituminous, or lignite coal dust may 
be worked by this process ; but the best results have been 
secured by combining bituminous dust with the other. 

The process in detail is as follows : The coal dust is 
heated to the requisite temperature, the asphaltum melted 
and the tempering oil mixed with it, and the mixture 
heated to the requisite degree. These are then thorough- 
ly combined in a mixer, which requires usually about 
three minutes. The cream of lime is then added to the 
hot mass, the mixing operation being continued until the 
water begins to vaporize. The mass is then delivered to 
a press while still hot and moist, and formed as quickly as 
possible into briquettes under heavy pressure. 



CHAPTER II. 

SOME ELEMENTARY DATA. 

PHYSICS. 

Q. What is meant by the term work? 

Work is done when resistance is overcome. If a force 
acts upon a body and produces motion in that body, the 
force is said to have done work; but if the force applied 
fails to produce motion in the body thus acted upon, no 
work has been done by that force. The work done by a 
force is measured by the product of the force into the dis- 
tance through which that force moves in its own direction, 
or work = force X distance. 

Q. What is unit of work? 

The unit of work adopted in this country is the foot- 
pound, or that quantity of work done if a body Weighing 
one pound be lifted one foot high against the action of 
gravity. The foot-pound is a gravitation unit, and is 
wholly independent of time. 

Q. What is meant by lost work? 

Of the work put into a machine a certain portion of it 
must be expended in merely keeping the different parts in 
motion, and the work thus absorbed is lost work. The 
friction diagram of a steam-engine, for example, represents 
so much lost work, inasmuch as it is necessary to overcome 
all the resistances represented by the diagram before any 



ELEMENTARY DATA. 49 

useful effect can be obtained. Lost work = force absorbed 
in overcoming internal resistances X the distance it acts. 

Q. What is meant by useful work? 

Useful work is the work given out by a machine after 
deducting the frictional and other resistances incident to 
running the machine empty at its normal speed. Suppose 
a steam-engine should indicate 220 H. P. and the friction 
diagram of the engine at the same speed indicated 25 H. 
P., the useful work of the engine would be : 220 — 25 = 195 
H. P., or, as it is sometimes expressed, the net horse 
power. Useful work = force given out X the distance it 
acts. 

Q. What is meant by the term power? 

Power is the rate of doing work. It is not the same as 
force ; it is not the same as pressure, because force and 
pressure act independently of time ; but time is an essen- 
tial element when estimating the quantity of work done by 
a man or by a machine. • 

Q. What is the unit of power? 

The unit of power in mechanical engineering is called 
the horse power. It is the rate of doing work at 33,000 
foot-pounds per minute. 

Q. How did the horse-power unit originate ? 

James Watt ascertained by experiment that an average 
cart horse could develop 22,000 foot-pounds of work per 
minute ; and being anxious to give good value to the pur- 
chasers of his engines, he added 50 per cent to this 
amount, thus obtaining (22,000 + 1 1,000) the 33,000 foot- 
pounds per minute unit, by which the power of steam and 
other engines has ever since been estimated (Jamison). 
4 



50 COMBUSTION OF COAL. 

Q. What is meant by the term energy? 

Energy is commonly explained as the capability of do- 
ing work, and by doing work is meant overcoming resist- 
ance. Energy is of two types, known as kinetic and poten- 
tial ; but more specifically we have : 

i. Kinetic energy. 

2. Gravitation energy. 

3. Heat. 

4. Energy of elasticity. 

5. Cohesion energy. 

6. Chemical energy. 

7. Electrical energy. 

8. Magnetic energy. 

9. Radiant energy. 

This list includes all known separate forms. 

Q. What is potential energy? 

Potential energy is the energy due to position, or that 
form of energy which a body possesses in virtue of its 
condition. Energy due to position may be illustrated in 
the case of a weight, say 50 pounds raised 10 feet high. 
This would represent a potential energy of 50 X 10 = 500 
foot-pounds, because if liberated it would through proper 
means accomplish that quantity of work. This can be 
considered, in the case of falling bodies, as gravitation 
energy. Energy due to condition may be illustrated in 
the case of the coiled spring of a clock, which when wound 
up can do work in driving the train of mechanism, an ex- 
ample of energy due to the elasticity of the steel spring. 
Coal when burned under proper conditions gives out heat 
which may be utilized for generating steam and doing; 
work through, the medium of a steam-engine. 



ENERGY. 5 1 

Q. What is kinetic energy? 

Kinetic energy is the energy due to motion. It is not 
easy to conceive of energy apart from motion, and this has 
led some physicists to the conclusion that all energy is 
probably kinetic. 

Q. Are the two types of energy, kinetic and potential, 
mutually independent? 

The energy of motion and the energy of position or con- 
dition are being continually changed one into the other. 
The conversion of one form of energy to another is seen 
in a head of water employed to turn a water wheel. The 
water possesses energy due to its height above the wheel. 
The weight of the water impinging against the buckets of 
the wheel gives it motion and is thus capable of doing 
work. 

Q. What is the great characteristic of enegy? 

That it may be transformed or transmuted from one 
kind of energy into another kind of energy; but through 
all its transformations the quantity present always remains 
the same, though known by different names, which after 
all are but those of convenience in classification. It has 
been suggested that each form of energy arises from a 
mode of motion of some portion or portions of substances 
or of matter, and that therefore all energy is kinetic. 

Q. What is meant by transmutation of energy? 

By transmutation of energy is meant the changing of 
one kind of energy into another. There are many varie- 
ties of visible energy, but there is energy which is invis- 
ible ; and the one may be converted into the other. The 
most common illustration of this is the conversion of work 



52 COMBUSTION OF COAL. 

into heat. This occurs when motion is arrested, whether 
by percussion or by friction. It is the conversion of vis- 
ible or actual energy into heat ; that is, into molecular or 
invisible energy. 

Q. What is meant by energy of fuel? 

Its capacity to do work. Taken altogether the heating 
power of coals will range ordinarily from 13,000 to 14,300 
heat units per pound. The energy of fuel or its power to 
do work may be easily computed thus : 

Suppose a sample of coal to equal 14,000 heat units per 
pound ; this multiplied by 772, the thermal unit known as 
Joule's equivalent, we have: 14,000 X 772 — 10,808,000 
pounds raised one foot high in one minute, this represent- 
ing the potential energy of one pound of coal. It will be 
understood that the above represents the maximum limit 
of work done by the complete combustion of one pound of 
coal, an amount of energy expressed in foot-pounds of 
work, far beyond any means at our command for its com- 
plete utilization. 

Q. Can energy be transferred from one form into 
another without loss? 

This is quite impossible; and it must not be supposed 
that the various forms of energy may be transformed into 
mechanical energy or made to do work without loss in- 
cident to the absorption by the various other forms of 
energy which are contiguous, and which are constantly 
seeking fresh supplies of energy from a higher source than 
their own. If these processes were not only transformable 
but reversible, then perpetual motion would be a fact. 
We know that heat, as a form of visible mechanical 
energy, is available only as we use it from a higher to a 



DISSIPATION OF ENERGY. 53 

lower temperature; and we know further that once the 
heat has spent its energy or capacity for doing work, there 
is no way by which it can be restored. Heat may be 
made to do work, and work may be transferred into heat, 
but the processes are not reversible. 

Q. What is meant by dissipation of energy ? 

The principle of dissipation of energy is that as any 
operation going on in nature involves a transformation of 
energy, and transformation involves a certain amount of 
degradation (degraded energy meaning energy less capable 
of being transformed than before), energy is therefore con- 
tinually becoming less and less transformable. As these 
changes are constantly going on in nature, the energy 
must of necessity be getting lower and lower in the scale, 
so that its ultimate form must be that of heat so diffused 
as to give all bodies the same temperature. In order to 
get any work out of heat, it is absolutely necessary to have 
a hotter body and a colder one ; but if all the energy be 
transformed into heat, and if it be in all bodies at the 
same temperature, then it is impossible to raise the small- 
est part of that energy into a more available form. 

Q. What is a thermometer? 

A thermometer is an instrument for measuring tempera- 
tures constructed upon the principle of the expansion of 
bodies by heat. 

It consists in its common form of a glass tube termi- 
nating in a bulb containing mercury, which fills the bulb 
and part of the tube ; and the rise or fall of the mercury 
in the tube, according as the mass of it in the bulb ex- 
pands or contracts, indicates any change of temperature in 
the surrounding medium. 



54 COMBUSTION OF COAL. 

Q. Why is mercury commonly used for indicating 
temperatures in a thermometer ? 

For general purposes mercury is the most suitable sub- 
stance for use in thermometers because the range between 
its points of solidification and ebullition is greater than 
that of any known fluid. It is also a good conductor of 
heat, and is consequently rapid in its indications and sen- 
sitive to sudden changes of temperature. Liquids are 
progressively more expansive at higher than at lower tem- 
peratures ; but in the case of mercury the higher expan- 
sion at higher temperatures is less than in any other fluid 
body. Hence it is better adapted than any of them for 
the construction of thermometers. 

Q. What are the limiting temperatures of a mercury 
thermometer ? 

Mercury freezes at — 40 F. and boils at 6oo° F. Re- 
liable readings of temperature of a mercury thermometer 
are therefore limited between — 30 to 550 F. 

Q. What constants are employed when fixing standards 
of temperature? 

In order to measure temperature, certain fixed tempera- 
tures must be determined upon. The constants generally 
employed are the melting point of ice and the boiling 
point of water at the average atmospheric pressure. 

Q. What is absolute zero? 

The absolute zero of temperature may be defined as the 
temperature corresponding to the disappearance of gaseous 
elasticity. It has been fixed by reasoning, and has never 
been measured. The law of expansion of a perfect gas is 
that, the temperature remaining the same, its volume is 
inversely proportional to the pressure of the gas ; so also, 



THERMOMETER. £5 

the pressure remaining the same, the volume of the gas 
will be proportional to the temperature. 

The rate of expansion of a perfect gas per degree is 
0.00203 at 32 F., so that for each degree in rise of tem- 
perature the gas increases ^l-g- in volume, therefore the' 
volume of the gas would be doubled if its temperature be 
raised 493 ° F. This law holds good above the freezing 
point, there is no reason for doubting that it holds equal- 
ly good for temperatures below freezing; we have then 
— 493 less 32 = — 46 1 ° F. as the absolute zero of tem- 
perature. 

Q. What are the two thermometric scales in common 
use ? 

The two thermometric scales in common use are the 
Fahrenheit and the Centigrade. The zero point in the 
Fahrenheit scale corresponds to that temperature obtained 
by a mixture of snow and salt, which is marked 3 2° below 
the freezing point of water. The height of the mercury 
at the boiling point of water at atmospheric pressure hav- 
ing been marked on the scale, the whole distance between 
the freezing and the boiling point of water is divided into 
180 equal parts, called degrees, and this graduation is con- 
tinued to the zero point, the whole number of degrees 
= 180 -f- 32 =: 212. 

The Centigrade scale has its zero at the freezing point 
of water, and the interval between the freezing and the 
boiling points of water at atmospheric pressure is divided 
into 100 equal parts called degrees. 

The freezing point of water is 3 2° on the Fahrenheit 
scale, and o° on the Centigrade. The boiling point of 
water at atmospheric pressure is 21 2° on the Fahrenheit 
scale and ioo° on the Centigrade. 



56 



COMBUSTION OF COAL. 



Table 



7. — Centigrade Temperatures with Corresponding Tem- 
peratures on the Fahrenheit Scale. 



Cent. 


Fahr. 


Cent. 


Fahr. 


Cent. 


Fahr. 


Cent. 


Fahr. 


- 40 


- 40 


6 


42.8 


52 


125.6 


98 


208.4 


- 39 


- 38.2 


7 


44-6 


53 


127.4 


99 


2I0.2 


- 38 


- 36.4 


8 


46.4 


54 


129.2 


100 


2I2.0 


- 37 


- 34-6 


9 


48.2 


55 


131. 


IOI 


213.8 


-36 


- 32.8 


10 


50.0 


56 


I32.8 


102 


215.6 


- 35 


- 31 


11 


51.8 


57 


I34.6 


103 


217.4 


— 34 


— 29.2 


12 


53-6 


58 


136.4 


104 


219.2 


- 33 


- 27.4 


13 


55-4 


59 


138.2 


105 


22I.O 


- 32 


— 25.6 


14 


57.2 


60 


140.O 


106 


222.8 


- 3i 


— 23.8 


15 


59-0 


61 


141. 8 


107 


224.6 


- 30 


— 22 


16 


60.8 


62 


143.6 


108 


226.4 


- 29 


— 20.2 


17 


62.6 


63 


145.4 


109 


228.2 


- 28 


- I8.+ 


18 


64.4 


64 


147.2 


no 


23O.O 


- 27 


- 16.6 


19 


66.2 


65 


149-0 


III 


231.8 


- 26 


-14.8 


20 


68.0 


66 


150.8 


112 


233.6 


- 25 


- 13 


21 


69.8 


67 


152.6 


113 


235.4 


- 24 


— II. 2 


22 


71.6 


68 


154-4 


114 


237.2 


- 23 


- 9-4 


23 


73.4 


69 


156.2 


115 


239.O 


— 22 


- 7-6 


24 


75-2 


70 


158.0 


Il6 


24O.8 


— 21 


- 5-8 


25 


77.o 


7i 


159.8 


117 


242.6 


— 20 


- 4 


26 


78.8 


72 


161. 6 


Il8 


244.4 


— 19 


— 2.2 


27 


80.6 


73 


163.4 


II 9 


246.2 


- 18 


- 0.4 


28 


82.4 


74 


165.2 


I20 


248.O 


- 17 


1.4 


29 


84.2 


75 


167.0 


121 


249.8 


- 16 


3-2 


30 


86.0 


76 


168.8 


122 


251.6 


- 15 


5.o 


31 


87.8 


77 


170.6 


123 


253.4 


- 14 


6.8 


32 


89.6 


78 


172.4 


124 


255.2 


- 13 


8.6 


33 


91.4 


79 


174.2 


125 


257.O 


— 12 


10.4 


34 


93-2 


80 


176.0 


126 


258.8 


— 11 


12.2 


35 


95.o 


81 


177.8 


127 


260.6 


— 10 


14.0 


36 


96.8 


82 


179.6 


128 


262.4 


— 9 


15.8 


37 


98.6 


•83 


181. 4 


129 


264.2 


- 8 


17.6 


38 


100.4 


84 


183.2 


I30 


266.O 


- 7 


19.4 


39 


102.2 


85 


185.0 


131 


267.8 


- 6 


21.2 


40 


104.0 


86 


186.8 


132 


269.6 


- 5 


23.0 


41 


105.8 


87 


188.6 


133 


271.4 


- 4 


24.8 


42 


107.6 


88 


190.4 


134 


273.2 


- 3 


26.6 


43 


109.4 


89 


192.2 


135 


275.0 


— 2 


28.4 


44 


Hi. 2 


90 


194.0 


I36 


276.8 


— 1 


30.2 


45 


113.0 


9i 


195.8 


137 


278.6 





32.0 


46 


1 14. 8 


92 


197.6 


138 


280.4 


1 


33-8 


47 


116.6 


93 


199.4 


139 


282.2 


2 


35-6 


48 


118. 4 


94 


201.2 


I40 


284.O 


3 


37.4 


49 


120.2 


95 


203.0 


141 


285.8 


4 


39-2 


50 


122.0 


96 


204.8 


142 


287.6 


5 


41.0 


5i 


123.8 


97 


206.6 


143 


289.4 



For other 
Cent, -j- 32 



temperatures 
= deg. Fahr. 



(Deg. Fahr. — 32) 



deg. Cent. ; § 



THERMOMETER. 57 

Q. How may the temperature readings on the Fahren- 
heit and Centigrade scales be interconverted ? 

The distance between the freezing and the boiling point 
of water is, of course, the same for both thermometers, but 
the Fahrenheit scale contains 1 80 divisions while the Cen- 
tigrade scale contains only 100 divisions between these two 
points. If these numbers are divided by 20, we have 9 
and 5 respectively; smaller, therefore more convenient 
numbers to be used in the conversion of one scale into the 
other. The zero point of the Fahrenheit scale is 3 2° be- 
low the freezing point of water. 

To convert one scale into the other is quite simple, 
thus : 

Fahr. = 32 -f- f- Cent, degrees, or 
Cent. = -| (Fahr. degrees — 32). 

that is, add 32 to -| of the number indicated on the Cen- 
tigrade scale and the result is the number which would be 
indicated by the Fahrenheit scale. Subtract 3 2° from the 
number indicated on the Fahrenheit scale, and f of the 
remainder is the number which would be indicated by the 
Centigrade scale. 

Example 1. What would be the Fahrenheit temperature 
corresponding to 1 30 C. ? 

32+f of 130 = 266 F. 

Example 2. What would be the Centigrade tempera- 
ture corresponding to 266 F. ? 

f of (266-32) = 1 30 C. 

Q. Does a thermometer indicate the quantity of heat in 
a substance ? 

It does not. The use of a thermometer is merely to 
indicate the sensible heat, or that which is capable of be- 



58 



COMBUSTION OF COAL. 



ing radiated or communicated from one material to another. 
Its indications are merely relative and do not express the 
actual amount of heat which a substance contains. 

CHEMISTRY. 
Q. What is an atom ? 

The atomic theory affirms that every portion of matter 
of sensible size is built up of a vast number of small par- 
ticles which are not themselves capable of further subdi- 
vision. Each particle corresponding to this definition 
would be called an atom (a term borrowed from the Greek), 
and means indivisible. In chemistry it means the small- 
est quantity by weight of an element which is capable of 
existing in a chemical compound. 

Q. What is meant by atomic weight ? 

One of the properties of matter is that it has weight ; 
atoms, therefore, have weight because an atom is a defi- 
nite and fixed quantity of matter. Hydrogen, being the 
lightest known substance, has by general consent been 
made the unit of comparison; the atomic weight of hydro- 
gen is always represented by I. 

Table 8. — Atomic and Combining Weights of Gases. 



Element. 

Hydrogen 

Nitrogen 

Oxygen 

Carbon (diamond burnt to C0 2 ) 




Combining weight. 

4| 
8 

3 



By combining weight is here meant the smallest mass 
of the element which combines with eight parts by weight 
of oxygen, or one part of hydrogen. 



MOLECULE. 

Table g. — Atomic Weights. 



59 



Name 

Calcium 

Carbon 

Hydrogen 

Nitrogen 

Oxygen 

Phosphorus 

Potassium 

Silicon 

Sodium 

Sulphur 



Symbol. 



Atomic weights. 



Ca 


40 


C 


12 


H 


1 


N 


14 





16 


P 


3i 


K 


39 


Si 


28.5 


Na 


23 


S 


32 



The above list of elements are those commonly found in 
coal by elementary analysis. Aluminum and iron are also 
found in the analysis of coal ashes. 



Q. What is a molecule ? 

A molecule is the smallest possible portion of a particu- 
lar substance, whether elementary or compound, which 
exhibits the characteristic properties of that substance. 
Every substance, therefore, whether simple or compound, 
has its own molecule; and if this molecule be divided, its 
parts are molecules of a different substance or substances 
from that of which the whole is a molecule. An atom is 
the smallest particle of an element which enters into the 
composition of molecules. In the case of the molecule of 
an element the atoms are all of one kind ; in the case of 
the molecule of a compound the atoms are of two or more 
than two different kinds. As the properties of the mole- 
cule of a compound are very different from the properties 
of the atoms which compose it, so it is probable that the 
properties of the molecule of an element are different 
from the properties of the atoms by the union of which 
the molecule is produced. 



60 COMBUSTION OF COAL. 

Q. What is one of the characteristics of molecules? 

That they are always in motion. These motions of 
molecules are, in the case of solid bodies, confined within 
so narrow a range that even with our best microscopes we 
cannot detect that they alter their places at all ; but in the 
case of liquids and of gases the molecules are not confined 
within any definite limits, but work their way through the 
whole mass, even when that mass is not disturbed by any 
visible motion. This process of diffusion, as it is called, 
which goes on in gases and liquids and even in some 
solids, can be subjected to experiment, and forms one of 
the most convincing proofs of the motion of molecules. 

Q. What is meant by symbolic notation ? 

Symbolic notation belongs to an agreed employment, as 
far as practicable, of the first letter of the Latin name of 
an element, by which it may be recognized at sight, thus 
facilitating the representation of chemical changes, by 
which reactions of a complicated character may be under- 
stood at a glance. Thus carbon is represented by the let- 
ter C, oxygen by O, hydrogen by H, etc. Carbonic oxide 
by the letters CO ; carbonic acid gas by the formula C0 2 , 
etc. 

Q. Give some examples of the symbolic notation of com- 
pounds occurring in the process of combustion? 

A combination of elements is represented by a combi- 
nation of symbols placed side by side. If one atom of 
carbon and one atom of oxygen be united we have the 
symbol CO, carbonic oxide. It will be understood that 
one atom each of carbon and oxygen unite and form, not one 
atom, but one molecule of carbonic oxide. So also in the 
previous question the combination of one atom of carbon 



SYMBOLIC NOTATION. 6 1 

with two atoms of oxygen, written C0 2 , is the symbolic 
expression of one molecule of carbonic-acid gas. Hydro- 
gen is represented by H ; its atomic weight is i . The 
formula H..O means that two atoms of hydrogen have 
united with one atom of oxygen to form two molecules of 
water. 

Q. Does this method of symbolic notation express other 
than an abbreviation of the name of an element? 

Yes, the symbols employed are not only abbreviations 
of the Latin names of the elements, but they represent 
the atomic weights of the several elements for which they 
stand. Thus carbon, represented by C, has an atomic 
weight of 12 ; and as there is no other element having an 
atomic weight of 12, the letter C and figure 12 may al- 
ways be thus associated. It will be understood that C 
always stands for one atom of carbon, the atomic weight 
of which is 12 ; and if more than one atom of an element 
appears in a formula, the number of such atoms are ex- 
pressed by numerals, thus : C0 2 for carbonic acid gas, 
meaning thereby that one atom of carbon and two atoms 
of oxygen have entered into chemical union. 

When two or more atoms of an element unite in the 
formation of a molecule of a compound substance the writ- 
ten formula is simplified by writing a small figure to the 
right of the symbolic letter and below the line. Thus C 3 
indicates three atoms of carbon, H 8 indicates eight atoms 
of hydrogen. The formula C 3 H 8 indicates one of the prod- 
ucts of coal occurring in the marsh gas series, and known 
as propyl hydride ; and this formula is the symbolic ex- 
pression of one molecule. 

Secondary compounds, such as salts, are expressed in 
an analogous way, the metal being usually placed first, 



62 COMBUSTION OF COAL 

CaC0 3 representing one molecule of carbonate of calcium, 
calcium being the metallic base. 

Q. What is meant by the chemical properties of a 
body? 

Those which relate to its action upon other bodies, and 
to the permanent changes which it experiences in itself, 
or which it effects upon them. When a body undergoes 
chemical change it almost invariably destroys the physical 
properties held by it previous to this change ; but experi- 
ment has fully demonstrated that matter is indestructible, 
so that whatever changes are made in the physical appear- 
ance or form of matter by any chemical process, none of 
it is destroyed. 

Q. What is meant by affinity? 

By affinity is commonly meant the unknown cause of the 
combination of atoms. Hydrogen and chlorine combine 
very readily. They have, as we say, a strong affinity for 
each other; yet they are monovalent with reference to 
each other. Carbon and chlorine do not combine readily. 
They do not have a strong affinity for each other, yet an 
atom of chlorine is capable of holding four atoms of car- 
bon in combination. The two properties, valency and 
affinity, are possessed by every atom, and exhibit, them- 
selves whenever atoms act upon one another, the latter 
determining the intensity of the reaction, the former the 
complexity of the resulting molecule. 

Q. What is meant by chemical affinity ? 

Chemical affinity is that property of bodies in virtue of 
which, when brought in contact, they react on each other, 
forming new bodies. It can be called a force, in so far as 



CHEMICAL ATTRACTION. 63 

by its action energy is produced — namely, heat, light, 
electrical or mechanical energy ; and vice versa, energy 
must be employed to reverse the action of chemical affinity 
and to decompose the combined substances. Nothing is 
known as yet about the nature of chemical affinity, nor 
has a satisfactory hypothesis been suggested concerning it. 

Q. What is meant by chemical attraction ? 

Chemical attraction is distinguished from other chemi- 
cal forces which act within minute distances by the com- 
plete change of characters which follows its exertion, and 
must from its very nature be exerted between dissimilar 
substances. Hydrogen and oxygen are both gaseous and 
are wholly dissimilar in their chemical properties; yet 
under proper conditions they will unite with great avidity, 
the combination forming gaseous steam, which upon cool- 
ing yields only pure water. 

The physical and other changes brought about as a re- 
sult of chemical attraction do not destroy the combining 
elements, but simply rearrange them in another form, and 
give to the new compound properties not held by any ele- 
ment singly. 

Q. What is meant by the term equivalent ? 

The equivalent of an element is that mass of an element 
which combines with one atom of hydrogen. In the case 
of oxygen it corresponds to half an atom, in that of nitro- 
gen to one-third the atom, and in that of carbon to one- 
fourth the atom. With those elements which do not com- 
bine with hydrogen some other element like hydrogen in 
respect to the ratio between the equivalent and atomic 
weight is taken as the measure of the equivalent. 



64 COMBUSTION OF COAL. 

Q. What law governs the combining weights of the 
elements ? 

The laws of chemical combination are all included in 
the two statements: i. The elements combine in the ra- 
tios of their combining weights, or in ratios which bear a 
simple relation to these. 2. The gaseous elements com- 
bine in the ratios of their combining volumes, or in ratios 
which bear a simple relation to these. 

By combining weight is here meant the smallest mass 
of an element which combines with unit mass of some 
specified element taken as a standard ; and by combining 
volume is meant the smallest volume of a gaseous element 
which combines with unit volume of some specified gas- 
eous element taken as a standard. The first statement has 
been amply verified by accurate experiment ; the second 
does not yet stand on so firm an experimental basis. 

Q. What is the law of definite proportions? 

The law of definite proportions may be stated thus : In 
any chemical compound the nature and the proportions of 
its constituent elements are fixed, definite, and invariable. 
For example : One hundred parts of water by weight con- 
tain 88.9 of oxygen and 11.1 of hydrogen. These gases 
will combine in no other proportions to form water, and 
any excess of either gas will remain unchanged. 

The law of definite proportion assumes that atoms have 
definite weight ; that an atom is a fixed and definite quan- 
tity; that atoms of the same substance are of the same 
size and weight. When the elements unite chemically, 
they invariably do so in the proportions by weight repre- 
sented by the numbers attached to them, as in Table 9, or 
in multiples of these numbers. Dalton accounted for this 
law by supposing that the constituent particles of matter are 



MULTIPLE PROPORTIONS. 6$ 

indivisible, and believed that if it were, possible to place 
such particles in the balance, their relative weights would 
be found to correspond with the numbers given in the table. 

Q. What is the law of multiple proportions? 

When two or more compounds are formed of the same 
elements, there is no gradual blending of one into the 
other, as in the case of mixtures, but each compound is 
sharply defined and exhibits properties distinct from those 
of the others, and of the elements of which the compounds 
are composed. For example : 

There are two compounds of carbon and oxygen — 

Carbon Oxygen Atomic 

by weight, by weight. weight. 

Carbonic oxide CO 12 16 28 

Carbonic acid gas C0 2 12 32 44 

It will be observed that, the quantity of carbon remaining 
the same, the quantity of oxygen must be doubled in order 
to form the other compound. These proportions consti- 
tute the only two direct inorganic compounds of carbon and 
oxygen. 

Q. Is the atomic value of an element changed by enter- 
ing into chemical combination with another element? 

No, the atomic value of each element in a compound 
remains unchanged, and the aggregate weight of the atoms 
forms the molecular weight of the compound thus : 

One molecule of carbonic oxide equals : 

1 atom of carbon, C, at wt. 12 = 12 
I atom of oxygen, O, at wt. 16 = 16 

Weight of one molecule CO =28 

One molecule of carbonic-acid gas equals : 

1 atom of carbon, C, at wt. 12 = 12 

2 atoms of oxygen, O, at wt. 16 = 32 

Weight of one molecule CO a = 44 



66 COMBUSTION OF COAL. 

Q. Is chemical attraction influenced by temperature ? 

In all cases of ordinary combustion it is essential that 
the temperature of the uniting substances be raised to the 
point of ignition. A mixture of oxygen and hydrogen 
may be preserved unchanged at ordinary temperatures any 
length of time, but a mere spark, or the introduction of a 
body heated to redness, so completely alters their mutual 
attraction that sudden combination attended with explosion 
is the result. This is as pure a case of augmentation of 
chemical attraction as can be met with, since both the 
components are thoroughly mixed ; and as both are perfect 
gases, heat cannot in this case act by diminished cohesion, 
and so bring their particles into more intimate contact. 

Q. What is meant by energy of chemical separation ? 

A combustible body like coal may be taken as a fair 
representative of potential energy because it occupies a 
position of advantage over a non-combustible body in this, 
that it will unite with another body for which it has 
chemical affinity like oxygen, and this energy of position 
leading, as it can in this case, to a process of chemical 
separation during the act of burning, in which we have 
potential energy or the energy possessed by the coal be- 
fore ignition, and the energy due to molecular activity by 
reason of the act of combustion, or the energy of motion 
changed into another form of energy represented by heat. 

The energy of chemical separation when produced by 
the combustion of coal is always intense, and as the ob- 
served effects are so much below the theoretical value 
ascribed to the fuel, it would seem as if for once the law 
of conservation of energy was at fault ; but this is not the 
case. Our methods of manipulation are wasteful and the 



ENERGY OF CHEMICAL SEPARATION. 6j 

ordinary construction of furnaces so faulty that a very 
large proportion of the waste can be directly accounted 
for. One thing with reference to the energy of chemical 
separation is certain, and that is, that any given quantity 
of carbon or other combustible under given conditions will 
always produce the same quantity of heat. 



CHAPTER III. 

THE ATMOSPHERE. 

Q. What is the composition of air? 

The composition of air free from water and carbonic 
acid is found to be, by weight : 77 per cent of nitrogen 
and 23 per cent of oxygen; or by volume: 79 volumes of 
nitrogen and 2 1 volumes of oxygen. In addition to these 
two gases atmospheric air contains aqueous vapor, car- 
bonic acid, ozone, ammonia, with traces of nitrous and ni- 
tric acids, etc. 

Air, owing to the oxygen it contains, is a magnetic sub- 
stance. 

Q. Is air a chemical compound? 

It is not. The union of these two gases in the propor- 
tions of 79 volumes of nitrogen to 21 of oxygen gives 
common air; and this union is distinguished by no proper- 
ties which may not be attributed individually to these 
gases. All experiments made thus far have shown no in- 
dication that the union is other than mechanical. 

Q. What proofs sustain the statement that air is not a 
chemical compound? 

That air is not a chemical compound of its component 
gases is proven by the facts : 

1 . That the gases nitrogen and oxygen are not present 
in any constant ratio. 



OXYGEN. 69 

•2. That air can be made by simply mixing its constitu- 
ents in the proportion indicated by the analysis of air, 
without contraction or any thermal disturbance resulting. 

3. That on treating air with water and expelling the 
dissolved air by boiling, the proportion of the oxygen to 
the nitrogen is found to be increased, and in amount cor- 
responding with the law of partial pressures. 

4. That the constituents of the air can be mechanically 
separated by processes of diffusion. 

5. That the refractive power of the air is equal to the 
mean of the refractive powers of its constituents, whereas 
in compound gases the refractive power is either greater 
or less than the refractive power of the elements in a state 
of mixture (Thorpe). 

Q. What is oxygen? 

Oxygen is present in the atmosphere in a free and un- 
combined state, forming 2 1 per cent of its total volume. 
Priestly first obtained the gas in 1774, and gave it the 
name depJilogisticated air. It was isolated independently 
and almost simultaneously by Scheele, who termed it 
empyreal, or fire air. Lavoisier regarded it as an essen- 
tial constituent of all acids, and hence gave it its present 
name oxygen. The discovery of oxygen was the means of 
leading Lavoisier to the true theory of combustion. 

Oxygen is somewhat heavier than the air, it having a 
specific gravity of 1.1056, air = 1.0000. One hundred 
cubic inches of oxygen weigh 34. 206 grains. The specific 
heat of oxygen for equal weights at constant pressure = 
0.2182; for constant volume = 0.1559. When pure, 
oxygen is colorless, tasteless, and inodorous. It is spar- 
ingly soluble in water. As with all gases the quantity 
dissolved depends on the tension of the oxygen in the at- 



JO COMBUSTION OF COAL. 

mosphere in contact with the water. Thus pure water 
shaken up in contact with pure oxygen will absorb nearly 
five times as much oxygen as it would when shaken up, at 
the same temperature and under the same pressure, with 
air, which only contains 21 per cent by volume of oxygen. 

Oxygen is the least refractive of all the gases. It is 
slightly magnetic, but its susceptibility in this respect is 
diminished or temporarily suspended by elevation of tem- 
perature. 

Though long regarded as a permanent gas, oxygen was 
liquefied in 1877 by Pictet, who attributed to liquid oxygen 
a density near that of water, about 0.9787. The critical 
temperature of oxygen is — 113 C, the pressure needed 
to liquefy it at that temperature being about 50 atmos- 
pheres. Liquid oxygen is a pale, steel-blue, transparent, 
and very mobile liquid, boiling at — 181 C. at ordinary 
pressures. When the pressure is reduced or removed, 
evaporation takes place so rapidly that a part of the oxygen 
is often frozen to a white solid. Liquid oxygen is a very 
perfect insulator, and is also comparatively inert in its 
chemical properties. 

There are only seven elements which do not unite di- 
rectly with oxygen, viz., fluorine, chlorine, bromine, iodine, 
silver, gold, and platinum. All the non-metallic elements 
with two exceptions unite with oxygen to form anhydrous 
acids. Of the exceptions hydrogen forms a neutral oxide 
(water), while no oxide of fluorine has yet been obtained. 

The product of the union of oxygen with another ele- 
ment is called an oxide. Thus when lead is heated in 
contact with air it combines with oxygen, forming lead 
oxide, PbO. Carbon burns in oxygen, forming carbon di- 
oxide, C0 2 . 

The chemical activity of air depends upon the oxygen 



NITROGEN. 71 

it contains, air being simply in its chemical relations 
oxygen diluted with nitrogen. Free oxygen, whether di- 
luted with nitrogen or not, manifests considerable chemi- 
cal activity, even at ordinary temperatures, this activity 
increasing with rise of temperature. With most sub- 
stances an initial heating is necessary to start free oxida- 
tion, the heat evolved being then sufficient to maintain it. 
Various substances which expose large surfaces to air (or 
oxygen) become gradually heated through slow oxidation 
or combustion ; and if the heat cannot get away, ignition 
eventually occurs. Thus oily or greasy woollen and cot- 
ton waste or rags and refuse are capable of absorbing 
oxygen very rapidly, and if present in any considerable 
quantity the heat produced may accumulate and cause 
spontaneous combustion; and this action is a not infre- 
quent cause of fires in factories. 

Q. What is nitrogen? 

Nitrogen, one of the most widely diffused of the ele- 
ments, occurs free in the air, of which it constitutes about 
79 per cent by volume. It is a colorless, inodorous, taste- 
less, neutral gas, of 0.972 specific gravity (air = 1) ; 100 
cubic inches at 6o° F. and 30 inches barometer pressure, 
weigh 30.052 grains. It is slightly soluble in water; 
100 volumes of water dissolve 1.5 volumes of nitrogen at 
1 5 C. The specific heat of nitrogen = 0.244, at constant 
pressure. Nitrogen has been liquefied by the cold pro- 
duced by its expansion from a compression of 300 atmos- 
pheres at + I 3° C. Liquid nitrogen boils at — 193 C. 
under atmospheric pressure. 

Q. Is nitrogen a supporter of combustion ? 

Nitrogen is incombustible, and does not support com- 
bustion. Its negative qualities are very pronounced ; it 



72 COMBUSTION OF COAL. 

will not take fire; it puts out the combustion of every- 
thing, and there is nothing that will burn in it in ordinary 
circumstances. It is not a poisonous gas, but animal life 
cannot be sustained in it for want of oxygen. 

Q. Are the negative qualities of nitrogen a hindrance 
in furnace combustion? 

The useful effect of nitrogen in combustion is that it 
lowers the intensity of the fire and makes it moderate, 
useful, and easily controlled. An atmosphere of oxygen 
without nitrogen would be wholly uncontrollable. The 
iron grate and furnace front would burn even more 
powerfully than coal, because iron is more combustible 
in oxygen than is carbon. The neutral qualities of ni- 
trogen then become of the greatest importance in com- 
bustion. 

Q. Is nitrogen then so inert that it will not combine 
with other substances? 

While it is true that nitrogen in its free state is re- 
markable for its inactivity in furnace combustion, it may 
be made to unite directly under certain conditions with 
hydrogen, oxygen and carbon — as, for example, when a 
series of electric sparks is passed through oxygen and ni- 
trogen gases, standing over a solution of caustic alkali, 
when a nitrate of the metal is produced. Traces of nitric 
acid and ammonium nitrate are produced by burning 
hydrogen gas mixed with nitrogen in an atmosphere of 
air and oxygen. Nitrogen can unite with hydrogen when 
one or both of the gases are in the nascent state, to form 
ammonia. Carbon and nitrogen unite directly when ni- 
trogen gas or atmospheric air is passed over an ignited 
mixture of charcoal and potash. 



CARBONIC ACID IN THE AIR. 73 

Q. What economic quality does nitrogen display in 
furnace combustion ? 

Nitrogen in its ordinary state is an active element, not- 
withstanding its negative qualities in the furnace. No 
action short of the most intense electric force, and then 
in small degree, can cause the nitrogen to combine direct- 
ly with the other element of the atmosphere, or with 
things round about it. It is perfectly indifferent, and 
therefore to say a safe substance. The part which nitro- 
gen plays in furnace combustion is analogous to that of a 
vessel in which the oxygen is delivered into the body of 
incandescent fuel. The oxygen then separates from the 
nitrogen to combine with the carbon of the fuel. This 
delivery having been made, the vessel is no longer of any 
value in that connection and passes on through the fire. 
By reason of its lighter gravity it assists in maintaining a 
good draught, a matter of prime importance in furnace 
combustion. 

Q. What quantity of carbonic acid is present in the 
air? 

There is in the air, besides the aqueous vapor, 3.36 
parts in every 10,000 of carbonic-acid gas. Any circum- 
stance which interferes with ready diffusion of the prod- 
ucts of respiration and the combustion of fuel will of 
course tend to increase the relative amount of carbonic 
acid of a town ; hence during fogs the amount may be as 
great as o. 1 per cent. The pressure exerted by the car- 
bonic acid in the air is so small that its amount is not per- 
ceptibly diminished by rain. The amount is also not 
sensibly altered in the higher regions of the atmosphere. 

Q. What quantity of ammonia is present in the air? 

Ammonia is present in the air in minute quantities 



74 COMBUSTION OF COAL. 

only; it exists mainly as carbonate and is subject to very 
great variations as to quantity. Rain water collected in 
towns always contains large quantities of ammonia, prob- 
ably due to the influence of animal life and to the constant 
presence in greater proportion than in the country of read- 
ily decomposable nitrogenous organic matter in the air. 

Q. What quantity of aqueous vapor is present in the 
air? 

Aqueous vapor in the air varies in quantity with the 
temperature; but more of it can be sustained in warm air 
than in cold. Air at a temperature of 32 ° F. can sustain 
the T -jt 7 part of its own weight of aqueous vapor, but at 
86° F. it can sustain yl-g- part of its own weight. The 
humidity of the air is usually estimated by means of 
hygrometers. .The barometer gives the combined weight 
of the oxygen, nitrogen, and gaseous vapor of the air, and 
the portion of this weight which is due to aqueous vapor 
is called the elastic force of vapor. With a barometer 
standing at 30 inches, and with a hygrometer indicating 
an elastic force of vapor of .45, very nearly one-fourth 
pound of the entire pressure of fifteen pounds is due to the 
vapor. When more vapor is generated than can be at 
once carried away, the barometer necessarily rises ; when 
vapor is condensed in the atmosphere the barometer falls ; 
when the temperature of saturated air is reduced from 8o° 
to 6o°, five grains of aqueous vapor are deposited from 
each cubic foot. This is the effective cause of rain. 

Q. Is ozone always present in the air? 

Ozone is always present in minute quantities in normal 
air. Atmospheric ozone is probably formed by the action 
of electricity on air and on the water contained in it, and 
by the evaporation of water. It appears that the amount 



ATMOSPHERIC PRESSURE. 75 

of ozone varies with the seasons ; it is greatest in spring, 
becomes gradually less during summer and autumn, and is 
least in winter. Ozone is more frequently observed on 
rainy days than in fine weather. Thunder storms, gales, 
and hurricanes are frequently accompanied by relatively 
strong manifestations of it. 

Q. What is the weight of air? 

The weight of one cubic foot of air at 32 ° F. is .080728 
pound, or 565. 1 grains; at 62 F. it is .076097 pound, or 
532.7 grains. The volume of one pound of air at 32 ° F. 
at ordinary atmospheric pressure (14.7 pounds) is 12.4 
cubic feet. 

Q. What is atmospheric pressure? 

Air in common with other bodies possesses the property 
of weight ; and as the pressure of water at the bottom of a 
tank is greater than near its upper surface, so the pressure 
of the atmosphere is greater at the level of the sea than at 
the top of a high mountain. We are not certain as to the 
height of the atmosphere, but it is commonly supposed to 
be not less than forty-five miles, measured from the sea 
level. Whatever its height, we know that a vertical col- 
umn of this air produces an average pressure on the earth's 
surface of about 14.73 pounds per square inch; but the 
pressure even at the same place is continually varying 
from a variety of causes. In steam engineering the press- 
ure of the atmosphere is commonly assumed to be fifteen 
pounds per square inch. 

Q. What is the unit of pressure? 

The unit of pressure adopted by European engineers and 
others, and styled an atmosphere, is an amount equal to the 
average pressure at the level of the sea. In British meas- 



?6 COMBUSTION OF COAL. 

ures an "atmosphere " is the pressure equivalent to 29.905 
inches of mercury at 32 ° F. at London, and is about 14.73 
pounds to the square inch. Steam engineers in this coun- 
try make their calculations for pressures in terms of pounds 
per square inch, it being a more convenient unit than an 
"atmosphere." 

Q. How is the pressure of the atmosphere measured? 

By means of an instrument called a barometer; one 
variety of which consists of a vertical glass tube of uni- 
form diameter, hermetically sealed at the top end, and of 
about 33 inches in length, into which mercury has been 
poured until it has been completely filled and then in- 
verted, its lower and open end being placed in a vessel 
also containing mercury. A graduated scale reading to 
inches, and by means of a vernier to hundredths of an 
inch is located near the top of the glass tube for read- 
ing the level of the mercury. The pressure of the 
atmosphere acting on the surface of the mercury in the 
open vessel causes a rise or fall of the mercury directly 
proportional to the pressure of the atmosphere. 

Q. Is the atmosphere of the same density throughout 
its height? 

The density of the air rapidly diminishes with the 
height. For air of constant temperature its density, or 
what comes to the same thing, the height of the baro- 
metric mercury column, should diminish in geometric pro- 
gression, while the distance from the earth increases in 
arithmetic progression. 

Q. How does the law of Mariotte and Boyle apply in 
determining the density of the air? 

Mariotte and Boyle have established the law that every 



HEATING AND COOLING AIR. J7 

time the pressure upon air is doubled its volume is halved. 
This is the obvious reason why air is more rare and light, 
bulk for bulk, at the higher regions of the atmosphere 
than it is near the surface of the earth. At a height of three 
miles the air has a doubled volume and half its original 
density. It is again doubled in volume at about six miles 
high ; and it is probable that no animal could continue to 
live and breathe at a height of eight miles. 

Q. How may pounds of air be converted into an equiv- 
alent volume in cubic feet? 

As we have no convenient means for weighing air in 
bulk, and as air is known to weigh 532.7 grains per cubic 
foot at 62 ° F., it will be a near enough approximation as 
between summer and winter temperatures to assume that 
one pound of air = 12. 5 cubic feet. 

Q. May air be readily heated and cooled? 

The difficulty in either heating or cooling air is its non- 
conducting capacity ; or, more strictly speaking, the diffi- 
culty in obtaining a sufficiently rapid convection of heat 
to and from the mass of air employed. To heat or cool 
air, very extensive surfaces, together with very great dif- 
ferences of temperature, are necessary. Siemen's regener- 
ators have about 1 7 pounds of fire brick for each increment 
of gaseous fuels that can be developed from one pound of 
coal. As, however, only about one-fourth of the total re- 
generative capacity is being heated to the full tempera- 
ture of the gases passing down through the ports, this 
amount has to be increased fourfold, so that nearly 70 
pounds of fire brick are probably used per pound of prod- 
uct of combustion. 



78 COMBUSTION OF COAL. 

Q. Does the density of the air affect the passage of 
heat through it ? 

An interesting phenomenon relating to the weight or 
density of the air is the variation in what is known as its 
diathermancy, or heat passing through it without being 
apparently absorbed. The greater the tenuity of the air, 
the more nearly diathermanous is it. Pure air is virtually 
quite pervious to heat ; none stops in the air, but all passes 
through. The absolute diathermacy of dry air accounts 
for the scorching heat of mountain tops as the retentive 
power of aqueous vapor does for the soft heat of low-lying 
regions in the tropics. 

Q. How is atmospheric air affected by heat? 

Air is expanded by increase of temperature, the increase 
in volume being T |~g part for each degree Fahrenheit. For 
example, 1,000 cubic inches at 32 ° F. would be increased 
at 212 to 1,336 cubic inches. 

Q. Why is it necessary to provide for a supply of air 
through the fuel in furnace combustion? 

Atmospheric air is the only available source of oxygen 
for supporting the combustion of fuels. 

Q. What is the physical effect of heat upon the air 
entering the fire ? 

The first physical effect of heat upon air is its expan- 
sion, and this of necessity takes place in the most confined 
space, namely, in the interstices of the fuel, and acts 
equally in all directions. Although all in motion upward 
through the fire, its upward portion, being most greatly 
expanded, is moving more rapidly than its less expanded 
lower portion ; and its expansive force, acting downward, 



HEATED AIR AND COMBUSTION. 79 

simply retards the upward flow of entering air. Lateral 
expansion aids in bringing fresh oxygen into contact with 
unconsumed carbon. Upward expansion aids, and down- 
ward expansion retards the draught. Now it is plain that 
this effect must be the greater the greater the degree of ex- 
pansion which takes place within the interstices of the fuel. 
With air supply at 6o° F. it is 5.7-fold; with equal air 
supply, by weight, at 385 F. it is 3. 5 -fold, as shown on 
page 80. 

Q. What would be the physical effects if air at 6o° 
F. be heated to 385 ° F. and supplied a furnace at the 
latter temperature? 

If to the sensible temperatures 6o° and 385 ° we add 
46 1 °, we shall have the corresponding absolute tempera- 
tures of 52 1 ° and 846 respectively; and the volume of 
the heated air will be increased in the ratio of these two 
numbers, or J-||- = 1.624. Therefore 8 cubic feet of air 
at 6o° would occupy 8 X 1.624 = 12.992, say 13 cubic feet 
at the higher temperature, at which we will suppose it to 
be conveyed to the fire. The density of the air will be 
in the same inverse ratio ; that is, 1 3 cubic feet of air at 
38 5 must be admitted to the fire and to contact with 
glowing fuel in order to introduce as much oxygen as 
would be contained in 8 cubic feet of the- air at 6o° F. 
Equally, of course, the entering velocity must be greater 
in the same proportion, since the aggregate area of all the 
orifices through the grates and fuel may be regarded as 
constant. This has been urged as an objection to heating 
air before its introduction to the fire. 

Q. Is the increase in volume due to preheating air, as 
suggested above, a valid objection to its use ? 

Cold air in necessary quantity will enter the ash pit and 



80 COMBUSTION OF COAL. 

will pass through the openings in the grates with less 
velocity than will the same quantity of heated air. But 
in these passages the area is amply large and the velocity 
moderate. It is also true that on entering the lower 
stratum of fuel the velocity of the heated air will be the 
greater. The very first effect of the chemical union of 
any part of the oxygen with any part of the carbon is to 
heat the gases associated with such oxygen — that is, its 
associated nitrogen and the atmospheric air yet containing 
its oxygen, together with the carbonic-acid gas resulting 
from such union or combustion, to the full extent to which 
the entire heat of combustion can raise the given mass of 
gases. This will approximate the temperature of the fur- 
nace, modified by the subsequent union of further portions 
of oxygen with new portions of carbon encountered during 
the farther progress of the mixed gases through the fuel, 
until they emerge at the surface of the fire. 

If their temperature be now 2500 F. or 2961 ° absolute, 
their volume will be ^-£±=$.7 times that of the air tem- 
perature, 6o° F., and ^^-=3.5 times that of air of 
temperature 385 F. Now it is this volume of the gases 
at their final emergence from the interstices of the fuel 
that determines their flow; determines the force of 
draft or blower required to produce that flow. The 
difference between 3. 5 times, as against 5.7 times, is favor- 
able and compensates, as far as it goes, for the greater 
force required to introduce the heated air with its greater 
volume and higher velocity. 

Q. What are the combined physical and chemical effects 
of heated air for furnace combustion? 

Carbon and oxygen will unite at all temperatures usually 
met. Coals waste in the open air by slow combustion, 



QUANTITY OF AIR REQUIRED. 8 1 

the resulting heat being dissipated by radiation and the 
convection of the air. The rapidity of combustion is aug- 
mented with the rise of temperature, and is very great at 
high incandescence. The temperature of the oxygen is no 
less important than that of the carbon; the higher the 
sum of their temperatures, the more rapid is their union. 
So far as the associated gases are concerned, their higher 
temperature only serves to communicate more heat to the 
mass, or, which amounts to the same thing, to abstract 
less heat from it. With heated air the resulting temper- 
ature is higher and the combustion will be more rapid. 

Q. How may the quantity of air required for the com- 
bustion of any fuel be determined ? 

The quantity of oxygen required for the complete com- 
bustion of any given quantity of carbon or hydrogen has 
been experimentally determined and is well known ; the 
quantity of oxygen in the atmosphere being practically 
constant, the process of determining the amount of air re- 
quired for these two elements is quite simple, thus : 

One pound of hydrogen requires 8 pounds of oxygen for 
its complete combustion ; this requires about 36 pounds of 
air. 

One pound of carbon requires 2^ pounds of oxygen for 
its complete combustion (to C0 2 ), or about 12 pounds of 
air. 

