D 11 t- -a ooc ' o f E. Chemistry and Physics. 53 Bulletin No. 325 Series < n' ^^ g

DEPARTMENT OF THE INTERIOR . 

UNITED STATES GEOLOGICAL SURVEY

GEORGE OTIS SMITH, DIRECTOR

A STUDY OF

FOUR HUNDRED STEAMING TESTS

MADE AT THE FUEL-TESTING PLANT, ST, LOUIS, 10, 

IN 1904,1905, AND 1906,

BY

LESTER P. BRECKENRIDGE

WASHINGTON

GOVERNMENT PRINTING OFFICE

1907

CONTENTS.

Page. 

Preface, by L. P. Breckenridge............................................. 7

Introduction, by Walter T. Ray............................................ 9

Relations of test data. ...................................................... ^ 11

Rate of combustion.................................................... 11

Supposed rate of heat evolution......................................... 13

Combustion-chamber temperature......'................................. 18

A. S. M. E. code boiler efficiency (72*)................................. 26

Moisture in coal....................................................... 32

Ash and clinker..................................................'..... 32

Average diameter of coal............................................... 45

Per cent of rated capacity developed ..............'..................... 51

Pyrometry.................^........................................... 52

Smoke................................................................. 56

Combustion and coal...................................................... 58

On "volatile matter," "fixed carbon," "water of Composition," and

1 ' combustible "........................................................ 58

Grate and combustion space......................'....................... 59

Velocity of combustion at various points along the flame.................. 60

Combustion-chamber baffle wall........................................ 62

Combustion-chamber temperature...................................... 63

Attempts to explain unaccounted-for loss in heat balance................. 64

Relation of nitrogen in flue gases to efficiency 72* and to size of coal, and

of per cent of CO to efficiency 72*...................................... 64

Relation of C02 in flue gases to per cent of completeness of combustion

(E3)................................................................. 65

Relation of differences of draft to pounds of dry chimney gases per pound

of "combustible".................................................... 66

Classification of coals....................................................... 68

Carbon-hydrogen ratio in air-dried coal.................................. 68

Carbon-hydrogen ratio in coal as received............................... 70

Carbon-hydrogen ratio in dry coal....:.................................... 77

Carbon-hydrogen ratio in coal as fired as affecting efficiency 72*........... 82

Relation of ratio of carbon to available hydrogen and of per cent of available hydrogen to efficiency 72*....................................... 83

Ratio of hydrogen to available hydrogen................................ 85

. Per cent of "volatile matter" in the "combustible"..................... 89

Fixed carbon (proximate analysis)...................................... 90

Relation of efficiency 72* to per cent of oxygen in "combustible"........ 92

British thermal units per pound of dry coal............................. 93

Ratio of ash to sulphur in dry coal...................................... 94
4 . CONTENTS.

Page.

Suggested'steam-turbine cycles, heat absorption, .and boiler efficiencies.... 95

The boiler and the furnace and their .efficiencies.......................... 95

High initial furnace temperature and its effect on economy..,.............. 100

Low steam pressure and its effect on economy............................ 102

Heat transmission through boiler tubes, and true boiler and furnace efficiencies...-. ............:......................;......;.............. 105

Theoretical considerations............................................... 109

True boiler efficiencies dependent only on physical size, shape, and arrangement of boiler.................................................. 112

Influence of velocity of gases on heat absorption......................... 113

Practical application of theory of heat absorption to a fire-tube boiler...... 118

Water circulation as affecting heat absorption............................ 120

Calculation of heat absorption along a fire tube. ............................ 121

Higher initial temperature means higher final 'temperature when heat

absorption is by convection only........... '..........................' 124

Modifying factors of the theory of heat transmission...................... 125

Temperature test of Perry's equation...............'.................... 132

Ratio modified in practice by initial temperature......................... 134

A conception of boiler and furnace efficiency. ...........................:. 137

The code form and a revised form of heat balance..................... 137

Derivation of the constant-capacity curves of fig. 65................... 141

Derivation of boiler efficiency (E5 ).................................. 142

Derivation of true boiler efficiency (E4)............................. 143

Method of estimating radiation. ................................... 143

Plotting of probability curves...................................... 146

Miscellaneous.............................................................. 149

Reliability of observation and data..................................... 149

Computations of a steaming test........................................ 151

Dissociation curves of carbon dioxide and water vapor. .1................. 153

Water-jacketed gas sampler............................................ 154

Comparison of readings of certain gas samplers............................ 155

Flue-gas sampler.................................^.................... 156

Unaccounted-for percentages probably too high........................... 156

Probability curves..................................................... 158

Relation of temperature of products of combustion to pounds of air used.. 159

Circulation indicator................................................... 160

C-shaped v. flat-bottomed tube tiles..................................... 164

Orsat totals............................................................. 164

 Per cent of CO in combustion chamber.......................... '. ....... 166

Pounds of dry chimney gas per pound of '' combustible "................. 167

Effect of direction, velocity, relative humidity, and temperature of wind

on efficiency 72*..................................................... 167

Relation of unaccounted-for loss to ash passing over bridge wall.......... 168

The law of mass action.................................................. 170

Dimensions of boilers and settings....................................... 173

True boiler efficiency................................................... 174

General conclusions....................................................... 174

Commercial considerations..........:....................................... 177

Bibliography. .............................................................. 179

Glossary................................................................... 180

Index.................................................................... 185
ILLUSTRATIONS.

Page. 

FIG . 1. Relations of rate of combustion to three stated factors................. 12

2. Relations of rate of combustion to three stated factors taken from heat

balance..................:................................-........ 12

3. Relations of rate of heat evolution to three stated factors.............. 13

4. Relations of rate of heat evolution to four stated factors................ 13

5. Relations of rate of heat evolution to two stated factors................ 14

6. Theoretical curves of factors affecting heat absorption.................. 15

7. Velocity of water circulation in boiler as affected by rate of steaming... 16

8. Relations of coal burned to rated capacity and to efficiency 72*....... 17

9. Variation of temperature with firing in Heine furnace.................. 18

10. Wanner optical pyrometer in position for standardizing............... 19

11. Combustion-chamber temperature as a function of two stated factors... 20

12. Relations of combustion-chamber temperature to three stated factors.. 21

13. Relation of flue-gas composition to combustion-chamber temperature.. 22

14. Relation of gas composition to temperature in rear of combustion

chamber........................................................... 23

15. Water-jacketed gas sampler. .......................... % ............... 24

16. Relation of combustion-chamber temperature to flue-gas temperature.. 24

17. Relations of combustion-chamber temperature to three stated factors.;. 25

18. Relations of efficiency 72* to CO and Cp2, and of C02 to efficiency 72*.. . 27

19. Relations of nitrogen to efficiency 72* and to size of coal, and of CO to

efficiency 72*.................................................... 28

20. Theoretical curves of heat absorption as affected by air supply.......... '29

21. Classifications on bases of efficiency. 72* and of clinker................. 30

22. Relation of moisture in coal to efficiency 72*, and of efficiency 72* to ash. 33

23. Relation between ratio of iron in coal to ash in coal and boiler efficiency

72*.............................................................. 35

24. Relations of clinker in refuse to four stated factors.................... 36

25. Coal classification based on carbon-hydrogen ratio in dry coal......... 37

26. Relation of per cent.of ash in dry coal to efficiency 73................ 40

27. Relations of per cent of ash to seven stated factors..................... 41

28. Relations of sulphtfr in coal to four stated factors...................... 43

29. Relations,of size of coal to eight stated factors: ....................... 46

30. Relations of size of .coal to seven stated factors....................... 48

31. Relation of C02 in flue gases to completeness of .combustion............ 51

32 Comparison of pyrometer and water-jacket temperatures in; combustion

chamber......................................................... 55

33. Smoke classification on basis of black smoke as 100 per cent........... 56

34. Gas-mixing wall built in the Heine safety water-tube boiler..;........ 62

35. Relations of combustion-chamber temperature to three stated heatbalance factors................................................... 63
6 ILLUSTRATIONS.

. Page. 

FIG. 36. Relations of differences of draft to pounds of dry chimney gases per

pound of "combustible"......................................... 66

37. Coal classification based on carbon-hydrogen ratio from analysis of airdried samples................................................... . 69

38. Coal classification based on carbon-hydrogen ratio.................... 71

39. Coal classification, Group K......................................... 74

40. Coal classification, Group M....................................... 75

41. Coal classification, Group 0................................ ^...... 76

42. Coal classification, Group A ....................................... 79

43. Coal' classification, Group B....................................... 80

44. Coal classification, Group D........................................ 81

45. Coal classification, Group Y........................................ 82

46. Efficiency curves of coal classified according to the per cent of rating.. 83

47. Classification of tests based on available hydrogen................:.. 84

48. Relation'between the ratio of volatile carbon to total carbon and efficiency 72*..................................................... 86

49. Coal classification based on ratio of hydrogen to available hydrogen... 87

50. Relations of "volatile matter" in the "combustible" to two statedfactors ........................................................ 89

51. Relations of "fixed carbon " to six stated factors..................... 91

52. Relations of efficiency 72* to per cent oxygen in '' combustible "...... 92

53. Relations of B. t. \i. value of coal to five stated factors................ 93

54. Temperature-entropy diagrams for boiler............................ 96

55. Availability to a boiler of heat of combustion of carbon............... 102

56. Temperature-entropy diagrams for steam-turbine cy*cles............. 105

57. Diagram illustrating the theory of the dislodgment of adhering gaseous

molecules....................................................... 110

58. Relative B. t. u. absorbed at different points in a boiler tube......... 123

59. Relative temperatures of the products of combustion passing through a

boiler tube....................................................... 125

60. Diagrams illustrating temperature gradients of moving gases......... 127

61. Relations of pounds of gas to-heat transmitted and of hea,t radiation to

actual temperature............................................... 131

62. Classification based on ratio of certain stated temperatures........... 133

63. Relation of ratio of certain stated temperatures to rated capacity...... 136

64. Relation of boiler efficiency to unaccounted-for heat; availability of

heat to boiler...................................................... 138

65. Curves of constant boiler efficiency (E5 ) and of constant capacity devel-

 oped.......................................................... 141

66. Curves of constant true boiler efficiency (E4 ) and of constant capacity

developed....................................................... 144

67. Probability curves (approximate)..............'.................... 147

68. Relation of unaccounted-for loss to CO loss..: ..................... 151

69. Dissociation curves of water vapor and carbon dioxide................ 154

70. Comparison of readings of multitubular gas sampler and of single tube

in stack....................................................... 155

71. Flue-gas sampler installed to replace A. S. M. E. multitubular sampler. 157

72. Diagram illustrating probability curve............................. 158

73. Theoretical curves showing relation of temperature to pounds of air

used .......................................................... 160

74. Circulation indicator mounted in'boiler............................ 161

75. Result of observations with circulation counter..................... 162

76. Dimensions and details of boiler setting............................. 174
PREFACE.

The fuel tests discussed in this paper were made under two Heine 

water-tube boilers by the boiler division of the United States Geological Survey fuel-testing plant at St. Louis, Mo. These tests began 

during the Louisiana Purchase Exposition, in 1903, and have been in 

progress since that time. The coals tested have been collected from 

all the prominent fields of the United States.

It has been the object to compare fuels by determining the evaporative performance of the boilers when using the various coals. Careful and complete observations have been made with each coal, so that 

it should be possible for engineers to determine from an examination 

of the records whether the conditions of the tests were favorable or 

unfavorable for the character of the coals tested.

The results of tests by the several divisions of the fuel-testing plant 

that have been published thus far appear in (a) Bulletins Nos. 261 and 

290 of the United States Geological Survey, giving preliminary reports 

of the operations of the plant; (&) Professional Paper No. 48 of the 

Survey, giving complete and detailed information of the tests made 

during the Exposition.

The steaming tests were in charge of D. T. Randall during the Exposition period and of Walter T. Ray since that time. These men have 

been ably assisted by a corps of trained observers and computers, who 

have been alert, patient, and painstaking.

As soon as a considerable number of tests were available, it seemed 

desirable to begin a comparison of the various tests on the basis of 

such usual factors as over-all efficiency, rate of combustion, temperature of escaping gases, evaporation per square foot of heating surface, 

etc. It soon developed that many interesting and apparently valuable results were brought out by these comparisons, and hence they 

were extended. The discussions of facts led to a search for theories, 

and the men of the division sought out available literature bearing on 

the various subjects under discussion. Thus has accumulated the 

material here presented. It is not the work of any one, but of all.

To Messrs. Walter T. Ray, Henry Kreisinger, and Harry W. Weeks 

should be accorded especial credit for preparing the larger part of this 

material. Except for the cooperation and careful work of the chemical division, under the supervision of Dr. N. W. Lord, much of the 

work here reported would not have been possible.

7
O PREFACE.

Many of the relations submitted have been worked out a't the suggestion of different engineers who were interested in particular phases 

of the work. Some repetition in the matter presented is perhaps 

unavoidable on account of the nature of the subject. Possibly much 

that is new has developed during the discussion, because never before 

have 400 boiler tests been made under two boilers (exactly alike) 

with coals and lignites from all sections of the United States and with 

all tests fired by the same expert fireman.

Acknowledgment is gratefully made to the many engineers of the 

country for helpful suggestions and kind criticisms that have come 

to me while endeavoring to direct the tests of this division so that 

they would prove of the greatest value to the industries of the nation, 

and to those engineers whose problem is still to furnish boilers of 

greater capacity and furnaces of higher economy. It must not be 

forgotten that all discussion is based.on the results obtained in a single furnace with one type of boiler, but many of the results should 

have wide application in any furnace and under any type of boiler. 

Helpful suggestions or criticisms from manufacturers or engineers are" 

again invited.

In submitting this paper I desire to thank Dr. Joseph A. Holmes, 

expert in charge of the fuel-testing plant, for his uniformly courteous 

.consideration of the plans and needs of the boiler division and for the 

freedom which he has always allowed us in carrying on the work. We 

have appreciated his confidence and can only hope that it has been 

merited.

L. P. BRECKENRIDGE, 

Engineer in Charge of the Boiler Division.

URBANA, ILL., January 14, 1'907.
A STUDY OF FOUR HUNDRED STEAMING TESTS.

By LESTER P. BRECKENRIDGE.

INTRODUCTION.

By WALTER T. BAY.

Origin of the bulletin. As the so-called "boiler tests," made by the 

fuel-testing plant at St. Louis, gradually accumulated, it became evident to the men making them that a great deal of incidental work 

was assuming the shape of a considerable compilation of plottings and 

calculations of various matters pertaining to the tests, and that certain details of the work were beginning to shed light on the inner 

reasons for the unreliability of tests of coals made under steam boilers. 

Much research work was being done in the boiler room simultaneously 

with the steaming tests proper, and of this work also certain details 

shed light on the same unreliabilities.

It was originally intended to insert these results in the regular bulletins of the fuel-testing plant, but the further the work went the less 

of a basis for general conclusions it seemed to be. For this reason 

publication was postponed until a-large amount of matter was on 

hand. In order to avoid undue bulk, no account of most of the work 

itself is given. Many of the negative results obtained are presented, 

however, on the general principle that negative results are usually 

worth as much as positive results.

Scope of the work. An especially striking instance of the value of 

negative results was noted in an attempt to check up the readings of 

an optical pyrometer used on the combustion chamber by calculating 

the initial temperatures of the gases entering the boiler in each test, 

so as to find whether the pyrometer read too high or too low when 

sighted on flame. The basis used for the calculation was the efficiency noted as "72*, efficiency of boiler, per cent" in the code of the 

American Society of Mechanical Engineers. The calculated temperatures of combustion were ridiculous, and were very puzzling for 

some weeks. Meanwhile a study was made of some chapters in John 

Perry's book, "The Steam Engine and Gas and Oil Engines," relating to the manner in which fluids give up heat and momentum, 'and
10 A STUDY OF FOUR HUNDRED STEAMING TESTS.

making application of these principles to steam boilers. A development of these ideas and their application to the apparatus used in 

these tests constitutes what is believed to be the most valuable part 

of this bulletin. It is thought that a fairly trustworthy separation 

has been effected for most tests of the true boiler efficiency and the 

percentage of completeness of combustion. Apparently the former is 

constant, as the theory indicates, and the "practical" boiler efficiency 

differs from it by only a very few per cent, the main cause of the difference apparently being that as a rule all of the fuel is not burned.

All of this work has been done with the hope of discovering new 

guiding principles for use in forecasting the results of burning any 

given fuel more accurately than can now be done from chemical analyses and observation of physical characteristics. It is true that at 

present the choice of coals in any market for any given use can be 

narrowed down to perhaps 20 per. cent of the coals considered by a 

consideration of market price, freight charges, chemical analysis, heating value, and physical characteristics; but the ambition of the boiler 

division is to work toward that completeness of knowledege whereby 

about three-fourths of the 20 per cent can also be discarded after 

laboratory investigations.

It is also the intention of the boiler division to study the principles 

of fuel combustion to such advantage that much coal can"be saved, 

and that cheap fuels can be used in certain operations where higherpriced ones are now considered necessary. Such savings will really 

redound to the benefit of producers of the best fuels of all grades quite 

as much as to the benefit of consumers. A number of new lines of 

work are suggested in the text; several of these it is planned to take 

up soon, and some of them may give data for determining the burning 

qualities of fuels independently of the apparatus in which the process 

takes place.

Perhaps the most important reason for doing the research work, 

and for making so many comparisons of the data obtained from all 

tests, was the feeling that the testing of fuels under boilers is at best 

only approximately .comparative. In short, it was the feeling that 

we were on the wrong track, without knowing of a better one, which 

led us to do the research work.

This work was performed and the results were prepared for publication under the direction of Prof. L. P. Breckenridge, engineer in 

charge of the boiler division, by the following men located at St. Louis: 

Walter T. Ray. Henry Kreisinger, Harry W. Weeks, Charles H. Green, 

Robert H. Kuss, Loyd R. Stowe, William M. Park, Ralph Gait, 

Fred 0. Pahmeyer, Raeburn H. Post, George S. Pope, 'Gilbert E.. 

Ryder, Fred J. Bird, Carl J. Fletcher, and Perry Barker.

Many of the opinions given in this volume are not shared by all the 

authors; some of them represent a compromise. The responsibility 

of selecting materials and deciding what views should be taken on 

many points naturally fell on Mr. Ray, who was the engineer locally
KELATIONS'OF TEST DATA. 11

in charge of steaming tests at St. Louis, and to him is to be charged 

the fault of any unjustified expressions of opinion or mistakes in text 

or figures.

It is realized that future work may show that some of the opinions 

advanced herein are faulty, and consequently the right is reserved to 

change them. Nevertheless, this work as a whole expresses the best 

present knowledge of the boiler division, and is given out for others 

to think about. It should be distinctly stated that the chemical 

division of this plant is in no way responsible for anything herein, 

although its members .have been consulted on some points and have 

very kindly made many suggestions.

Special attention is called to the "General conclusions/' page 174, 

and to the paragraphs entitled "Commercial considerations," page 177.

RELATIONS OF TEST DATA.

BATE OF COMBUSTION.

Fig. 1 should be considered in connection with fig. 2, the same tests 

being classified in both charts according to the pounds of dry coal 

burned per square foot of grate per hour. The figures in the small 

circles indicate the number of tests considered in determining the 

position of the points near which they are placed. In fig. 1 curve 

No. 1 is high for low rates of coal consumption, because it is hard to 

keep down the air supply. Curve No. 2 shows the per cent of stack 

loss. It drops at first because the air supply increases. (See curve 

No. 1.) It rises on the right because the gases leave the boiler at 

higher temperature, as shown by curve No. 3. The coals of the tests 

averaged on the left of the chart are in general of good quality and 

slower burning than those in the center; those on the right are somewhat lignitic in character. This perhaps explains why curve No. 3 is 

low in the center; the combustion-chamber temperatures were lower 

there, hence the flue temperatures were also lower. But, after all is 

said, the reason is in doubt, because the maximum flue-temperature 

range is only 50° F.

On comparing the flue-temperature curves of figs. 1 land 3 a difference will be seen in the left-hand ends. With reference to this curve 

in fig. 1, the coals toward the left end become better in quality and 

higher in "fixed carbon," so that although they burned slowly the 

combustion-chamber temperatures were fairly high, and consequently 

the stack temperatures were higher than in the center of the curve. 

With reference to the analogous curve of fig. 3, the coals to the left 

are both poorer and slower burning, and a larger air excess was used, 

relatively, which made the combustion-chamber temperature lower; 

consequently the flue temperature was lower. Further, the lower 

curve of fig. 1 is perhaps drawn a little too high at the left end, and 

that of fig. 3 a little too low.
12 A STUDY OF FOUR HUNDRED STEAMING TESTS.

Fig. 2 should be considered in connection with fig. 1. Little can 

be said of curve No. 1 (fig. 2), except that it rises slightly with 

increasing rates of combustion about three to five times as much

POUNDS. OF DRY COAL. BURNED PER SQUARE FOOT OF GAATE PER HOUR

PIG. 1. Relations of rate of combustion to pounds of dry chimney gases per pound of "combustible" 

(curve No. 1); per cent of loss up the stack, from heat balance (curve No. 2); and flue-gas temperature (°F.) taken under stack damper (curve No. 3). Classified on rate of combustion as basis; 

tests 126-355. ' '

as the broken line just below, connecting the CO averages. The rising of both is perhaps a consequence of decreasing air supply per

POUNDS Of DRY COAL BURNED PER SQUARE FOOT OF GRATE PER HOUR.

PIG. 2. Relations of rate of combustion to per cent unaccounted-for loss (curve No. 1); per cent of 

CO loss (curve No. 2); and per cent of loss up the stack (curve No: 3). Classified on rate of combustion as basis; tests 120-355.
RELATIONS OF TEST DATA. 13

pound of " combustible/ 5 as indicated by curve No. 1 of fig. 1. Curve 

No. 3 of fig. 2 is a reproduction of curve No. 2. of fig. 1.

e ez KJ R4 £5 ?6 ;

OF a T. U. SUPPOSEDLY EVOLVED PER 5T OC GRATE SURFACE PER HOUR.

FIG. 3. -Relations of rate of heat evolution to pounds of dry chimney gases per pound of" combustible" 

(curve No. 1); per cent of loss up the stack (curve No. 2); and flue-gas temperature (°F.) (curve No. 

3). Classified on rate of heat evolution as basis; tests 126-358.

SUPPOSED RATE OF HEAT EVOLUTION.

Fig. 3 should be considered in connection with. fig. 4. In 'both 

charts the same tests are grouped according to the number of B. t. u.

aoooa OF a T. u. SUPPOSEDLY EVOLVED PER SQUARE FOOT OP GOATE SURFACE PER HOUR

FIG. 4. Relations of rate of heat evolution to per cent unaccounted for (curve No. 1); per cent unaccounted for plus per cent of loss up the stack (curve No. 2); per cent of CO loss (curve No. 3); and per 

cent of loss up the stack (curve No. 4). Classified on rate of heat evolution as basis; tests 126-358.
14 A STUDY OF FOUR HUNDRED STEAMING TESTS.

supposedly liberated per square foot of grate surface per hour. Had 

it been practicable, -the six curves concerned would have been 

plotted on one chart. According to curve No. 1 the pounds of dry 

chimney gases per pound of "combustible" decrease rapidly at first, 

but for the right-hand half of the chart they remain constant. The 

left half of curve No. 2 shows a rapidly decreasing stack loss, which 

might be expected to remain about constant on the right, inasmuch 

as the pounds of dry chimney gases per pound of "combustible" 

remain constant. One explanation of its rising is that the circulation of water in the boiler fails to increase at as rapid a rate as the 

demands on it, in consequence of which the boiler is increasingly less 

efficient as a heat absorber, wherefore the gases escape at a higher

iQ.ooo's OF a: T. o. SUPPOSEDLY EVOL.VEO PER SQUARE FOOT OF GRATE PER HOUR

FIG. 5. Relations of rate of heat evolution to per cent of rated capacity developed (curve No. 1) and 

efficiency 72* (curve No. 2),.classified on rate of heat evolution as basis; tests 126-358.

temperature. This explanation would make curve No. 3 consist of 

two portions, the upward slope of the left half, which is due to rise 

of furnace temperature, being continued for the right half by the 

decreasing efficiency of the boiler.

For a comparison of the shapes of the flue-temperature curves of 

this chart and of fig. .1, see the text on the latter (p. il).

Fig. 4 should be considered in connection with fig. 3. In both of 

these charts, as already stated, the same tests are classified on the 

basis of heat supposedly evolved; and here the emphasis is on the 

word "supposedly," for fig. 4 implies by circumstantial evidence that 

some of the fuel never burned. Curve No. 1, the per cent "unaccounted for," rises about 5 per cent, and curve No. 3, the per cent
RELATIONS OF TEST DATA. 15

of CO loss, rises nearly 0.5 per cent along the same range of heat 

supposedly evolved. The implication is that the rise of CO loss is 

merely an indication of greater losses not ascertained, due probably 

to incomplete combustion.

Curve No. 4 in this figure, is the same as curve No. 2 of fig. 3, a 

tentative explanation of which is given in the text relating to that 

figure (p. 13). The arrows on the curves indicate which coordinate 

scales are to be used with each curve.

Fig. 5 is based on about two hundred tests of coals from all parts 

of the country. It is not true to any great extent .that the better 

coals are represented more in some parts of the curves than in others; 

therefore the following deductions are fairly reliable. The 10,000's

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FIG. 6. Theoretical curves of factors affecting heat absorption, based on furnace temperature.

of B. t. u. supposedly evolved per square foot of grate surface per 

hour was calculated by deducting the heat loss in CO and in combustible dropping through the grate from the heat value of the coal 

fired. Curve No. 1 shows that- within the usual working range the 

capacity is very nearly a straight-line function of the heat supposedly 

evolved in the furnace. Curve No. 2 is especially significant, showing a decided falling off in efficiency 72*,a as the amount of heat supposedly evolved increases. By reference to the lower curve of fig. 6 

it will be seen that the volume of the gases of combustion from 1 

pound of carbon is nearly constant whatever the air excess used, providing this excess is within reasonable limits of operation. Therefore 

the volume of gases passing through the combustion chamber per

oFor definition of efficiency 72* see " Efficiencies" in the glossary (p. 181).
16 A STUDY OF FOUR HUNDRED STEAMING TESTS.

second is almost entirely a function of the coal burned, or, as given 

here, of the number of B. t. u. supposedly evolved per hour; whence 

the velocity of the gases as they pass from the fuel bed to the boiler 

entrance is proportional to the number of B. t. u. supposedly evolved. 

The emphasis is on the word "supposedly," for it is likely that the 

incompleteness of combustion increases as the time occupied by the 

gases in traveling from fuel bed to boiler decreases. This reduction 

of time for combustion is perhaps the reason for the common remark 

that when a combustion chamber is " worked too hard" its efficiency 

decreases; it may mix a large volume of gases as thoroughly as it 

does a fraction of the volume, but the time available for combustion 

is less.

FIG. 7. Velocity of water circulation in boiler as affected by rate of steaming: Curve No. 1, determined 

by classifying on revolutions per minute; curve No. 2, determined by classifying on per cent of 

rated capacity developed. Instrument for measuring circulation placed in first tube left of center in 

second row from bottom at rear of boiler.

Another probable cause of the drop of over-all efficiency (efficiency 

of furnace and boiler) is the fact that the circulation of the water 

inside of the boiler does not keep up with the capacity. Fig. 7 

shows that the circulation of water does not increase in proportion 

to the capacity as it should. The consequence is that the water 

does not take the heat fast enough from the metal of the boiler, 

which therefore remains hotter at the higher capacities. When the 

heat-absorbing surface is at higher temperature less heat is available for the boiler, and hence the over-all efficiency drops. (§ee 

p. 137.) .
RELATIONS OF TEST DATA. 17

On comparing the curves of. capacity rise of figs. 5 and 8 it will 

be noticed that a given percentage change in B. t. u. supposedly 

evolved is accompanied by a much greater change in capacity than 

is the same percentage change in pounds of dry coal burned. The 

explanation is that as the pounds of dry coal burned per square foot 

of grate become less, the B. t. u. evolved do not on the average 

become much less, because some high-grade coals burn slowly; vice 

versa, some coals low in heating value burn rapidly. The capacity 

curve of fig. 8 may well have less slope than that of fig. 5. In studying the curves of fig. 8 it will also be noticed that when the pounds of 

dry coal burned per hour are doubled, efficiency 72* falls 5 per cent;

POUNDS OF DRV COAL. BURNE.O PER SOJARE POOT OF GRATE SURFACE PER HOUR.

FIG. 8. Relation of pounds of dry coal burned per square foot of grate to per cent'of rated capacity 

developed (curve No. 1) and efficiency 72* (curve No. 2). Tests 120-355.

whereas, referring to fig. 5, when the number of B. t. u. supposedly 

evolved is doubled, efficiency 72* falls 7 per cent, indicating both 

more incompleteness of combustion and poorer heat absorption.

Curves determined by classification of various coals on the basis 

of pounds of dry coal burned per square foot of grate per hour are 

only approximate; those based on the heat supposed^ (or ostensibly) evolved are of more value. The only correct classification 

would be on heat actually evolved as a basis. However, this involves 

the determination of the losses due to incomplete combustion of 

hydrocarbons and of solid particles of carbon escaping in smoke, and 

such determinations are very difficult to .make, perhaps impossible.

8400 Bull. 325 07 2
18 A STUDY OF POUR HUNDRED STEAMING TESTS. 

COMBUSTION-CHAMBER TEMPERATURE.

Fig. 9 shows variation of. temperature with firing in the Heine 

furnace. Variations of the temperatures in the fuel bed, over the 

fire, and in the combustion chamber are given with two very different coals. These temperatures were taken with the Wanner optical 

pyrometer (fig, 10), which was standardized before and after each 

series of observations. Every series of readings was taken without

2300-'

MPERATURE IN COMBUSTION CHAMBER

II 13 IS 17 19 21 23 25 27 29 31 33 35 37

TEMPERATURE N FUEL BEQ

li:54 56 53 1200

fEMPERATURE IN COMBUSTION CHAMBER

10 12 14 16 IB 20 22 24 26 2S 3O 32 34

TEMPERATURE ABOVE FIRE

30 22 24 26 2S 3O 32 34 36 3B 40 42

TEMPERATURE IN FUEL BED! ill i I I i I

' 11:04' 6^8' I'D ' 12 I i

__________TIME MINUTE5

FIG. 9. Variation of temperature with firing in Heine furnace.

disconnecting the pyrometer from the battery after the standardization. Owing to the fact that only one pyrometer was available the 

temperatures were not taken simultaneously. The chart (fig. 9) 

shows clearly the three things following:

1. During and shortly after each firing the temperature over the 

fire and to some extent the temperature in 'the fuel bed drops, and 

the temperature in the combustion chamber rises. The explana-
RELATIONS OF TEST DATA. 19

tion of this variation is that the distillation of "volatile matter" 

is a cooling process and is undoubtedly a partial cause of the drop 

of temperature in the fuel bed and over the fire, but the volatile 

matter distilled is carried into the combustion chamber, where it 

burns, causing a rise of temperature there.

2. The peaks in the curve for combustion-chamber temperature 

and the depressions in the curve for over-fire temperature are wider 

for Ohio No. 8, a coal high in volatile matter, than for West Virginia No. 19, a coal low in volatile matter, indicating that the volatile matter is distilled off and burned in shorter time in the West. 

Virginia coal than in the Ohio coal.

3. Combustion-chamber temperature is much higher with Ohio 

No. 8 than with West Virginia. No. 19, while, fuel-bed and over-fire 

temperatures are higher with West Virginia No. 19 than with Oh'^

MAT GLASS SCREEN

AMYL ACETATE 

LAMP

FIG. 10. Wanner optical pyrometer in position for standardizing.

No. 8. This contrast indicates that most of the West Virginia No. 

19 coal burns on the grate and only a little in the combustion chamber, while the opposite is true of Ohio No. 8.

The two similar curves of fig. 11 are based on. all tests (126-355) 

having combustion-chamber temperatures as read by the Wanner 

optical pyrometers. Coals from all parts of the country are included. 

To obtain the upper curve the tests were grouped according to 

pounds of dry coal burned per square foot of grate per hour; to 

obtain the lower curve they were grouped on 10,000's of B. t. u. supposedly evolved per square foot of grate per hour, the supposition 

being that all of the potential heat is liberated, after deducting for 

the loss of combustible in ash and for CO loss.

The rise in temperature throughout the whole range, for a doubling of the base values, is very nearly the same in the two curves. 

A significant feature of both curves is that the combustion-chamber
20 A STUDY OF FOUR HUNDRED STEAMING TESTS.

temperature rises with, the amount of heat liberated in the furnace; 

perhaps because conditions of combustion grow better at first, on 

advancing from poor coals at the left to the better ones in the center. 

Curves No. 1 in fig. 1 and No. 1 in fig. 3 show the direct cause of the 

decreasing rise in combustion-chamber temperature.

a.

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POUNDS OF DRV COAL BURNED PER SQUARE. FOOT OF GRATE PER HOUR

£

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TEMPERA! R 

8 i

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COMBUSTI 

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FIG. 11. Combustion-chamber temperature as a function of pounds of dry coal burned per square foot 

of grate per hour, classified on basis of pounds of dry coal burned (upper curve); and 10,000's of 

B.t.u. supposedly evolved per square foot of grate per hour, classified on basis of 10,000's of B. t. u. 

supposedly evolved (lower curve). Tests 126-355.

The curves of fig. 12 are based on one class of coals those from 

Illinois and Indiana. The only striking showing is that the code 

"boiler efficiency" (72*) is practically constant throughout the 

whole range of furnace temperature. All these coals are apt to 

evolve compounds difficult to burn, and thus it is that the lower the
RELATIONS OF TEST DATA. 21

percentage of oxygen present the less complete the combustion, notwithstanding the higher temperature resulting. With these coals, 

therefore, the decreasing completeness of combustion in our apparatus with rise of temperature seems to offset the increasing efficiency 

of the boiler as a heat absorber, which is only about 10 or 12 per 

cent within the range 1,850° to 2,850° F., according to the chart on 

page 141.

In this chart, as in all others, where capacity is shown as a function 

of furnace temperature, the two rise together. This relation will be 

clear on remembering that much heat is absorbed through the tile 

roof of the furnace; and the greater the amount of coal burned the 

less in percentage will this absorption amount to, so that the temperature at the last point of combustion is higher.

COMBUSTION-CHAHBEP TEMPERATURC (,"C)

FIG. 12. Relations of combustion-chamber temperature to per cent of rated capacity developed (curve 

No. 1); efficiency 72* (curve No. 2); and per cent unaccounted for plus per cent of loss up the stack 

(curve No. 3). Classified on basis of combustion-chamber temperature (°F.), Illinois and Indiana 

coals being used.

Fig. 13 is a companion to fig. 14, both charts being based on 

combustion-chamber temperature.

The arrows on the curves of fig. 13 indicate which coordinate scales 

are to be used with each. These thirty analyses were made at intervals of twenty minutes, on flue gases from the base of the stack, the 

combustion-chamber gases having been diluted with air by infiltration after entering the boiler. The curves of fig. .14 were computed 

on analyses of samples (taken half-hourly during about sixty tests) 

from the rear of the combustion chamber, through the water-jacketed 

gas sampler (fig. 15) described on page 154, so that these samples 

were probably undiluted.
22 A STUDY OF FOUR HUNDRED STEAMING TESTS.

As the temperature of combustion rises the oxygen percentage 

drops in a straight-line ratio and the C03 curve rises in nearly the 

same way; but the CO curve rises sharply after about 2,500° F. 

(1,370° C. ; the temperature indicated by curve No. 4 of fig. 14) 

has been reached. Of course the composition of the gases as affected 

by temperature probably varies from coal to coal. It should be 

remembered that on the whole the optical pyrometer probably indicated considerably lower temperatures than actually existed, because 

when burning short-flaming coals, or when running at' the lower 

capacities, little flame was visible, and the instrument was pointed 

at a side wall visibly cooler than even the clay-tube tiles forming the 

furnace roof.

JV0.4/

TEMPERATURE IN COMBUSTION CMAMBC.R f F)

FIG. 13. Relation of flue-gas composition to combustion-chamber temperature: Curve No. 1, 0$;. No. 2, 

COa; No. 3, CO. Determined by averaging individual readings; tests 151-181.

Curve No. 1 of fig. 14 shows a gradual decrease in the Orsat totals 

as the temperature is raised, accompanied by reduced air supply. 

As the temperature rises the volume of hydrocarbons might be 

expected to increase, but their proportional volume would be so small 

that they would not affect this curve.

Fig. 16 is a graphic representation of the relation, in our apparatus, 

of combustion-chamber temperature to flue temperature for 212 

tests, certain tests having doubtful readings being omitted. Both 

temperatures rise together. It is noticeable that the curve is less 

steep in the upper portion, which may be accidental, but indicates 

that at higher furnace temperatures the boiler absorbs a slightly
RELATIONS OF TEST DATA. 23

greater percentage of the heat available to it above steam temperature than at the lower furnace temperatures; that is, the true boiler 

efficiencies are not always the same. But no reliable conclusion, can 

be drawn. The significance of the curve is general only. "

Fig. 17 shows a classification of 217 tests on many coals from 

all parts of the United States based on temperature in the rear of the 

combustion chamber. In general the poorer coals fall at the left of

COMBUSTION-CHAMBER TEMPERATURE fp)

FIG. 14. Eolation of gas composition to temperature, both in rear of combustion chamber: Curve 

No. 1, COs+Os+CO; No. 2, 02 ; No. 3, CO-;; No. 4, CO. Samples of gas taken through water-jacketed 

iron pipe;.tests 318-382.

the chart. .The most interesting showing (curve No. 1) is that the 

code "boiler efficiency" (72*) rises only 2 per cent as the combustionchamber temperature rises from 1,800° to 2,700° F. This showing 

is in accordance with other charts and with the theory of boilers 

deduced on page 114, all being to the effect that a rise of about 1,000° 

F. in furnace temperature improves the efficiency of the boiler as a 

heat absorber only about 10 per cent. Most of this gain, however, is
24 A STUDY OF FOUR HUNDRED STEAMING TESTS.

offset by incompleteness of combustion chargeable to the restricted 

oxygen supply required to get the high temperatures.