One pound of carbon incompletely burnt, or to carbonic 
oxide (CO), requires ij^ pounds of oxygen, or about 6 
pounds of air. 

All the above are based on the assumption that 4.5 
pounds of air are required to supply 1 pound of oxygen. 

The above applies only to such fuels as have undergone 
analysis, the elemental constituents being known. 
6 



82 



COMBUSTION OF COAL. 



A table giving the theoretical quantity of air required 
for a variety of fuels was prepared by Rankine, and has 
very general acceptance. This table is here reproduced. 

Table io. — Am Required for Perfect Combustion. 



Fuel. 



Carbon. 



Hydrogen. 



Oxygen. 



Air 
Required. 



I. Charcoal, from wood. . 

from peat . . . 

II. Coke, good 

III. Coal, anthracite 

dry bituminous. . 

caking 

caking 

cannel 

dry long flaming 
lignite 

IV. Peat, dry 

V. Wood, dry 

VI. Mineral oil 



o.93 

0.80 

0.94* 

0.915 

0.87 

0.85 

o.75 
0.84 
0.77 
0.70 
0.58 
0.50 
0.85 







0.035 


0.026 


0.05 


0.04 


0.05 


0.06 


0.05 


0.05 


0.06 


0.08 


0.05 


0.15 


0.05 


0.20 


0.06 


0.31 







II. 16 

9.6 

11.28 
12.13 
12.06 

H-73 

10.58 

11.88 

10.32 

9-30 

7.68 

6.00 

15.65 



Q. What quantity of air is usually estimated per pound 
of coal ? 

The theoretical quantity of air required for boiler fur- 
naces is assumed to be 12 pounds of air for each pound of 
coal, regardless of its composition. From 18 to 24 
pounds of air per pound of coal burnt is a common allow- 
ance when making up estimates ; 24 pounds of air is a 
near approximation to the average quantity supplied the 
burning fuel per pound of coal. 

Q. What is the specific heat of air? 

The specific heat of air at constant pressure is 0.2374 
(Regnault). 

Q. Under what conditions may air be liquified? 

Under the critical pressure of 39 atmospheres, and at 
the low temperature of 31 2° below the Fahrenheit zero 
(— 191 ° C), air may be liquefied. 



CHAPTER IV. 

COMBUSTION. 

Q. What is combustion ? 

Any manifestation of chemical energy attended by com- 
bination and accompanied by production of much heat is, 
strictly speaking, an instance of combustion. In steam 
engineering it means the controlled chemical combination 
of the elements carbon and hydrogen in the fuel with the 
oxygen of the atmosphere, by which an evolution of heat 
is secured and maintained in a suitably constructed fur- 
nace for the purpose of generating steam. 

The term combustion, as commonly used, carries with 
it the idea of incandescence, or the glowing whiteness of 
a body caused by intense heat, which is quite character- 
istic of burning carbon; the term also includes that of 
inflammation, which is, however, best restricted to in- 
stances of combustion in which the incandescent sub- 
stances are gaseous. All phenomena of burning are in- 
stances of combustion, and in the great majority of cases 
they consist in the union of the oxygen of the atmosphere 
with the substance which is being burnt, the visible signs 
of combustion, i. e. , the heat and light, being the result im- 
mediate or proximate of the chemical energy so expended. 

Q. What is the nature of combustion as applied par- 
ticularly to coal ? 

Coal is mainly composed of the two elements, carbon 
and hydrogen, both of which have an affinity for oxygen ; 



84 COMBUSTION OF COAL. 

but before they unite chemically to produce heat it is 
necessary that certain conditions be fulfilled, the first of 
which is that a considerable mass of the coal must be 
heated to the point of ignition before the oxygen in the 
air will unite with it. 

The oxygen having a choice of two partners, as Profes- 
sor Tyndall happily puts it, closes with that for which it 
has the strongest attraction. It first unites with the hy- 
drogen and sets the carbon free. Innumerable solid par- 
ticles of carbon thus scattered in the midst of burning 
hydrogen are raised to a state of incandescence. The car- 
bon, however, in due time, closes with the oxygen, and 
becomes, or ought to become, carbonic acid. The light 
and heat produced by the burning of coal are due to the 
collision of atoms which have been urged together by their 
mutual attractions. 

An isolated piece of coal will not burn in the open air, 
because the temperature will soon fall below the point of 
ignition, consequently chemical action will cease; but an 
ignited mass of coal, as in a furnace or a stove, will give 
off great heat, depending upon the quality and quantity of 
coal burned ; but once the hydrogen having united with 
the oxygen to form water, and the carbon with the oxygen 
to form carbonic-acid gas, their mutual attractions are sat- 
isfied, and all the heat has been given off that is possible 
under any conditions. 

Q. In what proportion does oxygen unite with hydro- 
gen and with carbon ? 

Oxygen and hydrogen unite in the ordinary processes 
of combustion in one proportion only, viz., two atoms of 
hydrogen unite with one atom of oxygen, the product of 
the combustion being aqueous vapor, or water, H 2 0. 



OXYGEN A SUPPORTER OF COMBUSTION. 85 

Oxygen and carbon unite in the ordinary process of 
combustion in two proportions, viz., one atom of carbon 
and two atoms of oxygen, the product being carbonic-acid 
gas, C0 2 ; and one atom each of carbon and of oxygen, the 
product being carbonic-oxide gas, CO. 

Q. What are the ordinary combinations of hydrogen 
with carbon fuel? 

Hydrogen is rarely found in a free state, though it is 
an essential element in all organic substances, from which 
it may be separated by a process of destructive distilla- 
tion. It occurs in nature in combination with carbon. 
The compound which contains it in greatest abundance is 
marsh gas, of which hydrogen forms one-fourth, CH 4 . 
Olefiant gas consists of 2 atoms of carbon and 4 atoms of 
hydrogen, C 2 H 4 . These are the commonest proportions 
in which the two elements, hydrogen and carbon, are 
found in coal. The complete series, however, of hydro- 
carbons is so extended that it cannot be reproduced here. 
Reference can only be made to the Marsh gas and Olefiant 
gas series, which are given elsewhere in this volume. 

Q. Is oxygen a supporter of combustion ? 

Oxygen is an active supporter of combustion. It will 
unite chemically with the hydrogen and the carbon in the 
fuel, the burning of the latter accompanied by characteris- 
tic flames followed by a body of incandescent carbon on 
the grate, which will continue to burn at high temperature 
and with great brilliancy, until entirely consumed, if a 
proper supply of atmospheric oxygen is furnished. 

Oxygen will not unite with hydrogen and carbon at 
ordinary temperatures. A mixture of oxygen and hydro- 
gen may be thus kept for any length of time, but if the 



86 COMBUSTION OF COAL. 

temperature of any part of the mixture be raised to bright 
redness — either by an electric spark, by the presentation 
of a flame, or by other means — ignition at once takes 
place with explosive force throughout the whole mass. 

Q. How may the volume of oxygen required for com- 
bustion be estimated? 

By weight, air consists of 23 per cent of oxygen and J J 
per cent of nitrogen; therefore, 77-^23 = 3.391 pounds of 
nitrogen accompanies each pound of oxygen. 

By volume, one pound of air averages 12.5 cubic feet, 
of which 21 per cent, or 2.625 cubic feet, is oxygen, and 
79 per cent, or 9.875 cubic feet, is nitrogen. 

One pound of carbon requires for its complete combus- 
tion to C0 2 about 12 pounds of air, or 150 cubic feet, of 
which 21 per cent, or 31.5 cubic feet, is oxygen, and 79 
per cent, or 118.5 cubic feet, is nitrogen. 

One pound of hydrogen requires for its complete com- 
bustion to H 2 8 pounds of oxygen supplied by 3 1 pounds 
of air, or 387.5 cubic feet, of which 21 per cent, or 81.375 
cubic feet, is oxygen, and 79 per cent, or 306.125 cubic 
feet, is nitrogen. 

Q. What is meant by the term ignition ? 

Ignition is simply the incandescence of a body unat- 
tended by chemical change, and must not be confused 
with combustion. The ignition of solids is a source of 
light, the combustion of solids is a source of heat. Every 
combustible must be heated to a certain definite temper- 
ature before it will combine with oxygen. This temper- 
ature is usually called the point of ignition, or its kindling 
temperature. In furnace combustion the temperature of 
ignition cannot be much less than dull red heat, say 8qo° 



IGNITION TEMPERATURE OF GASES. 87 

to 900 F., and maintain an active fire. For steam-boiler 
furnaces the combustion is quite active, even for moderate 
fires, and the temperature of the incandescent bed of fuel 
seldom if ever below 1 ioo° to 1200 F. and usually much 
higher than that, while the full furnace temperature may 
range from 2000 to 3000 F. 

Q. What are the ignition temperatures of gases ? 

We have as yet no very exact information concerning 
the ignition temperatures of gases. The experimental 
difficulties in the way of carrying out such determinations 
are very considerable. It is, however, certain that the 
ignition temperatures of gaseous mixtures are as a rule by 
no means so high as is commonly supposed, and they lie 
within extremes of temperature admitting of comparative- 
ly easy determination. When once initiated, the continu- 
ance of the combination of unlimited amounts of the con- 
stituents of a combustible mixture, or, in other words, the 
continued existence of a flame, depends primarily upon the 
condition that the combining gases are maintained at the 
temperature required to bring about their union. Any 
agency or condition which lowers the temperature below 
this point will extinguish the flame. 

Q. What is the effect upon combustion if too little air 
is supplied the fire? 

So far as the carbon of the fuel is concerned the effect 
is a serious one. One pound of carbon combining with 
two pounds of oxygen results in perfect combustion, the 
product being carbonic-acid gas, C0 2 , developing 14,500 
heat units; but if too little air, which means too little 
oxygen, is present at the instant and focus of combustion, 
the carbonic-acid gas already formed will take up addi- 



88 COMBUSTION OF COAL. 

tional carbon, thus changing the product to carbonic 
oxide, or from C0 2 to CO, the latter developing only 4,450 
heat units, or 10,050 less than the first union. This 
represents a loss approximating 69 per cent of the fuel, 
merely as a result of too little air in the fire at the right 
time and place. 

Q. What is the effect upon combustion if too much air 
is supplied the fire ? 

The effect of too much air in the fire is the mechanical 
one of cooling the furnace. The carbon having united 
with its full combining weight of oxygen to form C0 2 can 
take up no more oxygen, and any surplus air in the furnace 
is merely a dilutant of the gases. Inasmuch as the free 
air abstracts heat from the furnace and does no useful 
work, its presence acts against the economy of the furnace. 

Q. Does so large an excess of air as 150 per cent over 
that necessary for complete combustion commonly occur 
in steam boiler furnaces? 

An excess of air as large as 150 per cent in steam-boiler 
furnaces is by no means uncommon. There is a general 
tendency to use a stronger draught than is necessary for 
the combustion of fuel. It so happens that 100 per cent 
excess of air in steam-boiler furnaces is an ordinary condi- 
tion, and 1 50 per cent excess is much more common than 
is generally supposed. 

Q. What advantages accompany the heating of air re- 
quired for furnace combustion? 

A direct economical effect of heating the air is that of 
raising the intensity of furnace combustion, and this may 
be explained on the probable hypothesis that the chemical 



HEATED AIR AND CHEMICAL ACTION. 89 

affinity of heated air for carbon is much greater than that 
of cold air ; one consequence of which is that, when heated 
air is employed, it is deprived of its oxygen within a very 
short travel, the combustion is thereby more concentrated 
and localized at the focus where the heat has to be applied 
and to do its work. This is favorable to the economy of 
fuel, for combustion and high temperature beyond the 
point where heat has to be applied are useless. 

Q. How may the effect of heated air and chemical 
action be estimated? 

It is known that one pound of carbon combined with 2-| 
pounds of oxygen will develop 14,500 heat units. This 
will require under theoretical conditions 12 pounds of air; 
but to place it under ordinary conditions, say 24 pounds 
of air. We have then 25 pounds of gaseous product, of 
which 3|- pounds will be carbonic-acid gas, and 2 im- 
pounds of inert waste gas. The more nitrogen there hap- 
pens to be mingled with the oxygen, the greater the 
weight of matter that will have to be uselessly heated; 
and the greater its capacity for absorbing heat — the 
greater its specific heat — the greater the amount of heat 
that would be taken up. 

The specific heat of carbonic acid gas = o. 2 1 7, of nitro- 
gen = o. 245. The mean of 3 J pounds of the first and 21^ 

pounds of the latter = 0.237. Then : — ^o —2,447° 

P 0.237x25 

F. as the temperature of the products of combustion, in 

the form of about 1,800 cubic feet of fire gases. 

Preheating the air facilitates the union of oxygen with 

the carbon, and the fourfold useless volume of nitrogen 

should not rob the furnace of heat at the very moment and 

focus of its combustion. A gain would also be effected 



90 COMBUSTION OF COAL. 

the more nearly the temperature of the nitrogen is raised 
to that of the fire ; and whatever can be done by means of 
the escaping gases is pure saving. 

Q. Is there an economical limit to the heating of air 
for combustion ? 

It has been found in practice that the greater the affinity 
of any fuel for oxygen, the lower need be the temperature 
of the air. It is hence used at a lower heat in charcoal 
furnaces than in coke furnaces, and less in the latter than 
in anthracite blast furnaces. This explains the fact, 
which has been found on trial, that a reverbatory furnace, 
supplied with hot air at the grate only, has actually been 
found to have its efficiency diminished and not increased. 
The gaseous combination or chemical union being thereby 
accelerated, the combustion takes place more on the grate 
and less in the body of the furnace, where the actual work 
has to be done. 



*. 



Q. What is flame ? 

Flame is the surface burning of an inflammable gas or 
vapor, the surface of which is in contact with or receives 
constant supplies of atmospheric air. As all flames de- 
pending upon oxygen for their support are specifically 
lighter than air, they naturally ascend in a stream from 
burning bodies. Flames are usually, though not neces- 
sarily, accompanied by luminosity at ordinary atmos- 
pheric pressure. 

Q. What is known regarding the nature of the chemical 
processes in flames? 

Attempts have been made to study the nature of the 
chemical processes in flames of candles and of coal gas by 
aspirating the gases from different parts of the flame and 



STRUCTURE OF FLAME. 9 1 

analyzing them. Such investigations can only give a very 
partial conception of the changes which occur, or have 
occurred, in the different areas of the flame, owing to the 
intense molecular movements, due to the high temperature 
and specific differences of diffusive power of the gaseous 
constituents. Nevertheless it is possible to obtain some 
idea of the manner in which the several combustible gases 
in such a complex mixture as that of coal gas, or of the 
gas obtained by the distillation of wax or tallow, behave 
toward oxygen, and to trace the rates at which they are 
severally burnt, Thus, broadly speaking, it is found that 
of these gases, the hydrogen up to a certain point is most 
rapidly consumed, then the carbonic oxide, next the marsh 
gas, while the heavy hydrocarbons burn comparatively 
slowly. The amounts of these gases burnt, and especially 
of the hydrogen and carbonic oxide, are, however, modified 
by processes of dissociation and by the mutual action of 
the products of combustion at high temperatures. At the 
very high temperatures water vapor and carbonic-acid gas 
are dissociated, while carbonic oxide is formed by the 
action of separated carbon upon carbonic-acid gas. 

Q. How is an isolated flame such as a candle built up ? 

It is usual to describe the structure of a flame as built 
up of four zones, as sketched in Fig. 1, intended to illus- 
trate the main reaction taking place in the flame of a 
burning candle, in which : 

A = the inner zone of heavy vapor. 

B = the inner zone of lighter gas. 

C = the luminous zone. 

D == the outer or cooling zone. 

The inner zone A, nearest to and surrounding the wick, 
is a vapor of the material of which the candle is composed. 



9 2 



COMBUSTION OF COAL. 



The zone B is an envelope of highly rarified vapor of A 
heated to the point of ignition. The zone C is luminous, 
and is that portion of the flame 
where the chemical reactions occur, 
beginning along the surface of the 
zone B and extending into the zone 
D. The outer zone D is that in 
which the cooling and diluting in- 
fluence of the entering air renders a 
thin layer non-luminous, and finally 
extinguishes it. 

It will be understood that flame 
does not consist of envelopes in such 
contrast as the engraving would seem 
to indicate. This is for the purpose 
of illustration only. 

y Q. What are the successive devel- 
opments of a luminous hydrocarbon 
flame? 

The hydrocarbon issues from the 
wick of the candle, Fig. i, let us 
suppose as a cylindrical column. This column is not 
sharply marked off from the air, but is so penetrated 
by the latter that we must suppose a gradual transition 
from the pure hydrocarbon in the centre of the column 
to the pure air outside. Take a thin, transverse slice 
of the flame, near the lower part of the wick. At 
what lateral distance from the centre will combustion be- 
gin? Clearly where enough oxygen has penetrated the 
column to give such partial combustion as takes place in 
the inner cone of a Bunsen burner. This, then, defines 
the blue region. 




Fig. 



STRUCTURE OF FLAME. 93 

Outside this, the combustion of the carbonic oxide, 
hydrogen, and any hydrocarbons which pass from the blue 
region takes place, and constitutes the faintly luminous 
region. 

These two layers form a sheath of active combustion, 
surrounding and intensely heating the hydrocarbons in the 
central parts of the column. These heated hydrocarbons 
rise, and are heated to a higher temperature as they as- 
cend. They are accordingly decomposed with the separa- 
tion of carbon in- the higher parts of the flame, giving us 
the yellow region ; but there remains a central cone in 
which neither is there any oxygen for combustion nor a 
sufficiently high temperature for decomposition. This 
constitutes the dark region of unburned gases. 

A flame is, however, not cylindrical, but has in the case 
of a candle an inverted peg-top shape. Again, the blue 
region only surrounds the lower part of the flame, while 
the faintly luminous part surrounds the whole. 

J Q. How will the processes outlined in the above question 
differ in parts above the small section of the flame ? 

Let us suppose that the changes have gone on in the 
small section of the flame exactly as described above. 
The central cone of unburned gases will pass up- 
ward, and may be treated as a new cylindrical column, 
which will undergo changes just as the original one, leav- 
ing, however, a smaller cone of unburned gases ; or, in 
other words, each succeeding section of the flame will be 
of smaller diameter. This is what gives the conical struc- 
ture to the flame. Again, the higher we go in the flame, 
the greater proportionally is the amount of separated car- 
bon, for we have not only the heat of laterally outlying 
combustion to affect decomposition, but also that of the 



94 COMBUSTION OF COAL. 

lower parts of the flame. The lower part of a luminous 
flame is accordingly cooler, and contains less separated 
carbon than the upper. 

Q. What chemical changes produce the blue region in 
a flame? 

When the hydrocarbons are cool until admixed with 
sufficient air for combustion, in the lower part of the 
flame, there is every facility for the occurrence of the 
chemical changes to which the existence of the blue re- 
gion has been ascribed, and the blue region here is most 
evident ; whereas in the upper parts of the flame, where 
the quantity of hydrocarbon decomposed (with separation 
of carbon) by heat is relatively much greater, there is not 
enough left to form outside the yellow part the mixture to 
which the blue region of flame is due. The blue region, 
therefore, rapidly thins off as we ascend the flame. 

Q. Are the several processes of flame development sup- 
ported by complete combustion? 

Whether the first combustion taking place within the 
flame is that of undecomposed hydrocarbon with limited 
oxygen, or of the decomposed hydrocarbon with limited 
oxygen, we may be sure that the products will contain 
carbonic oxide, and perhaps hydrogen ; and we shall there- 
fore have all round the flame a faintly luminous region of 
completed combustion. 

Q. Is the flame of a candle characteristic of other steady 
or continuous flames? 

In other steady, continuous flames these areas or zones, 
as shown in the candle, are very different in character and 
in number. In some the luminous cone is absent, and 
others have no mantle. All have, of course, the dark in- 



RATE OF PROPAGATION IN FLAME. 95 

ternal cone, and the majority have an area corresponding 
to the blue zone in the candle flame. The flame of car- 
bonic oxide consists of a dark internal cone of unburnt 
gas surrounded by a yellowish-red mantle, somewhat ill- 
defined at its external edge, and at the base is a compara- 
tively large blue zone. 

Q. How can it be shown that the flame of a candle is 
hollow ? 

The fact that the candle flame is hollow, and that the 
internal cone immediately surrounding the wick consists 
of comparatively cold, unignited gas free from oxygen, 
may be demonstrated by thrusting a fragment of burning 
phosphorus into the cone when its combustion ceases. 

A piece of stiff thick paper thrust down on the flame to 
the level of the dark internal area is seen to be charred 
on the upper surface in the form of a ring. If the paper 
be placed simply across the luminous area and above the 
dark cone, the charring is simply a circular patch. 

Q. What is the rate of propagation of combustion in 
flames of hydrogen and carbonic oxide ? 

Bunsen's investigations show that the rate of propaga- 
tion of the combustion of a mixture of oxygen and hydro- 
gen, and of carbonic oxide and oxygen, mixed in the exact 
quantities for complete combustion to be : 

In the oxyhydrogen mixture the velocity of the inflam- 
mation was 111:5 f eet per second; in that of carbonic 
oxide and oxygen it was less than 40 inches per second. 
By adding to the mixture increasing amounts of an indif- 
ferent gas the rate is rapidly diminished until the progress 
of the flame throughout the mass may be followed with 
the eye. 



96 COMBUSTION OF COAL. 

Q. Is combustion complete and the consequent high 
flame temperature maintained in cases where the combus- 
tible gases are mixed in their exact combining propor- 
tions ? 

According to Bunsen, in a mixture of carbonic oxide, 
CO, or hydrogen, with oxygen in the exact quantity 
needed for complete combination, only one-third of the 
carbonic oxide, CO, or hydrogen, is burnt at the maximum 
temperature, the remaining two-thirds at the high tem- 
perature (2558°-3033°) having lost the power of combina- 
tion. If an indifferent gas is present the temperature of 
the flame is reduced, and larger quantities of the gases 
combine together, as much as half the amount of carbonic 
oxide, CO, or hydrogen combining within a range of tem- 
perature between 247 1° and 1146 . 

It would appear therefore that gases in combining to- 
gether with the production of such an amount of heat as 
to produce flame unite, as it were, at a single leap, and 
that the combustion is not a continuous uninterrupted 
process. 

Q. What variations of temperature occur in flames in- 
cident to the combustion of carbonic oxide, CO? 

When two volumes of carbonic oxide, CO, are mixed 
with one volume of oxygen, both gases at o°, and the 
mixture is ignited, the temperature is raised to 303 3 °, and 
two-thirds of the CO is left unburnt. By radiation and 
conduction the temperature is lowered to 25 5 8° without 
any combustion of the CO. At a little below this point 
combustion recommences, and the temperature is again 
raised to 25 58 , but not above this point. This temper- 
ature continues until half the CO is burnt, when combus- 
tion ceases, until by cooling and radiation the gaseous 



LUMINOSITY OF FLAME. 97 

mixture has cooled to 1146 ; and these alternate phases 
of constant temperature and of decreasing temperature are 
repeated until the whole of the combustible gas is burnt. 

\ Q. What is the cause of the luminosity of flame? 

The main cause of the luminosity of flame was first 
traced by Davy as the outcome of experiments which led 
him to the invention of the safety lamp. It is, to use his 
own words, " owing to the decomposition of a part of a gas 
toward the interior of the flame, where the air was in 
smallest quantity, and the decomposition of solid charcoal, 
which first by its ignition and afterward by its combustion 
increases in a high degree the intensity of t he light^ ^- 

The proofs that solid carbon is present in luminous 
hydrocarbon flames are the following : 

1. Chlorine causes an increase in the luminosity of 
feebly luminous or non-luminous hydrocarbon flames. 
Since chlorine decomposes hydrocarbons at a red heat with 
separation of carbon, it follows that the increase in lumin- 
osity is due to the production of solid carbon particles. 

2. A rod held in the luminous flame soon becomes 
covered on its lower surface, i.e., the surface opposed to 
the issuing gas, with a deposit of soot. The solid soot is 
driven against the rod. If the soot existed as vapor within 
the luminous flame, its deposition would be due to a dimi- 
nution of the temperature of the flame, and would there- 
fore occur on all sides of the rod. 

3. A strongly heated surface also becomes covered with 
a deposit of soot. This result could not occur if the de- 
posit were due to the cooling action of the surface. 

4. The carbon particles in the luminous flame are ren- 
dered visible when the flame comes in contact with an- 
other flame, or with a heated surface. The separated par- 

7 



98 COMBUSTION OF COAL. 

tides are agglomerated into large masses, and the luminous 
mantle becomes filled with a number of glowing points, 
giving a very coarse grained soot. 

5. The transparency of a luminous flame is no greater 
than that of the approximately equally thick stratum of 
soot which rises from the flame of burning turpentine, and 
which is generally allowed to contain solid particles. A 
flame of hydrogen made luminous with solid chromic 
oxide, which is non-volatile, is as transparent as the hy- 
drocarbon flame. 

6. Flames which undoubtedly owe their luminosity to 
finely divided solid matter produce shadows in sunlight. 
The only luminous flames incapable of producing shadows 
are those consisting of glowing gases and vapors. 

7. Luminous hydrocarbon flames produce strongly 
marked shadows in sunlight. These flames, therefore, 
contain finely divided solid matter. This solid matter 
must be carbon, since no other substance capable of re- 
maining solid at the temperature of these flames is present. 
Moreover, if the soot in luminous flames is present as 
vapor, a high temperature after condensation should again 
cause it to assume the gaseous condition ; but soot is ab- 
solutely non- volatile, even at the highest temperatures. 

Q. What conditions affect the color of flame? 

The conditions under which a flame is produced not only 
modify its temperature, but also, as an effect of temper- 
ature, its color. Thus the prevailing tint of sulphur burn- 
ing in air is blue, and the mantle is correspondingly small 
and of a violet color. In oxygen the flame becomes hotter 
and the violet color is more pronounced. Precisely the 
same change is produced by heating the air or by burning 
a jet of heated sulphur vapor. Cold carbonic oxide gives 



TEMPERATURE OF FLAME. 99 

a blue flame in air, but it becomes yellowish-red if the gas 
be previously heated. 

The flame of a candle, whether of wax, tallow, or para- 
fin, is seen to consist of four distinct cones, which are 
comparatively sharply defined, and which are rendered evi- 
dent by their different appearance. Immediately surround- 
ing the wick is a dark inner cone of unburnt gases or vap- 
ors. Adjoining the inner cone is a light blue zone of 
small area consisting of combustible matter from the wick. 
Surrounding the inner cone is a bright luminous area, from 
which the greater part of the light emitted by the flame is 
derived. Surrounding the luminous area, which seems to 
constitute the greater portion of the visible flame, is an 
envelope or mantle of a faint yellowish color and of feeble 
luminosity. This consists of the final products of combus- 
tion of the constituents of the luminous cone mixed with 
atmospheric air heated to incandescence. 

Owing to the intense glare of the luminous cone the 
feebly luminous mantle is not readily perceived, but it 
may be rendered evident by holding a piece of card, of the 
shape of the flame, in such a manner as to hide the lumi- 
nous cone, when the mantle is seen lining the outer edge 
of the cone. 

Q. Upon what does the temperature of flame depend? 

The temperature of a flame depends mainly upon the 
heats of combination of the constituents and the specific 
heats of the products of combustion. Flames which de- 
pend upon the presence of oxygen are much hotter when 
the combustion takes place in an atmosphere of pure gas 
than in air. In the latter case the oxygen is mixed with 
four times its volume of nitrogen, which plays no part in 
the chemical reaction, and therefore contributes nothing 

LofC, 



<f 



IOO COMBUSTION OF COAL. 

to the heating effect; but, on the contrary, abstracts a 
considerable amount of heat from the products of combus- 
tion, and thereby lowers the temperature of the glowing 
mass of gas. Hence sulphur burning in oxygen gives a 
much hotter flame than when burning in air, and the oxy- 
hydrogen flame is much hotter than that of hydrogen in 
air. The effect of the indifferent gas in lowering the 
temperature is well illustrated by the following numbers 
given by Bunsen : 

Cent. Fahr. 

Flame of hydrogen burning in air 2,024° 3.675° 

" " " " " oxygen 2,844 5,151 

" " carbonic oxide burning in air J.997 3,626 

" oxygen 3,003 5,437 

Q. Is flame in immediate contact with the orifice from 
which the gas issues? 

If the flame of a candle or of coal gas be closely ex- 
amined it will be seen that the one does not touch the rim 
of the burner nor the other the wick. The intermediate 
space in the case of the coal gas may be increased by mix- 
ing it with an indifferent gas, as nitrogen or carbonic-acid 
gas, C0 2 . These phenomena are due to the cooling effect 
of the wick or the burner. 



-v 



Q. May flame be extinguished by a rapid absorption 
of its heat? 

A coal gas flame may be extinguished by a cold mass 
of copper, and a candle flame by a helix of cold copper 
wire. The metal abstracts sufficient heat from the gases 
to lower their temperature below the point of combination. 
If the metal is heated prior to its introduction into the 
flames, they are not extinguished. 



X 



FLAME OF ANTHRACITE COAL. IOI 

Q. May not a flame be extinguished in other ways 
than by the cooling action of metals ? 

A flame may be extinguished by mixing the combustible 
gases with a sufficiently large quantity of an indifferent 
gas, which will act by absorption of heat in the same way 
as metal. The effect even of small quantities of indiffer- 
ent or chemically inactive gases in lowering the temper- 
ature of a flame is very marked, and is well illustrated in 
the different characters of the flame of hydrogen burning 
in air and oxygen. In extinguishing a flame, say of a 
candle or coal gas, by blowing it out, the puff of air acts 
partly by suddenly scattering the glowing gases from the 
area of supply and partly by its cooling action. 

Q. What are the flame characteristics in the burning 
of anthracite coal? 

In burning, anthracite coal neither softens nor swells, 
and does not give off smoke. The flame is quite short 
and has a yellowish tinge when first thrown upon the fire, 
which soon changes to a faint blue, with occasionally a 
red tinge. The flame, being quite short and free from 
particles of solid carbon, has the appearance of being 
transparent. 

Q. How is the rapidity of flow, or the volume of air 
supplied a furnace-fire, estimated, when employing natural 
draft? 

By means of an instrument contrived for measuring the 
force and velocity of currents of air, called an anemometer. 
Those composed of a small light fan wheel, whose motion 
is transmitted to a counter which registers the number of 
turns, are most certain and convenient for use, though 
they must previously be tested, or the relation existing 



102 COMBUSTION OF COAL. 

between the velocity of the wind and the number of turns 
of the wings must be accurately determined. 

The anemometer shown in Fig. 2 is by Keuffel & Esser 
Company, New York. Each instrument is tested and a 




Fig. 



chart of corrections furnished with it, so that no calcula- 
tions are necessary for obtaining the velocity of the cur- 
rent in which it is placed. 



CHAPTER V. 

PRODUCTS OF COMBUSTION. 

Q. What are the principal products in the furnace after 
the combustion of coal ? 

The principal products in the furnace after the combus- 
tion of coal are : carbonic-acid gas, carbonic oxide, nitro- 
gen, air furnished in excess, and unconsumed, gaseous 
steam. 

Q. What is the product of the combustion of hydrogen ? 

Hydrogen unites with oxygen, forming gaseous steam, 
which, upon cooling, is condensed into water, H 2 0. This 
chemical combination is complete, and the product incom- 
bustible. 

Q. What are the products of the combustion of carbon ? 

The products of the combustion of carbon in oxygen are 
two in number, carbonic oxide, CO, and carbonic-acid gas, 
C0 2 , in which each compound is sharply defined and ex- 
hibits properties distinct from each other, and of the ele- 
ments of which they are composed. The quantity of 
carbon remaining the same, the quantity of oxygen must 
be doubled in order to form the other compound. These 
proportions constitute the only two direct inorganic com- 
pounds of carbon and oxygen. 



104 COMBUSTION OF COAL. 

Q. What are the properties of carbonic-acid gas? 

Carbonic-acid gas, C0 2 , is composed of one part or 
atom of carbon and two parts of oxygen, its atomic weight 
being 12 -f- (16 X 2) = 44. By percentage of volume: 
carbon = 27.27, oxygen = 72.73 = 100.00. Its specific 
gravity is 1.53, air = 1.00. It is a colorless, inodorous, 
heavy gas, neither combustible nor a supporter of combus- 
tion. 

It liquefies under a pressure of 36 atmospheres at o° C. 
The specific gravity of the liquid carbonic acid is 1.057 at 
— 34 C. Liquid carbonic acid is colorless, very soluble 
in alcohol, ether, and volatile oils, but does not mix with 
water. When the pressure is suddenly relieved, part of 
the carbonic acid immediately vaporizes, producing suffic- 
ient cold to solidify the remainder. Solid carbonic acid is 
a white flocculent, snowlike mass, and may be left exposed 
to the air for some time without sensible evaporation. An 
air or spirit thermometer immersed in it sinks to — 78 ° C. 
It can, however, be placed on the hand without any acute 
sensation of cold. By mixing with ether its refrigerating 
power is greatly increased. The cold produced in this 
manner is sufficient to solidify mercury and to liquefy 
several gases. 

Carbonic-acid gas is a constant constituent of the atmos- 
phere, which contains on an average about 0.034 per cent. 

In the combustion of coal, carbonic-acid gas is formed 
by the combination of the carbon in the coal by the oxy- 
gen of the air, and is thus a constant product of the ordi- 
nary processes of combustion. The presence of moisture 
is necessary for the burning of carbon in an atmosphere of 
pure oxygen. In furnace combustion the coal itself fur- 
nishes all the moisture needed for intense combustion. 



CARBONIC OXIDE. 105 

Q. What are the properties of carbonic oxide ? 

Carbonic oxide, CO, is composed of one part or atom 
each of carbon and oxygen, its atomic weight being 1 2 -f- 
16 = 28. By percentages of volume: carbon = 42.86, 
oxygen = 57.14 = 100.00. Its specific gravity is 0.9678, 
air = 1. 0000. It is a colorless, tasteless, combustible 
gas. Pure carbonic oxide forms a colorless, transparent 
liquid under 200 to 300 atmospheres pressure at — 139 
C, and solidifies to a snowy mass in vacuo at — 21 1° C. 

Carbonic oxide burns with a blue flame, which by pre- 
vious heating becomes red, generating carbonic-acid gas, 
C0 2 . The temperature of its flame in air is about 1400 C. 
When dry it is not changed by the electric current nor by 
ignited platinum wire, but when standing over water it is 
decomposed by a glowing platinum spiral ; when not abso- 
lutely dry it may be exploded with oxygen by the electric 
spark or by platinum wire heated to 300 C, or by spongy 
platinum at ordinary temperatures. Two molecules of 
carbonic oxide, CO, unite with 1 atom of oxygen, O, to 
form 2 molecules of carbonic-acid gas, C0 2 . The combina- 
tion takes place very slowly in the presence of small quan- 
tities of steam, and increases in rapidity with the quantity 
of steam present. Hence the steam acts as the carrier of 
oxygen to the carbonic oxide. Small quantities of other 
gases than steam have been tried. If the gas contained 
no hydrogen, no explosion occurred. When a mixture of 
carbonic oxide and steam is heated to about 6oo° C. a 
portion of carbonic oxide is oxidized. If the carbonic- 
acid gas is removed as it is formed, the whole may be oxi- 
dized. 

Carbonic oxide is a highly poisonous gas, producing 
giddiness and ultimate asphyxia when inhaled. 



106 COMBUSTION OF COAL. 

Q. What is the product of the combustion of sulphur? 

Sulphur combines with oxygen to form sulphurous oxide, 
S0 2 , a colorless gas, with a suffocating odor. It is a non- 
supporter of combustion, instantly extinguishing flame 
when brought within its influence. Sulphurous oxide, in 
absorbing vapor of water, changes from sulphurous oxide, 
S0 2 , to sulphurous acid, S0 2 , H 2 0. 

Q. What is the effect of sulphur in coal upon the sur- 
faces of steam boilers? 

If the sulphurous oxide generated by the combustion of 
sulphur in the furnace simply passed off with the other 
products of combustion, without lodging against the sur- 
faces of the boiler, no bad effects would follow ; but nu- 
merous instances are on record where sulphurous oxide 
was included in the deposits of soot in contact with por- 
tions of a steam boiler, which oxide had been converted 
into acid by the subsequent absorption of moisture. The 
transformation of sulphurous into sulphuric acid, under 
the action of water, or steam and air, in presence of a 
metal, is well known, and exterior corrosion of boilers at- 
tributed to the action of smoke is wholly confined to those 
parts of the iron which were wetted by infiltration or by 
accident. 

Q. What quantity of nitrogen is present in the products 
of combustion ? 

Whatever the quantity of air required for the perfect 
combustion of carbon or hydrogen there will remain in the 
furnace 3.35 pounds of nitrogen for every pound of oxygen 
combined with the fuel ; or by volume 3.76 volumes re- 
main in the furnace for each volume of oxygen uniting 
with the fuel. 



SURPLUS AIR IN FURNACE. 107 

Nitrogen is non-combustible, and so far as the other 
products of combustion in the furnace are concerned it is 
wholly inert. 

Q. What is the effect of surplus air in the furnace in 
combination with the products of combustion ? 

Surplus air, or air in excess of that necessary to supply 
oxygen to the burning fuel, acts as a dilutant of the fur- 
nace gases. Inasmuch as this surplus air has to be heated 
by the furnace to the temperature of the escaping gases, it 
occasions loss by abstracting heat from the furnace gases, 
which might otherwise be employed in doing useful work. 

Q. What weight of gases commonly emerges from a 
steam-boiler furnace for the combustion of each pound of 
carbon ? 

It is not easy to carry on complete combustion by means 
of natural draft with less than 100 per cent excess air; 
and some experiments, made by Hoadley, to ascertain the 
composition, volume, and temperature of the gases from 
seventeen boilers, burning good anthracite coal at known 
rate, with great care, and under most favorable conditions 
of draft, grate area, rate of combustion, area of heating 
surface, and general management, gave by analysis car- 
bonic-acid gas, C0 2 (no carbonic oxide, CO), nitrogen, and 
free atmospheric air, the latter being one-half the whole. 

A check upon the accuracy of these results was found 
in the temperature of the furnace. This should be, with 
double supply of air, about 2600 F. It was found to be 
a little over 2400 F. It appears therefore that it is un- 
derstating rather than overstating the matter to say that 
the average good practice would show a double supply of 
air. 



108 COMBUSTION OF COAL. 

Q. What weight of gases emerges from the furnace for 
perfect combustion of one pound of carbon ; also the ad- 
ditional weight occasioned by air in excess of that needed 
for combustion? 

In anthracite coal we may neglect all the constituents 
except carbon, which, when perfectly burned, with just 
sufficient air to supply the oxygen, will produce 12.6 
pounds of mixed gases for each pound of carbon. Thus : 

Carbon 1 . o Carbon 1 . 00 

Air 11. 6 Oxygen 2. 66 



12.6 Product C0 2 3.60 

Nitrogen 8.94 



12.60 



lb. carbon burnt with 0% excess of air = 12.6 lbs. gases. 

50 " " = 18.4 " 
" " " 100 " " = 24.2 " " 

125 " " = 27.1 " 
<< «< <« jg << " = 30. o " " 

Q. What is included in the term ashes? 

The term ashes includes all the mineral matter left on 
the grates after the complete combustion of fuel. Every 
variety of mineral fuel contains more or less incombustible 
matter called ashes. The presence of this incombustible 
substance in coal is due in part to the inorganic matter 
contained in the plants of which the coal is formed, and 
partly by the earthy matter in the drift of the coal period. 
The inorganic matter thus obtained frequently differs both 
in amount and in proximate composition from that origi- 
nally present in the unburnt substance. At the high tem- 
perature of burning some of the mineral constituents may 
be volatilized, or be mechanically carried away by the 



COMPOSITION OF ASHES. IO9 

gases which may be evolved, and changes in the proximate 
nature may be induced either by the heat itself or by the 
action of the heated carbonaceous substances. 

Q. What is the specific heat of ashes? 

The specific heat of ashes may be assumed to be 0.215 
without sensible error in engineering calculations. 

Q. Of what do ashes principally consist? 

Coal ashes are found to consist mainly of silica, alumina, 
lime, and oxide and bisulphide of iron. As wood contains 
from 1 to 3.5 per cent of ash, it is probable that much of 
the inorganic matter required to make up the five to ten 
per cent in coal is principally earthy substances drifting 
into and incorporated in the coal during its formation. 
The nature and color of coal ashes are greatly modified by 
the proportions in which the above substances are united 
in the composition. In all analyses of coal ashes, silica 
and alumina predominate. 

Q. What substances are found in analysis of ashes of 
anthracite coal? 

The analysis of ashes of Pennsylvania anthracite coal, 
by Professor Johnson, yielded : 

Silica 53. 60 

Alumina 36. 69 

Sesquioxide of iron 5.59 

Lime 2. 86 

Magnesia 1.08 

Oxide of magnesia 19 

100.01 



IIO COMBUSTION OF COAL. 

Q. What substances are found in the analysis of ashes 
from bituminous coal ? 

Ohio bituminous coal, containing 5.15 per cent of ash, 
yielded upon analysis : 

Silica 58.75 

Alumina 35. 30 

Sesquioxide of iron 2.09 

Lime c . 1 . 20 

Magnesia o. 68 

Potash and soda 1.08 

Phosphoric acid ' o. 13 

Sulphuric acid o. 24 

Sulphur combined 0.41 

99.88 

Block coal is a non-caking, bituminous coal found in 
Indiana. It occurs in thin laminae, separated by fibrous 
charcoal partings, with fractures occurring in the coal at 
right angles to the bed. A sample of this coal yielded 
2. 5 per cent of white ash, of which the composition was : 

Alumina . 48. 00 

Sesquioxide of iron 32. 80 

Silica, lime, magnesia, etc 19.20 

100. 00 

Of the sulphur present in this coal, 

.947 per cent, was in combination with iron. 
.483 " with other constituents. 

1.430 " of sulphur in the sample. 

Q. What does the color of coal ashes indicate? 

Coal ashes are usually either white, brown, or variously 
tinged with red. It is a common designation to say of 
coals that they are white-ash or red-ash. When the 
amount of iron is very small, or not sufficient to tinge the 



COLOR OF ASHES. Ill 

ashes, they are then usually white. A larger quantity of 
iron produces a red-ash. Thus the color enables one to 
judge of the probable nature of the ashes, whether they 
will clinker in the fire or not. The intensity of the red 
color, taken in connection with the amount of ashes in 
coal, may also serve as an indication of the proportion of 
sulphur existing in the state of pyrites. 

Q. Judging from the color of the ash alone, which 
coals will clinker least under high temperatures ? 

Those coals are best, the ashes of which are of nearly 
pure white, and which with large amounts of silica and 
alumina in their composition, contain little or no alkali, 
nor any lime, nor oxide of iron. Of this character are the 
earthy residue of the best white-ash anthracites of Penn- 
sylvania, and in an eminent degree the ashes of some of 
the semi-anthracites. In general, it requires a high tem- 
perature to fuse these ingredients when taken by them- 
selves, but the presence of the oxide of iron tends to lower 
the point of fusion. 

Q. Will not all coal ashes fuse, or clinker, under in- 
tense heat ? 

There are, perhaps, no coals whose ashes, when exposed 
to the extremest heats procurable by artificial blasts, will 
not soften to a cohering cinder, or even melt in part into 
a stony clinker ; but as the tendencies to these several de- 
grees of fusion are very various, it proves to be a distinc- 
tion affecting the practical value of coals, which is of the 
utmost importance. In domestic consumption, where the 
heat of combustion is comparatively moderate, the quan- 
tity rather than the quality or fusibility of the ashes is the 
point of greatest consideration; but where an excessive 



112 COMBUSTION OF COAL. 

and melting heat is required, as in many modes of gener- 
ating steam, the practicability of employing a coal at all 
will oftentimes be determined by this one quality of 
clinkering of the ashes. 

Q. What is the effect of the presence of oxide of iron 
in coal ashes? 

The amount of the oxide of iron present in coal ashes 
is one of great importance, especially as it unites with pot- 
ash, soda, lime, and silica, also present, to form clinker. 
The presence of oxide of iron in ashes, when in any con- 
siderable quantity, may be detected without analysis by 
the red color imparted to them. The particular objection 
to the combination and fusing of the silica, lime, potash, 
etc. , in the ashes of the coal into a vitreous mass is that, 
unless the greatest care is exercised, it will accumulate 
upon the grate bars in sufficient quantity to exclude the 
passage of the air needed for combustion, and thus lower 
the temperature of the furnace. 

Q. How is the presence of the oxide of iron accounted 
for in coal ashes ? 

Nearly every variety of coal contains more or less iron 
pyrites. This is the probable source of the oxide of iron 
in ashes. The greater part of the sulphur being expelled 
by heat, its equivalent of oxygen unites with the iron, 
with which hydrogen also combines, forming the sesqui- 
oxide of iron occurring in the analysis of coal ashes. 

Q. What is the effect of iron pyrites included in the 
ashes of coal? 

Coal always contains more or less of sulphur in its com- 
position, and this sulphur occurs mainly as a native bisul- 



SIJLPHUR IN ASHES. 



113 



phide of iron, or iron pyrites, a mineral of bright yellow 
color often mistaken for gold. Pyrites approximate equal 
parts of iron and sulphur with a ten-per-cent variation on 
either side. About one-half the sulphur may be driven 
off by heat ; and if the fire is intense, the remaining por- 
tion of the pyrite is present in the ashes as a black sul- 
phuret of iron, which, in combination with other sub- 
stances, may form a hard clinker, difficult to remove from 
the grates if once allowed to cool. 

Unless the conditions are favorable a less percentage 
of sulphur is distilled from the pyrites than that noted in 
the preceding paragraph, as indicated in tests made in 
Germany, on coals of the carboniferous period : 



Table ii. — Sulphur Evolved in the Burning of Coal and 
Retained in the Ashes. 



Ash in 100 
pounds of coal. 


Sulphur in 100 
pounds of coal. 


Sulphur in 100 
pounds of ash. 


Sulphur in the 

ash from 100 

pounds of coal. 


Sulphur evolved 
in burning 100 
pounds of coal. 


Pounds. 

7.360 

5.760 

I6.530 


Pounds. 
O.789 

0.973 
3.264 


Pounds. 

9.464 

14.663 

18.174 


Pounds. 
O.696 
O.844 
2.424 


Pounds. 
O.093 
O.I29 
O.84O 



Q. Is sulphur always present in coal as iron pyrites? 

There is no doubt that sulphur is present in coal in 
combination with the organic elements of which it is com- 
posed ; but what the definite compound may be which con- 
tains it is unknown. For example, a coal from New 
Zealand containing 2. 50 per cent of sulphur yielded an 
ash remarkably white; the coke contained 2. 35 per cent of 
sulphur. No sulphuric acid was detected in the hydro- 
chloric acid in which the powder of the coal had been 
boiled. It would appear that the sulphur was present in 
8 



114 COMBUSTION OF COAL. 

the same state of combination in the coal as that in which 
it exists in albumin, fibrine, etc. ; for it could not have 
been combined with iron, as in this case the ash would 
have had a decided red color. 

Q. What is clinker? 

Clinker is a product formed in the furnace by fusing 
together the impurities in the coal, such as oxide of iron, 
silica, lime, etc. There are few colored ashes, and espec- 
ially red ashes, that will not soften under the action of in- 
tense heat and form clinker; white-ash coals produce the 
least clinker. 

Q. How is alumina present in ashes? 

Alumina is the oxide of the metal aluminum ; it is the 
pure earth of clay. It is infusible in any temperature yet 
obtained in furnaces. The alumina present in ashes is in 
the form of a clay or a mixture of the two simple earths, 
alumina and silica, generally tinged with iron. The floor, 
or pavement, immediately under the coal beds is, almost 
without exception, a grayish slate-clay, which strongly re- 
sists the fire. This clay varies in thickness from a frac- 
tion of an inch to many feet, and is often disseminated 
through the shale found in coal. 

The presence of alumina in analyses of wood ashes from 
trees, such as beech, pine, fir, etc., is not easily accounted 
for inasmuch as no inorganic substance can find its way 
into a plant except in a state of solution in water, when it 
is absorbed by the roots ; and, certainly, neither rain water 
nor ordinary mineral water contains any salt of alumina, 
nor does water impregnated with carbonic acid, which dis- 
solves phosphate of lime or magnesia, dissolve even a trace 
of phosphate of alumina. 



SILICA IN ASHES. 115 

Ashes of lycopodium contain from 52 to 57 per cent of 
alumina, 13 per cent of silica, and 12 per cent of potash. 
This species of plants has contributed largely to the pro- 
duction of coal. It appears, therefore, that the inorganic 
matter in coal, of which alumina is a notable constituent, 
may have been in great measure derived from that origin- 
ally existing in the coal-forming plants, and the alumina 
originally present in these plants would be uniformly dif- 
fused through the mass of coal. 

Q. How is silica present in ashes ? 

The only known oxide of silicon [symbol, Si. ; atomic 
weight = 28.33] occurs abundantly in nature, pure, or 
nearly so, in quartz, flint, etc. It enters largely into the 
constitution of sandstones, felspar, and many other rocks. 
Silica, known also as silicic acid, silex (formula, Si0 2 ), is 
infusible except at very high temperatures ; it is non- vola- 
tile; it decomposes fused sodium carbonate and melts to a 
transparent glass. It is insoluble in water and all acids 
except hydrofluoric acid, which decomposes it into water 
and silicon fluoride. Silica dissolves readily, as a rule, in 
caustic alkalies, forming solutions of alkaline silicate 
(water-glass). Silica is decomposed at a red heat by car- 
bon in presence of iron and at white heat by carbon mon- 
oxide, CO, a metallic silicide being formed. 

Silica plays a very important part in the formation of 
slags, and fusion is not necessarily required to produce 
combination. Thus, when certain mixtures of silica and 
lime are strongly heated, there is not the slightest indica- 
tion of fusion, yet it is certain that the silica has entered 
into combination. The bases which most frequently occur 
in slags are lime, magnesia, protoxide of iron, potash in 
small quantity, and alumina. 



Il6 COMBUSTION OF COAL. 

Silica is an abundant element in the ashes of straw, as 
shown in the following : 

Per Cent. 

Potassa 10.51 

Soda 1 . 03 

Lime 5.91 

Magnesia 1.25 

Sesquioxide of iron 0.07 

, Sulphuric acid 2.14 

Silica 73.57 

Phosphoric acid 5.51 

Total 99. 99 

Q. How is potash present in ashes ? 

Potash occurring in ashes is in various states of combi- 
nation, as carbonate, sulphate, and as chloride of potash. 
The percentage of potash is much greater in wood than in 
coal ashes. The following table (12) shows, according to 
Hoss, the proportions of ash and potash in some of the 
leading woods : 

Table 12.— Potash Contained in Ashes of Several Woods. 