SECTION ON AB

FIG 15. Water-jacketed gas sampler.

Curve No. 2 shows a slight but persistent rise of C03 content in 

flue "gases with increasing furnace temperatures, as is reasonable; it

(:RATURE 

I

TEMPE SXVS 

S

FLUEin

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COM8USTIONCHAMBER-TEMPERATURE BASIS

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SA

oo e.e.00 2300 a4oo esoo e^'oo 8*700 

BUSTiON -CHAMBER TEMPERATURE ("f)

FIG. 16. Relation of temperature in rear of combustion chamber to flue-gas temperature taken under

stack damper; tests 150-400.
RELATIONS OF TEST DATA. 25

ought .to be more marked. Air infiltration through the settings 

reduced the C02 percentage by 10 to 35 per cent in extreme cases.

Curve No. 3 shows a decided increase in the amount of steam 

made as the temperature rises. Since capacity is the comparative 

rate of absorption of heat by the boiler, it must necessarily increase 

with the rise of combustion-chamber temperature, if the equation

 fet

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64

11.0

10.0 

9.0

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100

95

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FIG. 17. Relations of combustion-chamber temperature to efficiency 72* (curve No. 1); C02 in flue 

gases, samples taken in hood (curve No. 2); and per cent of rated capacity of boiler developed (curve 

No. 3). Classified on combustion-chamber temperature as basis; tests 150-400.

used in the derivation of Perry's equation for true boiler efficiency, 

given on page 110, is. true. The heat absorbed per second per unit 

of heating surface is

H-Cpv (T.-TJ.

Expressing the values of p and v in terms of T\, we have
26 A STUDY OF POUR HUNDRED STEAMING TESTS.

The latter equation states that the capacity varies directly as the 

difference of the temperature of the furnace gases and the temperature of the steam.

As stated in the description of the baffle wall (p. 62), the construction and location were so chosen as to have the stream of 

gases leaving the furnace impinge against a solid part of the wall 

and break into many smaller streams, thus effecting mixing. It 

was intended to obtain a splashing effect, similar to that seen when 

a stream of water is directed against a solid wall. That some such 

effect was attained was indicated by the high temperature taken 

through the opening just at the base of the bridge wall. This was 

invariably the highest temperature in the whole combustion space. 

Each of the temperatures given in the second column of the following table is the average of ten readings taken with the Wanner 

pyrometer at five different places in the furnace. Theco readings 

were taken successively through the side-wall openings from front 

to rear, so that, the averages may be considered to represent simultaneous temperatures at all five places. Twenty-four readings were 

also taken in the same way by an exposed platinum and platinumrhodium couple, connected to a galvanometer reading in degrees 

centigrade, giving the average temperatures at four places, as 

shown in the third column of the table.

Furnace temperature readings (test 359}.

Place.

Fuel bed. ........................................................................

Base of bridge wall .......................................

Rear of combustion chamber. .........

Wanner 

pyrometer.

°.F. 

2,470

2,586

2,826

0 QQQ

2,447

Galvanometer.

°C. 

913

1,075

1,280

1,035

The temperatures taken with the thermoelectric couple have only 

relative value, and are in fact much too low, the galvanometer having been recently repaired so that the divisions on the scale were 

not true degrees centigrade. The couple used had an exposed junction projecting from the end of a f-inch iron pipe.

A. S. M. E. CODE BOILER EFFICIENCY (72*).

Fig. 18 consists of two charts. In the upper chart 293 tests are 

grouped according to efficiency 72*, the averages being plotted for 

each group of the percentages of CO and C02 . All the higher 

efficiencies have low CO values and the lower efficiencies high CO 

values. The higher efficiencies have higher C02 values than the 

lower efficiencies, of course, though not much higher. The CO 

curve (No. 1) should be compared with curve No. 3 of fig. 19, which
KELATIONS OF TEST DATA. 27

is based on the same tests. The implication is the same- that high

CO is a danger signal.

In the lower chart the same 293 tests are classified according to 

the percentage of C02 in the flue-gas analyses. The points plotted 

are .the averages of the code "boiler efficiencies" (72*). It is evident that when once the C02 content gets beyond 9 per cent at the 

rear of the combustion chamber only about 1 per cent more at 

most only 2 per cent is to be gained by raising it higher. The perFIG. 18. Relations of efficiency 72* to per cent of CO, stack sample (curve No. 1);" per cent of C02 , 

stack sample (curve No. 2); and per cent of CO2 (curve No. 3). Tests 89-401.

centage of C02 in the furnace and boiler were really about 20 per 

cent higher on the average than here mentioned because of an air 

infiltration through the settings amounting to 10 per cent, or 50 per 

cent of the volume present in the rear of the combustion chamber.

There is a general resemblance between curve No. 3 and the curve 

in fig. 20 labeled ".Heat absorption as affected by combustionchamber temperature." The latter curve is closely dependent 

(theoretically) on the CO2 content, and it probably is no mere coin-
28 A STUDY OF FOUR HUNDRED STEAMING TESTS.

cidence that the two curves have much the same shape. The same 

remark applies to the analogous curve of fig. 6 (p. 15).

Fig. 21 represents an attempt to find relations between per cent 

of sulphur in coal (separately determined), per cent of clinker in 

refuse, and "boiler efficiency" (72*). It is agreed that clinkering 

is a consequence of the effects of high fuel-bed temperature on such

(U

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N NlTROGE.N B>VSIS

ei.o eas 81.0 si.s 82.0 ez.s 

PER CENT OF NITROGEN IN FLUE GASE.S

w ,. ,

sn «.

-M

JT)

CL,

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AS

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0 f»o .50 .60 /70 .80 .90 l!°0 

PER CENT OF CO IN FLUE GA3ES

FIG. 19. Relations of nitrogen to efficiency 72* (curve No. 1); nitrogen to average diameter of coal 

(curve No. 2); and per cer.t of CO to efficiency 72* (curve No. 3). Tests 89-400.

of the mineral constituents in the ash as will form a fusible mixture. 

It must be remembered that the fineness of subdivision and the distribution of the minerals throughout the coal are probably as important as the temperature and chemical composition. Thus it is that 

"sulphur" (pyrites) in the form of little balls is nearly harmless; in 

the form of veins or layers it is liable to cause trouble; but in the
BELATIOJSTS OF TEST DATA. 29

form of "black sulphur/' so finely distributed as to be invisible, it 

is most troublesome. From these remarks it is evident that the 

boiler room is not the proper place to make a scientific study of 

clinkering, but that it should be taken up in the laboratory along 

the following lines: (1) Ash analyses; (2) experimental determination of fusing points; (3) ascertaining the distribution of the ash 

and its various constituents throughout the coal.

To determine the fusing point of ash, all the combustible in the 

ash should be burned out at the lowest possible temperature. The 

ash could then be made into Seger cones, which could be heated in 

a furnace arid the temperature read with a pyrometer.

POUNDS OF GAS PER POUND OF CARBON

TEMPERATURE OF PRODUCT OF COMBUSTION

FIG. 20. Theoretical curves of heat absorption as afiected by air supply. Arrows on curves show

respective coordinates.

The distribution of the ash might be determined by laboratory 

washing processes. One method of doing this would be to grind the 

coal to a certain fineness and float it successively on solutions of potassium hydroxide of varying per cent dilution.

The chemical division, under the guidance of N. W. Lord, is carrying on some of the above investigations, and the writer is indebted 

to him for explanations of methods.

Notwithstanding the probability, implied above, that sulphur does 

not have a great' deal .to do with the formation of clinker, it was 

thought well to find out whether in general it helps or hinders 

efficiency.
30 A STUDY OF FOUR HUNDRED STEAMING TESTS.

The upper half of fig. 21 contains tests classified according to 

"boiler efficiency" (72*). In curve No. 1 each point is the average 

of the per cent of clinker in refuse for each group and in curve No. 2 

of the per cent of sulphur in coal. According to curve No. 1, the 

coals giving high efficiencies are apt to form a very slightly smaller

ETFFICIENCY

310

I

i 

3

H !

Z

PERCENT CLINKER IN REFUSE

FIG. 21. Relations of efficiency 72* to per cent of clinker in refuse (curve No. 1); efficiency 72* to per 

cent of sulphur in coal (curve No. 2); per cent of clinker in refuse to efficiency 72* (curve No. 3); and 

per cent of clinker in refuse to per cent of sulphur in coal (curve No. 4) Curves Nos. 1 and 2 classified on efficiency 72* basis; Nos. 3 and 4 on clinker basis. Tests 89-401.

percentage of clinker, and according to curve No. 2 the high-efficiency 

tests are likely to be made on coals low in sulphur, this relation being 

rather marked. However, it must be remembered that high-sulphur 

coals are usually high in ash also.
BELATIONS OF TEST DATA. 31

The indications of the curves of fig. 21, regarding the effect of 

sulphur, are at slight variance with those of fig. 28 (p. 43).

Careful records were kept regarding the appearance and distribution of the asli of each coal, but time has not been found to study 

and classify the information.

The lower half of fig. 21 was obtained by classifying the same tests 

according to the per cent of clinker in the refuse, which was done in 

order to determine the effect of clinker on efficiency. In curve No. 3 

the heavy line gives full weight to 16 tests on coals, some of which 

were of lignitic character and formed no clinker, but gave rather low 

efficiencies. Even considering this full portion of the-line, instead of 

the dotted portion above it, the clinker hardly affects efficiency until 

it reaches about 45 per cent, above which there is a rapid drop. 

Curve No. 4 indicates that high percentage of clinker accompanies 

high sulphur content; but it must be borne in mind that perhaps 

sulphur of itself has little to do with fusibility of ash and that the 

iron which is combined with a part of the sulphur is onty one of the 

factors in clinkering.

The classification of the relation of efficiency 72* to the sum of 

the percentages of ash and sulphur, given in the following table, was 

made by using 92 tests on coals from Illinois, Indiana, and Kentucky, all of which are much alike. To be more certain, the work 

was done in two ways by classifying the tests in groups of efficiencies 

and in groups of percentages of ash plus sulphur. The latter classification is not here given. The tests selected lay between Nos. 126 

and 401 and were more comparable than if some earlier ones had 

been included.

There was no special reason for using the sum of the percentages 

of ash and sulphur except that it is sometimes stated without cmalification. that ash and sulphur affect efficiency. The conclusion is 

that the sum of ash and sulphur has no visible effect on efficiency 72*.

Classification of average ash plus sulphur on basis of efficiency 72* (Indiana, Illinois, and

western Kentucky coals).

Efficiency 72*.

Up to 

57.5.

1

18. 80

57.5 to 

60.0.

58. 92 

14.22

60. 0 to 

02.5

8 

61.39 

15.93

62.5 to 

05.0.

28 

63.97 

16. 65

65.0 to 

67.5.

29 

66.16 

16.60

67.5 to 

70.0.

 17 

68. 50 

15. 41

70.0 up.

4 

70.82 

15.86

It was early noticed that the second test on a coal was generally no 

better as to over-all efficiency than the first. An inspection of the 

first hundred tests or so confirmed this opinion. Only tests made on 

the same shipment of the same commercial grade of coal were com-
32 A STUDY OF FOUR HUNDRED STEAMING TESTS.

pared; for instance, if the first test was run on a nut size and the 

second on screenings, these tests were not used.

It was usually the case that the man running the fire learned much 

the first day which was beneficial to the later tests, 'but which was 

more than offset by other factors. For instance, owing to the position of the chutes that discharge coal into the boiler-room bins and 

to the sloping bottoms of the bins the largest coal is obtained the 

first day.

The following tabulation has been made on 196 tests and shows 

that one test on a coal is sufficient:

Averages of five series of tests for efficiency 72*.

First 

tests.

77

66.05

Second 

tests.

77

66.02

Third 

tests.

32

65.87

Fourth 

tests.

8

64.99

Fifth 

tests.

2

67.76

The efficiency 72* is that of the furnace and boiler combined, figured 

from pounds of "combustible" actually ascending from the grate.

MOISTURE IN COAL.

The two curves of fig. 22 are based on the same tests. The upper 

curve is somewhat misleading, because the poorer coals contained 

on the average more free moisture. Just what effect different percentages of free moisture would have in the case of the same coal, 

reckoning above dry coal, is still undetermined. This line of investigation will be taken up in the future. This curve merely indicates 

that coals high in free moiature should be suspected and watched, 

especially when burning them in furnaces of this particular type.

The great variability of the lower curve suggests that ordinary 

percentages of ash have little effect on efficiency, and that the best 

efficiencies are obtained only with low ash. No doubt other appliances 

and furnaces are available which would give better results on dirty 

coal than have been obtained by hand firing on a plain grate.

ASH AND CLINKER.

In order to eliminate one nonuniformity in testing for the effect 

of percentage of ash in coal as fired on efficiency 72*, only the coals from 

Illinois, Indiana, and western Kentucky were used. The subjoined 

table shows that for the range of ash in these coals the efficiency 

is almost constant.

Fig. 22, in which all the coals tested are classified, shows the effect 

on efficiency 72* of percentage of ash in coal as fired.'
EELATIONS OF TEST DATA. 33

Classification of efficiency 72* on basis of 'per cent of ash (proximate analysis) in coal as 

Jired (Indiana, Illinois, and western Kentucky coals}.

Average per cent of asli in coal as 

firod. ..............................

Percent of ash.

4 to 6.

3

5.68 

C5.53

6 to 8.

10

7.20 

05.81

8 to 10.

22

8.99 

04.02

10 to 12.

22

10.86 

05.01

12 to 14.

19

13. 14 

0.5.05

14 to 10.

lllS. 11 

00.08

10 to IS.

3

10.81 

07.03

18 to 20.

2

18. 81 

05.27

The subjoined table indicates that very few coals burn without 

clinker. Of the few which do, those high in sulphur are lignites. 

Pennsylvania No. 7, of test 307, was exposed to weather for four and 

a half months before it was tested. The same coal when tested

66

*

F.I 6S

IGIENCY Tl

J8 

U. 

U

«.

SI.

&0

J

O39

o

Q

in

(0

2 

U

JH,ULTIM

CENT AJ

0

S

T 1* r

60.30^

\

Jj

fe= .J 13.6*

ra^v0

S

-A

S,

(30 |\

71.^ 

55.

\

7

SS

\ ^

V^

70.5E.

34.46

^

CLASSIFIED ON PERCENT

MOISTURE AS BASIS

i

\

\

53

\

\

\

\

.

\

\

PER CENT MO 

S f

\

a

/

(s)

/

i

CLASSIFED 

EFFICIENCY '

54 55 se,

/

jl

(1

^

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)

1

n.3

53.

^T

6

5

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y

as

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4

46

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ro.i

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 3

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STURE- PROXIMATE ANAL.Y5 

i 10 ie 14- 1

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t

ON 

72* BASI

57 58

i

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s

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r

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EFFICIENCY 7S* 

59 60 61 Si 6}

/

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^ so.;

S

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<

s

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sj ^

SOFCOA1-AS FIRED

'° is ao

(?

.

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n)

,

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*

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f

<

^

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 g.

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kOO

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^o

TIG. 22. Relations of per cent of moisture (proximate analysis) in coal to efficiency 72*, as shown by 

tests 101-400 (curve No. 1); and of efficiency 72* to per cent of ash (ultimate analysis) in dry coal, as 

shown by tests 120-400 (curve No. 2).

(test 198) soon after it arrived at the plant formed clinker amounting 

to more than one-half of the total ash.

The temperatures at which the lignites were burned are rather low, 

and it is probable that they might have clinkered with high tempera8400 Bull. 325 07 3
34 A STUDY OF FOTJK HUNDKED STEAMING TESTS.

tures. The conclusion must not be drawn that some coals represented in this table did not clinker because they were'low in sulphur.

Coals burned without producing clinker.

Test

No.

172

173

196

210

213

290

291

298

307

Coal.

Brazil No. 1 ...........

.....do.................

.....do.................

.....do.................

Washington No. IB..

.....do.................

Combus- tionchamber

temperature. 

°F.

1,900

1,858

1,950

2,200

2, 142

2,047

2,119

2,269

2,220

Sulphur,

separately 

determined in

coal as

fired.

Per cent.

3.02

4.53

4.78

4.37

5.52

.69

.80

.79

2.36

!

Test

No.

387

389

391

392

396

397

398

Coal.

.....do.................

New Mexico No. 3 A. . .

Combus- tionchamber

temperature.

°F.

2,371

2,225

2,432

' 2,420

2, 333

2,330

2,534

Sulphur,

separately 

determined in

coal as

fired.

Per cent.

0.81

.74

.09

.75

.74

.61

.00

The curves of fig. 21 (p. 30) show that the efficiency as based on 

the coal ascending from the grate (72*) is not influenced by the per 

cent of clinker in refuse until the latter exceeds 45 per cent, after 

which the efficiency drops 3 or 4 per cent. Inasmuch as clinker may 

prevent fine coal from falling through the grate, the same classification was made to learn how per cent of clinker in refuse affected code 

item 73, which is the over-all efficiency of boiler and grate. This 

classification is given in the following table. There is only a slight 

tendency for efficiency to decrease at.the high clinker values, whence 

the deduction can be made that although clinker may hinder combustion it saves almost enough fine coal .to compensate for its bad 

effects. However, it should be noted that the tests showing extremely 

high clinker were few in number.

Classification of efficiency 73 on basis of per cent of clinker in refuse.

Per cent of clinker.

Average per cent of clinker in

Average efficiency (item 73). .

Under 

30.

30

11

62.95

30 to 35.

13

33

65.19

35 to 40.

12

37

03.57

40 to 45.

44

42

63.96

45 to 50.

47

47

64.65-

50 to 55.

55

52

64.31

55 to 00.

36

57

62.95

60 to 65.

. 26

61

63.16

65 up.

7

67

62.45

Clinker is an interesting item, as it gets the blame for many things. 

Figs. 21 and 23 treat some phases of the subject, but the subjoined 

table has not been plotted. -

The impression is general that iron causes clinkering. The tabulation partially confirms the impression, as the percentage of iron in 

dry coal increases in general with the clinker. Nevertheless iron is 

only one cause of clinker, and its presence in considerable quantity 

does not necessarily mean that a coal will clinker.
RELATIONS OF TEST DATA. 35

Classification of per cent of iron on basis of per cent of clinker in refuse.

Average per cent of clinker in refuse. .

Average per cent of iron in dry coal. .

Per cent of clinker in refuse.

Under 

30.

3

12

1.01

30 to 35.

5

32

0.95

35 to 40.

2

3S

1.7(5

40 to 45.

0

42

1.54

45 to 50.

47

1.02

50 to 55.

17

52

1.69

55 to 60.

7,

57

1.81

Over 

60.

5

63

2.34

The curves of fig. 24 present a classification of tests on the basis of 

per cent of clinker in refuse. (See also discussion of fig. 28, p. 43.) 

The table on page 41 was compiled with the object of ascertaining 

whether any relation exists between the amount of clinker and the

PERCENT OF IRON IN COAL DIVIDED BY PERCENT Or ASIFIG. 23. Relation between ratio of per cent of iron in coal to per cent of ash in coal (proximate analysis)

and boiler efficiency 72*.

average size of the coal and shows that there is very little such relation. 

One significant feature shown is that the highest value of average 

size of coal is grouped with the highest value of per cent of clinker, 

and vice versa.

The curves of fig. 25 show a classification of coals on the basis of 

carbon-hydrogen ratio. It may be noted that as the per cent of 

clinker decreases the per cent of CO loss decreases; in fact, the two 

curves are nearly parallel. The efficiency 72* curve varies inversely 

with the CO loss and clinker curves. The curve of average diameter 

on this chart shows that the largest sizes of coal and highest values of 

clinker are grouped together. The pounds of dry chimney gases per
36 A STUDY OF FOUR HUNDRED STEAMING TESTS.

pound of ' 'combustible'' are almost of constant value. This relation is 

a corroboration of the text relating to fig. 28 (p. 43) regarding incomplete combustion and the decrease of efficiency 72* by the formation 

of clinker.

It is also likely that although the size of coal burned can not be 

determined by the amount of clinker formed, it is possible to estimate the amount of clinker that will.result from burning different

tl.

W19 .

Z400

uoa

Zioo

2IOQ

100

85

90 

9Z_

69 

88

-1,4

\

k.

^

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v

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/

''

X,

\

/

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^

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s

**

 ~v

0

y

s

/

^

i

f~

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Xr

/

^

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/

'~-

s

\

S*

1

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*-*

\

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- .

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s"

4-

A

b

~\

i

;

\

\

\

V

N

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j

/

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V

M

\

^

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0- 1 _

0.

0.

\

a

i

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W

^

-^

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A

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47

-o-

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-X

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N

-0

8

So

"°.

V

0 2.0 JO 40 )0 fcO 

PER CENT OT CLINKER IN REfUSE

FIG. 24. Relations of per cent of clinker in refuse to pounds of dry chimney gases per pound of "combustible" (curve No. 1); combustion-cbamber temperature (°F.) (curve No. 2); per cent of rated 

capacity developed (curve No. 3); and per cent of completeness of combustion (Ea) (curve No. 4). 

Tests 89-400.

sizes of the same kind of coal. With any one kind of coal the amount 

of clinker formed is related to the distribution and the nature of the 

ash. Generally the ash is distributed through the coal in thin or 

thick layers. In coal which is crushed to small sizes these layers 

become separated from the coal; and when such crushed coal is 

thrown into the furnace, the particles of ash, being heavier than the 

coal, soon pass down into the colder layers of ash and fuel near the
RELATIONS OF TEST DATA. 37

grate and are therefore not heated to a temperature high enough to 

melt. In large-sized coal, on the other hand, the ash remains more 

in the lumps of coal and is held near the top of the fuel b'ed, 'where the 

temperature is usually above the melting point of the ash.

In plotting the curves of fig. 23 (p. 35) an attempt was made to 

determine the effect on efficiency 72* of per cent of iron in coal as 

fired. The ratio of iron in coal to ash in coal was taken as a basis,

AT £=,9.3,

"6501

95 129

90 >

as 

eo

2500

2400

2300

2200

III

.4S_..--~ -9J*

ATs-19-31

CARBON-HYDROGEN RAT 0 IN DRY COAL

FIG. 25. Classification based on carbon-hydrogen ratio in dry coal: Curve No. 1, theoretical efficiency 

of boiler as a heat absorber at various temperatures; No. 2, per cent of CO loss; No. 3, efficiency /2*; 

No. 4, per cent of rated capacity developed; No. 5, combustion-chamber temperature (°F.); No. C, 

pounds of dry chimney gases per pound of' 'combustible;" No. 7, average diameter of coal; No. 8, per 

cent of clinker in refuse. Tests 120-380.

because it seemed that there was a close relation between the two; 

for instance, a large amount of ash and a high iron value would not 

be expected to cause as much trouble as a high iron value and a low 

percentage of ash.

Since only about 60 iron determinations were available, it seemed 

best to plot the individual points instead of average points. The
38 A STUDY OF FOUR HUNDRED STEAMING TESTS.

slope of the band inclosing the points shows that the ratio of iron in 

coal to ash in coal has perhaps a slight effect on efficiency 72*. This 

effect is probably due to the formation of nonporous clinker.

The relation of iron in dry coal to clinker in refuse was ascertained 

by classifying the data on the basis of per cent of clinker, the results 

showing a large increase in per cent of iron as the per cent of clinker 

increased. See text relating to figs. 24 and 28 (pp. 43-44) and table 

on page 35.

L. H. Hartley Smith, writing to Power in 1905, called attention to 

the fact that the refuse drawn from the ash pit and off the grate when 

cleaning fires seemed to contain less carbon when the percentage of 

clinker was high. An inspection of the data of a few of our tests 

confirmed the observation, and later the following tabulation was 

made on about 370 tests. The probable explanation is that when 

clinker forms on .the grate it keeps fine coal from falling through.

Classification of per cent of combustible on basis of per cent of clinker in refuse.

Per cent of clinker.

Average per cent of clinker . . . Average per cent of combusUnder 

30.

38

10.9 

25.65

30 to 

35

16

32.4

OQ OQ

35 to 

40.

16

37.0 

24.10

40 to 

45.

56

42.1 

23.70

45 to 

50.

 59

47.1 

21.75

50 to 

55.

70

52.0 

on 4^

55 to 

60.

50

57. G 

18.53

60to 

65.

45

61.3 

19 40

65 up.

11

66.9

1 C CO

Sulphur is an undesirable element in coal. It generally occurs in 

combination with iron, as iron pyrites, and in combination with calcium, as calcium sulphate or gypsum. Pyrites can readily be recognized by its heavy weight, bright brass!ike color, and crystalline 

structure. The calcium sulphate occurs in small, thin, white flakes, 

more or less transparent. Of the two sulphur compounds, the pyrites is generally contained in larger quantity in coal, and is harmful 

because it increases the tendency of the coal to clinker. The clinkering is especially bad if the percentage of ash is small in proportion to 

the sulphur. In such coals the pyrites and the ash fuse together 

and form a thin la}rer of solid clinker, which effectively stops the 

passage of air through the grate, thereby permitting the grate bars 

to become heated from the hot fuel bed just above. The clinker 

then melts down into the spaces between the bars and the sulphur 

seems to combine with the iron of the grate. The heat warps the 

grate bars, and the clinker has such corrosive action on the hot iron 

that a set of grate bars is destroyed in the course of a few days. 

When such clinkering occurs, any attempt to slice the fire fails, and 

only slow and very difficult cleaning of the fires will remove the 

clinkers. Ordinarily, with coals forming loose clinkers, the cleaning 

of the fires took from seven to twelve minutes.

Virginia No. 4, West Virginia Nos. 14 and 15, and most of the 

Kansas coals clinker badly because the ash is low in proportion to
RELATIONS OF TEST DATA. - 39

the sulphur content 0.3 to 6 per cent of sulphur and 3.5 to 10 per 

cent of ash. When such coals are burned on a plain or a rocking 

grate trouble with clinkers may generally be prevented by blowing 

steam under the grate. The usually assigned cause of this effect is 

that as the steam passes through the hot clinkers it is decomposed 

into hydrogen and oxygen. This decomposition is a cooling process 

and the heat needed to effect it is taken from the grate and the hot 

clinker, thus keeping the latter cool and preventing the fusing of 

the clinker into the grate.

The use of steam to prevent the clinkers from melting into the 

grate was found to work satisfactorily with all the coals high in sulphur and ash. However, for coals very low in ash this method 

sometimes proved to be insufficient. In such cases crushed limestone spread over the thin, clean fire bed immediately on starting

the test, prevented the clinkers from adhering to the grate, and was 

used for the second tests on West Virginia No. 14 and Virginia No. 4 

coals. The cleaning of the fires after the first tests on these coals, 

when limestone was not used, took forty-five and thirty minutes, 

respectively. On the second tests, when limestone was used, the 

cleaning took eight and ten minutes, respectively.

To make a general statement, it may be loosely said that the tendency of a coal to clinker varies directly with the sulphur (iron pyrites) 

and inversely with the ash in the "coal.

The statements of this paragraph regarding the effect of sulphur 

are at slight variance with those on page 34.

The curves of fig. 26 are based on 286 reliable tests, classified 

according to each of the two items, per cent of ash (ultimate analysis) in dry coal and over-all efficiency (item 73), the latter being the 

ratio of "the heat'put into the water to the potential heat in the coal 

put on the grate. Examination of the upper curve shows that the 

ash affects the efficiency by only 2 or 3 per cent until the ash cojitent 

rises above 20 per cent,-when the efficiency falls rapidly; however, 

not so many tests are represented in the last two points of the curve 

as in the others.

The lower curve shows the same fact inversely that is, the highefficiency tests are on coals low in ash. It indicates that an ash increase of 1 per cent causes a drop in efficiency of about 2 per cent, 

whereas the upper curve indicates a general drop of about 0.5 per 

cent in efficiency for each per cent of ash, or only one-fourth as 

much. The average, then, is about 1 per cent decrease in efficiency 

for 1 per cent increase in ash. The five points at the left end of the 

lower curve contain tests on clean lignites, and are therefore really 

not comparable with the other points. These five tests are individually given in the subjoined table.
40 A STUDY OF POUR HUNDRED STEAMING TESTS.

The two curves show that ash is undesirable; but even so, the commercial choice of coals, so far as ash is concerned, is more a question 

of market price, freight rates, labor costs, and storage capacity, and 

of whether or not the present boiler plant is crowded.

t*. 

&s.

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E.FFCENCY TEM

6 ss <io

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C.X.

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FIG. 26. Relation of per cent of ash (ultimate analysis) in dry coal to efficiency 73, classified on each

as a basis; tests 120-410.

Coals classed in first group of classification on basis of orer-all efficiency (item 73}.

Test 

No.

303

298

401

400

402

Coal.

Texas No. 4 .

.....do.............. ..... .........

Rhode Island No. 1 .......

Wyoming No. 6.... ...... Utah No. 2........ " ----------------

Efficiency 

. 73.

49.00

51.16

40 91

52 74

44.18

Per cent of 

ash (ultimate analysis) in 

dry coal.

12. 95

12. 80

16.87

The table which follows shows that size has no evident influence on 

clinkering, which is the same finding as stated under "Classification 

on basis of average diameter of coal" (p. 47). These two tables are' 

the converse of each other.
RELATIONS OF TEST DATA. 41

Classification of average diameter of coal on basis of per cent of clinker in refuse.

Average per cent of

Average of average diameter of coal, inches.

Per cent of clinker.

Up to 

10.

15 

0 

0.89

10 to 20.

4 

13 

0.83

20 to 

25.

4 

23 

0.50

25 to 

30.

G

28

o.co

30 to 

35.

14 

33 

0.89

35 to 

40.

13 

37 

0.85

40 to 

45.

40 

42 

0.76

45 to 

50.

43 

47 

0.78

50 to 

55.

53 

52 

0.83

55 to 

60.

42 

57 

0.82

Over 

60.

28 

62 

1.20

The curves of fig. 27 are plotted from the results of about 300'tests, 

and differ from those of fig. 26 in being based on the per-cent of ash in 

coal as fired instead of in dry coal. Thus the ash is always less than

fi

V

S)

81. 

Z500. 

1400.

«00.

tlOO. 

fclO. 

600. 

590 

580 

5 TO, 

5 to.

IS F6Sn IZ'O 

PER CENT OT A3H IN COM- j PROXIMATE ANALV35.

FIG. 27. Relations .of per cent of ash in coal (proximate analysis) to: Efficiency 72* (curve No. 1); per 

cent of rated capacity developed (curve No. 2); combustion-chamber temperatures (°F.) (curve No. 

3); flue-gas temperature (°F.) (curve No. 4); pounds of dry chimney gases per pound of " combustible " 

(curve No. 5); carbon-hydrogen ratio in dry coal (curve No. 6); and per cent of completeness of combustion (K3) (curve No. 7). Tests 89-401.

in the dry-coal percentage, but by -varying amounts, which perhaps 

explains the greater irregularity of the code "boiler-efficiency" line 

(72*), compared with the analogous line of fig. 26, based on over-all
42 A STUDY OF FOUR HUNDEED STEAMING TESTS.

efficiency (code item 73). The tendency of the 72* line to fall is 

apparent.

A glance at curve No. 2 shows that ash has a worse effect on amount 

of steam generated, the decrease of which is considerable, than on 

efficiency.

Curve No. 3, combustion-chamber temperature, shows a steady 

drop of a few hundred degrees due to increasingly poorer fuel-bed 

conditions along with falling rates of steam generation.

Curve No. 4, flue-gas temperature, shows a slight drop on account 

of lower furnace temperatures.

Curve No. 5, the pounds of dry chimney gases per pound of "combustible/' shows a marked and steady rise which is the chief reason 

for the decreasing-furnace and flue-gas temperatures just referred to. 

It is usually hard to keep the fuel bed in good condition when a coal 

is high in ash.

Curve No. 6 gives the averages for each group of the ratios of the 

carbon to the total hydrogen in the dry coal. This line drops, showing that the coals become poorer. The coals in the left-hand groups 

contain less oxygen in their molecules, so that their hydrogen, though 

decreasing in percentage, is available in larger amount. The fact 

that on going to the right the carbon-hydrogen ratio decreases partly 

accounts for the falling efficiencies shown by curve No. 1. (See p. 68.)

Curve No. 7, per cent of completeness of combustion* (E3 ), indicates 

approximately the percentage of total heat liberated from the coal 

which ascended from the grate. It rises decidedly toward the right 

in spite of the poorer fuel-bed conditions. The explanation is that 

inasmuch as the furnace temperature was almost always above the 

ignition temperatures of all the combustible gases and smoke particles present combustion was retarded more on the left than on the 

right, because less oxygen was present. For this reason more of the 

possible heat was generated with the higher ash coals.

It is worthy of note that the high and low efficiencies (72*) in each 

group (values not shown here) do not vary much between groups. 

Commercially this similarity of highest efficiencies means that buying coal on the basis of per cent of ash shown by proximate analysis 

of coal as fired is an uncertain matter so far as obtaining high efficiency thereby is concerned. Classification of the tests made on Illinois, Indiana, and western Kentucky coals on an ash basis shows no 

more than the minor importance of ash above mentioned.

In making tests on sized coal, as given on pages 45 to 48, there would 

be an opportunity for research on the question of per cent of ash as 

affecting the results of boiler trials. Coals of the same size could be 

classified on the basis of per cent of ash and the effect of the ash thus 

studied separately from the effect of size. It does not seem, howaSee glossary (p. 181), under "Efficiencies."
RELATIONS OF TEST DATA. 43

ever, that for the range of per cent of ash found in coal this investigation would be important, for it is not the amount of ash, but its composition and distribution, that affects the results of a steaming test.

With a knowledge of ash composition it could be decided how the 

coal was to be burned. For instance, a coal which did not clinker 

badly, but which burned leaving free ash, would be burned under 

ideal conditions on a rocking grate no matter how high the per cent 

of ash. A coal which clinkered badly at high temperatures should

60.

W,

0,5.

M

63

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3i

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U

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to

1500 

Z400

iSOQ

ZJOQ

ZIOQJ

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0 £ 3 A 5 6 7 

PERCENT Op SULPHUR IN DRV COAL.

FlQ. 28. Relations of per cent of sulphur in coal to boiler efficiency 72* (curve No. 1); per cent of completeness of combustion (E3) (curve No. 2); pounds of dry chimney gases per pound of "combustible" 

(curve No. 3); and combustion-chamber temperature (°P.) (curve No. 4) Tests 89-400.

be gasified at a low temperature, 

ering that would stop up the air 

from adhering to the grate. It 

with the manner of distribution 

The curves of fig. 28 present 

sulphur in dry coal. For the 

variation in efficiency 72*. As

thereby avoiding an amount of clinkpassages and also preventing clinkers 

is a study of ash composition along 

of the ash in the coal that is needed, 

a classification based on per cent of 

low sulphur values there is a wide 

the per cent of sulphur increases, up
44 A STUDY OF FOUR HUNDRED STEAMING TESTS.

to 5 per cent, there is a gradual drop in efficiency 72*. There were 

16 tests in which the per cent of sulphur was over 5.4. At the high 

values of sulphur the efficiency 72* curve rises, probably because the 

sulphur is in different form and also differently distributed. A 

curve through the average efficiency points shows a drop of 5 per 

cent, with an increase of 5 per cent in the sulphur, or, in other words, 

every increase in the per cent of sulphur in dry coal decreases the 

efficiency in equal amount.

Curve No. 2 shows the per cent of completeness of combustion (E3 ), 

and is nearly parallel to the efficiency 72* curve.

Curve No. 3 shows the pounds of dry chimney gases per pound of 

"combustible," and rises slightly with the per cent of sulphur.

Curve No. 4 shows the combustion-chamber temperature, which, 

except for the high sulphur values, decreases as the per cent of 

sulphur increases, indicating a value at the high sulphur values 

about 300° F. higher than an average curve through the combustionchamber, temperature points would indicate that it should be. The 

curves of fig. 17 (p. 25) show that this increase of temperature nearly 

accounts for the increase of efficiency 72* at the high-sulphur values.

The curves of fig. 21 (p. 30) show that as the per cent of clinker in 

the refuse increases the per cent of sulphur increases; also that all 

the highest values for per cent of clinker are grouped with the higher 

values for per cent of sulphur. The low per cent of values for sulphur 

are grouped with the high values for per cent of efficiency 72*, and 

vice versa. At the highest values for "per cent of clinker the efficiency 72* is lowest, and with high efficiency 72* the per cent of 

clinker is the lowest. This relation was determined from two different classifications one on per cent of clinker in refuse and one 

on efficiency 72*. The classification on per cent of clinker in refuse 

shows that efficiency 72* is more influenced by per cent of clinker 

than the per cent of clinker is influenced by this efficiency. The 

latter influence was determined by classifying on an efficiency 72* 

basis.

On referring to fig. 24 (p. 36), a classification on the basis of per 

cent of clinker in refuse, it is to be noted that for all values of per 

cent of clinker the combustion-chamber temperature and pounds 

of dry chimney gases are about constant.

The general conclusion is that the per cent of sulphur does affect 

efficiency 72* indirectly by the formation of clinker. Since the 

amount of air used is a constant value, it is quite possible that the 

decreasing value of efficiency 72* with increasing per cent of sulphur 

is due to the effect of clinker on the distribution of the air supply. 

Moreover, with the high values for per cent of clinker probably more 

of the air enters the furnace over the fire.
RELATIONS OF TEST DATA. 45

AVERAGE DIAMETER OF COAL.

Preliminary to the discussion of the results produced by using coal 

of different sizes it may be of value to state how the coal is received 

at the fuel-testing plant and how the size is determined, and to suggest how further research work.might be done on the influence of 

size.