Wood. 


Ash 
Per Cent. 


Potash 
Per Cent. 


Pine 


•34 

.58 - 
1.22 
1-35 
2-55 
2.80 


.045 
.127 
.074 
.150 

•390 

.285 




Ash 


Oak 


Elm , 


Willow 





Pure, dry carbonate of potash is a hard, white solid, 
specific gravity of 2.207, having a strong alkaline reaction 
and taste. It melts at a full red heat, and at a higher 
temperature slowly volatilizes. 



LIME PRESENT IN ASHES. 117 

The following, from Berthier's original analysis, shows 
the composition of pine-tree ash : 

Solution in water: Per Cent. 

Carbonate of potash 1. 86 

Sulphate of potash 3. 63 

Chloride of potash 1.88 

Carbonate of soda 6. 03 

Silica 18 

Insoluble in water : 

Lime 38. 51 

Magnesia 9-5° 

Oxide of iron 09 

Oxide of manganese 36 

Carbonic acid 32. 77 

Phosphoric acid 91 

Silicic acid 4. 19 

99-97 

Q. How is lime present in ashes? 

Lime occurring in ashes is a product of one of the car- 
bonates present in the coal, in which its contained carbonic 
acid is driven off by heat, leaving a white or pale gray 
substance, acrid and caustic to the taste, and exhibits a 
powerful alkaline reaction. Lime heated by itself is one 
of the most refractory substances known, and no temper- 
ature has as yet been attained which has caused it to ex- 
hibit the slightest indication of fusion ; but lime promotes 
the fusion of some other oxides in a remarkable manner, 
and hence it is used as a flux. Carbonate of lime is an 
essential ingredient in all fertile soils, and occurs in every 
kind of rock. 

Q. How do the substances which form clinker affect the* 
efficiencies of coals ? 

The several substances, silica, lime, potash, etc., occur- 
ring in coal ashes are variable in their nature ; and thus 



Il8 COMBUSTION OF COAL. 

by the forms they take under different intensities of com- 
bustion much affect the efficiencies of the coals to which 
they belong. Being differently fusible themselves, and 
affecting differently the fusion of each other, no two of the 
earths, alkalies, or metallic oxides of the ashes but differ 
in their agency when subjected to an elevated heat; and 
their mutual reactions are moreover changed, as the tem- 
peratures are changed to which they are exposed. It 
hence arises that the residue from many coals melts to a 
large extent, under no very intense combustion, into vari- 
ous descriptions of hard, semi-vitreous slags ; others yield 
a less stony clinker ; and some again at a far more elevated 
heat result only in a partially agglutinated, spongy, open 
cinder, or even in a pulverulent or flaky ash. 

Q. What quantity of ash is present after the complete 
combustion of coal ? 

The percentage of ash varies considerably for different 
coals, but it is generally less in anthracite than in the bi- 
tuminous varieties. Taking hard and soft coals as a whole, 
the average quantity of ash will lie between five and ten 
per cent, with occasional variations on either side. 

Q. What is smoke ? 

Smoke is a general term often applied to all the prod- 
ucts of combustion escaping from the furnace, whether 
visible or invisible. In a more restricted application it 
denotes the sooty products of the furnace escaping with 
the waste gases. These sooty particles are solid carbon, 
and usually very light and small. So far as mere weight 
is concerned, the blackest smoke is not perceptibly heavier 
than if the products of combustion were transparent. The 
objection to black smoke, as such, is not the actual loss in 



SMOKE PREVENTION. II9 

weight of carbon. It is rather that in cities and towns 
these sooty particles find their way through the ordinary 
currents of air into business places, dwellings, etc., the 
sooty deposit being practically constant in the neighbor- 
hood of such a chimney, causing much annoyance to 
housekeepers, merchants, and others. Colored smoke is a 
product of incomplete combustion. 

Q. Is colored smoke then no indication of waste in 
furnace combustion? 

Colored smoke is sure evidence of wasteful combustion, 
because it indicates a low temperature of furnace. An- 
thracite coal and coke give off no sooty particles when 
burning. In the case of bituminous coal the first effect 
of the heat is to detach small particles of carbon from, the 
surfaces next the incandescent fuel on the grate. These 
particles are so light that they are easily carried out of the 
furnace and up the chimney by the mechanical agency 
of the draft. If the furnace temperature was sufficiently 
high, and there was enough free oxygen over the bed of 
fuel to burn these soot particles, they would be converted 
into carbonic-acid gas and become wholly invisible. 
Black smoke is not a product of a high, but always that of 
a low furnace temperature. 

Q. How may smoke prevention be accomplished ? 

Bituminous coals, rich in hydrocarbons, require a fur- 
nace of much greater cubic content to render their com- 
bustion complete and wholly smokeless, than is required 
for anthracite coal or coke. The combustion chamber for 
bituminous coal ought always to be large and roomy. The 
temperature must always be high. Provision must be 
made for a controlled air admission above the fuel to sup- 



120 COMBUSTION OF COAL. 

ply the additional oxygen required for the conversion of 
the carbonic oxide into carbonic-acid gas. The fuel should 
be free from large lumps, and either frequently or con- 
tinuously fed to the furnace. 

In admitting air above the fuel, unless it can be sup- 
plied at the right place and time, and in the right quan- 
tity, it may prove a worse evil than the smoke itself, by 
lowering the temperature of the gases in the furnace to 
a point below which ignition is insured. 

In an ordinary boiler furnace, with flat grates, a nearly 
smokeless fire can be maintained by breaking up the coal 
and banking it immediately inside the fire door, that the 
gases may distill from the coal slowly. These gases pass- 
ing over the bed of incandescent coke, through which an 
excess of air is passing, will burn the volatile combustible 
of the coal smokelessly. When the fuel is well coked, it 
can be broken up, distributed over the grates, and a fresh 
supply of raw coal banked up as before. 

Q. What rule is there for measuring the shades of in- 
tensity of smoke? 

In any thorough study of smoke a scale of intensity is 
very important. As to the number of shades of intensity 
it has been proposed variously from three to ten. The lat- 
ter was adopted by the South Kensington and Manchester 
Smoke Abatement Commissions (1881), and upon trial 
was found to be quite undesirable, as it was difficult to 
discriminate between so many slightly differing shades. 
The second English Smoke Commission, in 1895, adopted 
a scale of only three shades — faint, medium, and black; 
but three shades were found to be too few, as ten were 
found to be too many. 

The best scale to adopt, according to the view now held 



RINGLEMANN S SMOKE SCALE. 121 

by most of the authorities, seems to be one having five 
shades, viz. : 
'I. White transparent vapor. 

2. Light brown smoke. 

3. Brownish-gray smoke. 

4. Dense smoke. 

5. Thick black smoke. 

The determining of the different shades is largely em- 
pirical, the shade varying with each observer according to 
his sight and sense of color. 

Professor Ringlemann's smoke scale adopts the five 
shades, and his plan is to represent the different grays 
into which the shades of smoke are naturally divided by 
black cross lines on white paper. Seen at a given dis- 
tance from the observer, these black and white diagrams 
show different shades of gray, representing the desired 
smoke tints. Variations in the shade can be obtained by 
varying the thickness of black lines or the size of the in- 
terstices of white left between them. A given cross line 
arrangement will represent one shade of gray when seen 
at a distance, say, of 80 to 100 feet from the observer, 
while if the black lines be doubled in thickness and the 
white intervals between them correspondingly diminished 
by half, another and darker shade of gray will at the same 
distance be shown (see Fig. 3). 

The principles on which the Ringlemann smoke scales 
are designed are as follows : 

No. o. No smoke. All white. 

1 . Light gray smoke. Black lines 1 mm. thick, and 
white spaces of 9 mm. between, all crossed at right angles 
like a chess board. 

2. Darker gray smoke. Black lines 2.3 mm. thick, J.J 
mm. apart. 



122 



COMBUSTION OF COAL. 





































































































































































































































No 


. 1. 





































































































































































































































































































































































































































































« 
















No. 2. 




No. 3. No. 4. 

Fig. 3.— Professor Ringlemann's Smoke Chart. 



SMOKELESS FIRING IN LOCOMOTIVES. 123 

3. Very dark gray smoke. Black lines 3.7 mm. thick, 
6.3 mm. apart. 

4. Black smoke. Black lines 5.5 mm. thick, 4.5 mm. 
apart. 

5. Very black smoke. All black. 

This is probably the best smoke scale yet produced. It 
is in use in portions of England, France, and in the United 
States. 

Q. Can soft coal be burned without smoke in ordinary 
locomotive fire boxes ? 

That railway smoke nuisance can be almost, if not 
wholly, abated, by simply exercising proper care and judg- 
ment in firing, is the expressed opinion of Mr. Angus 
Sinclair, an engineer of wide experience and excellent 
judgment. His recommendations, based upon actual prac- 
tice, consist merely in reducing the coal to small sizes, no 
large lumps, and firing in what is known as the single- 
shovelful method. 

The practical working of this method of firing has 
shown, according to the records of the Burlington, Cedar 
Rapids & Northern Railway, that bituminous coal burning 
locomotives, without any specially contrived fire box or fix- 
tures (except the ordinary brick arch), can be operated in 
any service from yard switching to heavy freight trains, 
quite as smokeless as if anthracite coal were used. This 
method of firing now permits passenger trains to be run 
comfortably over that road with the windows open. Fur- 
ther, an economy of about one-sixth of the money former- 
ly paid for coal is now saved to the company; the engines 
steam much more freely than under the old method of 
heavy intermittent firing; the annoyance of leaky tubes 
has almost ceased; there is no filling up of smoke boxes 



124 



COMBUSTION OF COAL. 



with cinders ; and there has been a decided reduction in 
the work of the boiler- maker ; and last, but "not least, the 
fireman has less work of coal- throwing to do, and he and 
the engineer are acting together to produce satisfactory 
results. 

Q. What results have been accomplished on the Cin- 
cinnati, New Orleans & Texas Pacific Railway in smoke- 
less firing with bituminous coal? 

Mr. J. W. Murphy, superintendent of the above road, 
says there is no detail in connection with the operation of 




Fig. 4. 

the road to which the management gives so much special 
and continued attention as in the efforts to prevent the 
emission of black smoke by locomotives on passenger 
trains. 

To secure these results, it was necessary, first, to equip 
the engines with brick arches, as indicated in Fig. 4. 
Four holes are shown on each side of the fire box for the 
purpose of admitting air. Four tubes run through the 
arch, and the outside air, passing through these tubes, is 



INSTRUCTIONS TO FIREMEN. 125 

heated to a high temperature. This heated air supplies 
oxygen to the unconsumed gases and produces complete 
combustion. The four holes in each side of the fire box 
are located twelve inches above the grates, and into these 
openings are inserted the Sharp patent deflecting air tubes, 
deflecting the air to the fire. 

Q. What instructions were issued to engineers for firing 
passenger locomotives on the " Queen and Crescent Limited,' ' 
Cin., N. 0. & T. P. Ry.? 

After firing each shovelful of coal, the door must be left 
open one or two inches for a few seconds, admitting enough 
air to produce complete combustion of the gases driven off 
from the coal. Care must be taken not to leave the door 
open longer than necessary to consume the gases. 

Firemen must learn to work with as light a fire as pos- 
sible. Great care must be taken that steam is not wasted 
at the safety valve, either when the train is in motion or 
when standing still. 

Before starting, the blower must be put on and a suffic- 
ient supply of coal put into the fire box to insure a good 
solid fire. After the coal has been put in, the door must 
be left partly open by placing the latch on the first notch 
of the catch, so to remain until the smoke entirely disap- 
pears, when the door must be closed. 

After starting the door must be left partly open after 
each shovelful of coal is put into the fire box, by placing 
the latch on the first notch of the catch until such time as 
the smoke disappears, when the door must be closed. 

On approaching tunnels the fire must be replenished in 
ample time, obtaining sufficient fire to carry the train 
through the tunnel without smoke, the door to be kept 
closed while passing through tunnels. 



126 COMBUSTION OF COAL. 

The engineman should so arrange the water supply that 
the fireman may be able to fire the engine regularly and 
economically, and this can be done best when the water is 
supplied to the boiler continuously. 

Firemen must pay particular attention to the manner 
in which the engineman works the injector and handles 
the engine, in order to regulate the fire accordingly. 

Care must be taken to have the blower applied and the 
door partly open when approaching a station where a stop 
is to be made, and no smoke must be allowed to show 
from the stack at such times or when descending grades. 

While the blower is being used, except when approach- 
ing a station where a stop is to be made, care should be 
taken to keep the door closed as much as possible, more 
especially when cleaning the fire, as the blower causes- the 
cold air to be drawn into the flues. 

While lying on side tracks, both dampers should be 
closed to save the fire. 

Grates should be shaken only when absolutely neces- 
sary, as too frequent shaking causes a loss of fuel by al- 
lowing the unconsumed coal to fall into the ashpan, where 
it ignites and causes the pan to heat and warp. Ashpans 
should be examined as frequently as stops will permit, and 
under no circumstances must they be allowed to become 
filled. 

When possible to avoid it, the fire box must not be left 
wide open. To leave the fire door wide open is especially 
bad when using steam or blower. 

It is beneficial to wet the coal before firing, and firemen 
should, as far as possible, use wet coal. 

Intelligent firing and economical results in the use of 
fuel will be considered in the selection of firemen for pas- 
senger engines or for promotion to freight enginemen. 



SMOKELESS COMBUSTION. \2J 

These rules must be strictly observed on night as well 
as on day passenger trains. 

Q. How may smokeless combustion be best secured in 
locomotive practice? 

The best examples of smokeless firing occur in locomo- 
tives using no device but the brick arch in connection 
with careful firing. A general sentiment, based upon ex- 
perience on Western railroads, where soft coal only is used 
for fuel, is that a good fireman without a special device is 
productive of better results than any of the mechanical 
devices if poorly managed. The conclusion reached in 
Chicago, St. Louis, and other Western cities where efforts 
have been made to reduce the amount of smoke made by 
locomotives, is that steam jets and other similar devices 
are not to be seriously considered as successful smoke 
preventives; and, second, the most effectual method of 
preventing smoke is by the use of the brick arch and skil- 
ful firing. 

Q. What is the device for smoke prevention by the 
Locomotive Smoke Preventer Company? 

This device as applied to a locomotive is shown in Fig. 
5, and further illustrated in detail in Fig. 6, which shows 
the heating coil in the smoke-box extension; Fig. 6a, 
which is another view of the heating coil ; Fig. 7, which 
shows plan arrangement of the manifold, a group of three 
jets passing through the front end of the fire box; Fig. 8, 
an enlarged section of the combined steam and air jet, 
and the seamless water jacket. The elevation of a loco- 
motive (Fig. 5) shows the entire device when applied; it 
consists of a funnel-shaped pipe A, which is attached to 
the smoke box at B; this pipe continues to one end of a 



128 



COMBUSTION OF COAL. 




LOCOMOTIVE SMOKE PREVENTER COMPANY. 



2 9 



series of bends or coils of pipe called the heater C, 
whose axis is parallel with the axis of the boiler shell — 




Fig. 6. 



Fig. 6a. 



the other end being attached to a pipe which leaves the 
smoke box at D on the opposite side from A. By means 
of an elbow it connects to the pipe E extending along the 
side of the boiler close under the running boards back to a 



PIPE TO SMOKE BOX 




^-iijjreQ 



Fig. 



point in front of the throat sheet — where by 45 ° elbows it 
passes under the barrel and enters at the centre of the 
9 



130 



COMBUSTION OF COAL. 



manifold F placed in front and close to the throat sheet. 
The three or more openings in the manifold exactly tally 
with the air ducts leading into the fire box. In the inside 




of the fire box at the tube sheet and close to the under 
side of the fire-brick arch are three or more cylindrical 
tapered water-jackets, G, G, which screw into the tube 
sheet and extend into the fire box a distance of about 
twelve or fourteen inches, their interior being open direct 
to the water leg of the boiler; concentric with the jacket 





Fig. 9. 



and extending from the throat sheet through the water leg 
and jacket is the air tube H referred to, above, its ends 
being expanded and beaded into the sheet and jacket re- 
spectively. It will thus be seen that we have a contin- 



OBJECTION TO STEAM AND AIR JETS. I3I 

uous air passage from the air funnel at the front of the 
engine through the hot smoke box to the fire zone in the 
fire box. 

A side elevation and plan of manifold F, together with 
the method of attaching the steam jets, is shown in Figs. 
7 and 8. The manifold is tapped for a one-fourth inch 
pipe terminating in an one-eighth inch opening in the air 
tube H. The flow of steam through it is controlled by a 
valve J in the cab. The special function of this jet is to 
force hot air into the fire box when the engine is at rest, 
or when running with the throttle shut. When an appli- 
cation of coal is made, it is met by a large volume of air 
heated to the point of ignition by previous contact with 
the incandescent fire-brick arch, thus furnishing oxygen 
where it is most needed to produce smokeless combustion. 

The door sheet nozzles shown in Fig. 9 are used on en- 
gines having long fire boxes and a comparatively short fire- 
brick arch. 

Q. What is the objection to a combined steam and air 
jet in a locomotive furnace ? 

Steam jets which introduce both steam and air above 
the fire have a temporary dampening effect when the en- 
gine is standing, as they produce a pressure on the fire 
box equal to the draft, and the current of gas and smoke 
through the stack is stopped. In other words, smoke is 
prevented because combustion has almost ceased. When 
the engine is working, the effect of the steam jets is very 
slight. The steam is condensed by contact with cold air, 
and it enters the fire box as moisture, and its effect must 
be to lower the temperature of the gases, and it does not 
support combustion. The air which is drawn in is also 
cool, and there is no real combination with the gases until 



132 COMBUSTION OF COAL. 

it is heated up to their temperature. From any point of 
view, according to the committee of the Western Railway 
Club on smoke prevention, the steam and air jet cannot be 
considered as a promising device from which any success- 
ful smoke preventer may be evolved, and the committee 
believe it to be important that this fact be emphasized for 
two reasons : first, because valuable time has been wasted 
already in continued and unsuccessful experiments with 
steam jets; and second, because their presence on the 
engine and occasional use have the effect of relieving both 
master mechanic and engineman of responsibility to a 
certain extent. If the steam jet is given up as hopeless, 
then more attention and effort will be directed toward 
better proportions of fire box and other features in the 
original construction of the locomotive. 

Q. What is an econometer? 

The econometer, designed by Max Arndt, and shown 
in Fig. 10, is a gas- weighing machine on an entirely new 
principle, fixed in an air-tight case 7 with a plate of glass 
in front. In the case 7 there are two connecting joints, 
39 and 40, 40 is connected by a y§" pipe to the flue of the 
boiler about two feet from the damper, and 39 is con- 
nected by a -§■" pipe to an aspirator in the main flue be- 
tween the damper and the chimney, or the chimney itself, 
and which constantly draws a sample of the gases from 
the boiler flue through filters, gas pipes, and balance, dis- 
charging it into the chimney. In the interior of the 
econometer case 7, the joint 40 is connected with the as- 
cending pipe 23, and the joint 39 with the descending 
pipe 22 by means of India rubber tubes 34 and 35. 

The gas-weighing machine itself consists of a very fine- 
ly adjusted, highly sensitive balance, to which is fixed the 



MAX ARNDT S ECONOMETER. 



133 



pointer or index 17. On one end of the balance is sus- 
pended an open glass globe 18, with a capacity of about a 
pint, and on the opposite end a compensating rod 32, to 
which is affixed a scale pan with a number of glass beads 
and filings by which the gas holder can be balanced. The 




11 Sa^ 



134 COMBUSTION OF COAL. 

knife-edges of the balance are steel gilded, and the caps 
are agate. The whole balance works on a pillar screwed 
on a cast plate 28. The latter has adjusting screws by 
which the balance is set, both horizontally and vertically. 
For this purpose a small pendulum is attached to the sup- 
porting pillar. A frame 27 is fixed on the pillar in which 
is inserted the scale. 

The gas-ascending pipe 23 reaches into the gas holder 
or weighing globe 18, which has a neck 20 open below 
and surrounded by cup 21 open above. The neck 20 has 
free play around glass tube 19, as well as cup 21, so that 
the gas holder can swing free from resistance. 

The combustion gases, having to pass through filters and 
drying chambers, enter the weighing globe thoroughly 
cleaned and dried. 

As carbonic acid is about 50 per cent heavier than at- 
mospheric air and the other gases contained in combustion 
gases, so the gases which continually fill the weighing 
globe must be heavier in proportion to the amount of car- 
bonic acid contained therein. The scale 27 is so divided 
that the movement of the pointer 17 of the gas balance 
from one dividing line to another corresponds with the 
volume per cent of C0 2 in the gases to be weighed. The 
amount of carbonic acid in the gases can therefore be 
read off at all times. 

Q. What is the object of the econometer? 

In Europe, where coal economy has received the great- 
est attention, it has long been the custom to provide en- 
gineers with chemical apparatus, by which the percentage 
of carbonic-acid gas could be determined at intervals. 
This determination, though irregular, proved of the great- 
est value, and led to the invention of the econometer, 



max arndt's econometer. 135 

which indicates continuously the exact percentage of 
carbonic acid contained in the escaping products of 
combustion. The value of having a continuous indication, 
rather than one obtained at infrequent intervals, can hardly 
be overestimated, for a constant guide to firing is thus 
obtained. 

In order to produce combustion, carbon, the vital ele- 
ment in the coal, must unite with oxygen, which it does 
in certain unvarying proportions. In the first stage of 
combustion, one part of carbon unites with one part of 
oxygen, forming a combustible gas, known as carbon mon- 
oxide, and in this process about one-fourth of the heat is 
liberated. In the second stage, the carbon monoxide ab- 
sorbs another part of oxygen, forming a gas known as car- 
bon dioxide or carbonic acid, and in this process the bal- 
ance of the heat is liberated.* As there is twenty-one per 
cent of oxygen in the air that is conveyed to the carbon, 
it is easily seen that perfect combustion would produce 
twenty-one per cent of carbonic acid, since all of the oxy- 
gen would unite with all of the carbon and every heat unit 
contained in the coal would be liberated. 

It is next to impossible to obtain perfect combustion in 
any steam-boiler furnace for many reasons, but it is pos- 
sible to obtain and maintain good combustion, with proper 
firing and correct manipulation of the draughts and damp- 
ers. It is easy to see that the only test to be applied is 
that of determining the percentage of carbonic acid pres- 
ent in the escaping gases, and that the value received 
from the burning of all coal is in exact proportion to this 
percentage of gas. Chemistry has determined these 

* This is from Arndt's point of view. The generally accepted theory is 
that C0 2 is first formed, which passing up through the bed of incandescent 
fuel takes up another equivalent of carbon, resulting in CO. — Ed. 



136 COMBUSTION OF COAL. 

values, so that when the per cent of carbonic acid is 
known, the value received from the burning of any coal 
can be ascertained. Table 13 shows the relative values, 
from which the difference between burning coal properly 
and improperly can be ascertained at a glance. 

Q. How are the econometer percentages of carbonic- 
acid gas affected by excessive air supply? 

Carbonic acid is fifty per cent heavier than air, and thus 
the greater the percentage contained in any given volume 
of flue gases the greater the weight of that volume. In 
the econometer, a sample of the escaping gas from the 
boiler is drawn continuously through a balance scale, sus- 
pended in air, and the variations in weight that are pro- 
duced by the different states of combustion are made to 
record the percentage of carbonic acid. The weight of 
this gas varies with the temperature, but in the eco- 
nometer, the sample to be weighed, and the air in which 
the weighing is done, assume the temperature of the room, 
so that the proportion remains exact. 

It is plainly evident that for each pound of coal a 
fixed amount of air is necessary for combustion, varying 
as the percentage of carbon varies in the different coals. 
For a pound of average quality, about one hundred and 
twenty-five cubic feet of air is necessary, and it is the 
inability to convey this precise amount to the furnace 
that prevents our obtaining and maintaining perfect com- 
bustion. 

If too little air is admitted, combustion becomes imper- 
fect because the carbon monpxide cannot find the neces- 
sary oxygen to complete its transformation into carbon 
dioxide, and this is the most wasteful condition of firing, 
for the largest part of the heat is given off in the second 



LOSS BY IMPERFECT COMBUSTION. 



137 



* 



*" ^ 



3 -if 

•5 <* « 

» - 

: i 



V 



Per cent 
carbonic 
acid. 


Times the 
theoreti- 
c a 1 re- 
quire- 
ments. 


Cubic feet 
of super- 
flous air 
heatedto 

a tem- 
perature 
of usual- 
ly 5 1 8 ° 
Fahr. 


q 




vr> 


CO 



d 


W 


rf 


■* 


CO 

00 


co 


to 


10 


O 
IT) 


<* 


n 





CO 

co 


\n 


H 


r- 


co 

M 


O 


O 







co 

M 


O* 


w 


CO 




O 


OO 




CO 



co 


CO 


r^ 




vr> 
OS 
CO 




O 


CO 


co 

vO 

co 

in 


O 

co 


\r> 


00 

CO 


co 

O 


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CO 


<* 




in 

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CO 


CO 


ID 


O 
O 


w 


IT) 


vO 



O 


u 

<u 

a 


c 




■Si 

«4H 




Then the quantity 
of air passing 
through the flues 
is 




With a surplus sup- 
ply of air of 30 
per cent or about 
166 cubic feet of 
necessary air per 
pound of fuel, 
there will still be 
a further excess 
of about . . 




a* 

°Pn c 

C/5 •*- 
0° " 

,-5 CO •*- 

■£ c 








•A}iren 


3 


9SBJ9AB JO JBOD JO j[ 









138 COMBUSTION OF COAL. 

stage of combustion. * This case is seldom met with in 
practice, for most boiler furnaces are supplied with too 
much air. Then the combustion is poor because there is 
a large amount of air passing through the fire, the oxygen 
of which cannot be consumed. This surplus air must be 
heated to the same temperature as the escaping gases, 
thereby absorbing the heat already generated, which 
should pass instead into the water contained in the boiler. 

Q. In what manner may loss of fuel through imperfect 
furnace detail or management be detected by the econom- 
eter ? 

Loss of fuel calculated and shown in Table 1 3 can be 
caused in a variety of ways, and is to be sought for in all 
of the accessories of the furnace. It may result from an 
excessive or defective draft, from faulty grates or wrong 
proportion of grate surface, there may be defects in the 
boiler setting or in the fire and ash-pit doors, that should 
be remedied. The proper thickness of fire is something 
that must be determined, varying as it does with the many 
different conditions surrounding all steam plants. 

By first obtaining the percentage of carbonic acid in the 
gases produced with ordinary firing and then experiment- 
ing with the boiler in connection with the econometer, any 
fireman can soon ascertain the proper thickness of fire and 
draft necessary to insure good combustion. If with a 
high percentage of carbonic acid the gauges should show 
too much steam, a case often experienced in practice, it is 
evident that the grate surface should be reduced, which 
can be done by bricking up at the back end of the ashpit, 
or at the back end or sides of grates over the bars. 

A very common source of waste is the formation of 

* See foot note on page 135. 



LOSS BY IMPERFECT COMBUSTION. 1 39 

holes in the fire, and of the presence of these, the econo- 
meter is a never-failing indicator. By drawing samples 
of gas from the entrance and exit of the flues, and com- 
paring the percentage of carbonic acid, any existing de- 
fects in the setting and brickwork will be discovered. 



CHAPTER VI. 

HEAT DEVELOPED BY COMBUSTION. 

Q. What is heat? 

In steam engineering heat is regarded from the dynam- 
ical or mechanical theory only, on the supposition that 
heat and mechanical force are convertible one into the 
other. From the great number of experiments in the gen- 
eration of heat by mechanical processes, by friction, by 
the arrest of motion, either gradually or by percussion, by 
the change in the quantity of heat observed in the case of 
expansion, etc., has led investigators to the conclusion that 
heat is simply a motion of ultimate particles, and that the 
molecular structure of bodies has much to do with their ca- 
pacities for heat ; and an increase or decrease of tempera- 
ture is simply an increase or decrease of molecular motion. 

Q. What numerical value, in heat units, should be 
used in estimating the calorific power of carbon in con- 
nection with coal analysis ? 

Carefully conducted experiments by the earlier as well 
as the more recent investigators have yielded practically 
the same results. Three numerical values for carbon are 
in common use, viz., 14,544, 14,540, 14,500 heat units. 
These are so nearly alike as to cause no confusion, and 
practically no error in any calculations relating to the 
calorific value of fuel. The latter is the one in very gen- 
eral use. 



HEAT GENERATED BY COMBUSTION. 141 

In the examples given in this book the writer has fol- 
lowed as nearly as possible the numerical values given by 
investigators, those used in geological reports, and in any 
correspondence relating to the coal then under considera- 
tion. 

Q. What quantity of heat is generated by the con- 
version of carbonic oxide, CO, into carbonic-acid gas, C0 2 ? 

Calorimeter tests show that one pound of carbonic oxide 
burnt to carbonic-acid gas develops 4,325 heat units. 

It will be seen that a loss of heat occurs even though all 
the carbonic oxide in the furnace be converted into car- 
bonic-acid gas, because the chemical union which produces 
the latter gas yields 14,500 heat units, whereas burning 
carbon to carbonic oxide yields only 4,450 heat units, and 
the burning of CO into C0 2 yields 4,325 heat units, or a 
total of 8,775 neat units. This is 5,725 heat units per 
pound less than the direct conversion of carbon into car- 
bonic-acid gas, a loss of 39 per cent. 

Q. Can the loss of heat occasioned by burning carbon 
to carbonic oxide, CO, be recovered by its subsequent con- 
version into carbonic-acid gas, C0 2 , before it leaves the 
furnace ? 

The burning of carbonic oxide, CO, in the combustion 
chamber above the fire is a wholly distinct operation from 
the combustion of the coal on the grates, one result of 
which is the formation of the CO. 

There are two methods by which this conversion from 
CO to C0 2 may be accomplished : first, by the admission 
of surplus air through the bed of incandescent fuel ; sec- 
ond, by the admission of air through perforations in the 
lining of the fire door, through the side walls of the fur- 



142 COMBUSTION OF COAL. 

nace, through a perforated pipe in the furnace, through 
perforations in or adjoining the bridge wall. All of the 
above connect in some manner with the atmosphere. 
Shortening the grates so as to leave a space at the end to 
allow passage of air between the grates and the bridge 
wall. All of these methods have been tried with more or 
less success depending upon local conditions. 

Q. Upon what is the temperature of fire conditioned? 

The temperature of combustion is conditioned upon the 
nature of the fuel burned,; the nature of the products of 
combustion ; the quantity of the products of combustion ; 
the specific heat of the gases present in the furnace result- 
ing from combustion, including the quantity of air present 
at the moment of combustion in order to render it com- 
plete. 

Q. How may the temperature of the combustion of 
carbon be estimated ? 

In the complete combustion of one pound of carbon we 
have: 

Carbon I 

Oxygen 2.67 

3-67 

pounds of carbonic-acid gas. 

In addition thereto we have 8.94 pounds of nitrogen left 
after the separation of the oxygen from the atmospheric air. 
The specific heat of carbonic-acid gas is 0.216, and that 
of nitrogen 0.244. We have then : 

„ . _ Specific Heat 

Products ' Pounds ' heat. units. 

Carbonic-acid gas 3. 67 X . 216 = . 794 

Nitrogen 8.94 X .244 = 2. 181 

Total 2.975 



TEMPERATURE OF COMBUSTION. 143 

heat units absorbed in raising the temperature of the prod- 
ucts of combustion of one pound of carbon, i°F. 

The combined weight of the two products are 3.67 -f- 

, r^, Heat units 2.975 

8.Q4 = 12.61 pounds. I hen: ^ = -=- = 0.236, 

r Pounds 12.61 J 

their mean specific heat. 

The total heat of the combustion of one pound of car- 
bon in oxygen gas is 14,544 heat units; divide this by the 

14,544 

2.075 heat units absorbed, we have: = 4880° F. 

2.975 * * 

as the highest theoretical temperature attainable by 

the complete combustion of one pound of carbon, using 

1 1. 6 1 pounds of air per pound of carbon, the minimum 

theoretical limit. 

Example 2. Suppose that eighteen pounds of air are used 

instead of the theoretical quantity given above, and that the 

combustion is complete, we then have 

Carbon 1 

Oxygen 2.67 

Nitrogen 8. 94 

Surplus air 6. 39 

19.00 

pounds of furnace products. 

The specific heat of air is 0.237, proceeding as before : 

Products. Pounds. , t 

heat. units. 

Carbonic-acid gas 3. 67 X • 216 = . 794 

Nitrogen 8.94 X -244 = 2. 181 

Air, uncombined 6. 39 X • 237 = 1 . 5 19 

Totals 19.00 4-494 

4.494 14,544 

Then: — — =0.237, the mean specific heat. - — - — = 
19 0/> ^ 4.494 

32 36 F., the temperature of the fire under the above 

conditions. It will be noted that a reduction of 1653 F. 



144 



COMBUSTION OF COAL. 



occurs through the admission of 50 per cent more air than 
was needed for combustion. Had double the quantity of 
air passed through the fire, the temperature would be 
about 2450 F. 



-Table 14. — Weight and Specific Heat of the Products of Com- 
eustion, and the temperature of combustion. 

(From D. K. Clark's Rules, Tables, and Data.) 



One pound of combustible. 



Hydrogen 

Olefiant gas 

Coal (average) 

Carbon, or pure coke 

Alcohol 

Light carburetted hydrogen. . . 

Sulphur 

Coal, with double supply of air 



Gaseous Products for One Pound of Com- 
bustible. 



Weight. 



Pounds. 
35-8 

15.9 

II.94 

12.6 

IO.O9 

18.4 

5-35 
22.64 



Mean 

specific 

heat. 



Water = 
.302 

• 257 
.246 
.236 
.270 
.268 
.211 
.242 



Heat to 

raise 
tempera- 
ture i° F. 



Units. 
IO.814 
4.089 
2-935 
2.973 
2.680 

4-933 
1. 128 

5.478 



Temperature of 
combustion. 



Deg. F. 

5744 
5219 
4879 
4877 
4825 
4766 

3575 
2614 



Ratio. 

IOO 

91 

85 
85 
84 
83 
62 

45 



Q. How may the quantity of heat developed by com- 
bustion be determined? 

The heat developed by chemical action or combustion 
is best determined by the use of an apparatus known as a 
calorimeter, by means of which a combustible is burnt in 
oxygen gas, the heat liberated by combustion being ab- 
sorbed by the water which surrounds the combustion 
chamber. The weight of combustible, the oxygen, and 
the water being known, the quantity of heat evolved by 
the combustion of each substance can easily be calculated 
by the rise in temperature of the water. 

The apparatus used by Favre and Silberman for meas- 
uring the heat evolved by the combustion of various sub- 



FAVRE AND SILBERMANN'S CALORIMETER. 145 



stances in oxygen gas is represented, with the omission of 
minor details, in Fig. 11, in which C is a vessel of gilt 
brass plate, immersed in a water calorimeter, A A, of sil- 
vered copper plate, and the latter is enclosed in an outer 
vessel, B B, the space between A and B being filled with 
swandown to prevent the escape of heat from the water 
A. The vessels A and B are 
closed with lids having aper- 
tures for the insertion of tubes 
and thermometers. The com- 
bustions are performed in the 
vessel C, into which oxygen is 
introduced through the tube 
c d y and the gaseous products 
of the combustion escape by 
the tube, e f g h, the lower 
part of which is bent in nu- 
merous coils, to facilitate as 
much as possible the trans- 
mission of the heat of these 
gases to the water in the cal- 
orimeter. The extremity, k> 
of this tube is connected with 

a gasometer or with an absorbing apparatus. To insure 
uniformity of temperature in the water, a flat ring of metal, 
i z, is moved up and down by means of the rod Ki. Com- 
bustible gases were introduced into the vessel C, by means 
of fine tubes, the gas being previously set on fire at the 
aperture. Solid bodies were attached to fine platinum 
wires suspended from the lid of the calorimeter. The liq- 
uids were burned in small capsules or in lamps with 
asbestos wicks. Charcoal was disposed in a layer on a 
sieve-formed bottom, through the openings of which the 
10 




Fig. 11. 



146 



COMBUSTION OF COAL. 



oxygen had access to it. The heat evolved was measured 
by the rise of temperature of the known quantity of water 
in the calorimeter. 



Table 15. — Quantities of Heat Evolved by the Combustion of 
One Pound of Combustible with Oxygen. (Favre and Silberman) . 



Substances. 



Gases : 

Hydrogen 

Carbonic oxide 

Marsh gas 

Olefiant gas 

Liquids : 

Oil of turpentine, 

Alcohol 

Spermaceti (solid) 

Sulphate of carbon ......... 

Solids : 

Carbon (wood charcoal) 

Gas coke 

Graphite from blast furnaces 

Native graphite 

Sulphur (native) 

Phosphorus (by Andrews) . . . 



Formula. 



H ... 
CO... 
CH 4 . 
C 2 H 4 



C10 Hi6 . . . 

C 2 H 6 0... 

C32 H 6 4 O2. 

CS 2 . 



Product. 



H 2 

co 2 

C0 2 and H : 
C0 2 andH< 



C0 2 and H 2 O 
C0 2 and H 2 O 
C0 2 and H 2 O 
C0 2 and S0 2 



CO. 

co 2 



so 2 .. 
P205. 



British 
thermal units. 



62,032 

4,325 

23,513 

21,343 

19,533 

12,931 

18,616 

6,122 

4,45i 
14,544 
14,485 
13,972 
14,035 

4,048 
10,715 



Q. What are the relations between quantity of heat 
and temperature developed in combustion ? 

The actual amount of heat given out during the com- 
plete oxidation of any substance is the same whether the 
combination is slow or rapid, and is carried on in air or in 
oxygen. But it is quite different in regard to the temper- 
ature developed, this depending on the concentration of 
the heat ; and so being higher, the more rapid the com- 
bustion and the less extraneous matter is present to absorb 
the heat. The temperature of a hydrogen or a coal-gas 
flame burning in oxygen is very much higher than that of 
a similar flame burning in air. 



WHERE THE COAL GOES. 



IA7 



HEAT 
UNITS 



WASTED, USED JJN EIRING UP, LEFT IN BOX, STANDING 
IDLE ETC. — ^ 



LOST IN HEATED AIR, GASES AND VAPOR .. 



EVAPORATING MOISTURE IN COAL 

HEATING COAL TO IGNITION 

HEAT AND UNCONSUMED COAL IN ASHES 



UNCONSUMED GASES 



LOST .IN r 'SPA'RKS" 



RADIATION FROM BOILER, FIRE BOX ETC. - 
HEAT LOST IN ENTRAINED WATER. .23 LB8. 

8EAJIJN.G JjEED WAXER-(55° TO .212°) 



LATENT HEAT AT 361 (OF SEPARATION ONLY 
775.8 H.U. 



FRICTION IN PORTS, STEAM PASSAGES-ETC^ 

CLEARANCE O'fc. 

CYLINDER CONDENSATION --fliT'Ct' 

BACK PRESSURE ABOVE ATMOSPHERE" ---f^-O 
BACK PRESSURE BELOW ATMOSPHERE"— *8,8-"* 2 *-£ : ;- 

PER COMPRESSION 2.-8 ----": 

LOST EFFECTIVE .WORK 'BY INCOMPLETE EXPANSION, J 
IN CYU ETC. , 

MACHINERY FRICTION AND HEAD RESISTANCE-^2-9--. 

TRACTION OF ENGIN.B B9rS" " " "S- - ■ 

TRACTION OF CARS -"""__. 

TRACTION OF LOAD (NET USEFUL EEFECfJ. 



J ASSUMED AT Wffi 



-50% IN EXCESS OF THEORETICAL.AMQUN.T, 
(9. LBS. AIR PER LB. COAL) 



-ESTIMATED AVERAGE. 
-THOS. BOX. 
• ~2% EXCLUDING "WASTE" 



_kENT LOSS 2% TO 30%. LOVELL'S 
EXPERIMENTS N.P. RY. 1896. \3<f„. 



-5$ ASSUMED, EXCLUDING WASTE. 

ASSUMED AT 5% OF APPARENT 
EVAPORATION 



-(BOILER EFFICIENCY 61. 79$, LOSSES 
48.21$). 



L_1'MEA"N EVAPORATION 4. 66 LBS. WATER 
LESS 5% PRIMAGE, MEAN OF FIVE TESTS) 



DROP IN PRESSURE FROM BOILER TO CYL. 
/ 140* TO 125* 
/ RATIO EXPANSION 1.83, CLEARANCE 1%, 
V COMPRESSION 3%% 
' , 'ACTUAL 

',-'8 LBS. ABOVE ATMOSPHERE 
',--14.7 LBS. ABSOLUTE 
--kOF CLEARANCE 

---INCLUDES EXPANSION AGAINST 

ATMOSPHERE , 
"ASSUMED AT 10% NET EFFECT | VE 

- ?B_TONS 15^ OF TOTAL; PRESSURE 0N 



273 
"193 



60% 



PISTON = 
H.U. 



423 



* This item includes errors of assumption .as follows: That expansion is hyper- 
bolic, that latent heat of separation is a constant at all temperature's, andithat no 
latent heat (of separation) Tsrfransformed into work. The net .error probably 
does not exceed 25 h. u. 

Where the Coal Goe& When Biinrred in a Locomotive Firebox. 
Fig. 12. 



148 COMBUSTION OF COAL. 

Q. What is the heating power of sulphur contained in coal ? 

The quantity of sulphur in good coal is so small that its 
calorific value is commonly neglected in any calculations 
relating to the heating power of coal. 

The quantity of heat evolved in the complete combus- 
tion of one pound of sulphur in oxygen gas, as determined 
by Favre and Silberman, is 4,048 heat units. The equiva- 
lent evaporation from and at 21 2° F. would be 4048 -f- 966 
= 4.19 pounds of water per pound of sulphur. The tem- 
perature of the combustion of sulphur is about 3 5 75 ° F. 

Q. How is the heat evolved from coal distributed in 
locomotive practice? 

The accompanying diagram (Fig. 12), by E. H. Mc- 
Henry, chief engineer Northern Pacific Railway, shows 
heat losses and net effective work of one pound of Red 
Lodge coal burned in a typical Mogul engine, in ordinary 
service, Northern Pacific Railway. 

Mogul engine; Class D2 ; cyl., iS^i in. by 24 in. ; 
boiler pressure, 140 pounds; cut off, 12-f in.; ind. h. p., 
381 ; speed, 16 miles an hour; weight of engine and train, 
550 tons. Red Lodge coal (by analysis), 10,000 heat 
units per pound. 

1 pound coal =0.168 h. p. hour. 
5.95 pounds coal per h. p. hour. 
27.73 pounds water per h. p. hour. 

[51 per cent of the theoretically available 

heat in the steam by a non-condensing 

engine. 

36.2 per cent of the theoretically available 

heat in the steam by a condensing engine. 

7.4 per cent of the total heat in the steam. 

3.8 per cent of the total heat in the coal. 



The motion 
of the train 
represents 
the conver- 
sion into 
work of but 



CHEMICAL CHANGES. 149 

The chart was compiled from actual tests of a Mogul 
engine on the Yellowstone Division of the Northern Pa- 
cific Railway, in which the coal was weighed and the 
water measured, frequent indicator cards taken, and the 
final net effective traction at the periphery of the drivers 
determined by a dynamometer, thus affording an opportu- 
nity of checking the calculations at several points in the 
length of the column, with the effect of localizing minor 
errors. The efficiency of some modern engines is consid- 
erably higher than that shown, but the chart will closely 
apply to the great majority of the engines in present ser- 
vice all over the United States. 

Q. Is heat generated by chemical action convertible into 
mechanical energy ? 

Chemical changes are either atomic or molecular, and 
all differences in the temperature of bodies are due to the 
changes in their molecular condition ; therefore, chemical 
action, heat, and mechanical energy should be mutually 
convertible. Chemical changes are always attended by a 
change in the thermal conditions of the bodies acted upon, 
in which combinations as a rule produce heat, while de- 
compositions produce cold or a disappearance of heat. 
The amount of heat any particular body is capable of giv- 
ing off must be determined as yet experimentally. The 
researches of Favre and Silberman, Andrews, Thompson, 
Joule, and others, have given us a very close approxima- 
tion to the dynamic value of heat and the heating power 
of different fuels. 

Q. What is the effect of heat upon water? 

Water within the range of its solidifying point and that 
at which it becomes an elastic vapor is subject to very 
great irregularities. If water be taken in a solid state, or 



i5o 



COMBUSTION OF COAL. 



at a temperature of 32 ° F. before it has solidified, and 
heat be communicated to it, instead of expanding, it act- 
ually contracts until it marks about 39.4 F., at which it 
has attained its greatest density. Above this it expands 
in the same ratio that the contraction took place for an 
equal number of degrees, but beyond that point it obeys 
the general law. 

Q. What is the effect of heat upon gases? 

All gases at ordinary temperatures are in a state in 
which the atomical aggregation manifests a highly repul- 
sive tendency. It is evident, therefore, that gases will be 
influenced to a greater extent by heat than either solids or 
liquids. 

A remarkable coincidence or uniformity exists among 
the different gases ; and knowing the rate of expansion of 
one, the same may be taken as the expansive power of the 
other permanent gases when subjected to an equal increase 
of temperature. It was found, however, by Magnus and 
Regnault, that the operation of this law is not perfectly 
uniform, especially with reference to the easily liquefied 
gases, which are more expansible than air when exposed to 
equal increments of heat, as the following table will show : 

Table 16. — Expansion of Gases Between 32 and 212° Fahr. 



Gases 

Air 

Nitrogen 

Hydrogen 

Carbonic oxide 

Carbonic acid 

Nitrous oxide 

Cyanogen 

Sulphurous acid 



Constant 
volume. 



Constant 
pressure. 



O.3665 
O.3668 
O.3667 
O.3667 
O.3688 
O.3676 
O.3829 
0.3845 



O.3670 

O.3661 
O.3669 
O.3710 
O.3720 

0-3877 
O.3903 



UNITS OF HEAT. I 5 I 

A sensible increase in the rate of expansion is also 
found when the gas is submitted to pressure, compared 
with that which takes place when it is in a rarefied state. 
The expansion of perfect gases has been employed in the 
enunciation and perfecting of a new scale of temperature, 
known as the absolute scale of temperature. 

Q. What is the rate of expansion of air by the appli- 
cation of heat ? 

By former investigations this was found to amount to 
about 375 parts in 1,000 of air when heated from the 
freezing to the boiling point of water. Later researches, 
however, have shown that the true expansion of air within 

these limits is 365 parts, or of the whole for each 

493-2 

degree of the Fahrenheit scale. Below the freezing and 
above the boiling point of water the expansion is in the 
same ratio.. 

Q. What is the British thermal unit ? 

A British thermal unit is that quantity of heat neces- 
sary to raise the temperature of one pound of water from 
39 to 40 F., the former being the temperature of its 
greatest density. This is equivalent to 772 foot-pounds. 

Q. What is a calorie? 

A calorie is the metric unit of heat. It is that quantity 
of heat required to raise one gram of water from 4 to 5 
C. Some writers give the range of temperature from o° 
to i° C. , which is in error, as the greatest density of 
water occurs at 3.94 C, or 39.4 F. 

1 calorie = 3.968 British thermal units. 

1 British thermal unit = .252 calorie. 



152 COMBUSTION OF COAL. 

Q. What is the relation of atomic weights to specific 
heat? 

In regard to the atomic weights and their relation to 
specific heat, it is a noteworthy fact that as the specific 
heat increases the atomic weight diminishes, and vice 
versa ; so that the product of the atomic weight and spe- 
cific heat is, in almost all cases, a sensible constant quan- 
tity. For equal weights the specific heat of the several 
gases entering into the problem of coal combustion ought 
to bear a direct relation to each other, for example : 

The specific heat, for equal weights, of the following 
gases, were found by Regnault to be : 

Air, specific heat for equal weight o. 237 

Oxygen " " " " 0.218 

Nitrogen l< " " " 0.244 

Hydrogen " " " 3. 409 

On the supposition that, for equal volumes, gases con- 
tain the same number of atoms, we should expect the gases 
oxygen and nitrogen, as well as the mixture of the two lat- 
ter to form air, to have the specific heat of each practically 
equal, according to their atomic weights. The atomic 
weight of hydrogen is 1, and its specific heat is 3.409. 
We should then expect : 

3.409 -4- 14 = 0.243, specific heat nitrogen, N 14. 
3.409 -7- 16 = 0.213, " " oxygen, O 16. 

0.237, " " 23$ O 16, 77$ N 16 = air. 

A result which experimentally verifies the above con- 
clusion so far as these two gases are concerned. 

The temperatures at which determinations were made 
were: Carbon, 980 C. ; sodium, — 34 to -|- 7° C. ; sili- 
con, 232 C. ; phosphorus, —yS° to -(- io° C. ; potassium, 
-78 to+ io° C. ; mercury, -78 to -40 C. For all 



SPECIFIC HEATS OF SOLIDS. 



153 



the other elements the determinations were made some- 
where between o° and ioo° C. The numbers in these 
cases may be regarded as approximately representing the 
mean specific heats for the temperature interval, 40 to 
6o° C. 

Table 17. — Specific Heats of the Solid Elements. 



Element. 



Carbon 

Sodium 

Magnesium 

Aluminum • 

Silicon 

Phosphorus 

Sulphur 

Potassium 

Calcium 

Manganese . . 

Iron 

Nickel 

Copper 

Zinc 

Silver 

Tin 

Antimony 

Platinum 

Gold 

Mercury (solid) . 

Lead 

Bismuth 



Specific heat, 



.463 

.293 

.25 

.214 

.203 

.174 

.178 

.166 

.170 

.122 

.114 

.108 

•095 

•095 

.057 

.0562 

.0508 

.0324 

.0324 

.0319 

.0307 

.0308 



Atomic 
weight. 



11.97 

2 3 

24 

27.02 

28 

30.96 

31.98 

39.04 

39-9 

55 

55-9 

58.6 

63-4 

64.9 

107.66 

117. 8 

120 

195 

197 

199.8 

206.4 

208 



Specific heat 
X atomic 
weight. 



5-5 

6.7 

6 

5-8 

5-7 

5.4 

5-7 

6.5 

6.8 

6.7 
6.4 
6.3 
6.1 
6.2 
6.1 
6.6 
6.0 
6.3 
6.4 
6.4 
6.3 
6.3 



Observer. 



Weber. 
Regnault. 



Weber. 
Regnault. 



Bunsen. 
Regnault. 



Q. What is the specific heat of water? 

Water exists in three states — solid, liquid, gaseous or 
steam. The specific heats of each are as follows : Ice, 
0.504; water, 1.000; gaseous steam, 0.622. 