Nearly all of the coal tested was passed through a crusher, and 

consequently coals of widely varying characteristics were reduced to 

the same size. Therefore by classifying coals on a size basis, as we 

have done, we have averaged a good eastern coal with a poor-grade 

western coal. While size shows, on the average, some few general 

relations, it would seem that the best comparable data could be 

obtained by taking one coal, say, run of mine, and after separating 

the various sizes, making a series of tests on each size. Even such 

tests would not be made on the same grade of coal, as the smaller 

sizes are sure to be higher in ash; but nevertheless this side of the 

problem is of commercial importance.

After the sample of the coal tested has been.quartered and a part 

sent to the chemist for analysis, the remainder is passed through a 

revolving screen perforated its entire length with round holes ranging 

from one-eighth to 1 inch in diameter, These holes are arranged in 

strips or sets of rows, the width of which decreases as the size of hole 

increases. The coal passing through each set of holes is weighed 

separately and the data from the boiler room are reported, as follows:

Determination of average diameter of coal samples.

Diameter 

of holes 

(inches).

Pounds of coal through 

each set of holes.

Actual.

1. 2.

J

4 i i

li

20 

14 

18 

12

27 

4

3

98

Reduced to 

100-pound

basis.

2

20.4 

14.3 

18.4 

12.2 

27.6 

4.1 

3.0

Weight of coal, 

determining 

average size.

4.

2.0 

3.6 

6.9 

6.1 

20.7 

4.1 

4.5

100.0 ,R , 

i 4=Ld =0.49 

! 100.0

Column 2 shows that 98 pounds of coal was sized. No attempt is 

ever made to weigh out exactly 100 pounds, so the weights must be 

reduced to 100, as has been done in column 3, thereby obtaining the 

percentages of the various sizes of coal. From the construction of 

the revolving screen it follows that in an average diameter each of 

the percentages has a "weight of observation" proportional to the
46 A STUDY OF FOUR HUNDRED STEAMING TESTS.

diameter which it represents. In getting average diameter, then, 

column 3 is multiplied by column 1, obtaining column 4, and the 

sum of this column of products divided by 100, therefore, gives the 

weighted average size of the coal.

The classification plotted in the curves of fig. 29 was made on the 

coals tested in tests 89 to 401, and shows that as the average diameter 

increased from 0.35 to 1.26 inches (1) the capacity increased about 15

2500

2400

ZZOQ

2300

2100

600

590

580

570

100

95

90

85

QO

22

21

665 

66. 

65.S 

65. 

64.5

93

92

91

90

ia

3>

(7.

16.5

16

15.5

SOS

so 

i as

i%

18.5

55 AS S75

AVERAGE DIAMETER OF COAL , INCHES.

FIG. 29. Relations of size of coal to combustion-chamber temperature (°F.) (curve Nc. 1); flue-gas 

temperature (°F.) (curve No. 2); per cent of rated capacity developed (curve No. 3); pounds of dry 

chimney gases per pound of "combustible" (curve No. 4); efficiency 72* (curve No.5); percent of 

completeness of combustion (Es) (curve No. C); carbon-hydrogen ratio in dry coal (curve No. 7); 

and ratio of carbon to available hydrogen (curve No. 8). Tests 89-401.

per cent (curve No. 3); (2) the highest efficiency 72* values were 

obtained with the smallest sizes (curve No. 5); (3) there was practically no change in the per cent of completeness of combustion (curve 

No. 6); (4) there was a slight decrease in the pounds of dry chimney 

gases per pound of "combustible" (curve No. 4); and (5) the carbonhydrogen ratio figured from the dry coal decreased considerably 

(curve No. 7), showing that the good coals fall in the groups of small-
EELATIONS OF TEST DATA. 47

est average diameter, this result being probably due to the fact that 

some of the good coals broke up badly in transportation and in passing 

through the crusher; (6) the combustion - chamber temperature 

increased about 400° F. (curve No. 1).

It should be borne in mind in considering these general results, 

which are so different from the usual conclusions, that they .are only 

tentative, because other conditions varied so widely. The study of 

effect of size as above outlined is not specialized enough, for undoubtedly other factors than average size are influential e. g., perhaps, 

percentage of voids, as dependent on percentage of various sizes forming average diameter, shape of pieces, etc.

In discussing the effect of average size of coal as based on these tests 

it is well to remember that none of the coal is really fine, for the lowest 

sizes averaged about 0.3 inch. On the other hand, the largest sizes 

averaged only 1.25 inches.

The tabulation headed " Classification of per cent of clinker on basis 

of average diameter of coal," which follows, was made to ascertain 

whether the size of coal had any influence on its tendency to clinker. 

About 300 tests were used, but they were on all kinds of coal, from 

all parts of the country, and no such influence is indicated. (See 

"Classification on basis of per cent of clinker in refuse/' p. 41.) '

Classification of per cent of clinker in refuse on basis of average diameter of coal.

Average diameter of coal 

(inches) .................. v 

Average per cent of clinker in'

Average diameter (inches) .

Below 

0.40.

.15 

0.35 

44

0.40 to 

0.50.

16 

.0.44 

40

0.50 to 

0.00.

19 

0. 50 . 

35

O.liO to 

0.70.

41 

0.65 

43

0.70 to 

0.80.

r i

0.75 

40

0.80 to 

0.90.

45 

0.84 

47

0.90 to 

1.00.

,33 

' 0.94 

50

1.00 to 

J.10.

19 

1.04 

40

1.10 to 

1.20.

8 

1.14 

34

Over 

1.20.

21 

1.25 

45

Fig. 30 shows some of the many variations encountered when making sizing tests. The seven tests from which this chart was plotted 

were made on mixed bituminous coals, made up of several of they 

officially numbered coals, and accurately sized by passing through a 

revolving screen. The per cent of sulphur and per cent of moisture 

were about constant in the mixtures. The fact that the carbonhydrogen ratio of the dry coal used decreased as the coal became larger 

(curve No. 1) seems to indicate that the tests were not run on uniform 

mixtures of coals; perhaps certain coals were finer or coarser than 

others before mixing. The coals were accidentally mixed in a general 

heap, in consecjuence of a fire in the washer plant, and it was not 

known just what they consisted of except that they came from the 

so-called Illinois and Missouri coal basins.

A significant fact brought out by the chart is that the efficiency 72* 

was about constant for all the sizes.
48 A STUDY OF FOUR HUNDRED "STEAMING TESTS.

Certain values varied as the size of the coal increased. Curve No. 1 

shows that the carbon-hydrogen ratio in dry coal decreased, and 

thereby tended to lower efficiency 72*. Curve No. 2 shows a slight 

rise of efficiency 72*. Curve No. 3 shows a steady increase in the difference between the draft in the stack and that over the fire, for which 

no explanation is offered. Curve No. 4 shows an irregular but decided 

increase in pounds of coal burned per square foot of grate per hour a

61

60

S3

se 

u>

55 

50 

43 

40 

3S ' 

13

10

69

£1.5

150

ZM

20.0

14

13

SIZE.. OF COAL

FIG. 30. Relations developed on accurately sizing mixed bituminous coal: Curve No. 1, carbon-hydrogen ratio in dry coal; No. 2, efficiency 72*; No. 3, difference between draft in stack and draft over fire; 

No. 4, pounds of dry coal burned per square foot of grate surface per hour; No. 5, per cent of rated 

capacity developed; No.6, pounds of dry chimney gases per pound of "combustible;" No.7,percent 

of ash in coal (proximate analysis).

direct consequence of the increase in size of the coal. It should be 

borne in mind that the stack draft available was always about the 

same. Curve No. 5 is of the same shape in detail as No. 4, and shows 

an increase in the rate of steam production. Curve No. 6 is practically level, except-at the left end, where it is high perhaps because 

the coal was so fine that it caked and allowed cracks to form in the
RELATIONS OP TEST DATA. 49

fuel bed, or because the ash contained was high. Curve No. 7 shows 

that much of the ash went into the fine coal. It is worthy of remark 

that the finer and dirtier sizes gave nearly as high efficiency as the 

larger sizes.

The sole advantage of the larger sizes of coal over the smaller, so far 

as shown by these few tests, was that a higher rate of steam production 

was attained.

An attempt was made to determine the effect of £-inch size (in 

Indiana, Illinois, and western Kentucky coals) on efficiency 72*, per 

cent of CO loss, and combustion-chamber temperature; but the 

results were negative, and emphasize the statements made on 

page 47, that the study of the effects of the various elements of size 

of coal has not been made in sufficient detail. It is also likely that 

the effects of size are obscured greatly by other factors, such as caking, moisture, etc. The following table of results does not seem to 

indicate much:

Classification of efficiency 72*, per cent of CO in jlue gas, and combustion-chamber temperature on basis of per cent of %-inch coal (Illinois, Indiana, and western Kentucky 

coals).

Average combustion-chamber temperature 

(«F.). ....................:................

Average combustion-chamber temperature 

(°F7>. .....................................

Per cent of J-inch coal.

Oto5.

4 

4.0 

05.02 

0.11 

3

2,612

5 to 10.

13 

8.2 

63.74 

0.27

8

2,483

10 to 12.

9 

11.1 

66.18 

0.19

7

2,367

12 to 14.

4 

12.2 

68.05 

0.19 

3

2,302

14 to 1C.

4 

14.9 

05. 57 

0.30

2

2,240

16 to 17.

7 

16.2 

65. 88 

0.18 

6

2, 370

17 to 18.

7 

17.6 

63.88 

0.17 

2

2,393

Per cent of £-inch coal.

18 to 19.

4 

18.4 

66.74 

0.24

2

2,371

19 to 21.

9 

19.9 

04.98 

0.26 

4

2,299

21 to 23!

6 

22.0 

65.84 

0.16 

3

2, .104

23 to 25.

6 

24.0 

65.92 0:13

5 

2,245

25 to 30.

6 

20.2 

06.67 

0.14 

4

2,245

30 to 40.

5 

32.7 

65. 84 

0.27 

4

2,378

a Fewer tests were used to obtain the average combustion-chamber temperature than for the other 

averages, owing to the fact that the questionable results were eliminated.

The coals used for sizing came from Illinois, Indiana, and western 

Kentucky. Not many tests are used here and the results would not 

be expected to convey much information even had the coals come 

from one locality; because, for example, from the State of Illinois it 

is possible.to obtain about as good and as poor bituminous coal as is 

mined. The results, given in the table on the following page, show 

a small increase in efficiency 72* and a large increase in combustion-chamber temperature as the size of coal increases.

8400 Bull. 325 07 4
50 A STUDY OF FOUR HUNDRED STEAMING TESTS.

Classification of efficiency 7%*, per cent of CO in flue gas, and combustion-chamber temperature on basis of average diameter of coal (Illinois, Indiana, and western Kentucky coals).

Averages of average diameter (inches)

Average per cent of CO in Hue gas. . .

Average combustion-chamber ternAverage diameter (inches).

Up to 

0.5.

9 

0.39 

64.83 

0.18

7

2,080

0.5 to 

0.6.

4 

0.58 

07. 69 

0.31

2

2,406

0.6 to 

0.7.

16 

0.60 

65.75 

 0.16

7

2,258

0.7 to 

0.8.

22 

0.74 

65.19 

0.23 

14

2,357

0.8 to 

0.9. 

15 

0.83 

65.00 

0.20 

11

2,405

0.9 to 

1.0.

7 

0.95 

66. 88 

0.34 

5

2; 412

1.0 to 

1.2.

3 

1.04 

68.50 

0.15 

3

2,542

1.2 up.

8 

2.51 

63.68 

0.11 

4

2, 576

o Fewer tests were used to obtain the average combustion-chamber temperature than for the other 

averages, owing to the fact that the questionable results were eliminated.

Increasing the size of fuel by briquetting would seem from 

theoretical reasoning to be a move in the wrong direction. Other 

things being equal, it is self-evident that the more nearly the size of 

a particle of coal approaches that of an atom the better, for then 

each particle will burn instantly on coming in contact with two 

atoms of oxygen. It is also self-evident that the-smaller the individual particles of coal put into a furnace or gas producer the less will, 

be the protecting effect of the surface coating of ash formed b}^ the 

burning away of the outer portions of the grains. From a mathematical standpoint it can be seen that the volume of a body increases 

proportionately to the cube of its diameter, but the exposed surface 

increases only as the square of its diameter, and in combustion it is 

exposed surface that counts for rapidity. Therefore, to repeat, it 

would seem that on this basis alone, artificially increasing the size 

of fuels is, to speak generally, working in the wrong direction. It is 

recognized that improved results are obtained by briquetting some 

fuels, but that probably still better results can and will be obtained in 

the future by devising furnaces and gas producers of such types as 

will utilize fine coal better than coarse. So far the only step made 

in this direction has been the burning of pulverized coal in furnaces. 

Perhaps the slowness of development in this field is attributable to 

the expense of grinding the coal, which has never had a fair trial 

on a large scale, and also indirectly to the softening of the fire-brick 

lining due to the fact that pulverized-coal furnaces are customarily 

run too hot. The work done by the boiler division, and set forth on 

pages 20, 23, 56, shows the error of the general impression that very 

high furnace temperatures are necessary for very high over-all efficiencies. Viewed from this standpoint, it is not improbable that in 

the future the burning of fine and pulverized coal, perhaps even 

without extreme pulverization, will increase largely. In cement 

kilns, for instance, such coal has been a great success for the reason that 

the lining of the kiln is protected by the material itself which it is 

desired to melt. One reason for the nonutilization of slack coal is 

because too little attention has been given to this general subject.
KELATIONS OF TEST DATA. 51

As indicating a right trend in this matter, attention may be called 

to the success of the large power houses of the country in burning 

fine coals, which a few years ago were used as railroad ballast or 

thrown on dump heaps. The over-all efficiencies are in many cases 

quite equal to those which could have been obtained with the stokers 

and grates of a few years ago when using cleaner coals, of larger and 

more uniform size. Perhaps in a few more'years no complaint will 

be heard against fine coal. Every engineer knows that, whereas egg 

and lump coal used to be sought after, the large power houses now 

put all their coal through crushers which reduce it to a size which 

a few years ago would have been thought almost useless.

PER CENT OF RATED CAPACITY DEVELOPED.

No attempt is made here to -discuss in detail the causes of the 

showing of the following table, which is one of the most significant in 

this volume. It indicates that for every capacity group the "boiler 

efficiency" (72*) is independent of the combustion-chamber ternPER CENT OF C0a IN FUUE OASES

FIG. 31. Relation of percent of CO2 in flue gases to percent of completeness of combustion (Ea ),

tests 89-401.

perature and practically constant throughout the whole range of temperature. The suggested explanation is that as the temperature of 

combustion rises the oxygen content of the gases decreases, which 

reduces the completeness of combustion sufficiently (see figs. 13, p. 

22; 14, p. 23; and 31) to neutralize the slight rise of boiler efficiency 

due to higher initial temperatures. This same result is shown for all 

tests grouped with regard to amount of coal burned (figs. 12, p. 21; 

and 17, p. 25).
r

52 A STUDY OE FOUR HUNDRED STEAMING TESTS.

Classification of combustion-chamber temperature and efficiency 12* on basis of per cent 

of rated capacity developed.

Per cent of rated capacity developed.

70 to 75.

H

 *ta

2ft 

-fj

1,870

1,936

2,253

w

0)

o

IH 

rO

S

fc

1

2

1

*'

(N

^

H0)

o

W

66.38

64.07

65.04

o64.89

75 to 80.

fs

*sS §

o

1,880

1,967

2,039

2,118

2,247

2,350

»

1

o

§

fc

1

2

3

1

1

2

£

(^

§

1

60.89

59.79

66.35

65.95

68.54

63.68

o64.12

80 to 85.

n .

i

H*

.2 a

3 ft .

a S

o

1,961

2,046

2,163

2,259

2,325

2,419

2,597

0}

o

H

0)

£1

ti

fc

1

4

3

11

5

5

1

£

(^

§

1' '

67.64

62.33

67.68

65.79

67.39

66.87

66.82

a66.06

85 to 90.

n . 

|?

d 3

.2 oj

3 ft ^2 a

a §

o

2,067

2,140

2,231

2,354

2,421

2,525

2,672

1

o

H

O 

fl

|

fc

6

2

9

8

5

1

2

£

j^

 s

o

sd

W

65.93

64.56

66.13

64.83

65.79

65.25

65.94

o65.59

Per cent of rated capacity developed.

90 to 95.

»H .

bustion-ch 

nperature

gs

O

2,050

2, 178

2,244

2,359

2,456

2,546

2,637

2,708

iber oftest

*

fc

2

2

3

12

8

5

1

1

iency 72*.

tS

H

67.46

65.88

69.23

65.45

65.88

69.41

68.61

64.97

"66.60

95 to 100.

t-i

bustion-ch 

nperature

a s

o

2,248

2,368

2,457

2,554

2,627

2,722

of ibertest

s

6

7

11

6

2

1

iency 72*.

W

67.32

65.63

65.83

64.88

65.80

68.06

"65.95

100 to 105.

1?

bustion-ch 

nperature

0.®

o

2,256

2,327

2,474

2,550

2,660

2,839

iber oftest

*

2

3

4

5

1

2

iency 72*.

65.09

66.46

67.55

66.10

65.22

66.55

"66.38

105 to 110.

n

bustion-ch 

nperature

II 

o

2,290

2,345

2,448

2,534

2,653

2,708

2,864

ra

iber oftest

S

3

3

9

1

5

1

1

#'

0

a

W

66.19

67.44

65.03

65.83

65.01

64.61

73.64

"65.88

a Average. 

PYROMETRY.

For measuring the furnace and the combustion-chamber temperatures, both a Wanner optical pyrometer and a thermoelectric couple 

of platinum and platinum rhodium were used.

The Wanner optical pyrometer (fig. 10, p. 19) was the more reliable and by far the more convenient to use. The working of this 

instrument is based on the relation which exists between the temperature of a hot body and the intensity of the light which it emits.a 

The instrument itself makes use of an incandescent lamp which is

a. For the theoretical discussion of this subject see Waidner, C. W., and Burgess, O.K., Optical pyrometry: Bull. No. 2, Bureau of Standards, U. S. Dept. Commerce and Labor.
RELATIONS OF TEST DATA. 53

standardized by comparison with an amyl-acetate standard lamp, 

and consists of a photometer for comparing the light emitted by the 

body whose temperature is to be measured with a steady light of 

known intensity. The comparison light is a 6-volt incandescent 

lamp, supplied by a storage battery, illuminating a ground-glass 

surface. A beam of monochromatic (red) light from this source 

produced by-means of a direct-vision spectroscope and a screen, cutting out all but a narrow band in the red and a similar beam from 

the hot body are passed into a photometric telescope, each beam 

illuminating one-half of the telescopic field. The photometric comparison is made by adjusting to equal brightness both halves of the 

telescopic field by means of a polarizing arrangement.

One of the advantages of the optical pyrometer is that it is more 

apt to take the average temperature of a strip across the furnace from 

wall to wall. Furthermore, it gives temperature changes instantaneously and in absolute measure, which, even in case the flames appear 

hotter than they really are, can hardly be in error more than 150° F. 

This error is probably more than offset by the fact that the furnace 

is not a perfect "black body."

The most serious source of error, except when special precautions 

are taken, is the variation in brightness of the electric comparison 

lamp due to variation in the current furnished by the three-cell storage battery, the percentage of change in light being of the order of six 

times the percentage of change in current through the lamp. Breaking the circuit and then making it again may cause an apparent 

change of more than 20° C. It has been found that for a series of 

observations lasting from one-half hour to two hours it is better to 

take all readings, after once standardizing the instrument, without 

breaking the lamp circuit, instead of breaking it after every single 

reading.

Before standardizing the instrument the amyl-acetate standard 

lamp should be allowed to burn from five to ten minutes to get a 

steady flame. To supply the incandescent lamp a 20-ampere-hour 

storage battery was used for most of the readings recorded in this 

work.

The thermoelectric couple used for pyrometric tests was connected 

either to a millivoltmeter equipped with a scale of temperatures or to 

a Callendar recording instrument. There were two of the latter 

instruments; one was to be used with the thermoelectric-couple 

pyrometer and the other with an electric-resistance pyrometer. 

Owing to the fact that these pyrometers, as sold, do not stand the 

furnace temperatures for any great length of time there was no 

opportunity to give the recording instruments a fair trial, and therefore they are not considered in detail in this report.
54 A STUDY OF FOUR HUNDRED STEAMING TESTS.

The thermoelectric couple as it came from the maker consisted of 

a platinum and platinum-rhodium junction inclosed in a porcelain 

tube of f-inch bore and f inch outside diameter. However, this 

porcelain tube could not stand the high temperature, and particularly 

the slagging action of the furnace gases. The slag accumulated on 

the surface of the tube and seemed to change the composition of 

the porcelain. The tube partly melted, and then, after it had 

been in the combustion chamber for two hours, broke off, although 

there was nothing in the chamber to strike it. A water-jacketed 

iron pipe, similar to the gas sampler shown in fig. 15 (p. 24), was 

tried instead of the porcelain tube, the two wires being insulated 

from each other and from the pipe by pieces of small glass tubing. 

The thermoelectric junction projected 3 inches from the end of the 

iron pipe, and was held in two. stems of penny clay pipes. This 

arrangement lasted over a week in the combustion chamber and gave 

fairly satisfactory results. During this time the couple was continually connected to the Callendar recording instrument.

The records obtained with the thermoelectric apparatus had a value 

only so far as the relative temperatures were concerned. For absolute temperature the apparatus could not be depended on, because it 

was impossible to apply any scale or rule to the record when the mass 

around the junction of the couple was one fused mass of slag. It was 

also found that the variations in temperature shown by this couple 

were lagging from six to eight minutes. A couple fitted with a waterjacketed iron pipe had to be rigidly connected to a water supply. 

On that account such an arrangement could not be used for measuring temperatures in different parts of the furnace, and for this purpose a plain ^-inch iron pipe was used. The junction of the wires 

was, as before, held in two clay pipestems, which projected about 2 

inches from the end of the iron pipe. Clay pipestems had to be used 

also for insulating the wires inside of the iron pipe for a length of 

about a foot back from the end, on account of the high temperature 

to which the end was subjected. Even with this special arrangement 

the thermoelectric couple could be exposed to the high temperature 

of the furnace only long enough to get the projecting junction hot and 

take the reading. This exposure usually lasted fifteen to twenty 

seconds, after which the instrument had to be withdrawn and cooled 

off. Even with this care the iron pipe lasted for only thirty to fifty 

single readings, after which it became so burned that it had to be 

replaced by a new one. This instrument also could be depended on 

only for relative temperatures in different parts of the furnace.

After all the difficulties that are encountered in using a thermoelectric couple for measuring furnace temperatures, this apparatus 

measures only the temperature of a very small part of the furnace,
RELATIONS OF TEST DATA. 55

where the instrument is inserted, and the temperature midway 

between the side walls may be much higher than it is at points 

reached by the couple, 8 inches from the walls.

Fig. 32 gives a comparison of the combustion-chamber temperatures 

taken with the Wanner optical pyrometer with the rise in temperature of water from a water-jacketed gas sampler inserted in the rear 

of the combustion chamber. A mercury thermometer was inserted

2500

110- 

100- 

90 

80-

^;

-

TEMPERATURE OF

UTEMPERATURC IN COMBUSTION CHAMBER 

PYROMETER

iAJi liAMPLCR

OF FEEDWM,T3

P s$8

8'? e 

i i t

Z\ L.U 

VOLATILE MACARB FTXED§IN DRY CO

FIG. 32. Comparison of Wanner optical pyrometer temperatures in combustion chamber with rise in 

temperature of water from a jacketed gas sampler.

into the water outlet of the gas sampler and was read simultaneously 

with the optical pyrometer. The two curves agree very well, the 

temperature of the water lagging slightly. The elevation of temperature at A, B, C in the water-temperature curve is due to reduction of pressure in the water main caused by the taking of water into 

the measuring tanks for feeding the boiler. But for this circumstance 

the curve would run as shown by the dotted lines A, D, C.
56 A STUDY OF FOUR HUNDRED STEAMING TESTS.

SMOKE.

The curves of fig. 33 are plotted on the basis of per cent of black 

smoke. Curve No. 1 indicates that the efficiency 72* rises a little 

more than 1 per cent until about 20 per cent of black smoke is reached, 

and then gradually drops. This drop in efficiency amounts 'to about 

2.5 per cent within the range of 20 to 50 per cent of black smoke. 

The drop in efficiency when there is little or no smoke can be explained 

by noting that a greater amount of air was used for combustion of

NOT

£.£00. 

AO.

M.4

SMOKE-, PERCENT BU<VCK

FIG. 33. Relations of smoke per cent to boiler efficiency 72* (curve No. 1); per cent of unaccounted 

for loss taken from heat balance (curve No. 2); combustion-chamber temperature (°F.) (curve No. 

3); per cent of CO in flue gases (curve No. 4); per cent of oxygen (ultimate analysis) in dry coal (curve 

No. 5); per cent of available hydrogen in "combustible" (curve No. 6); and per cent; of fixed carbon 

(proximate analysis) (curve No. 7). Series of 1905-6; black smoke taken as 100 per cent.

the coals producing little smoke, probably owing to the fact that 

many lignites were included in these groups, the excess of air reducing the heat available for the boiler and causing a greater loss of 

heat up the stack. The loss up the stack decreases and the efficiency 

72* rises with reduction in the supply of air until the point is reached 

at which the loss due to incomplete combustion becomes larger than
KELATIONS OF TEST DATA. 57

the gain obtained by reducing the loss up the stack. Curves Nos. 3 

and 4 support this explanation.

Curve No. 3 shows that the combustion-chamber temperature rises 

in direct proportion with the per cent of black smoke. Rise in combustion-chamber temperature always indicates a decrease in air

supplyCurve No. 4 shows a gradual increase in CO in the flue gases. The

unaccounted-for loss, represented by curve No. 2, also rises as the 

smoke increases. It is reasonable to say that the greater part of the 

increase in the unaccounted-for loss is due to incomplete combustion 

of hydrocarbon gases and to the escape of solid particles of carbonforming smoke.

Curve No. 5 shows but a small increase in oxygen in coal, and therefore does not indicate that oxygen in coal is a direct cause of smoke.

Curves Nos. 6 and 7 indicate that, excepting the first point at the 

extreme left, good or bad coals have not been prevalent in any one 

group.

The direct cause of the smoke seems to be shown in curve No. 3, 

which indicates increased rate of combustion and decreased supply 

of air.

The table which follows indicates that eastern coals are about as 

apt to smoke as western. It should be stated here that if these 

coals had been handled as suggested below most of them would 

probably have burned entirely without smoke, and the remainder 

with less smoke than they produced as actually handled.

Average per cent of black smoke produced by burning coals from certain localities under a

Heine boiler.

Locality.

Brazil........................

New Afexico

Number 

of tests.

8

2

1

35

30

2

3

7

8

Average 

per cent 

of black 

smoke.

10.2

0

0

54.8

18

26

22.7

18.5'

5.2

17

17.0

Locality.

North Dakota. ...............

Texas ........................

Number 

of tests.

1

25

18

1

29

3

10

4

23

8

Average 

per cent 

of black 

smoke.

0

32.2

18.3

0

14.0

8.7

2.8

19

22.9

14.7

The following table includes coals from many localities; some of 

them are usually called "smoky coals." It is quite probable.that 

most other coals which produced smoke could have been burned 

smokelessly if the boiler division had not worked for the greater part 

of 1905 under trio idea that.very high temperatures are needed to 

get good over-all efficiencies. As shown elsewhere, extremely high 

furnace temperatures and a high degree of completeness of combustion in the furnace are incompatible. More air should usually have
58 A STUDY OF POUK HUNDRED STEAMING TESTS.

been admitted through the smoke-preventer openings to the space 

over the fire; this precaution might have prevented almost wholly 

in most cases the formation of the smoke without affecting the overall efficiency of the outfit.

Coals burned under Heine boiler without producing smoke.

Test No.

390

378

;.. 293,294 

. .. 308, 309

340

Alabama No. 3.............

Alabama No. 4.....:.......

Arkansas No. 7 A..........

Arkansas No. 8 (washed).....

Arkansas No. 10. ..........

Brazil No. 1. ................... 172,173

Illinois No. 6 B (briquets) ..... 313

Illinois No. 11 C (briquets) ..... 312

Illinois No. 20.................. 292

Illinois No. 21.................. 316

Illinois No. 21 (briquets) ....... 318

Illinois No. 23 A (washed)...... 317

Illinois No. 25.................. 338,339

Indiana No. 7 B (briquets) .... 288

Maryland No. 1 (washed)....... 231

Missouri No. 5.................. 320

New Mexico No. 3 B........... 389

North Dakota No. 3............

Pennsylvania No. 8.............

Pennsylvania No. 8 (dried).....

Rhode Island No. 1.............

Tennessee No. 5................

Tennessee No. 6................

Tennessee Nos. 8 A and 8 B 

(washed).....................

Tennessee No. 9 (washed, briquets) .......................

Texas No. 4....... ...........

West Virginia No. 19...........

West Virginia No. 19 (briquets) .

West Virginia No. 21...........

Wyoming No. 2 B..............'.

Wyoming No. 3.................

Test No. 

206

236, 237 

242 

401 

352

379, 381

388

393

291

285, 289

331

297

210

211

COMBUSTION AND COAL.

"VOLATILE MATTER," "FIXED CARBON," "WATER OF COMPOSITION,'^ AND

"COMBUSTIBLE."

There still lingers a trace of an old idea that coal consists of particles of carbon cemented together with a sort of natural bitumen. 

The present tendency is to regard bituminous coal as a mixture of 

dozens, or even hundreds, of organic compounds, most of them derived from cellulose and many of them containing nitrogen and sulphur organically combined. It is true that for most kinds of coal 

group formulas can be devised which represent very closely the 

chemical compositions of the respective groups as shown by ultimate analyses; but it must be distinctly borne in mind that the 

devisers of these formulas do not mean that any one coal under consideration consists of one compound expressed by the formula proposed. Such formulas are meant as collective only; in exactly the 

same way as physiologists speak of the normal or average man, 

whose height, weight, etc., bear certain accurate relations to each 

other, although there is not in the world any one man who fits the 

description exactly.

When coal is heated, some or most of its constituent compounds are 

always broken down more or less, but are broken down differently, 

according to the particulars of the distillation method. That poro For definition of " water of composition," see the glossary, p. 183.
COMBUSTION AND COAL. 59

tion which is distilled ofl' from coal when it is heated under certain 

" standard" conditions is called "volatile matter." But inasmuch as 

the "standard" conditions are seldom exactly alike, and inasmuch 

as "volatile matter" is the product of a change, it is a mistake to 

say that coal contains any stated percentage of "volatile matter," 

or even that it contains "volatile matter" at all. The terms "fixed 

carbon/' "volatile carbon," and "water of composition" are equally 

misleading. Coals do not literally contain these constituents in any 

more exact sense than cane sugar consists of "water" and "charcoal," although hydrogen and oxygen are contained in cane sugar 

in exactly such proportions as form water and leave carbon when 

the sugar is heated.

GKATE AND COMBUSTION SPACE.

Any furnace consists of the grate and the combustion space. 

The combustion space extends from the top of the fuel bed to the 

opening into the tube chamber, and its rear portion is termed the 

"combustion chamber." The function of the grate and fuel bed 

is to distill the "volatile matter" and partly to burn the "fixed 

carbon" of the coal. The function of the combustion space is to 

burn the "volatile matter." With coals high in "fixed carbon" 

combustion is nearly complete a short distance from the top of 

the fuel bed; with highly volatile coals the combustion is incomplete, 

even at the rear of the combustion chamber.

Samples of furnace gas collected at the top of the fuel bed are very 

commonly rich in combustible ingredients In the subjoined table 

is given the chemical composition of gas collected at the top of the 

fuel bed and also from the combustion chamber, determined from 

samples collected with the water-jacketed sampler. The samplers 

projected about 10 inches into the furnace, both being inserted 

through holes in the side wall, the first sampler resting oh the surface of the fuel bed.

Analyses of samples of'gas collected at top of fuel bed and rear of combustion chamber.

Collections:

Tost 302:

Test 304:

Test 307:

Rear of combustion chamber..

Time.

/ 8.40

\ 10.40 

f 8.30

1 10.30

/ 8.15

\ 8.30

\ 12.30

( 7.30 

{ 9.30

( 11.20 

[ 7.30

\ 9.30

11.30

C02 .

C.I

10.8 

11.4

14.4

8.4

12.0

12.0

4.4

5.2 

13.3

15.5

14.0

02 .

0

5.0

1 7.7

3.0

8.9

0 

0

5.0

7.4 

0

.2 

0

.0

.2

CO.

17.9

2.2 

0

0

'2

20.3 

0

0

9.5 

23 (j

23.8 

.9

.7

1

II 2.

7.8

0

0

1.2

7 Q

5.4

CH4 .

3.0

0

0

2.7

2.4 

1.2

1.8

CnH2 n+2.

0.2

.0

0

0

.8 

.2

0
60 A STUDY OF FOUR HUNDRED STEAMING TESTS.

It is difficult to say whether the samples collected with the waterjacketed sampler are really representative samples of the furnace 

gases. Some constituents of the gas may decompose and reunite in 

different ways when suddenly cooled by the water-cooled surface. 

Chemical analyses of gas collected at the end of the combustion 

chamber seldom show much CO or any H2 and CH4 .

Samples collected at the base of the stack show dilution of 25 to 

30 per cent. The following table gives the chemical analyses of 

some gas samples collected simultaneously at the base of the stack 

and from the rear of the combustion chamber:

Analyses of samples of gas collected in test 805.

Place.

Do.............................................

Do.............................................

Do..................:..........................

Do.............................................

AverOifirG6

Do.............................................

Do.............................................

Do.............................................

DO......................:......................

Time.

9.00

9.30

10.30

12.30

1.30

. 9.00

9.30

10.30

12.30

1.30

C02 .

13.4

15.0

14.4

15.4

14. C

14.5

10.0

11.0

11.2

11.0

10.5

10.7

02 .

4.6

3.6

3.4

1.8

3.2

3.3

9.2

7.8

7.6

7.9

7.9

8.1

CO.

0

0

0

0

0

0

0

0

0

0

0

CH4 .

0.4

0

Sum.

18

19

17.5

17.2

17.8

17.8

19.2

18.8

18.8

18.9-

18.4

18.8

The above analyses give 17.5 and 23.2 pounds of gas, respectively, 

per pound of carbon.

If the flue-gas analyses determine the control (if the fire, it is important that the samples analyzed be collected before the gas is diluted. 

As it is almost impossible to have a perfectly air-tight boiler setting, 

it is perhaps best to take the sample from the combustion chamber.

VELOCITY OF COMBUSTION AT VARIOUS POINTS ALONG THE FLAME.

The chemical law of mass action for two reacting substances states 

that, other things being equal, the number of new molecules of resulting compound (in the present case C02 ) formed per second is proportional to the product of the masses of the reacting substances present 

per unit of volume (of gases in the present case), these masses being 

expressed in terms of gram molecules. (The gram molecule of a substance is the weight of the substance, in grams,, numerically equal to 

its molecular weight.) . There are two atoms in an ordinary molecule 

of oxygen gas, each weighing sixteen times as much as an atom of 

hydrogen. Therefore the molecular weight of gaseous oxygen is 32. 

The molecular weight of CO is 12 +16 = 28.

Actual volumetric analyses of the simultaneous compositions of gas 

samples collected from two points along the gas stream of combustion 

are given on the following page.
COMBUSTION AND COAL. . 61

/

Volumetric analyses of samples of gas collected in test '851.

Place.

Top of fuel bed. ................................................................

CO2 .

12.60

10.90

02 .

1.70

8.23

CO.

7.10

.20

The hydrocarbon and hydrogen values are omitted for this problem, although they sometimes amount to several per cent at the surface of the fire; in this calculation the effect of considering -them 

would simply be to intensify the final conclusion. At the top of the 

fuel bed there was present by volume 1.70 per cent of oxygen and 7.10 

per cent of CO. Multiplying each .percentage by its specific gravity 

(so as to get numbers proportional to the masses present), and dividing in each case by the molecular weights above given, we have:

1.70X1.105-^32 = 0.0588 

7.10 X 0.967 H-28 = .245

If we assume that the reaction between CO and O2 is trimolecular, 

which is probably the case, because two molecules of CO react with 

one of 02 , then the rapidity with which CO burns is proportional to 

COxCOx02 , or C02 X02 , and the rapidity of combustion of CO in 

the two places is, at the top of the fuel bed, 0.2452 X 0.0588 = 0.00353; 

at the end of the combustion space, 0.00681 2 X 0.284 = 0.00001337. 

0.00353 is considerably larger than 0.00001337 and therefore the 

rapidity of combustion is much greater at the top of the fuel bed than 

at the end of the combustion space (the difference in temperature 

being neglected).

The curve of chemical activity would drop off rapidly as the gases 

proceeded along their path in the combustion chamber, so that if the 

rates of combustion were plotted as ordinates along a base of travel 

of gases, the resulting curve would look much like the expansion curve 

of an engine-indicator diagram.

The practical value of such calculations is that they afford a mathematical verification of a fact frequently observed that mere length 

of combustion chamber counts for little compared with some device 

for thoroughly mixing the gases of the flame stream; one good mixing 

wall or baffle is probably worth many feet of undisturbed flow.

The possibility that many of the molecules of oxygen gas are dissociated at high temperatures into their component atoms does not 

affect the above calculation, because there would then be more atoms 

of oxygen looking for molecules of CO, per volume of gases, in just 

the proportion that the total volume occupied by a given mass of 

gases would be increased by the dissociation.
62 A STUDY OF FOUR HUNDRED STEAMING TESTS.

COMBUSTION-CHAMBER BAFFLE WALL.

A baffle wall, constructed of special fire brick, was built in the combustion chamber. The object of this wall was to divert the gases from 

their straight course in order to mix the free oxygen more thoroughly 

with the unburnt volatile matter of the coal. It was also intended to 

act as a heat regenerator, absorbing heat when the temperature of 

the gases was high, and giving. it out when the temperature was low, 

thus keeping the temperature above the ignition temperature of the 

distilled gases.

It was learned by experiment that only large blocks made of the 

best material could stand the high temperature and the slagging action

StCTION A-B.

FIG. 34. Gas-mixing wall built in the Heine safety water-tube boiler.

of the gases for any length of time. The baffle wall shown in fig. 34 

was built of large fire brick, 18 by 12 by 6 inches, said to be of the 

best material that could be obtained. The wall was built in three 

sections. The bottom consisted of seven blocks set on end, forming 

pillars, on top of which six similar blocks were laid diagonally across. 

The space between the baffle thus formed and the tile roof was filled 

with small bricks of good material, so that the spaces between the pillars gave the only passage left for the gases. The object of this construction was to divert the stream of furnace gases, which struck the 

upper portion of the baffle, and break it into many smaller streams,
COMBUSTION AND COAL. 63

thus mixing the distilled gases and the free oxygen. It is probable 

that eddies caused by the obstacles in the path of the gases greatly 

aided the mixing. The first baffle wall of this construction lasted just 

six months, but later ones were not so durable, and such walls were 

finally abandoned, at least temporarily, and replaced by three small 

piers set on the bridge wall. The first baffles, however, were far more 

efficient as smoke preventers and heat regenerators, although they 

absorbed considerably more draft.

COMBUSTION-CHAMBER TEMPERATURE.

Fig.' 35 shows the manner in which the "unaccounted-for" and flue 

losses of about 260 tests vary to some extent inversely. The encircled

FIG. 35. Relations of combustion-chamber temperature (°F.) to heat balance (with Illinois and Indiana 

coals): Curve No. 1, per cent of unaccounted-for loss plus per cent of loss up stack; curve No. 2, per 

cent of loss up stack; curve No. 3, per cent of unaccounted-for loss.

numbers near the points indicate the number of tests falling within 

each .temperature group. The inverse variation of these curves is a 

consequence of the facts that the flue-gas analyses, though accurate 

in themselves, were misleading because of air infiltration, and that 

the flue temperatures obtained were unreliable because of inherent 

difficulties; both these causes are discussed in the section devoted 

to accuracy and reliability of data (pp. 149-151). It is noticeable on 

this chart that the sum of the flue loss and unaccounted-for loss increases slightly with rise of temperature, notwithstanding the fact 

that the efficiency of the boiler as a heat absorber increases several 

per cent with the rise of temperature; thus again the indication is 

that higher temperatures accompany less complete combustion.
64 A STUDY OP FOUR HUNDRED STEAMING TESTS.

ATTEMPTS TO EXPLAIN UNACCOUNTED-FOR LOSS IN HEAT BALANCE.

The large percentage of "unaccounted-for" loss appearing in the 

heat balances of the many tests made by the boiler division has long 

been a cause of discussion.

The settings of the boilers used for testing the various coals have 

been, even with the utmost diligence, in a very unsatisfactory condition. There were numerous air leaks, so that the furnace gases 

were always diluted when they reached the base of the stack. It 

was thought that this dilution of gases introduced error in the calculation of heat loss up the stack. It also seemed that the radiation 

loss was larger than it should be.

Recently a new setting has been built and completely inclosed by a 

sheet-iron casing made with air-tight joints, so that the leakage was 

reduced to a minimum. The walls of the new setting were built of 

hollow tiles and this with the addition of a sheet-metal casing should 

have reduced the radiation loss; at least this loss could not be greater 

than formerly. Still the unaccounted-for loss continues.

A great many classifications have been made on the data and 

results obtained from our tests. In all cases a few relations continually appear. The important one in this discussion is that low 

efficiency is always accompanied by the highest per cent of CO in 

the flue-gas analysis, and the highest efficiency by the lowest per cent 

of CO. Moreover, the high CO values always go with the highest 

combustion-chamber temperatures. It is also found that as the combustion-chamber temperature increases the per cent of black smoke 

increases.

It is not possible to account for very much of the loss in burning 

coal by the amount of CO found in the gas analysis. Therefore it 

seems that this appearance of CO in the gas analysis is indicative of

bad conditions, such as an irregular fuel bed or the escape of hydrocarbons unburned.

RELATION OF' NITROGEN IN FLUE GASES TO EFFICIENCY 72* AND TO SIZE 

OF COAL, AND OF PER CENT OF CO TO EFFICIENCY 72*.

The curves of fig. 19 (p. 28), based on tests 89 to 401, inclusive, 

present a combination of two charts. The upper one classifies the 

tests on a nitrogen basis. This nitrogen is presumably what is left 

in the flue gases after subtracting from 100 the sum of the percentages by volume of carbon dioxide, oxygen, and carbon monoxide, 

neglecting any small traces of hydrocarbons which may have been 

present and were not determined. Curve No. 1 indicates that the 

code "boiler efficiency" (72*) increases markedly when the nitrogen 

content rises from 80 to 81 per cent that is, when Orsat gasanalysis totals decrease from 20 to 19 per cent. The reacter. can
COMBUSTION AND COAL. 65

choose between the many possible conjectures as to the fundamental 

significance of this curve.

Curve No. 2 indicates that for any size of coal, up to maximum 

size, two different gas analyses may be obtained. The reader may 

make whatever conjectures he chooses.

Curve No. 3, in the lower chart, is very significant. It indicates 

that a volumetric percentage of CO above 0.4 per cent is threatening 

to efficiency. Inasmuch as these were analyses of flue gases, into 

which 10 to 50 per cent of air had filtered after the gases of combustion passed through the combustion chamber (p. 64), this CO content 

represents a much larger value. The significant fact is that an 

increase of CO content from 0.3 to 1 per cent is of itself sufficient to 

account for only about .one-third of the drop from 65 to 54 per cent 

in code "boiler efficiency" (72*); Figs. 13 (p. 22) and 14 (p. 23) 

show that the percentage of CO rises with the temperature of combustion; further, the efficiency of the boiler as a heat absorber 

increases slightly with a rise of furnace temperature; we therefore 

reach the inevitable conclusion that at least two-thirds of the large 

drop in code "boiler efficiency'' (72*) with rise of CO is due to incomplete combustion losses not represented by CO, so that high CO is a 

decided danger signal. Curve No. 1 of fig. 18 (p. 27) shows exactly 

the same thing, with grouping on a "boiler efficiency" (72*) basis. 

With CO rising from 0.3 to 0.6 per cent the "efficiency" drops from 

60 to 55 per cent. The same range of CO in fig. 19 (p. 28) gives the 

same amount (65 to 60 per cent) of efficiency drop though in a different region which is explained by the fact that in grouping any set 

of related occurrences in different ways the same tests will not often 

fall in successive groups. For instance, only part of the tests falling 

in the middle group in one classification are apt to fall in the middle 

group in any other classification.

RELATION OF C02 IN FLUE OASES TO PEE CENT OF COMPLETENESS OF 

COMBUSTION (E3 ).

The curve of fig. 31 (p. 51) was obtained by grouping tests according to volumetric CO2 content of flue gases and then averaging the 

per cent of completeness of combustion (E3 ) of each group. These 

values of E3 were obtained by the mathematical calculation explained 

on page 139, and although many or all of them may be considerably 

in error, it is likely that the general shape and the amount of drop 

of this curve are nearly correct.

The curve shows clearly that as the oxygen is decreased simultaneously with a rise of C02 content the completeness of combustion 

decreases, which is just what we should expect when reducing the 

proportion of oxygen molecules present, according to the law of 

mass action discussed on pages 170-172. 

8400 Bull. 325 07 5
66 A STUDY OF FOUR HUNDRED STEAMING TESTS.

Thus even in furnaces as long as those of the boilers used in the 

work of the boiler division the increasing incompleteness of combustion with rising temperature is practically sufficient to offset an 

increase of a few per-cent in the efficiency of the fyoiler as a heat 

absorber after the furnace temperature has reached about 2,400° F.

EELATION OF DIFFEEENCES OF DRAFT TO POUNDS OF DRY CHIMNEY GASES 

PER POUND OF "COMBUSTIBLE."

The curves of fig. 36 were determined by plotting differences 

between draft in stack and draft over fire with pounds of dry chimney gases per pound of "combustible." Curve No. 1 represents

u

EC.

zo

a

Snia.

" COMBU

J

.R POUNDOf

a

i

i

X,,

u. 

0

I"

18

n

(I1)

-

^

. /

/

A

0

^

S^

t)

(

^

(

10

4

/

(ll

-c

0

^

/

)

>

4

--

N

,,-

/

N

\

a

^

~

 ^

0. i

-t

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DRAFT UNDER STACK DAMPER MINUS DRAFT OVER FIRE., INCHES OF WOTER.

j

FIG. 36. Relation of differences between draft in stack and draft over fire to pounds of dry chimney 

gases per pound of "combustible:" Curve No. 1, figured from analysis of gas in stack, tests 120-400; 

curve No. 2, figured from analysis of gas in rear of combustion chamber, tests 318-380.

about 200 tests. The values for pounds of dry chimney gases per 

pound of'' combustible'' were figured from stack samples. Curve No. 2 

is the average of only a few points. The values for pounds of dry
COMBUSTION AND COAL. 67

chimney gases per pound of " combustible " were figured from samples 

taken in the combustion chamber. The general direction of the 

curve was determined by curve No. 1.

Low difference of draft readings occurs in two ways by carrying 

a low-stack draft accompanied by a thin fire or by carrying a highstack draft and a thick fire. On most of these tests the stack draft 

is comparatively high as regards the amount of draft obtainable, 

hence the average points on the low difference of draft may be 

assumed to result from thick fires.

The use of a thick fire causes resistance to the passage of air 

through the fuel bed. When high-stack draft is used the difference 

between the pressure of the gases on the inside of the boiler setting 

and the atmospheric pressure outside is large, and thereby the absolute amount of leakage of air into the setting is increased. However, since, in general, high-stack draft has been carried, it follows

that on the chart the per cent of leakage is a maximum at the 

points of low-draft differences. That is to say, as the draft difference increases the pounds of dry chimney gases per pound of combustible increase, the per cent of air leakage decreases, and more of 

the air comes through the fuel bed. This condition holds up to a 

point where the fire is thin, as indicated by a high-draft difference. 

The air now enters more freely through the fuel bed, increasing the 

rate of combustion, thereby decreasing the pounds of dry chimney 

gases per pound of " combustible." Another cause for the decrease of 

the pounds of dry chimney gases at the high-draft difference points 

is the very low per cent of air leakage. Thus it is shown that with 

two widely varying conditions we may obtain the same weight of 

dry chimney gases per pound of " combustible."

The curves have no bearing on efficiency. The variation in the 

slope of curves Nos. 1 and 2 is probably due to air leakage.
68 A STUDY OP FOUR HUNDRED STEAMING TESTS.

The following table gives figures on pounds of dry gases per pound 

of carbon, calculated from gas analyses taken simultaneously at 

different parts of the boiler:

Infiltration of air through setting.

Test 

No.

SIS319 

320 

321 

323 

324 

325 

326 

327 

328 

329 

330 

332 

334 

344 

347 

348 

349 

349 

350 

351 

352 

353 

354

Pounds of gas per pound of carbon.

Over 

fire.

10.22 

12.12 

7.77 

11.15 

10.54 

12.73

15.17

Combustion 

chamber.

18.38 

24.02 

23.76 

. 16. 85 

16.17 

19.93 

19.44 

20.38 

23.21 

17.96

21.70

19.40 

17.53 

14.76 

15. 78 

16.31 

22.91 

20.51 

22.15 

25.27

Front 

water 

leg.

19.20 

27.89 

25.31 

19.64 

17.88 

23.75 

22.40 

23.83 

25.50 

21.00 

23.38 

21.51 

18.62 

21.09

24.25 

26.87 

20.61 

27.83

Stack.

23.34 

32.42 

28.37 

23.20 

21.60 

26.51 

27.30 

31.45 

28.87 

24.42 

26.90 

25.09 

23.60 

' 24. 26 

27.85 

26.80 

24.52 

20.86

23.41 

30. 25 

27! 21 

25.57 

32.00

Per cent 

of leakage, combustion 

chain ber 

to stack.

27.0 

34.9 

21.5 

37.7 

33.6 

33.0 

40.4 

54.3 

24.3 

35.9

27.7 

38.1 

39.9 

41.3

43.5 

32.0 

32.6 

15.3 

26.6

Test 

No.

355 

356 

357 

359 

360 

361 

362 

363 

364 

365 

366 

367 

369

370 

371 

372 

375 

376 

377

378 

379 

380 

381

Pounds of gas per pound of carbon.

Over 

fire.

15.29 

18.22 

13.65

.,

13.27

12.45

11.77

Combustion 

chamber.

20.90 

19.84 

20.68 

21.88

20.50

19.04

22.48 

21.81

19.15 

21.10

22.29 

18.44 

21.89

22.22

30.90

19.14

20.02

22.48

26.26 

30.48

25.02 

25.80

28.21

Front 

water 

leg.

25.42 22.50' 

18.38

19.89

18.14

16.85

Stack.

26.78 

25.28 

29.12 

26.78 

25. 16 

25.49 

29.70 

27.17 

25.30 

29.18 

26.02 

26.40 

27. 73 

27.78 

37.05 

24.54 

26.48 

30.05 

34.48 

32.05 

27.72 

30.70 

32.20

Per cent 

of leakage, combustion 

chamber 

to stack.

28.0 

27.3 

40.8 

22.4 

22.7 

33.8 

32.2 

24.4 

32.1 

38.3 

16.8 

43.2 

26.7 

24.9 

19.9 

28.2 

32.1 

33.7 

31.3 

5.1 

10.8 

19.0 

14.2

Average per cent increase from surface of fire to combustion chamber, 52.33; from combustion chamber to front leg, 8.43; from front leg to stack, 21.25; from combustion chamber to stack, 28.48.

CLASSIFICATION OF COALS.

CARBON-HYDROGEN RATIO IN AIR-DRIED COAL.

In the belief that coals of approximately the -same proportions of 

constituents, as shown by chemical analysis, should behave more

nearly alike when subjected to similar treatment than coals in which 

the proportions of the constituents vary widely, the following attempts 

have been made to classify the coals burned by the boiler division, 

according to their performance under a boiler.

In accordance with the method proposed by Marius R. Campbell,a 

the ratios of carbon to hydrogen in the ultimate analyses of airdried car samples were computed. One hundred and seventy-four 

tests on about 75 different coals were employed for this purpose, 

washed, dried, and briquetted coals being rejected. It was not 

expected that this classification (fig. 37) would be of as much service 

as one based on the same ratio of either coal as received or dry coal, 

since the amount of drying to which a sample is subjected is dependent on the local conditions, which vary from day to day. The statement just made seems to be borne out by the fact that the average

a Prof. Paper U. S. Geol. Survey No. 48,1906, pp. 156-173.
CLASSIFICATION OF COALS.

'69

points from which the general efficiency curve (No. 1) is derived fall 

farther from such a curve than is the case with general curves derived 

from the ratio of carbon to hydrogen, based on either coal as received 

or dry coal.

The ratio of carbon to hydrogen should have been obtained from 

the ultimate analysis of the boiler-test sample after air drying, but 

these data were not available. The ratio used is calculated on the

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CARBON-HYDROQCN RATIO IN A R-DRIC.D COAL.

110 Jt.

FIG. 37. Coal classification based on carbon-hydrogen ratio from ultimate analysis of air-dried car 

samples as related to efficiency 72*, tests 120-401 (curve No. 1); per cent of rated capacity developed 

(curve No. 2); and efficiency 72*-at about rated capacity, tests 1-78 (curve No. 3). General curves, 

omitting tests of washed, dried, and briquetted coals.

air-dried coal of the car sample a fact which might account for some 

of the variations of some of the points from the curve.

The broken line, curve No. 2, is drawn through the average per cent 

ratings for all tests coming in each group. The per cent rating 

attained does not seem to influence the efficiency, as it does in other 

classifications which follow.
70 A. STUDY OF FOUR HUNDRED STEAMING TESTS.

Curve No. 3 shows the relations between carbon-hydrogen ratios on 

air-dried coal and efficiency from boiler tests conducted during 1904. 

The tests in which washed and briquetted coals were burned are 

omitted. It was decided to abandon this classification and to use the 

ratio of carbon to hydrogen of coal, as received, and of dry coal. The 

curves and conclusions on classifications based on carbon-hydrogen 

ratios of coal, as received, and of dry coal, were derived from approximately 250 boiler tests run in one series. The tests included raw, 

washed, briquetted, and a few mixed coals. The relative values of 

the classifications were based on the uniformity of the general efficiency curves, efficiency here meaning the efficiency of the boiler on 

the combustible basis (the combustible consumed, as shown by 

proximate analysis, less the combustible lost through the grate, 

as determined by an analysis of the refuse). The item used for the 

efficiency is 72* of the A. S. M. E. code.

CARBON-HYDROGEN RATIO IN COAL AS RECEIVED.

The carbon-hydrogen ratios of fig. 38 were computed from the ultimate analyses made by the chemical division on boiler-test samples. 

These ratios were divided into six groups, as follows: Group K, 

including all values up to 11.2; group L, from 11.2 to 12.5; group M, 

from 12.5 to 14.5; group N, from 14.5 to 15.5; group 0, from 15.5 to 

17.0, and group P, all values over 17.0. The several items in each 

group were then averaged and curves plotted on the basis of (1) efficiency 72*; (2) per cent of CO loss; (3) combustion-chamber temperature (by Wanner optical pyrometer); (4) per cent of rated capacity of 

boiler; (5) pounds of dry chimney gases per pound of "combustible' 7 

(coal free from ash and moisture), and (6) B. t. u. per pound of dry 

coal.

A comparison of the averages just mentioned shows that no one 

item was maintained, even approximately, constant, so that whatever conclusions may be drawn therefrom must necessarily be considered anything but absolute. Particular mention should be made 

of the per cent of rated capacity attained in the trials, which, if 

maintained constant, might have aided materially in defining more 

closely the relative causes and effects as indicated by the other items, 

although it is believed that these items are as much dependent on the 

kind of coal as on the per cent of rated capacity attained.

The averages of all of the like items of each group are graphically 

represented on the accompanying charts (figs. 39-45), on which the 

ratio of carbon to hydrogen appears as an abscissa.

The curves of efficiency 72* in figs. 38 and 39 do not agree; but it 

is hardly to be expected that items should vary alike when tests are 

classified on such an illogical basis as the carbon-hydrogen ratio in coal 

as fired, inasmuch as the hydrogen of the free moisture is also included.
CLASSIFICATION OF COALS. 71

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CARBON-HYDROGEN RATIO IN COAL AS RECEJVE.O

FIG. 38. Coal classification based on carbon-hydrogen ratio as related to theoretical relative elTiciency 

of boiler as a heat absorber at various temperatures (curve No. 1); per cent of CO loss (curve No. 2); 

efficiency 72* (curve No. 3); per cent of rated capacity developed (curve No. 4); combustion-chamber 

temperature (°F.) (curve No. 5); B. t. u. per pound of dry coal (curve No. C); and pounds of dry chimney gases per pound of "combustible" (curve No. 7). General curves, samples as received, tests 

120-380.

The following list gives the coals appearing in each group and their 

respective carbon-hydrogen ratios:

Average carbon-hydrogen ratios determined from analysis of boiler-test samples of coal as

fired, including moisture.

Group P (all values over 17.0):

Arkansas No. 8 .............. 20. 32

Maryland No. 1 ............. 19.13

Maryland No. 1 (washed) .... 18.28

Pennsylvania No. 8 ......... 18.02

West Virginia No. 19......... 17.16

Group 0 (from 15.5 to 17.0):

West Virginia No. 19......... 16. 93

Arkansas No. 7 A ............ 16. 79

West Virginia No. 17......... 16. 27

West Virginia No. 17 (washed) 16.15

Group 0 (from 15.5'to 37.0) Continued. 

Virginia No. 3 ............... 16.02

Pennsylvania No. 7 ......... 15. 65

West Virginia No. 18......... 15. 63

Group N (from 14.5 to ]5.5):

Virginia No. 3 ............... 15.46

West Virginia No. 14......... 15.45

Pennsylvania No. 4 ......... 15.27

Pennsylvania No. 7 (washed). 15.10 

Ohio No. 5 .................. 15.15

Pennsylvania No. 6 ......... 15.10
A STUDY OF FOUR HUNDRED STEAMING TESTS.

Group N (from 14.5 to 15.5) Continued.

West Virginia No. 13......... 15.04

West Virginia No. 20......... 14. 97

Virginia No. 4 ............... 14. 86

West Virginia No. 15......... 14. 84

Virginia No. 2 ............... 14. 83

Tennessee No. 6 ............. 14. 78

Kentucky No. 5 ............. 14. 77

Pennsylvania No. 10 ........ 14. 74

Pennsylvania No. 7 ......... 14. 72

West Virginia No. 20 (washed) 14. 72 

Tennessee No. 9 .............. 14. 70

Pennsylvania No.-5 (washed). 14. 66

West Virginia No. 21......... 14. 57

Group M (from 12.5 to 14.5):

West Virginia No. 21......... 14.43

Tennessee No. 9 ............. 14.40

West Virginia No. 21 (washed). 14. 36

Pennsylvania No. 5 ......... 14. 25

Kentucky No. 1 C ........... 14.17

Kentucky No. 6 ............. 14.16

Virginia No. 1 B............. 14.14

Ohio No. 9 A ............... 14.11

Ohio No. 9 B (washed and

dried) .................... 13.98

. Ohio No. 5 .................. 13. 89

Ohio No. 4 .................. 13. 89

Ohio No. 4 (washed)......... 13. 76

Tennessee No. 7 A-! ......... 13. 73

Ohio No. 6 (washed) ......... 13. 73

Tennessee No. 2 ............. 13.70

. Alabama No. 4 ..'............ 13. 63

Tennessee No. 1............. 13. 62

Ohio No. 6 ................... 13. 55

Washington No. 2 ........... 13.38

Tennessee No. 5 ............. 13.24

Tennessee No. 4 ............. 13.04

Tennessee No. 3 ............. 13.01

Illinois No. 11 A ............ 12. 92

Ohio No. 7 .................. 12.76

Illinois No. 16 .............. 12.73

Illinois No. 19 B ............ 12.73

Ohio No. 9 B (washed)...... 12. 52

Group L (from 11.2 to 12.5):

Kansas No. 6 ................ 12.41

Ohio No. 3 (washed)......... 12. 33

Ohio No. 9 B ............... 12. 31

Illinois No. 13' (washed). .... 12.27

Kentucky No. 7 ............. 12. 22

Illinois No. 13 .............. 12. 22

Illinois No. 19 A ............ 12.11

Indiana No. 11 .............. 12.00

Illinois No. 12 . . ............ 11. 95

Ohio No. 8 ................ A 11. 91

Group L (from -11.2 to 12.5) Continued.

Illinois No. 12 (washed)..... 11. 85

Ohio No. 2 (washed) . -. ...... 11. 77

Indiana No. 7 A ...... .'...... 11. 71

Ohio No. 2 .................. 11. 62

Kansas No. 6 (washed)....... 11. 61

Indiana No. 8 ............... 11. 49

Ohio No. 1.................. 11.47

Indiana No. 7 B ............. 11.43

Indiana No. 7 B (briquetted). 11. 38

Ohio No. 1 (washed) . ....... 11. 38

Illinois No. 22 A ............ 11. 35

Indiana No. 5 ............... 11. 32

Illinois No. 15 . . ............ 11. 25

Indiana No. 6 ............... 11. 21

Group K (all values .up to 11.2):

Indiana No. 6 (washed) ...... 11.18

Indiana No. 8 (washed) ...... 11.13

Indiana No. 5 ............... 11.12

Illinois No. 15 (washed)..... 11. 07

Illinois No. 22 A ............ 10. 98

Illinois No. 9 B ............. 10. 95

Illinois No. 24 B ............ 10. 92

Illinois No. 7 D . ............ 10. 91

Indiana No. 12 (washed) ..... 10. 87

Indiana No. 10 (washed) ..... 10. 86

Indiana No.. 9 A ............. 10. 84

Illinois No. 14.............. 10. 83

Indiana No. 9 B ............. 10. 80

' Indiana No. 10 ....... f...... 10. 79

Wyoming No. 2 B ............ 10. 79

Indiana No. 4 (washed) ...... 10. 75

Illinois No. 18 .............. 10. 70

Indiana No. 12 .............. 10. 68

Missouri No. 6.............. 10. 67

Illinois No. 22 A (washed).... 10.65

Indiana No. 4 ............... 10. 52

Illinois No. 25.............. 10.51

Missouri No. 5 . .°............ 10. 4.7

Illinois-No. 21. . .......'..... 10.46

Illinois No. 26 .............. 10.43

Indiana No. 3 ............... 10. 38

Illinois No. 20 . . ............ 10.15

Illinois No. 23 A (washed).... 10.10

Illinois No. 14 (washed)..... 10.09

Illinois No. 18 (washed)..... 10.03

Illinois No. 20 (washed)..... 9. 96

Mixed coal.................. 9.95

Illinois No. 23 A ............ 9. 90

Illinois No. 7 C (washed).... 9. 82

Illinois No. 27. ............. 9,71

Missouri No. 7 (washed)..... 9. 67

Washington No. 1 B ......... 9. 61

Wyoming No. 3 ............. 9. 44

Wyoming No. 3 (washed) .... 8. 94
CLASSIFICATION OF COALS. 73

The curve drawn along the average-efficiency points on the chart 

is so uniform that the conclusion might easily be reached that a classification such as the ratio of carbon to hydrogen is of great value. If 

an individual group is selected there is no such close agreement, as is 

shown by the range of efficiencies noted at each point of the generalefficiency curve. The curve shows a gradual increase of efficiency 

as the ratio of carbon to hydrogen increases, becoming horizontal for 

the high ratios.

A comparison of the highest efficiencies of the groups shows a 

marked uniformity. The range of efficiencies in each group (not 

shown on the chart) decreases as the ratio of carbon to hydrogen 

increases, seeming to indicate that efficient burning of coals of a lower 

carbon-hydrogen ratio is a matter of much greater uncertainty than 

when the ratio is high.

The curve of per cent of CO loss indicates maximum incomplete 

combustion in the low-ratio groups, decreasing to nearly zero in the 

high-ratio groups. This is in accord with the statement made regarding the uncertainty of burning coals of a low carbon-hydrogen ratio.

The B. t. u. curve, No. 6, rises as the carbon-hydrogen ratio 

increases.

A broken line connecting the averages of the per cent of rated 

capacity of each group is shown, curve No. 4. This line points out a 

wide variation in capacity attained. The figures given with each 

point on the general curve show a much wider range of the same item 

as between the different trials of each group than between groups. 

The variation of per cent of rating tended to remove the average efficiency from a uniform efficiency curve; the average efficiency 

increased, in general, as the average per cent of rating decreased.

From the points showing combustion-chamber temperature we 

obtain a broken line which is very nearly parallel to the line of per 

cent of rated capacity, as on many other charts. The highest temperatures were obtained in the middle groups, the lowest temperatures in the highest groups.

The line representing the number of pounds of dry chimney gases 

per pound of combustible (curve No. 7) Can best be studied on the 

charts of the separate groups; on the general chart it is difficult to 

arrive at conclusions so far as this one. item is concerned.

Curve No. 1 in the chart is merely tentative and is put on to show 

relatively the theoretical efficiency of the boiler as an absorber of heat 

generated, the calculation being based on the theory, developed on 

pages 107-108, that the heat absorption is a function varying slightly 

with combustion-chamber temperature; for this purpose the temperatures used are those on the line of combustion-chamber temperatures. 

It will be noticed that the line of theoretical boiler efficiencies varies 

less than 2 per cent; it may be too high or too low at every point by 2 

per cent, but it does show that in the lower groups the distance is
A STUDY OP FOUE HUNDBED STEAMING TESTS.

greater between this line and that of efficiency 72*. This fact 

seems to indicate that in the lower groups there was more incomplete 

combustion an indication which is verified by curve No. 2, giving 

per cent of CO loss. It is noteworthy that the best actual efficiencies 

72* in all groups were about the same (a fact which is not shown on 

the chart), indicating that when enough is known about combustion 

and when special grates, stokers, furnaces, etc., are applied, it will

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CARBOCW-IYDROSEN RATIO IN COM- A3 RKOVEO.

FIG. 39. Coal classification based on carbon-hydrogen ratio as related to per cent of CO loss (curve 

No. 1); efficiency 72* (curve No. 2); per cent of rated capacity developed (curve No. 3); combustionchamber temperature (°F) (curve No. 4); and pounds of dry chimney gases per pound of ' 'combustible "(curve No. 5). Group K, all values up to 11.2, samples as fired.

be possible to burn very poor coals with nearly the same efficiencies 

as good ones.

In order to discover the variations within the individual groups 

three charts have been plotted involving the same items as shown 

on the general chart.

Since the general curve shows a gradual increase in efficiency with 

an increase of the ratio of carbon to hydrogen, one would naturally
CLASSIFICATION OF COALS. 75

look for a similar increase in efficiency within' individual groups. 

This is not true, however, because of wide variations in the other 

items within each group.

 The efficiency line (fig. 39) in group K varies inversely with the per 

cent of rating and to a much more marked degree than in the general 

chart. Also the efficiency falls as the combustion-chamber temperature 

rises, and vice versa. The line for combustion-chamber .temperature 

is parallel to the line for per cent of rating, as in many other places.

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CARBON-HYDROGEN RATIO INCOMES RECEIVED 

FIG. 40. Coal classification based on carbon-hydrogen ratio as related to per cent of CO loss (curve 

No. 1); efficiency 72* (curve No. 2); per cent of rated capacity developed (curve No. 3); combustionchamber temperature (°F) (curve No. 4); and pounds of dry chimney gases per pound of " combustible" (curve No. 5). G roup M, values from 12.5 to 14.5, samples as fired.

The line for per cent of CO loss varies inversely with the line for pounds 

of dry chimney gases per pound of "combustible," as would be expected 

from the chemical law of mass action; and in turn the line denoting 

pounds of air per pound of " combustible " runs parallel in most places 

with the efficiency line.

Fig. 40 shows that for group M the lines representing the per cent 

of rating, combustion-chamber temperature, and per cent of CO loss
76 A STUDY O.F FOUR HUNDRED STEAMING TESTS.

run parallel to one another and vary inversely with the line giving 

pounds of dry chimney gases per pound of combustible and also in a 

general way, inversely with the efficiency line; all of which interrelations are much the same as in group K (fig. 39). Relations between 

variables are brought out very clearly in fig. 40. The general chart 

shows that group M was the one in which the highest combustionIts

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154 155 l%6 15.1 156 S3 IW» W IW I6J I6y»- IC£ It* 16.1 16.8 l& ITP 

CARBON-HYDROGEN RAT O IN COAL AS RECEIVED

FIG. 41. Coal classification based on carbon-hydrogen ratio as related to per cent of CO loss (curve 

No. 1); ratio of hydrogen to available hydrogen (curve No. 2); efficiency 72* (curve No. 3); per cent of 

rated capacity developed (curve No. 4); combustion-chamber temperature (°F) (curve No. 5); and 

pounds of dry chimney gases per pound of " combustible" (curve No. 6). Group 0, values from 15.5 

to 17.0, samples as fired.

chamber temperatures and the highest per cent of rating were 

obtained.

In group O (fig. 41) the lines of combustion-chamber temperature 

and per cent of rating are shown parallel with the efficiency line. 

The per cent of CO loss is small at all times in this group, so little 

effect could be expected from this cause. The additional curve 

showing the ratio of hydrogen to available hydrogen is parallel to
CLASSIFICATION OF COALS. 77

the efficiency line. The line for pounds of dry chimney gases, instead 

of being parallel with the efficiency line, as in other groups, varies 

inversely with that line, a variation that is concordant with the fact 

that the small CO loss indicates very little incomplete combustion.

CARBON-HYDKOGEN EATIO IN DKY COAL.

Another classification has been made (fig. 25, p. 37) by using the 

ratio of carbon to total hydrogen, as determined by the ultimate analysis of dry coal. By this method that portion of the hydrogen which 

appears in the moisture determined by the proximate analyses is 

eliminated, and consequently there should result a more nearly constant carbon-hydrogen ratio for any given coal. The ratios were 

divided into seven groups, as follows: Group A, including all values 

up to 14.5; group B, from 14.5 to 15.0; group C, from 15.0 to 15.5; 

group D, from 15.5 to 16.0; group E, from 16.0 to 16.5; group X, 

from 16.5 to 17.5; group Y, all values of 17.5 and over.

As in the previous classification (p. 70) all the values in each group 

were averaged and each average was plotted with its corresponding 

average of carbon-hydrogen ratio. The following list shows the 

coals in each group and their corresponding carbon-hydrogen ratios:

Average carbons-hydrogen ratios determined from ultimate analysis of dry coal.

Group Y (all values of 17.5 and over): 

Arkansas No. 8 .............. 22. 60.

Maryland No. 1............... 20.16

Maryland No. 1 (washed)..... 20.14

Arkansas No. 7 A ............ 19. 50

Pennsylvania No. 8........... 19.37

West Virginia No. 19......... 18. 23

West Virginia No. 17......... 17. 92

West Virginia No. 17 (washed)! 17.91

Group X (from 16.5 to 17.5):

Pennsylvania No. 7........... 17.04

Pennsylvania No. 7 (washed). 17.03 

West Virginia No. 18......... 16. 71

Illinois No. 19 A.............. 16. 67

Virginia No. 3 ............... 16. 64

Kentucky No. 5.............. 16. 56

Group E (from 16 to 16.5):

West Virginia No. 14......... 16.45

West Virginia No. 13......... 16.44

Ohio No. 9 A.................. 16.38

Illinois No. 19 B.............. 16.21

Virginia No. 4....:.........! 16.13

Pennsylvania No. 4........... 16.11

Pennsylvania No. 6........... 16.07

Tennessee No. 9.............. 16.01

Group D (from 15.5 to 16.0):

Virginia No. 2 ............... 15.96

Tennessee No. 6.............. 15. 90

Group D (from 15.5 to 16.0) Continued. 

Illinois No. 16................ 15.85

West Virginia No. 20......... 15. 85

West Virginia No. 20 (washed). 15.81 

Indiana No. 11..:........... 15. 78

Virginia No. 1 B............. 15. 73

Kentucky No. 6.............. 15. 72

West Virginia No. 21......... 15. 71

West Virginia No. 21 (washed). 15. 71 

Pennsylvania No. 10.......... 15. 65

Pennsylvania No. 5........... 15. 64

Pennsylvania No. 5 (washed). 15. 63 

West Virginia No. 15......... 15. 58

Illinois No. 11 A.............. 15.57

Kentucky No. 1 C............. 15. 54

Group C (from 15 to 15.5):

Illinois No: 13................ 15.46

Illinois No. 13 (washed)...... 15.43

Ohio No. 5................... 15.37

Alabama No. 4................ 15. 29

Kentucky No. 7.............. 15.29

Tennessee No. 2.............. 15.26

Kansas No. 6................ 15. 21

Kansas No. 6 (washed)....... 15. 20

Tennessee No. 5......'........ 15.17

Ohio No. 3 (washed).....:.... 15.09

- Ohio No. 4................... 15.08

Ohio No. 4 (washed).......... 15.07
78 A STUDY OF FOUR HUNDRED STEAMING TESTS.

Group C (from 15 to 15.5) Continued. 

Tennessee No. 1.............. 15.04

Illinois No. 21................ 15.03

Indiana No. 4 ............... 15.01

Indiana No. 4 (washed)...... 15.01

Illinois No. 12................ 15.00

Group B (from 14.5 to 15.0):

Indiana No. 4 ............... 14. 99

Illinois No. 12................ 14.97

Illinois No. 12 (washed)....... 14. 94

Tennessee No. 4.............. 14. 94

Ohio No. 9 B (washed)........ 14. 94

Ohio No. 9B...............:. 14.93

Mixed coal.................. 14. 92

Illinois No. 26................ 14.86

Illinois No. 22 A.............. 14. 77

Tennessee No. 3.............. 14.77

Tennessee No. 7 A............ 14. 77

Illinois No. 22 A (washed).... 14. 76

Ohio No. 7.................... 14.76

Ohio No. 6................... 14.74

Ohio No. 6 (washed).......... 14. 71

Missouri No. 6.................. 14. 70

Illinois No. 20................ 14. 63

Illinois No. 20 (washed)....... 14.61

Indiana No. 5 ............... 14.59

Illinois No. 24 B.............. 14. 56

Missouri No. 7 (washed)....... 14.51

Group A (all values up to 14.5): 

Ohio No. 9 B (washed and

dried).-................... 14.48

Indiana No. 8 (washed)...... 14.48

Indiana No. 8............... 14.46

Indiana No. 12.............. 14.46

Indiana No. 12 (washed)..... 14.45

Group A (all values up to 14.5) Cont'd. 

Illinois No. 14................ 14.45

Washington No. 2............. 14.45

Mixed coal.................. 14.43

Indiana No. 9 A ............. 14.42

Ohio No. 8.............'...... 14.42

Illinois No. 14 (washed)....... 14.42

Illinois No. 15 (washed)....... 14.40

Indiana No. 7 B (briq.)...... 14.40

Illinois No. 15................ 14. 39

Indiana No. 7 B ............. 14.36

Missouri No. 5................ 14.34

Ohio No. 2................... 14.32

Ohio No. 2 (washed).......... 14. 30

Illinois No. 27................ 14.30

Indiana No. 6............... 14.30

Indiana No. 6 (washed)...... 14. 29

Indiana No. 7 A ............. 14.18

Illinois No. 7 C (washed)...... 14.14

Illinois No. 7 D.............. 14.11

Indiana No. 3 ............... 14.01

Illinois No. 9 B............... 13.96

Indiana No. 9 B ............. 13. 95

Illinois No. 23 A (washed).... 13. 93

Illinois No. 23 A.............. 13.92

Washington No. 1 B........... 13. 85

Illinois No. 25................ 13. 81

Ohio No. 1 (washed).......... 13. 75

Ohio No. 1................... 13.73

Illinois No. 18 (washed)....... 13. 71

Wyoming No. 2 B............. 13.71

Wyoming No. 3............... 13. 69

Wyoming No. 3 (washed)..... 13. 68

. Illinois No. 18................ 13.67

Indiana No. 10 (washed)..... 13. 61

Indiana No. 10.............. 13.58

There is no particular difference in the general curves as derived 

from the two classifications based on dry coal and coal as received. 