Q. What is meant by conduction of heat? 

This property of heat, although by many supposed to 
be due to radiation, owing to the particles of matter not 



154 COMBUSTION OF COAL. 

being in absolute contact, is, however, generally acknowl- 
edged to be due to a distinct action, that of conduction. 
Dense and heavy substances are generally good conduc- 
tors; light and porous bodies have this property only 
imperfectly. 

Table 18. — Thermal Conductivity of Metals. 

Silver ioo. o 

Copper 73.6 

Gold 53.2 

Brass 23. 6 

Tin 14. 5 

Iron 11. 9 

Lead 8.5 

Platinum 6.4 

German Silver 6.3 

Bismuth 1.8 

Liquids in general are bad conductors of heat ; but liquids 
do conduct heat in some measure, subject to the same laws 
as solids, although as regards water and other such mobile 
liquids, very feebly. 

Q. Do all bodies conduct heat alike? 

They do not. Good conductors are those bodies in 
which any inequality of temperature is quickly equalized, 
the excess of heat being transmitted with great prompti- 
tude and facility from particle to particle. The metals in 
general are good conductors, but different metals have dif- 
ferent degrees of conductivity. 

Imperfect conductors are those bodies in which the heat 
passes more slowly and imperfectly through the dimensions 
of a body, and in which, therefore, the equilibrium of tem- 
perature is more slowly established. 

Non-conductors are bodies in which the excess of heat 
fails to be transmitted from particle to particle before it 



CONVECTION OF HEAT. I 55 

has been dissipated in other ways. Earths and woods are 
bad conductors, and soft or spongy substances still worse. 

Q. What is meant by convection of heat? 

Convection means to carry or to convey. As applied to 
the transfer of heat to liquids and gases it means the car- 
rying or conveying of heat from one particle to another by 
an actual movement of each heated particle among those 
of lower temperature, and as each colder particle with 
which the heated particle comes in contact takes up a por- 
tion of the heat, the movement of all the particles will 
continue until all are of equal temperature. 

Q. What is the practical or useful effect of the convec- 
tion of heat in furnace gases? 

The application of currents of heated air is of great 
practical importance; for example, the heat derived from 
the combustion of coal on the grate expands the air and 
gases in the furnace and causes their ascent up the chim- 
ney, while an influx of air to the fire, through the ash pit, 
takes its place. The force of the current or draft thus 
formed will be in proportion to the greater expansion of a 
column of air of the height of the chimney than that of an 
equal column externally. Common air like other gases 
increases nearly ^L of its bulk for each degree Fahrenheit. 
Hence by ascertaining the internal temperature and height 
of the chimney the force of the draft may be calculated. 

Q. How do gases conduct heat? 

Gases resemble liquids in their mode of conducting heat 
— that is to say, their power of actual conduction is inap- 
preciable ; but by their property of convection currents are 
instituted by which the heat is disseminated throughout the 



156 COMBUSTION OF COAL. 

mass. To observe this, hold the hand by the side of a 
lighted candle and then at the same distance above it. 
Little heat is received by the hand in its first position, 
while in the second the increase of temperature is immedi- 
ately obvious, the greater portion of the heat being carried 
off by the ascending current, which in gases is more active 
than in liquids, owing to their power of expansion being 
so much greater. 

Q. What is radiation of heat? 

When heat emanates, or is thrown off by a body, as from 
a bar of hot iron, heat is said to be radiated from it, and 
is denominated radiant heat. The rate of cooling expresses 
the radiating power ; and the radiating power of bodies is 
more influenced by the state of their surface than by the 
nature of the material. Bright or polished surfaces radi- 
ate heat much more slowly than rough or black ones. 

Q. What is meant by the term latent heat? 

Latent heat is the quantity of heat which must be com- 
municated to a body in a given state in order to convert 
it into another state without changing its temperature ; or, 
to put it in another form, it is that quantity of heat which 
disappears, or becomes concealed in a body, while produc- 
ing some change in it other than a rise in temperature. 
By exactly reversing the change, the quantity of heat 
which had disappeared is reproduced. Latent heat is 
commonly divided into latent heat of fusion and latent 
heat of evaporation. 

Q. What is latent heat of fusion? 

The act of liquefaction, such as the melting 'of ice, con- 
sists of interior work — that is, of work expended in mov- 
ing the atoms into new positions. If a piece of ice, re- 



joule's equivalent. 



157 



duced in temperature to, say, o° F., is subjected to the 
influence of heat, its temperature will rise progressively 
for each increment of heat received, until the temperature 
of the ice reaches 32 F. , when the melting of the ice will 
begin. It will also be observed that, continuing the ap- 
plication of the heat to the ice, as before, there is no cor- 
responding rise in temperature either in the ice or in the 
water in contact with the ice so long as any of the latter 
remains unmelted; and that during the process of melting 
the temperature of the water is constant, and at 32 F. 

This change of state from solid to liquid, in the melting 
of one pound of ice, requires 143 units of heat, the tem- 
perature being constant at 32 F. The heat does not 
raise the temperature of the ice, but disappears in causing 
its condition to change from the solid to the liquid state. 
This is called the latent heat of fusion. 

Q. What is Joule's equivalent? 

The exact mechanical equivalent of heat was first demon- 
strated experimentally by Dr. Joule, of Manchester, Eng- 




FlG. 13. 



land, the apparatus employed by him being represented in 
Fig. 13. A known weight was connected by means of 



158 COMBUSTION OF COAL. 

cords to a shaft /, mounted on friction wheels not shown 
in the illustration. On this shaft a pulley was secured, 
which through the medium of another cord imparted motion 
to the shaft r, and caused it to revolve. At the lower end 
of this shaft r were fitted eight sets of paddles, which, when 
connected by means of a pin P, revolved with it. To the 
interior of the copper vessel B were attached four station- 
ary vanes, cut out in such manner as to permit the free 
revolution of the revolving paddles. Precautions were 
taken to prevent a transfer of heat from the vessel B, 
which need not be described here. This vessel was filled 
with a known weight of water, at the temperature of its 
greatest density, 39 F. , and a thermometer / was inserted 
in the vessel B, to mark the rise in the temperature of the 
water. The experiment consisted in allowing the weight 
to descend by its own gravity, and, through the medium of 
the cords, to cause the paddles to revolve and agitate the 
water in the vessel B. 

After many hundreds of experiments extending through 
several years, Dr. Joule finally fixed upon 772 pounds, 
raised one foot high against the action of gravity, as 
the mechanical equivalent of the quantity of heat neces- 
sary to raise the temperature of one pound of water 
through 1 ° F. , at the maximum density of water, 39 to 
40 F. 

Q. Is the relation between heat and mechanical energy 
a fixed or definite one ? 

Heat and mechanical energy are mutually convertible ; 
and heat requires for its production, and produces by its 
disappearance, mechanical energy in the proportion of 772 
foot-pounds for each British unit of heat, the said unit 
being the amount of heat required to raise the tempera- 






SPECIFIC HEAT. I 59 

ture of one pound of water by i° F., near the temperature 
of its greatest density, 39 to 40 F. 

Q. What is specific heat? 

The specific heat of a substance means the quantity of 
heat which must be transferred to a unit of weight (such 
as a pound) of a given substance, in order to raise its tem- 
perature, by one degree, as compared with that quantity 
of heat necessary to raise an equal weight of water through 
one degree at its greatest density, i.e., from 39 to 40 F. 
The specific heat of water is greater than that of any other 
known substance ; it thus becomes the standard for com- 
parison. 

For ordinary calculations we may assume : Woods aver- 
age one-half the specific heat of water ; coal and coke, two- 
tenths the specific heat of water ; wood charcoal, one-fourth 
the specific heat of water. 

The specific heat of gases varies as between specific 
heat under constant volume, and specific heat under con- 
stant pressure. Suppose one pound of gas to be heated — 
air, for example; a rise in temperature occurs, and if the 
air is free to expand additional heat will be required to 
perform the work thus done by expansion ; but if the air 
is confined so that no expansion can occur, less heat will 
be required to raise its temperature through one degree. 
The specific heat of air for equal weights (water = 1) at 
constant pressure is 0.2377, at constant volume it is 
0.1688, the difference in quantity of heat is 0.2377 -7- 
0.1688 = 1. 408 1 times. 



CHAPTER VII. 

FUEL ANALYSIS. 

Q. What is meant by the elementary analysis of coal ? 

The separation of coal into its constituent elements 
may be simply to know what elements compose it ; such a 
process is called qualitative analysis. When the quantity 
of each element is to be determined, it is then known as 
quantitative analysis. 

The elementary analysis of coal shows it to be princi- 
pally composed of the following simple substances : car- 
bon, hydrogen, nitrogen, oxygen, sulphur, ash. Ash is 
not a simple substance, but represents the incombustible 
matter of whatever composition remaining in the furnace 
after combustion. 

The elementary analysis of coal is not now the general 
practice ; for all ordinary purposes the shorter method of 
determining the moisture, volatile combustible matter, the 
fixed carbon and ash by proximate analysis is employed in 
furnace work. 

Q. What is carbon? 

Carbon is one of the most widely diffused and abundant 
of the elements. It occurs in nature in a free state and 
in combination with other elements, notably in the form 
of carbonates and as an essential constituent of organic 
bodies. 

Carbon in its free state is a solid, infusible, non-volatile 



CARBON. 



I6l 



substance, without taste or smell, exhibiting great diver- 
sity in the physical characteristics of its three allotropic 
forms — diamond, graphite, and charcoal. It is the princi- 
pal constituent of anthracite coal. It constitutes about 
one-half of bituminous coal. It may be separated from 
wood in the form of charcoal by distilling off the more 
volatile elements. 

Carbon unites directly with oxygen, sulphur, nitrogen, 
and a few of the metals, the latter at high temperatures 
only. The two direct inorganic compounds of carbon and 
oxygen are known as carbonic oxide, CO, and carbonic acid, 
C0 2 . The proportions are shown in the following table : 



Table 19. 



■Elementary Composition of Carbonic Oxide and 
Carbonic Acid Gases. 





Composition. 




By weight. 


Percentage. 




Carbon. 


Oxygen. 


Total. 


Carbon. 


Oxygen. 


Total. 


Carbonic oxide CO. 
Carbonic acid C0 2 . 


12 
12 


16 
32 


28 
44 


42.86 
27.27 


57.14 
72.73 


IOO 
IOO 



These are the two principal gases formed in the furnace 
by the combustion of the carbonaceous portions of the 
fuel. 

Carbon and hydrogen unite in the production of an ex- 
tended series of hydrocarbons, the simpler ones being the 
marsh gas series, the olefiant gas series, and the benzole 
series. When carbon and hydrogen are further combined 
with the addition of nitrogen the hydrocarbon series is 
greatly extended, including aniline, pyridine, etc., all of 
which may be obtained by the distillation of coal. 

Almost all the elementary substances of which the spe- 
11 



1 62 



COMBUSTION OF COAL, 



cific heat and atomic weight are known, give, when these 
two properties are multiplied into each other, a product 
averaging not far from 6.34. Carbon is one of the excep- 
tions, as shown in the accompanying table. 

Weber, about 1872, made a careful series of determina- 
tions of the specific heat of carbon, the results of which 
are as follows : 



Table 20. — Specific Heat of Carbon. 



Carbon (diamond) 



Carbon (graphite) 



Porous wood carbon. 



Temperature. 



- 5o u C. 
+ 10 

85 
250 
606 
985 

- 5o 
+ 10 

61 

201 

250 

641 

978 
o°— 23° C 
o°— 99 
o° — 223 



Specific heat. 



.0635 
.1128 
.1765 
.3026 

.4408 

.4589 
.1138 
.1604 
.1990 
.2966 
.325 

• 4554 

• 457 
.1653 
.1935 
.2385 



Specific heat 
X atomic weight. 



O.76 

1-35 
2.12 

3.63 
5.29 
5.51 
1.37 
1.93 
2.39 
3.56 
3.88 
5-35 
5.50 
1.95 
2.07 
2.84 



These numbers show that the specific heat of carbon in- 
creases as the temperature increases, and that the value of 
this increase for a given temperature is considerably less 
at high than at low temperatures. 

Q. What is meant by the allotropic states of carbon? 

The term allotropic merely expresses the several condi- 
tions in which carbon exists, each condition having widely 
different physical properties, while the chemical properties 
remain the same. Carbon occurs as diamond, graphite, 
and charcoal. These three solids are wholly unlike in 



DIAMOND. 163 

physical properties, yet chemically they are the same — 
that is, they yield upon analysis nothing but pure carbon. 
Investigations by Petersen, undertaken with a view to 
determine, if possible, the relation between changes of 
volume and of energy in passing from one allotropic modi- 
fication of an element to another, led him to the conclusion 
that true allotropic varieties differ in the variety of energy 
they contain, in specific gravity, in specific heat, and in 
solubility. Color and crystalline form he considers of 
secondary importance. His results are : 

Carbon. ^aSff (°C0 2 ). Atomic volume " 

Amorphous 965.310969.8 6. 7 to 8.0 

Graphite 933-6 5-3 

Diamond 932.410945.5 3.4 

Q. What are the physical properties of the diamond? 

The diamond is a natural form of carbon, crystallizing 
in the cubic system. It was shown to be combustible in 
1694, and Lavoisier proved that the sole product of its 
combustion was carbonic-acid gas, C0 2 . The diamond is 
noted for its great hardness. Its specific gravity ranges 
from 3.51 to 3. 55, averaging about 3.51. The purest 
stones are practically colorless. The index of refraction 
is higher in the diamond than in any other known trans- 
parent substance. 

On exposure to the heat of the electric arc the diamond 
swells up, cracks on the surface, and becomes coated with 
a substance resembling graphite. The study of the action 
of heat upon the diamond, with and without the presence 
of air, gave the earliest clew to its chemical composition. 
On the combustion of the diamond there remains a quan- 
tity of a colorless or reddish ash, varying from ^^ to 2 * 
of the original weight of the mineral. Microscopic ex- 



164 COMBUSTION OF COAL. 

amination of this delicate spongy ash has led investiga- 
tors to the belief that it shows traces of cellular tissue, 
suggestive of a vegetable origin. In its ordinary state the 
diamond does not conduct electricity, but the cokelike 
mass obtained by exposure to the arc is a good conductor. 

Q. What are the physical properties of graphite ? 

Graphite is an impure variety of native carbon, known 
also as plumbago, and popularly known as black lead. It 
occurs usually in compact and crystalline masses, but oc- 
casionally in six-sided tabular crystals which cleave into 
flexible laminae parallel to the basal plane. Its color is 
iron black or steel gray, with metallic lustre. Its specific 
gravity is 1.9 to 2.6. 

Graphite is largely used in the manufacture of crucibles 
and other objects required to withstand high temperatures. 
It is also used in the manufacture of lead pencils, as a 
lubricating agent, as a stove polish, as a paint, etc. 

Graphite is a good conductor of electricity, and is much 
used in electrotyping, the moulds upon which the metal is 
to be deposited receiving a conducting surface by being 
coated with finely divided graphite. 

Q. What are the physical properties of charcoal? 

Charcoal is the carbonaceous residue from wood or other 
vegetable matter, partially burnt under circumstances which 
exclude the air, and from which all watery and other vola- 
tile matter has been expelled by heat. 

The composition of charcoal depends on the temperature 
at which it is produced. At high temperatures all the 
oxygen and hydrogen are expelled and the black charcoal 
consists of carbon and the mineral matter (ash) originally 
present. When produced at lower temperatures the char- 



CHARCOAL. 



I6 5 



ring is imperfect, and a reddish charcoal results, which 
contains both hydrogen and oxygen. 

Good charcoal is black, gives a sonorous ring when 
struck, and breaks with more or less conchoidal fracture 
and a ligneous texture. It is easily pulverizable, but does 
not crumble under moderate pressure. It burns without 
smoke and in separate pieces without flame. The specific 
gravity of wood charcoal, exclusive of pores, is 1.5 to 2; 
inclusive of pores, from 0.20 to 0.35 in soft charcoal, and 
from 0.35 to 0.50 in hard charcoal. 

Q. How is charcoal affected by the temperature at which 
it is made ? 

The composition of charcoal produced at various tem- 
peratures, as determined by Violette — the wood experi- 
mented on being that of black alder or alder buckthorn, 
which furnishes a charcoal suitable for gunpowder — is 
given in the annexed table : 

Table 21. — Composition of Charcoal. (Violette.) 



Temperature 
of carbonization. 



3 02°F 

392 

482 

572 

662 

810 

1873 
2012 
2282 
2372 
2732 



Composition of the Solid Product. 






Oxygen, 




Carbon. 


Hydrogen. 


nitrogen 


Ash. 


Per cent. 


Per cent. 


and loss. 
Per cent. 


Per cent. 


47.51 


6.12 


46.29 


O.08 


51.82 


3-99 


43.98 


O.23 


65.59 


4.81 


28.97 


O.63 


73-24 


4.25 


21.96 


0.57 


76.64 


4.14 


18.44 


O.61 


8T.64 


4.96 


15.24 


1. 61 


81.97 


2.30 


14.15 


I.60 


83.29 


I.70 


13-79 


1.22 


88.14 


I.42 


9.26 


I.20 


90.81 


1.58 


6.49 


I- 15 


94-57 


O.74 


3-84 


0.66 



Carbon 

for a given 

weight 

of wood. 

Per cent. 



47.51 

39-88 
32.98 
24.61 
22.42 
15.40 
15.30 
15.32 
15.80 
15.85 
16.36 



The products obtained at the first two temperatures, viz., 
302 , 392 F. , cannot be properly termed charcoal. 



l66 COMBUSTION OF COAL. 

Q. How is the combustibility of charcoal affected by the 
temperature at which it is made ? 

Regarding the combustibility of charcoal, that made at 
500 F. burns most easily; and that made between 1832 
and 2732 F. cannot be ignited like ordinary charcoal ; 
that made at a constant temperature of 572 F. takes fire 
in the air when heated to between 68o° and 71 5 F., ac- 
cording to the nature of the wood from which it has been 
derived. Charcoal from light woods, other things being 
equal, ignites most easily. Charcoal produces a greater 
heat than an equal weight of wood. 

Charcoal, not being decomposable by water or air, will 
endure for any length of time without alteration. 

Q. What elementary substances and compounds enter 
into the composition of charcoal ? 

The following analysis of charcoal shows the percent- 
ages of elements and compounds entering into its com- 
position, instead of reducing to elements alone : 

Carbon, C 85.10 per cent. 

Carbonic acid gas, C0 2 3. 26 

Carbonic oxide, CO 1.36 

Marsh gas, CH 4 o. 70 

Hydrogen, H 0.07 

Nitrogen, N o. 5 1 

Water, H 2 7.00 

Ash 2. 00 



100.00 



Qo What is the object of converting wood into charcoal ? 

The carbonization of wood is intended to remove those 
constituents which absorb heat, and to concentrate the 
carbon, which possesses great heating power. The sub- 
stances absorbing heat are the hygroscopic water and oxy- 
gen contained in the wood, which, on combustion, cause 



HEATING POWER OF CARBON. 167 

the formation of so much water that the temperature is 
decreased to a considerable degree. Slow charring and 
low heat will produce the largest amount of charcoal, but 
it will be weak. A brisk heat, well conducted, will fur- 
nish less, but will make a strong coal. This determines 
which mode of charring is most profitable to maker and 
user. With a well-conducted operation in a pit contain- 
ing at least 50 cords of wood the yield for air-dried wood 
ought to be in the proportion here shown : 



Kind of wood. Yield by weight. Yield by measure. 

Oak 23 per cent. 74 per cent. 

Beech 22 " 73 

Pine 25 " 63 " 

A cord of 128 cubic feet of oak ought to furnish 64 bushels 
of 2,600 cubic inches each ; pine wood must yield 54 bush- 
els. This measure is actually reached by good burners, 
though not by the average workman. 

Q. Is the heating power of carbon affected by its den- 
sity ? 

Gruner has shown that the less the density of any form 
of carbon, the greater is its heating power. The tests he 
records also show that the coals containing hydrogen give 
a greater heating power than that calculated by theory 
from their elementary composition. It would naturally 
be inferred, therefore, that the coals which have the least 
density, and which contain the largest percentage of dis- 
posable hydrogen, would have the greatest heating power. 
Yet the reverse of this appears to be true, so that after 
the disposable hydrogen reaches four per cent its further 
increase seems to be actually accompanied by a decrease 
of heating power, as determined by a calorimeter, and by 
a still greater decrease, as shown in the diminution of 



168 COMBUSTION OF COAL. 

efficiency, from 65 to 55 per cent in the industrial or 
steaming power. It is difficult to explain the anomaly, 
except upon the hypothesis that the calorimetric determi- 
nations of the more volatile coals were inaccurate (Kent). 

Q. What is sulphur? 

Sulphur is often found in coal in combination with iron, 
and is known as iron pyrites. Sulphur is highly inflam- 
mable, and when heated in the air to a temperature of 
about 482 F. it takes fire and burns with a clear blue, 
feebly luminous flame, being converted into sulphurous 
oxide, S0 2 . In its chemical relations sulphur is the rep- 
resentative of oxygen, to which it is equivalent, atom to 
atom. Oxygen gas and sulphur vapor alike support the 
combustion of hydrogen, charcoal, phosphorus, and the 
metals to form precisely analogous compounds. The 
atomic weight of sulphur is 32; symbol S; specific heat, 
0.1776; specific gravity, 2.00. 

Q. What is hydrogen ? 

Hydrogen is found free in nature among the gases 
evolved from certain volcanoes; also in the gases given 
off from the oil wells of Pennsylvania. It is one of the 
many gases of which coal gas is a mixture. It exists in 
air in small quantities, in combination with nitrogen as 
ammonia. 

Hydrogen when pure is a colorless, invisible gas, with- 
out smell or taste. It is the lightest body known, and 
has a specific gravity of 0.0693 (air = 1.0000). It is but 
slightly soluble in water. The specific heat of hydrogen 
for equal weights at constant pressure = 3.4046; for con- 
stant volume == 2.4096. 

Hydrogen burns in the air with an almost colorless 



HYDROGEN. I 69 

flame, but under certain conditions, even when pure, the 
centre of the flame is colored green while the external 
portions are of a violet blue color. On reducing the press- 
ure the blue color is transferred to green, and from that 
successively to yellow, orange, and red. The refrangibil- 
ity of the emitted light becomes less when the intensity 
of combustion is reduced by a diminution in the supply of 
oxygen or by a reduction of pressure. A lighted taper is 
extinguished on being placed in a jar of hydrogen, and the 
gas burns at the mouth of the jar, rapidly if the jar be 
mouth upward, slowly if mouth downward. 

When mix«ed with air or oxygen, hydrogen burns with 
explosive rapidity. The loudest explosion is obtained by 
mixing two volumes of hydrogen and one volume of oxy- 
gen. The maximum explosive effect with air is obtained 
by mixing one volume of hydrogen with two and a half 
volumes of air, but the explosion in this case is not so 
powerful on account of the nitrogen present. In each of 
these cases the two gases are present in the proportion in 
which they unite to form water. This mixture of hydro- 
gen and oxygen is not explosive at greatly reduced press- 
ure. A rarefaction produced by diminution of pressure is 
more effective in weakening the force of an explosion than 
diluting the mixture with an indifferent gas. 

Favre and Silbermann ascertained the heat of one pound 
of hydrogen burned in oxygen to be sufficient to raise the 
temperature of 62,032 pounds of water i°F. This is not 
equalled by any other known substance. 

The liquefaction and solidifying of hydrogen was ac- 
complished by Pictet in 1878. The melting point of 
hydrogen ice as given by Dewar is 16 or 17 absolute 
(—257° or — 256 C). Solid hydrogen seems to possess 
the properties of the non-metallic elements rather than 



170 COMBUSTION OF COAL. 

that of the metals, among which it has been usual to class 
hydrogen. 

Q. What is carbureted hydrogen? 

Carbureted hydrogen is obtained by the distillation of 
the volatile portions of bituminous coal. It has long been 
employed as an illuminating agent. Coal gas will vary 
according to the coal from which it is distilled, but the 
following fairly represents the average composition of car- 
bureted hydrogen : 

Hydrogen 41. 85 

Marsh gas . . . . , » . . . . 39. 1 1 

Carbonic oxide 5. 86 

Olefines 7. 95 

Nitrogen 5.01 

Carbonic acid 22 

100.00 

Q. What is marsh gas? 

Marsh gas is emitted from the surface of the ground in 
many parts of the world, notably in Italy, North America, 
and in the vicinity of the Caspian Sea. It is formed by 
the putrefaction of vegetable matter under water, and 
hence occurs in marshy places. It also occurs in the coal 
measures, where it is known as fire damp, being produced 
by the destructive distillation of carbonaceous matter, oc- 
curring to the extent of about forty per cent by volume in 
coal gas. 

Marsh gas (methyl hydride) is colorless and odorless, 
and forms an explosive mixture with air. Its specific 
gravity is 0.5596 (air = 1.0000). 

The marsh gas series consists of : 

Formula. Specific gravity. 

Methyl hydride CH 4 o. 5596 

Ethyl '• C 2 H 6 1.037 

Propyl " C 3 H 8 1.522 



OLEFIANT GAS. \Jl 

Formula. Specific gravity. 

Butyl hydride C 4 H 10 2.005 

Amyl " C 5 H 12 2.489 

Hexyl " C 6 H 14 0.669 

Octyl " C H H 1H 0.726 

Decyl " C10H22 

Q. What is olefiant gas? 

This gas occurs through the dry distillation of many 
organic bodies ; hence occurs to the extent of four to five 
per cent in coal gas. 

It is a colorless gas, and liquefies at a pressure of 42^ 
atmospheres at — 1.1 C. It forms an explosive mixture 
with oxygen. 

The olefiant gas series consists of : 

Formula. Specific gravity. 

Methylene CH 2 o. 484 

Ethylene (olefiant gas) C 2 H 4 0.978 

Prophylene (tritylene) C3H6 1-452 

Butylene . . . C 4 H 8 J -936 

Amylene C5H10 2.419 

Caproylene (hexylene) C 6 Hi 2 2.970 

CEnanthylene C 7 Hi 4 3.320 

As a product of the dry distillation of coal it is largely 
used because it is an abundant illuminating constituent in 
coal gas, its technical name being ethylene, C 2 H 4 . Pure 
ethylene burnt at the rate of 5 cubic feet per hour emits 
a light equal to 68.5 standard candles. The illuminating 
power of a given quantity of ethylene is increased by 
moderate admixture with hydrogen, carbonic oxide, or 
marsh gas, although the actual amount of light given per 
cubic foot of the mixture is less than that given by pure 
ethylene. The intrinsic illuminating power is reduced by 
admixture with nitrogen, carbonic acid gas, water vapor, 
but increased by oxygen. 



172 COMBUSTION OF COAL.' 

Q. What quantity of moisture or water is present in 
coal ? 

All coals contain a certain amount of water in their 
composition. This water can be evaporated by the appli- 
cation of heat, but coals thus deprived of moisture will 
regain by absorption from the atmosphere the precise 
quantity which had been previously expelled. 

The quantity of moisture in coal varies with the density 
and structure, so that no averages can be given ; for ex- 
ample : 

Lignites vary from 5 to 30 per cent. 

Bituminous coals from 1 to 12 " 

Semi-bituminous coals from 1 to 5 " 

Anthracite coals from 1 to 2 " 

Q. What is meant by hygroscopic moisture? 

The hygroscopic moisture in fuel is that quantity which 
is always held by the fuel when exposed to the atmosphere. 
All fuels contain a certain amount of moisture in their 
composition, which may be expressed as " water of condi- 
tion. " This moisture may be temporarily expelled by 
heat, only to be reabsorbed from the atmosphere in the 
exact amount thus driven off. The quantity of hygro- 
scopic moisture thus held by any fuel is dependent upon 
its structure and density ; the greater the density the less 
the contained moisture. 

Q. What is the method employed for obtaining the 
proximate analysis of coal? 

In order to estimate the value of a fuel, it is necessary 
to determine the moisture, volatile matter, fixed carbon, 
and sulphur. Professor Thorpe states that in the metal- 
lurgical laboratory of the Normal School of Science and 



PROXIMATE ANALYSIS. 173 

Royal School of Mines these assays are performed in the 
following manner : 

i. Hygroscopic moisture. In a water bath heat for an 
hour 20 grains of powdered sample placed in a watch 
glass. Weigh repeatedly until the result is constant. 

2. Coke. Heat 1,000 grains of finely powdered sample 
in large covered earthen crucible in furnace until no 
flame is evolved. Weigh when cold, or, better, heat 50 
grains in platinum crucible with lid on, the loss of weight 
giving volatile matter. 

3. Ash. Heat 20 grains of finely powdered sample in 
platinum capsule until no trace of carbon is left. 

4. Sulphur. Deflagrate in platinum crucible 20 grains 
of powdered sample with 500 grains of a mixture of salt 
and nitre (2:1), dissolve in water, dilute to one-half pint, 
add HC1 in slight excess, heat for twenty minutes, filter, 
and to filtrate add BaCl 2 . Allow to stand for twelve 
hours, filter, weigh precipitate. 

Q. Why does not the percentage of sulphur in coal ap- 
pear in statements accompanying proximate analyses ? 

Because the proximate analysis determines, first, the 
volatile and non-volatile quantities; and, second, the com- 
bustible and non-combustible quantities of the coal. 

No sulphur is driven off in the heating of the coal to 
expel its moisture. 

When heating the coal to distil off its volatile combus- 
tible matter some of the sulphur passes off with the hydro- 
carbon gases. The sulphur is burnt to sulphurous acid, 
then a certain portion of this is oxidized to sulphuric 
acid. The amount so oxidized will depend upon circum- 
stances. If the sulphurous acid is kept hot in the presence 
of moisture, then oxidation goes on more rapidly; but if 



174 COMBUSTION OF COAL. 

it be cooled down almost immediately after it is formed, 
the action is very slow. 

Whatever sulphur is not thus driven off remains in the 
fixed carbon and burns during the ordinary progress of the 
fire, a portion uniting with the earthy matters in the ash, 
becoming more or less inert. 

Q. What is natural gas? 

Natural gas is found locally in Western Pennsylvania, 
Northern Ohio, and Central Indiana in paying quantities ; 
in lesser quantities it is found in many other localities. 
The composition of natural gas at Findlay, Ohio, is : 

By weight. By volume. 

Hydrogen 0.27 2.18 

Marsh gas 90. 38 92. 60 

Carbonic oxide o. 86 o. 50 

Olefiant gas 0.53 0.31 

Carbonic acid o. 70 o. 26 

Nitrogen 6.18 3.61 

Oxygen o. 66 o. 34 

Sulphydric acid o. 42 o. 20 

100.00 100.00 

The heat units in one pound of this gas = 21,520; the 
evaporative power of one pound of this gas from and at 
212 F. = 22.27 pounds of water. 

Tests of natural gas for steam-making conducted at 
Pittsburg, Pa., show that one pound of good bituminous 
coal equals from 7^ to 12^ cubic feet of natural gas. 
Other experiments show that 1,000 cubic feet of natural 
gas equal from 80 to 133 pounds of bituminous coal, a 
variation of more than 60 per cent between the two ex- 
tremes. Quality of coal and manipulation of furnace ac- 
counts for much of this difference. 

The chemical composition of natural gas, as shown by 
an average of four samples from Indiana and three from 



NATURAL GAS. 175 

Ohio, by Prof. C. C. Howard, for the eleventh annual re- 
port of the U. S. Geological Survey, is as follows : 

Marsh gas, CH 4 93-36 

Nitrogen 3. 28 

Hydrogen 1.76 

Carbon monoxide 53 

Oxygen 29 

Olefiant gas 28 

Carbon dioxide 25 

Hydrogen sulphide 18 

Total 99-93 

The heat-producing value of natural gas, as compared 
with other fuel gases per 1,000 cubic feet at 40 F. and 
at atmospheric pressure, is given by Hosea Webster ap- 
proximately as follows : 

Natural gas 1,103,300 heat units. 

Coal gas 735,000 " 

Water gas 322,000 

Producer gas ( heated) 1 56,000 ' ' 

Assuming the generation of steam at 21 2° from water 
at 6o°, the comparative value of natural gas per 1,000 
cubic feet at atmospheric pressure is approximately as 
follows : 

1,000 cubic feet natural gas evaporate 900 pounds. 

1,000 " • coal " 600 " 

1,000 " water " " 250 " 

1,000 " producer" " 115 " 

Natural gas is an ideal fuel if used near the source of 
supply, as no labor is required in its use except to regu- 
late the supply in the furnace. It is not difficult to regu- 
late the supply of air to insure perfect combustion. There 
is no soot, ashes, or other debris. 

Q. What is producer gas? 

Producer gas is a general name which covers any method 
of generating gas from a fuel by a process resembling dis- 



iy6 COMBUSTION OF COAL. 

tillation, the gases generated being conducted to the place 
where the heat of combustion is to be utilized, then mixed 
with air, ignited and consumed. This system offers a 
remedy for the imperfections of the ordinary fire and of 
various fuels. There is no cinder, no ashes, so that the 
surface of the bodies receiving the heat is not altered. 
The heating is effected by radiation as well as by conduc- 
tion, and inferior classes of fuel may be used. 

A higher calorific power may be obtained by producer 
gas or gaseous fuel, generally on account of the smaller 
quantity of air required for combustion and the conse- 
quently lessened dilution of heat by inert nitrogen and 
carbonic acid. The gas from producers worked by inter- 
nal combustion contains 25 to 45. per cent of combustible 
ingredients, and has a calorific intensity of 2867 to 
3992 F. 

Water gas and ordinary illuminating gas contain 86 to 
97 per cent combustible matter. The waste gases from 
furnaces may be used instead of producer gas when very 
high temperatures are not required, and where variations 
in temperatures are permissible, as steam boilers, hot 
blast, etc. Blast furnace gases rarely contain 30 per cent 
carbonic oxide, usually from 25 to 29 (Thorpe). 

Q. What is the composition of water gas ? 

A sample of water gas from Lowe's gas producers, after 
passing through purifier at Novelties Exhibition, Philadel- 
phia, 1885, analyzed as follows: 

Carbonic oxide, CO 44-5 volume. 

Hydrogen, H 50-9 " 

Oxygen, O) { j .7 '] 

Nitrogen, N f alr ( 2. 8 

Undetermined 1. 1 ." 

100. o " 



GASEOUS FUELS. 177 

One cubic foot of water gas of the above composition will 
develop in burning 327 heat units, including the latent 
heat of evaporation of the superheated steam which es- 
capes in the chimney. 

Q. What is Siemen's gas? 

Siemen's gas is a fuel gas generated in a furnace con- 
structed upon principles developed by and named after its 
inventor. 

The average composition of Siemen's gas, made at the 
Midvale Steel Works, Philadelphia, Pa., is: 

Carbonic acid gas, C0 2 1.5 volume. 

Carbonic oxide, CO 23. 6 " 

Hydrogen, H 6. o " 

Marsh gas, CH 4 3.0 

Nitrogen, N 65.9 

100. o " 

Q. What are the calorific values of the ordinary gase- 
ous fuels ? 

The comparative heating effects of the ordinary gaseous 
fuels are given below, together with hydrogen : 

Table 22. — Heating Power of Gaseous Fuels. 



Heat units 

yielded by i 

cubic foot. 


183. 1 

153. 1 
51.8 

178.3 
57I.O 



Cubic feet 

needed to 

evaporate 

100 lbs. water 

at 212 Fahr. 



Hydrogen, H 

Water gas (from coke) 

Blast furnace gas 

Carbonic oxide, CO. . 
Marsh gas, CH 4 

12 



293 
351 

1,038 

313 
93. 



CHAPTER VIII. 

HEATING POWER OF FUEL. 

Q. How may the calorific value of fuel be determined ? 

It may be closely estimated by calculation if the mois- 
ture, volatile matter, and fixed carbon have been previously 
obtained by proximate analysis, or it may be determined 
directly by means of a calorimeter. The total amount of 
heat obtainable on combustion of various fuels has been 
determined by Rumford, Lavoisier, Andrews, Favre and 
Silbermann, and others. The general principle of their 
methods consisted in the use of an apparatus (calorimeter) 
in which the entire heat of combustion was absorbed by a 
known weight of water, the increase in the temperature of 
the latter being ascertained by the indication of thermom- 
eters suspended in it. 

Q. Knowing the calorific value of each of the con- 
stituents of any fuel, may not the total calorific power of 
fuel be determined by calculation ? 

The calorific power of a fuel may be calculated from the 
results of an organic analysis ; but in any such calculation 
the oxygen must be considered to be in combination with 
sufficient hydrogen to form water, H 2 0. It is thus only 
the excess of carbon and hydrogen (disposable hydrogen) 
after this deduction that is available for the generation of 
heat. Such calculations have been found only to approxi- 
mate to the truth, coals, excluding lignite, giving a 



MOISTURE IN COAL. 1 79 

higher calorific power with the calorimeter than that ob- 
tained by calculation. 

Q. What is the effect of moisture in coal ? 

Whatever moisture or water is contained in coal must 
of necessity be evaporated in the fire before any useful 
effect is obtained. Inasmuch as some of the poorer varie- 
ties of coal contain ten or even fifteen per cent of water, 
this evaporation is carried on at considerable loss in the 
furnace. 

Q. How may the loss by evaporation of moisture in 
coal be estimated ? 

Suppose a furnace requires 10,000 pounds of coal per 
day, the coal containing 1 2 per cent moisture, we have : 

10,000 X • I2 = 1,200 pounds of water to be evaporated. 
If the coal is 6o° F. it must be raised to 212 , and the 
contained water then converted into steam at 21 2°, after 
which it abstracts heat from the furnace until the steam 
and gases are of the same temperature, say 2,000° F. ; we 
have then : 

212 — 6o° = 152 difference in temp. 

Heat units per pound of water re- 
quired to effect the conversion 
of water at 21 2° into steam at 
212° = 966 

Total 1,118 heat units per pound of 

water, or, for 1,200 pounds of 

water = 1,118 X 1,200 = 1,341,600 

Heat units to be supplied 1,200 
pounds of steam at 21 2° to raise 

it tO 2,000°= 2,000° — 212° X 

1,200 = 2,145,600 

Total 3.487, 200 heat units, representing 

lost work in the furnace. 



180 COMBUSTION OF COAL. 

Q. How should the evaporation of the contained water 
in coal be credited with reference to the furnace ? 

Nothing should be credited the furnace but heat avail- 
able for useful work. The evaporation of water from 
coal in the furnace is not, in steam-making, useful work. 
It counts, therefore, against the coal, but not against the 
possible efficiency of the boiler, for the reason that if a 
drier and better quality of coal were burnt, higher evapo- 
rative results would naturally follow. Coals heavily 
charged with moisture are used only because drier coals 
are not usually available at a price which would reduce the 
cost of steam-making. 

Q. How is the calorific power of fuel expressed ? 

In expressing the calorific power of fuel, the amount of 
heat generated by the combustion of carbon to carbonic 
acid gas, C0 2 , is taken as the standard of comparison. 
Experimental results vary only in slight degree, so that it 
is generally agreed that 14,500 heat units are evolved by 
the complete combustion of one pound of carbon in oxygen 
to C0 2 . As the unit of heat varies with the thermometric 
scale and the unit of weight employed, it will be understood 
that the above refers to the British thermal unit, or that 
amount of heat required to raise one pound of water 
through i° F. (39 to 40 ). 

Q. What is the unit of horse power for steam boilers ? 

The standard unit of horse power is the equivalent of 
33,000 pounds raised one foot high in one minute. It is 
apparent that no such standard can be applied to steam 
boilers. The evaporation of 30 pounds of water from a 
temperature of ioo° F. into steam of 70 pounds pressure 
above the atmosphere was the standard adopted for steam 



EVAPORATIVE POWER OF COAL. l8l 

boilers by the Centennial Committee, on the belief that 
30 pounds of water evaporated per hour represented the 
average requirement of steam engines per indicated horse 
power (1876). This is nearly equivalent to 34^ pounds 
of water evaporated from and at 21 2° F., this latter re- 
quiring 33,305 heat units. 

Q. Is there any fixed relation between the quantity of 
fuel burnt in a boiler furnace and the unit of horse 
power ? 

The quantity of fuel required to evaporate the water in 
a boiler into steam has nothing whatever to do with the 
horse-power unit. But if we may assume as fair average 
practice an evaporation of 8 pounds of water per pound of 
fuel, and a consumption of 3.75 pounds of fuel per horse 
power, we reach the figure of 30 pounds of steam per 
horse power per hour. For a horizontal tubular boiler set 
in brick work, 1 5 square feet of heating surface per horse 
power is a common allowance, and will develop a horse 
power of steam under all ordinary conditions, the ratio of 
grate surface to heating surface being commonly 30 to 1. 

Q. What is meant by the evaporative power of coal ? 

By evaporative power of coal is meant the number of 
pounds of water, which, under certain conditions, are capa- 
ble of being evaporated per pound of coal. In making a 
complete evaporative test it is necessary to know the tem- 
perature of the feed water, the pressure and temperature 
of the steam, the number of pounds of coal burnt on the 
grate, and the number of pounds of water evaporated in a 
given time. The simple evaporation is determined by 
dividing the number of pounds of water evaporated in a 
given time, say ten hours, by the number of pounds of 
coal actually burnt during the same time ; but when the 



1 82 COMBUSTION OF COAL. 

temperatures of the feed water and of the steam are to be 
taken into account, it is then commonly referred to as 
evaporation from and at 21 2°. 

Q. What quantity of heat is absorbed by the internal work 
done in liberating the volatile combustible from coal ? 

The investigations of E. T. Cox, formerly State geolo- 
gist, Indiana, upon the coals of that State, showed that the 
average thermal value of the volatile combustible matter 
liberated from bituminous coal by heat during its combus- 
tion was 20, 1 1 5 heat units, and that to liberate one pound 
of these gases 3,600 heat units were expended in over- 
coming the internal resistances in the coal. This latter 
amount, 3,600 heat units, should therefore be deducted 
from the total heat evolved in any calculations based upon 
proximate analyses, to get accurate thermal values. 

The calorific value of coal calculated in accordance with 
the above paragraph would be as follows : 

A sample of Indiana bituminous coal yielded by proxi- 
mate analysis — 

Fixed carbon 49-51 per cent. 

Volatile combustible. 37. 64 " 

Moisture 4. 30 " 

Ash 8.55 " 

100.00 " 

The theoretical calorific value with Professor Cox's de- 
duction would be calculated thus — 

British 
thermal units. 

Volatile combustible .3764 X 20,115 = 7,571.29 

Less 3764 X 3,6oo = 1,355.04 

Net value of volatile combustible 6,216. 25 

Carbon 4951 X 14,544 = 7.200.73 

Total calorific value 13,416.98 



HEATING VALUE OF COAL. 



183 



Q. Knowing the quantity of fixed carbon in any coal, 
may the approximate heating value of such a coal be 
determined by calculation ? 

Having the ultimate analysis of a coal, Kent states that 
by the use of Dulong's law, it can be predicted what that 
coal will give in the calorimeter within three per cent. 
Having only the proximate analysis one can predict even 
from that very closely what the heating value of the coal 
is. Dulong's formula, as modified by Mahler, is — 



-i-r 

100 L 



8,140-)- 34, 500 H 



(O + N 



*] 



in which O is quantity of heat in Centigrade units, and 
H, O, and N the percentages of hydrogen, oxygen, and 
nitrogen. 

Mahler's results indicate a law of relation between the 
composition of the coal as determined by proximate analy- 
sis and the heating value. The percentage of fixed carbon 
in the dry coal, free from ash, may, in the case of all coals 
containing over 58 percent of fixed carbon, have the heat- 
ing power predicted with a limit of error of 3 per cent. 

Table 23. — Approximate Heating Value of Coals Based upon 
Mahler's Tests. 



Carbon, per 


Heating Value. 


Carbon, per 
cent, dry and 
free from ash. 


Heating Value. 


cent, dry and 
free from ash. 


Calories. 


British 
thermal units. 


Calories. 


British 
thermal units. 


07 


8,200 
8,400 
8,600 
8,700 
8,800 
8,700 
8,600 


14,760 
15,120 
15,480 
I5,66o 
15,840 
15,660 
15,840 


63 

60 


8,400 
8,IOO 
7,800 
7,400 
7,000 
6,800 


15,120 
14,580 
14,040 

13,320 


04 


QO 


57 


87 


54 


8O. 


51 . ... 


72 


50 


12,240 


68 







Q. What is Mahler's formula ? 

Mahler's formula for expressing the calorific power of 



1 84 COMBUSTION OF COAL. 

coal and hydrocarbon fuels is a modification of Dulong's; 

formula, and is thus given by William Kent : 

Mahler's formula — . 

_ 8,140 C -f- 34, 500 H— 3,000 (O -f- N) 
100 

The maximum difference between Dulong's formula and 

the actual result in any single case is a little over three 

per cent ; and between Mahler's formula and the actual, 

four per cent. 

Dulong's formula, Q = ^.[8,080 + 34>5oo (H - £)], 
has the advantage of being more strictly a theoretical for- 
mula, based merely upon the observed heating power of the 
two elements, carbon and hydrogen, and the assumption 
that the oxygen renders unavailable for heating power yfa 
of its weight of hydrogen, while Mahler's formula intro- 
duces a coefficient, 3,000, which is entirely empirical, and 
only on his own observations. 

The figures given in the above formula are French and 
not British thermal units. 

Q. What is Dulong's formula ? 

Dulong proposed the following formula as expressive of 
the calorific power of the elements carbon and hydrogen 
when burnt to carbonic acid gas, C0 2 , and steam, H 2 : 

Dulong's formula — P = 8,080 C -f- 34,462 (H — •§), 
when P = heating power ; C = weight of carbon ; O = 
weight of oxygen; H = free hydrogen, i.e.> total hydrogen 
less that already burnt to water by the oxygen which the 
based coal contains. 

The figures in the above formula are French and not 
British thermal units. 

It is now established by the labors of Favre, Silbermann, 
Regnault, Bertholet, and others, that the heat of combus- 



THOMPSON S CALORIMETER. 



85 



tion, like specific heat, varies with the density; for ex- 
ample : 

Calories. 



Carbon from charcoal develops 8, 080 

Carbon of gas retorts, more dense 8,047 

Natural graphite 7, 797 

Diamond 7, 770 



British 
thermal units. 

15,544 
14,484 

14,034 
13,986 



Q. What are the details of construction of the Thomp- 
son calorimeter? 

Referring to Fig. 14, the Thompson calorimeter consists 
of a glass cylinder A closed at the 
lower end only, to contain a given 
weight of water. B is a cylindrical 
copper vessel called the condenser, 
closed at one end with a copper cover, 
in which is fixed a metal tube C, com- 
municating with the interior of the ves- 
sel B, and fitted at its upper extremity 
with a stopcock. The other end of B 
is open, and it is perforated near the 
open end by a series of holes, b, b. D is 
a metal base upon which B is fixed by 
means of three springs, which are at- 
tached to D, and press against the in- 
ternal surface of B, but which are omit- 
ted from the engraving. A series of 
holes is arranged round the circumfer- 
ence of D to facilitate raising the 
apparatus through the water. E is a 
copper cylinder, called the furnace, 
closed at the lower end only, which 
fits into a metal ring or seat on the 
centre of D. 



J 



1 86 COMBUSTION OF COAL. 

Q. In what manner are the results obtained in the 
Thompson calorimeter ? 

A known weight of fuel is burnt by means of chlorate 
of potash and nitre at the bottom of a vessel containing a 
known weight of water. The heat produced by the com- 
bustion of the fuel is communicated to the water, and 
from the rise in temperature of the latter is calculated the 
number of parts of water which the combustion of one 
part of the fuel will raise one degree in temperature. 
This number being divided by the latent heat of steam, 
967 heat units, gives the evaporative power of the fuel, 
which one pound of the fuel is theoretically capable of 
evaporating. 

In the instrument described, it is intended that 30 
grains of the fuel should be burnt, and that 29,010 grains, 
or 967 times this weight, of water should be employed. 
Hence the rise in the temperature of the water expressed 
in degrees Fahrenheit is equal to the number of pounds of 
water which one pound of the fuel theoretically will evap- 
orate ; but ten per cent is directed to be added to this num- 
ber as a correction for the quantity of heat absorbed by the 
apparatus itself, and consequently not expended in raising 
the temperature of the water. 

Q. In what manner are experiments conducted with the 
Thompson calorimeter ? 

Thirty grains of finely powdered fuel is intimately mixed 
with from ten to twelve times its weight of a perfectly dry 
mixture of : Chlorate of potash, 3 parts ; nitre, 1 part. 
The resulting mixture, which, for the sake of distinction, 
may be called the fuel mixture, is introduced into the fur- 
nace E, and carefully pressed or shaken down. The end 
of a slow fuse, about half an inch long, is next inserted in 



BARRUS' CALORIMETER. 1 87 

a small hole made in the top of the fuel mixture, and is 
fixed there by pressing the latter around it. The furnace 
is then placed in its seat on the metal base D, and the 
fuse lighted, and the condenser B with its stopcock shut 
fixed over the furnace. 

The cylinder A is previously charged with 29,010 grains 
of water, the temperature of which must be recorded, and 
the apparatus is now quickly submerged in it. The fuse 
ignites the fuel mixture, and when the combustion is fin- 
ished (indicated by the cessation of the bubbles of gas, 
produced by the combustion, which rise through the water), 
the stopcock is opened, and the water enters the condenser 
by the holes b, b. By moving the condenser up and down, 
the water is thoroughly mixed and acquires a uniform tem- 
perature, which is then recorded. By adding ten per cent 
to the number of degrees Fahrenheit which the water has 
risen in temperature, the theoretical evaporative power of 
the coal is at once approximately determined. 

The furnace shown in Fig. 14 is intended to be used 
when bituminous coals are to be operated upon ; but in 
experimenting on coke, anthracite, and other difficult com- 
bustible fuels, a wider and shorter furnace is preferred, 
and the fuel mixture should not be pressed down. 

Q. What is the construction of the Barrus' coal calorim- 
eter ? 

The Barms' coal calorimeter, shown in Fig. 15, consists 
of a glass beaker, 5 inches in diameter and 10 inches high, 
which can be obtained of most dealers in chemical appa- 
ratus. The combustion chamber is of special form, and 
consists of a glass bell having a notched rib around the 
lower edge, and a bead just above the top, with a tube pro- 
jecting a considerable distance above the upper end. The 



i88 



COMBUSTION OF COAL. 