To the general chart (p. 37) two more curves have been added one 

for average diameter of coal (No. 7), and one for per cent of clinker 

in refuse (No. 8). The curve of average diameter of coal as fired 

shows that as the ratios of carbon to hydrogen increase there is a 

gradual reduction in average diameter. Nearly all the coals used 

in the tests passed through the same crusher. It is not to be assumed 

that the ratio of carbon to hydrogen influences the ease with which 

the coal breaks, for this can be accounted for in other ways. The 

coals of low carbon-hydrogen ratio give the highest per cent of 

clinker in refuse.

Curve No. 1, theoretical efficiency of boiler as a heat absorber at 

temperature below, is relative only; it is probably as a whole either 

too high or too low, and the various points of it may be high or low
CLASSIFICATION OF COALS. 79

relative to one another, but it serves its general purpose to show 

less complete combustion of -the coals low in carbon-hydrogen ratio. 

The distance between this curve and the efficiency 72* curve is 

greater the lower the carbon-hydrogen ratio.

Four charts were made detailing groups A, B, D, and Y.

In group A the lines (fig. 42) representing per cent of rating, per 

cent of CO loss, and combustion-chamber temperature are parallel

MO

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CARBOKl-HYDROCCN RATIO IN ORY COAL

I'lG. 42. Coal classification based on carbon-hydrogen ratio as related to per cent of CO loss (curve No. 

1); ratio of hydrogen to available hydrogen (curve No. 2); efficiency 72* (curve No. 3); per cent of 

rated capacity developed (curve No. 4); combustion-chamber temperature (° F.) (curve No. 5); and 

pounds of dry chimney gases per pound of "combustible" (curve No. 6). Group A, all values up to 

14.5, dry coal.

to one another, and their slope is inverse, in a general way, to that 

of the lines representing hydrogen over available hydrogen and 

pounds of dry chimney gases per pound of " combustible." This group 

contains tests varying 13 per cent in efficiency, indicating the 

uncertainty of attaining the higher efficiency with coals of low 

carbon-hydrogen ratio. No other relations occur in this group such 

as occur in the higher groups.
80 A STUDY OF FOUR HUNDRED STEAMING TESTS.

Group B gives very marked relations. The lines (fig. 43) representing the per cent of rating, combustion-chamber temperature, 

per cent of CO loss, efficiency 72*, and per cent of clinker in refuse 

run in the same general direction and the values vary inversely with 

the pounds of dry chimney gases per pound of "combustible" and 

hydrogen over available hydrogen. Why the line for efficiency 7.2* 

should parallel the line of CO loss is not clear, especially as the latter

1.2.0 

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FfOGCN RATIO IN CflY COAL

FIG. 43. Coal classification based on carbon-hydrogen ratio as related to percent of CO loss (curve No. 

1); ratio of hydrogen to available hydrogen (curve No. 2); efficiency 72* (curve No. 3); per cent of 

rated capacity developed (curve No. 4); combustion-chamber temperature (° F.) (curve No. 5); 

pounds of dry chimney gases per pound of "combustible" (curve No. 6); and per cent of clinker in 

refuse (curve No. 7). Group B, values from 14.5 to 15.0, dry coal.

is high and the combustion-chamber temperature varies but little; 

however, not many .tests are considered.

In group D (fig. 44) the lines representing the per cent of rating, 

combustion-chamber temperature, per cent of CO loss, and per cent 

of clinker in refuse are parallel to one another, and for the most part
CLASSIFICATION OF COALS. 81

that of hydrogen over available hydrogen follows the three in 

direction. The curves for efficiency and pounds of dry chimney gases 

per pound of " combustible " are parallel to each other and run inversely 

with all the rest.

The same characteristics appear in group Y (fig. 45) as in group D 

(fig. 44).

FIG. 44. Coal classification based on carbon-hydrogen ratio as related to per cent of CO loss (curve 

No. 1); ratio of hydrogen to available hydrogen (curve No. 2); efficiency 72* (curve No. 3); per cent 

of rated capacity developed (curve No. 4); combustion-chamber temperature (° F.) (curve No. 5); 

pounds of dry chimney gases per pound of" combustible" (curve No. 6); per cent of clinker in refuse 

(curve No. 7); and average diameter of coal (curve No. 8). Group D, values from 15.5 to 16.0, dry 

coal.

Attempts were also made to classify coals according to the available hydrogen figured froni the "combustible" in the coal; according to the ratio of carbon to available hydrogen, and according 

to the moisture over the per cent of air-drying loss. None of these 

were of much value.

3400 Bull. 325 07 6
82 A STUDY OF FOUR HUNDRED STEAMING TESTS. 

CARBON-HYDROGEN RATIO IN COAL AS FIRED AS AFFECTING EFFICIENCY 72*.

Fig. 46 shows the effect of the carbon-hydrogen ratio of coal as 

received (fired) on efficiency 72* for each of three capacity groups. 

The curves determined by plotting efficiency 72* with carbon-hydrogen ratio for a nearly constant per cent of rating are very uniform.

CARBON-HYDROGEN RATIO IN DRY COAL

FIG. 45. Coal classification based on carbon-hydrogen ratio as related to per cent of CO loss (curve 

No. 1); ratio of hydrogen to available hydrogen (curve No. 2); efficiency 72* (curve No. 3); per cent 

of rated capacity developed (curve No. 4); combustion-chamber temperature (° F.) (curve No. 5); 

and pounds of dry chimney gases per pound of "combustible" (curve No. 6). Group Y, values of 

17.5 and over, dry coal.

Three curves were plotted, Nos. 1, 2, and 3, at capacities of 95 to 

105, 85 to 95, and 75 to 85, respectively. The efficiency 72* range 

on any one curve decreases as the per cent of rated capacity decreases. 

A probable explanation of this chart is that, with the low carbonhydrogen ratios, the efficient burning of coal is rather uncertain. 

As the capacity is increased the combustion-chamber temperature 

is raised; therefore the high-rating curves are the high-temperature 

curves. This relation probably has considerable to do with the
CLASSIFICATION OF COALS. 83

efficiency ranges, on the three curves. It is also evident from this 

chart that the high capacities were obtained with the coals of low 

and medium carbon-hydrogen ratios.

£^ ^

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CARBON-HYDROGEN RATIO IN CC*L A3 RC.CCIVCO.

FIG. 46. Coal classification based on per cent of rating. Efficiency curves: No. 1, from 95 to 105 per 

cent; No. 2, from 85 to 95 per cent; No. 3, from 75 to 85 percent.

RELATION OF RATIO OF CARBON TO AVAILABLE HYDROGEN AND OF PER CENT 

OF AVAILABLE HYDROGEN TO EFFICIENCY 72*.

Fig. 47 is a graphic representation of efficiency 72* on the basis of 

ratio of carbon to available hydrogen. As this ratio increases there 

is a considerable increase in efficiency 72*; but the curve is very 

irregular. Curves Nos. 1 and 2 are similar, but are from two different series of tests. Curve No. 3 is a representation of efficiency 72* 

on an available hydrogen basis. The efficiency varies but little over 

the entire range of available hydrogen ratio.

The subjoined table shows two classifications based on the ratio of 

per cent of "volatile carbon"" to per cent of total carbon. The

oFor definition of "volatile carbon" see glossary (p. 183). For information on the " volatile carbon" of coals see Parr, S. W., Bull. Illinois Geol. Survey No. 3, Urbana, 111.
84 A STUDY OP FOUR HUNDRED STEAMING TESTS.

first (column 1) gives average efficiency 72* for .average ratio of 

volatile carbon to total carbon values, showing that for the low ratio 

values we have the high efficiency 72* values and vice versa. There 

is, however, as the chart (fig. 48) shows, no uniformity of drop in 

efficiency as the value of the ratio increases. The second classification (columns 2-7) gives the values of average efficiency 72*

fix

bhC 

6*6 

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6*5 

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m

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FIG. 47. General curves showing classification of tests: No. 1 (tests 120-380) and No. 2 (tests 1-78), 

based on ratio of carbon to available hydrogen; No. 3 (tests 120-380), based on available hydrogen.

for the average values of the volatile carbon to total carbon, grouping them according to the number of B. t. u. supposedly evolved 

per square foot of grate surface per hour, and shows the same general relations as the preceding classification. The explanation may 

be that coals high in the ratio of volatile carbon to total carbon are 

harder to burn than those in which that ratio is low.
CLASSIFICATION OF COALS- 85 

Classifications of efficiency 72* on basis of average ratio of volatile carbon to total carbon.

Range of average ratio. '

Under 15:

From 15 to 17:

Averase efficiency 72*

From 17 to 19:

From 19 to 21: 

Number of tests. ......................

From 21 to 23:

From 23 to 25:

From 25 to 27: 

Number of tests........ ......... .

Average ratio X 100 ...................

From 27 to 29:

Average ratio X 100 ............... . .

Average efficiency 72*. ............... .

From 29 to 31: 

Number of tests ............. .

From 31 to 33: 

Number of tests ................. .

Average ratio X 100 ........... .

Average efficiency 72*.............. . .

From 33 to 35: 

Number of tests. .............. .

Average ratio X 100 ............... : ...

Average efficiency 72*. ......... .

Over 35:

Average ratio X 100 ................... 

Average efficiency 72*. .................

First 

classifi- cation 

not 

grouped.

1.

10 

7.25 

C7. 35

3 

15.94 

05. G3

1 

18.75 

03. C3

5

20.10 

05. 59

18 

22.18 

04.97

28 

24.08

07.22

52 

 20. 10 

00.42

03 

27.91 

05.04

33 

29.94 

03. 87 '

37 

31.86 

04.70

10 

33.82 

02.90

9 

30.81 

58.14

Second classification grouped according to 

10,000's of B. t. u. supposedly evolved per 

square foot of grate surface per hour.

Under

22.

2.

6 

8.00 

08.20

1 

10.14 

08.51

1 

20.09 

08.21

1 

21.97 

07.08

6 

20.27 

07.58

7 

28.05 

60.98

4 

29.54 

00.48

6 

31.09 

00. 05

1 

34.32

02.18

22 to 24.

3.

0 

8.87 

67.34

1 

10.65 

67.24

1 

20.52 

03.40

5

22.24 

07.27

5 

23.05 

08.83

 10 

20.28 

07.09

5 

27.70 

60. 33

4 

30.25 

06.55

11 

31.94 

04.07

2 

33.89 

59.55

1 

35.15 

00.25

24 to 26.

4.

1

8.97 

05.18

2 

19.95 

05.27

5 

21.85 

08.00

9 

24.50 

07.19

10 

20.16 

68.96

14 

27.84 

00.08

3

29.86 

63.86

13 

31.86 

04.64

4 

33.89 

64.71

1 

38.38 

61.37

26 to 28.

5.

2 

6. 41 

68. 1.0

1 

20.30 

65. 78

1 

22.10 

05. 00

4 

24.15 

09.32

4 

20. 05 

05.84

7 

27.91 

65.49

8 

29.82 

04.12

2 

31.40 

61.71

2 

35.17 

61.70

28 to 30.

0.

1 

2.50 

62.92

1

18. 75

63. 03

11 

26.01 

64.70

7 

27.47 

65.43

1 

30. 03 

01.70

4 

31.81 

65.10

2 

33.78 

63.83

30 and 

over.

7.

1. 

15.04 

61. 13

3

20. 50 

00, 51

0 

27.90 

03. 76

4 

30. 28 

01. 17

1

33.03 

01.88

5 

37.23 

55.95

RATIO OF HYDROGEN TO AVAILABLE HYDROGEN.

The ratio of hydrogen to available hydrogen was computed on about 

200 ultimate analyses of dry coals using boiler-test samples (see fig. 

49). This ratio and also the ratio of carbon to available hydrogen 

were suggested by Fred M. Stanton, of the chemical laboratory of this 

plant. These ratios were grouped according to values, as follows: 

Group R, all values up to 11.0; .group S, from 11.0 to 12.0; group T, 

from 12.0 to 13.0; group U, from 13.0 to 14.0; and group V, 14.0 and 

over.

Curves showing the relations between the ratio of hydrogen to available hydrogen and efficiency 72*, per cent of rated capacity, per cent 

of CO loss, and combustion-chamber temperature were obtained by
86 A STUDY OF FOUR HUNDRED STEAMING TESTS.

averaging the total number of values for each of these ratio groups 

and plotting this average against the average of the ratios for the corresponding groups. The resulting efficiency line shows a gradual fall 

with an increase of the ratio of hydrogen to available hydrogen. The 

per cent of CO loss shows a gradual increase in value. The lines for 

per cent of rated capacity and combustion-chamber temperature are 

parallel and have maximum points where the ratio of hydrogen to 

available hydrogen has a value of about 1.25, this being the middle of 

the values for ratio of hydrogen to available hydrogen. The efficiency 

seems to be independent of both per cent of rating attained arid combustion-chamber temperature. The range of efficiency for each group 

is shown by the figures near each point of the efficiency line. The 

range decreases, as in the other classifications, as the region of better 

coals is approached; likewise the best tests of all groups are about 

equally good.

RATIO OF VOLATILE CARBON IN COMBUSTIBLE TO TOTAL CARBON IN COMBUSTIBLE

FIG. 48. Eelation between the ratio of volatile carbon to total carbon and efficiency 72*; tests 120-400.

Classifications have also been made on the following bases:

Per cent of sulphur from ultimate analysis of dry coal. (See fig. 28, p. 43.) 

Per cent of ash in coal as fired. (See fig. 27, p. 41.) 

Per cent of volatile matter in the "combustible." (See fig. 50, p. 89.) 

Per cent of "fixed carbon," proximate analysis of coal as fired. (See fig. 51, p. 91.) 

Per cent of free moisture, proximate analysis of coal as fired. (See fig. 22, p. 33.) 

. Per cent of ash, ultimate analysis of dry coal. (See fig. 26, p. 40.) 

Per cent of oxygen in "combustible." (See"fig. 52, p. 92.) 

B. t. u. per pound of dry coal. (See fig. 53, p. 93.)

A study of the classifications of the ratios of carbon to hydrogen 

and hydrogen to available hydrogen and of single items from the 

proximate analysis of coal as fired and also the ultimate analysis of 

dry coal reveals the fact that while the points determining the curves
CLASSIFICATION OF COALS. 87

of efficiency 72* on the ratio bases fall rather uniformly on the 

curves, certain peculiarities are averaged out, as shown by the small 

variation of efficiency values over the entire range of the ratio. The 

classifications based on separate items from the chemical analysis of 

the coal give a much wider range of efficiency 72*.

The most valuable classification seems to be the one based on per 

cent of "fixed carbon" from the proximate analysis of the coal as fired.

( yna. z

63

92-5 

9OO 

BV

850 

WOO

Z300 

ItOO 

EIOO

RATIO OF HYOROGCN TO W/MLABLE HYDBOGtN

FIG. 49. Coal classification based on ratio of hydrogen to available hydrogen as related to per cent of 

CO loss (curve No. 1); efficiency 72*, tests 124-380 (curve No. 2); per cent of rated capacity developed 

(curve No. 3); combustion-chamber temperature (°F.) (curve No. 4); and efficiency 72-1= (tests 1-78, 

excluding tests on washed and briquetted coals) (curve No. 5).

(See fig. 51.) A classification nearly as good, and giving a little 

larger range of efficiency is that based 011 per cent of " volatile matter " 

in the " combustible." (See fig. 50.) The practical value of a classification for estimating the efficiency 72* at which a coal can be 

burned depends largely on the ease with which the item on which 

the classification is based can be determined. Both per cent of 

"fixed carbon" and per cent of "volatile matter" are obtained from
A STUDY OF FOUR HUNDRED STEAMING TESTS.

a proximate analysis of coal, which can be made with very little 

difficulty.

The reason for deciding on fixed carbon in coal as fired in preference to volatile matter in " combustible " was based on a comparison 

of the curves for combustion-chamber temperature on figs. 50 and 51. 

With the exception of the two end points, all the curves of fig. 51 

are fairly regular.

The subjoined classification of efficiency 72* on a basis of carbonhydrogen ratio in dry coal for varying ranges of combustion-chamber 

temperature is but a subdivision of the carbon-hydrogen averages 

shown on fig. 25 (p. 37). It was thought that for any single carbonhydrogen ratio group the efficiency 72* might increase or decrease 

with an increase of combustion-chamber temperature. However, 

after the tests have been separated according to combustion-chamber 

temperatures there are so few points in each grouping that any conclusion would be unreliable.

The tabulation shows the familiar general relation of increase of 

efficiency 72* as the carbon-hydrogen ratio increases. Nothing else 

is shown.

Classification of efficiency 72* on basis of carbon-hydrogen ratio in dry coal.

Temperature range 1,900° to 

2,200° F.:

Average carbon-hydrogen ratio in dry coal . 

Average efficiency 72*. . . . 

Temperature range 2,200° to 

2,300° F.:

Average carbon-hydrogen ratio in dry coal . . . 

Average efficiency 72*. . . . 

Temperature range 2,300° to 

2,400° F.:

Average carbon-hydrogen ratio in dry coal . . . 

Average efficiency 72*. ... 

Temperature range 2,400° to 

2,500° F.:

Average carbon-hydrogen ratio in dry coal . . . 

Average efficiency 72*. . . . 

Temperature range 2,500° to 

2,600° F.:

Average carbon-hyd roTemperature range 2,600° to 

2,900° F.:

Average carbon-hyd roCarbon-hydrogen ratio in dry coal.

13.5 to 

14.

8

13.75 

63.85

2

13. 60 

61.79

2

13.84 

63.00

3

13.78 

61.62

14 to 

14.5.

3

14.33 

63. Cl

5

14.40 

65.03

12

14. 39 

65.63

6

14.42 

63.83

4

14.33 

64.54

2

14.31 

62.35

14.5 to 

15.

4

14.83 

66.16

7

14.80 

61.71

6

14. 68 

65.88

5

14.81 

66.61

4

14.73 

65.44

9

14.75 

64.96

15 to 

15.5.

6

15.17 

64.36

3

15.12 

66.26

7

15.15 

64. 60

11

15.16 

66.00

5

15.22 

65.88

4

15.24 

63.33

15-5 to 

16.

1

15.55 

65.95

5

15.71 

66.25

5

15.72 

64. 12

6

15.70 

66.13

8

15.81 

67.45

7

15.68 

68. 64

16 to 

16.5.

4

16.31 

64.18

8

16.06 

66. 74

4

16.35 

68.61

10

16.29 

67.61

1

16.14

65.77

16.5 to 

17.

2

16.67 

67. 18

2

16.71 

66.32

1

17.93 

67.94

2

16.67 

64.59

2

16.69 

.69.06

2 

16.64

68. 77

17 to 

18.

2

17.48 

OS. 18

2

17. 04

67.88

18 up.

7

20.39 

07.56

2

19.35

67.76

4

19.47 

66.48

2

20.42 

66.84
CLASSIFICATION OF COALS. 89 

PER CENT OF "VOLATILE MATTER" IN THE "COMBUSTIBLE."

The curves of fig. 50 are based on about 300 tests made on coals 

from all parts of the United States, classified according to the percentage of "volatile matter" in the " combustible," considering as 

" combustible " that portion of the coal which remains after taking out 

the moisture and ash as determined by the proximate analysis. As 

stated elsewhere the word "combustible" is.really a misnomer.

FIG. 50. Relations of percent of "volatile matter" in the "combustible" to efficiency 72* (curve No. 1) 

and combustion-chamber temperature (°F.-) (curve No. 2). Tests 101-400.

The proximate analysis is also capable of considerable variation, 

but nevertheless it gives a clew.

Curve No. 1 is similar to many obtained by other investigators. 

It means that one should beware of a high percentage of " volatile 

matter," but not necessarily that a coal of high volatile matter is 

poor, for a great deal depends on the composition of the coal, inasmuch as coals break down very differently on heating. It has been
90 A STUDY OP FOUR HUNDRED STEAMING TESTS.

noted that, in general, the coals of high volatile matter have some 

other undesirable features, such as high ash content. The most 

important thing to emphasize is that even with a good furnace the 

coals high in volatile matter are at a slight disadvantage.

Curve No. 2 shows that the combustion-chamber temperature rises 

with the volatile matter of coal up to about 38 per cent and then 

drops. The rise of the temperature is due to the fact that the volatile 

matter of the coal is driven off the fuel bed and burns in the combustion chamber, so that the temperature of the gases of combustion is 

measured before the heat is dissipated from them. The rise is also 

due to the increased rate of combustion. As the volatile matter 

increases the coal burns more rapidly and less air is used to burn 1 

-pound of combustible. Beyond 38 per cent of volatile matter the 

coals become high in ash and moisture; in fact all the lignites are 

classed among the coals at the right-hand end. Both the ash and 

moisture reduce the combustion-chamber temperature. The high 

ash causes a slower rate of combustion and consequently more air is 

used per pound of combustible. The moisture lowers the temperature directly by its high specific heat. Work on the constitution of 

the cellulose derivatives of coals, now being prosecuted at this plant 

and at several other places, should give some valuable information 

on such practical questions as these. The customary "proximate 

analysis" is only an empirical method and can be expected to give 

nothing more than clews; much more is to be expected from ultimate 

analyses.

As in all other curves of this bulletin the small numbers, by the 

points, indicate the number of tests and the four-place numbers indicate the highest and lowest efficiencies of each group.

FIXED CARBON (PROXIMATE ANALYSIS).

The chart shown in fig. 51 (p. 91) is one of a series based on the 

"proximate analysis" of "coal as fired." It is realized that such an 

analysis is purely empirical and capable of giving results varying 

considerably; nevertheless it is of some value.

Curve No. 1 shows a general rise of efficiency up.to a "fixed carbon" content of 60 per cent and perhaps an inclination to fall off 

past that point. This 60 per cent point is roughly the place of 

maximum B. t. u. value per pound of moist coal. The numbers 

inclosed in circles show the number of tests falling in each group.

Curve No. 2, per cent of rated capacity developed, is practically 

uninfluenced.

Curve No. 3, combustion-chamber temperature, shows a general 

tendency to rise and has a hump in the middle. This is perhaps 

explained by the fact that the coals low in fixed carbon are of poor 

grade high in ash and moisture and for that reason it is difficult
CLASSIFICATION OF COALS. 91

to get a hot fire with these coals. With coals high in fixed carbon 

nearly all of the combustion takes place in the fuel bed, so that the 

gases have cooled considerably by the time they reach the rear of 

the furnace. These coals also burn slowly and therefore require 

more air for combustion. The coals of moderate fixed carbon give 

a long, hot, luminous flame.

It is stated elsewhere in this bulletin that the capacity is a function

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'FIXED CARBON", PROXIMATE ANALYSIS

FIG. 51. Relations of "fixed carbon" to efficiency 72* (curve No. 1); percent of rated capacity developed (curve No. 2); combustion-chamber temperature (°F.) (curve No. 3); Uue-gas temperature (°F.) 

(curve No. 4); pounds of dry chimney gases per pound of "combustible" (curve No. 5); and per cent 

completeness of combustion (Es) (curve No. 6). Tests 89-401.

of initial temperature of the furnace gases. This is plainly shown by 

curves Nos. 2 and 3, which are parallel.

Curve No. 4, flue-gas temperature, is closely parallel to No. 3. This 

is only another illustration of the fact that with the boilers of this 

plant flue temperatures increase with furnace temperatures, and, so 

far as the authors can see, it must be so with all boilers, even when 

liberating the same quantity of heat in the furnace per second with 

various percentages of air excess. (See p. 24.)
92 A STUDY OF FOtiR HUNDRED STEAMING TESTS.

Curve No. 5 shows the pounds of dry chimney gases per pound 

of ''combustible." It is very little affected, tending to rise with 

the "fixed carbon." It varies -inversely with furnace and flue 

temperatures.

Curve No. 6 shows the per cent of completeness of combustion, 

being the percentage of the heat of the combustible which was actually 

generated. It rises with increase of "fixed carbon" and its value of 

about 90 per cent indicates a wide margin for improvement.

BELATION OF EFFICIENCY 72* TO PEE CENT OF OXYGEN IN "COMBUSTIBLE."

The chart shown in fig. 52 contains two curves plotted on the 

same data. The upper one was obtained by classifying the tests 

according.to code "boiler efficiency" (72*) and the lower by classify-

"COMBUSTIBLE". OXY&EN INPER CEtsfT

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.PERCENT OXYGEN IN 'COMBUSTIBLE.'

FIG. 52. Relation of efficiency 72* to per cent of oxygen in' 'combustible," classified on each as a basis.

Tests 101-400.

ing them according to the per cent of oxygen in the " combustible." 

By the ' ' combustible" is meant what is left of the coal after taking 

out the moisture, sulphur, and ash. This remnant has been designated as "pure coal/' which is preferable to calling it "combustible."
CLASSIFICATION- OF COALS. 93

Both curves show unmistakably that somehow the oxygen of the 

coal, which is chemically combined, exerts a harmful influence. It 

seems plausible that there is nothing inherent in the presence of oxygen in a coal molecule which makes it impossible to break it down 

and burn it as well as any molecule lacking oxygen. This assumption puts the blame on our furnaces.

This chart is in agreement with that of fig. 33 (p. 56), which presents a classification of several items on a smoke basis. The "unaccounted-for" loss, CO loss, and per cent of oxygen all rise with the 

increase of smoke and the efficiency falls very slightly.

BRITISH THERMAL UNITS PER POUND OF DRY COAL.

The curves of fig. 53 are based on 296 tests made on coals from 

all parts of the country. In general, the eastern coals fall on the

11000 12000

B. T. U. PER POUND OF DRY COAL.

VIG. 53. Relations of B. t. u. value of dry coal to boiler efficiency 72* (curve No. 1); per cent rated 

capacity developed (curve No. 2); combustion-chamber temperature (°F.) (curve No. 3); pounds of 

dry chimney gases per pound of "combustible" (curve No. 4); per cent completeness of combustion 

(E3 ) (curve No. 5). Tests 89-400.

right and the lignites on the left part of the curve. On curve 

No. 1 the small number near each point gives the number of- tests
94 A STUDY OF FOUR HUNDRED. STEAMING TESTS.

falling in that B. t. u. group. Each of the o^her four curves below 

is based on the same number of tests in the various groups. The 

four-place numbers in pairs on curve No. 1 indicate the highest and 

lowest efficiencies 72 * falling in each group. It will be noted that 

the highest efficiencies are nearly as good in the left groups as in 

the right, indicating that it is possible to burn coals of low heating 

value as efficiently as high-grade coals. The increase of average 

efficiencies is only about 7 per cent for the range of 5,000 B. t. u.

The average capacity, as shown by curve No. 2, rises considerably 

as the coal improves in heating value. Perhaps most of the low 

B. t. u. coals could be made to furnish as much steam if burned on 

a larger grate. If the coal did not clinker seriously, the use of a 

rocking grate would increase the- capacity. On some coals the use 

of the automatic stoker might give better results.

Curve No. 4, pounds of dry chimney gases per pound of "combustible," descends with the better coals', partly because they are usually 

more manageable on the fuel bed and because they seem to break 

down on heating with evolution of gaseous compounds easier to 

burn, on which account the air supply can be reduced with safety.

Curve No. 5 gives the average "furnace efficiency," or, better, the 

per cent of completeness of combustion. These calculated efficiencies 

are only approximate.

RATIO OF ASH TO SULPHUR IN DRY COAL.

It is sometimes said that although sulphur in coal does not of 

itself materially reduce the value of the coal for steam making, a 

low percentage of ash with a high percentage of sulphur is apt to 

make trouble. To test this possibility a classification was made of 

many tests on many coals, the tests being grouped according to .the 

ratio of total ash to sulphur. The corresponding values of the averages of efficiencies 72* are practically constant.

As a check on this work a classification was also made of the ratio 

of ash to sulphur in dry coal on an efficiency 72* basis. As the 

efficiency 72* increases there is practically no change in the value of 

the ash to sulphur ratio. (See figs. 21, p. 30, and 28, p. 43.)

A table of efficiencies 72* classified on the basis of per cent of ash 

plus sulphur in dry coal shows little variation between the average 

efficiency values for the several groups. Tables showing the three 

classifications follow:

Classification of efficiency 72* on basis of ratio of ash to sulphur in dry coal.

Average ratio of ash to sulRatio of ash to sulphur.

0 to 2.5.

27

2.23 

04.83

2.5 to 

5.0.

106

3.39 

64.57

5.0 to

7.5.

73

6.06 

66.45

7.5 to 

10.

' 27

8.69 

66. 09

10 to 15.

8

12.10 

05.76

15 to 20.

17

17.11 

64.67

20 to 25.

9

22.64 

64.90

25 to 30.

4

26.46 

65.98

Over 

30.

4

33.29 

66.26
HEAT ABSORPTION AND BOILER EFFICIENCIES. 95 

Classification of ratio of ash to sulphur in dry coal on basis of efficiency 72*.

Number of

tests.........

Average efficiency 72*. . . .

Average ratio

of ash to sulphur in dry

coal.........

Efficiency 72*.

Up to

53.

1

52.01

'16. 27

53 to

57.

. 5

55.49

6.24

57 to

59.

12

58.20

5.77

59 to

62.

26

CO. 62

6.61

62 to

63.

15

62.49

4.40

63 to

64.

19

63.45

7.67

64 to

65.

28

64.44

4.81

65 to

66.

43

65.54

8.82

66 to

67.

32

66.41

6.31

67 to

68.

36

67.47

7.30

68 to 69 and

69.

25

68.38

6.51

over.

34

70. 18

8.64'

Classification of efficiency 72* on per cent of ash plus sulphur in dry coal (Indiana, Illinois, and western Kentucky coals).

Percent of ash plus sulphur.

Average per cent of ash plus

Up to 9.

3

7.40

66. 00

9 to 11.

13

10.38

65.73

11 to 13.

11.95

68.03

13 to 15.

16

14.14

63.44

15 to 17.

14

15.98

64.73

17 to 19.

14

18.12

64.10

19 to 21.

8

20.02

65.47

21 to 23.

12

21.90

66. '33

23 up.

5

24.83

66.47

SUGGESTED STEAM-TURBINE CYCLES, HEAT ABSORPTION, 

AND BOILER EFFICIENCIES.

THE BOIIEE AND THE FURNACE AND THEIR EFFICIENCIES.

The boiler with its setting consists mainly of two parts, the furnace and the boiler proper. The furnace is the heat generator and 

the boiler the heat absorber. In practice both are imperfect in their 

functions. A perfect furnace would burn the fuel completely. A 

perfect boiler would absorb-all the heat evolved in the furnace provided the temperature of the- water in the boiler was that of the 

atmosphere. It follows, then, that the furnace efficiency is the 

ratio of the heat evolved in the furnace to the potential heat of the 

fuel fired, and that the boiler efficiency is the ratio of the heat absorbed by the boiler to the heat evolved in the furnace; the combined efficiency of the furnace and boiler being the ratio of the heat 

absorbed by the boiler to the potential heat of the fuel fired. The 

grate is taken as a part of the furnace. The true boiler efficiency is 

the ratio of the heat absorbed to the heat which is available to the 

boiler, this available heat being that portion of the heat in the furnace gases which is above the temperature of the steam.

If the wording in the above definitions is somewhat changed another set of efficiencies is obtained, which may be called the thermodynamic efficiencies. The efficiency of the furnace is the ratio of the 

heat made available to the boiler to the potential heat of the fuel 

fired. The efficiency of the boiler is the ratio of that portion of the 

heat absorbed which is available for power purposes (engine or. tur-
96 A STUDY OF POUR HUNDRED STEAMING TESTS.

bine) to the heat available to the boiler. The combined efficiency 

of the furnace and boiler is the ratio of the heat made available for 

power purposes to the heat value of the fuel fired. The fact is that 

the steam engine is usually blamed for wasting heat which is not 

available to it.

To illustrate the above definitions let the various heat values be 

represented by diagrams. For the representation of the heat in the 

furnace a diagram such as given in A, fig. 54, can be used. This 

diagram has absolute temperature for the ordinates, and a factor 

proportional to the specific heat of the furnace gases multiplied by 

their weight as abscissas. In the same chart (fig. 54, B] is an ideal 

cycle of a steam engine or turbine plotted on temperature-entropy

3000 

Z500

1 

E_TCMPtRCTURC, ABSOLUTE 

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.pXVI -SPE.CIF C HEAT OF GASES AT CONSTANT 

PR ESSURE. TIMES WEIGHT OF GASES

5

f

X

X

*" X

T

-13-

0->- ENTROPY

w

FIG. 54. Temperature-entropy diagrams for boiler: A, For air and coal; B, for water and steam.

plane. It must be understood that the abscissas of these two diagrams are in different units. The abscissa in B is taken in entropy 

units because the adiabatic expansion and the availability of heat to 

the steam engine or turbine can be best shown' by temperatureentropy diagrams.

On the assumption that 1 pound of combustible is completely 

burned, the various quantities of heat in the furnace are represented 

in A as follows: The areaABCD represents the potential heat in the 

fuel and also the heat developed in the furnace. The heat available 

for the boiler, represented in the diagram by the area OBCP, is the 

heat above the temperature of the steam and is the limit of the heat 

which the boiler can absorb. The remainder of the heat, repre-
HEAT ABSORPTION AND BOILER EFFICIENCIES. 97

sented by the area AOPD, is below the temperature of the steam 

and therefore can not be absorbed by the boiler.

In B the area RSTUW represents the heat absorbed by the boiler 

and delivered to the engine. Of this heat only a portion, represented by the area STTJV, is available for the engine to be converted into mechanical energy. The remainder of the heat, represented by the area RSVW, is below the atmospheric temperature 

and can not be converted by the steam engine into mechanical energy. It may be said here that the limit for adiabatic expansion of 

steam in a steam engine or turbine is set by the temperature of the 

cooling water in the condenser. However, as the cooling water is 

nearly at the temperature of the atmosphere, the atmospheric temperature may be taken as the limit. It is entirely out of the question to obtain lower pressure in a condenser than that corresponding

to the steam temperature equal to the temperature of the cooling 

water, no matter how perfect the air pump may be. For this reason 

it is said that the heat which is left in steam after it has been expanded adiabatically to the temperature of the atmosphere is below 

the atmospheric temperature. Of course this reasoning does not 

apply to a case where the steam is used for heating purposes.

During the process of transmitting the heat from the boiler furnace to the engine, the heat loses much of its availability, the greatest 

drop being in the transmission of the heat from the furnace gases 

into the boiler water. During this transmission there is a great 

drop in temperature, and with it drops the availability.

To show what efficiency could be obtained from an ideal steamgenerating outfit and a steam engine working on a perfect cycle, as 

shown in B, fig. 54, an example is given below:

Suppose that 1 pound of " combustible" of the coal of test No. 204 

is burned with 18.3 pounds of .air in a perfect furnace. The heat 

value of 1 pound of this "combustible " is 14,660 B. t. u., and if we 

assume the atmospheric temperature to be 50° F. and the steam 

pressure 80 pounds by gage,' the various heat quantities are as follows: Heat evolved in furnace, 14,660 B. t. u.; heat available for 

boiler, 13,320 B. t. u. The remaining portion of the heat evolved 

in the furnace is below 324° F., the temperature of the steam, and is 

either in the gases or in the moisture formed by burning the hydrogen of the "combustible." As this is an ideal case, all the heat which 

is available to the boiler is absorbed by it. On the assumption that 

there is no radiation from the boiler and the pipe connections, the 

heat delivered to the engine is 13,320 B. t. u. Of this heat only 4,056 

B. t. u. is available for the engine. This last quantity can be obtained from a steam table (such as Reeve's) in the following manner:

The total heat of 1 pound of saturated steam at 80 pounds gage pressure is 1,180.3 B. t. u., and the entropy is 1.5976. Within the limit this 

8400 Bull. 325 07 7
98 A STUDY OF FOUR HUNDRED STEAMING TESTS.

steam can be expanded to atmospheric temperature, which in this 

assumed case is 50° F. The corresponding absolute pressure of steam, 

is given in the table as 0.36 inch of mercury. The total heat of 1 

pound of steam at this pressure is 1,096.8 B. t. u. and the entropy 

2.1478. The heat of 1 pound of water at 50° F. is 18.08 B. t. u., and 

the entropy is 0.0360 in the table, the heats and entropies being 

counted from feed water at 32° F.

As the temperature of the feed water is nearly that of the atmosphere, which in the assumed case is 50° F., the heats and entropies 

used in this problem are counted from feed water at 50° F. These 

heats and entropies can be obtained by subtracting from the values 

given in the table the heat and entropy of water at 50° F. Inasmuch 

as with adiabatic expansion the entropy remains constant, the quality 

of the steam at the end of the expansion of steam from 80 pounds 

gage to 0.36 inch of mercury absolute pressure is:

1.5976-.0360 1.5616 n

= 74 er cent 2.1478-.0360 2.1118 

The heat left in 1 pound of steam at the end of the expansion is 

(1,096.8 - 18.08) X .74 = 797.1.

The total heat left in the steam at the end of the expansion when

13,320 , 

 ;. QA 0 1Q no pounds or steam is used is

IjloU.o lo.Uo

13,320 ' v 7Q7 1 Q 9R4 1 1,180.3-18.08 A ' y ' y ' D* -i<

Then the heat converted into work is 13,320 - 9,264.1 =4,056 B. t. u.

In this case the heat in the condensed steam does not enter into 

the computation because it is at the temperature of the feed water.

In the example just given the various efficiencies are as follows: 

Furnace efficienc}^ = 14,660 -f- 14,660 = 100 per cent; boiler efficiency = 13,320 -T- 14,660 = 90.9 per cent; boiler and furnace efficiency = 

13,320 -- 14,660 = 90.9 per cent; true boiler efficiency = 13,320-r13,320 = 100 per cent. The thermodynamic efficiencies are: Furnace 

efficiency =13,320-7-14,660 = 90.9 per cent; boiler efficiency = 4,056-=- 

13,320 = 30.45 per.cent; efficiency of furnace and boiler = 4,056-r14,660 = 27.67 per cent.

Of course by means of the economizer' and by using superheated 

steam these ideal efficiencies could be somewhat raised. Steam 

boilers are not as efficient for power purposes as the figures obtained 

from boiler trials ordinarily imply.

In the above discussion only the limiting case was considered. In 

practice there are many losses which reduce the boiler efficiency to 

less than two-thirds and the total efficiency of the steam-outfit to 

less than one-lialf.
HEAT ABSORPTION AND BOILER EFFICIENCIES. 99

As the process of heat evolution and heat transmission goes on in 

the furnace and the boiler the principal sources of loss are about as 

follows:

(a) Part of the combustible drops through the grate into the ash 

pit and is not burned.

(6) Part of the coal is gasified, and the gases escape before they are 

burned.

(c) Part of the heat evolved in the furnace is radiated through the 

fire doors and the furnace walls.

Of these three losses, the second is perhaps the most serious and 

increases rapidly after the content of C02 in the flue gases passes a 

certain limit. (See fig. 31, p. 51.) Losses a and Z> diminish the heat 

which is actually evolved in the furnace, and the temperature of the 

gases of combustion. In fig. 54 these losses are represented by the 

area EBCF. Loss c further decreases the heat which has already 

been evolved in the furnace. In the diagram this loss of heat is 

represented by the area GEFH.

(d) No boiler cools the furnace gases to the temperature of the 

steam; the gases leave the heating surface of the boiler at a temperature from 100° to 300° F. higher than that of the steam. The 

heat lost in the waste gases is represented by the area AJID.

(e) As the gases pass through the boiler setting cold air leaks in, 

lowers their temperature, and by increasing their weight increases 

the loss up the stack. The heat loss in the waste gases is then represented by the area AKLQ, and the loss due to the leakage of air 

is represented by the difference of the areas AKLQ and AJID.

(/) The total moisture (from the coal and air, the water of composition, and the moisture formed by the burning of the available 

hydrogen of the coal) lowers the temperature of combustion and with 

its high specific and latent heat increases the loss up the stack.

The heat value of the coal is represented by the total area ABCD, 

the heat actually evolved in the furnace by the area AEFD, the heat 

available to the boiler by the area JGHI, and the heat absorbed by 

the boiler, if there were no leakage of air, by the area JGHL When 

air leaks into the setting the heat absorbed by the boiler is represented by the difference between the area AGHD and the area AKLQ.

In most of the commercial appliances for making steam the 

process of heat absorption begins before the process of heat evolution has been completed; in fact, the two processes go on together 

as soon as the temperature of the gases has risen sufficiently above 

the temperature of the steam. This is true to a great extent with all 

furnaces having no clay-tile roof and no combustion chamber and 

with all internally fired boilers. Even in a furnace of the Heine type 

a considerable portion of the heat is absorbed by the boiler through 

the tile roof. Such abstraction of heat necessarily reduces the final 

temperature of the products of combustion.
100 A STUDY OF FOUR HUNDRED STEAMING TESTS.

HIGH INITIAL FURNACE TEMPEEATURE AND ITS 'EFFECT ON ECONOMY.

From what is said in the paragraphs on efficiencies it appears that 

more heat can be made available for the boiler if higher initial temperature and lower steam pressure be used. In general this proposition is true; however, both conditions have their limits beyond which 

new losses coming into play more than counterbalance the gain.

First let the relative gain and loss due to high initial temperature 

be considered. In order to obtain high initial temperature it is necessary to reduce the weight of gases per pound of " combustible." This 

condition means that less air is admitted into the furnace and less free 

oxygen is present in the gases. The reduction of free oxygen in the 

gases necessarily increases the amount of incomplete combustion, as 

shown in figs. 13 (p. 22), 14 (p. 23), and 31 (p. 51). The curve of 

fig. 31 indicates that the furnace efficiency drops very rapidly after 

the C02 content in the flue gas has reached about 9 per cent (perhaps 

11 or 12 per cent in the furnace, before the gases have been diluted 

by leaks).

The loss up the stack is not reduced so much as the reduction of the 

weight of the gases per pound of " combustible " would indicate, because 

with the rise of the initial temperature the flue-gas temperature also 

rises. The curve of fig. 16 (p. 24) shows this relation of the flue-gas 

temperature to the initial (combustion-chamber) temperature.

To show that extremes either in high or low initial temperature 

may reduce the combined efficiency of the furnace and boiler, three 

cases were computed, and the results are given on page 101.

Suppose that the coal of test 204 is burned with three different furnace-gas compositions, having C02 contents of 7.0, 10.0, and 13.0. 

per cent, the respective percentages of completeness of combustion 

as obtained from the curve of fig. 31 will be 91.8, 90.5, and 86.4 per 

cent. To account for the loss in incomplete combustion the flue-gas 

analyses might be about as given below:

Hypothetical fue-gas analyses.

Gas.

C02 ...... 

0.........

CO.......

CH«...... 

H, .......

CjH<..... 

Ni.. ......

Case 1.

7.0 

12.0

.2

.15 

.1

.05 

80.5

100.00

Case 2.

10.0 

8.0

.4

.2 

.2

.1 

81.1

100.0

Case 3.

13.0 

5.0

1.0

.4 

.3

.2 

80.1

100.0

Except perhaps CO, all the combustible gases in all three cases are 

by ordinary methods undeterminable; it is simply assumed that they 

are present. The heat loss due to each combustible.gas in the as-
HEAT ABSORPTION AND BOILER EFFICIENCIES. 101

sumed composition of flue gases is computed by the following general 

formulas: .

(a) Loss due to CO =

_______2SCO______ (per cent of carbon 1 v 409 K 

12 (CO, + CO + CH4 + 2C2H4 ) x \ in " combustible "} x *'^°'

(&) Loss clue to CH4 =

_______16CH4_____vlPer ceQk °^ cai>bonl oq Kin 

12 (C02 + CO+ CH4 + 2C2H4 ) X I in "combustible"} x ^OJUv

(c) Loss due to H2 = .

_________ 2H2 ______ vlPer cent °f carbon 1 R0 nqn

12 (C02 + CO + CH4 + 2C2H4 ) X 1 in "combustible"} x oz 'Ut5U "

vper cent of caronlarbon

4 + 2C2H4 ) X 1 in "combustible"} x

($} Loss due to C2H4 = 

_____ 28C2H4 

12 (C02 + CO + O

The number at the end of each formula is the heat value of 1 pound 

of that particular gas. The results obtained are in B. t. u.

The loss due to the presence of each gas in each of the three cases, 

together with the calculated results, is shown below.

Calculated losses and results due to the presence of combustible gases in the flue gases in the 

three cases (steam pressure taken to be 80 pounds gage).

Loss clue to 

co ...............:...................................

CH<... ................................................

Hi....................................:...............

CjI-I...................................................

Total loss .................................'..........

Calculated results:" 

Heat value of 1 pound of ' ' combustible " ............. ......B. t. u..

........do....

do

Temperature of product of combustion (if completeness of combustion were 100 per cent) . . ....... °Va

........ ..°F..

........do....

......B.t.u..

Case 1.

227 

529 

110 

280

1,152

14.060 

13, 460 

14.23 

0.5887

2,075 

91.8 

1,903 

543 

9,424 

69.9 

64.2

Case 2.

313

487 

ICO 

387

1,347

14, 660 

13, 270 

19.3 

0.5887

2,900 

90.5 

2,624 

598 

10,053 

75.9 

68.7

Case 3.

572 

710 

176 

564

2,022

14,660 

. 12,670 

27.71 

0.5887

3.850 

86.4 

3, 310 

039 

9,875 

77.8 

67.3

o Specific heats assumed to be constant.

The diagrams giving the representation of the various quantities 

of heat of the three cases discussed are presented in fig. 55. Each of 

the areas ABCD is the potential heat in the coal; the areas BCFE are 

the incomplete combustion losses; each of the areas AEFD is the 

heat actually evolved in the furnace. Of the heat evolved in the 

furnace only the area GEFH in each diagram is the heat absorbed 

by the boiler. The minor losses are not represented in detail.
102 A STUDY OF FOUR HUNDRED STEAMING TESTS.

The over-all efficiency indicates that it is better to burn the coal 

with the initial temperature given in case II than with the high initial 

temperature given in case HI, although the latter gives much better 

results than the low temperature in case I. On account of the 

increased radiation at high temperature, the actual results in case III 

might not show so much advantage over case I as the calculated 

results.

Another disadvantage of high initial temperature is the deterioration of the furnace. When high furnace temperatures are used the 

bridge wall has to be rebuilt often and the side walls lined. A hot 

fuel bed melts the refuse on the grate and causes the formation of 

clinkers. Hot clinker warps and destroys the grate bars, besides

3950 

3450

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Ol 23456? '01 234 0 

CpX W-SPECIFIC HEAT OF GASES AT CONSTANT PRESSURE TIMES WEIGHT OF GASES.

431

a-

\

BM

71 T

^S:

30 f

i&

m

TAG

2

s

3

c

H._

FIG. 55. Availability to a boiler of heat of combustion of carbon in three different cases.

making the fires very hard to clean and disturbing the evenness of the 

air supply through the fuel bed.

Fig. 17 shows that in general the capacity of the boiler increases 

as the combustion-chamber or initial temperature rises. The advantages and disadvantages of high initial temperature may be summarized as follows: Advantages (a) Increase in boiler efficiency; (6) 

increase in capacity. Disadvantages (a) More loss by incomplete 

combustion; (6) increased radiation; (c) deterioration of furnace.

LOW STEAM PRESSURE AND ITS EFFECT ON ECONOMY.

It has been said that more heat could be made available and more 

heat would be absorbed by the boiler if lower steam pressure were 

used. For power purposes, however, the gain in boiler efficiency
HEAT ABSOKPTION AND BOILEK EFFICIENCIES. 103

would be more than offset, by the loss in availability of the heat for 

the engine. If, however, the steam, at low pressure be highly superheated and used in a steam turbine specially designed, an increase of 

1 to 4 per cent in the thermodynamic efficiency of the outfit might be 

' expected.

In the following paragraph is a conservative computation of the 

probable increase of the efficiencies of a boiler and a steam turbine 

resulting from the reduction of steam pressure and the superheatingof the steam. In the computation of the steam-turbine efficiencies 

it has been assumed that the friction of the steam through the nozzles 

and the turbine blades would decrease as the pressure dropped, and. 

that the expansion of the steam would therefore be more nearly 

adiabatic. This reduction of friction can be reasonably expected, 

because the friction of fluids against a solid increases directly as the 

density of the fluid. Furthermore, the expansion of highly superheated steam at low pressure will take place entirely in the superheated region, and thus friction due to condensed steam, which is a 

serious item in .steam turbines as ordinarily built and operated, will 

be avoided.

Let four cases be considered case 4, gage pressure 200 pounds, 

superheat 200° to 587.5° F.; case 3, gage pressure 100 pounds, superheat to 800° F.; case 2, gage pressure 25 pounds, superheat to 800° F.; 

case 1, gage pressure 15 pounds, superheat to 800° F.; temperature 

of feed water, 82° F.; condenser vacuum, 1.2 pounds absolute pressure (28 inches mercury below an atmospheric pressure of 14.7 

pounds). Assume the coal of test 204 to be burned with the resulting 

product of combustion equal to 19.3 pounds of dry chimney gases 

per pound of " combustible. " The heat in chimney gases .per 1° F. per 

pound of combustible is, in dry gases, 19.3 X 0.24 = 4.63 B. t. u.; 

in moisture, 0.5887 X 0.48 '= 0.28 B. t. u.; total, 4.91 B. t. u. The 

heating value of 1 pound of combustible is 14,660 B. t. u. About 

83 per cent of the increase in the heat available for the boiler due to 

the drop of steam temperature will be absorbed (the true boiler 

efficiency being taken at about 83 per cent).

Calculated increase of boiler efficiency due to drop in steam temperature.

Drop of steam pressure 

(pounds) from 200 to 

100.

244 

1,00

 25.

491 

3.35

15.

504 

3.85

This increase in boiler efficiency may seem small. However, the 

great reduction of the first cost of installation of a plant makes the 

reduction in steam pressure appear more practicable for instance,
104 A STUDY OF FOUR HUNDRED STEAMING TESTS.

multitubular boilers would then be as safe as water-tube boilers. 

Further, 83 per cent true boiler efficiency should be far surpassed in 

the future.

Quantities used in calculation and probable results of the use of steam of low pressure 

and high superheat in steam turbines.

Total heat of superheated steam above 82 °F. (Ai) . ..B, t. u. . 

Total heat in steam at 28-inch vacuum above 82 °F. (As). .do. .

Assumed coefficient of friction of steam in nozzle and blades 

(see p. 103) ..................................................

Coefficient of friction calculated from the law of friction of

Heat converted intov work, Hw, calculated with the assumed

Combined thermodynamic efficiency of boiler and turbine. . . . 

Gain in combined thermodynamic efficiency of boiler and turCase 1.

15 

29.7 

249.5 

800 

1,200.3 

1,372.5 

1,035 

337.5

0.10 

. 0. 084

303.0 

22.1 

08.85 

15.2

16.1

Case 2.

25 

39.7 

267.0 

800 

1,260.8 

1,369.0 

1,031 

338

0.12 

0.10

297.5 

21.7 

68.35 

14.8

13.0

Case 3.

100 

114.7 

327.0 

800 

'1260.8 

1357. 0 

978 

379

0.24 

0.22

288.0 

21.2 

66.66 

14.1

7.6

Case 4.

200 

214.7 

 387.5 

587.5 

1,048.3 

1,245.0 

888 

357

0.30

250.0 

20.1 

65.0 

13.1

The coefficient of friction of steam in nozzles and blades was 

assumed to be 0.3 for case 4, which is in close agreement with practice. 

The coefficients of friction for the other three cases were taken 

somewhat larger than those calculated from the law of friction of 

fluids, in order to be safe.

The over-all efficiency of a steam-generating outfit in case 4 was 

assumed to be 65.0, which can be attained in a well-operated boiler 

room. The over-all boiler efficiencies in the other three cases were 

obtained by adding to 65 the increase in efficiency as calculated in 

the preceding paragraphs.

Fig. 56 shows the cycle of thermodynamic processes of each of the 

four cases. In the chart the subscripts 1, 2, 3, and 4 of the letters 

refer to cases 1, 2, 3, and 4, respectively; letters having no subscripts 

are applicable to all cases.

Take case 4 for example: The area under AB4 represents the sensible heat of the water, the area under B4C4 the latent heat of steam, 

and the area under C4D4 the heat in the steam due to superheat at 

constant pressure; the total heat in the superheated steam as it 

reaches the steam turbine is then represented by the area under 

AB4C4D4 . If there were no friction of steam during the expansion in 

the steam nozzle and the blades the expansion would be purely 

adiabatic, and in the diagram it would be represented by'a vertical 

line from the point D4 . However, since friction comes into play 

during the expansion and changes part of the velocity of steam back 

into heat, the expansion is a combination of the processes of adiabatic expansion and heating at constant pressure, and is represented
HEAT ABSORPTION" AND BOILER EFFICIENCIES. 105

in the chart by the curve D4F4 . The heat rejected to the condenser 

is the heat under AEF4 . In cases 1 and 2 the heat rejected is the 

heat under AEEnE\ and AEITF2 , respectively, since the steam reaches 

the condenser in a slightly superheated state. The difference between 

the heat delivered to the turbine and the heat rejected to the condenser is the heat which has been transformed into the velocity of 

steam which is represented by the area under AB4C4D4 minus the 

area under AEF4 . It must be understood that the heat changed into 

motion is not represented by the area inclosed by EB4C4D4F4 .

12606. .

1800.

. PRESSURE

100 LB. PRESSURE.

o «>oa

TIT

25-LB. PRESSURE

5 IB. PRESSURE

FIG. 56. Temperature-entropy diagrams for steam-turbine cycles.

HEAT TRANSMISSION THROUGH BOILER TUBES, AND TRUE BOILER AND 

FURNACE EFFICIENCIES.

From the very start of the steaming tests those conducting them 

sought to separate the performance of the boiler as a heat absorber 

from the performance of the fuel bed and furnace as a heat producer. 

In writing up the stages through which opinions progressed it seems 

best to adopt the historical method and outline all attempts, up to 

the last calculations, which are both theoretical and practical, being 

determined from about 400 tests. This last work must be taken as
106 A STUDY OF FOUR HUNDRED STEAMING TESTS.

neither final nor even necessarily correct; it is simply the best we 

know at present. All opinions expressed or deductions drawn must 

be understood as merely tentative, and the right is reserved to change 

part or all of them at any future time.

The first definite calculations on boiler efficiency were made in 

January, 1906, in an attempt to check the temperature indications 

of a Wanner optical pyrometer, which had been used to ascertain 

the temperatures in the rear of the combustion chamber. Sometimes the observation was taken by looking at flame, in which case it 

was postulated that the flames of various coals differ in brightness 

at the same temperature; and, perhaps, although the particles of 

incandescent carbon from which the pyrometer received its light 

were really at the temperature as read off the scale, such a likely 

condition was no assurance that the molecules of gas between were 

as hot; the reasonable assumption would be that they were cooler. 

Or, worse yet, when a coal and the conditions of a test were such as 

to give short flames, or none, in the rear of the combustion chamber, 

and the pyrometer received its light from the opposite side wall, it 

was plainly evident on observation that the temperature as read 

from the instrument- was too low, because the side wall was cooler 

than the tile furnace roof, on account of its radiating heat to the bare 

water tubes near by, which the tile roof could not do. Even the 

tiles of the roof were conducting heat through to the tubes which they 

protected. These and other considerations put the indications of 

the optical pyrometer in question, through no fault of its own. 

Attempts were made to check the pyrometer with a platinum and 

platinum-rhodium thermoelectric couple, but the porcelain tubes 

slagged and melted away within an hour or so under the high temperatures used, and a satisfactory protection for the junction was 

not made to work reliably until too late for this purpose. By this 

time it had been learned that the ascertainment of the temperature 

of the gases entering the boiler was not, after all, of such overwhelming importance. So this tedious checking of the optical pyrometer 

was dropped for more fruitful work. There is a general impression 

among the observers that the pyrometer when used on such furnaces as these is usually correct within 50° C. or 100° F. (For a 

description of the method of protecting the thermoelectric couple 

with a water jacket and cheap clay pipestems see p. 54.)

These calculations on boiler efficiency were made because an 

attempt to obtain any curve of relationship between combustionchamber temperatures (obtained by the Wanner optical pyrometer) 

and over-all efficiency of the furnace and boiler combined resulted 

in a failure, the points falling all over the sheet of coordinate paper. 

At that time the impression of the staff was that the following formula
HEAT ABSORPTION AND BOILER EFFICIENCIES. 107

applied to boilers as well as to condensers, and. so it does, but that is 

only one-third of the story:

Efficiency of boiler as a heat absorber = ~1~^-J where tL = initial

temperature of gases above atmosphere, and t2 = final temperature 

of gases above atmosphere.

Many of the staff believed at that time that if the air supply per 

pound of coal were reduced, without decreasing the completeness of 

combustion (in consequence, of which the initial temperature tx 

would rise), the final temperature t2 would fall, or at least not rise 

proportionately with tr It is frequently stated by authorities on 

boiler testing that if the same number of heat units be liberated in 

a furnace per second in two cases first, with a small air excess, and 

second, with a large air excess the final or flue temperature in the 

first case will be the lower. This assumption may be true with some 

boilers,.or with most boilers, or even with those of this plant, but 

after careful investigation 'of large numbers of actual simultaneous 

readings, the staff has become convinced that such a theory is both 

practically and theoretically untrue; and that, on the contrary, a 

rise of furnace temperature usually causes a proportionate rise of 

flue temperature, the ratio between these temperatures being 

almost independent of the mass of gases passing. For a long time this 

conclusion was hard to believe, for on closing the stack damper a 

little, at times, the combustion-chamber temperature rose and the 

stack temperature fell; yet nothing appears more certain on observation than that the sun moves around the earth.

It seemed almost axiomatic that the higher the initial temperature 

the greater the amount of heat which would pass into the boiler because 

of the greater temperature difference between gases and water, yet 

this proposition is only slightly true. Likewise it seemed axiomatic 

that a high combustion temperature would certainly aid combustion 

of smoke and hydrocarbons, which it would do if other accompanying conditions were not usually adverse enough to neutralize all gain. 

Because of these two propositions, which were apparently axiomatic, it was concluded that when the optical-pyrometer temperatures and the over-all efficiencies of the fuel bed, furnace, and boiler 

(72*) failed to agree, the pyrometer was given unreliable indications, 

through no fault of its own. So the first calculation was incidentally made of what was then called true boiler efficiency, in order to 

figure backward to the combustion-chamber temperatures, by means

of the above formula, 1 + 2 - The so-called true boiler efficiency

was calculated for each of about 125 tests by means of the formula.

True boiler efficiency =

_____________ Efficiency 72*_______________

100 [CO loss in p. ct. + (unaccounted-for item in p. ct. 3 p. ct.)]'
108 A STUDY OF FOUR HUNDRED STEAMING TESTS.

All the above percentages were taken from the tests as calculated 

by the A. S. M. E. code. It will be noticed that the incompletecombustion loss was taken as being the unaccounted-for item minus 

3 per cent radiation. This was very crude, but the. best we knew. 

The results were disappointing and not clear, but as negative results 

they were very instructive. Eighty-eight per cent of the so-called 

true boiler efficiencies fell between 70 and 75 per cent, and such 

uniformity surprised everyone. The combustion-chamber temperatures, calculated backward by equating these efficiencies to the expression l , 2| in which t2 was known, turned out ridiculously low *i

and the individual temperatures were very' erratic. On leaving 

out a few abnormal tests, more than 90 per cent of those remaining 

had a so-called "true boiler efficiency" between 70 and 75 per cent. 

These calculations took much hard work, the details of which areomitted, inasmuch as it gave only negative and prophetic results that 

were of little value in themselves.

The great value of the work lay in the result that it shook previously 

conceived ideas, some of which were widely believed. The consequent 

inquiry took two forms (a) a general mathematical study of the 

impartation of heat from fluids (including gases) to solids and vice 

versa,a and (&) a routine analysis of samples of gases from the rear 

of the combustion chamber and the stack for minute traces of hydrogen and hydrocarbons.

An ordinary Hemple pipette and absorption bulbs for analysis of 

illuminating gas are accurate only to about 0.2 or 0.3 per cent when 

very carefully manipulated. Unfortunately a mere trace of methane for instance, to the extent of 0.1 per cent by volume in the flue 

gases is sufficient to represent ordinarily a loss of 2 per cent of the 

coal due to incomplete combustion. (See p. 100.) Nevertheless, for 

some weeks several analyses were made daily for traces of hydrogen 

and hydrocarbons, and on several days these constituents occurred 

persistently and very appreciably, so as to indicate losses of many per 

cent due to incomplete combustion. On account of the well-known 

difficulty of obtaining accuracy in determinations of this kind, due to 

the small volumes of these gases that are ordinarily present, this work 

will not be published. It has, however, along with many kinds of circumstantial evidence, strengthened the belief that the losses due to 

incomplete combustion generally amount to several per cent of the 

potential heat in the coal burned. This presumptive loss will also 

be investigated in one or two other ways.

Incidentally it may be remarked that, if developed, such methods 

of measuring minute traces of hydrogen and hydrocarbons will be

a It was fortunately found that John Perry had done much excellent, but mathematically involved, 

work on this subject; an account of it is given in his book "Steam Engines and Gas and Oil Engines."
HEAT ABSOBPTION AND BOILER EFFICIENCIES. 109

useful when applied to gas-engine exhaust gases. The mere analysis 

of exhaust gases for C02; 02 , and CO, resulting in no trace of CO, 

does not prove complete combustion by any means.

THEORETICAL CONSIDERATIONS.

The tentative formulas developed by Perry are so significant and 

so important that a general outline of them is here given. According 

to his theory the rate of heat impartation to a boiler tube is, for ordinary gases, proportional to (1) temperature differences of the gases 

and the metallic surface; (2) density of the gas; (3) velocity of the gas 

parallel to the metallic surface, and (4) specific heat, of the gases at 

constant pressure. The first of these factors is the only one usually 

thought of, and its applicability is perhaps self-evident.

In. considering factor 2 it is plain that the individual molecules of 

gas give up their heat by vibrating against the metal. The greater 

the number of molecular impacts per second against a unit area of 

the tube the greater the amount of vibration (heat) imparted to the 

molecules of the metal. But the number of impacts is directly proportional to the density, or weight per liter or cubic foot. At a constant pressure (a little less than atmospheric in boiler practice), the 

density is inversely proportional to the absolute temperature, and at 

high-furnace temperature it is almost inversely proportional even to 

the temperature reckoned above steam temperature. Oh this account 

there is a direct neutralization of gain when striving for high temperature in steam-boiler practice, for as the temperature is raised the 

number of molecules in action against any portion of the heating surface is reduced.

In considering factor 3 a mental image should be formed of the 

appearance of a cross section of intensely magnified heating surface. 

The. molecules of the metal would probably appear to be in an extremely rapid state of vibration, with spaces between them much 

larger than the molecules. Entangled among the outer molecules 

there would be comparatively stationary molecules of gas held close 

together in a dense film next to the metal. Farther out normal gas 

is reached, where the molecules are widely scattered. All these gaseous molecules, from those entangled among the surface molecules of 

metal to those in the gas of normal density, would be in an invisibly 

rapid state of vibration, but those close to the metal would be more 

or less "bound" by the attraction of the metal. Now, this layer of 

condensed gas, so to speak, is very adherent to the metal, and conserquently a very poor conductor of heat (since heat in material bodies 

is a matter of the vibration of their molecules), so that the hope of 

getting heat through it lies in the possibility. of dislodging slowly 

vibrating (cold) molecules from this layer and replacing them with 

rapidly vibrating (hot) ones. It can be imagined that as a stream
110 A STUDY OF FOUK HUNDEED STEAMING TESTS.

of hot gas moves along the metal parallel to its surface, an average of 

one-third of its molecules are flying back and forth perpendicular to 

the surface, and the dislodging, sweeping, or scrubbing effect of these 

molecules on the layer of gas molecules adhering to the metal is proportional to the velocity of the mass of gas parallel to the heating surface. Thus it is that the velocity of gases through a boiler tube (a 

fire tube, for instance) is an important factor in heat absorption. It 

is this dislodgment that makes a boiler respond in amount of steam 

made to any reasonable demands put on it. If twice the mass of gas 

is put through the tube per second at the same initial temperature, 

very nearly twice as much steam will be generated on the other side 

of the tube.

In considering factor 4, the specific heat of the gas at constant pres- 

.sure, it is evident that inasmuch as a cubic centimeter of any gas at 

any temperature and pressure contains the same number of molecules 

as a cubic centimeter of any other gas under the same conditions 

(Avogadro's law), and inasmuch as various gases on cooling give up 

various amounts of heat per degree of temperature drop that is, 

they" have different specific heats at constant pressure a given number of molecular impacts of different gases will give up more or less 

energy, according as the specific heats of the gases are respectively 

more or less.

The relation between the heat transmitted per second per unit of 

heating surface and the four factors is expressed by the equation 

H = CPv (Tt-T.)

where H = the amount of heat transmitted;

C =the specific heat times a constant; 

 p = density of the gas;

v = velocity of the gas parallel to the metallic surface ; 

(T\ Ts) = the difference of temperatures of the gases and the water. 

Perry* arrives at the above equation by the following reasoning: 

Referring to fig. 57, let AB represent a small portion of «a heating

surface. Gl to G4 are molecules of the gas 

that are entangled among the molecules of 

the metal and therefore have no velocity 

parallel to the surface of the boiler plate;

Velocity of translation , ;1 111 i , < 

 however, these molecules have velocity or 

vibration in all planes due to their temperatures. M and M: are molecules of the gas 

theory of the dislodgment of which have not only the velocity of vibraheating surface. Inasmuch as the conductivity of the metal itself in a boiler flue is so great that there is 

very little difference of temperature between the gas surface, and

o Steam Engines and Gas and Oil Engines, pp. 587-591.
HEAT ABSORPTION AND BOILEE EFFICIENCIES. Ill

the water surface, the heat transmitted through the metal may 

be taken to be equal to the heat imparted to the film of the 

gas adhering to the metal. This assumption makes the temperature of the film equal to the temperature of the metal and also to 

that of the .water. Now, suppose n represents the number of the 

molecules (M) which'enter the adhering film of the gas, and also the 

number of molecules (G) which leave the film of the elementary surface AB per unit of gas. Let T\ be the average temperature of the 

entering molecules, and Ts the temperature of the film and of the 

leaving molecules. The molecules enter and leave the film with an 

average momentum in the axial direction that is proportional to the 

axial velocity (v) of the gases through the flue. The force of friction 

(F) is the axially directed momentum given .to the adhering layer of 

molecules, so that per unit area the friction (F) is proportional to 

HV (as the momentum of a body is the product of its weight and its 

velocity). The heat (H) given to the film per second per unit surface AB is proportional to n (T1 T8 ), or 

(1) H = Cn (T! Ts), where C is a constant.

(2) ButasF = Cnv,

T^ /m _ rr\ \

(3) Then. H = K. , where K is another constant.

Now, the friction of fluids against a solid varies directly as the 

density and the square of the velocity of the fluid, or 

(4) F = Cpv2 , where p is the density of the fluid.

By substituting for F in equation 3 its value in equation 4, the 

fundamental equation as given before is obtained:

'(5) H = Cpv (T.-Ts).

In the foregoing equations the C and K are constants employed 

so that the sign of equality could be used.

Equation 5 gives the amount of heat transmitted per second per 

elementary area of heating surface. If the amounts of heat transmitted by every elementary area are added, the heat transmitted by 

the entire heating surface per second can be obtained. This can be 

done by the use of calculus, as follows:

Take Tx Ts =@; Tj being the absolute temperature of the gases 

at the distance x from the furnace end of a flue of a total length 1 

and diameter D, and Ts being the temperature of the steam. Let 

W pounds of gases flow through the flue per second and let the 

specific heat be a constant:

p 1 = v' -, andv = CT

where C and C' are temporary constants.

C" 

(6) Then p = TFT, where C" is a consolidation of C and C' just above.

W 7rD2v Also volume per second = = r , where D is the diameter of

the fire tube and 7r = 3.1416.
112 A STUDY OF FOUK HUNDRED STEAMING TESTS.

KW K'WT

(7) Whence v = ^ = T\T~, where K and K' are constants.

Equations 6 and 7 are derived also from the laws that (1) the 

density of the gases varies inversely as the absolute temperature and 

(2) the velocity varies directly as the weight of the gas that passes 

through the flue in a second and as the absolute temperature, and 

inversely as the square of the diameter of the flue. By substituting 

the values of p and v from equations 6 and 7, equation 5 becomes 

Cv©_ C'W0 

T ~~ D2 

Hence in a short length (dx) of the boiler flue the heat transmitted 

to the boiler is 

n _ , _ C'W® _ _ CW&dx 

 - CpWd& = p2 X D ndx = £ 

 . Cd9 rCdx T ^ Cx _ But J -Q- = - / -jj- . Integrating, loge@ = - ^j + K.

Cl When x = 0, K = loge©0 - When x = 1, loge®i = - + loge@0 and

' (8) .'. 0,= 00e"-

The heat absorbed by the whole flue of the boiler per second is 

.(9) H = Cp 

and the true efficiency of the flue is 

TRUE BOILER EFFICIENCIES DEPENDENT ONLY . ON PHYSICAL SIZE, SHAPE, 

AND ARRANGEMENT OF BOILER.

Equation 10 states that the true efficiency of the boiler flue depends 

only on its length and diameter and not on the initial temperature of 

the gases. What is true about one flue holds good for all together.

The efficiency expressed by equation 10 is the- true boiler-flue efficiency that is, it is the ratio of the heat absorbed by the boiler flue 

to the heat available for absorption.

It must be remembered that in this discussion only the heat that is 

imparted to the boiler flue by convection and conduction has been 

considered. In reality the boilers receive heat also by radiation 

directly from the fire and from the hot walls of the furnace. According to the law of Stefan and Boltzmann the amount of energy radiated 

by a black-body surface to another body is proportional to the difference of the fourth powers of their absolute temperatures. The boiler 

furnace radiating heat to the boiler is nearly a black-body surface, so
HEAT ABSORPTION AND BOILEE EFFICIENCIES. 113

that the heat received by the boiler by radiation may be expressed 

by the equation 

H = C (TV-T.4 ) ' where T1 is the absolute temperature of the furnace, T8 the absolute 

temperature of the boiler tubes, and C a constant.

INFLUENCE OF VELOCITY OF GASES ON HEAT ABSOEPTION.

The influence of the velocity of gases on the heat absorption may 

appear at first somewhat improbable. However, inasmuch as high 

capacities of all types of boilers are obtained simply by burning more 

coal, which means making more hot gases and passing them over the 

heating surface at a higher velocity, it must be admitted that such an 

influence exists. Thus, for example, in locomotive practice the capacity is increased two or three times by doubling or tripling the rate of 

combustion and therefore doubling or tripling the velocity through 

the boiler flues. Of course the rate of heat absorption by the fire box 

is affected principally by the initial temperature.

In fig. 6 (p. 15) the following three factors in heat absorption are 

shown, with their product, for the gas mixtures resulting when 1 

pound of carbon is burned with various amounts of excess air: (1) 

Temperature difference, (2) density of gases; (3) volume of gases, 

which is proportional to velocity parallel to the heating surfaces.

The specific heats of products of combustion with the various air 

excesses are nearly constant at 0.24, and therefore any errors introduced by neglecting to consider such varying compositions would be 

less than about 1 per cent. In the case of some wet lignites the error 

might be more, because of the presence of considerable percentages of 

water vapor with a specific heat of 0.48 or higher. The temperatures 

of combustion were calculated on the assumptions that complete combustion is possible, and that the specific heats of oxygen, nitrogen, and 

carbon dioxide remain constant, which is not likely. Any error thus 

introduced into .the calculated temperature is neutralized, by an opposite and very nearly proportionate secondary error, introduced into the 

calculated density as a consequence of the primary error. On account 

of these compensating errors the uppermost "products" curve is as 

reliable as the whole theory.

The assumption was made that 1 pound of carbon was always 

burned in the same length of time, with various air excesses, and the 

resulting temperatures were calculated in degrees Fahrenheit. On 

the same data the relative densities of the resulting gaseous mixtures 

were calculated, each at its respective temperature, taking as unit 

density that of the gases at 320° F. (the temperature of the boiler 

water in this plant).

The lower curve, relative volume of products of combustion with 

increasing air supply, indicates that with large air excesses that is, 

8400 Bull. 325 07 8
114 A STUDY OF FOUK HUNDKED STEAMING TESTS.

with low furnace temperatures the actual volumes are comparatively high, but within the reasonable working range of even poor and 

good firing the volume of the products is nearly constant; as the air 

excess is reduced the temperature rises almost as fast and the effect 

on the resulting total volume is to decrease it very slightly.

Relative volume was used because the velocity of passage of the 

gases through the boiler is directly proportional to it, other things 

being equal, and, as already stated, velocity is one of the three most 

important factors determining the amount of heat imparted to the 

metal of the boiler tube.

It is assumed that in each case the products of combustion, generated always in the same length of time, are passed through a boiler 

fire tube. The upper ("products") curve gives by its ordinate the 

amount of heat absorbed by the first small portion of the tube during 

that length of time. On page 110 it is shown that this curve represents 

not only the amount of heat absorbed by the first short length of a 

tube but by the whole tube, so that this curve can be applied to the 

whole heat absorption of a boiler so far as absorption by convection 

is concerned; but it can not be applied to heat absorption due to 

radiation from fuel bed or hot brickwork.

The upper and final curve was obtained by multiplying together, 

for each of several temperatures along the whole range, the three 

factors (1) relative density of gases, (2) temperature of gases minus 

temperature of steam (T^ Ts), (3) relative volume. The curve 

starts at zero heat absorption, because, although the density and volume are high, the temperature difference at 320° F. is zero, consequently the product of the three is zero. The ordinate figures at the 

left have no specific names, but merely furnish a scale on which to 

indicate relative magnitudes of volume, density, and products of these 

two, and temperature excess above that of boiler water. As applied 

to the upper curve these ordinates on the vertical scale do not mean 

B. t. u., though they are proportional to actual numbers of B. t. u. 

absorbed in any specific case.

On inspecting the upper curve the striking fact is its rapid approach 

to the horizontal, beginning at comparatively low furnace temperatures. For instance, at a furnace temperature of 2,000° F. (1,100° 

C.) ordinary temperature scale; see second temperature scale at 

foot of chart a temperature very easy to attain even with poor 

coals, the ordinate at the left is 9.0. At a furnace temperature of 

3,000° F. (1,650° C.) second temperature scale at bottom of chart 

a temperature rather hard to attain and destructive to good fire 

bricks, the ordinate at the left is 9.5, only 5.5 per cent more than 9.0. 

Thus for all the extra trouble and expense of attaining the higher 

furnace temperature there is a gain in the efficiency of the boiler as a 

heat absorber of only 5.5 per cent, reckoning the efficiency calcula-
HEAT ABSORPTION AND BOILER EFFICIENCIES. 115

tion above atmospheric temperature. This gain is often largely neutralized by less complete combustion. The fact that the efficiency 

72* is not improved by high combustion-chamber temperature is 

well illustrated in fig. 12 (p. 21), which is compiled from actual tests 

on coals of the same class from Illinois and Indiana.

It must be understood that this whole chart refers only to that 

part of a boiler which absorbs heat by contact with the hot gases. 

In a locomotive boiler this includes the tubes and to some extent the 

fire box. For a water-tube boiler of the Heine type, with the lower 

row of tubes inclosed in clay tiles, the chart includes all of the boiler 

except the lower row of tubes, which are exposed in the rear to radiation and are analogous to the fire box of a locomotive.