#*— S> 



bell is 2y 2 inches inside diameter, 5^ inches high, and the 
tube above is $/q inch inside diameter, and extends be- 
yond the bell a distance of 9 inches. The base consists 
of a circular plate of brass, 4 inches in diameter, with 

three clips fastened on the up- 
per side for holding down the 
combustion chamber. The base 
is perforated, and the under side 
has three pieces of cork at- 
tached, which serve as feet. To 
the centre of the upper side of 
the plate is attached a cup for 
holding the platinum crucible, 
in which the coal is burned. To 
the upper end of the bell be- 
neath the bead, a hood is at- 
tached, made of wire gauze, 
which serves to intercept the 
rising bubbles of gas and retard 
their escape from the water. 
The top of the tube is fitted 
with a cork, and through this is 
inserted a small glass tube which 
carries the oxygen to the lower 
part of the combustion chamber. 
The tube is movable up and 
down, and to some extent sideways, so as to direct the 
current of oxygen to any part of the crucible, and adjust 
it to a proper distance from the burning coal. 

In addition to the apparatus here shown there is. required 
a tank of oxygen, such as the calcium light companies 
furnish, scales for weighing water, and delicate balances 
for weighing coal, besides a delicate thermometer for tak- 




FlG. 15. 



BARRUS' CALORIMETER. 1 89 

ing the temperature of the water, and another for show- 
ing the temperature of the atmosphere. The former 
should be graduated to tenths of a degree Fahrenheit. 

The quantity of coal used for a test is one gram, and of 
water 2,000 grams. The equivalent calorific value of the 
material of the instrument is 185 milligrams. One degree 
rise of temperature of the water corresponds to a total 
heat of combustion of 2,185 British thermal units. The 
number of degrees rise of temperature for ordinary coals 
varies from 5^ to 6}4° F. Radiation is allowed for by 
commencing the test with a temperature as many degrees 
below the atmosphere as the temperature rises above the 
atmosphere at the end of the test. When very smoky 
coals are used, the sample is mixed with a small propor- 
tion of anthracite of known calorific value ; and when an- 
thracite coal is used, a small percentage of bituminous coal 
is likewise mixed with it. 

Q. What is the process of making a test with the 
Barrus' calorimeter ? 

Having dried and pulverized the coal, and weighed out 
the desired quantities of coal and water, the combustion 
chamber is immersed in the water for a short time, so as 
to make the temperature of the whole instrument uniform 
with that of the water. On its removal, the initial tem- 
perature of the water is observed, the top of the chamber 
lifted, the gas turned on, and the coal quickly lighted, a 
small paper fuse having previously been inserted in the 
crucible for this purpose. The top of the combustion 
chamber is quickly replaced, and the whole returned to its 
submerged position in the water. The combustion is care- 
fully watched as the process goes on, and the current of 
oxygen is directed in such a way as to secure the desired 



190 



COMBUSTION OF COAL 



rate and conditions for satisfactory combustion. When 
the coal is entirely consumed, the interior chamber is 
moved up and down in the water until the temperature of 
the whole has become uniform, and finally it is withdrawn 
and the crucible removed. The final temperature of the 
water is then observed, and the weight of the resulting ash. 
The initial temperature of the water is so fixed by suit- 
ably mixing warm and cold water that it stands at the 
same number of degrees below the temperature of the sur- 
rounding atmosphere (or approximately the same), as it is 
raised at the end of the process above the temperature of 
the air. In this way the effect of radiation from the ap- 
paratus is overcome, so that no provision in the matter of 
insulation is required, and no allowance needs to be made 
for its effect. 

Q. What are some of the results obtained by the use 
of the Barrus' calorimeter ? 

A few results of tests with the Barrus' coal calorimeter 

are here given : 

Table 24. 







Total Heat of Combustion 


Kind of coal. 


Per cent of 


per Pound of — 










Coal. 


Combustible. 


Georges Creek, bituminous. . . . 


5.0 


13,487 


14,196 


" " 


6.5 


12,921 


13,819 


" " 


7.0 


I3,36o 


14,365 


" " 


8.6 


12,874 


14,085 


Pocahontas, bituminous 


3.2 


14,603 


15,085 


< < it 


4.0 


14,121 


14,709 


" " ..;.... 


5.o 


14,114 


14,856 


" " 


6.5 


13,697 


14,649 


New River, bituminous 


1.0 


14,455 


I4,6oi 


" " 


3-5 


13,922 


14,426 


< < « < 


5.o 


13,858 


14,857 


Youghiogheny, bituminous lump 


5-9 


12,941 


13,752 


slack 


10.2 


11,664 


12,988 
12,765 


Frontenac, Kansas, bituminous. 


17.7 


10,506 



CARPENTER S CALORIMETER. 



I 9 I 



Q. What are the details of construc- 
tion of the Carpenter calorimeter ? 




Referring to Fig. 16, the appa- 
ratus consists of the combustion 
chamber 15, which has a removable 
bottom. The chamber is supplied 
with oxygen for combustion through 
tube 23, the products of combustion 
being conducted through spiral tube 
28, 29, 31. The tube ends in a 
hose nipple 30, from which a hose 
connection is made to a small cham- 
ber 39, attached 
to the outer case 
and provided 
with a siphon 
gauge 40. A 
plug, 41, with 
pinhole, is at- 
tached to the 
chamber for the 
discharge of 
gases. The si- 
phon gauge indi- 
cates the press- 
ure of the gases. 
Surrounding 
the combustion 
chamber is a 
larger closed 
chamber 1, filled 
with water and 
connected with an open glass tube with attached scale 9 




Fig. 16. 



I92 COMBUSTION OF COAL. 

and 10. Above the water chamber is a diaphragm 12, 
which is used to adjust the zero level by means of screw 
14 in the open glass tube at any desired point. 

A glass for observing the process of combustion is in- 
serted at 33 in top of the combustion chamber, at 34 in 
top of water chamber, and at 36 in top of outer case. An 
opening for filling is provided by removing the plug screw 
at 37, which can also be used for emptying if desired. 
The plug 17, which stops up the bottom of the combus- 
tion chamber, carries a dish 22, in which the fuel for com- 
bustion is placed, also two wires 26, 27, passing through 
tubes of vulcanized fibre, which are adjustable in a verti- 
cal direction and connected with a thin platinum wire at 
the ends. These wires are connected to an electric cur- 
rent and used for firing the fuel. On the top part of this 
plug is placed a silver mirror 38, to deflect any radiant 
heat. Through the centre of this plug passes a tube 23, 
through which oxygen passes to supply combustion. The 
plug is made of alternate layers of rubber and asbestos 
fibre, the outside only being of metal, which being in con- 
tact with the wall of the water chamber can transfer little 
or no heat to the outside. The instrument readily slips 
into an outer case, which is nickel-plated and polished on 
the inside so as to reduce radiation. It is supported on 
strips of felting, 5 and 6. The combustion chamber can 
be subjected to considerable pressure; however, 10 inches 
water pressure has usually been found sufficient. The ca- 
pacity of the instrument is about 5 pounds of water, and 
is large enough for the combustion of 2 grams of coal. 

Q. What advantages are possessed by the Carpenter 
calorimeter ? 

The calorimeter designed by R. C. Carpenter differs 
from other calorimeters by the provision made in the appa- 



COPPER-BALL CALORIMETER. I93 

ratus itself, for giving the calorific power of fuels almost 
direct in British thermal units, dispensing also with some 
of the objectionable features, such as the errors involved 
in the thermometer, the determination of the water equiv- 
alent of the calorimeter, correction for evaporation, radia- 
tion, and specific heats, thus enabling the operator to do 
his work quickly and accurately. This apparatus, shown 
in Fig. 16, is in principle a large thermometer, in the bulb 
of which combustion takes place, the heat being absorbed 
by the liquid which is within the bulb. The absorption 
of heat is proportional to the height to which a column of 
liquid rises in the attached glass tube. 

Q. How may a copper -ball calorimeter, suitable for 
ascertaining smoke-box temperatures, be made ? 

At the Purdue University such a calorimeter is employed 
in locomotive tests, and is constructed as follows : 

A piece of i-inch steam pipe, threaded at one end, is 
screwed through the shell from the inside of the smoke 
box. It is set radially about 4 inches from the front tube 
sheet, and inclines from the centre of the smoke box down- 
ward. The threaded end passes through the shell a suffi- 
cient distance to receive a cap. The cap serves to close 
the end of the pipe, and also to carry a light rod, to the 
opposite end of which is attached a simple piston fitting 
loosely to the bore of the pipe. A copper ball, T/% inch in 
diameter, and a copper vessel suitably enclosed to prevent 
radiation, complete the outfit. In using the apparatus, the 
copper ball is inserted in the bore of the pipe, the piston 
applied below it, and both are pushed up the pipe until the 
cap at the lower extremity of the piston rod meets the 
lower end of the pipe. The cap is then screwed in place, 
closing the pipe and retaining the ball at the centre of the 
13 



194 COMBUSTION OF COAL. 

smoke box. Here it is allowed to remain from 40 to 60 
minutes, after which interval it is assumed to have come 
to the temperature of the smoke box. The cap is then 
unscrewed and the piston quickly withdrawn, allowing the 
ball to roll down the pipe into the water contained in the 
copper vessel. From the known weight of the ball, the 
water, and the copper vessel, and from observed changes 
in temperature, the original temperature of the ball is cal- 
culated. The average result of three such determinations 
is assumed to be the temperature of the smoke box for the 
test. 

Q. Is the amount of heat evolved by combustion in 
proportion to the amount of oxygen consumed? 

In the erroneous belief that the amount of heat evolved 
on combustion was in proportion to the amount of oxygen 
consumed, Berthier determined the calorific power of 
fuel by burning it by the oxygen contained in oxide of 
lead, PbO, and ascertaining the weight of the resulting 
button of lead. 

The calorific powers of various fuels as thus determined 
are as follows : 

•Tories. he^tl. 

Air-dried wood with 20% H 2 2,800 5.040 

Charred wood 3>6oo 6,480 

Wood charcoal with 20$ H 2 6,000 10, 800 

Dry charcoal 7.050 12,690 

Peat with 20$ H 2 3. 600 6,480 

Dried peat 4, 800 8,640 

Peat charcoal 5> 800 10,440 

Average bituminous coal 7, 500 13, 500 

Good coke 7.050 12,690 

Coke with 5$ ash 6,000 io, 800 

4,360 7,848 



Air-dried lignite to 

6 ( 5,4io 9,738 

Hydrogen 34, 462 62, 032 

Carbon burnt to CO 2,473 4.451 



BERTHIER S CALORIMETER. I95 

Carbon burnt to C0 2 8, 080 14, 544 

CO, burnt to CO a 2,403 4, 325 

Marsh gas 13,063 23,513 

defiant gas 11,858 21,344 

Q. What is the Berthier method of coal calorimetry ? 

The apparatus consists of gas furnace and crucible 
clearly shown in Fig. 17, which are so simple as to be self- 
explanatory. Berthier 's method of coal calorimetry uses 





Fig 



oxide of lead, PbO, as the source of oxygen. It requires 
only accurate weighing of the sample of fuel and an easily 
controllable fire for heating a clay crucible to a low red 
heat. There are no corrections for radiation and no deli- 
cate measurements of temperature to be made. These are 
apparently the great sources of error in the use of oxygen 
gas. 

The heating power of fuels may be ascertained by mix- 
ing intimately 1 part by weight of the substance, in the 
finest state of division, with at least 20, but not more than 



196 



COMBUSTION OF COAL. 



40, parts of litharge. Charcoal, coke, or coal may be 
readily pulverized ; but in the case of wood the sawdust 
produced by a fine saw or rasp must be employed. The 
mixture is put into a close-grained conical clay crucible, 
and covered with 20 or 30 times its weight of pure litharge. 
The crucible, which should not be more than half full, is 
covered and then heated gradually until the litharge is 
melted and evolution of gas has ceased. At first the mix- 
ture softens and froths. When the fusion is complete, the 
crucible should be heated more strongly for about ten min- 
utes, so that the reduced lead may thoroughly subside and 
collect into one button at the bottom. Care must be taken 
to prevent the reduction of any of the litharge by the gases 
of the furnace. The crucible, while hot, should be taken 
out of the fire and left to cool ; when cold, it is broken, 
and the button of lead detached, cleaned, and weighed. 
The accuracy of the result should be tested by repetition. 



Table 25. — Comparison of Oxygen and Litharge Methods. 



Fuel. 



r 

Carbon from | 
gran u 1 a t e d J 
sugar. Ash, j 

o.44^ I 

I 
f 

Bituminous | 
slack from^J 
West Vir- I 
ginia t 

r 

Anthracite coal | 
from Lehigh -{ 
Valley | 



Weight of 
Fuel, Grams. 



Oxy. Lith. 



310 

377 
468 
204 
812 
328 
372 
394 
538 
262 



2.18 



882 
879 
767 
919 

937 
197 
306 

453 
502 

877 

4535 

3165 

0000 

0000 

9675 



Heating 
Power. 



Oxy. 



u 
14,720 

14,090 
14,520 
14,320 
15,460 
12,660 
12,370 
12,520 
12,230 
14,000 



Lith. 



14,64c 
14,800 
14,550 
13,920 

13,590 
14,480 
11,420 
11,53^ 
11,460 
11,520 
11,420 
I3,50O 
13,650 
13,604 
13,622 
13,643 



Results. 



Oxy. Lith. 



14,620 



12,760 



All 
14,330 

1,2,3.6 
14,617 



H,470 



13,616 



Probable 

Error 
Per Cent. 



Oxy. 



9Det 
± 2.6 



± 1.: 



±1.7 



Lith. 



6 Bet. 
± O.76 

± O.14 

± O.08 



CALORIFIC VALUE OF WOOD. 1 97 

The purpose of covering the mixture of fuel and litharge 
in the crucible with a quantity of pure litharge is not only 
to prevent access of air to the fuel, but also to prevent the 
escape unoxidized of the more volatile portions of the fuel. 
And this covering of pure litharge must likewise be pro- 
tected from the furnace gases. This apparatus is fully 
described in theoretical detail by C. V. Kerr, Trans. A. 
S. M. E., i 



Q. What is the calorific value of wood ? 

The large percentage of moisture in wood renders it un- 
suitable as fuel where high temperatures are required. 
The hydrogen present in wood is not available as fuel owing 
to the presence of oxygen, these two gases uniting to form 
water. Carbon is the only combustible available in wood 
for generating heat. This element is present in all woods, 
averaging about 50 per cent of the total weight when dry. 

A cord of wood contains 128 cubic feet; its weight is 
about 2,700 pounds, or 21 pounds per cubic foot. 2.12 
cords, or 2.55 tons of pine wood, were found to be equal to 
1 ton Cumberland coal, 1 pound of the latter equalling 
2.55 pounds of wood. In evaporative power the pine wood 
had but two- fifths of that of coal, equal to about 2^ pounds 
of water evaporated per pound of pine. This is much less 
than the results obtained by Prof. W. R. Johnson in 1844, 
who found that 1 pound of dry pine would, by careful 
management, evaporate 4.69 pounds of water. 

The American Society of Mechanical Engineers, in their 
rules for boiler tests, assume one pound of wood to equal 
0.4 pound of coal. 

Q. How does wood compare with cotton stalks, brush- 
wood, or straw as a fuel? 

The evaporative values, given by John Head, for the 



igS COMBUSTION OF COAL. 

following substances, when burnt in a tubular boiler, com- 
pare as follows : 

Eight pounds of water evaporated by I pound good coal ; 
2 pounds dry peat; 2.25 to 2.3 pounds dry wood; 2.5 to 3 
pounds cotton stalks or brushwood; 3.25 to 3.75 pounds 
straw. 

Q. What is the calorific value of peat? 

Very little use has been made of peat in this country, 
owing to the abundance, cheapness, and superior heating 
power of bituminous coal. Carefully conducted tests 
abroad show that peat, air-dried, containing not more than 
14 per cent of moisture, has about one-half the evaporative 
power of good coal, and is superior to that of ordinary air- 
dried wood. 

The calorific power of peat varies from 5,400 heat units 
for ordinary air-dried peat, to 9,400 heat units per pound 
when thoroughly dry. This corresponds to an evaporation, 
from and at 21 2° F., of 5.6 pounds of water for the for- 
mer, and 9.79 pounds for the latter. 

Q. What is the calorific value of lignite ? 

Freshly mined lignite contains an excess of moisture, to 
which is generally attributed its low heating power. The 
large amount of volatile combustible matter contained in 
lignite causes it to burn with a long smoky flame. The 
calorific value of lignites will vary from 6,500 to 11,000 
heat units, and occasionally higher for the better qualities. 
This is equal to an equivalent evaporation from and at 
212 F. of 6.73 pounds of water for the former, and 11.38 
pounds for the latter. 

Q. What is the calorific value of bituminous coal ? 

The calorific value of bituminous coal for the lower 
grades depends almost wholly upon the amount of its fixed 



CALORIFIC VALUE OF COKE. 199 

carbon, the moisture and excess of oxygen operating 
against the efficiency of the fire as a whole ; some of the 
lower grades of coal developing not more than 8,000 heat 
units, corresponding to an equivalent evaporation of 8.28 
pounds of water from and at 21 2° F. per pound of coal. 

The better grades of bituminous coal develop from. 13,- 
000 to 14,500 heat units per pound of coal, corresponding 
to an equivalent evaporation of 13.45 pounds of water for 
the former, and 15.01 pounds for the latter, both from and 
at 212 F. 

A good average for the best varieties of bituminous coal 
is 13,600 heat units, corresponding to an evaporation of 
14.08 pounds of water from and at 212 F. per pound of 
coal. 

Q. What is the calorific value of coke ? 

The calorific power of coke should be very high, inas- 
much as it is nearly pure carbon. Deducting the ash and 
other impurities, coke should yield 12,500 to 13,800 heat 
units per pound, which corresponds to an equivalent evap- 
oration of 12.94 pounds of water for the former, and 14.28 
pounds for the latter, from and at 21 2° F. per pound of 
coke. 

D. K. Clark states that the best experience of the com- 
bustion of coke has been derived from the practice of loco- 
motives. A rapid draught is required for effecting the 
complete combustion of coke, preventing the reaction 
which is likely to take place when currents of carbonic 
acid traverse ignited coke, and convert it into carbonic 
oxide. He showed by a process of mechanical analysis 
that the combustion of coke in the fire box of the ordinary 
coal-burning locomotive was complete. The total heat of 
combustion of one pound of good sound coke was found 



200 COMBUSTION OF COAL. 

ordinarily to be disposed of as follows, when the tempera- 
ture in the smoke box did not exceed 6oo° F. : 78.0 per 
cent in the formation of steam; 16. 5 per cent by the heat 
of burnt gases in smoke box; 5.5 per cent drawback by 
ash and waste. 

Q.'What is the calorific value of anthracite coal? 

Anthracite coals are principally carbon and ash. Ex- 
cluding the moisture, there is not enough available hydro- 
gen in the volatile matter to be of any heating value, after 
deducting the energy required to dissociate the volatile 
combustible from the fixed carbon. The volatile combus- 
tible may, therefore, be wholly neglected without sensible 
loss, and the coal treated . according to its percentage of 
carbon. 

Beaver Meadow, Carbon County, Pa., anthracite coal 
(Geol. Surv., Pa.). 

Specific gravity, 1.55 = 96.88 pounds per cubic foot. 

Fixed carbon 90. 20 per cent. 

Volatile matter 2. 52 " 

Earthy matter, ash 6. 13 " 

98.85 "' 

Neglecting the 1.15 per cent loss in the analysis, we 
have as the calorific power of this fuel : 

Carbon 9020X14,544= 13, 119 

Volatile matter 0252 X 20,115 = 507 

Less 0252 X 3,600= 91= 416 

Total heat units 13, 535 

Then: — ^— = 14.01 pounds of water evaporated per 
pound of coal from and at 21 2° F. 



CHAPTER IX. 

STEAM GENERATION. 

Q. What is the nature of the heat problem in a steam 
engine ? 

It is to convert the heat generated in the furnace by the 
combustion of fuel into the sensible motion of ponderable 
masses — a piston, fly wheel, etc. ; and the degree in which 
it is possible for it to accomplish this (every imperfection 
and every source of loss eliminated) is the ratio which the 
difference of temperature of initial and exhaust steam (or 
its range) bears to the absolute temperature of initial 

T — T 

steam ; that is, — ^-= — l , where T is the absolute initial 

■*■ 

temperature, and T 1 the absolute final temperature. 

Example : Suppose a locomotive takes steam up to the 

point of cut off at 120 pounds gauge pressure, to which 

we add the pressure of the atmosphere, 14.7 pounds— 134.7 

pounds absolute pressure ; its sensible temperature would 

be 350 F. and its absolute temperature 46 1° more, or 

350 -f- 46 1 ° = 81 1°. If this steam be exhausted under 

pressure a little greater than that of the atmosphere, say 

15 pounds absolute, its sensible temperature would be 

2 1 3 F., and its absolute temperature 46 1° more, or 

674. ° Now if T = 81 1 °, and T, = 674, we have: 

To-T, 811-674 137 

— T^= 811 =8l7 = - 169 ' 

or say 16.9 per cent. That is, the range of temperature 



202 COMBUSTION OF COAL. 

between initial and exhaust steam being 137 F., and the 
absolute initial temperature being 81 1° F., such a steam 
engine, on account of being obliged to let the steam go 
while it still has a temperature of 213 F. or 674 ° abso- 
lute, has within its reach, if it could save it all, only 16.9 
per cent of the whole work contained in the initial steam 
in the form of heat. Such an engine will in fact yield 
about 6 per cent ; and dividing this 6 per cent by the 16.9 

per cent we have —p— = .355, or 35.5 per cent, as the 

ratio of usual engine performance to perfect performance of 
perfect heat engine under the above usual conditions. 
About two-thirds, then, of the heat work that may at least 
be striven for is usually lost (Hoadley). 

Q. What is meant by the range of temperature in a 
steam engine ? 

It is the difference between the temperature of the steam 
entering the cylinder and the temperature of its exhaust. 
These temperatures should be expressed in terms of the 
absolute scale of temperatures, and not that of the ordinary 
thermometer. 

Q. Does water conduct heat readily ? 

Water conducts heat very slowly from above downward. 
The effect observed is very different when, instead of ap- 
plying heat at the upper surface, it is communicated to the 
under part, or to the bottom of a vessel in which liquid is 
contained. In this case the particles in immediate contact 
with the heat-giving body are expanded. This, by render- 
ing them lighter than the succeeding ones, causes them to 
ascend ; fresh particles succeed, and these rise in similar 
manner. Currents are thus determined in the liquid, and 
the whole mass is readily heated. This, however, is not 



LATENT HEAT OF EVAPORATION. 203 

a case of conduction from particle to particle ; neither is 
it due to radiation, but it is the effect of convection — that 
is to say, the actual conveyance or distribution of the heated 
portion throughout the mass. 

Q. What is the limiting difference in temperature be- 
tween the heated gases in contact with a steam boiler, 
and the temperature of the steam within ? 

A common steam pressure in stationary boilers is 80 
pounds by gauge, or 95 pounds absolute, the correspond- 
ing temperature being 324 F., which represents the cool- 
ing surface to which the hot furnace gases are exposed. 
It is probable that there can be no active transmission of 
heat from the gases without to the water within a boiler, 
with less than 75 ° F. difference of temperature. Pyrom- 
eter observations made by Hoadley, in the smoke box of a 
return tubular boiler, at all stages of the fire, satisfied him 
that in excellent boilers, well fired, having a ratio of heat- 
ing surface to grate area as large as 36, the temperature of 
the escaping gases rarely, if ever, falls lower than 75 ° F. 
above the temperature due to the steam pressure, except 
when the fire doors are open and there is great and un- 
usual excess of air admitted. Adding 75 ° to the tempera- 
ture corresponding to 80 pounds gauge pressure, 324 , we 
have, say, 400 F. as the lowest practical temperature of 
escaping gases. This will be confirmed by the best prac- 
tice under favorable conditions ; and the actual tempera- 
ture will range through a low average of 500 F. and a 
high average of 600 ° F. up to 8oo° F. or over. 

Q. What is the latent heat of evaporation ? 

When water has been raised to a temperature of 21 2° F. 
in a vessel open to the atmosphere, the continued applica- 
tion of heat does not cause a further rise in temperature. 



204 COMBUSTION OF COAL. 

It will be observed that much more heat is required to 
evaporate a given quantity of water from and at 21 2° than 
was necessary to bring its temperature up to the boiling 
point. 

The quantity of heat required to evaporate 1 pound of 
water from and at 21 2° has been experimentally shown to 
be equal to 966 British thermal units. 

The total heat in 1 pound of steam at 21 2° F. is 1146 
units, of which 212 — 32 = 180 are necessary to bring 
the water from the freezing to the boiling point ; and 966 
units of heat per pound of water are expended in doing the 
internal work of pulling the liquid molecules asunder, to 
which must also be added the exterior work of forcing 
back the atmosphere when the liquid becomes vapor. 

The heat thus expended in the conversion of water into 
steam from and at 21 2° F., viz., 966 heat units per pound 
of water, and of which the thermometer gives no record, is 
the latent heat of evaporation. 

Q. How may the latent heat in steam be proven by 
the quantity of water required for its condensation ? 

If the feed water and the water for condensation are 6o° 
F., the water leaving the condenser at 120 F., the steam 
being condensed from 21 2° F. , we have : Total heat in 
one pound of steam from water at 32 ° = 1,146 heat units. 

The water entering the boiler at 6o° instead of 32 , 
there is a gain of 60 — 32 = 28 , the heat expended being 
1 146 — 28 — 1 1 18 heat units. Subtracting the tempera- 
ture of the injection from that of the discharge water 
we have : 120 — 60 = 6o° difference. Then 1 1 14 -^ 60 
= 18.63 times as much water required to condense the 
steam as was evaporated to make it. In practice, 25 times 
is the usual allowance. 



FACTOR OF EVAPORATION. 205 

Q. Is the latent heat of evaporation wholly lost in 
steam engineering practice ? 

In the case of non-condensing engines exhausting di- 
rectly into the atmosphere, the latent heat contained in 
the steam is lost ; and this is the principal loss which oc- 
curs in the steam engine when considered as a heat engine. 

In a condensing engine a partial recovery of this loss is 
had by the condensation of the exhaust steam, and conse- 
quent utilization of the pressure of the atmosphere upon 
the engine piston corresponding to the vacuum obtained, 
from which must be deducted the quantity of work ex- 
pended in operating the air pump. 

Q. What is meant by factor of evaporation? 

A factor of evaporation is found by subtracting the 
temperature of the feed water above 32 ° F. from the total 
heat in steam above 3 2° F. at its pressure above vacuum, 
and dividing the remainder by 966, or the latent heat of 
steam at atmospheric pressure. It is commonly expressed 
by the formula : 

Factor of evaporation = — ^z~> i n which H and h are 

respectively the total heat in steam of the average observed 
pressure, and in water of the average observed temperature 
of the feed. 

If we suppose water to enter a boiler at yo° F. , the steam 
pressure to be 100 pounds by gauge or 1 15 pounds abso- 
lute, the factor of evaporation would be found thus : 

The total heat in steam above 32 F. at 115 pounds ab- 
solute = 1 185. 

Temperature of feed, yo° — 32 ° = 38. 

H85 — 38 
Factor of evaporation = ^ = 1.187. 



206 



COMBUSTION OF COAL. 



A table of factors of evaporation is here given for steam 
pressures by gauge from 60 to 200 pounds per square inch, 
varying by 10 pounds, together with feed water tempera- 
tures from 32 to 210 , varying by io° F. 

The use of the table will be illustrated in the solution 
of the following example : 

Suppose a boiler to evaporate 9 pounds of water per 
pound of coal, the feed water entering at 70 F., the steam 
pressure to be 100 pounds by gauge, what is the equiva- 
lent evaporation from and at 212 ? 

The factor of evaporation corresponding to the steam 
pressure and temperature of feed water shown in Table 26 
is 1. 1 87, which multiplied by the pounds of water evapo- 
rated will be: 1.1 87 X9 = 10.683 pounds of water per 
pound of coal. 

Table 26. — Factors of Evaporation. 



if* 


Steam Pressure by Gauge. 


, w "3q 


60 


70 


80 


90 
1.225 


100 


no 


120 


130 


140 

1.234 


150 


160 
1.237 


170 


180 


190 
1. 241 


200 


32 


1. 216 


1.220 


1.222 


1.227 


1.229 


1.231 


1.232 


1.236 


1.239 


1.240 


1.243 


.40 


1.209 


1. 212 


1.214 


1. 216 


1. 219 


1.220 


1.222 


1.224 


1.226 


1.227 


1.229 


1.230 


1.232 


x .233 


1.234 


50 


1. 197 


1. 201 


1.204 


1.206 


1.208 


1. 210 


1. 212 


1. 214 


1. 215 


1. 217 


1. 218 


1.220 


1.221 


1.225 


1.224 


60 


1. 188 


1. 191 


1. 193 


1. 196 


1. 198 


1.200 


1.202 


1.203 


1.205 


1.207 


1.208 


1. 210 


1. 211 


1. 212 


1.214 


70 


1. 178 


1. 180 


1.183 


1. 185 


1. 187 


1. 189 


1. 191 


I- 193 


1. 194 


1.196 


1. 197 


1. 199 


1.200 


1.202 


1.203 


80 


1.167 


1. 170 


i- 173 


i- 175 


1. 177 


1. 179 


1. 181 


1. 183 


1. 184 


1. 186 


1. 187 


1. 189 


1. 190 


1. 192 


1 -193 


90 


"57 


1. 160 


1. 162 


1. 165 


1. 167 


1. 169 


1. 170 


1. 172 


1. 174 


1. 176 


1. 177 


1. 179 


1. 180 


1. 181 


1. 183 


100 


1. 147 


1. 150 


1.152 


"54 


1.156 


1. 158 


1.160 


1. 162 


t.164 


1.165 


1. 167 


1.168 


1. 170 


1. 171 


1. 172 


no 


1. 136 


i- 139 


1. 142 


1. 144 


1. 146 


1. 148 


1. 150 


1. 152 


"53 


1. 155 


1. 156 


1. 158 


1 -159 


1. 160 


1.162 


120 


1.126 


1. 129 


1.131 


i- 1.33 


1.13b 


i.i3» 


1. 140 


1. 141 


I.I43 


"45 


1. 146 


1. 147 


1. 149 


1-150 


1. 151 


130 


1. 116 


1. 118 


1. 121 


1. 123 


1. 125 


1. 127 


1. 129 


1. 130 


1. 132 


"34 


1. 136 


I-I37 


1. 138 


1. 140 


1. 141 


140 


1. 105 


1. 108 


1. 100 


1. 113 


1,115 


1.117 


1.119 


1.120 


1. 122 


1. 124 


1. 125 


1. 127 


j. 128 


1. 129 


1. 131 


150 


1.095 


1.098 


1. 100 


1. 102 


1. 104 


1. 106 


1.108 


1. no 


1. in 


1.113 


1. 115 


1. 116 


I.118 


1. 119 


1. 120 


160 


1.084 


1.087 


1.090 


1.092 


1.094 


1.096 


1.098 


1. 100 


I.IOI 


1. 103 


1. 104 


1. 106 


J. 107 


1.108 


1. no 


170 


1.074 


1.077 


1.079 


1.081 


1.083 


1.085 


1.087 


1.089 


1. 091 


1.092 


1.094 


1.095 


I.097 


1.098 


1.099 


180 


1.063 


1.066 


1.069 


1. 071 


1-073 


1.075 


1.077 


1.079 


1.080 


1.082 


1.083 


1.085 


1.086 


1.088 


1.089 


190 


i-°53 


1.056 


1.058 


1.060 


1.063 


1.065 


1.066 


1.068 


1.070 


1.071 


1-073 


1.074 


1.076 


1.077 


1.078 


200 


1.043 


1.045 


i.o 4 8 


1.050 


1.052 


1.054 


1.056 


1.058 


1.059 


1. 061 


1.063 


1.064 


1.065 


1.067 


1.068 


210 


1.032 


1-035 


1.037 


1.040 


1.042 


1.044 


1.046 


1.047 


1.049 


1.051 


1.052 


1-053 


i-°55 


1.056 


!-057 



Factors of equivalent evaporation show the proportionate 
cost in heat or fuel of producing steam at any given press- 
ure as compared with atmospheric pressure. To ascer- 



TOTAL HEAT IN STEAM. 



207 



tain the equivalent evaporation at any pressure, multiply 
the given evaporation by the factor of its pressure, and di- 
vide the product by the factor of the desired pressure. 

Each degree of difference in temperature of feed water 
makes a difference of .00104 in the amount of evaporation. 
Hence to ascertain the equivalent evaporation from any 
other temperature of feed than 2 1 2°, add to the factor given 
as many times .00104 as the temperature of feed water in 
degrees below 2 1 2°. For other pressures than those given 
it will be practically correct to take the proportion of the 
difference between the nearest pressures in Table 27, 
adapted from table published by Babcock & Wilcox Com- 
pany. 

Table 27. — Factor of Equivalent Evaporation at 212 F. 



Total pressure above 

vacuum in pounds per 

square inch. 



15 
20 

25 
30 

35 
40 

45 
50 
55 

60 

65 
70 

75 

So 

85 



Factor 
of equivalent 
evaporation at 



I.OOO3 
1. 0051 
I.OO99 
I. OI29 

1. 0157 
I. Ol82 
I.0205 
1.0225 

I.0245 
I.0263 
I.O280 
I.O295 
I.O309 
I.0323 
I.0337 



Total pressure above 

/acuum in pounds per 

square inch. 



90 

95 
100 
105 
no 

"5 

120 

125 
130 
140 
150 
160 
170 
180 



Factor 
of equivalent 
evaporation at 



I.O350 
I.O362 

1.0374 
I.O385 
I.0396 
I.O406 
I. O416 
I.O426 
I.0435 
1.0453 
I.O470 
I.O486 
I.0502 
1. 0517 



Q. What is meant by total heat in steam ? 

The total heat in steam includes the sensible tempera- 
ture of the steam above 3 2°, plus the latent heat of evapo- 
ration corresponding to the pressure under which the steam 
is generated. 



208 



COMBUSTION OF COAL. 



Table 28.— Properties of Saturated Steam, Pressure, Tempera- 
ture, Volume and Density. (Haswell's Table. ) 



Pressure 


Pressure 


Tem- 


Total heat 


Volume 


Density, 


per 

square inch, 

pounds. 


in mercury, 
inches. 


perature, 
degrees. 


from water at 
32°. 


of one pound, 
cubic feet. 


or weight of 

one cubic foot, 

pounds. 


I 


2.04 


I02. 1 


III2.5 


330.36 


.003 


5 


I0.I8 


162.3 


H30.9 


72.66 


.OI38 


10 


20.36 


193-3 


1 140. 3 


37.84 


.0264 


14.7 


29.92 


212 


II46.I 


26.36 


.03802 


20 


40.72 


228 


■ II50.9 


19.72 


•0507 


25 


50.9 


24O.I 


II54.6 


15-99 


.0625 


30 


6I.08 


25O.4 


II57.8 


13.46 


.0743 


35 


71.26 


259-3 


1 160. 5 


H.65 


.0858 


40 


81.43 


267.3 


1162.9 


IO.27 


.0974 


45 


9I.61 


274-4 


1165.1 


9.18 


.IO89 


50 


101.8 


281 


1167.1 


8.31 


.1202 


55 


in. 98 


287.1 


1169 


7.61 


.1314 


60 


122.16 


292.7 


1170.7 


7.0I 


.1425 


65 


132.34 


298 


1172.3 


6.49 


.1538 


70 


142.52 


302.9 


1173.8 


6.07 


.1648 


75 


152.69 


307.5 


1175.2 


5.68 


' -1759 


80 


162.87 


312 


1176.5 


5-35 


.1869 


85 


173.05 


316. 1 


1177.9 


5.05 


.I98 


90 


183.23 


320.2 


1179.1 


4-79 


.2089 


95 


I93-4I 


324.1 


1180.3 


4.55 


.2198 


100 


203.59 


327.9 


1181.4 


4-33 


.2307 


105 


213.77 


331-3 


T182.4 


4.14 


.2414 


110 


223.95 


334-6 


1183.5 


3-97 


.2521 


115 


234-13 


338 


1184.5 


3.8 


.2628 


120 


244.31 


34i. 1 


1185:4 


3.65 


.2738 


125 


254.49 


344-2 


1186.4 


3.5i 


.2845 


130 


264.67 


347-2 


1187.3 


3.38 


•2955 


135 


274.85 


350.1 


1188.2 


3.27 


.306 


140 


285.03 


352.9 


1189 


3.16 


.3162 


145 


295.21 


355-6 


1189.9 


3.06 


.3273 


149 


303.35 


357-8 


1 190. 5 


2.98 


•3357 


150 


305.39 


358.3 


1 190. 7 


2.96 


• 3377 


155 


315.57 


361 


ngi-5 


2.87 


.3484 


160 


325.75 


363-4 


1192.2 


2.79 


• 359 


165 


335-93 


366 


1192.9 


2.71 


.3695 


170 


346.11 


368.2 


II93-7 


2.63 


.3798 


175 


356.29 


370.8 


II94-4 


2.56 


.3899 


180 


366.47 


372.9 


1195.1 


2.49 


.4009 


185 


376.65 


375-3 


1195.8 


2.43 


.4117 


190 


386.83 


377-5 


1196.5 


2.37 


.4222 


195 


397.01 


379-7 


1197.2 


2.31 


.4327 


200 


407.19 


381.7 


1197.8 


2.26 


.4431 



TOTAL HEAT IN STEAM. 2(X) 

At atmospheric pressure we have : 21 2° F., the sensible 
temperature of steam ; 966 heat units, the latent heat of 
evaporation. Then 

212 — 32 = 180 

Latent heat = 966 

Total heat in one pound of steam = 1146 heat units. 

The amount of heat absorbed in vaporization, or rendered 
latent by each pound of water in its conversion into steam, 
varies according to the pressure at which the steam is gen- 
erated, being greatest at atmospheric pressure and de- 
creasing as the steam pressure increases. For example : 

At 100 pounds gauge pressure or 115 pounds absolute 
we have a corresponding temperature of 338 F. The 
latent heat of vaporization at this temperature and pressure 
is 876 units of heat per pound of water evaporated. We 
have then : 

Temperature of the steam 338 — 32 = 306 
Latent heat of evaporization = 876 

Total heat in steam = 11 82 British thermal units. 

A result which varies slightly from that given in Table 
28. As the tabular numbers are those obtained by direct 
experiment, they are to be followed in all cases. 

Q. What is the effect of the withdrawal of heat from 
steam ? 

When heat is withdrawn from steam it condenses to 
form water, and the same quantity of heat necessary to 
produce the steam reappears in the water used to condense 
the steam, and bring it back to the original temperature 
of the feed water. This property is made use of in steam 
heating, where steam of very low pressure is made to give 
up its heat through the sides of the radiating coils, the 
14 



210 COMBUSTION OF COAL. 

water of condensation returning to the boiler at a temper- 
ature approximating the boiling point, depending some- 
what on the details of the piping. 

Q. What is meant by evaporation per pound of com- 
bustible ? 

Evaporation per pound of combustible is the net evapo- 
ration per pound of coal after making due allowance for 
the ashes and the unburnt coal falling through the grates. 

Suppose 1,000 pounds of coal be fed to the furnace and 
evaporated 8,500 pounds of water, this would be an evapo- 
ration of 8.5 pounds of water per pound of coal. If 130 
pounds of ashes remain after the combustion of the coal, 
we have : 1,000 — 1 30 = 870 pounds of combustible, evapo- 
rating 8, 500 pounds of water. The evaporation would 
then be: 8,500 -f- 870 = 9.77 pounds of water per pound 
of combustible. 

Q. How may water evaporated per pound of coal be con- 
verted into equivalent evaporation from and at 212 F. 
per pound of combustible ? 

Taking a case from actual practice in which : Steam 
pressure by gauge, 95 pounds; feed water entering boiler, 
138 F. ; bituminous coal; coal fed to the furnace deduct- 
ing moisture, 6,817 pounds; ashes, 859 pounds; total 
combustible, 5,958 pounds; water evaporated per pound 
of coal, 9.04 pounds ; water evaporated per pound of com- 
bustible, 10.34 pounds. 

Example 1. What is the equivalent evaporation from 
and at 21 2° per pound of coal? 

Ninety-five pounds gauge pressure =110 pounds abso- 
lute. 

Heat units in steam no pounds absolute pressure from 
water at 32 = 1 183.5 ( see Table 28). 



EQUIVALENT EVAPORATION. 2 I I 

The water entering the boiler at 138 instead of 32 , 
there is a gain of 138 — 32 = 106 . 

Then : 1 183. 5 — 106 = 1077. 5 units of heat. 

Heat units in steam 1077.5 

Latent heat of evap. — 966 ™ " 5 ' P • 

9.04 X 1 -II 5 = 10.08 pounds of water evaporated from 
and at 21 2° per pound of coal. 

Example 2. What is the equivalent evaporation from 
and at 21 2° per pound of combustible? 

Proceed as above to obtain a multiplier, then the prod- 
uct of the water evaporated per pound of combustible into 
the multiplier will be the answer, thus : 10. 34 X 1. 1 1 5 = 
11.54 pounds of water evaporated from and at 21 2° per 
pound of combustible. 

Q. What is meant by an equivalent evaporation from 
and at 212 F.? 

Evaporation from and at 21 2° F. takes into account the 
latent heat of evaporation. The rise in temperature of 
the feed water in the boiler proceeds regularly with each 
increment of heat received by it, until the temperature 
212 is reached, at which point the water continues to 
receive heat, but records no rise in temperature until 966 
units of heat have been absorbed per pound of water, after 
which the thermometer begins to record higher tempera- 
tures corresponding to the pressure of steam. 

In making computations from and at 21 2° the process 
is divided into three parts : 

1. Heat required to bring feed water up to 212 . 

2. Heat required to convert one pound of water at 21 2° 
into steam at 21 2° — 966 units. 

3. Heat in steam at 21 2° F., or 1,146 units, to that 
corresponding to the steam pressure. 



212 COMBUSTION OF COAL. 

As water freezes at 32 ° F. this temperature is always 
to be deducted from the temperature of the feed. 

The equivalent evaporation from and at 21 2° is found 
by dividing the total heat in the steam by 966, which gives 
a multiplier by which the weight of water actually evapo- 
rated per pound of coal is to be multiplied. For example : 

A boiler evaporates S}4 pounds of water per pound of 
coal from feed water at 75 ° F., the steam pressure being 
100 pounds by gauge or 115 pounds absolute. What is 
the equivalent evaporation from and at 21 2° F. ? 

Referring to Table 28 we find the total heat required 
to generate one pound of steam from water at 32 under 
a pressure of 115 pounds absolute is 1 184.5 neat units. 
The water entering the boiler at 75 ° instead of 3 2°, there 
is a gain of 75 — 32 = 43 . Then: 1 184.5 — 43 = II 4 I -5 

1184.5 
units of heat; — >^- = 1. 182, the multiplier ; 8.5 x 1.182 

== 10.05 pounds, the equivalent evaporation from and at 
212 at atmospheric pressure. 

Q. How may the equivalent evaporation from and at 
212 be estimated, when only the total heat of combustion 
of the fuel is known? 

When the total heat of combustion of one pound of the 
combustible is known, the equivalent evaporation from and 
at 212 may be determined by dividing the number of 
heat units required to convert water at 21 2° into steam at 
atmospheric pressure. 

Example : Suppose a bituminous coal to have devel- 
oped by calorimeter test 13,200 heat units per pound, 
what would be the equivalent evaporation from and at 

1 3 200 
212 ? — ^- — 13.67 pounds of water, at atmos- 
pheric pressure. 



AVAILABLE HEAT OF COMBUSTION. 213 

Q. What is the object in reducing evaporative results 
to an equivalent evaporation from and at 212 , at atmos- 
pheric pressure ? 

Equivalent evaporation from and at 21 2° F. , at atmos- 
pheric pressure, has been accepted by engineers as being 
at once the readiest, most convenient, and most intelligible 
basis yet suggested for estimating the comparative evaporat- 
ing power of different kinds of fuel. It represents the 
weight of water which would have been evaporated by each 
pound of fuel had the water been both supplied and evap- 
orated at the boiling point corresponding to the mean at- 
mospheric pressure. 

Q. What is the ordinary rate of evaporation per pound 
of small anthracite coal when burnt in horizontal tubular 
boiler furnaces ? 

The ordinary rate of evaporation per pound of small an- 
thracite coal, from feed water at 6o° F., under 80 pounds 
gauge pressure, say 324 F., is placed by Hoadley as be- 
ing in general below 8 pounds. Indeed, 8 pounds of dry 
steam is a fair result; 8.25 is a good result; 8.5 pounds 
very good ; and 9 pounds about the best attainable, being 
rather over 10,000 thermal units, which corresponds to 69 
per cent of the full calorific power of the carbon, and is 
for coal consisting of 83.33 P er cent oi carbon a high re- 
sult. 

Q. What is the available heat of combustion? 

The available heat of combustion of one pound of any 
fuel is that part of the total heat of combustion which is 
communicated to the body, to heat which the fuel is 
burnt ; the water in a steam boiler, for example. The 
theoretical heat of any fuel is easily determined, its proxi- 
mate or elementary analysis being known; but the actual 



214 COMBUSTION OF COAL. 

available heat can be determined only by a series of more 
or less elaborate experiments or trials in actual use. 

The disposition of the heat generated in the furnace of 
a steam boiler of the ordinary horizontal tubular form set 
in brickwork, and provided with a special air-heating ar- 
rangement which lowered the temperature of the flue gases 
to about 2 1 3 F., and raised that of the air supplied to the 
furnace about 300 F. , was ascertained by Hoadley to be 
as follows : 

Per cent. 
Waste in flue gases including evaporation of moisture in 
coal and heating vapor in air when these losses are not 

separately given 5.04 

Evaporating moisture in coal 1.55 

Heating vapor in air 18 

Imperfect combustion 1.44 

Radiation and heat not otherwise accounted for 4.00 

Heating and evaporation of water 87.79 

The high efficiency here given is due in great part to 
the recovery of heat from the escaping gases and the pre- 
heating of air entering the furnace, as well as the unusual 
care and skill exercised during the test. These results 
are in percentages of the total amount of heat accounted 
for in heating and evaporating water in the boiler, and 
are fully one-third greater than obtains in good ordinary 
practice. 



CHAPTER X. 

STATIONARY FURNACE DETAILS. 

Q. What is the efficiency of a furnace ? 

The efficiency of a furnace for a given sort of fuel is 
the proportion which the available heat bears to the total 
heat generated in the furnace. By furnace is meant not 
merely the chamber in which the combustion takes place, 
but the whole apparatus for burning the fuel and transfer- 
ring heat to the body to be heated, including ash pit, com- 
bustion chamber, flues, and chimney. 

Q. What losses occur in a furnace by which its effi- 
ciency is lowered? 

The heat generated in a furnace can never be wholly 
utilized. Heat, like water or steam, must flow from a 
higher to a lower level in order to become available, and 
in any such transfer there are always losses, among which 
occur : 

Loss due to radiation of heat from the sides of the fur- 
nace. 

Loss occasioned by difference of temperature between 
the escaping gases and that of the atmosphere necessary 
to produce natural draught. 

Loss by the waste of unburned fuel falling through 
into the ash pit. 

Loss by imperfect combustion — that is, by the forma- 
tion of carbonic oxide instead of carbonic-acid gas. 



2l6 



COMBUSTION OF COAL. 



Loss by excess of air passing through the furnace, doing 
no useful work. 



Q. How is the efficiency of a steam boiler measured? 

In steam boilers 
the efficiency of the 
furnace is measured 
by the pounds of 
water evaporated 
per pound of coal 
burned on the grate, 
under known con- 
ditions. The effi- 
ciency is expressed 
in a percentage in- 
dicating how nearly 
the actual perform- 
ance attains to the 
theoretical. If the 
latter be expressed 
by ioo, the effici- 
ency will always be 
a less number. 

Suppose a coal is 
known to contain 
13,100 heat units 
by calorimeter test, 
the equivalent evap- 
oration from and 
at 212 F. would 
be 13,100 -f- 966 = 
13.56 pounds of 
water per pound of 




FURNACE DIMENSIONS. 



217 



coal. By actual test 9.25 pounds of water are evaporated 

per pound of coal. We then have : 

T^rc • 9-25 X 100 ^ 

Efficiency - — J ' — = 68.22 per cent. 

13.56 
The loss of heat in this case amounts to 31.78 per cent 
of the total heat generated in the furnace. This loss, 

PLAN AT A B 







HALF SECTION AND ELEVATIONTOF FRONT. 
Fig. 19. 

which is largely unavoidable, may be accounted for as on 
page 215. 

Good boilers, properly set and well managed, will average 
nearly the same efficiency, approximating 65 per cent. 

Q. What are the ordinary furnace dimensions for a 
horizontal tubular boiler ? 

There are no standard dimensions for boiler settings or 



218 



COMBUSTION OF COAL. 




FURNACE DIMENSIONS. 



219 



•3UOJJ JO ippTjW 


U 


fa 


O 




7 


O 
in 


O 
1 

in 


O 
vO 


1 





CO 


1 

CO 




4 uojj jo iqSpH 


* 


c 


0> 




CO 




00 


O 
1 


CI 

1 


O 





CO 

1 




7 




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jajioq uaaMjaq aandg 


s 


g 


01 


CI 


CI 


M 


CI 


CI 


N 


N 


CI 


cq cm 


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uaaMjaq jb3j ui ' ao^dg 


H 


.G* 

a 




CM 







(N 


O 

CJ 




CI 


CI 

CI 


CI 


CO 
CI 




CO 




co co 


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05 \\va\ aSpuq jo doj^ 


H 


J3 

g 


c 


O 


O 


O 


CM 


<M 


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* 


c 
fa 


H 

a* 


A 


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1 


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CM 


co 


1 


1 


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japun oj Jo'oy jo doj, 


> 


c 





CI 

in 


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in 


in 


in 

in 


in 


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in 


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XT} 




10 


CO 

in 


s 


CO 




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a 


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co 


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un 


in 








CI 


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t^ CO 


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% 


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<* 


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-t- 


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in 


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O 






CI 


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1^ co 


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japun 01 sajBjS jo doj. 


K 


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G 


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CI 





CO 
CM 


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CO 




CO 




en 




co co 


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Of 


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CI 


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CI 


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CI 


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CI 


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CO 


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h 


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a 


in 
CI 


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en 




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CO 




CO 


CO 

co 


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CO 


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© 



c 


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in 


in 


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<3- ^f 


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CO 


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1 




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1 


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V 


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^c 
A J. 

M M 


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\\eA\ iuojj jo ssaujpiqj. 


h 


.d 

u 

c 


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MMMCMdMNCMCMCMN 


■s\\eM. 
apis apisui jo ssampiqx 


' 


G 


CI 


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O 


O O 


■s^bay apis 
apisjno jo ssaujpiqj, 


fe 


J3 

G 


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co 


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co 


co 


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co co 


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c 


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r* co 



220 COMBUSTION OF COAL. 

furnaces ; the practice varies as between East and West, 
and between anthracite and bituminous fuels. A very- 
good design is shown in Fig. 20 in sectional elevation. 
This design is by the Bigelow Company, New Haven, 
Conn. A plan is shown in Fig. 1 8 and a half front eleva- 
tion and half section is shown in Fig. 19. 

The bottom of the front should set up 5 inches (2 
bricks) above the floor level. Front edge of moulding on 
bottom of front should set back 2 inches from front edge 
of brick work. Both of these details are shown in Fig. 
20. All measurements given in Table 26 are based on 




Fig. 21. 

the front being set as stated above. Ash pits under the 
grates should slope down from bottom of ash door to floor 
level. The front wing brackets on the boiler should rest 
directly on the wall plates so that all the expansion will 
go to the rear, provision being made for this longitudinal 
movement by rollers placed between the rear wing brack- 
ets and the wall plate underneath. 

The inside walls in this design taper, beginning at the 
top of the grates and extending to a line 4 inches under 
the bracket, giving a space of 2 inches between the side 
of boiler and inside of wall, as shown at Z in Fig. 19. 
The inside wall should close in to the boiler on a line 2\ 
inches (1 brick) under the brackets. The outside and in- 
side walls have a 2- inch air space between them. Head- 
ers should be run from wall to wall, say, every 18 inches, 
but not tied together. Fire brick in the furnace should 
be laid with a course of headers every five or six courses, 



RENTS BOILER SETTING. 22 1 

so that portions of the wall can be easily taken out and 
repaired. Boilers should be covered on top with some 
non-conducting material ; if with a brick arch, an air 
space of 2 inches should be left between the boiler and 
the brick work. The arch tee bars for back connection 
should be lined with fire brick laid endwise before the 
bars are placed in position, as in Fig. 21. 

Q. What are the details of construction of Kent's fur- 
nace for steam boilers ? 

This design of furnace, shown in longitudinal sectional 
elevation in Fig. 22, is intended especially for furnaces 
which use bituminous coal, lignite, peat, tan bark, or other 
fuel which contains large quantities of tarry or gaseous 
matter, and which in burning distils a large amount of 
combustible gases. 

The fire chamber, built of brick, extends out in front of 
the boiler; in it the fuel is burned, either on the ordinary 
grate bars, or by any one of the numerous stokers now in 
the market. A bridge wall is provided at the end of the 
grates, over which the gaseous products of combustion pass 
on their way to the heating surfaces of the boiler. Two 
wing walls are built parallel to and at some distance in the 
rear of the bridge wall, as shown in Fig. 23. A gas-mix- 
ing chamber is thus formed between the bridge and wing 
walls. The combustion chamber is the next into which 
the gases travel from the passage between the wing walls. 
In this chamber are several piers of fire brick projecting 
in front of the wall at the rear of the combustion chamber. 
The remaining details of the setting are those of the Bab- 
cock and Wilcox boiler, and readily understood. 

In the operation of this furnace, with ordinary grates 
and with bituminous coal or other gaseous fuel, the alter- 



222 



COMBUSTION OF COAL. 




KENT S BOILER SETTING. 



223 




nate method of feeding coal is preferred — that is, the fresh 
coal is spread alternately on the right and left sides of 
the grate, an interval of some minutes of time elapsing 
between the feeding 
on the right and on 
the left side. Immedi- 
ately after fresh coal 
is put on one side of 
the furnace dense 
smoky gases arise 
from it, which in the 
ordinary boiler setting 
would pass out of the 
chimney unburned, 
since in the ordinary 
setting there is no 
means provided for 
mixing with them an 
abundant supply of 
highly heated air; but 
in this furnace such 
air is supplied through 
the bed of partially 
burned and very hot 
coal and coke on the 
other side of the 
grate. The two cur- 
rents, one of cool 
smoky gas arising 
from the fresh coal on 
one side of the grate 
and the other of clear 
and very hot gas con- 






II 



m] 



bBaWVHO 
3NIXIW SVO 



H" 



r H 



H 



■ 4 , , .■■. v l oy^^^ 



224 COMBUSTION OF COAL. 

» 

taining a large excess of air, pass together over the bridge 
wall and are compelled by the wing walls to change 
their direction and to mix together in the gas-mixing 
chamber and in the contracted vertical passage between 
the wing walls. The combustion of the unburned gas 
is further rendered more certain and complete by passing 
through the large combustion chamber, whose walls, to- 
gether with the fire-brick piers, are in a highly heated 
state and perform the functions of a regenerative furnace 
— that is, they absorb heat from the burned gases at such 
times as they are most intensely heated, and radiate or 
give up heat at such times as the gases are not so hot, as 
during the first minute after feeding fresh coal, when 
there is a great excess of freshly distilled and rather cool 
gases. 

By this means complete combustion of the smoky gases 
is secured in the combustion chamber when reasonable 
care is used by the fireman, and the resulting thoroughly 
burned products of combustion are then in the right con- 
dition to be allowed to traverse the gas passages through 
the tubes and give up their heat to the boiler. 

Q. What are the details of construction of the O'Brien 
and Pickles down-draft furnace ? 

A longitudinal section of this furnace is shown in Fig. 
24. It consists, in common with down-draft furnaces 
generally, of two grates, an upper and a lower one ; the 
raw fuel being fed to the upper grate where it burns, 
the draft passing in through openings in the upper fire 
door, down through the fuel on the upper grate, and under 
the inner manifold shown immediately over the bridge 
wall. This manifold has communication with the boiler 
by the elbow and connections clearly shown. On top of 



DOWN-DRAFT FURNACE. 



225 



the inner manifold is a fire-brick partition closing the 
space between it and the boiler, and compelling the 
draft to flow downward. 

The front manifold is placed directly under the front 
end of the boiler, and between it and the inner manifold 




BORMA.r k CO., EN5I 



Fig. 24. 



are tubular grates, through which water circulates from 
one manifold to the other. 

Any fuel that falls through the upper grate is caught 
by the lower one, upon which it burns, the draft pass 
ing in through the lower or ash-pit door, up through 
the grate and beneath the inner manifold. The grate 
bars for the lower series are of the ordinary pattern, 
the spaces being much finer than obtain in the upper 
series. 

i5 



226 



COMBUSTION OF COAL. 



Q. What is the construction and operation of the Bab- 
cock and Wilcox automatic stoker? 

This is an endless-chain grate stoker. It is shown in 
perspective in Fig. 25, wholly withdrawn from the furnace. 
The grate is made up of a series of short cast-iron bars 
linked together and engaging sprockets at the front and 
rear, by the movement of which the upper portion of the 
grate is carried constantly forward. The coal is fed 




Fig. 



through a hopper of the full width of the grate, and the 
depth of the layer is regulated by a door which can be 
lifted or lowered. The coal is ignited near the front and 
is carried slowly backward, the speed of the grate being 
adjusted so that the time of travel is sufficient for the 
complete combustion of the fuel, the ash and refuse being 
carried over at the back end and falling into the ash pit. 
A fire-brick arch at the front end of the furnace facilitates 
the coking of the fresh fuel as it enters, and the combus- 



RONEY S MECHANICAL STOKER. 



227 



tion of the volatile gases evolved. The apparatus as a 
whole is mounted on wheels running on rails placed on the 
sides of the ash pit, and can be drawn out clear of the 
boiler for inspection or repairs, or to give room when nec- 
essary to replace furnace linings. 

Q. What is the construction and operation of the Roney 
mechanical stoker ? 

This stoker is shown in connection with a horizontal 
tubular boiler setting in Fig. 26 and in detail in Fig. 27. 




Fig. 26. 

It consists of a hopper for receiving the coal, a set of 
rocking stepped grate bars, inclined at an angle of 37 
from the horizontal, and a dumping grate at the bottom of 
the incline for receiving and discharging the ash and 
clinker. 

The coal is fed on to the inclined grates from the hop- 
per by a reciprocating pusher, which is actuated by the 
agitator and agitator sector. The grate bars rock through 



228 



COMBUSTION OF COAL. 



an arc of 30 , assuming alternately the stepped and the 
inclined position. They receive their motion from the 
rocker bar and connecting rod, and these, with the pusher, 
are actuated by the agitator, which receives its motion 
through the eccentric from a shaft attached to the stoker 
front under the hopper. The range of motion of the 



BOILER FRONT 
TILE-CLAMP 

-COKING-ARCH 



AGITATOR 
FEED-WHEEL' 



AG1TRTOR SECTOR 



SHEATH-NUT 



SHEATH 
LOCK-NUTS 




Fig. 27. 



pusher is regulated by the feed wheel from no stroke to 
full stroke, and the amount of coal pushed into the fur- 
nace adjusted, according to the demand for steam. The 
motion of the grate bars is similarly regulated and con- 
trolled by the position of the sheath-nut and lock-nuts on 
the connecting rod. Each grate bar is composed of two 
p^rts: a vertical web provided with trunnions at each 
end, which rest in seats in the side bearers, and a fuel 



WILKINSON S MECHANICAL STOKER. 



229 



plate ribbed on its under side, which bolts to the web. 
These fuel plates carry the bed of burning coal, and be- 
ing wearing parts are made detachable to facilitate repairs. 
The webs are perforated with longitudinal slots, so placed 
that the condition of the fire can be seen at all times with- 
out opening the doors ; and free access had to all parts of 
the grate to assist, when necessary, the removal of clinker. 
For bituminous coal a coking arch of fire brick is sprung 
across the furnace, covering the upper part of the grate 
and forming a reverberatory furnace and gas producer, 
whose action is to coke the fresh fuel 'as it enters and re- 
lease its gases. These, mingling with the heated air sup- 
plied in small streams through the perforated tile above 
the dead plate, are quickly burned in the large combustion 
chamber above the bed of incandescent coke on the lower 
part of the grate. 

Q. What is the construction of the Wilkinson auto- 
matic stoker ? 

Three views are shown of this stoker, Fig. 28 being a 
front view, Fig. 29 the furnace view, Fig. 30 a sectional 




Fig. 28. 



230 



COMBUSTION OF COAL. 



elevation, to which has been added a rtsumt of the process 
of combustion. The grate bars are hollow, as shown in 




Fig. 29. 



Fig. 30. They are placed side by side and inclined toward 
the bottom of the furnace at an angle suited to the repose 




STEAM 

OXYGEN 

"HYDROGEN 

ALL BURN AS GAS 

/ ®>y 

AIR ) ^ 6y cl L '^ s 

OXYGEN \ °*OVX 

nitrogen' 
onlyV b combustible 



COMPOSITION OF WATER GAS 

carbonic oxide, hydrogen 



Fig. 30. 



AYRES AND RANGER STOKER. 23 1 

of the fuel, and they are so constructed as to admit of suffi- 
cient air through the fire to the combustion chamber. 
The lower ends of these grates slide upon and are sup- 
ported by a cast-iron box. This box has finger grates, 
about 1 5 inches long, secured to its rear face. Through- 
out the inclined length of each grate is cast a succession 
of steps. Through the rise of each step a vent of about 
Y± X 3 inches is provided to admit air through the fire to 
the combustion chamber. A continuous back and forth 
motion is given the grates for the purpose of maintaining 
a uniform thickness of fire by a gradual descent of the 
fuel from the top to the bottom of the grate, depositing 
the clinker and ash on the stationary grate shown project- 
ing from the cast-iron box forming the lower bearing bar 
at the ash pit. The accumulated ash is pushed off this 
stationary grate into the ash pit by the reciprocating mo- 
tion of the bars, to be removed in the usual manner. 

The blast is saturated steam through a nozzle of -J-g-inch 
diameter, giving an induced current of air controlled by a 
regulating valve. 

The motor for operating the grates may be either hy- 
draulic or steam attached to each stoker, or a small engine 
may be employed for operating several stokers. 

Q. What are the details of construction of the Ayres 
and Ranger mechanical stoker ? 

This stoker is shown in connection with the flue of an 
internally fired boiler in Fig. 31; a front elevation is 
shown in Fig. 32. This stoker belongs to the class known 
as coking stokers. The coal is fed into the hopper shown 
at the front end of boiler; at the bottom of this hopper is 
a series of propeller- shaped blades joined to and radiating 
from a sleeve mounted on a shaft, which is caused to ro- 



232 



COMBUSTION OF COAL. 



tate intermittently at any desired speed ; and by these the 
coal is propelled through an opening in the furnace, on to 
an inclined guide plate, and from this upon a perforated 
dead plate below, and by this means the coal is equally 
distributed across the front of the furnace, forming a bank 
or ridge of coal to be there coked, and to be then carried 
by moving fire bars to the back of the furnace. The fire 
bars are so arranged that every other one is stationary ; 
the moving bars are actuated by a cam or other device by 
which an up-and-down vertical movement may be imparted 
to the front end of the bars. This cam in continuing its 
movement then engages the .end of the moving bar and 






Fig. 31. 

pushes it in the direction of the arrow, Fig. 31. The end 
of the bar being tapered rides up on the roller at the rear 
of the furnace, and thus raises that end of the bar. By 
the return motion of the cam the bar is brought back to 
its normal position. This continual motion of the mova- 



THE MURPHY FURNACE. 



"233 



ble bars carries the fuel gradually from the front to the 
rear of the furnace. It also serves to break up the clink- 
ers, clear the air spaces, ultimately depositing the ex- 
hausted portion of the fuel 
into the ash or clinker pit at 
P the end of the bars in the 

It N / Jl usual way. 

Q. What are the principal 
details of the Murphy furnace ? 

A cross-sectional elevation 
of the Murphy self-feeding 
furnace is shown in Fig. 33. 
The grate bars are arranged 
on opposite sides of the fur- 
nace chamber and incline 
downwardly toward the cen- 
tre, the fuel being introduced 
at the top and fed down tow- 
ard the middle, in which there 
is a device for mechanically removing the clinkers. A fire- 
brick arch spans the combustion chamber. A coal maga- 
zine is located at each side of the furnace and is provided 
with discharge openings and coal pushers. The latter 
have a reciprocating motion imparted to each by a rock 
shaft, rack, and pinion. 

The inclined grate surface is composed of stationary and 
movable grate bars, alternately placed. The upper ends 
of the stationary grate bars abut against a compensating 
plate, which permits the bars to expand readily with the 
heat. The movable grate bars are connected to vibrating 
levers, from whence they derive their motion. In connec- 
tion with this motion the movement of the rock shaft im- 




234 



COMBUSTION OF COAL. 



parts motion to the coal pushers in a manner to feed the 
coal just in proportion to the requirements of the furnace. 
The crushing and removal of the ashes and clinkers is 
effected by a clinker bar at the bottom of the grates. The 
clinker bar is provided on the outside with teeth which 




_L„_ 



w&'/xw&y/ /W* 



W/^^^V'*\v/W'A^WMW>W<W^'&>*li»'- 



Fig. 



extend spirally around the bar, and the approximate inner 
edges of the grate bearers are provided with similar teeth 
to aid in crushing the clinkers when the clinker bar is 
rocked. 

The furnace is especially adapted for the use of small 
sized bituminous coal and slack, which is put into maga- 
zines at the side of the combustion chamber. Air is ad- 



THE AMERICAN STOKER. 235 

mitted through a register at the front, passes through flues 
up over the arch, and there takes up heat from the front, 
arch, and arch plate, passing down through the small 
openings in the arch plate to the coking fuel. It is 
claimed that this furnace has a coking capacity sufficient 
to feed 50 pounds of coal per square foot of grate per 
hour. 

On the side of a battery of boilers is placed an engine 
with proper gearing for operating a reciprocating bar across 
the outside of the entire front, and to which all the work 
ing parts are attached by links. 

Q. What is the construction and operation of the Ameri- 
can stoker? 

This stoker belongs to the not very numerous class of 
underfeeding devices. The illustration Fig. 34 shows it 
in longitudinal section, and Fig. 35 in cross-sectional ele- 
vation. The stoker consists of a coal hopper, a conveyor 
pipe, a screw conveyor, a coal magazine under the furnace 
level, a wind box, and a reciprocating piston motor with a 
ratchet-feed attachment for operating the screw conveyor. 
The rate of feeding coal is controlled by the speed of the 
motor, this being effected by the simple means of throt- 
tling the steam in the supply pipe to the motor. 

The coal is fed into the hopper either by hand or by 
overhead conveyor mechanism. It descends of course into 
the receptacle below, in which is contained the screw 
which conveys it into the magazine in the furnace proper. 
The continuous supply causes the coal thus fed to over- 
flow on both sides, and spread upon the side grates, shown 
in Fig. 35. As the fresh coal approaches the fire in its 
upward course it is slowly roasted or coked. The gases 
released from the coal mingle with the incoming air 



236 



COMBUSTION OF COAL. 



through the tuyeres and are burned, leaving only the in- 
candescent coke for delivery on the side grates. 

The non-combustible ash and clinker is deposited on the 
side grates by the constant upward feeding of the coal. 
One open grate against each wall admits air mixed with 




Fig. 34. 

the exhaust steam from the motor, which serves to prevent 
the clinker sticking to the walls. To clean, a slice bar is 
run along over the grate, the clinker raised and drawn out 
with a hook. The central part of the fire is never dis- 
turbed, as the constant feeding does all the stoking neces- 
sary. The fire doors.are never opened except when clean- 
ing. 

This stoker requires a blower for supplying the air nee- 



THE JONES UNDERFEED STOKER. 



237 



essary for combustion, the air pressure varying from 1 to 
1 Y? ounces, depending upon the quality of fuel and depth 
of fire. The latter is ordinarily from 14 to 18 inches 
thick above the tuyere blocks. 







^s 







Q. What is the construction and operation of the Jones 
underfeed mechanical stoker ? 

This stoker is shown in sectional elevation in Fig. 36, 
and in cross section on the line A-B in Fig. 37. The 
stoker consists of a steam cylinder or ram, with a coal hop- 
per, outside of the furnace proper; a retort or fuel maga- 
zine inside the furnace, on the sides of which are placed 
tuyere blocks for the admission of air. The retort also 
contains at its lowest point an auxiliary ram or pusher 



2 3 8 



COMBUSTION OF COAL. 



which causes the coal to be evenly distributed. This 
pusher is in a position where the fire never reaches. 

The retort is first filled with coal, on a level or a little 
above the tuyere blocks. The fire is then started along 
each side of the retort, the air chambers reaching to the 
tuyere blocks being opened. As soon as the fire is well 
under way, the air chamber opening is closed and the 
blower started ; the fire will then be built up very rapidly. 







c — — - - - • - 



— -■ "' '■" ■*—--— ->--- - ■ --- -. U_„ — -_^>.- -.:— 




□DQDDDDD 



A 



n 



QNE BLOCK IN PLACE 



BQQ 



Fig. 36. 



Coal being in the hopper, and the ram plunger on its 
forward stroke, when more coal is needed the plunger is 
shifted back by moving the lever, coal then falls in front 
of the plunger, steam is admitted to the cylinder and the 
plunger forced forward, pushing the coal into the retort. 
Coal is pushed into the retort as needed to replenish that 
consumed. 

Air at low pressure is admitted into the air chamber 
and through the tuyere blocks, over the top of the green 
fuel in the retort, but under and through the burning fuel ; 
the result is that the heat from the burning fuel over the 
retort slowly liberates the gas from the green fuel, this 



THE M 1 CLAVE GRATE. 



239 



gas being thoroughly mixed with the incoming air before 
it passes through the burning fuel, resulting in a bright, 
clear fire, free from smoke. The retort being air tight 
from below, and the fuel being in a compact mass, the 
air moves upward and combustion takes place only above 
the air slots. The retort is thus kept cool and not subject 
to the action of the fire. The incoming fresh fuel from 
the retort forces the resulting ash and clinker over the top 
of the tuyere blocks on to the side plates, from which they 




CROSS SECTION 
LINE A-B 



can be easily removed at any time without interfering 
with the fire in the centre of the furnace. 

Q. What is the construction of the McClave grate ? 

This grate is shown in Fig. 38, which represents the 
shaking movement, and Fig. 39, which represents the cut- 
off movement. The shaking movement is adapted for 
breaking up a soft coal fire when it cakes, or to remove 
fine ashes from a hard coal fire when there is but little or 
no clinker formed. In this movement there is no increase 
of openings during the operation, the bars keeping equi- 
distant from each other in their travel from the normal 
position downward and return. 



240 



COMBUSTION OF COAL. 



The cut-off movement is used principally for fine an- 
thracite fuel, such as culm, buckwheat, and pea coal. 
Small anthracite fuels should not be shaken or stirred up 




in any manner until it becomes necessary to give the fire a 
thorough cleaning. It should then be cleaned as quickly 
as possible. For all free-burning varieties of coal that do 
not produce large slabs of clinkers this movement removes 




Fig. 39. 



the clinkers and ashes from the bottom of the fire quickly 
and thoroughly without opening the fire door. 



THE FISHER BAGASSE FURNACE. 24I 

Single lever connections are used for grates less than 5 
feet in length, and the width of the grates is generally 
made in two or more rows. To clean a fire when the fuel 
clinkers badly, the unconsumed fuel of one row can be 
shoved over on the other row, and with the full cut-off 
movement the clinkers and ashes can be cut down into the 
ash pit ; then shove all the unconsumed fuel on to the 
clean row of bars and cut the clinkers down the same as 
before; then redistribute the unconsumed fuel over the 
whole grate. 

Q. What are the details of construction of the Fisher 
apparatus for feeding bagasse to steam boiler furnaces? 

The feeding of bagasse to a boiler furnace by Fisher's 
method is shown in Fig. 40, which consists of an inclined 
chute down which the bagasse is fed. At the lower end 
and near the furnace front is a roller having radial blades, 
which roller is driven by any suitable mechanism. Be- 
tween this roller and the furnace front is a perforated 
steam or air-blast pipe extending across the chute. There 
is attached to the furnace front a pivoted door extending 
over both the perforated blast pipe and bladed roller. A 
second door is hinged to the one just referred to and is 
adapted for closing the chute. These doors fit in between 
the sides of the chute, and thus being practically air tight 
prevent the escape of any sparks which might otherwise 
fly out from the mouth of the furnace. 

The bagasse after being discharged upon the chute 
slides down to the bladed roller, which is constantly rotat- 
ing and which feeds the bagasse along over the perforated 
pipe, from which latter let it be supposed there is escaping 
a blast of air or steam under pressure. As the material 
16 



242 



COMBUSTION OF COAL. 



passes over this perforated pipe, the blast of air or steam 
escaping therefrom lifts the material and scatters it in all di- 




FlG. 40. 



rections over the furnace grate, thus rendering it impossi- 
ble for any large mass of the material to fall in one spot 
and there retard combustion. Besides the function of 



HEGGEM S FIRE BOX. 



243 



scattering the finely divided particles of the fuel over the 

grate bars the blast of steam or air will create a better 

draft in the furnace, and thus materially assist combus- 
tion. 

Q. What are the details of construction of Heggem's 
boiler for burning straw ? 

This boiler is particularly adapted for agricultural use, 
and is of the usual portable type; but the object of the 




FIG. 4 



present design is that the boiler shall be capable of burn- 
ing alternately either straw or solid fuel, as may be desired, 



244 



COMBUSTION OF COAL. 



the fire box being provided with a draft apparatus that may 
be made applicable in each case for the particular fuel 
burned. This boiler is shown in sectional elevation in 
Fig. 41, and shows the arrangement of dampers when 
using straw as fuel, in which case a funnel is fitted to the 
usual fire-door opening; this funnel being provided with a 




tmmmsmmm 



Fig. 42. 



hinged door, the free end of which is adapted to rest con- 
tinually against the straw as it is forced into the fire box. 
The damper under the barrel of the boiler being raised, 
as shown in the engraving, causes the draft to flow into 
the fire box, as indicated by the arrows, causing the 



ALLEN AND TIBBITTS FURNACE. 245 

straw to burn at the ends, as it is forced in through the 
funnel. 

Fig. 42 shows the same boiler with the straw-feeding 
funnel removed, the regular fire door in place, the closing 
of the damper under the barrel of the boiler and the open- 
ing of the damper or ash-pit door under the fire door, and 
the use of coal as fuel. 

Q. What are the details of construction of the Allen 
and Tibbitts apparatus for feeding comminuted fuel to 
furnaces ? 

A vertical section of a steam boiler furnace showing the 
apparatus in operation is given in Fig. 43. The operation 
consists in spraying the fine particles of fuel into the fur- 
nace by means of rapidly revolving distributing rollers. 
On the circumference of the rollers are provided ribs, 
which are fixed in diagonal lines from the middle to the 
ends of the rollers. These rollers are given rapid revolv- 
ing motion, and are designed for throwing the fine fuel 
into the furnace by their centrifugal force. There is a 
rotary vertical spiral conveyor enclosed in a pipe and 
stepped in the bottom of a coal supply pit in the floor in 
front of the furnace. At the top of this pipe are branch 
pipes leading from the head of the vertical pipe and ex- 
tending over and communicating with the interior of the 
boxes containing the revolving rollers, by which the fuel 
is delivered into the furnace in a shower or spray in the 
upper part of the combustion chamber, so that the parti- 
cles will catch fire in transit and be consumed or partly 
consumed before falling upon the fire floor, the draft 
being through the grated doors, thus avoiding the opening 
of the doors for feeding purposes. In instances when the 
fire dust is used no grate bars need be employed in the 



246 



COMBUSTION OF COAL. 



floor; but as a general rule, when the coarser grades of 
fuel are used, grate bars should be used for providing a 
draft upward into the fire. 




Fig. 43- 



THE ROGERS FURNACE FEEDER. 247 

Q. What are the details of construction of the Rogers 
apparatus for feeding fine fuel ? 

This apparatus is designed for feeding fine fuels, such 
as rice hulls, cotton hulls, sawdust, etc. A cross section- 
al elevation of a boiler furnace with the apparatus also in 
section is shown in Fig. 44. This apparatus consists of a 
hopper placed at the side of the furnace and near the front 
end of the boiler, a steam blast pipe, and a nozzle for dis- 
tributing the fuel over the grate. This nozzle is made with 
one straight side placed parallel to the boiler front ; the 
opposite or rear side is formed obliquely toward the bridge 
wall. A sliding gate opens or closes communication be- 
tween the hopper and the furnace. For the purpose of 
superheating the steam used in the blast nozzle, its supply 
pipe passes along the side of the boiler, to the rear and 
return, thence into the discharging pipe. 

The fire may be started in the furnace in any approved 
way and with any desired fuel. The sliding gate is then 
opened, as is also the steam cock, whereupon the hulls or 
sawdust resting in the hopper and chute are caused by the 
suction of the steam blasts to discharge through the nozzle 
into the furnace, over the fire bed in thin sheets, in the 
manner illustrated in the engraving. Should the supply 
become excessive, the sliding gate and steam cocks are 
closed. When the gate is closed, no back blast through 
the hopper can occur, and danger from fire in the hopper 
or chute will be prevented at such times as the feeder 
may not be in use. 



248 






COMBUSTION OF COAL. 




Fig. 



CHAPTER XL 

LOCOMOTIVE FURNACE DETAILS. 

Q. What are the ordinary limitations of a locomotive 
fire box ? 

The width of the fire box is limited to the distance be- 
tween the frames inside of the driving wheels ; the neces- 
sary outside clearance ; and the thickness of the two water 
legs from out to out. The inside width will be about 
41^2 inches. The length of the fire box will depend 
somewhat upon the size and type of the boiler and the 
arrangement of the axles for the driving wheels ; in gen- 
eral, this length is limited to about 10 feet. 

Q. What are the objections to a long fire box? 

Mainly the inconvenience occasioned in firing, as the 
proper distribution of coal by means of a hand shovel, 
through an opening some 12 x 16 inches, to a point, 10 
feet distant, is one requiring great skill. In the case of 
caking coals, the longer the fire box the more difficult is 
the task of breaking up the fire through the fire door open- 
ing. 

Q. What are the advantages of large grate area ? 

It lowers the rate of combustion, and thus permits the 
use of inferior grades of fuel which could not be economi- 
cally employed in locomotives having a small ratio of grate 
area to total heating surface. 



2 50 COMBUSTION OF COAL. 

For locomotives of great power, a large grate surface is 
essential, even under the highest economical rates of com- 
bustion, and for this reason boilers with an extended grate 
surface, such as the Wootten, become more or less a 
necessity. 

Q. What is the rate of combustion in locomotive boiler 
practice ? 

The rate of combustion will vary with the type and size 
of locomotive, the contour of the railroad, the weight and 
speed of trains, etc. From 80 to 125 pounds may fairly 
represent ordinary practice, but the extreme limit to 
economical combustion appears to be about 150 pounds 
per square foot of grate surface per hour ; a higher rate of 
combustion is apt to lift the coal from the grates and loss 
of efficiency occurs. 

Q. What is the special function of the fire-brick arch 
in locomotive fire boxes ? 

The supplying of fuel in a locomotive fire box is an 
intermittent operation; consequently, the temperature of 
the fire is constantly changing from high to low, depend- 
ing upon the quantity of fresh fuel laid upon the fire. 
The fire-brick arch gets white hot by reason of its posi 
tion over the fire; this stored -up heat assists in driving 
out the volatile combustible matter in the fuel ; as there 
is almost always an excess of air passing through the fire, 
the gases driven off by the combined heat of the fire and 
the incandescent fire-brick arch are raised to a very high 
temperature while in intimate contact and mixture, com- 
bustion ensues under the most favorable conditions for 
completeness, economy, and high temperature. The prod- 
ucts of combustion are then diverted to the rear of the 



BRICK ARCH FOR LOCOMOTIVES. 



251 



fire box, where a change of direction is necessary before 
passing forward toward the tubes. 

By its use the combustion of bituminous coal is im- 
proved, smoke is prevented, cinder sparks are arrested, the 
flame and gases from the fire are cleaner, that is, carry 
less soot and impurity, the dragging of the fire is reduced, 
and the fuel is, therefore, used in a more economical man- 
ner than in the ordinary fire box. 

Q. What is the usual construction of the brick arch in 
locomotive fire boxes? 

The brick arch consists usually of fire-brick tiles laid on 
tubular bearing bars. Fig. 45 shows one form of con- 




struction in which the tubular bearing bars are secured to 
the tube sheet at one end, the other end being secured to 
the crown sheet. There is a water circulation through 
these pipes which prevents their burning out in the fur- 
nace. Another design is shown in Fig. 46, in which the 
tubular bearing bars extend the whole length of the fire 
box, the water connection being such that a constant cir- 
culation is had. The fire-brick tiles extend across the 
fire box from side to side ; the arch is lowest next the tube 



252 



COMBUSTION OF COAL. 



sheet, and inclines upward as it approaches the rear end 
of the fire box ; the length of the arch and angle of incli- 
nation vary with the size of the fire box, but the rear end 
must always be high enough properly to feed and care for 
the fire. 

Another method of construction is to build a curved 
arch across the fire box from side to side, as shown in Figs. 
68 and 69. 

Q. Does the brick arch cause leaky flues? 

This question, raised by M. D. Corbus, in Locomotive 
Engineering (January, 1900), is accompanied by the state- 




FlG. 46. 



ment that practice has demonstrated positively in some 
locomotives that a brick arch in a fire box causes the flues 
to leak, beginning directly after the arch is put in, and the 
engine does hard labor. The arches as described by him 
are in three pieces, placed lengthwise in the fire box and 
resting on four plugs screwed into the side sheets. The 
brick is cut away next the flue sheet and side sheets, to 
allow cinders and fine coal to drop down to the grates; 



FIRE-BRICK ARCHES. 253 

only about 6 inches of each corner of the arch rests against 
flue sheet, from 6 to 10 inches below the flues. 

In replying to the above, George B. Nicholson, through 
the same journal, asks: What causes flues to leak? Is it 
not a too rapid expansion and contraction of the metals of 
the flue sheet and flues ? Then will a brick arch cause this 
expansion and contraction ? Suppose an engine with a 
brick arch to be fired up and gradually heated to the work- 
ing point, the heat of the fire box probably being between 
2,000° and 2,500° F. The brick arch attains and will hold 
this temperature for a considerable time after the fire has 
been knocked out of the engine. Now this brick arch, 
representing an almost fixed number of heat units, is 
placed within from 4 to 6 inches of the flues and flue 
sheet; there is nothing about this that is likely to cause 
an undue variation in the temperatures of either. The 
real reason is that the fire is not maintained under the 
flues as it should be, quite frequently getting into such a 
condition that cold air is drawn rapidly through the grates 
and up through the flues ; the flow may last but a few 
seconds, still long enough considerably to reduce the tem- 
perature of the metals ; it is then cut off by the applica- 
tion of a shovelful of green coal when the great, almost 
permanent heat of the arch will cause the temperature to 
rise much more rapidly than would be the case in waiting 
for the coal to ignite, and the heat of the fire cause the 
change. This, being repeated from time to time, starts 
the flues to leak; the engine is brought in, the arch 
knocked out and condemned, when the trouble was not the 
arch, but in the method of firing. 

If brick arches are put in with just enough space be- 
tween the arch and flues to permit of the free circulation 
of the gases, and at the same time not to allow the opening 



254 



COMBUSTION OF COAL. 



to become blocked with cinders, and high enough that a 
good fire can be kept under them with reasonable ease, a 
decided improvement in steaming qualities will be secured, 
as well as lessened fuel consumption and increased life of 
the flues. 

Q. What kind of grates are commonly supplied locomo- 
tive fire boxes ? 

The present practice is confined almost wholly to shak- 
ing grates, because of the facility afforded for cleaning the 
fire on the road, and for dumping the contents of the fire 
box at the end of the trip. 

Q. What is the construction of the tubular water 
grate ? 

The water grate consists of tubes extending from the 
tube sheet in the fire box to the opposite sheet at the rear, 




Fig, 47, A.— Plan. 



as shown in Fig. 47. These water tubes are placed side by 
side across the width of the fire box with such interval 
between them, for air space, as shall best adapt them for 
the fuel to be used ; they usually incline slightly, to give 



PLAIN FIRE GRATE. 



255 



better circulation than when laid horizontally. The circu- 
lation of water through these tubes prevents their burn- 







'<WA 


SB 


OOOOOOO' 00000 


\,/,/A 


S2Z 


000 00 000 0000 


/mA 


J™ 




.ijj. 


OOOOOOOOUOO 


-£",, it, 



Fig. 47, B.— Longitudinal Section. 



CJ 



OOOO 



ob oo°0(Po o o o o 



OOOOO 



OOOO 



OOOOO 



Fig. 47. C— Cross Section. 

ing out, unless they become filled with scale, which is a 
not infrequent occurrence. 

Q. What are the ordinary details of a locomotive fire- 
box grate ? 

For coal-burning locomotives the grates in use include 
the plain grate bars with drop plate for the removal of 
ashes, etc. , at the end of the run ; such a grate is shown 
in Fig. 48, in which 1 represents the grate bars; 2, a 
dead plate; 3, the end holder; 4, the drop plate; 5, the 
drop-plate handle; 6, the drop-plate handle supports; 7, 
the drop-plate shaft ; 8, the drop-plate shaft bearing. 

Shaking grates are now in very general use in locomo- 
tive practice. The ordinary details are much the same 
for all grates, but there is a wide diversity in minor de- 
tails. Fig. 49, from Grimshavv's " Locomotive Catechism," 
shows the salient points of shaking-grate mechanism as 



256 



COMBUSTION OF COAL. 



ordinarily applied to locomotives, in which 1 represents a 
series of grates, each consisting of a central bar with fin- 
gers passing each other, with suitable air space between, 



sssssgssss 



i_n_n 



«v* 



^TmT 





SHAKING GRATE, 



257 




-luo^jr 



the whole forming when in normal condition a flat surface 
for the fuel; 2, the frame carrying the rocking grates; 3, 
a connecting bar by which all the rocking-grate bars are 
17 



258 COMBUSTION OF COAL. 

operated simultaneously; 4, a lever extending up into the 
cab for operating the grates; 5, a connecting link; 6, a 
lever handle, removable ; 7, a drop plate to facilitate clean- 
ing the fire box of unburned fuel, ashes, and clinkers ; 8, 
drop-plate rod; 9, drop-plate crank; 10, drop-plate crank 
handle ; 11, drop-plate crank bearing. 

Q. How do anthracite and bituminous coals compare in 
evaporative power in locomotive practice ? 

It would naturally be expected that as anthracite is 
richer in carbon than the average quality of bituminous 
coal (82 and 58 per cent, respectively, being the mean of 
several analyses), anthracite coal should yield a higher 
evaporative duty. Service trials, however, prove that the 
difference existing is wholly in favor of bituminous coal, 
fully bearing out the assertion frequently made by firemen, 
that a tender load of soft coal will go further than a like 
quantity of hard coal. 

Recent experiments on the N. Y., L. E. and W. R.R., 
with high-class modern locomotives, gave evaporative rates 
from and at 21 2° F. per pound of coal, of 5.68 for an- 
thracite and 7.2 for bituminous. 

The theoretical evaporative power of anthracite coal con- 
taining 82 per cent of carbon and 7.4 per cent of volatile 
matter is 15.25 pounds, from and at 21 2° F. , while that of 
bituminous coal containing 58 per cent of carbon is about 
1 2 pounds, due allowance being made for other component 
parts (Dixon). 

Q. Is the ordinary operation of a locomotive boiler 
favorable to high duty? 

The operation of a locomotive boiler militates against a 
high duty; its exposure to constantly changing atmos- 



SINGLE-SHOVEL FIRING. 259 

pheric conditions cannot but be a fruitful source of loss, 
and the remarkable differences of opinion with regard to 
boiler proportions, grates, and draft appliances, prove that 
some boilers, at least, do not have a fair chance to per- 
form their functions in an economical manner. The effi- 
ciency of a well-designed bituminous coal-burning boiler 

7.2 X 100 
may be taken at : = 60 per cent, which, consid- 
ering the disadvantages under which it labors, is a cred- 
itable figure (Dixon). 

Q. What evaporative performances are had of locomotive 
boilers in practice ? 

From a number of locomotive tests made, rather to test 
the coal than to test the locomotive, evaporations are shown, 
according to W. O. Webber, from 6^ to 8}4 and 9 pounds 
of water per pound of combustible, and the fuel consumed 
per square foot of grate surface 90 pounds, and running 
from there to 136 pounds. These engines were small; 
one on which most of the tests were made was an engine 
with a fire box only 3 feet wide by 5 feet long, with a 
boiler 42 inches diameter, 114 2-inch flues, 2^ inch ex- 
haust nozzle. Engine 15* x 22", and only 740 total 
square feet of heating surface. The standard American 
locomotive will develop on an average a horse-power for 
each 27 pounds of water evaporated when not overloaded; 
the evaporation under ordinary conditions will run from 
$}4 to 6}4 pounds of water per pound of coal. 

Q. What are some of the practical results of single- 
shovelful firing ? 

Mr. Angus Sinclair's observations while riding on loco- 
motives on the B., C. R. and N. Ry., where firing tests were 



260 COMBUSTION OF COAL. 

being made, was that the coal was broken to small lumps, 
and the fireman kept up the necessary supply of fuel in 
the fire box by putting on a single shovelful at a time. 
When the engine with a long freight train was pulling 
hard on a long grade, the coal thrown into the fire box 
averaged 5 shovelfuls per mile, each containing about 
18 pounds of coal, which was 90 pounds to the mile. On 
the level it was about 5 shovelfuls for every two miles. 
The fire always looked clear and bright, and all the en- 
gines steamed admirably. The engineer always filled up 
the boiler well going into a station, and then shut off the 
injector for a few minutes in starting, to let the fireman 
make up a good fire. As soon as the train was going the 
engineer hooked up the engine as far as he could to avoid 
tearing the fresh fire to pieces. When the engine was 
running for a grade, a fairly heavy fire was gradually put 
upon the grates, and it was maintained during the heavy 
pull ; but was made up by single shovelfuls, or, at most, 
two shovelfuls at one time. There were no special smoke- 
preventing appliances used ; the fire boxes were supplied 
with a brick arch, but no means were employed to admit 
air above the fire. 

Q. Is there a saving in coal by light firing in loco- 
motive practice? 

Mr. Fred McArdle, an engineer on the B., C. R. and 
N. Ry. , writes that the single-shovelful method of firing 
has brought about a great saving in coal, making less work 
for the fireman, and more pleasant for the engineer. The 
engine is not popping off continuously while standing at 
stations. The cab and train are not smothered in dense 
black smoke from the time the engine is shut off until the 
train is again started. Prior to the time that light firing 



BEST METHOD OF FIRING. 26 1 

was adopted passenger engines were fired with three to 
five shovels of coal to a fire ; the same engines are now 
fired with one shovel of coal to a fire, and at no time ex- 
ceeding two, and they only when starting away from sta- 
tions and going over heavy grades. At the present time 
engines are running from 155 to 250 miles without taking 
coal, and savings of 2 to 3^2 tons of coal are now effected 
on each round trip. The trains are from 3 to 6 coaches ; 
engines 15x24 to 17x24 inches. Through freight en- 
gines on all divisions are 18x24 —6 wheel connected, 
fired with one and two shovels to a fire, rarely throwing 
out black smoke between stations; they run 96 to 105 
miles with one tank of coal. These trains save 2 to 4 
tons of coal each round trip over the former method of 
firing. 

Q. What is the best method of firing a locomotive ? 

Referring again to Mr. McArdle's communication, he 
made the excellent suggestion that to make a success of 
light firing the engineer and fireman must work together. 
The fireman should carry a clean, light fire, keeping the 
fire thin enough for plenty of air to be admitted for com- 
bustion. This he cannot do if his engineer, in starting, 
allows his lever to remain at full stroke for a quarter of a 
mile before he begins to cut it back. Under such condi- 
tions the fireman with a light fire would have very little 
fire left in his box by the time the train had moved half 
its length. 

Under the old method of firing, a shovelful of coal was 
put in each corner of the box, and one or two down in the 
centre ; that method of firing has been demonstrated to be 
a mistake, as they now fire the same engines with one or 
two shovels of coal at a time. 



262 COMBUSTION OF COAL. 

Q. What are the noticable improvements in connection 
with light firing and boiler repairs? 

Mr. Henry Raps, foreman boilermaker for the B., C. R. 
and N. Ry., reports freer steaming qualities; longer life 
and more uniform wear of brick arches ; a decrease in the 
number of burned and broken grates ; a decrease in the 
number of bent and broken ash-pan dampers and their fas- 
tenings ; a fewer number of stopped-up flues ; a longer life 
of nettings and stacks ; the total absence of burned smoke 
arches and extensions, and the non-accumulation of cinders 
in the front end, 

Q What is the direct saving upon the brick arches by 
light firing ? 

On account of fires not being so thick in light firing, 
there is not as much liability to throw coal against the 
arch. As there is less fire to clean out at the end of the 
trip, there is less danger of the arch being struck by the 
clinker bar ; for these reasons brick arches last longer, A 
comparison may be instituted thus : 5 1 brick arches ap 
plied to locomotives under the old method of firing aver- 
aged 7,863 miles per arch. 

Forty-five brick arches under the single-shovelful method 
of firing averaged 9,703 miles per arch, a gain of more than 
23 per cent. 

The average cost, including maintenance, of one arch 
under the old method of firing was $6.41 ; an average cost 
of 8 T Yo cents per 100 miles. The average cost, including 
maintenance, of one arch under the light firing was $4.61 ; 
an average of 4^-0 cents per 100 miles. 

Q. What are the principal furnace details of the Wootten 
boiler ? 

Previously to the invention of the Wootten boiler by 



WOOTTEN FIRE BOX. 



263 



John E. Wootten, in 1877, it had been the general prac- 
tice to make the fire boxes of locomotives of a width de- 
termined by the distance 
between the inner faces 
of the opposite driving 
wheels; Wootten's in- 
vention consisted in in- 
creasing the area of the 
grate by arranging the 
fire box and grate above 
and extending them 
laterally over the driving 
wheels, without raising 
the body of the boiler 
to any material extent. 
Figs. 50 and 51 are 
reproductions of the 
original patent office 

drawing, in which it will be seen that the fire box A later- 
ally overhangs the driving wheels B, B' ; the grate D also 
overhangs the wheels and extends across the interior of 




Fig. 




Fig. si. 



264 COMBUSTION OF COAL. 

the fire box. The ash pan G collects the ashes and di- 
rects them into the receptacle h. 

A bridge wall M extends across the fire box or combus- 
tion chamber and may be either a water space or made of 
fire brick ; this bridge wall plays an important part, for the 
grate being necessarily elevated, a corresponding elevation 
of the body of the boiler would be demanded in the ab- 
sence of the bridge, in order that the tubes m might be 
at a proper height above the grate, to prevent the direct 
escape of fuel through the tubes, and this elevation of the 
body of the boiler would render the boiler topheavy. 
The arrangement of the bridge wall, as shown, permits the 
placing of the tubes low down so that the body of the 
boiler may be as low as usual, and, therefore, not top- 
heavy. 

Q. What advantages were attained by the fire box de- 
signed by Wootten ? 

Important advantages are attained by the increased 
grate-bar area due to the lateral extension of the fire box. 
The fuel can be consumed in comparatively thin layers 
more gently and economically, and with less injury to the 
fire box than the thick mass of intensely heated fuel in an 
ordinary contracted fire box. The increased grate area 
dispenses with the usual contracted exhaust opening for 
creating an artificial draft, a larger exhaust opening being 
adopted, and, consequently, the tearing up of the fuel in 
the fire box is avoided, the forcible expulsion of hard par- 
ticles of fuel through the tubes, and the consequent waste 
of fuel, is prevented, and the usual spark-arrester dis- 
pensed with ; these advantages are attained without ren- 
dering the locomotive topheavy by the combination of the 
laterally extended fire box with the bridge M. 



WOOTTEN FIRE BOX. 



265 



Q. Was the combination of bridge wall and combustion 
chamber adhered to in the Wootten boiler ? 

In 1886, Wootten patented another firebox in which the 
combustion chamber, which formed so prominent a feature 







/ 








^_ 






























7=======^ 


11 












"OTJ 










2 





Fig. 52. 



in the original patent, was dispensed with, and a bridge 
wall only employed ; this design in one of several forms 
is shown in Figs. 52, 53, and 54, and consists of a fire 
bridge located wholly within the fire box and supported 




fig. 53. 



266 



COMBUSTION OF COAL. 



above the grate in such relation to the tube sheet as to 
form a space or chamber in the rear, which is closed at the 
bottom and open at the top, for the free passage of the 
products of combustion from the fire box to the tubes. 

This later design, while retaining to a substantial de- 
gree the advantageous features of wide fire-box boilers, by 
this time approved in practical service, affords the advan- 
tages of a reduction in cost and an increased amount of 




Fig. s4- 

area of tube-heating surface relatively thereto. The fire 
bridge can be readily applied and fitted in position and is 
conveniently accessible for renewal and repair, and the 
grate area attainable in boilers of this type is so ample 
that no objection results from such curtailment as is in- 
volved in locating the fire bridge and combustion space 
within the fire box and above a portion of the grate. 

Q. What are the disadvantages of a wide fire box? 

Fault has been found with wide fire boxes because of 
their supposed greater liability to leakage by reason of ex- 
pansion and contraction; but the real reason for leaky 
joints, broken stay bolts, etc., which caused much annoy- 



BARNES LOCOMOTIVE BOILER. 267 

ance with the earlier Wootten fire-box designs, was due 
rather to the flat surfaces and other defects in the general 
design, than is traceable to large grate area, apart from 
other considerations. 

Q. What advantages are claimed for the division of 
the wide fire box into two separate furnaces ? 

In many instances, especially where the fuel employed 
is of low grade, free burning, and contains a considerable 
percentage of hydrocarbons tending to evolve smoke, the 
use of two furnaces has been deemed desirable, provided 
it can be accomplished without undue expense or compli- 
cation of construction, or incidental curtailment of grate 
area to any objectionable degree. Two furnaces permit of 
a better system of alternate firing, and thus reduce the in- 
tensity of smoke when burning bituminous coals of low 
grade, than is the case with a single fire box under ordi- 
nary conditions. 

Q. What are the general details of the fire box of the 
Barnes locomotive boiler ? 

This boiler is of the wide fire-box type, in which a 
laterally extended fire box and a combustion chamber are 
provided. At the rear end of the combustion chamber is 
a water wall, which is open at the bottom to the water 
space in the waist below the combustion chamber, and ex- 
tends a sufficient distance above the bottom of the com- 
bustion chamber to serve as the forward boundary wall of 
the bed of fuel on the grate (see Fig. 55). The interior of 
the fire box is divided into two separate and independent 
furnaces, by a central longitudinal water wall, which is 
closed at bottom by a water- space bar, and at its front end 
is open at bottom to the waist of the boiler and to the 



268 



COMBUSTION OF COAL. 

-~- t?_ ^> o ^ ^» ^ ' ^ ^i (^ ri 




Fig. 55. 

water wall above referred to, Fig. 56. In the case of a 
double combustion chamber, as in Fig. 57, the central 




Fig. 56. 



BARNES LOCOMOTIVE BOILER 



269 



water wall is open to the waist at both top and bottom. 
The side sheets of the water wall, in the middle of the 
furnace, are connected at their upper ends to the crown 




Fig. 57. 



sheets of the furnaces, or may be made integral with the 
crown sheets as shown in the engraving. Fig. 57 shows 
in plan the double combustion chamber, and Fig. 58 a 
single combustion chamber common to both furnaces. A 



270 



COMBUSTION OF COAL. 



material increase of fire-box heating surface is provided 
by the central water wall. By the use of the two independ- 
ent furnaces, the fire may be kept in better condition than 
is practicable with a single and exceptionally large furnace. 



nnnnnnnijinnnnnnn 




Fig. 58. 



Q. What is the best modern practice in the means 
adopted to increase the production of steam by increased 
draft in locomotives? 



EXHAUST PIPES AND TIPS. 27 I 

Mr. C. H. Quereau, Denver and Rio Grande R. R., ob- 
tained data for the Sixth Session of the International 
Railway Congress, from the Motive Power Departments 
of railroads owning some 15,000 out of more than 36,000 
locomotives in use in the United States, Canada, and 
Mexico; these results are given in the following ten ques- 
tions. 

Q. What evaporative results are had in average loco- 
motive practice ? 

Coal, with evaporative results varying from 10.76 to 
3. 10 pounds of water per pound of coal, is the almost uni- 
versal fuel, though in the West, where the quality of the 
coal is poor and the cost high, fuel oil is used success- 
fully. 