The following table gives a laborious method of calculating the 

relative amount of heat absorbed by the boiler when 1 pound of carbon is burned with various amounts of excess air. The table was

calculated by first figuring the relative volume, the relative density, 

and the temperature elevation of the gases; then by multiplying these 

three together the relative heat absorption was obtained for the corresponding excesses" of air. The curves of fig. 6 (p. 15) were plotted 

from the values "given in this table:

Arithmetical calculation of relative amounts of heat absorbed by a hypothetical boiler.

Excess of air. .... .per cent. . 

1. Pounds of O2 per pound

2. Pounds of airper pound 

of carbon (4 parts N, 1

3. Cp of products of com4. Temperature rise clue to 

cornbustion= 

14,000 oF

Cp (pounds of air+1) 

5. Temperature rise + 50 

(which is atmospheric 

temperature) ..... °F. . 

6. Absolute temperature of

7. Relative volume of unit 

mass of gases at temperature of line C when 

volume at 401° F. ab8. Relative total volumes 

of products of combustion, each at its final 

temperature of combustion=line 7Xline 2.. 

Elevation of temperature of 

combustion above steam 

temperature: 

9. At 320° F., 75 pounds

on ftftfff* O V

10. At390° F., 205 pounds

r»n fffi PY* ° R

11. Density of products of 

combustion, each at its 

final temperature of 

combustion when density at 320° F.= 1 ...... 

12. Line HXline OXline 8=

HO.....................

1.

0 

2.67

13.33

0.2360

4,325

4,375 

4,836

10.49

1, 139. 8 

4,055

3,985

0. 1615 

916

2.

25 

3.33

16.67

3,486

3,536 

3 997

8.67

144.5 

3,216

0. 1956 

909

3.

50 

 4.00

20.00

0. 2373

9 W\

2,980 

3,441

7.47

149.4 

2,660

2,590

0. 2269 

902

4.

75 

4.67

23.33

0. 2375

2,526

2,576 

3,037

6.59

153.5 

2,256

2,186

0. 2568 

889

5.

100 

5.33

26.67

0. 2376

2,220

2,270 

2,731

5.92

157. 88 

1,950

1,880

0. 2856 

879

6.

150 

6.67

33.33

0. 2378

1,788

1,738

9 9QQ

4.98

165.9 

1,518

1,448

0. 3397 

855

7.

200 

8.00

40.00

0. 2380

1,496

1,546 

9 nn?

4.35

174.0 

1,226

1,156

0. 3891 

830

8.

300 

10.67

53.33

0. 2385

1 127

1,177 

1,638

3.55

189.3

787

0. 4768

 774

9.

1,595 

d<\ on

226 00

O oonn

270

320

7fi1

1 69

382.0 

0

0

1. 000 

0

oThis H is merely a number proportional to the heat absorbed.
116 A STUDY OF FOUE HTJNDEED STEAMING TESTS.

The relative amount of heat absorbed by a boiler when various 

percentages of excess of air are used for combustion can be easily 

obtained by the following formula:

(11) H = CW(^^f

which is obtained as follows:

Let C = a constant, having a fixed value for each case.

p = the density of the gases, relative to any standard.

V = velocity past'any small portion of heating surface under

consideration, in any units.

T = absolute temperature of gases at any point under consideration, on any thermometric scale. 

t = absolute temperature of boiler water on the same scale

asT. 

W = weight of gases resulting from combustion of 1 pound of

carbon, expressed in any units of any system. 

W 1 = weight of air used per pound of carbon. 

K= Ta (temperature of atmosphere) -ft.

According to our fundamental assumption (equation 5, p. Ill), the 

heat transmitted per second per unit of heating surface is 

(5) H = CpV (T-t).

C' /" W ~N But p = rp ( TTT 7 \ where C' is a new temporary constant. Also

V = C" TW, where C" is a new temporary constant.

The last two equations are derived from the fundamental proper- 

'ties of gases; the first one states that when 1 pound of carbon is 

burned with air the density of the resulting gases approaches that of 

air as the amount of air increases, which increase reduces the influence of the amount of C02 present; and the second, that the density 

decreases directly as the absolute temperature (T) of the resulting 

mixture increases. C' is some constant, whose value will not be 

determined because all these results are relative only. This statement applies to all the C's used. Substituting the values of p and V 

in equation 5, we have 

W \ C' CW2 * ' » ^ ft" rpTlT /rr\ j.\ _ ^ '' /rr\ j\ 

J.VV \ i. \j) -TTT -, \JL 1 1

on arbitrarily assuming that all constants, C, C', and C", are consolidated into a new C, as the result sought is to be relative only.

14,600 60,900 i ~ ia ~6.24W~ W 

hence

60,900 i = ^ + ia

in which 14,600 = B. t. u. value of 1 pound of carbon and 0.24==
HEAT ABSOKPTION AND BOILEB EFFICIENCIES. 11 7

specific heat (approximately) of 1 pound of the gases of combustion at constant pressure. Substituting again, we have 

which is the equation given first above.

It was suspected that these calculations of heat imparted to the 

boiler surface might be slightly vitiated by the fact that C02 , 02 , 

and N2 have different specific heats. A trial calculation with two 

very different air supplies showed that this error could not be more 

than 1 per cent in favor of greater heat absorption with a low air 

supply.

The curves of fig. 20 (p. 29) were plotted from data obtained by 

formulas developed in the preceding paragraphs. This chart shows 

the same facts as fig. 6 (p. 15), but they are differently represented.

The two charts were calculated at different times by different men, 

who used slightly different constants in some ways. One of them 

took account of the slight variation of composite specific heats of 

the gases with different air excesses and the other did not. Nevertheless, the two charts show graphically the same conclusion that 

at low air excesses and high initial temperatures the heat absorption 

by the boiler increases only a few per cent as compared with moderate furnace temperatures. If we use the same temperature range as 

in the discussion of the curves of fig. 6 (p. 15) 2,000° F. (1,100° C.) 

to 3,000° F. (1,650° C.) the amount of heat absorbed increases 

7 per cent, as figured from the ordinate at the left. The increase 

calculated from the chart was 5.5 per cent.

The arrows attached to each curve indicate the coordinates to be 

used with it. The ordinate on the left, "Heat transmitted per second per unit of heating surface times a constant," is relative only, 

as indicated by the phrase "times a constant." This constant 

varies with the boilers. Every boiler has an individual constant, 

and according to this theory it is unchangeable except by changes 

in baffling, when it becomes another boiler with a new individual 

constant.

The curve labeled "Combustion temperature as affected by air 

supply" was calculated as explained for the chart shown in fig. 6 

using constant specific heats.

The curve labeled "Heat absorption as affected by combustion 

temperature" is precisely the same curve as the upper curve of 

fig. 6, with the exception of the calculation as explained above.

The curve labeled "Heat absorption as affected by air supply" 

shows the same fact as the upper curve with reference to air supply 

per pound of carbon instead of the resulting temperature of 

combustion.
118 A STUDY OF FOTTB HtJNDftED STEAMING TESTS.

With 14 pounds of air per pound of carbon the ordinate at the 

left is 6.2. With 28 pounds of air the ordinate is 5.55 a decrease 

of about 10.4 per cent. The latter amount of air is high in practice. 

To reduce the heat absorption to 50 per cent of what it would be if 

the carbon were completely burned with the theoretical amount of 

air (11.50 pounds) would require 108 pounds of air per pound of 

carbon an enormous excess.

In all such calculations of heat absorption it is plain that the 

more nearly the temperature of the absorbing medium approaches 

that of the atmosphere that is, the lower the steam pressure the 

less the harm done by excessive amounts of air and the larger the 

percentage of total heat absorbed. This is an argument in favor of 

low steam pressures with high superheats, as suggested-tentatively 

on pages 102-105.

PRACTICAL APPLICATION OF THEORY OF HEAT ABSORPTION TO A FIRE-TUBE

BOILER.

As a practical illustration of the meaning of these theoretical principles, several calculations were made in the case of a fire-tube boiler 

assumed to consist of a single tube 0.1 foot in internal diameter and 

10 feet long.

From the work of page 112 is taken the equation, which expresses 

the quantity of heat passing through any given portion of the tube.

(9) (

_ CXi _ CX2 \

D D JX0.24

e -e /

in which H = heat absorbed in B. t. u.

@0 . = elevation of initial temperatures above boiler-water

temperature.

@Xl = elevation of temperature of gases above that of boiler 

water at a point xx feet from the entrance end of 

the tube.

@X2 = elevation of temperature of gases above that of boiler 

water at a point x2 feet from the entrance end of 

the tube (x2 is farther along the tube than xj. 

W = pounds of gases per pound of carbon. 

e = base of hyperbolic system of logarithms = 2.718. 

D = internal diameter of tube in feet, 

c = a constant for any particular tube.

0.24 = the approximate specific heat of gases of combustion 

at constant pressure. This factor might well have 

been omitted and its effect on the equation accomplished by giving the constant "c," in the exponents 

of e, another value.

The following calculations assume that the metal of the tube is 

always kept at the water temperature, which is not true, inasmuch
lid

.as there must be a difference of temperature in order to make the 

heat flow from the metal into the water. It must be understood at 

the outset that these calculations are not given for the purpose of 

proving anything, but merely to illustrate the concrete consequences 

of the theory. Other methods will be used and applied to actual 

boiler tests to show how closely the formula fits actual performances. 

An ordinary locomotive boiler evaporates about 11.65 pounds of 

water (equivalent evaporation from and at 212° F.) per square foot 

of heating surface per hour. Our hypothetical boiler consists of one 

fire tube 10.0 feet long and of 0.1 foot internal diameter. Its heating

surface is 3.1416 square feet and every second Any fin = 3.15 B. t. u.

are transmitted through each square foot.

Take the pounds of air per pound of carbon as 23.33, or 75 per cent 

excess above the theoretical, giving 24.33 pounds of gases of combustion per pound of carbon. The theoretical temperature of combustion is 2,576° F., assuming atmospheric temperature to be 50° F. 

In our case this is 2,576°-320° = 2,256° F. above boiler water temperature. This 2,256° F. is our 00 .

These calculations are to be for one second of time. It is more 

consistent with practice to assume that 1 pound of carbon is not 

burned in one second for 3.1416 square-feet of heating surface, but 

in about 3,230 seconds.

Introducing this 3,230 as a correction'factor in the above equation, 

and substituting all the above-calculated quantities, we get the follow 

ing equation to be solved for "c," the physical or "size and shape" 

constant of this particular boiler:

04 33 cxQ-o cxio-Q 

3.1416 = 0.24X^-^X2,256X2.718 o- 1 -2,718 0.1

whence, on solving by logarithms, c = 0.0147.

Now let us take this hypothetical boiler of one fire tube and feed 

it with the gases resulting from the combustion of 1 pound of carbon 

completely burned (which is both theoretically and practically 

impossible with air supplies only a little above the theoretical), with 

increasing percentages of air excess. The factors are all grouped 

under case 1 of the table below; under case 2 are given parallel data 

for burning 2 pounds of carbon in the same time (3,230 seconds), and 

under case 3 for burning 10 pounds. The factors are repeated in the 

second and third cases to impress the fact that within reasonable 

limits the efficiency of a boiler proper as a heat absorber is independent of the capacity.
120 A STUDY OF FOUR HUNDRED STEAMING TESTS. 

Calculations of the heat absorbed by a hypothetical boiler.

Excess 

of air 

(per 

cent) .

0 

25 

50 

75 

100 

150 

200 

300 

1,596

Case 1 (1 pound of carbon 

burned) .

W.

14' 33 nnn44T 3,230 °- 00443--- 

17.67

3,230- -«K47... 

21.00

3,230 - OOKi0 --- 

24.33

3,230 °°'"3 --- 

27.67

3,230 O08"-'--- 

34.33 3,230- - 010 - 3 --- 

41.00 3,230- - Oim -- 

54.^3

3,230 - 01082--- 

227 3,230" -O'O^7 ---

®o4,055 

3,216 

2,660 

2,25C 

1,950 

1, 518 

1,226 

857 

0

H.

3. 3218 

3.2530 

3. 1972 

3. 1416 

3.0866 

2. 9839 

2. 8769 

2. 6655 

0.0000

Case 2 (2 pounds of carbon 

burned) .

W.

(14-33)2

3,230 ^°- 00880 

(17-67)2 3,230 - - 01094 

(21-00)2 3,230 - - UMUU 

(24' 33)2 0"OG 3,230 - - U "-°l

(27.67)2

3,230 '" ' 

(34.33)2 3,230 Uz' Ub 

(41-00)2 3,230 ~ ' U""J6 

(54.33)2 -

3,230 - - 037<14 

(227)2 , jn _. 3,230- 140°4

©o.

4,055 

3,21C

2, 6CO 

2,256 

1, 950 

1,518 

1,226 

857 

0

H.

6. 6436 

6. 5060 

6. 3944 

6.2832 

6. 1732 

5. 9678 

5. 7538 

5. 3310 

0.0000

Case 3 (10 pounds of carbon 

burned).

W.

(14-33)10 3,230 U ' U44u 

(17-67)10 3,230 - 0517 

(2LOO)1° ' 0650 3,230 - 0h5U 

(24.33)10 3,230 '°753 

(27.67)10 3,230 -°85t) 

(34.33)10

3 230 '

(4i!oo)ia 10ffl) 3,230 ' U69 

(54.33)10_

3,230 ^ 

(227)10 700?

3,230 . ' 

©0-

4,055 

3,216 

2,660 

2,256 

1,950 

1,518 

] . 226 

857 

0

H.

33. 218 

32. 530 

31.972 

31. 416 

30. 8fi6 

29. 839 

28. 7>" 9 

26. 655 

00.000

If it be true that by raising the initial temperature of the gases 

entering a boiler by 1,000° F. the amount of heat put into the boiler 

for every pound of fuel is increased by only a few per cent, and if it 

also be true that the small amount of oxygen present in case of high 

temperatures tends to reduce the speed and consequently the completeness of combustion, how, then, does it happen that (as is undoubtedly a matter of common observation) a large air excess certainly lowers the over-all efficiency decidedly? The explanation 

probably is that when the air excess is large it is probably very large 

through the holes in the fire, and insufficient through the little hills 

and cakes of coal on the grate, especially if the latter are underlaid 

with clinker; the result is that along with a general large air excess

there may be much incomplete combustion. It comes back to the

old story that the fuel bed and combustion space are to blame. The 

remedy lies in a more even fuel bed and gas-mixing structures in the 

combustion chamber, rather than a low air excess or a thick fuel bed. 

With gas-mixing structures a stronger draft must be used if the 

capacity is to be kept up.

In confirmation of the above supposition, that the air excess may 

be insufficient through cakes of.coal, reference may be had to page 

59, where analyses are given of gases collected at the surface of the 

fuel bed through a water-jacketed sampling tube. Many samples 

contain large percentages of CO, hydrocarbons, and hydrogen, and

no02 .

WATER CIRCULATION AS AFFECTING HEAT ABSORPTION.

It is assumed that in every case the water circulates rapidly, with 

the utmost freedom, and with the utmost responsiveness to variations 

in the amount of heat absorbed, so as to keep the metal of the tube
HEAT ABSOKPTlOtf AM) BOlLEfi EFFICIENCIES. l2l

always at water temperature. In practice this would not be true, 

if for no other reason than because twice the rate of heat absorption 

would perhaps require twice the speed of circulation; but, whereas 

the forces impelling circulation may, perhaps, increase directly with 

the increase in steam production, the retarding forces of friction 

increase as the square of the speed of circulation. The latter suggestions, however, are as yet only suppositions.

In each of the several calculations in the preceding table the

 £?! . _cxj

quantity e fi reduces to 1.0 because xt = 0; also the quantity e D has 

the constant value of 0.2295 because c and D are always the same 

and x2 is taken in the table always as 10.0 feet. Therefore, the 

quantity in the parenthesis reduces to (1-0.2295) = (0.7705). This 

constant is fixed once for all by the builder of the boiler when he 

chooses the length and diameter of the tubes. Consequently the 

heat absorbed by the tubes is directly proportional to the product of 

W and ©0 , which represent respectively the weight of gases flowing 

per second and their initial elevation in temperature above that of 

the boiler water. All the calculations made in the case of this 

hypothetical boiler are for the purpose of giving specific instances 

showing that the product of W and & is very nearly constant for 

all reasonable conditions of good firing.

It has been stated before that the heat absorbed by a boiler is 

proportional to the initial temperature elevation above that of boiler 

water, times initial density relative to any (fixed) standard, times 

velocity of translation over the heating surface. A moment's 

reflection will make it clear that the product of the last two factors 

is at all times proportional to the mass (or weight) of gases passing 

per unit of time.

CALCULATION OF HEAT ABSORPTION ALONG A FIBE TUBE.

As an illustration of the method of-using formula 9, a numerical 

example applied to the hypothetical boiler having a single tube of 

0.1 feet internal diameter and 10 feet long is given below.

Assume that 1 pound of carbon is burned in 3,230 seconds with 

25 per cent of excess of air. This is the same condition as given by 

the second line in the preceding table, case 1:

W = 0.00547 pound. 

@0 = 3,216° "F.

_d

Substituting these values, and also the value of (1 e D)for this 

particular boiler as calculated above, in equation 9, H = W 00

cl

(1 e ~ D )X0.24, the heat absorbed becomes 

H = 0.00547 X 3,216 X 0.7705 X 0.24-3,253 B. t. u.
A STUDY OF POUR HUNDRED STEAMING TESTS.

Instead of using formula 9, which has been derived by calculus, 

the amount of heat absorbed by the single- tube boiler can be approximately obtained by applying in steps the fundamental principle 

expressed by equation 5, H = Cvp (T t). Let the length of the tube 

be divided into twenty parts, and the heat absorbed by each part 

calculated by the above equation. Before these calculations can 

be made the constant C must be determined. This can be done by 

substituting in equation 9 the value of 0.5 for 1, the already calculated .value 0.0147 for c; and also the values of W and & of case 2 in 

the table (p. 120) and solving for H. This will be the heat absorbed 

by the first half foot of the tube. Substituting this value for H in 

equation 5 and also the calculated values for velocity, density, and 

the excess of temperature of the gases from tables on pages 115 and 

120, and solving, we determine the value. of C:

0.0147X0-5

(9) H = 0.00547X3,216 (l-e~ 1 )X0.24 = 0.291 

(5) 0.291=3,216X19.45X0.1955X0,

and hence

0 = 0.0000238.

This procedure of determining the value of C had to be employed 

in order to put the two methods of calculating the heat absorbed 

on the same basis, making them comparable.

As 0.291 B. t. u. was absorbed from the gases by the first half foot.

0 291 the temperature was reduced Q 24 x Q QQ547 = 222° F.; the elevation

of temperature above that of boiler water at the entrance to the next 

or second half foot of the tube = (3,216° -222°) =2,994° F.

The absolute temperature corresponding to 3,216° above steam 

temperature = 3,216 + 320 + 461 = 3,997° F. Likewise the absolute 

temperature corresponding to 2,994° F. above steam temperature 

= 2,994° + 320° + 461° = 3,775° F. Therefore the new velocity of the

3 775 

gas at entrance on the second half foot of the tube is e/nny X 19.45 =

18.38 feet per second, inasmuch as the velocities are directly proportional to the volumes. Likewise the new relative density is

3 997 0 ' _ x 0.1956 = 0.2070. It will be noticed that the simultaneous 3,775

changes in velocity and density neutralize each other, but both are 

carried through the calculations for the sake of the principle.

To go back to the fundamental principle, the amount of heat 

absorbed by the second half foot is equal to 2,994 X 18.38 X 0.2070 X 

0.0000238 = 0.272 B. t. u.; and so on for each of the remaining 

eighteen half feet of the tube. On adding together all the partial 

H's the sum is 3.214 B. t. u., which is close to the value 3.253 obtained
HEAT ABS6B£»±I6ff Atfft SOILED 123

o

by calculus. The step-by-step and calculus curves are both shown 

on the chart (fig. 58). The areas under these curves do not represent 

anything; the vertical ordinates to the curves merely denote for each 

small length the number of B. t. u. absorbed in that length.

On the same chart (fig. 58) is also given a curve obtained by calculus showing the amounts of heat absorbed per second when the 

same quantity of carbon is burned with 100 per cent of air excess.

For the sake of clearness it is stated again that the step-by-step 

process was merely an approximate arithmetical method of integrating the formula 

H = B. t. u. absorbed for length under consideration = '

*fc

Mas

ILSfe

.TANCE AL-ONS TUBE, IN rAT

FIG. 58. Relative B. t. u. absorbed at different points in a boiler tube 10 feet long and 0.1 foot internal 

diameter: Curve No. 1, calculated by calculus, using 25 per cent of air excess; No. 2, calculated by 

steps, using 25 per cent of air excess; No. 3, calculated by calculus, using 100 per cent of air excess

The arithmetical method gives results about 1 per cent smaller in 

this individual case than the integration by calculus.

Inasmuch as an illustration has been given showing how closely 

(within about 1 per cent) the arithmetically calculated absorption of 

heat agrees with the more correct value calculated by calculus when 

the carbon is burned with 25 per cent excess of air, the arithmetical 

calculation was not repeated for 100 per cent excess of air. The 

curves of heat absorption and of drop of temperature along the length 

of the boiler tube, 0.1 foot internal diameter and 10.0 feet long, are
A STUDY OF FOUB HUNDBED STEAMING TESTS.

given in figs. 58 and 59. It will be noticed that the total heat absorbed is 3.0866 B. t. u., which is only 5.2 per cent less than with the 

smaller air supply. This result is an illustration of the statement 

that a boiler will absorb about the same percentage of the heat of a 

pound of fuel completely burned, whatever the air supply per pound 

of fuel, if the variation is within reasonable limits.

The curves of temperatures along the tube, when using 25 and 

100 per cent excess of air, shown on fig. 59 (p. 125), were obtained 

as follows: Those on the step-by-step curve were taken directly from 

the column headed " @0 " in the following table:

Heat absorption along a hypothetical boiler tube, by sections, at 25 per cent of air excess.

Half foot:

Third......................................

Fifth......................................

Eighth ....................................

Twelfth ...................................

- Thirteenth ................................

Initial minus 

boiler-water 

temperature 

<°F.). 

®o

3,216

2,994

2,787

2, 595

2,416

2,250

2,095

1,951

1,861

1,691

1,574

1,465

1,364

1,270

1,183

1,102

1,026

955

890

829

772

Velocity of 

gas at entrance to 

each section 

(feet per 

second)."

V

19.45

18.38

17.38

16.45

15.59

14.80

14.06

13.36

12.70

12.12

11.55

11.02

10.54

10.09

9.65

9.26

8.89

8.54

8.26

7.97

Density of 

gas at entrance to 

each section. 

Gas at 

320°= 1. 

P

0. 1956

.2070

.2189

.2312

.2440

.2571

.2709

.2850

.3000

. 3149

.3301

.3460

.3620

.3780

.3950

.4110

.4290

.4460

.4590

.4760

Partial heat 

absorbed 

(B. t. u.). 

H=®xvX 

PXC.6

0.291

.272

.252

.236

.218

.203

.190

.177

.165

.154

.143

.133

.124

.115

.107

.100

.093

.086

.080

.075

3.214

« Weight of gases per second in pounds= 3030 =0-00547. 

» Constant=0.0000238.

The five points on the curves obtained by calculus were located by 

using formula 8 for five lengths of tube, 0 to 2 feet, 0 to 4 feet, 0 to 6 

feet, 0 to 8 feet, .and 0 to 10 feet.

HIGHER INITIAL TEMPERATURE MEANS HIGHER FINAL TEMPERATURE WHEN 

HEAT ABSORPTION IS BY CONVECTION ONLY.

Regarding the two curves of temperature changes along the length 

of the hypothetical boiler tube when using 25 per cent and 100 per cent 

excess of air, it appears that however long the tube might be, the upper 

temperature line would never meet the lower one, and would never 

cross it. This statement is also borne out by a consideration of the 

mathematical equation on which the curves are based. It is in direct 

contradiction to a statement often made that the higher the initial 

temperature the lower the final, provided the amount of heat liberated
HEAT ABSORPTION AND BOILER EFFICIENCIES. 125

per unit of time is the same in every case. For many months most 

of the authors of this bulletin thoroughly believed this idea, and it 

was only when they took many cases and tried to plot the relations 

between combustion-chamber and stack temperature that they saw 

the two rise and fall together. Later on the work of Perry on the 

boiler as a heat absorber was developed and it was realized that the 

facts, at the testing plant at least, agreed somewhat with the theory 

and pointed in the right direction. In this connection it must be 

remembered that a lower flue temperature does not always indicate a 

lower B. t. u. loss, but generally a larger one, because the mass of 

gases is more than enough larger to make up the difference; but in 

any one boiler the net difference is usually within 5 to 15 per cent.

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OI3TANCC XVl-ONG TUBE IN FCBT

FIG. 59. Relative temperatures of the products of combustion passing through a boiler tube 10 feet 

long and 0.1-foot internal diameter: Curve No. 1, calculated by steps, using 25 per cent of air excess; 

No. 2, calculated by calculus, using 25 per cent of air excess; No. 3, calculated by calculus, using 100 

per cent of air excess.

MODIFYING FACTORS OF THE THEORY OF HEAT TRANSMISSION.

In the section on the theory of heat transmission the assumption 

was made that the gas comes directly into contact with the metal 

surface of the boiler flue, and also that the water in the boiler absorbs 

the heat as fast as the metal can transmit it. In a commercially 

operated boiler neither of these assumptions is true. The metal of 

the boiler flue is insulated from the gas with a layer of soot, and from 

the water with a layer of scale and, perhaps, a layer of steam. As 

these layers of soot, scale, and steam are very poor conductors, a resistance many times greater than that of the metal of the boiler tube itself 

is offered to the passage of heat. It is evident that under such conditions the difference of temperature between the first layer of gas and
126 A STUDY OF FOUR HUNDRED STEAMING. TESTS.

that of the first layer of water must be greater than it would have 

to be if the insulating layer of soot, scale, and steam were not present, 

in order that the heat should flow from the gas to the water at a certain desired rate. This temperature difference must, be larger the 

greater the required rates of heat transmission and the thicker .the 

insulating scales. Inasmuch as capacity is the rate of heat absorption, this explains why at higher capacities the gases leave the heating surface of a boiler at higher temperatures than they do at lower 

capacities. It is clear, then, that in order to have the heating surface 

efficient it must be kept free from soot and scale, and the bubbles of 

steam must be removed from the surface as fast as they form, so that 

the water can come directly into contact with the metal. This lastrequirement emphasizes the importance of water circulation in the 

boiler. The faster the circulation of water the faster are the bubbles 

of steam carried away and the better is the contact between the 

metal and the water.

It is reasonable to expect that in the Heine boiler when the capacity is increased the rate of circulation of water should be increased 

in about the same proportion, in order that the metal surface maybe 

kept free from steam bubbles. To what extent this is true is shown 

in the chart (fig. 7, p. 16) that gives the relation between the circulation of water in a water tube boiler and the capacity.

The effect of the above-named modifying factors that is, the 

resistance offered to heat passage by soot, metal, scale, and steam 

is to increase the temperature difference between the outside surface 

of the adhering gas film and the film of water coming into contact 

with the steam layer when the rate of heat transmission that is, the 

capacity increases. By taking into consideration these factors, and 

also the fact that the adhering film of gas does not consist of a layer 

1 molecule thick, but has a sufficient thickness to offer an appreciable 

resistance to the passage of heat through it, a formula similar to that 

whose derivation is shown on pages 110 to 112 can be obtained that 

.will agree very closely with the actual peiformances. Fig. 60 gives the 

temperature gradient of the moving gases and also the temperature 

gradients along the surfaces of contact of the different resistanceproducing layers. Let dl be any elementary length of the heating 

surface; T tl the temperature difference between the moving gases 

and the outside surface of the adhering film of the gas, and tx t the 

temperature difference between the latter and the water film coming 

into contact with the layer of steam. The temperature differences 

between the individual layers are expressed by a b, b Cj etc., as 

shown in the figure. The heat transmission from the moving gases 

at the temperature T to the adhering immovable film at the temperature tj occurs by convection, according to the relation expressed by 

equation 1, H = Cpv (T tx ), and the heat transmission from the
HEAT ABSORPTION AND BOILER EFFICIENCIES. 127

gas film through the layers of gas, soot, metal, scale, and steam into 

the water at temperature t occurs purely by conduction, and follows 

the law expressed by equation 12:

I= k(t -t)

where k is the average conductivity for heat of the materials comprisk . ing the layers and b their total thickness. As r- is a constant, H

varies only with the value of (tt t).

If the rate of heat impartation by convection is higher than the rate 

of transmission by conduction, the heat will accumulate in the resistTHICKNESS OF LAYERS » 

abcdef- TEMPERATURE

FIG. 00. Diagrams illustrating temperature gradients of moving gases. The diagram at the left represents qualitatively the successive temperatures along the line of travel of gases through a boiler 

(ire tube. The diagram at the right shows, qualitatively, the temperature gradients between gases 

and water at point T of the left diagram.

ing layers on the gas side and tj will rise. The rise of ti will decrease 

the rate of heat impartation by convection and increase the rate of 

heat transmission by conduction. The opposite will occur if the rate 

by convection is lower than the rate by conduction. There is a constant equalization of the two rates, so that equations 1 and 12 can be 

written as follows:

The heat transmitted per second by any portion of the heating 

surface is then expressed by equation 1, H = Cpv(T tj, in which 

T and tt are variables, T depending on the conditions of combustion
128 A STUDY OF FOUR HUNDRED STEAMING TESTS.

and the rate of heat impartation, whereas tt depends on the rate of 

heat impartation only. From equation 12 

Substituting this value for ^ inequation 1, and simplifying, we get 

equation 14:

- cp(T-t)

Let W be the weight of gases passing the heating surface per

C'

second, then as p = ~ and v = C" W T; C p v = C: W, where C^ is a new

constant. 

Let Cx j- = K, and (T t)=©; on substituting these values in

.K

equation 14 it becomes 

f! Wf) (15) H = '

{ } 1+KW.

and the heat absorbed by any elementary length of heating surface

P W@

per second is Wd@ = 1 TT W dl, or 

(16) d@ - Oi dl 

^ ; @ i + KW

On integrating equation 16, there results 

When 1 = O, loge @0 = K. Hence

loge©-loge@o= ~

whence 

Gil

(17) @=00 e I+KW

The heat absorbed by the length of heating surface equal to 1 is 

di

(18) H = 0.24W00 l-e I+KW

and the true efficiency of the heating surface is 

Gil

(19) E = l-e I+KW.

Equation 19 states that the true efficiency of the heating surface is 

independent of the initial temperature of the gases so far as heat 

absorption by convection is concerned and that it decreases when the 

weight of gases passing over the heating surface increases that is, 

when the capacity increases. The constant K depends on the condi-
HEAT ABSORPTION AND BOILER EFFICIENCIES. 129

tion as regards cleanliness of both sides of the heating surface. If 

there were no resistance to the passage of heat, K would be equal to 

0, the denominator would reduce to 1, and equation 19 would be the 

same as equation 10, D being constant in any one boiler, fixed once 

for all by the maker.

It is probable that the film of gas which is -entangled in the rough 

sooty surface is of considerable thickness and that rather a large part 

of the resistance to the passage of heat is perhaps clue to this film. It 

is also very likely that as the velocity of the gases increases their 

scrubbing action reduces the thickness of this film. This probably 

again adds to the importance of the velocity of gases along the heating 

surface.

The influence of the velocity of gases on the thickness of the film 

has not been taken into consideration in the derivation of equation 

18. It would somewhat lessen the effect of W on the true efficiency; 

that is, it would make the true boiler efficiency more nearly constant 

for all rates of working.

The velocity of circulation of water in the boiler is equal in importance to the velocity of the gases on the outside of the heating surface. 

The same mathematical reasoning can be applied to the influence of 

velocity of gases on the impartation of heat. The amount of steam 

formed increases directly with the rate of heat transmission, and if the 

scrubbing action of the circulation of water is insufficient to remove 

it from the heating surface the resistance due to the layer of steam 

formed will rise with the rate of making steam. Lack of adequate 

circulation of water in a boiler is a check to capacity. The fact is 

becoming well known that small automobile boilers are making steam 

ten to twenty (or even more) times as fast per unit of heating surface 

as stationary boilers in power plants, and at better efficiency. This 

increased rate of steaming is attained purely by high velocit}r of water 

and steam circulation over the heating surface.

Formulas 17, 18, and 19 apply only to heat imparted to the boiler 

by convection and conduction. The heat which is received by radiation perhaps follows nearly the radiation law of Stefan and Boltzmann, expressed by equation 20,

(20) H = C (T4 -V),

where T is the absolute temperature of the heat-radiating body, tt 

the absolute temperature of the heat-receiving body, and C a constant.

In the case of a boiler, tj is the temperature of the outside layer of 

soot on the heating surface, and is a variable, depending on the rate 

of heat transmission through the sooted and scaled boiler plate. The 

heat transmitted through the boiler plate is given by equation 12,

H=i-(t1 t). As the heat transmitted through the boiler plate is 

§400 Bull, 32o 07 9
130 A STUDY OF FOUR HUNDRED STEAMING TESTS.

equal to the heat received by the surface of the plate by radiation, 

equations 12 and 20 can be written as follows:

C (T*-t1 *) = H = ^(t1 -t).

On substituting the value of tj from equation 12 in equation 20, the 

latter becomes 

(20) H = C[~T4 - (H

This is an equation of the fourth degree, and the value of H can be 

obtained by the method of approximation.

By the use of equations 18 and 20 it is possible to obtain the total 

heat absorbed by any boiler and its true efficiency. However, 

before the equations can be used the constants in them must be determined for any particular boiler. The four constants in the two equations were determined for the Heine boilers at the fuel-testing plant 

in this way : Four specific cases were selected from the results of 

boiler trials and from the resulting equations ,the values of the constants were approximated. The two equations applied to these 

Heine boilers are 

(18) HC = 0,24W@0 (i- e ~ i+5:^iw), and

H = __ FT4 -

r 540 + 101

where t at 80 pounds gage pressure is 785° F. absolute and @0 is T t, 

T being the actual absolute temperature in the furnace in degrees 

Fahrenheit; Hc the heat received per second by the boiler by convection and conduction; Hr the heat received per second by radiation from the brickwork, etc., of the combustion chamber; and W 

the weight of gases in pounds passing over the heating surface per

second. Within the workable temperature range from 2,461° to 

3,361° F. absolute, Hr is obtained with fair accuracy by the simple 

straight-line equation 

(21) Hr = 0.14.41-294.

The per cent of heat received by radiation referred to total heat 

available is 

.OON -a (0.144T-294)X100

{ } r 0.144l-294 + 0.24W00

and the per cent of heat received by convection referred to total 

heat available is 

2.7

(23) Ec = 100 (1-e 1+0- 1524W )X(l-Er).

The true boiler efficiency is then expressed by equation 24:

(24) E4 = Er + Ec . 

Heat which is radiated to the boiler during the combustion of fuel 

is not sensible heat, because it does not raise the temperature of the 

gases. This is the reason why the heat radiated is added to the
HEAT ABSOKPTION AND BOILEK EFFICIENCIES. 131

heat in the gases at the temperature T to obtain the total heat available for the boiler. Er has been calculated by formula 22 for five 

values of W and the results are plotted on the lower part of fig. 61. E \ ' ' 

^has been calculated by equation 23 and the results are plotted on the upper part of fig. 61. The true efficiency of tnese par77 79 81 63 BS 

PER CENT OF HEAT RECEIVED BV CONVECTION

£561 Z76I 2961 3161

AVERAGE ACTUAL. TEMPERATURE. IN FURNACE (°AB6.).

FIG. 01. Relation of pounds of gases passing through boiler per second to per cent of heat received by 

convection (upper curve); also the relation between ratio of per cent of heat received by radiation to 

total heat available and the average actual temperature (degrees F. absolute) in furnace (flvc lower 

curves).

ticular Heine boilers can be obtained for any condition within the 

practice of operation by a simple multiplication and addition.

Example 1. Let 5 pounds of gases pass over the heating surface in 

a second, and let the actual furnace temperature be 2,961° F. abso-
132 A STUDY OF FOUR HUNDRED STEAMING TESTS.

lute. In fig. 61 (lower part), where W = 5 pounds and T = 2,961° F. 

absolute, Er = 4.85. In the upper curve of fig. 61, where W = 5 pounds,

E° =78.15. Then E4 = Er + Ec = 4.85 + 78.15 X (100-4.85) =

100 -li/r

79.15.

Example 2. Let W = 3 and T = 3,261° F. absolute. Then Er = 9

and ^c =84.2. E4 = Er'+ Ec = 9 + 84.2 X (100 - 9) = 85.62.

100 Ji/r

Example 3. Let .W = 5 pounds, and T = 3,261 ° F. . absolute. Then

Er = 5.6and- T, =78.15. E4 = Er + Ec = 5.6 + 78.15 X (100-5.6) = 100 sLT

80.4. .

In examples 2 and 3 the capacities are to each other very nearly 

as 3 is to 5; that is, if .the capacity is 90 per cent in example 2 it is 

nearly 150 per cent in example 3.

Equations 18 to 24 are rational formulas, and are interesting 

because they are derived purely by mathematical reasoning from 

the fundamental laws of . physics that is, the laws of convection, 

conduction, and radiation of heat. It is gratifying that the actual 

performance of two individual boilers throughout wide ranges of 

furnace temperature and rates of combustion has been very closely 

approximated by a formula based on fundamental principles of physics the laws of the kinetic theory of gases and liquids and of the 

transfer of heat by conduction and radiation.

TEMPERATURE TEST OF PERRY'S EQUATION.

For the purpose of testing Perry's equation, that "The temperature 

above boiler water of the gases entering a boiler = the temperature 

above boiler water of gases leaving the boiler, times a constant," 

all tests on which approximate combustion-chamber temperatures 

were taken by a Wanner optical pyrometer were used a total of 215 

tests. For convenience, the temperature of the water in the boiler 

was assumed to have been always 317° F. This temperature varied 

5° or 6° in different tests. The resulting constants, which ranged 

from 4 to 14, were collected in groups, showing that two fall between 

4.5 and 5, six between 5 and 5.5, nineteen between 5.5 and 6, etc. 