Q. What is the present tendency as between single or 
double exhaust pipes ? 

The single exhaust pipe is evidently the preference of 
most roads and apparently is displacing the double pipe. 
There has been a very decided shortening of the length 
of the pipe during the past ten years, notwithstanding 
that the average diameter of the smoke box must have 
increased in the same period. Because of the very gen- 
eral adoption of this change and the considerable amount 
the pipes have been shortened, it seems reasonable to as- 
sume that it must have been noticeably beneficial. 

Q. What is the most efficient form of exhaust tip? 

The tip shown at b, Fig. 59, is essentially that recom- 
mended by the Master Mechanics' committee. That 60 
per cent of the roads reporting use this form as standard 
is presumptive evidence that it is the most efficient form. 
The tips, c and d, vary but little from a in the shape of 



272 



COMBUSTION OF COAL. 



the exhaust and the absence of a shoulder, which must 
produce back pressure. If these are classed with b, the 
result is that 84 per cent of the tips have no shoulder. A 
reasonable interpretation of these facts is that tips with 
shoulders are less efficient than those without. There is 
one advantage in the shouldered tip; namely, that it will 
not gum up by the accumulation of oil from the exhaust. 

There are good reasons for the extensive use of the sin- 
gle exhaust tip, which presupposes the use of a single 



a b 

□ o 



Fig. 59. 



exhaust pipe. The following table gives the areas in 
square inches of different tips : 



Average Exhaust Tips. 



Cylinders. 


Single. 


Double. 


Diameter. 


Area. 


Diameter. 


Area. 


17 X 24 in 

18 X 24 " 

19 X 24 " 

20 X 24 " 

20 X 26 " 


4X in- 
A l A " 
4^ " 
5 " 
5 " 


14.2 sq. in. 

15.9 " 
17.7 " 
19.6 " 
I9.6 " 


3 l A in. 
3 3 A " 
3tt " 

3 3 A " 
3Yz " 


7.7 sq. in. 
8.9 •< 
8.9 ■« 
8.9 " 
9.6 » 



The area of the single exhaust tip is shown to be rough- 
ly twice that of the double tip. It is reasonable to as- 
sume that each is as large as it can be made, and produces a 



BEST FORM OF STACK. 273 

satisfactory amount of steam under service conditions ; also 
that two cylinders exhausting alternately through a single 
tip will meet less resistance, hence produce less back 
pressure, than the same cylinders exhausting each through 
a separate tip half the area of the single tip ; hence, that 
the single tip is more efficient than the double. This 
conclusion would be unwarranted unless it had been shown 
that with the single exhaust pipe and tip and a partition of 
the proper height between the exhausts, the exhausts from 
one cylinder do not interfere with those from the other. 
The use of a bridge or bar in the exhaust tip is universally 
condemned, except as a temporary expedient. 

Q. What is the best form of stack? 

The cast-iron choke, or tapered stack, is the choice 
of 80 per cent of the roads reporting, and growing in 
favor. 

There is also an increasing tendency to reduce the di- 
ameter of the stack, the cylinders remaining the same. 
The diamond stack is standard on but one railroad 
system, and it is a significant fact that two roads, which 
at one time were under the control of the system on which 
the diamond stack is standard and inherited it, have begun 
to discard the diamond stack for the tapered design. From 
these facts it seems reasonable to conclude that experience 
has shown the diamond stack to be less efficient than 
either the straight or taper form. With the diamond 
stack the exhaust steam cannot escape in a direct line be- 
cause of the cone, and the netting area through which the 
gases must escape is less than with either of the others. 

There appear to be no rules for varying the stack di- 
mension for different sizes of cylinder. It is evident that 
the rule given by the Master Mechanics' committee con- 
18 



274 COMBUSTION OF COAL. 

cerning the best relation between the stack and the ex- 
haust tip has had considerable influence. See Fig. 66. 

Q. What is the function of the diaphragm in the smoke 
box ? 

The chief function of the diaphragm, which is used only 
with straight or tapered stacks, is to regulate the distri- 
bution of the draft through the flues and grates. They 
are used incidentally to extinguish and break the sparks 
coming through the flues. The Michigan Central has 
increased their efficiency in this respect by lining the sur- 
faces of the baffle plates against which the sparks strike 
with steel netting, having 2^x2^ meshes per square 
inch, and wire o. 109 inch in diameter. These functions 
apply both to the diaphragms wholly back of the exhaust 
pipe and to those extending in front of the exhaust pipe. 
The advantage claimed for the latter over the former is 
their action in sweeping practically all the cinders from 
the smoke box. The Chicago Great Western has found 
that the diaphragm when extending forward of the exhaust 
pipe causes excessive wear to both this and the steam 
pipes. 

Q. What advantages are to be gained by the use of 
draft pipes? 

The use of draft pipes with extension front ends has 
increased considerably during the past few years. There 
can be little reason for doubt, judging by the reports, that 
their use materially increases the draft, which must result 
in increasing the efficiency of the exhaust by allowing an 
increase in the diameter of the tip and the consequent re- 
duction in back pressure. On the other hand, there is no 
doubt that this advantage is accompanied by occasional 



SMOKE-BOX EXTENSION. 275 

delays for lack of steam, due to the petticoat pipes work- 
ing out of adjustment or becoming warped by heat. Such 
delays are frequently due to poor designs, and more fre- 
quently to carelessness on the part of roundhouse men 
whose duty it is to adjust these parts, but a certain amount 
of such careless work can never be entirely obviated, be- 
cause of the class of men to which this work must almost 
necessarily be intrusted. Again, it is entirely probable 
that a considerable number of these delays are not known 
to the heads of the motive power departments. 

Q. What is the object in the smoke-box extension of 
locomotives ? 

The original purpose for which the extended front end 
was designed was to serve as a receptacle for cinders (see 
Fig. 63). That it is not very efficient in accomplishing 
this end was shown by the results of a test with the 
mounted locomotive at Purdue University. The locomo- 
tive tested had 17.5 square feet of grate area, and a front 
end 52 inches in diameter by 64 inches long, including the 
extension ; cylinders, 17x24 inches ; exhaust tip double, 
each 3 inches in diameter. The average speed in miles per 
hour was 25, and the duration of the test six hours, mak- 
ing it equivalent to a run of 150 miles. As the locomo- 
tive was mounted on wheels controlled by friction brakes, 
and did not move in relation to the earth, the opportunities 
for making accurate observations and measurements were 
all that could be desired. The results showed that 75 
pounds of sparks were retained in the front end at the end 
of the run, while 294 pounds had passed through the 
stack. 

The fact that sixteen out of twenty-five roads reporting 
have shortened their extensions an average of 1 7 inches in 



276 COMBUSTION OF COAL. 

the past ten years shows quite conclusively that experience 
has demonstrated it does not accomplish the end for which 
it was designed, or that the gain in draft by shortening is 
more valuable than the original purpose. 

Q. Does the efficiency of draft appliances in locomotives 
vary with locality or with quality of fuel used? 

The statement has frequently been made that draft ap- 
pliances which have been proved by extended experience 
and experiments to be the best adapted for a given quality 
of coal or section of the country do not, and will not, 
prove at all adapted for similar classes of coal in other 
sections, and that it is necessary to use entirely different 
designs. This seems an unreasonable proposition. 

The sole purpose of the draft appliances is to produce 
a vacuum by means of which the necessary oxygen for the 
combustion of the fuel is provided, and properly to distrib- 
ute this. The primary source of the forced draft neces- 
sary with locomotives is the force of the exhaust steam, 
and the most efficient design of draft arrangements is that 
which will produce the required vacuum with the least 
loss of power, that is, with the least back pressure. As- 
suming that such a design has been devised and its effi- 
ciency established, it follows that it must be the most 
efficient whatever the locality in which it may be used, 
and whatever the grade of coal, and the only reasonable 
change in the design which should be allowed is to in- 
crease or decrease the vacuum to meet the necessities of 
the case by increasing or decreasing the back pressure. 

No claim is made that this most efficient arrangement 
has been designed, but it seems reasonable to believe it is 
within the range of possibility, and when designed should 
be universally the most efficient. For instance, it having 
been shown that the shorter the front end, the more effi- 



DRAFT IN LOCOMOTIVES. 277 

cient the exhaust jet is, this remains true the world over, 
no matter what the fuel or other conditions may be ; as 
the most efficient method of regulating the back pressure 
has been shown to be by means of the tip, any design 
which fails to make the area of the tip less than that of 
every section between it and the cylinder must be faulty, 
wherever used. 

Q. What conclusions were reached by Mr. Quereau re- 
garding the means adopted to increase the production of 
steam by increased draft ? 

This topic naturally falls under two heads. The pro- 
ducing of the vacuum, and the distribution of the draft : 

The Production of the Vacuum. 

1. The most efficient means of producing the vacuum 
are evidently those which accomplish the result with the 
least back pressure in the cylinders. 

2. These can best be determined with a locomotive on 
a testing plant where the conditions can be made those of 
regular service. 

3. The proper basis for determining efficiency is that 
which compares the cause, back pressure, with the result, 
vacuum, and conclusions drawn solely from the vacuum 
obtained are of doubtful value. 

4. The steam passages from the cylinder should be of 
ample proportions. 

5. The exhaust pipe passages should gradually contract 
from the bottom to the tip, without abrupt curves. 

6. The area of the opening through the tip should be 
less than that of any section between it and the cylinder. 

7. The exhaust pipe should be single, with a partition 
but little if any higher than 13 inches, and the total 



278 COMBUSTION OF COAL. 

height as short as possible consistent with easy curves in 
the pipe and a proper arrangement of the netting, provid- 
ing the height is not less than 19 inches. 

8. The steam passage in the exhaust tip should be of 
the shape shown at b, Fig. 59. 

9. Crossbars in the tip lessen the efficiency of the ex- 
haust jet. 

10. The front end should be as short as possible. 

11. With front ends more than 60 inches in diameter, 
double draft pipes increase the efficiency, but careful de- 
signing and thorough workmanship are necessary to pre- 
vent them from warping and working out of adjustment. If 
they become displaced they are worse than useless. 

12. With properly designed draft pipes it is probable 
that the greater the distance from the exhaust tip to the 
base, or choke, of the stack the greater the efficiency. 

13. Either the taper or straight stack is more efficient 
than the diamond stack. 

14. Probably the taper stack is somewhat more efficient 
than the straight, when the proportions of each are the 
best for any given case, because of the more easy approach 
and exit afforded the gases by the former. 

15. The correct rules for the most efficient stack pro- 
portions are still open to question. 

16. The theory of the adjustable exhaust tip is admir- 
able, but the results of experience have been that those 
designs tried so far soon become inoperative. To be per- 
manently successful a design should be automatic and be- 
yond the control of the engineman — connected with the 
reversing gear, for instance. 

17. As far as practicable the plane of the netting should 
be at right angles to the currents of gases passing through 
it, so as to offer as little resistance as possible. 



PREVENTION OF FIRES CAUSED BY SPARKS. 279 

18. The area of the openings through the netting should 
be greater than that through the flues, when possible. 

The Distribution of the Draft. 

So far as known there are no published results of the 
most efficient arrangement of diaphragm plates or draft 
pipes, so that conclusions concerning them are largely 
matters of opinion or personal experience. 

19. With diamond stacks the distribution of the draft 
is best accomplished by the use of draft, or petticoat, 
pipes. 

20. With extended front ends and straight or taper 
stacks the baffle plates are almost entirely depended on for 
regulating the distribution. 

21. It seems entirely probable that with the extended 
front end a design may be developed which will leave out 
the baffle plates and depend entirely on draft pipes for the 
distribution of the draft, and that such a design would be 
more efficient than those which depend on the baffle 
plates. 

Q. What conclusions were reached by Mr. Quereau re- 
garding the means for preventing fires caused by sparks 
from the stack ? 

The following conclusions follow, in numerical order, 
the answers to the previous question : 

22. The extended front end is of little practical use as 
a receptacle for cinders. 

23. The baffle plates and netting should be so designed 
as to extinguish the sparks, break the cinders up, and then 
discharge them into the open air. 

24. Systematic and competent inspection of front end 
arrangments, especially the netting, at regular intervals, 



280 COMBUSTION OF COAL. 

in connection with a permanent record showing the condi- 
tion at the time of inspection and the repairs made. 

25. The use of fire guards made by ploughing two or 
three furrows as far from the track as possible, and then 
burning over the ground between the tracks and furrows. 

Q. What is the best method for utilizing the heat of 
exhaust steam in locomotives? 

Mr. Quereau concludes that : 

26. American practice has not yet developed a success- 
ful design for this purpose, though two roads are making 
the attempt. 

27. The exhaust from the air pump is being success- 
fully used by a number of roads to heat the water in the 
tender. 

28. Because of the fact that most American locomo- 
tives are equipped with injectors, instead of pumps, for 
feeding the boiler with water, and that the injectors will 
not work with feed water hotter than about 120 F., it 
seems probable that the maximum benefits of heating the 
feed water by means of the air-pump exhaust will not be 
derived till the control of the temperature of the feed 
water is made automatic. Experiments with this end in 
view are being made. 

Q. What are the details of construction of the Strong 
locomotive fire box ? 

The corrugated fire box adopted for the Strong locomo- 
tive boilers is a somewhat radical departure from the de- 
signs which have long been employed in locomotive con- 
struction. By reference to Figs. 60, 61, 62, it will be 
seen that there are two corrugated furnaces, which, by 
means of a junction piece, lead into a single corrugated 
combustion chamber, the latter terminating in the back 



STRONG S LOCOMOTIVE FIRE BOX. 



281 



tube sheet, from which the tubes proceed forward, as in 
the ordinary locomotive, to the smoke box. 

The ordinary soft-coal burning boiler 52 inches in di- 
ameter has about 900 stay bolts, but this boiler has none 
whatever. There is not a rigid connection between the 




~*>v> *, li ^ iijp 



^bT 



Fig. 60. 



inner and outer parts of the boiler, and only two connec- 
tions of any kind between the ends, the functions of which 
are to support the inner shell; there is nothing whatever 
to resist expansion and contraction, and thus hurtfully act 
upon the material. The corrugations doubtless contribute 
to freedom of movement, but even if they do not the 



282 



COMBUSTION OF COAL. 



plates of the outer shell have the usual opportunity to 
buckle. 

The crown sheet, being the upper half of a cylinder, 
easily parts with scale which may form upon it, and in 
this respect is in direct contrast with the common, flat 




Fig. 6i. 



horizontal crown sheets covered with bolts and crown bars, 
which are a sufficient means of anchoring all scale which 
forms upon the sheet, and equally efficient means of pre- 
venting inspection and cleaning. The crown sheet of this 
boiler is accessible from end to end; an inspector can 
crawl all over it, examine every portion, and remove any 
scale or dirt which may have lodged upon it. The cir- 



STRONG S LOCOMOTIVE FIRE BOX. 



283 



dilation of water is entirely unimpeded ; the water un- 
der the fire box is free to rise without any obstruction 
whatever. 

The inner shell has no joint which is in contact with 
the fire, except that connecting the back tube plate and 
combustion chamber, which does not differ from common 
practice. The life of this boiler, as shown by actual ex- 
perience, is three to four times that of the ordinary stayed 




Fig. 62. 



boiler with the same surface, proving that the construction 
is not only theoretically correct, but practically in advance 
of boilers of the ordinary type. 

By the system of double furnaces with alternate firing, 
almost absolute perfection in combustion is secured, with 
total absence of smoke and almost total absence of fire 
from the stack, as a very light draft can be used, steaming 
freely with 2^2 to 3 inches of vacuum, while the ordinary 



284 COMBUSTION OF COAL. 

locomotive would require under the same conditions of 
working from 8 to 12 inches. 

Q. How is the smokeless combustion of bituminous coal 
carried out in practice ? 

The smokeless combustion of bituminous coal is being 
very successfully carried out in locomotives on the South- 
ern Pacific Railway, burning a coal known as Castle Gate, 
mined in Utah, analzying as follows : 

Moisture 2.15 per cent. 

Volatile combustible 39. 10 ' ' 

Fixed carbon 50. 75 " 

Ash 7.40 " 

Sulphur ■ . . .60 ' ' 

Mr. J. Snowden Bell, a locomotive expert, made a care- 
ful examination into all the conditions which obtain in that 
road, both as regards fire-box design and draft appliances, 
and the method of firing. The engine on which Mr. Bell 
made his observations was a 10-wheeled Schenectady, of 
the 1800 class, having 20x26 inch cylinders. When rid- 
ing on the engine up a 108-foot grade, hauling 6 passenger 
coaches, the fire was kept clear and bright, without either 
being heavy or having holes in it; steam was maintained 
at 1 80 pounds, and the fire door was never closed. Mr. 
Bell says he never saw a soft- coal burning engine, either 
on a level or on a grade, which could be compared as to 
freedom from smoke ; the light and frequent firing which 
was practised was, in his opinion, the correct and intelli- 
gent one, and involved less fatigue on the fireman than 
the ordinary heavy firing. 

Mr. H. T. Small, superintendent motive power of the 
above road, contributes detail drawings of all the mechani- 
cal features which contribute to this result, as applied es- 
pecially to 12-wheel, 22x26 inch locomotives. 



FRONT ENDS OF LOCOMOTIVES. 



285 



Q. What are the details of the front ends of locomo- 
tives, Southern Pacific Railway ? 

The interior arrangement of front ends, shown in Figs. 
63 and 64, is also practically the same as recommended 
by the Master Mechanics' Association in 1896, and is 
giving satisfactory results. It has been adopted as stand- 




FlG. 63. 



ard by the Southern Pacific, notwithstanding that it is 
necessary to use 7x7 mesh netting, and during the dry 
summer months 8x8 mesh netting in engines running 
through the valley district. The exhaust pipe and nozzle 
for the twelve-wheeler class are given in Fig. 65. 

The standard cast-iron stack and saddle (Fig. 66) are 
used on several classes of engines, and the results obtained 
in service are entirely satisfactory. Although incorrect in 
theory, it has been fully demonstrated that it is really un- 



286 



COMBUSTION OF COAL. 




Fig. 6 4 . 



these have been used since 
1890. It will be noted that 
the stack shown is practically 




necessary to incur 
the expense of 
maintaining a 
special pattern of 
stack for each 
class of engines, 
and as a matter of 
fact the Southern 
Pacific has only 
three patterns of 
stacks for the en- 
tire system, and 




Fig. 65. 



Fig. 66. 



FURNACE DOOR FOR LOCOMOTIVES. 



287 



the same as that recommended by the Master Mechanics' 
Association in 1896. 

Q. What are the details of furnace door on locomotives, 
Southern Pacific Railway? 

The furnace door (Fig. 67) is used on all coal-burning 
engines, the door proper being in two sections. The up- 
per section, commonly called the "trap," is left open con- 




FlG. 67. 



tinually while the engine is working, and through this 
opening, which is 6 x 1 5 inches for the large engines, the 
fireman charges coal into the fire box. It will be noted 
that the deflector, projecting through the door and opening 
into the fire box, is adjustable to any angle desired; it so 
guides the air admitted through the " trap " as to best aid 
combustion, and its proper position is determined very 
readily by the enginemen. It also serves as a check on 



COMBUSTION OF COAL. 



firing with large lumps of coal, or large amounts of coal 
regardless of size. 

The small fire-door opening was a novelty to Mr. Bell, 
as it will be to others, but is obviously an excellent fea- 
ture, and this, with the thorough and uniform distribution 
of air and support of fuel by Mr. Heintselman's latest de- 
sign of grate, an effective ash pan, and proper front-end 
arrangements, are clearly the factors to which, with good 
firing, the results are due. 

Q. What are the details of brick arch used in locomo- 
tives of Southern Pacific Railway? 

The arrangement of the brick arch which is of the ordi- 
nary type and shown in Figs. 68 and 69 needs no special 




Fig. 69. 



LOCOMOTIVE GRATE AND ASH PAN. 289 

mention, excepting that it is considered an important fac- 
tor, and helps to produce perfect combustion and economy 
in fuel consumption. 

Q. What are the details of grate used in locomotives 
on Southern Pacific Railway? 

The improved finger grates and bearings shown in de- 
tail in Fig. 70 are novel, as is also the manner of hanging 
the grates from the fire-box sheets. It will be seen that 
the hanging of the side bars is so arranged as to compen- 
sate for the expansion and contraction of the grate bars, 
and by means of the collar at the end of each trunnion 
bearing the grates are held central at all times, keeping 
the air spaces equally divided between the fingers. The 
air spaces through the body of the grate bar and fingers 
serve to distribute the air to the fire more evenly, and at 
the same time the thickness of the metal in the body and 
fingers is reduced to a minimum. The fingers being de- 
tachable, they can readily be removed and replaced when 
change of air openings or spaces between fingers is desired 
to suit different kinds of coal ; or, in case any number of 
fingers become damaged in any way they can be replaced, 
thereby saving the remainder of the grate. The fingers 
are applied to the grate bars in the rough, or just as re- 
ceived from the foundry. 

Q. What are the details of ash pan used on locomotives 
of the Southern Pacific Railway? 

The general arrangement of the self-dumping ash pan 
(adapted to twelve-wheelers) operated by compressed air is 
shown in Fig. 71, and the application of air valves to the 
sides of the ash pan is shown in Fig. 72 ; these side valves 
are also worked by compressed air. This style of ash pan 
is considered an important improvement, and has resulted 
19 



290 



COMBUSTION OF COAL. 




TRAVELLING FIREMAN. 29 1 

in a saving of fuel and a saving in labor and delays to 
trains on account of cleaning. The side dampers distrib- 
ute the draft through the grates evenly, whereas, in 
former arrangements with only end dampers, the draft was 
excessive through the centre of the grate and insufficient 
at the sides and ends. Clinkers no longer form on the 
sides of the fire box, and the fireman is always free to 
shake the grates, knowing that the ash pan will not become 
filled up, as the new pans can be dumped in a few seconds 
by a single movement of a valve. Therefore a light fire 
can always be carried, and there are no delays for clean- 
ing. With former styles of ash pans where the fireman re- 
moved the ashes with a hoe, trains were sometimes de- 
layed on this account as long as thirty minutes. The new 
ash pans are so arranged that there is no chance of sparks 
dropping, and when drifting down grades all the dampers, 
if required, can be closed with one movement of the air 
valve, or the openings can be partially closed to suit the 
conditions. 

Q. What facts are given in the daily report of the 
Travelling Fireman on the Southern Pacific Railway? 

One thing contributing to the success of the Southern 
Pacific in burning bituminous coal is the daily report 
made by the Travelling Fireman. This is of value in 
keeping the head of the department posted as to whether 
the work of firing is being properly attended to. The 
blank used for this report gives the number of the train, 
date, names of the enginemen, and between what stations 
the report covers. The questions are well designed to 
bring out any failures of the men or machinery, and are as 
follows : 

Kind of coal, and was it broken to suitable size ? 



292 



COMBUSTION OF COAL. 




DETAILS OF ASH PAN. 



293 




294 COMBUSTION OF COAL. 

Was draft on fire properly equalized ; if not, what sug- 
gestions have you to offer ? 

Was there any trouble due to clinkers or dirty fire ? If 
so, state cause. 

How many times was it necessary to clean fire over the 
division ; and time consumed in each case ? 

If any trouble was experienced for want of steam, what, 
in your opinion, was the cause of it ? 

What was the condition of the fire and ash pan on arrival 
at terminal ? 

Was fireman disposed to comply with instructions and 
practise economy, and prevent black smoke ? 

Was the general condition of the engine such that would 
indicate any neglect whatever on the part of the fireman? 

Was engine slipped unnecessarily? 

Were injectors handled so as to obtain the best results 
in fuel economy ? 

Was engine in good serviceable condition ? If not, state 
defects. 

The Travelling Fireman is also expected to note on the 
report or write a letter regarding any other things that may 
be noticed while travelling or at terminals, that in any way 
would better the engine service or effect a saving. 



PART II. 

HYDROCARBON OIL AS A FUEL FOR LOCO- 
MOTIVES. 

Q. Is oil used as fuel in locomotives ? 

It has long been in use in the Russian oil fields ; it has 
been tested experimentally near the Pennsylvania and Ohio 
oil fields ; and has been used for fuel for several years past on 
the Pacific coast. The Southern California Railroad began 
burning oil in 1894, and have used it more or less ever 
since. Various minor changes have been made with a 
view to improve the process; but in the main the arrange- 
ment has been about the same for the last three or four 
years ; and according to Locomotive Engineering, about 
all their engines burn oil now. The Southern Pacific 
Company also burn oil in some of their locomotives. The 
oil burners being easily removable, they burn either oil or 
coal according to the relative prices of the two fuels. 

Q. What advantages are claimed for petroleum as a 
fuel? 

It is claimed for petroleum : 

1. That its heating power is greater per pound than that 
of any solid fuel. 

2. That it permits of continuous firing in a closed fur- 
nace, free from drafts of cold air. 

3. That the quantity of heat required to maintain a con- 
stant pressure of steam may be controlled by the simple 
adjustment of a valve in the oil-supply pipe. 



296 COMBUSTION OF COAL. 

4. Absence of debris; there being no ashes or clinkers 
left in the furnace. 

5. That the fire is not only easily started, but can be 
instantly discontinued without loss of fuel. 

Q. What is petroleum? 

Petroleum is a natural hydrocarbon oil; in its widest 
application, the term covers all the mineral oils found in 
this country. It is of a dark-brown color, having a green- 
ish tinge. In specific gravity the crude oil averages about 
0.8, with variations of .025 on either side; equivalent to 
50 pounds per cubic foot. 

The composition of crude oil is by no means constant, 
but it will approximate closely : 

Carbon 84 per cent. 

Hydrogen 14 " 

Oxygen 2 " 

100 " 

The theoretical heating power of oil by this analysis 
would be : 

Heat units. 

Carbon 84 X 14,544 = 12,217 

Hydrogen (available) 1375X62,032— 8,529 

Total heat units =20, 746 

The evaporating equivalent of which would be 21.47 
pounds of water from and at 21 2° F. per pound of oil. 

Q. What is the calorific value of petroleum? 

The heating power of crude oil is greater than the re- 
fined oil, and when employed as a fuel it is the crude oil 
that is commonly used except locally, where the thick oily 
residuum from the refineries is used ; which is always with 
good effect, when the furnace details are properly adapted 
for burning it. 



HEATING POWER OF OIL. 297 

The calorific power of crude oil approximates the fol- 
lowing : 

British 
thermal units. 

Pennsylvania, light 17, 933 

Ohio, heavy 18,718 

West Virginia, heavy 18, 324 

West Virginia, light 18,401 

An oil averaging 18,500 heat units per pound would 
yield an equivalent evaporation of 19.15 pounds of water 
from and at 21 2° F. 

The boiler plant at the World's Fair, Chicago, was sup- 
plied with crude oil from the Lima, Ohio, district for fuel. 
The quantity of petroleum used for firing the main boiler 
plant was upward of 31,000 tons, and the work done was 
stated to have been 32,316,000 horse-power hours, or 
about 2.1 pounds of oil per horse power per hour. 

Q. What is the calorific power of refined mineral oil? 

A commercial product known as " mineral seal " yielded 
upon analysis : 

Carbon 83. 3 per cent. 

Hydrogen 13.2 " 

Oxygen, nitrogen, and loss 3. 5 

100. o " 

This oil has a density of 40 Baume, which corresponds 
to a specific gravity of .83. The flash test was 266 F., 
and the fire test 31 1° F. It is a pure mineral oil. The 
calculated heat units are : 

British 
thermal units. 

Carbon 14,500 X .833 = 12,079 

Hydrogen 52, 370 X- 132= 6,913 

18,992 

The average result obtained by experiment is 18,790 



298 COMBUSTION OF COAL. 

heat units, which is 1 . 1 per cent lower than the value cal- 
culated from the analysis (Jacobus). 

Q. What success has attended the use of liquid fuel as 
auxiliary to coal for locomotive engines? 

Experiments made in England, on the Great Eastern 
Railway, have been quite successful in the use of liquid 
fuel as an auxiliary to coal in locomotive engines. The 
fluid used is tar, and to it is added a certain proportion of 
green oil which was also obtained from the works where 
the tar was produced, the cost being about 3 cents per gal- 
lon. Each of the 12 or 14 engines, ft appears, used about 
1 2 pounds of coal and over a gallon of oil, which is equal 
to about 1 1 pounds fluid fuel per train mile as against 34 
pounds of coal. The relative cost of the combined mate- 
rial is rather less than coal, but the value of the oil injector 
is seen to special advantage on gradients where an extra 
supply of steam is required. 

Q. What success has attended the burning of the heavy 
residuum obtained by the distillation of bituminous shale ? 

Not much attention has been given to the distillation of 

oil from bituminous shale in this country. Some lignites, 

for example those found in Ouachita County, Ark., have 

been experimentally dealt with ; the lignite was soft enough 

to be cut with a knife, solid, heavy, compact, of a bluish - 

brown color, disintegrating by exposure to the atmosphere. 

It consisted of : 

Fixed carbon 34. 50 per cent. 

Volatile matter .... 60. 50 " 

Ash 5.00 " 

100.00 " 

When distilled in an iron crucible, the first product that 
came over was gas having a feeble odor of sulphurous acid 



BURNING OIL IN LOCOMOTIVES. 299 

and burning with a tolerably bright flame. The gas was 
soon accompanied by ammoniacal water, a yellowish oil, 
and a waxy product which when condensed had the con- 
sistency of lard and the color of beeswax. The last 
products which came over were lubricating oil and par- 
affin. The products of this distillation were : 

Coke 37. 83 per cent. 

Watery solution containing sulphurous acid, or- 
ganic acids, and ammonia 34- 3 2 

Crude oil 12.16 

Gas and loss 15-69 

100.00 

From this analysis 2,000 pounds of lignite would yield 
35.40 gallons of crude oil. 

Crude residue, not unlike the above, left after extract- 
ing oil from bituminous shale, was applied for heating 
purposes at the Forth bridge. In appearance this residue 
resembled butter, and would not burn upon the application 
of a lighted match. By melting it and forcing it in jets 
with superheated steam against previously heated fire-clay 
surfaces with an induced current of air, it burned freely 
and developed great heat. 

Q. What changes are necessary to convert a coal into 
an oil burning locomotive ? 

To change from coal to oil fuel on the Southern Califor- 
nia Railroad the grates are taken out, and a cast-iron plate 
is placed 4 to 6 inches below the mud ring, extending 
over the entire space under the fire box. This plate has 
three openings for air to come up into the fire box, 9x15 
inches, one of these air openings being in the middle of 
the fire box, one near the front end, and one near the back 
end. The plate is protected from the heat of the fire 
above by a covering of fire brick. The ash pan and damp- 



300 COMBUSTION OF COAL. 

ers are left the same as a coal burner. The sides of the 
fire box are also protected from the direct force of the in- 
tense heat by a fire-brick wall about 5 inches thick, which 
comes up to the flues in front, up above the flare of the 
fire box on the sides and to the bottom of the door at the 
back. There is a brick arch extending across the fire box 
from side to side, reaching back pretty well toward the 
door, just the same as in a soft-coal burner. Some of the 
engines also have a narrow arch just under the door, which 
serves to keep the intense heat from the door ring. 

The atomizer which separates the oil into a fine spray 
and blows it into the fire box is located just under the 
mud ring, pointed a little upward, so the stream of oil 
spray and steam would strike the opposite wall a few 
inches above the bottom, if it was to fly clear across the 
box. Deep fire boxes have the atomizer at the back end 
of the box, while the shallow and long fire boxes have it 
located at the front end, pointed back. The shallow boxes 
have the same arrangement of side walls that the deep ones 
have, but the arch is put in differently. Some of them 
have three small arches extending from side to side, but 
clapping over each other from front to back, so as to di- 
vide the current of flame and heat into several parts, and 
thus distribute it over the long, shallow box more evenly. 
A good deal depends on the size and position of the arch, 
which has the same effect on the steaming of an oil burner 
that the diaphragm in the front end has on the draft of a 
coal burner. No air is admitted above the fire of the 
atomized oil. 

Q. How are the atomizers constructed for burning oil on 
the Southern California Railroad? 

The atomizers, one for each engine, are of brass, 12 
inches long, 4^ inches wide from side to side, and 2 



DETAILS OF OIL BURNER. . 301 

inches thick from top to bottom, divided into two parts 
by a partition in the middle. Steam comes into the bot- 
tom part, heats the atomizer, and issues through a slit -^ 
by 4 inches. The oil flows into the top part of the 
atomizer over the hot partition, and on running out of 
the front end is caught by the steam issuing from the 
slit in the bottom part, and is sprayed into the fire, which, 
when the engine is working, is a mass of flame, fitting 
the fire box under the arch, and most of the time the 
whole box. 

The supply of steam and oil to the atomizer is regulated 
by the fireman from the cab, the handles for the steam and 
oil supply valves being placed where he can have his hands 
on them when on his seat box. Before the oil is fed into 
the atomizer it passes through a small heater made of 
brass, having a steam pipe through it; this steam pipe also 
leads to a coil in the bottom of the oil tank to warm the 
oil so it will flow easily. The oil on the Pacific coast is not 
at all like the fuel oil from the Indiana and Lima fields. 
Some of the oil has a generous portion of thick stuff like 
asphaltum in it, so it does not flow very easily ; while other 
kinds are thin as water and almost as clear. The oil tank 
is located in the pit of the water tank, usually assigned for 
coal. 

Q. How is the oil supplied to the burner under pressure ? 

An air pipe leads from the main reservoir to the oil 
tank, with a reducing valve similar to the one used in the 
air-signal line, but with a different spring box, so as to 
bring the air pressure down to 4 pounds, which is main- 
tained in the oil tank, at which pressure the oil comes out 
freely. Self-closing valves are provided to shut off the 
flow of oil in case of accident. 



302 COMBUSTION OF COAL. 

Q. What size of exhaust nozzle is used when burning 
oil? 

It is about the same size as is used when burning good 
coal. Frequently no changes are made in the front end 
except to take out the netting; others have a low nozzle 
and petticoat pipe put in instead of high nozzle and a dia- 
phragm or apron. 

Q. Are oil fires smokeless? 

An oil fire requires as careful attention as does soft coal 
to render its combustion smokeless. The fireman and en- 
gineer must work coincidently to get the best results. 
Every time the engineer changes his lever or throttle the 
fireman must change his fire. He must keep his eye on the 
water in the boiler, must know the road, etc. — in fact, a 
good fireman on an oil-burning locomotive must keep his 
eyes open, for he can make or waste more for the company 
than he could on a coal burner. 

Q. What is the effect of the products of combustion of 
an oil fire upon the tubes of the boiler? 

The products of combustion from an oil fire make a 
sticky deposit in the flues, which soon coats them and in- 
terferes with the steaming. To cure this difficulty, the 
fireman sticks a long funnel through a hole in the fire-box 
door, made for that purpose, and gives the flues a dose of 
about four quarts of sand, which is drawn through the flues 
and scours them out. 

Q. What is the relative cost of oil and coal as a fuel in 
locomotive practice ? 

In California coal is high priced ; good coal at Los An- 
geles costs $6.50 to $7.50 per ton; oil costs about $2 per 
ton less. With coal at $4.80 per ton it is profitable to 



PRESCOTT S OIL BURNER. 303 

change a locomotive into an oil burner, with oil at $1 per 
barrel. Engines do not steam as freely with coal, so they 
cannot make as good time or handle as large a train at as 
high a rate of speed. There is apparently no limit to the 
steaming power of an oil burner. 

Q. What are the general details of construction of the 
Prescott burner for liquid hydrocarbons ? 

A locomotive fire box equipped with an oil burner by 
George W. Prescott is shown in Fig. 73. The fire box is 
lined with fire brick, and fitted with front and back arches 
as shown. An air-supply pipe with damper, adjustable 
from the cab, is also shown. Fig. 74 is a plan sectional 
view of a double burner provided with a central oil-receiv- 
ing chamber, also shown in Fig. 75. This oil chamber is 
located inside a larger chamber in which water or steam 
under pressure may be used for the purpose of raising or 
lowering the temperature of the oil. The casing of this 
burner is rectangular in shape, and provided with exit 
passages, into which the oil is fed from the oil chamber 
before passing into the combustion chamber. These exit 
passages are irregular in shape or larger at their induct 
portions than at their outlets, so as to contract the supply 
of oil at the outlet, so that when the burner is tilted at an 
angle, as indicated in Fig. 75, the upper level of the oil 
will be above the upper surface of the contact opening and 
form a trap, as it were, to prevent gas or heated products 
from flowing back into the oil chamber to cause an explo- 
sion therein. 

The casing of the burner at its lowest portion is pro- 
vided with steam chambers having tapered, slotted open- 
ings, in which are movably mounted tapered slide valves. 
The exit openings of these chambers, in which these 



304 



COMBUSTION OF COAL. 




prescott's oil burner. 



305 




306 COMBUSTION OF COAL. 

"atomizing valves " are arranged, are located immediately 




under the exit openings of the liquid hydrocarbons, and 
the steam chamber is connected with the source of steam 



PRESCOTT S OIL BURNER, 



307 



under pressure, so that when the valves are opened steam 
under pressure contacts with the liquid hydrocarbon im- 
mediately, atomizes the same, and drives it into the fuel 
chamber with sufficient force to meet the incoming atmos- 
pheric air and promote combustion. 

The steam- supply chamber in which the valves are 



rfifa 



m 



g ffi r lirfl M 



■R m / 



rn^mm 




Fig. 76. 

located is connected by means of a pipe with the source 
of steam supply, so that steam under pressure may be fur- 
nished the casing to atomize the oil. The steam-supply 
pipe is fitted with a drip valve, the parts of which are so 
arranged that when steam under sufficient pressure is fur- 
nished to the chamber the drip valve is kept closed ; but 
as soon as the pressure is lowered sufficiently, the valve is 
opened by means of the tension spring and the water of 



308 COMBUSTION OF COAL. 

condensation allowed to drip out and empty the chamber 
and the pipe. 

The plug valves shown in Fig. 76 govern the supply of 
oil to the burner, and can be operated from the cab, either 
independently or simultaneously. 

Each atomizing valve in the burner is provided with a 
stem that projects out of the rear end of the casing, and 
further provided with screw threads, worm, and worm gear 
for adjustment. 

The steam or water chamber is provided with a steam 
pipe, leading to the source of supply for heating the oil ; 
and another pipe connecting with the water tank, should 
cooling instead of heating be desired. 

As shown in Fig. 73, the burner is arranged at a slight 
inclination from the horizontal, so as to provide a trap and 
prevent back flow of gas from entering, igniting, and ex- 
ploding in the oil reservoir. 



CHAPTER XII. 

CHIMNEYS AND MECHANICAL DRAFT. 

Q. What service does a chimney render in connection 
with a steam-boiler furnace ? 

It is the means generally employed for the purpose of 
maintaining a draft of air through the body of burning fuel 
in the furnace. Its effectiveness is due to that quality 
which it possesses of maintaining an unbalanced pressure 
between the interior or combustion chamber of the fur- 
nace and the atmospheric pressure without. 

Q. What is the cause of draft in steam-boiler furnaces ? 

Furnace draft is caused by the difference in weight or 
pressure of the column of cold air outside of the chimney, 
and the weight of the column of heated gases within it. 
Air and gases, when heated, expand in volume, and be- 
come less dense than for equal volumes at a lower tem- 
perature ; this difference in density is the draft-producing 
quality of heated gases. 

Q. How does this unbalanced pressure originate in a 
chimney, and how is it maintained? 

The unbalanced pressure originates in the fact that hot 
gases occupy a larger volume for a given weight than cold 
gases. As there is no exit for the hot gases generated in 
the furnace except through the chimney, a current is at 
once established in that direction. By reason of the 
height of the chimney above the furnace, and the fact that 



3io 



COMBUSTION OF COAL. 



it is filled with gases of higher temperature, and conse- 
quently of less density than that of the air outside of the 
chimney, an upward current of hot gases will be main- 
tained so long as any unbalanced pressure exists between 
the outside and inside of the chimney. 

Q. What is the rate of increase in volume for different 
temperatures of gases escaping by the chimney ? 

Let us suppose that 18 pounds of air pass through the 
furnace per pound of coal ; we then have 1 8 — [— I = 19 
pounds of gases. If the temperature of the air flowing 
into the furnace is 68° F., its volume will be 241 cubic 
feet; if the temperature of the escaping gases be 572 F. , 
the volume will have been increased to 471 cubic feet, a 
difference of 471 -=- 241 = 1.95 times increase in volume 
of the hot gases over that of the cold air, a ratio approxi- 
mately of 2 to 1. 

Table 30. — Volume of Escaping Gases in Cubic Feet per Pound 
of Coal Burned. (Rankine.) 





Pounds of Air per Pound of Coal. 


Temperature. 


Twelve pounds, 
cubic feet. 


Eighteen pounds, 
cubic feet. 


Twenty-four pounds, 
cubic feet. 


32° F 


I50 
I6l 
172 
205 
259 
314 
369 
479 
588 
697 
906 


225 
241 

258 

3°7 
389 
471 

553 

718 

882 

1,046 

1,359 


300 
322 

344 
409 

519 

628 


68 


I04 


212 


3Q2 


572 


752 

1,112 


738 

957 

1,176 

i,395 
1,812 


1,472 


1,832 


2,500 







As the lighter gases are confined to the chimney they 
rise to the top by reason of their lesser gravity, and within 



AREA OF CHIMNEY. $11 

certain limitations the higher the chimney and the higher 
the temperature of the escaping gases the stronger or 
more intense will be the draft. 

Q. How is the area of a chimney determined for a 
given boiler plant? 

This detail in steam engineering has been practically 
fixed by Ishewood's experiments, and further corroborated 
by observations extending over many years, including all 
kinds of fuel, and in connection with almost every im- 
maginable furnace contrivance, grates, etc. 

It is a common practice to make the area of the chim- 
ney bear some relation to the grate surface, although the 
latter does not bear, in practice, a fixed relation to the 
boiler-heating surface ; and not always to the quantity of 
fuel to be burned, nor to the rate of combustion. 

After a series of elaborate experiments Mr. Ishewood 
fixed upon yi of the grate area as being the best propor- 
tion for draft area, and this recommendation holds good 
for both hard and soft coal at ordinary rates of combustion. 

In practice the sectional areas of chimneys will be found 
to vary between l and ^ of the grate surfaces to which 
they may be attached; the latter proportions being for 
very large plants and in connection with unusual height 
of chimney. 

The area of chimney may be based upon the quantity of 
coal burnt. Up to 1,000 horse power the most satisfactory 
chimneys are those in which from I % to 2 square inches 
of chimney area are had for each pound of coal burnt per 
hour. If, say, 600 pounds of coal are supplied a steam- 
boiler furnace per hour, we have : 

600 X 1. 5 = 900 sq. in., or 34 in. diameter. 
600 X 2 = 1,200 " " 39 " " 



312 



COMBUSTION OF COAL. 



In which case 
be selected. 



a 36 or 40 inch chimney would probably 



Q. How is the height of a chimney determined ? 

In the larger cities the height of a chimney is often 
determined by the height of buildings in the immediate 
vicinity ; city, chimneys are often, for this reason, much 
higher than necessary for the mere purpose of securing 
proper draft. 

Where there are no local restrictions governing the 
height of a chimney, those for small powers, say 30 H. 
P t and less, the height may be 50 to 60 feet; for 100 H. 
P. the height may be 70 to 90 feet; and for 1,000 H. P. 
1 50 feet in height will be found ample for draft purposes. 

A rule sometimes met with would fix the height at 25 
times the internal diameter of the chimney; this is a good 
rule for a few sizes, but it will not apply to all diameters. 
Small chimneys must have a certain height to get sufficient 
draft to burn the fuel. The height of large chimneys is kept 
down to reduce cost of construction. The following heights 
come within the range of good practice : 

A 2-foot chimney 70 feet high = 35 diameters. 



90 
100 
120 
130 
140 
150 



= 30 
= 25 
= 24 
= 21.67 
= 20 
-18.75 



Q. In estimating chimney draft where should the chim- 
ney measurement begin? 

Draft properly begins at the level where the air passes 
through the fire, and not at the level of the ground at the 
base of the chimney. 



INTENSITY OF DRAFT. 313 

Q. What is the best temperature for chimney draft? 

The ordinary limit of temperature for escaping gases 
from steam boilers is approximately ioo° F. above the 
temperature of the steam. If steam is being generated at 
100 pounds pressure by gauge, the corresponding temper- 
ature would be 338°+ ioo° = 438° F., the lowest tem- 
perature for the escaping gases. On the other hand, the 
maximum temperature would be about 584 F., because 
at that temperature the gases are about one-half the den- 
sity of the atmospheric air. The best working temperature 
will be found to lie between these two limits. 

Q. What is meant by intensity of draft? 

Intensity of draft denotes the velocity of flow of air 
through the furnace. Intensity is secured by height of 
chimney, by high temperature of escaping gases, or both 
combined. Anthracite coal requires a greater intensity of 
draft than is necessary for bituminous coal, and it is for 
this reason chimneys for the latter coal can be 1 5 to 20 
per cent lower than for anthracite. The intensity of 
draft for anthracite coal will vary from ^ to 1 inch of 
water ; for bituminous coals, ^ to ^ inch of water will 
suffice. 

Q. How may the intensity of chimney draft be esti- 
mated ? 

Intensity of chimney draft is usually measured in inches 
of water. Suppose a chimney to be 150 feet high and the 
temperature of the escaping gases 6oo° F., the tempera- 
ture of the atmosphere 75 ° F., the draft in inches of water 
may be found thus : To the sensible temperature 600 ° and 
75° we must add the absolute temperature 460 F. ; then : 

460 + 600 ° 159000 

150 X r o o = -^ = 2 97 feet ; 2 97 — 1 5° = 

D ^ 460°+ 75 535 *' ' *' D 



314 COMBUSTION OF COAL. 

147 feet, the motive column. Water is 820 times heavier 

820 X 297 
than air, we have then: — = 1656, which ex- 

presses the relation of weight as compared with water. 
• If we divide the motive column by this amount we have 

147 
—p—p = .0887 foot. Then .0887 X 12 = 1.064 mcn > say 

iyL- inches of water by draft gauge, or the height of a 
column of water lifted by the action of a chimney corre- 
sponding to the height and temperature above given. 

The above example may be regarded as an extreme case ; 
a much lower set of conditions are here given : 

Suppose a chimney 100 feet high, escaping gases 500° 
F., atmosphere 6o° F., what will be the draft in inches 
of water ? 

460 + 500 96000 n . 

100 X \ o V- o = ~ = 184 feet. 

460 -f 6o° 520 ^ 

184 — 100 = 84 feet. The motive column. 

T , 820 X 

Then : jr- 

84 

pared with water. 

84 
Dividing the motive column by this ratio : -? = 

.0467 foot. 

Then .0467 X 12 = .560 inch of water, or about -^ inch. 

Q. Why is maximum economical chimney temperature 
taken to be about 584 F.? 

Chimney temperature is for draft purposes only; draft 
increases with the temperature of the gases in the chim- 
ney; from 32 to 300 F. the draft augments very rapidly, 
from 300 to 750 the draft varies but little, and then 



■ , 820 X 184 •, . ' . , 

Then : — 1 796, the ratio of weight as com- 






PROPORTIONS FOR CHIMNEYS. 315 

gradually diminishes in intensity with higher tempera- 
tures. 

An ordinary steam pressure for high-grade, triple-expan- 
sion engine is 185 pounds by gauge, or 200 pounds abso- 
lute; the temperature of which is 382° F., to which we 
add ioo° for excess temperature, difference of hot gases 
over that of the steam = 483 F. 

The best draft is had when the density of gases within 
and without the chimney is as 2 to 1. Suppose an aver- 
age air temperature of 62 F., the absolute temperature 
would be 62° + 460°= 5 22 ; the best draft would be 
522 X2= 1,044° absolute, or 1,044° — 4^0° = 584°, the 
temperature of the gases in the chimney. 

Q. What rule governs the proportions for chimneys as 
given in Table 31 ? 

Proportions for chimneys from 20 to 90 horse power are 
for a single boiler and furnace in which the grate area is 
assumed to be 9 times that of the tube area for the small- 
est horizontal tubular boiler, diminishing to 7 times the 
tube area for the largest boiler. A commercial horse- 
power rating approximating 1 5 square feet of heating sur- 
face per horse power is assumed for all boilers included in 
the above grouping. 

For chimneys from 100 to 1,000 horse power, the di- 
mensions are suited to two or more boilers set in a battery 
and working together; a horse power in this portion of the 
table is based on 4 pounds of coal per horse power per 
hour. 

The rate of combustion is assumed to be 12 pounds per 
square foot of grate surface per hour. The proportion of 
grate to chimney area varies from l for the 100 horse- 
power boiler to ^ for the 1,000 horse-power boiler. 



3i6 



COMBUSTION OF COAL. 



Table 31. — Chimney Dimensions for Steam-Boiler Furnaces from 
20 to 1,000 Horse Power. 











Diameters 
round 

chimney, 
inches. 


Height for — 


Horse 
power. 


Grate area, 
square feet. 


Coal 
per hou 
pound 


Area 
r, of chimney, 
;. square feet. 


Bituminous 

coal, free 

burning, 

feet. 


Small 
anthracite 
coal, feet. 


20 


12 




2.02 


20 


50 


60 


30 


14 




2.28 


20 


55 


65 


40 


17 




2.9I 


24 


55 


70 


50 


23 




3-67 


26 


60 


70 


60 


24 




3.8o 


27 


60 


75 


70 


29 




4.35 


28 


65 


80 


80 


34 




4.88 


30 


65 


85 


90 


38 




5.00 


30 


70 


90 


IOO 


40 


40( 


> 4-76 


30 


70 


90 


I50 


50 


6oc 


) 6.82 


36 


75 


95 


200 


67 


8OC 


) 8.69 


40 


80 


IOO 


250 


83 


I,OOC 


) IO.64 


44 


85 


105 


300 


IOO 


l,20( 


) I2.50 


48 


85 


105 


350 


117 


1,40c 


) 14.18 


5i 


90 


no 


400 


133 


1, 60c 


) 16.OO 


55 


90 


115 


450 


150 


i,8oc 


> 17.65 


57 


90 


115 


500 


167 


2,OOC 


j 19.25 


60 


95 


120 


550 


183 


2,20( 


) 20.65 


62 


95 


120 


60O 


200 


2,40( 


) 22.22 


64 


IOO 


125 


650 


217 


2,60( 


) 23.65 


66 


IOO 


125 


700 


233 


2,80( 


) 25.OI 


68 


105 


130 


750 


250 


3,ooc 


) 26.32 


70 


105 


135 


800 


267 


3,20( 


) 27.6l 


72 


no 


135 


850 


283 


3,40< 


3 28.82 


73 


no 


140 


gOO 


300 


3>6o( 


) 3O.OO 


74 


115 


145 


95° 


317 


3,8o( 


5 3I-67 


76 


"5 


145 


1,000 


333 


4, OCX 


> 33-33 


78 


120 


150 



Q. How may the draft of a chimney be modified ? 

If the chimney draft is sluggish it may be increased by 
means of a specially contrived blower exhausting upward 
in the chimney as in Fig. yj. In small boiler plants, and 
especially where a sheet-iron stack is employed, the ex- 
haust pipe from a non-condensing engine is quite frequent- 



STEAM BLOWER. 



317 



ly led into the stack, the pipe turned 
nating in a contracted orifice ; the 
being usually determined by 
local conditions. 

Excess of draft may be con- 
trolled by means of a damper, 
placed between the exit of the 
gases from the boilers, and the 
chimney. In small boiler plants, 
and especially those having a 
sheet-iron stack, the damper 
is commonly placed either in 
the breeching or in the stack 
itself. 



Q. What is the construction of 
the argand steam blower ? 

This blower, as made by 
James Beggs & Co., is shown 
in section in Fig. 78, and one 
method of applying it through 
a side wall of a boiler furnace 
is shown in Fig. 79. The blast 
is regulated to suit the require- 
ments of any furnace by means 
of a globe valve in the steam- 
supply pipe. Should the small 
holes in the argand ring become 
clogged with loose scales from 
the steam pipe or other cause, 
they can be cleansed with a 
bent wire (hook shaped), when 
steam is turned on full force. 



upward, and termi- 
size of the latter 




Fig. 77. 



3i8 



COMBUSTION OF COAL. 




Fig. 78. 

Q. What is the best location for a steam blower in 
connection with a boiler furnace? 

It is generally conceded by those who have given the 
subject special attention that a blast furnished by under- 

grate combined air and steam 
blowers, properly proportioned, 
is better adapted to burn the 
smaller anthracite fuels than 
either a strong natural draft 
or a draft produced by a jet or 
jets in the stack. 

Both of the latter methods 
so relieve the pressure on the 
upper surface of the fire that 
the unconsumed gases escape 
into the stack before they 
have time to ignite, whereas 
with the forced draft a pressure is produced between the 
uptake and the upper surface of the fire which retards 
the gases long enough for them to ignite, whereby the 
boiler can be heated more effectively than by the radiant 
heat alone which is emitted from the incandescent carbon 
and radiated against a small portion of the heating surface 




Fig. 79. 



STEAM-JET BLOWER. 319 

only. Then, again, the steam has a mechanical effect, in 
that it keeps the clinkers soft and porous, so that the blast 
will readily pass up through the entire bed of fuel uni- 
formly, instead of being forced to pass between solid 
clinkers wherever it can find an opening, as is the usual 
case with a fan blast, for an all-air blast tends to form the 
clinkers into compact slabs, through which the air cannot 
pass. 

Another mechanical effect of the steam is that it mois- 
tens the fine ashes in the lower strata of the fire, which 
keeps them from being blown up into the burning surface 
to choke it by filling the interstices between the particles 
of fuel. 

Q. What special preparation of fuel is recommended in 
connection with a steam-jet blower in the ash pit? 

In all cases where anthracite culm is used for fuel, it 
should be sprinkled with water before putting it on the 
fire, not so as to make it sloppy and heavy, but just enough 
to make the dust adhere to the particles of small coal. 
Anthracite screenings from coal yards should be treated 
in the same manner, and if they have lain out in the 
weather for any considerable length of time, it will be 
found advantageous to mix them with about one-fifth their 
bulk of bituminous slack, where it is available. 

A very simple yet very important feature in burning 
fine fuels successfully, where the argand blowers are used 
to furnish blast, is to close the damper in the chimney, or 
stack, to a point where the burning gases will not blow out 
through the fire door when opened, for where there is a 
strong chimney or stack draft in connection with the under- 
grate blowers a large percentage of the gases escape with- 
out igniting. Therefore one should not fail to so regulate 



320 COMBUSTION OF COAL. 

the damper that the largest possible volume of gaseous 
flame may be produced in the furnace. Where the chim- 
ney draft is weak, it may be necessary to keep the damper 
wide open, but it has been found that in the majority of cases 
it is not only beneficial, but absolutely essential, to regu- 
late the dampers as described in order to produce the best 
results. 

Q. What is mechanical draft ? 

This name is commonly applied to any system of press- 
ure or exhaust fans driven by a separate mechanism, by 
which, in the case of a blower, a current of air is forced 
through the fire ; or by exhaustion of the products of com- 
bustion by means of a vacuum created by a revolving fan 
placed beyond the uptake or in the breeching leading to 
the chimney. In either case the air needed for combus- 
tion is supplied the fire through mechanical means and 
not by natural draft. 

Q. What are the ordinary methods of application of 
mechanical draft? 

The commonest method is by means of a centrifugal 
fan, or fan blower, by means of which the air needed for 
combustion is forced through the fire. The air supply in 
stationary boiler practice is usually forced into an air- 
tight ash pit, and as there is no other escape for the air it 
is forced through the fuel, and thus becomes a "forced" 
draft. Another method, frequently employed on steam- 
ships, is to make the fire-room air tight and force the air 
into it at such pressure and in such volume as may be 
needed for the combustion of the fuel. 

A typical arrangement of the B. F. Sturtevant Com- 
pany's steam fan for the production of under- grate-forced 
draft is shown in Fig. 80. The fan discharges the air 



322 



COMBUSTION OF COAL. 



into an underground-brick duct extending along the front 
of the battery of boilers. From this duct smaller 
branches, two to each boiler, extend to the ash pits, to 
which the air is admitted in the requisite amount through 
ash-pit dampers of the type shown in Fig. 81. There is 




Fig. 8i. 



thus maintained within the ducts and ash pits a pressure 
greater than that of the atmosphere by an amount depend- 
ent upon the speed of the fan, which may be regulated at 
will. 

Q. What objections are there to the closed ash-pit 
system ? 

An objection to the direct introduction of air under press- 
ure by means of a pipe in the bottom of or through one 
side of a closed ash pit, is found in the failure properly to 



MECHANICAL DRAFT. 



323 



distribute the air in 
the ash pit (see Fig. 
82), resulting in un- 
equal combustion, lo- 
calizing the heat in 
certain portions of 
the grate, and pro- 
ducing blow-holes in 
others. 

The air pressure in 
the ash pit, being in 
excess of that of the 
atmosphere, necessi- 
tates keeping the ash- 
pit doors closed ; this 
pressure also causes 
all leakage to be out- 
ward. The tendency 
is, therefore, to blow 

the ashes out of the ash pit, and the flame, smoke, 
fuel out of the fire doors. 




Fig. 82. 



and 



Q. How may the objections to the closed ash-pit system 
be overcome ? 

So far as the localization of the combustion is concerned 
it may be overcome by deflecting the air entering, the ash 
pit by means of a damper as shown in Fig. 83. This de- 
vice, by the B. F. Sturtevant Company, insures a thorough 
distribution of the air throughout the ash pit before it rises 
to the grate. The air duct is in this case constructed with- 
in the bridge wall, there being one or more dampers for 
each boiler. The amount of opening is regulated by the 
handle shown in the engraving. 



324 



COMBUSTION OF COAL. 



A hollow-blast grate is one of the devices for equably 
distributing the air and stimulating draft in connection 




Fig. 83. 

with mechanical draft apparatus. The Gordon hollow- 
blast grates in combination with a Sturtevant fan are 




Fig. 84. 



shown in Fig. 84. The grate bars are cast hollow, and 
have suitable openings adapted for burning coal, coal ref- 



INDUCED DRAFT. 325 

use, bagasse, tanbark, etc. The main blast pipe enters 
the ash pit through one of the side walls ; suitable tubes 
connect the blast pipe, and the grate bars above, thus es- 
tablishing an air connection between the two. 

Q. What is the induced system of draft? 

The induced suction or vacuum method for obtaining 
a suitable draft for furnace combustion consists in the in- 
troduction of an exhausting fan in the place of a chimney. 
The fan serves to maintain the vacuum which would exist 
if a chimney were employed, and its capacity can be made 
such as to handle the gases which result from the proc- 
esses of combustion. As the draft is thus rendered prac- 
tically independent of all conditions except the speed of 
the fan, it is necessary to provide only a short outlet pipe 
to carry the gases to a sufficient height to permit of their 
harmless discharge to the atmosphere. In practice the 
capacity of an induced draft fan, as measured by the 
weight of air or gases moved, necessarily varies with the 
temperature of the gases it is designed to handle. There- 
fore the density, which varies inversely as the absolute 
temperature, should enter as a factor in all such calcula- 
tions. The simplest arrangement for an ordinary boiler 
plant consists in placing the fan immediately above the 
boiler, leading the smoke flue directly to the fan-inlet 
connection, and discharging the gases upward through a 
short pipe extending just above the boiler-house roof. 

The induced draft system is, on the whole, better sub- 
ject to control than the other systems; its leakage is 
always inward, avoiding inconvenience from flame and 
smoke at the fire doors, it lends itself readily to control 
by the dampers which may be introduced for the pur- 
pose. 



326 COMBUSTION OF COAL. 

An induced- draft plant is shown in Fig. 85, consisting 
of 4 Manning boilers, each boiler containing 180 tubes 
2^/ 2 inches in diameter, 15 feet long; fire box 6 feet in 
diameter, 28.27 square feet of grate surface, and 1,823 
square feet of total heating surface for each boiler. The 
economizer contains 192 tubes, 4^ inches in diameter; 
the square feet of heating surface is 2,304. The two 
Sturtevant fans have a somewhat novel arrangement, 
whereby a relay is provided and the floor area occupied is 
reduced to a mimimum. Each fan has a wheel 7 feet in 
diameter, and driven by direct-connected engine. By 
means of an arrangement of dampers, the gases may be 
caused to pass through the economizer, and thence to 
either one or both fans, whence they are discharged 
through a short, vertical stack. The experimental results 
obtained furnish an interesting commentary upon the re- 
lations between fan speed, volume moved, pressure cre- 
ated, and horse power required. Up to a certain speed 
the natural draft of the short stack is equal to, or actually 
exceeds, that created by the operation of the fans; but 
when the draft produced by the fans exceeds that which 
the stack is capable of creating, the additional work is 
thrown upon the fans, and the power increases practically 
as the cube of the number of revolutions. 

Q. What is the proper kind of fan for use in connec- 
tion with a mechanical draft apparatus ? 

Two types of fans exist. The first, known as the disc 
or propeller wheel, is constructed on the order of a screw 
propeller, and moves the air in lines parallel to its axis, 
the blades acting on the principle of the inclined plane. 
The second, or fan blower proper, consists in its simplest 
form of a number of blades extending radially from the 



328 COMBUSTION OF COAL. 

axis, and presenting practically flat surfaces to the air as 
they revolve. By the action of the wheel the air is drawn 
in axially at the centre and delivered from the tips of the 
blades in a tangential direction. This type may be sim- 
ply designated as the centrifugal fan, or, more properly, as 
the peripheral discharge fan. 

The propeller or disc fan is practically useless as a 
means of draft production. The desired results can be 
secured only by the use of the peripheral discharge type. 

Theoretically there should be a difference in the form 
of wheels designed for creating pressure and creating a 
vacuum ; practically the distinction between a blower and 
an exhauster is one of adaptation rather than of construc- 
tion. 

Q. What are the advantages claimed for mechanical 
draft ? 

The advantages claimed may be summarized, for land 
requirements as distinguished from marine, in that by its 
introduction greater economy in the first cost or running 
expense of a steam plant may be secured. 

As compared with chimney draft, a chimney requires 
certain fixed and practically unalterable conditions for its 
location and erection, and is only to a limited extent 
adaptable to changes in its requirements. Mechanical 
draft apparatus may, on the contrary, be adapted to a great 
variety of conditions, such as accommodation to restricted 
space ; or it may be placed in any convenient location 
and not necessarily in the fire or engine rooms. 

Perfect control may always be maintained over the action 
of mechanical draft. With a chimney the intensity of the 
draft is least when the fire is low ; with the fan it is pos- 
sible instantly to produce the maximum draft under these 
conditions. 






MECHANICAL DRAFT. 329 

Climatic conditions do not affect mechanical draft; it 
can be made as strong in summer as in winter, and on a 
muggy day as on one that is bright and clear. 

Increased rates of combustion are readily had by means 
of mechanical draft, and the capacity of a boiler largely 
increased at any time to suit temporary or permanent con- 
ditions. 

The burning of cheap and low-grade fuels is best ac- 
complished by means of a mechanical draft. 

The prevention of smoke, usually a mere incident to the 
application of mechanical draft, has sometimes been a 
purpose sufficient in itself to warrant its installation, not 
that a direct saving in cost of fuel is had, but that cheap 
and low-grade fuels may be used in localities where smoke- 
prevention laws are enforced. This is on the assumption 
that the furnace is properly designed, and the introduction 
of a fan blast merely insures rapid combustion: 

The utilization of waste heat in gases by the use of an 
economizer is practicable only in the case of a chimney 
when the escaping gases are of a comparatively high tem- 
perature. When the draft is produced by a fan, the draft 
is independent of the temperature of the gases, the condi- 
tions then are favorable for utilizing the heat which is un- 
avoidably lost in the case of a chimney. The saving in 
fuel which may be accomplished under working conditions 
by the combined use of mechanical draft and economizer 
has been experimentally shown to range between 10 and 
20 per cent. 



CHAPTER XIII. 

SPONTANEOUS COMBUSTION. 

Q. What is meant by spontaneous combustion ? 

Spontaneous combustion means self-ignition; it is a 
name given to fires which have their origin in the heat 
generated by chemical action, or by the rapid oxidation of 
the substances thus ignited. The spontaneous combus- 
tion of coal is due to the chemical action set up between 
the carbon constituents and the atmospheric oxygen which 
is absorbed by coal ; the volume of oxygen so absorbed de- 
pends upon the surface exposed and the porosity of the 
coal; the chemical action evolves heat, and when this heat 
is confined it results in a constantly increasing tempera- 
ture, and this accelerates the process of oxidation. 

Q. What is the probable action set up in spontaneous 
combustion between the coal and the oxygen of the at- 
mosphere ? 

The surface of each particle of coal is active in attract- 
ing and condensing the atmospheric oxygen, and the oxygen 
so absorbed is largely rid of the dilutent nitrogen and, there- 
fore, is better fitted for the process of oxidation which be- 
gins slowly, but at once. In this process two actions are 
set up : first the combination of oxygen with what is called 
the disposable hydrogen in the coal to form water; sec- 
ondly, the combination of oxygen with the carbon, forming 
carbonic acid gas, and heat is evolved as the result of both 



SPONTANEOUS COMBUSTION. 33 I 

actions. In the initial stage it is not sensible, nor is it 
apparent as in the case of iron, where visible rust indicates 
the process. When this heat is subjected to the cooling 
effect of the atmosphere, or when it can be conducted from 
its source, no danger is to be apprehended; but where the 
evolved heat is not so conducted or cooled, as in the case 
of a mass of fine coal, the temperature will rise and con- 
tinue with accelerated rapidity as the ignition point is ap- 
proached (Howard). 

Q. How much oxygen will coal absorb ? 

It has been experimentally determined that certain 
English coals absorbed twice their own volume of oxygen, 
and in a pulverized state this absorption equalled 2 per cent 
of its own weight. 

Q. What is Richter's theory regarding the spontaneous 
combustion of coal? 

The theory worked out by Richter is that two of the 
constituent elements of bituminous coal, viz., the carbon 
and the hydrocarbons, have a strong attraction for atmos- 
pheric oxygen, and under ordinary conditions this absorp- 
tion of oxygen will be in proportion to the surface exposed, 
to the porosity of the coal, and to the temperature of the 
mass. 

Q. Have experiments been made to prove the correct- 
ness of Richter's theory? 

The absorption of oxygen by, and chemical combination 
with, pulverized bituminous coal is known to occur, and 
approximately under the following conditions : 

At a low temperature the action is slow; but it rapidly 
increased when ioo° F. was exceeded. Powdered coal 
has been known to fire in a few hours at a steady tempera- 



332 COMBUSTION OF COAL. 

ture of 250 F. Under ordinary conditions, however, the 
absorption was in proportion to the surface exposed, to the 
porosity of the coal, and to its temperature. 

Q. To what element in the coal is spontaneous com- 
bustion generally attributed ? 

Sulphur was once believed to be the real cause of spon- 
taneous combustion in coal, for the reason, probably, that 
if it is present in the coal it is in the form of pyrites, and 
this was associated with a well-known fact that heaped-up 
pyrites in shale, when wetted, often cause the combustion 
of the pile. The sulphur theory received the support of 
the noted Swedish chemist Berzelius. 

Q. What are the objections to the sulphur theory in 
the spontaneous combustion of coal ? 

It is objected to because it does not account for the 
numerous cases of the spontaneous combustion of coal in 
which sulphur is not present. The investigations of Dr. 
Percy in England and of Dr. Richter in Germany showed 
that the sulphur theory did not account for all the dis- 
covered facts. 

Coals almost free from sulphur have been observed to 
be dangerous, and others heavily charged with it compara- 
tively safe. Further the sulphur theory does not account 
for the ignition of charcoal, or of oily waste, nor of wool 
when saturated with animal or vegetable oils and sub- 
jected to favoring temperatures. 

Iron pyrites, or disulphide of iron, is the only sulphur 
compound found in coal which by oxidizing under favor- 
able conditions will gradually develop heat sufficient to 
make self-ignition a possibility. Sometimes, however, 
the pyrites will rapidly oxidize, and at others it will re- 






SPONTANEOUS COMBUSTION. 333 

main unchanged for a long period. The recent conclu- 
sions seem to point out that pyrite is merely accessory to 
the trouble, in that through oxidation it lowers the point 
of ignition in the surrounding mass of coal, and in the 
process it swells, causing disintegration of the lumps, and 
consequently increases the absorbing surface of the coal. 
The temperature of ignition of sulphur is 482 F., whereas 
coal requires from 700 ° to 900 F. 

Q. Can the safety of coals as regards spontaneous com- 
bustion be determined by analysis ? 

The difference between safe and unsafe coals cannot be 
determined by proximate or ultimate analysis. It is the 
deep mass of small and fine coal that constitutes the dan- 
ger ; and coals of a firing tendency are dangerous, some at 
one depth of pile and some at another. 

Q. How does carbon spontaneously ignite ? 

Carbon in a finely divided state has the power of con- 
densing oxygen within its pores ; now, to condense a gas, 
force is consumed and heat is produced. In the fire 
syringe, a piece of tinder is set on fire by the heat 
evolved by the condensation of the air. When charcoal 
condenses oxygen heat is liberated, and, if the charcoal is 
freshly burned, the rapidity of the action will produce 
such an amount of heat as to cause the chemical combina- 
tion of the oxygen and carbon, when, of course, combus- 
tion takes place with evolution of light and heat. The 
initial temperature of the action is here due to the sudden 
squeezing together of the gaseous molecules, for if the air 
be admitted to the freshly burned charcoal by slow degrees 
no combustion takes place. 



334 COMBUSTION OF COAL. 

Q. Is wood liable to spontaneous combustion when placed 
against or in close proximity to hot surfaces ? 

The fact that a hot steam pipe will char and eventually 
ignite wood is well known to fire-insurance inspectors. 
The application of moderate heat to wood dries up its 
juices, renders it brittle, and ultimately causes its com- 
plete disintegration and combustion if air is supplied, 
though the process is exceedingly slow. At the ordinary 
temperature of the air, oxygen has so little action upon 
wood that it is practically indestructible. 

Q. How should permanent woodwork passing through 
large masses of bituminous coal be protected? 

By covering the woodwork with sheet iron well painted 
to protect it, as iron also suffers from oxidation. 

Q. Does the presence of wood in a pile of coal affect 
favorably or otherwise the conditions leading to the 
spontaneous combustion of coal ? 

It is a well-established fact that the presence of wood 
in a pile of coal, whether present as loose chips or as 
forming supports, contributes materially to the fire risk. 
The surfaces of the wood through a process analogous to 
dry distillation become charred and converted into char- 
coal or tinder. The tendency to oxidation which carbon 
and carbon compounds, existing in such a substance as 
charcoal, possess, is favored by the condensation of oxygen 
within its pores, whereby the intimate contact between 
the carbon and oxygen particles is promoted. Hence the 
development of heat and the establishment of oxidation 
occur simultaneously, the latter is accelerated as the heat 
accumulates, and chemical action is thus promoted, and 
may, in course of time, proceed so energetically that the 



SPONTANEOUS COMBUSTION. 335 

carbon or carbo-hydrogen particles may be heated to the 
igniting point. 

Q. Does the height of a pile of coal contribute to spon- 
taneous combustion? 

The higher the pile of coal the greater is the fire risk, 
especially if the coal is very fine. It is a matter of gen- 
eral observation that when fires break out on shipboard, 
they originate directly under the main hatchways, or under 
the coaling chutes, or in the middle or near the bottom 
of a deep cargo. 

Q. Is coal liable to spontaneous combustion when placed 
against or over hot surfaces ? 

So long ago as 1852 Graham pointed out that the ten- 
dency of coals to spontaneous ignition is increased by a 
moderate heat. In one case coal had taken fire by being 
heaped for a length of time against a heated wall, the tem- 
perature of which could be easily borne by the hand. In 
another, coal ignited spontaneously after remaining for a 
few days upon stone flags covering a flue, of which the 
temperature never rose beyond 150 F. Examples are 
sufficiently numerous to fully establish the fact that 
masses of coal exposed to even a moderate heat become 
hazardous as a fire risk. 

Q. Will small bodies of coal ignite spontaneously? 

Coal in small quantity and in a cool place never ignites 
spontaneously; it does not, therefore, follow that all the 
conditions leading up to spontaneous combustion are absent, 
only that one of them, and that an all-important one, the 
means of accumulating heat, is absent, since the barriers 
interposed to its escape are not sufficiently close-fitting. 



336 COMBUSTION OF COAL. 

Q. What would be the effect of forcing air into a body 
of coal as a means of preventing spontaneous combustion 
by forced ventilation? 

When air is forced into a body of coal more or less 
oxidation occurs, followed by a rise in temperature, the 
heat present or liberated by its increased oxidation is ab- 
sorbed by the coal, fresh supplies of air being continually 
forced in, passes over and around the oxidizing surfaces 
of the coal becoming hotter and hotter, the air itself be- 
comes heated, and all the conditions for combustion ob- 
tain, which, if once begun, continue more and more rapidly 
with each increment of air supply. 

Q. Is wet coal more liable to spontaneous combustion 
than dry coal? 

Water does not assist in the spontaneous combustion of 
coal except where pyrites are concerned. There is much 
misunderstanding as to the part played by water in the 
changes leading to spontaneous combustion. The water 
itself is not decomposed, as some have imagined. The 
heat evolved during the combustion of hydrogen and 
oxygen to form water (62,000 heat units) must be sup- 
plied before they can be again torn apart, so that so far 
from water being a producer of heat, it is likely to be a 
consumer. 



INDEX. 



Absolute zero, 54 
Affinity, 62 

Air, advantages of heated, 88 
ammonia in, 73 
and steam jets for locomo- 
tives, 129 
carbonic acid in, 73 
composition of, 68 
conversion of pounds into 

cubic feet, 77 
density and passage of heat, 

78 
economical limit to heating, 

90 
effect of pre-heating, 79 
surplus, 107 
too little, 87 
too much, 88 
excess of, in combustion, 82 
expansion of, by heat, 78, 

151 
heated and chemical action, 
89 
physical and chemical 
effects, 80 
heating and cooling of, 77 

coils for locomotives, 129 
increase in bulk by heat, 155 
liquefaction of, 82 
measuring flow of, 101 
non-admission of, over oil 
fires, 300 
22 



Air not a chemical compound, 
68 

ozone in, 74 

physical effects of heat upon, 
78 

pre-heated, objections to, 79 

quantity required for com- 
bustion, 81 
per pound of coal, 82 

specific heat of, 82, 143, 152 

vapor in, 74 

weight of, 75 
Allen and Tibbitts furnace feed- 
er, 245 
Alumina in ashes, 114 
American stoker, 235 
Analysis, elementary, 160 

proximate, 172 

qualitative, 160 
Anemometer, 102 
Anthracite coal, 13 

air required for, 108 

ashes from, 109 

classification of, 13 

composition of, 14 

physical properties of, 11 

small sizes, 14 
Anthracite fire, cleaning of, 240 
Arch, brick, endurance of, 262 

Murphy's, 124 

oil-burning locomotives, 300 

Prescott's oil burner, 303 



338 



INDEX. 



Area of chimney, 311 
Argand steam blower, 317 
Arkansas lignite, 33 
Arndt, Max, econometer, 132 
Artificial fuel, advantages of, 44 
Ash-forming constituents in coal, 

12 
Ashes, alumina in, 114 

Berthier's analysis, 117 

color of, no 

composition of, 109 

definition of term, 108 

from lignites, 34 

fusing of, in 

iron pyrites in, 112 

lime present in, 117 

oxide of iron in, 112 

potash in, 116 

quantity after combustion, 
118 

silica in, 115 

specific heat of, 109 
Ash-pit damper, 322 

system of forced draft, 322 
Ash pan operated by compressed 
air, 289 

Southern Pacific Railway, 
289 

when to be examined, 126 

with side valves, 291 
Atmosphere, 68 

density and height, 76 

pressure of, 75 
Atom, 58 
Atomic value in compounds, 65 

weight, 58 

and specific heat, 152 
and symbolic notation, 
61 
Atomizers for burning oil, 300 
Attraction, chemical, 63 



Available heat of combustion, 

213 
Ayers and Ranger, stoker, 231 

Babcock & Wilcox Co., quoted, 
207 

stoker, 226 
Baffle plates in locomotives, 279 
Bagasse, 36 

Fisher's furnace for, 241 
Barnes' locomotive boiler, 266 
Barometer, 76 

Barrus, G. H., calorimeter, 187 
Beggs, James & Co., blower, 317 
Bell, J. Snowden, quoted, 284 
Berthier's calorimeter, 195 

results PbO tests, 194 
Biglow Co. 's boiler setting, 219 
Bitumen, no organic structure in, 

18 
Bituminous coal, 18 

ashes from, no 

calorific value, 198 

classification of, 22 

composition of, 19 

table of American, 20 
Block coal, 28 

ashes from, no 
Blossburg, Pa., semi-bituminous 

coal, 18 
Blower, steam, argand, 317 
Boiler, Barnes' locomotive, 266 

efficiency, 216 

furnaces, stationary, 217 
Kent's, 221 

horse-power, 180 

Strong's locomotive, 280 

tubes and oil fires, 302 

Wootten's locomotive, 263 
Boyle's law and density of air, 
76 



INDEX. 



339 



Breckenridge, Ky., cannel coal, 

26 
Brick arches and light firing, 262 

and soft coal, 127 

construction of, 251 

for oil burning, 300 

leaky flues, 252 

locomotive, 250 

Murphy's, 124 

Southern Pacific Railway, 
288 
Bridge wall, locomotive, 265 
Briquettes of fuel, 42 
British thermal unit, 151 
Brown coal, 29 

Thorp's analysis, 30 
Buck Mountain, Pa., coal, 15 
Burlington, C, R. & N smoke- 
less firing, 123 
Burning residuum from shale, 
298 

Caking coals, 22 

Calorie, 151 

Calorific value of fuel, 178, 182 

Calorimeter, Barrus', 187 

Berthier's, 195 

Carpenter's, 191 

copper-ball, 193 

Favre & Silberman's, 144 

Thompson's, 185 
Cannel coal, 25 
Carbon, 160 

air required for, 81 

allotropic states of, 162 

and hydrogen, 161 

dioxide, see Carbonic Acid 

estimating temperature of 
combustion, 142 

heating power and density, 
167 



Carbon monoxide, see Carbonic 
Oxide 

specific heat of, 162 
Carbonic acid, 161 

heat units, 141 

in the air, 73 
Carbonic acid gas, liquefaction 
of, 104 

measurement of, 134 

properties of, 104 
Carbonic oxide, 161 

combustion of, 105 

heat units, 141 

liquefaction of, 105 

properties of, 105 
Carburetted hydrogen, 170 
Carpenter, R. C, calorimeter, 

191 
Castle Gate, Utah, bituminous 

coal, 284 
Charcoal, composition, 165 

physical properties, 164 
Chemical action and mechanical 
energy, 149 

affinity, 62 

attraction, 63 

and temperature, 66 

properties of a body, 62 

separation, energy of, 66 
Chevandier, M., quoted, 35 
Chimney, 309 

area of, 311 

draft, 313 

height, 312 

increasing draft in, 316 

intensity of draft, 313 

object of, 309 

proportions, 315 

table of dimensions, 316 

temperature, economical, 311 

unbalanced pressure in, 309 



340 



INDEX. 



Centennial, boiler horse-power, 

181 
Centigrade and Fahrenheit ta- 
ble, 56 

scale of. temperature, 5 5 
Cincinnati N. O. & T. P. Rail- 
way smokeless firing, 124 
Cinders, collecting in front end, 

279 
Clark, D. K., quoted, 199 
Cleaning fires, 241 
Clinker, 114 

and ashes, locomotive fire 

box, 291 
and color of ashes, in 
and efficiency of coal, 117 
Coal, 10 

absorbs oxygen, 331 
analysis and spontaneous 

combustion, 333 
and oil, relative cost, 302 
ash-forming constituents, 12 
commercial classification, 11 
evaporation by, in locomo- 
tives, 258 
evaporative power of, 181 
exposed to hot surface, 335 
Gruner's classification, 11 
height of pile, fire risk in, 

335 
moisture in, 172 
net calorific value, 182 
proximate analysis of, 172 
saved by light firing, 260 
theoretical calorific value, 

182 
volume of gases from, 310 
wet and spontaneous com- 
bustion, 336 
where it goes in a locomo- 
tive, 147 



Coke, 23 

calorific value of, 199 

coal for making the best, 
25 

from lignite, 34 

properties of, 24 
Colorado lignite, 32 
Combining weight, 58, 64 
Combustible, equivalent evapo- 
ration, 210 
Combustion, 83 

available heat of, 213 

chamber, locomotive, 265 

effect of nitrogen, 72 

heat developed by, 144 

localization of, 323 

nature of, 83 

products of, 103 

rate of, in locomotives, 250 

spontaneous, 330 
Composition of fuel, table, 10 
Compounds, atomic value un- 
changed. 65 
Compressed air, operating ash 

pan by, 289 
Condensation and latent heat, 

204 
Conduction of heat, 153 
Conductivity of metals, 154 
Connellsville, Pa., coke, 23 
Convection of heat, 155, 203 
Copper-ball calorimeter, 193 
Corbus, M. D., and brick arches, 

252 
Coming's patent fuel, 460 
Corrugated fire box, 281 
Cost of oil and coal compared, 

302 
Cotton hulls, feeding to furnace, 
247 

stalks, evaporation by, 198 



INDEX. 



341 



Cox, E. T. , analysis of cannel 
coal, 27 
calorific value of coal, 182 
Coxe Bros. & Co. standards for 

small coal, 14 
Culm, 16 

preparation for burning, 319 
Cumberland, Md., semi-bitumi- 
nous coal, 17 

Daily report, travelling fireman, 

291 
Damper, 317 

ash pit, 322 
Definite proportions, law of, 64 
Density of steam, 208 
Diamond, physical properties, 

163 
Diaphragm in smoke box, 274 

plates, 279 
Dimensions, boiler furnace, 217 

chimneys, 316 
Dissipation of energy, 53 
Double furnaces, locomotive, 
Barnes', 267 

locomotive, Strong's, 281 
Down-draft furnace, 224 
Draft, advantages of mechani- 
cal, 328 

appliances, efficiency of, 276 

best variety of fan for, 328 

caused by expansion of 
gases, 155 

chimney, estimating, 312 
how modified, 316 

distribution of, 279 

forced, 320 

furnace, how caused, 309 

induced system of, 325 

locomotive, 270, 283 

mechanical, 320 



Draft pipes, 274 

double, 278 
sluggish in chimneys, 316 
Dry coals, defined, 12 
Dulong's formula, 183 

Econometer, Arndt's, 132 

and air supply, 136 

detects fuel loss, 138 
Efficiency, furnace, 215 

how measured, 216 

locomotive boiler, 259 
Elementary analysis, 160 
Energy, 50 

characteristics of, 51 

chemical separation, 66 

dissipation of, 53 

fuel, 52 

kinetic, 51 

potential, 50 
Equivalent, 63 

evaporation, factors of, 207 
from and at 212 °, 210 
Escaping gases and temperature 

of steam, 203 
Evaporation and horse-power, 
180 

factor of, 205 

latent heat of, 203 

locomotive, 258 

moisture in coal, 179 

object of reducing to, from 
and at 212 , 213 

ordinary rate of, 213 

per pound combustible, 210 
Evaporative factor, defined, 12 

power of coal, 181 

results in locomotives, 271 
Exhaust nozzle for oil, 302 

pipe and nozzle, S. P. Ry., 
285 



342 



INDEX. 



Exhaust pipe passages, 277 

single, 277 

single and double, 271 
steam, heat lost in, 205 
utilizing heat in, 280 
tip, adjustable, 278 

best form, 271 

cross bar in, 278 

size of, 272 
Expansion of air by heat, 151 
of gases, table of , 150 

Factor of evaporation, 205 
Fahrenheit scale of tempera- 
ture, 55 
Fan for forced draft, 326 
Fat coals, denned, 11 
Favre and Silberman's calorim- 
eter, 145 
Feed water, limit of temperature 

in locomotives, 280 
Findlay, O., natural gas, 174 
Fire, cleaning of, 241 

temperature of, 142 
Fire box, corrugated, Strong's, 
280 
disadvantages of wide, 266 
for straw and coal, 243 
limitations, locomotive, 249 
objections to long, 249 
wide, locomotive, 263 
with two furnaces, 266 
Fire door, instructions regard- 
ing, 126 
Firing, best method, 261 

intelligent, and promotion 

for, 126 
light and boiler repairs, 262 

and brick arches, 262 
practical suggestions, 261 
saving by light, 260 



Firing, single shovel, 259 

Southern Pacific Railway, 
284 

Fisher's bagasse furnace, 241 

Flame, 90 

anthracite coal, 10 1 
blue region in, 94 
candle, hollow, 95 
carbonic oxide. 105 
cause of luminosity in, 97 
chemical processes in, 90 
color in, 98 
dark region in, 93 
extinguished by cooling, 100 
faintly luminous region, 94 
not a continuous process, 96 
not in contact with orifice, 

100 
proof of solid carbon in, 97 
rate of propagation, 95 
structure of, 91 
successive developments in, 

92 
temperature of, 99 
variations of temperature in, 

96 
yellow region in, 93 

Flues, leaky, and brick arch, 
252 
cause of, 253 

Forced draft, 320 

best fan for, 326 
ventilation of coal piles, 336 

French unit of heat, 151 

Frontenac, Kan., coal, 190 

Front ends, Southern Pacific 
Railway locomotive, 285 

Fuel, 9 

analysis, 160 

and horse-power unit, 181 

calorific power of, 180 



INDEX. 



343 



Fuel, elementary constitution, 9 
energy of, 52 

feeding fine, to furnace, 245 
fine, preparation of, 319 

Rogers feeder, 247 
liquid, advantages of, 295 
loss with 2 to 15 per cent. 

C0 2 in gases, 137 
preparation of, for steam jet, 

319 
Furnace, boiler, dimensions of, 
217 

bagasse, 241 

coals, defined, 12 

door, Southern Pacific Rail- 
way, 287 

double, locomotive, 281 

down-draft, 224 
1 efficiency of, 215 

feeder for fine fuel, 245 

Kent's, boiler, 221 

locomotive, double, 266 

losses in, 215 

Murphy's, 233 

stationary, details of, 215 
Fusion, latent heat of , 156 

Gas coals, 12 

Gas, compared with coal, 174 

effects of heat upon, 150 

evaporative power of, 175 

natural, 174 

producer, 176 

rate of expansion, 55 

Siemen's, 177 

water, 176 
Gaseous fuels, calorific values, 

177 
Gases, conduction of heat in, 
155 

ignition temperature of, 87 



Gases, rate of increase in vol- 
ume, 310 
volume of escaping, 310 
weight of, from furnace, 107 
Georges Creek coal, 190 
Gordon's hollow blast grate, 324 
Grant's patent fuel, 45 
Graphite, physical properties, 

164 
Grate area, advantages of large, 
249 
increase of, in locomo- 
tives, 264 
hollow-blast, 324 
McClave's, 239 
plain, locomotive, 255 
shaking, details of, 257 

Southern Pacific Rail- 
way, 289 
water-tube, 254 
when to be shaken, 126 
Grimshaw, Robert, quoted, 255 
Gruner's classification of coals, 



Haswell, C. H., table, proper- 
ties of steam, 208 
Heat, 140 

Heat and chemical action, 149 
mechanical energy, 158 
water, 202 
work, 53 
combustion of carbon, 143 
conduction of, 153 
convection of, 155, 203 
developed by combustion, 

140, 144 
distribution of, in locomo- 
tives. 147 
effect upon gases, 150 
upon water, 149 



344 



INDEX. 






Heat evolved by calorimeter 
tests, 146 
by combustion, 194 
good conductors of, 154 
imperfect conductors of, 154 
how gases conduct, 155 
in exhaust steam, utilizing, 

280 
in steam, 208 
latent, 156 

lost, burning to carbonic ox- 
ide, 141 
mechanical equivalent of, 

157 
non-conductors of, 154 
problem in steam engine, 201 
radiation of, 156 
specific, 159 
Heat, unit of, 151 

carbon burned to CO and 

C0 2 , 141 
natural gas, 174 
Heating power of fuels, 178 
petroleum, 296 
sulphur, 148 
Heggem's straw-burning fur- 
nace, 243 
Height of chimney, 317 
Heintselman's grate, 288 
Hoadley, J. C, quoted, 107 

temperature tests, 203 
Horse-power of boilers, 180 

unit of, 49 
Hot-steam pipes and wood igni- 
tion, 334 
Howard, C. C, analysis natural 

gas, 175 
Hydrocarbon oil burner, 303 
from shale, 298 
fuel for locomotives, 295 
Hydrogen, 168 



Hydrogen, air for combustion of, 
81 
liquefaction of, 169 
product of combustion of, 

103 
specific heat of, 152 
union with carbon, 84 
Hygroscopic moisture, 172 

Ignition, 86 

temperature of gases, 87 
Indiana block coal, 28 
Induced system of draft, 325 
Injectors, limit of feed tempera- 
ture, 280 
Instructions to locomotive fire- 
men, 125 
Internal work in liberating gas 

from bituminous coal, 182 
Iron pyrites and ashes, 112 

and spontaneous com- 
bustion, 332 



Jones' underfeed stoker, 
Joule's equivalent, 157 



237 



Kent, William, quoted, 184 
Kent's boiler furnace, 221 
Kentucky brown coal, 30 
Kinetic energy, 51 

Latent heat, 156 

and condensation, 204 
of evaporation, 203 
of fusion, 156 
Lean coals defined, 11 
Lehigh anthracite coal, 14 
Lesley, J. P., on anthracite for- 
mation, 13 
Light firing, Southern Pacific 
Railway, 291 



INDEX. 



345 



Lignite, 30 

ashes from, 34 

calorific value of, 198 

coke from, 34 

composition of, 32 

occurrence, 31 

properties of, 30 
Lime, how present m ashes, 117 
Liquefaction, interior work, 156 
Liquids bad conductors of heat, 

154 
Locomotive, air and steam jets 
for, 129 
boiler, Barnes', 266 
efficiency, 259 
Strong's, 280 
Wootten's, 262 
brick arch, 250 
changing coal to oil, 299 
combustion chamber, 265, 280 
draft in, 270 

evaporative performance, 259 
fire boxes, smokeless, 123 
double, 266, 280 
limitations, 249 
wide, 263 
firing instructions, 125 
furnace details, 249 
rate of combustion, 250 
Smoke Preventer Co., 127 
smokeless combustion, 284 
where the coal goes, 147 
Losses in a furnace, 215 
Lost work, 48 

Mahler's formula, 184 
Mariotte's law and density of 

air, 76 
Marsh gas, 170 
Master Mechanics Association — 

front ends, 285 



McArdle, Frederick, quoted, 260 
McClave, grate by James Beggs 

& Co., 239 
McHenry, E. H., diagram: 
"Where the coal goes when 
burned in a locomotive fire 
box," 148 
Mechanical draft, advantages of, 
320, 328 
energy and heat, 158 
equivalent of heat, 157 
stoker, American, 235 

Ayers and Ranger, 231 
Babcock & Wilcox, 226 
Jones, 237 
Roney, 227 
Wilkinson, 229 
Mercury, boiling point of, 54 

freezing point of, 54 
Metals, thermal conductivity of, 

154 
Mogul engine, 148 
Moisture in coal, 172, 180 
Molecule, 59 
Multiple proportions, law of, 

65 
Murphy, J. W., locomotive fire 

box, 124 
Murphy's furnace, 233 

Nagle, A. F., quoted, 29 

Natural gas, 174 

heat units in, 174 
Howard's analysis, 175 

Netting, area of openings, 279 
location of, 278 

New River coal, 190 

Nicholson, George B., quoted, 

253 
Nitrogen, 71 

economic qualities of, 73 



346 



INDEX. 



Nitrogen in products of combus- 
tion, 106 
liquid and solid, 71 
negative qualities of, 72 
non-supporter of combus- 
tion, 71 
specific heat of, 71, 152 
Non-caking coals, burning of, 28 
Non-condensing engine, heat lost 

in, 205 
Northern Pacific Railway Mogul 

engine, 148 
Notation, symbolic, 60 

O'Brien & Pickle's furnace, 224 

Oil, advantages of as fuel, 295 
and coal, relative cost, 302 
auxiliary to coal, 298 
burner, Prescott's, 303 
burning locomotive, change 
from coal, 299 
locomotive, size of ex- 
haust nozzle, 302 

Oil fires and boiler tubes, 302 
are they smokeless? 302 
no air admitted above, 300 
no limit to steaming capac- 
ity, 303 
products of combustion, 302 

Oil of the Pacific coast, 301 

Olefiant gas, 171 

Oxygen, 69 

absorbed by coal, 331 
and litharge fuel tests, 196 
and spontaneous combus- 
tion, 71 
chemical activity of, 71 
estimation of volume, 86 
liquid and solid, 70 
specific heat of, 69, 152 
supporter of combustion, 85 



Oxygen, union with carbon, 84 

Oxide, defined, 70 

of iron in coal ashes, 112 

of lead calorimeter tests, 194 

Ozone in the atmosphere, 74 

Parrot coal, 26 
Patent fuels, 43 

Coming's, 46 

Grant's, 45 

Strong's, 45 

Warleck's, 43 
Peat, 37 

calorific value of, 198 

charcoal, 40 

classification, 41 

composition, 38 

density, 39 

occurrence, 41 

preparation for fuel, 40 
Percy, John, definition of coal 
(numerous quotations from) , 
10 
Petroleum, analysis of, 296 

heating power of, 296 
Pictet, Raoul, liquid oxygen, 70 
Pocahontas coal, 190 
Potash, carbonate of, 116 

in ashes of wood, 116 
Potential energy, 50 
Power, unit of, 49 
Prescott, George W., oil burner, 

303 
Pressure of atmosphere, 75 

unit of, 75 
Producer gas, 176 
Products of combustion, 103 

of oil fires, 302 
Properties of saturated steam, 

208 
Proportions for chimneys, 315 



INDEX. 



347 



Proximate analysis of coal, 172 
Purdue University, calorimeter, 

193 
locomotive test, 275 

Quereau, C. H., quoted, 270 et 
seq. 

Radiation of heat, 156 
Raps, Henry, quoted, 262 
Rate of combustion, locomotive, 

250 
Red Lodge coal, 148 
Rice hulls, feeding to furnace, 

247 
Richter's theory of spontaneous 

combustion, 331 
Ringlemann's smoke scale, 121 
Rogers' furnace feeder, 247 
Roney's mechanical stoker, 227 

Sawdust, feeding to furnace, 247 
Scale and corrugated furnace, 

282 
Schenectady locomotive, 284 
Semi-anthracite coal, 16 
Semi-bituminous coal, 17 
Shaking grate, 257 

Southern Pacific Railway, 
289 
Shale, hydrocarbon residuum 

from, 298 
Sieman's gas, 177 
Silica in ashes, 115 
Sinclair, Angus, quoted, 123, 

259 
Small, H. T., superintendent 
Southern Pacific Railway, 284 
Smoke, defined, 118 

from locomotives, 123 
oil fires, 302 



Smoke, indication of waste, 119 

intensity of, 120 

prevention, 119, 127 

Ringlemann's scale, 121 
Smoke box, diaphragm in, 274 

extension, object of, 275 
Smokeless combustion, 127, 284 

firing, 123, 260 
Southern Pacific Railway ash 
pan, 289 

brick arch, 288 

details of grate, 289 

exhaust pipe and nozzle, 285 

front end of locomotives, 285 

furnace door, 287 

oil for fuel, 295 

oil-burning device, 299 

smokeless combustion, 284 

travelling fireman, 291 
Sparks, baffle plates, and net- 
tings, 279 
Specific heat, 159 

air, 82, 143 

and atomic weight, 152 

ashes, 109 

carbon, 162 

gases, 152 

nitrogen, 71 

of oxygen, 69 

solids, table of, 153 

water, 153 
Splint coal, 12 
Spontaneous combustion, 330 

and coal analysis, 333 
iron pyrites, 332 

Richter's theory, 331 

sulphur, 331 
Stack and baffle plates, 279 

diamond and draft pipe 

279 
locomotive, best form, 273 



348 



INDEX. 



Stack, taper better than dia- 
mond, 278 
Standards of temperature, 54 
Stationary furnace details, 215 
Stations, preparing fire for, 126 
Steam and air jets in locomotive 

furnaces, objections -to, 131 
Steam blower, best location, 318 
Steam, condensation of, 204 
effect of, in furnace, 319 
engine, heat problem in, 201 
generation of, 201 
heat lost in exhaust, 205 
neanng, 209 
jets for smoke prevention, 

127 
properties of, 208 
total heat in, 207 
withdrawal of heat from, 209 
Stokers, mechanical, Ayers & 
Ranger, 231 
Babcock & Wilcox, 226 
Roney, 227 
Wilkinson, 229 
Straw-burning furnace, 243 

evaporation by, 198 
Strong, G. S., locomotive fire 

box, 280 
Strong's patent fuel, 45 
Sturtevant, B. F. Co., ash-pit 
dampers, 322, 324 
forced-draft system, 320 
induced-draft system, 325 
Sulphur, 168 

and spontaneous combus- 
tion, 331 
combustion of, 106 
heating power of, 148 
in coal, 173 

effects of, 106 
occurrence, 113 



Sulphurous oxide, 106 
Symbolic notation, 60 

and atomic weight, 61 

Tamaqua, Pa., anthracite coal, 
14 

Tan as a fuel, 37 

Temperature best for chimney 
draft, 313 
burning carbon, 142 
chimney, economical, 314 
fire, conditioned, 142 
gases and steam, 203 
range in steam engine. 202 
standards for, 54 
steam, 208 

Texas lignite, 34 

Thermal unit, British, 151 
French, 151 

Thermometer, 53 

and quantity of heat, 57 
indicates sensible heat, 57 

Thompson's calorimeter, 185 

Thorpe, Professor (numerous 
quotations follow), 42 

Total heat in steam, 207 

Travelling fireman, Southern 
Pacific Railway, 291 

Tunnels, preparing fire for, 
125 

Unit of boiler horse-power, 
180 

British thermal, 151 

French thermal. 151 

horse-power, 49 

power, 49 

pressure, 75 

work, 48 
Useful work, 49 
Utah bituminous coal, 284 



INDEX. 



349 



Vacuum in locomotive fire boxes, 

277 
Vancouver's island lignite, 33 
Vapor of water in atmosphere, 

74 
Velna's fuel briquettes, 42 
Violette, M., quoted, 36 
Volume of one pound steam, 208 

Washington lignite, 32 
Water, boiling point, 55 

conducts heat slowly down- 
ward, 202 
effect of heat upon, 149 
freezing point of, 55 
specific heat of, 153 
Webber, W. O., quoted, 259 
Webster, Hosea, on natural gas, 

175 
Weight of the air, 75 

of steam, 208 
Wilkesbarre, Pa., semi-anthra- 
cite, 15 



Wilkinson's mechanical stoker, 

229 
Wood as a fuel, 36 

calorific value of, 197 

classification of, 34 

composition of, 35 

in coal liable to self-ignition, 

334 

moisture in, 35 

spontaneous ignition of, 
334 
Wootten, John E., boiler, 263 
Work, 48 

and heat, 53 

lost, 48 

unit of, 48 

useful, 49 

YOUGHIOGHENY COal, I90 

Zero, absolute, 54 
Centigrade, 55 
Fahrenheit, 55 



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*** Prepaid to any address on receipt of price. 

NORMAN W. HENLEY & CO., Publishers. 
132 Nassau St., New York. 



JUST PUBLISHED. 



THIRD EDITION 



The Modern machinist, 

By JOHN T. USHER, Machinist. 



PRICE, - S2.50. 



Specially Adapted to the Use of Machinists, Apprentices, 
Designers, Engineers and Constructors. 



A practical treatise embracing the most approved methods of modern machine-shop practice, 
embracing the applications of recent improved appliances, tools, and devices for facilitating, duplicating, 
and expediting the construction of machines and their parts. 

A NEW BOOK FROH COVER TO COVER. 

Every illustration in this book represents a new device in machine-shop 
practice, and the engravings have been made specially for it. 



8vo. 322 Pages. 257 Illustrations. Price, $2.50. 



What is said of " The Modern Machinist." 

This is anew work of merit. It is on " Modern Machine Shop Methods," as its name implies. 
It is thoroughly up to date, was written by one of the best-known and progressive machinists of the. day, 
is the modern exponent of the science, and all its subjects are treated according to latest developments. 
In short, the book is new from cover to to cover, and is one that every machinist, apprentice, designer, 
engineer, or constructor should possess. — Scientific Machinist. 

This book is the most complete treatise of its kind that has yet come under our observation, and 
contains all that is most modern and approved and of the highest efficiency in machine-shop practice, 
ete., etc.— Agb op Steel. 

There is nothing experimental or visionary about this book, all devices being in actual use and 
giving good results. It might perhaps be called a compendium of shop methods, showing a variety of 
special tools and appliances which will give new ideas to many mechanics, from the superintendent to 
the man at the bench. It will be found a valuable addition to any library, and will be consulted 
Whenever a new or difficult job is to be done.— Machinery, 



NORMAN W. HENLEY 6k CO., pubushms, 
132 NASSAU STREET, NEW YORK. 

* # » Copies of the above sent prepaid on receipt of price. 



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