These relations, plotted on the chart (fig. 62) , show that the peak comes 

at 7.25; the arithmetical average of all the values is 7.43. It will be 

noticed on the curve that there are more high values than low values, 

whereas a true probability curve is symmetrical on both sides of the 

vertical axis.

On looking up the high values, especially those between 10 and 10.5, 

the average point of which is rather high, it is found that they belong 

to tests having flue temperatures that are suspiciously low for various 

reasons. But leaving in this point and casting out the six tests hav-
HEAT ABSORPTION AND BOILER EFFICIENCIES. 133

ing the highest values of the constant (all of which have the suspiciously low flue temperatures), the remaining 209 tests average 7.3 

about the same value as that of the peak of the curve.

This means that if the excess of combustion-chamber temperature 

above steam temperature be divided by 7.25 the quotient will be the 

probable excess of flue temperature above steam temperature. This

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O OF TEMPERATURES (°F)OF COMBUSTION CHAMBER MINUS STEAM TO FLUE GAS MINUS STEAM

FIG. 62. Classification on basis of ratio of temperatures of combustion chamber minus stearn to flue 

gas minus stearn: Curve No. 1, probability curve of ratio (maximum point, 7.25); No. 2, relation of 

ratio to combustion-chamber temperature (°F.1.

result is now to be compared with the "true boiler efficiency/' which 

was tentatively found to be 82.7 per cent. The calculation to be 

made assumes that the specific heat of the gas mixture is constant up 

to 2,500° F., which is probably not true. It is also assumed that no 

cold air leaks into the gas stream between the entrance to the boiler 

and the flue, which we know is far from true.
1.34 A STUDY OF FOUR HUNDRED STEAMING TESTS.

On the assumption that the initial temperature of the gases is 2,500° 

F., this is 2,500°-317° = 2,183° F. above steam temperature; 2,183° 

divided by 7.25 = 301° F. the probable excess of flue temperature over 

boiler-water temperature. Now, out of the maximum possible 2,183 

B. t. u. that might be absorbed by a boiler from each 4.15 or CoiT ) 

pound of furnace gases, this boiler absorbed 2,183 301 = 1,882 B. t. u., 

which is 86.2 per cent of 2,183. That is, the true boiler efficiency calculated from initial and final temperature of gases is 8.6.2 per cent, 

which is fairly close to the 82.7 per cent found above.

Into this method of calculating the "true boiler-efficiency constant" 

there enter two errors, which will be roughly corrected in a specific 

calculation. The combustion-chamber temperature, as read by the 

optical pyrometer, is known to have been usually low. In this calculation it will be assumed that the pyrometer read 100° low, making 

the true initial temperature 2,600° F.; also it will be assumed that the 

air which leaked through the r etting amounted to 20 per cent in mass 

of the gases which entered the boiler, which is an approximately true 

average, and that all of this air entered the stream of gas after leaving 

the boiler and before reaching the flue thermometer, which is not true.

The initial temperature is 2,600°-317° = 2,283° F above steam 

temperature. If we use the old constant, 7.25, the flue temperature 

should be 2,283° F. -T- 7.25 = 315° F. above steam temperature, which 

would make the flue temperature 632° F., say 630°. Remembering 

that this 630° is the result of the cooling of the gases by the boiler and 

also of the addition of cold air at 60° F. to the extent of 20 per cent, 

we can calculate that the flue temperature would have been about 

768° F. had this admixture not occurred. Subtracting 317° from 

768°, we have left 451° F. Thus out of the maximum 2,283 B. t. u., 

which a boiler might possibly be built to absorb from every 4.16 

pounds'of gases, this boiler absorbs 2,283 451 = 1,832 B. t. u., which 

is 80.3 per cent of 2,283. That is, the true boiler efficiency thus 

approximated by initial and final temperature of furnace gases is 80.3 

per cent; before correction it was 86.3 per cent. The mean is close to 

the value 82.7 found by the entirely different heat-balance method.

RATIO MODIFIED IN PRACTICE BY INITIAL TEMPERATURE.

The lower curve of fig. 62 (p. 133) was formed for all the individual 

tests from the same ratios as the. upper curve! The ratios of excess 

of furnace temperature to excess of flue-gas temperature were all 

plotted preliminarily on a sheet of coordinate paper, and the average 

value of the ratios falling in each horizontal temperature strip 50° 

wide was determined. These average values are given by the positions of the small circles, the number beside each giving the number 

of tests falling in that horizontal temperature strip. It will be noticed 

that the heavy line, drawn through the points from these averages
HEAT ABSORPTION AND BOILER EFFICIENCIES. 135

with regard to their respective weights, slopes upward to the right 

that is, with the higher furnace temperatures the boilers absorb a 

slightly larger portion of the heat available to them, only that heat in 

the gases which is above steam temperature being considered as available. The dotted line marks the boundary of the field covered by the 

individual ratio points.

As a numerical example let us take two cases and figure backward 

from the ratios to the "true boiler efficiencies."

Case 1: From the curve (the lower one) we see that when the temperature of the combustion chamber minus steam temperature equals 

1,700° F., the ratio averages 7.0. Dividing 1,700° by 7.0, we get 243°, 

the average excess of the flue temperature above steam temperature 

at this initial-temperature excess.

1.700-243 oc ' , . i -i a, 

 ' = 85.7 per cent = true boiler efficiency.

Case 2: From the same curve take initial temperature excess = 

2,400° F.; the ratio is 8.2; 2,400 -v- 8.2 = 293°, the average excess of flue 

temperature over steam temperature under these conditions.

' ~, ' = 87.7 per cent = true boiler efficiency.

The value in the first case was 85.7 per cent. The second case then 

gives an increase of 2 per cent of the heat which could possibly be 

absorbed.-

One tentative explanation of this slight increase of efficiency at 

higher temperatures is that the boiler absorbs heat not only by convection from the gases among its tubes, an action to which Perry's 

tentative theory is applicable, but also, more or less, by radiation from 

the bottom and sides of the combustion chamber onto the bare tubes 

in the rear, where the gases leave the combustion chamber. This 

radiation does not increase directly with the furnace temperature, but 

varies as the difference of the fourth powers of the absolute temperatures of the radiating and receiving bodies. That is, if TF represents 

the absolute temperature of the furnace walls "visible" to the exposed 

tubes, and TT the absolute temperature of the outer surface of the 

cold tubes, the heat absorbed by the tubes due to radiation is proportional lo (TF4 TT4 ). It is easily seen that inasmuch as TT is 

practically constant, changes in TF will change the value of the 

parenthesis a great deal. Consequently, as the temperature of the 

combustion-chamber walls rises the amount of heat absorbed by the 

exposed portion of the lower row will increase much more rapidly; and 

though this heat is only a part of the total heat absorbed by the whole 

boiler, its rapid rate of increase may raise the "true boiler efficiency" 

a little.

The lower curve of fig. 62 (p. 133) bends to the right as it ascends. 

If the radiation increased directly as the temperature difference
136 A STUDY OP FOUR HUNDRED STEAMING TESTS.

between the furnace walls and bare tubes, the line might well be 

straight; but as it increases according to the fourth-power law, the 

curve should bend to the right.

Thus by two entirely different and independent methods we have 

arrived at the conclusion that the true efficiency of these boilers is 

nearly constant. These methods are the heat-balance method described on pages 139-141, and the excess-temperature-ratio method 

just given. On pages 143-145 another independent method arriving at

FIG. 63. Relation between ratio of furnace temperature minus steam temperature to flue-gas temperature minus steam temperature and per cent of rated capacity, based on varying values of furnace 

temperature minus steam temperature.

the same conclusion is given, with the additional refinement that true 

boiler efficiency increases slightly not only with increase of furnace 

temperature, but also with decrease in the amount of steam made. 

It must be distinctly understood that all these ideas are advanced 

tentatively only, as another attempt to separate furnace and boiler. 

The indication that the true boiler efficiency is so nearly constant 

and so little affected by initial furnace temperature is gratifying, as
HEAT ABSORPTION AND BOILER EFFICIENCIES. 137

suggesting that some such formula as Perry's must be nearly correct. 

Thus encouragement is given to the hope that there is a way to determine once for all one constant boiler efficiency, from which we can 

calculate backward and obtain the combustion efficiency or per 

cent of completeness of combustion the vital point in fuel testing. 

This applies only to boilers obtaining their heat by convection, not 

by radiation.

Fig. 63 is based on exactly the same data as those of fig. 62 (p. 

133), which are elsewhere explained. It is intended to show the relation of flue-gas temperature to capacity when the furnace temperature remains nearly constant. The tests were arranged in six groups 

in such a way that the variation of the furnace temperature was less 

than 100° F. in each group.

The tests in each of these groups were then classified on the basis 

of the ratio of temperature of furnace minus that "of steam to temperature of flue gas minus that of steam, and this ratio was plotted 

against the average capacity of each class.

The curves show a general tendency of the capacity to rise with 

the low-temperature ratios. This is in accordance with equation 17; 

as the furnace temperature remains nearly constant, higher capacities are obtained by increasing the weight of gases passing over, the 

heating surface-per second. The. increase of the weight of gases 

causes, according to equation 17, the rise in flue-gas temperature.

In other words, this rise, of flue-gas temperature is probably due 

to two causes: (1) When more heat is put through the outer gas 

film, soot, metal, scale, and inner steam film or bubbles the temperature gradient must necessarily be steeper, and since the conductivity 

of all these layers except the metal is low, the rise of temperature of 

the outer soot layer and its entangled gases may be several hundred 

degrees, whence it becomes a less active heat absorber, and consequently the gas escapes at a higher temperature, so that the efficiency of the boiler is less. (2) As shown in fig. 7 (p. 16), the circulation of water does not keep up to requirements, so that the steam 

film on the scale becomes thicker, or more of the surface is covered 

with bubbles, which again makes the boiler a poorer heat absorber.

A CONCEPTION OF BOILER AND FURNACE EFFICIENCY. 

THE CODE FORM AND A REVISED FORM OF HEAT BALANCE.

The "boiler efficiency" given in the A. S. M. E. code as item 72* 

is the ratio of the heat absorbed in the boiler and carried away in the 

steam to the highest possible amount of heat that could be generated 

in the furnace. The denominator of this ratio is calculated by subtracting from the total pounds of "combustible" fired the number of 

pounds of combustible in the ash and multiplying this difference by 

the calorific value of 1 pound of "combustible."
138 A STUDY OF FOUR HUNDRED STEAMING TESTS.

The efficiency represented by code item 72* is, then, the over-all 

efficiency of the whole steam-generating apparatus, as combustible 

found in the ash is considered as if it had never been fired. It often 

happens that, on account of incomplete combustion, the quantity of 

heat represented by the denominator of the above ratio is not really 

developed in the furnace. Carbon monoxide in the analysis of the 

stack gases is one indication of this incomplete combustion.

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FIG. 64. Relation of unaccounted-for loss, including radiation loss (upper curve) to boiler efficiency 

(code item 72*); and availability of heat to a boiler, as affected by changes in air supply to fuel 

(lower curve). 

The ratio of the heat that is actually generated in the furnace to 

the maximum amount of heat that could be developed may be called 

the efficiency of the furnace or the furnace efficiency. The ratio of the 

heat absorbed by the boiler and carried away in steam to the heat 

actually generated from the burning of the fuel may be termed the 

boiler efficiency, and represents the ability of the boiler to absorb 

heat under given conditions. The efficiency given by code item 72* 

is the product of the boiler and furnace efficiencies as above denned.
HEAT ABSORPTION AND BOILER EFFICIENCIES. 139

Carbon monoxide is not the only resultant of incomplete combustion, although the heat lost by it is the only loss due to incomplete 

combustion that has been taken account of in the heat balance. 

The remainder of the incomplete combustion losses appear in the 

" unaccounted for." A high unaccounted-for loss, then, should be 

an indication of low furnace efficiency.

The upper curve of fig. 64 shows the relation between "boiler efficiency" (code item 72*) and the unaccounted-for loss plus radiation 

loss (heat balance, item 6). All the tests chosen for this chart have 

an average of 9 per cent or more of carbon dioxide in the escaping 

gases, which indicates that they must all have had comparatively 

high furnace temperatures. It has always been thought that when 

a high furnace temperature is maintained the boiler would absorb a 

high per cent of the heat developed in the furnace; therefore, the 

boiler efficiency as defined above must have been relatively high for 

all the tests of this chart.

It will be noticed that the sum of the ordinate and abscissa for 

any point of this curve* is constant at 77 per cent. For instance, 

when item 72* is 73 per cent the unaccounted-for loss is 4 per cent; 

sum, 77 per cent. When item 72* is 57 per cent, the unaccountedfor loss is 20 per cent; sum, 77 per cent. The curve should have 

been drawn more nearly horizontal for the low unaccounted-for 

values.

The decrease of the combined efficiency of boiler and furnace 

(code item 72*) with the increase of the unaccounted-for loss must 

then be due to the decrease of furnace efficiency.

With this idea of furnace efficiency in mind, a new form of heat 

balance, shown below, is compared with the heat balance given in 

the A. S. M. E. code.

Heat balance as given in the code.

0 Per cent.

1. Heat absorbed by boiler................................................ 60.30

2. Loss due to moisture in coal............................................ . 20 '

3. Loss due to moisture formed by burning of hydrogen..................... 4.09

4. Loss due to heat carried away in dry chimney gases...................... 14. 96

5. Loss due to incomplete combustion of carbon (CO loss)................... 2.17

6. Loss due to unconsumed hydrogen and hydrocarbons, to heating the mois- 

	ture in the air, to radiation, and unaccounted for...'................... 18.22

A revised form of heat balance.

1. Heat absorbed by boiler................................................ 60. 30

2. Loss due to moisture in coal............................................ .26

3. Loss due to moisture formed by burning of hydrogen..................... 3. 26

4. Loss due to heat carried away in dry chimney gases..................... 11. 93

5. Loss due to radiation .................................................. 3. 97

Total heat generated ................................................ 79. 72

6. Loss clue to incomplete combustion of carbon '(CO loss)................... 2.17

7. Loss due to other forms of incomplete combustion....................... 18.11
140 A STUDY OF FOUR HUNDRED STEAMING TESTS.

In the new heat balance the subtotal 79.72 represents the per cent 

of the calorific value of the fuel that has been generated. It may 

be taken as the efficiency of the furnace, or, to speak more properly, 

the per cent of completeness of combustion. The latter phrase will 

be used in this discussion for this subtotal, which is denned as the 

ratio of the heat generated by burning a unit weight of combustible 

in the furnace to the heat obtained by burning the same weight of 

combustible in the calorimeter. This efficiency is designated elsewhere in this bulletin by the symbol E3 .

The method of determining the radiation loss is given on page 143. 

It is noticed that items 3 and 4 are smaller in the revised heat balance than in .the heat balance of the code. This is because they 

have been multiplied by the per cent of completeness of combustion. 

This correction was made on the assumption that if only 79.72 per 

cent of the calorific value of tne fuel was realized, only 79.72 per 

cent of each constituent of the moisture and ash-free coal was 

burned. This may not be the state of affairs in incomplete 'combustion, but the assumption furnishes a ba'sis for calculations and 

perhaps the correction made on this assumption reduces the error 

of the calculation within the limits of accuracy of the analysis of 

the escaping gases.

In the revised heat balance the ratio of 60.30 to 79.72 is the boiler 

efficiency, which may be defined as the ratio of the heat absorbed 

by the boiler and carried away in the steam to the heat actually 

generated by the burning of the fuel. This ratio is elsewhere in this 

bulletin designated by the symbol E5 . The product of the furnace 

and boiler efficiencies is the efficiency of the boiler and furnace combined and is the same as that given in the code as item 72*. As 

explained above, this combined efficiency may be considered as the 

over-all efficiency of the steam-generating apparatus if the combustible in the ash is considered as not being fired.

As the calculations for these charts are somewhat lengthy, one 

test has been taken as an example and the calculations for it are 

given at the end of this discussion. The number of pounds of gas 

passing over the water-heating surface per hour and also the theoretical initial temperature of the gas have been calculated for each 

test. The term initial temperature is used in this paper to mean 

that temperature to which the gases would rise if it were possible to 

prevent loss of heat from them by either conduction or radiation 

until all combustion had ceased. In figuring the initial temperature 

it was assumed that the specific heat remains constant.

All the steaming tests made at the testing plant were arranged in 

groups according to per cent of rated capacity, as follows: 65 to 75, 

75 to 85, 85 to 95, etc. Then the tests of each of these groups were 

rearranged according to their'Calculated initial temperatures into the
HEAT ABSORPTION AND BOILER EFFICIENCIES. 141

following-groups: 1,600° to 1,800° F., 1,800° to 2,000° F., 2,000° to 

2,200° F., etc. Each of these 40 smaller groups was averaged for 

(1) initial temperature (calculated); (2) pounds of gas passing over 

the water-heating surface per hour; (3) percentage of rated capacity 

developed; (4) boiler efficiency (E5 ), and (5) true boiler efficiency 

(E4 ). The first four averages for each group were considered as

FIG. 05 Curves cf constant boiler efficiency (Es) and of constant capacity developed.

data of one representative test and were plotted on the chart shown 

in fig. 65, and the first three and the fifth in fig. 66.

DERIVATION OF THE CONSTANT-CAPACITY CURVES OF FIG. 65.

Each of the above forty representative tests was plotted on rec-. 

tangular axes, the theoretical temperatures being used as ordinates 

(see fig. 65) and the number of pounds of gas passing over the water-
142 A STUDY OF FOUR HUNDRED STEAMING TESTS.

heating surface per hour as abscissas. When a point was located 

it was marked with the average capacity, the number of actual testa 

that were averaged, and the average boiler efficiency E5 . (See note 

at top of the chart.) In the.upper left-hand corner there is a point 

which is marked "76.5, 2, and 88.7." This means that two tests 

were averaged, that the average E5 was 76.5, and that the average 

capacity was 88.7 per cent of the builder's rated capacity; and the 

position of the point on the chart shows that the average number 

of pounds of gas passing over the water-heating surface per hour 

was 9,300. When the forty representative tests were plotted in this 

manner it was found that lines of constant capacity could be drawn 

through these points. The lines extending from the upper left-hand 

corner to the lower right-hand corner of the chart are these constant-capacity lines. They are labeled with their respective percentages of rated capacity developed.

DERIVATION OF BOILER EFFICIENCY (E5 ).

Moisture is always present in the products of combustion, and it 

takes an appreciable amount of the heat generated in the furnace to 

convert this from water into steam. The rest of the heat generated 

goes to raising the temperature of the gases. It was found that the 

average amount of latent heat in 1 pound of the escaping gases was 

26.65 B. t. u. ; which is enough to raise the temperature of 1 pound 

of gas 111° F. In these calculations the specific heat of the dry gases 

was taken as 0.24 for all temperatures and the specific heat of steam 

as 0.48. On this assumption the same amount of he'at is used to raise 

the temperature of 1 pound of steam 1° as is required to raise the temperature of 2 pounds of dry gases 1°, so in order to use 0.24 as the 

specific heat of all the products of combustion the number of pounds 

of steam in the gases was multiplied by 2.

Let the lower curve of fig. 64 (p. 138) be one of the constant-capacity 

curves shown in fig. 65. The scale to the left of the chart represents 

the B. t. u. available for raising the temperature of 1 pound of gas 

from atmospheric to furnace temperature. The theoretical furnace 

temperatures to the right of the chart are obtained by dividing by 

0.24 the B. t. u. available for raising the temperature of 1 pound of 

gas and adding to the quotient the temperature of the atmosphere, 

which is taken as 70° F. The line CD is drawn in such a manner that 

the distance ED represents on the scale to the left 26.65 B. t. u., 

which was found to be the average amount of latent heat in 1 pound 

of furnace gas. The area ABCD represents the total heat generated in 

the furnace; the area CDEF shows the latent heat in the gases and the 

area ABEF shows the heat available for raising the temperature of EF 

pounds of gas from 70° F. to the initial furnace temperature A. Since 

the curve is one representing constant capacity, the heat absorbed
HEAT ABSORPTION AND BOILEE EFFICIENCIES. 148

by the boiler in all tests on this curve will be a constant and this 

constant divided by the area ABCD will be the boiler efficiency E5 

for the point B. 'By using the ratio of the constant heat' absorbed 

by the boiler to the area ABCD, those positions of B which represent 

efficiencies 61,62, and 63 per cent, etc., were found. By this means lines 

of constant-boiler efficiency (E5 ) were found and drawn on the chart 

(fig. 65). It will be noticed that the efficiency of the plotted points 

generally falls within about 1 per cent of their allotted position as 

determined by these constant-efficiency lines.

DERIVATION OF TRUE BOILER EFFICIENCY (E4 ).

The constant-capacity lines are of the form xyn = constant, where 

x = number of pounds of gas passing over the water-heating surface 

per hour and y = the calculated initial temperature. The curves 

are all asymptotic to the lines x = 0 and y = 325° F. (See fig. 64.) 

The temperature of the steam in the boiler at about 80 pounds pressure is 325° F. Now, if the boiler were infinitely long and there 

were no heat lost in radiation, the boiler could never cool the gases 

below a temperature of 325° F. In other words, only the heat represented by the area ABGH is available to the boiler. The ratio of 

the heat absorbed by the boiler and carried away in the steam 

(which is constant for any point on the constant-capacity line) to the 

heat available for the boiler, area ABHG, has been termed the trueboiler efficiency (E4 ). (This definition of E4 differs very slightly 

from the one finally chosen, for which see glossary, p. 182.)

This efficiency E4 has been calculated for each test and the method 

used is shown with the other calculations on page 145. The chart 

shown in fig. 66 is similar to that of fig. 65 in every respect except 

that E4 is used instead of E5 .

METHOD OF ESTIMATING RADIATION.

It was necessary to devise some method for estimating the radiation losses in order to calculate the per cent of completeness of combustion (E3 ). The method used was very crude and was based on 

the following reasoning:

The radiation from the top of the boiler drum and the front and 

rear water legs is very nearly constant and was determined as follows: 

With no fire under the boiler the uptake was closed by laying boards 

across the opening at the base of the stack and covering them with 

cement. This prevented any air from going up the stack. The fire 

doors and ash pit were bricked up to prevent air from entering the 

setting. After drawing the water out of the boiler it was filled with 

steam from another boiler carrying 80 pounds pressure. This pressure was maintained until the temperature in the combustion chamber became constant. The amount of condensed steam per hour was
144 A STUDY OF POUR HUNDRED STEAMING TESTS.

then weighed and was taken as a measure of the heat radiated per 

hour. The radiation from the brick setting and fire doors was considered to increase with the capacity. When the boiler developed 90 

per cent of its rated capacity the variable radiation was taken as threefifths and the constant radiation as two-fifths of the total heat radiated. 

The increase of the variable radiation with capacity was such as to

NOTE THE NUMBERS BY THE POINTS 

AffE ARRANGED IN THE, FOLLOWINO

ORDER:

TSUE BOILER EFFICIENCY 

"NUMBER OF TESTS. AVERAOED

FIG. 66. Curves of constant true boiler efficiency (BO and of constant capacity developed.

make the total B. t. u. radiated per hour 395,000 at 50 per cent of the 

rated capacity and 500,000 B. t. u. at 120 per cent of the-rated capacity. A chart (not given here) was drawn having B. t. u. radiated per 

hour as ordinates and per cent of the rated capacity developed as 

abscissas, and the two above points were plotted on it. By connect-
HEAT ABSORPTION AND BOILER EFFICIENCIES. 145

ing these points with a straight line the B. t. u. radiated per hour 

could be estimated for any capacity.

The heat required to change 1 pound of water at 70° F. to steam at 

212° F. = (212 - 70) X1 + 966 = 142 (0.48 + 0.52) + 966 = (0.48 X142) + 

(0.52 X142) + 966 = 68 + 74 4- 966 = 68 +1,040.

The heat required to raise 2 pounds of dry gas from 70° F. to 212° 

F. = (212-70)X0.24X2 = 68.

It is evident from the above that 1,040 more B. t. u. are required to 

change 1 pound of water from 70° F. to steam at 212° F. than are 

required to raise 2 pounds of gas through the same range of temperature. However, at any temperature above 212° F. the same amount 

of heat is required to raise the temperature of 2 pounds of gas 1° F. 

as is required to raise the temperature of 1 pound of steam 1° F. 

Therefore in calculating the total heat and the initial temperature of 

the gases, 1 pound of water may be considered as the equivalent of 2 

pounds of dry gas, provided that in the case of the 1 pound of water 

account is taken of the 1,040 B. t. u. which are not available for raising temperature.

The following calculations were made on test 216, the heat balance 

of which is given on page 139:

Calculations based on test 216 to deduce a better heat balance.

Per cent of completeness of combustion (E3 ): Per cent. 

Per cent of rated capacity developed................................. 103

.Calorific value of 1 pound of "combustible" taken as................... 100

A. Heat absorbed by boiler (heat-balance item 1)...................... 60. 30

B. Heat carried away in moisture of coal (heat-balance item 2)......... .26

C. Heat carried away in moisture formed by burning hydrogen (heatbalance item 3)......................................... (4. 09 H-100XE3)

D. Heat carried away in dry gases (heat-balance item 4)....... (14. 96-^100xE3 )

E. Heat lost in radiation............................................ 3. 97

E3 (per cent of calorific value of fuel that has been generated.)=A+B-|-

C+D+E....................................................... 79.72

Boiler efficiency (E5 )=AXlOO-^-E3 ................................ 75. 64

Total pounds of equivalent dry gas passing over water-heating surface per

hour: Pounds. 

F. Moisture in coal for every pound of "combustible" (figured from

proximate analysis)........................................... 0. 03

Hydrogen per pound of '' combustible " (ultimate analysis)........; . 0543

G. Moisture formed by burning of hydrogen=9X0.0543XE3 .. ..'.....'.. ,39

H. Total moisture in gases formed from 1 pound of " combustible " =

F+G......................................................... .42

Dry gas per pound of "combustible," assuming E3 =100 (figured 

from gas analysis)............................................. 18. 35

I. Actual dry gas per pound of "combustible" as fired=18.35XE3 ^... 14. 63 

J. "Equivalent" dry gas per pound of "combustible" as fired =

I+(2XH) (see discussion of calculations)........................ 15. 47

Total combustible ascending from grate per hour (code item 47*).... 775. 0

Total equivalent dry gas passing over the water-heating surface per 

hour=15.47X775.0............................................. 11, 990

8400 Bull. 325 07 10
146 A STUDY OF FOUR HUNDRED STEAMING TESTS.

Heat in gases below 325° F. (steam temperature): B. t. u. 

K. Heat in the gases, from 1 pound of "combustible," which is unavailable

for raising temperature=HXl,040 (see discussion of calculation).. 437 

L. Heat required to raise the temperature of gases formed from 1 pound

of'' combustible " taken from 70° F. to 325° F. = J X 612.......... 947

M. Total heat below 325° F. in the gases from 1 pound of "combustible " =K+L........................................:.......... 1, 384

Heat above 325° F. in the gases from 1 pound of "combustible" that is, heat 

available to the boiler:

Calorific value of 1 pound of "combustible" (item 51) ............. 15,423

N. B. t. u. generated from 1 pound of " combustible " = E3 X 15,423.... 12, 295

0. Heat available for the boiler per pound of " combustible "=N M... 10,911 

True boiler efficiency (E4):

P. Heat absorbed by the boiler per pound of "combustible" (from heat « 

balance)....................................................... 9,300

E4=P-r-0=85.23 per cent. 

Theoretical initial temperature:

Heat above.325° F. in 1 pound of gas=0-4-J............................ 705.3

705.3 B. t. u. will raise the temperature of 1 pound of gas 705.3-^-0.24, or

2,939° F. 

Initial temperature = 2,939°+ 325°= 3,264° F.

As explained in the discussion on page 140, the calculated initial 

temperature as given by the scale to the left of figs. 65 (p. 141) and 

66 (p. 144) is that temperature to which the gases would rise provided 

no heat were lost by conduction or radiation until combustion had 

ceased, 0.24 being used as the specific heat of the gases at all temperatures. However, these conditions never exist in practice. A 

large amount of heat is lost from the gases by both conduction and 

radiation before combustion ceases; furthermore, the specific heat 

of the gases at high temperature may be higher than 0.24. For 

these reasons the calculated furnace temperature is much higher than 

that actually attained.

In order to obtain a calculated initial temperature of 3,480° F., it 

is necessary to have an average of about 12.5 per cent of C02 in the 

escaping gases and to burn a coal of about 14,000 B. t. u. per pound 

of dry coal. This temperature is about the highest that could be 

obtained by a hand-fired furnace. If it were possible to maintain 

a completeness of combustion of 100 per cent at this temperature 

the efficiency of the boiler (72*) would be 76 per cent, which is the 

highest over-all efficiency attainable. (See fig. 65.)

PLOTTING OF PROBABILITY CURVES.

After having obtained the values of furnace and true boiler efficiencies as explained on pages 143-145, the true boiler efficiencies were 

arranged in groups according to their values, and the number of each 

group was plotted according to its magnitude as shown in the upper 

curve of fig. 67, called the probability curve. (See p. 158.) If a 

line be drawn through these points a curve results quite as sym-
HEAT ABSORPTION AND BOILER EFFICIENCIES. 147

metrical on both sides as a probability curve and shaped very much 

like it.

The lower curve of fig. 67 is a similar plotting of the number of 

efficiency 72* values for the same tests falling within each group, the 

curve being drawn through the points. It lacks the symmetry of 

the upper curve, and the joints do not fall so near the peak. The 

symmetry of the upper curve and its similarity to a mathematical 

probability curve suggest that the true boiler efficiency (E.,) is much 

more nearly constant than efficiency 72*, and that the attempt 

made to find a constant true boiler efficiency is along the right track. 

But the curves of fig. 66, discussed on page 143, show that this 

"constant0 ' true boiler efficiency is subject to variations when capacity

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approximate curve based on boiler efficiency 72*. Tests 89-401.

and furnace temperature are changed, although they are comparatively slight. By referring to the upper curve of fig. 67, it will be 

seen that most of the tests fall between 77 and 87 per cent, the greater 

number being close to 83.7 per cent, the position of the peak. This 

means that under average conditions the boilers at the fuel-testing 

plant will absorb about 83.7 per cent of the heat available to them.

The meaning of constant-capacity curves for boiler efficiency (E5 ) 

could perhaps be made plainer by taking from the chart (fig. 65, 

p. 141) four specific examples:

Example 1. Taking the furnace temperature at 2,500° F., and moving from left to right on the chart, we cut lines of higher capacity and 

lower boiler efficiency (E5); with a capacity increase from 70 to 120
148 A STUDY OF FOUR HUNDRED STEAMING TESTS.

per cent, the boiler efficiency drops from 71 to 67 per cent. Inasmuch as the furnace temperature remains constant the quantity of 

heat received by the lower row of tubes by conduction through the 

encircling tiles and by radiation from the hot brickwork is perhaps 

the same. Therefore the decrease in boiler efficiency must be charged 

to the tubes which are farther from the furnace and receive their 

heat from the gases by convection and conduction.

A possible explanation of lower boiler efficiencies with "higher 

capacities is that a steeper temperature gradient is required to transmit more heat through the soot, metal, and scale. There is also a 

thicker layer of steam bubbles on the heating surface, which increases 

the resistance to the passage of heat. These effects cause the flue 

gases to leave the heating surface of the boiler at higher temperatures 

as the capacity increases.

Example 2. Using the scale at the foot of the chart and following 

the line of 15,000 pounds of gas passing over the heating surface per 

hour, we find that with a calculated furnace temperature of 2,100° 

F. the boiler efficiency (E5) is about 67 per cent and the capacity 

about 70 per cent. Moving vertically upward the pounds of air 

must be slightly reduced and more coal burned in order to obtain 

higher furnace temperature and at the same time keep the pounds 

of gas per hour constant. By doing this more heat becomes available for raising the temperature of the gases, as shown by the ordinate 

on the right of the chart. At a furnace temperature of 3,300° F., 

the capacity is 130 per cent and the boiler efficiency (E5) 75 per cent, 

an increase of 8 per cent over the efficiency with a temperature of 

2,100° F.

Example 3. Taking the curve of 100 per cent rated capacity we 

find that rated capacity can be obtained with many conditions. 

The first extreme is with a furnace temperature of 2,100° F., when 

passing 21,000 pounds of gas through the boiler per hour; obtaining 

a boiler efficiency (E5) of 64 per cent. The second extreme is with 

a furnace temperature of about 3,500° F., and a boiler efficiency of 

76 per cent, when passing about 11,000 pound of gas through the 

boiler per hour.

Example 4. A boiler efficiency of 70 per cent can be attained under 

many conditions. The lowest temperature on the chart with which 

this efficiency can be obtained is 2,400° F. at a capacity of 70 per cent, 

when passing about 12,000 pounds of gas through the boiler per hour. 

In order to maintain this high efficiency when working at 130 per cent 

of rated capacity, it is necessary to increase the furnace temperature to 2,800° F. by burning more coal with decreased air supply.

The curves of fig. 66 (p. 144) differ from those of fig. 65 (p. 141) in 

that true boiler efficiency (E4 ) is used instead of boiler efficiency (E5 ). 

The true boiler efficiency is based on the heat available to the boiler,
KELIABILITY OF OBSERVATIONS AND DATA. 149

considering only that part of the heat in the gases as available which 

is above the temperature of the steam. If the steam and water in 

the boiler were at atmospheric temperature, the two efficiencies, E5 

and E4 , would be the same; but as the temperature of the water in 

the boilers is always from 150° to 200° F. above the atmospheric 

temperature less heat is available for the boiler.

The general significance of the chart is (1) that true boiler efficiency increases with initial temperature, perhaps because an increasing amount of heat is absorbed by the lower row of tubes on account 

of conduction through the encircling tiles and of radiation on 

them, where they are bare in the rear, from the brickwork of the 

combustion chamber, and also because the higher temperature of the 

gases causes a steeper temperature gradient through the soot, metal, 

and scale, so as to cause a higher rate of flow of heat. All these

causes are apart from the simplest statement of Perry's suggested 

theory of constant true boiler efficiency and are modifying factors of 

it in practice. The further general significance of this chart is (2) 

that at the same initial temperature the true boiler efficiency 

decreases as the mass of gases passed over the heating surface 

increases that is, as the capacity increases. The explanation of the 

fact that the true boiler efficiency (EJ is lower with these conditions 

is that inasmuch as capacity is proportional to the rate of heat 

absorption by the boiler the temperature difference between the 

water in the boiler and the first layer of gases on the outside must be 

greater in order that more heat be transmitted into the water in the 

same length of time. This increase in the temperature gradient 

causes the gases to leave the heating surface of the boiler at a higher 

temperature than in the cases of low capacity. The efficiency range 

of this chart is not very large only from 77 to 85 per cent and few 

points are near the extremes.

MISCELLANEOUS.

RELIABILITY OF OBSERVATIONS AND DATA.

The following remarks are given to facilitate the utilization of the 

actual data of the tests which are discussed in this volume:

Item 2: Duration of trial. This item is important for its effect on the water level 

in the boiler, which is easily changed several inches by opening or closing the steam 

valve, or by starting or stopping a large engine. Perhaps the usual error on this 

account was a fraction of 1 per cent of the evaporation. The item also enters into 

the errors of estimating the amount of fuel on the grate at starting and stopping. This 

estimating was always done with care, but the error on ten-hour tests may have been 

sometimes as much as 1 per cent of the coal burned, especially if the amount was 

small. As regards the fuel, when estimating accuracy, the real question is, How 

much coal was burned? not, How long did the test last?

Item 3: Grate surface, square feet. Boiler No. 1 was equipped with a plain grate, 

having an area of 40.55 square feet. Boiler No. 2 was equipped with a McClave rock-
150 A STUDY OF FOUB HUNDRED STEAMING TESTS.

ing grate, having an area of 36.4 square feet. These areas were maintained constant 

during the 1905 tests.

Item 11: Barometer, inches of mercury. This observation was always obtained 

from the Weather Bureau, and no correction was made for difference in elevation 

between the Weather Bureau station and the fuel-testing plant, which was only a few 

feet.

Item 11.1: Steam pressure. This reading was sometimes taken from a calibrated 

steam gage and sometimes from a recording-instrument chart. It is correct within a 

pound.

Items 12 and 13: Draft readings. These readings are accurate to 0.02 inch.

Item 16: Temperature of fireroom. Correct within 2°.

Item 17: Temperature of steam, calculated.

Item 18: Correct unless otherwise noted.

Item 20: Correct unless otherwise noted.

Item 21: Generally low, owing to air leakage, and apt to be in error in extreme 

instances, as much as 100° F., this error being the aggregate of the thermometer error 

and the greater error due to the difficulty of obtaining a true average temperature in 

the stack by the use of a single thermometer. Large errors are noted in their respective 

tests.

Item 21.1: Average temperature of furnace. Read by means of a Wanner optical 

pyrometer. All observations were made looking into the combustion chamber, about 

2 feet from the rear end, 1 foot below the tile roof. When looking at flame, as was generally the case, the indications were perhaps well within 200° F. of the right value, 

generally perhaps within 100° F., although this is merely an estimate based on circumstantial evidence. In the absence of flame, light was received from the opposite wall, 

which was plainly cooler than the gases, as was evident on comparing it by eye with the 

tile roof near by; and even this latter was cooler than the gases which heated it, 

because heat was constantly passing upward through the tile into the. water tubes. 

How much too low such readings are is only a guess perhaps 100° to 200° F. In general, the tests on coals high in "fixed carbon" have combustion-chamber temperatures 

too low.

Item 28: Total weight of ash and refuse. Refuse was taken to mean everything 

which fell through the grate plus the ash and clinker pulled out of the furnace during 

cleaning of fire. It is noteworthy that the weight of earthy matter in the refuse from

a test is usually 15 or 20 per cent short of the amount that the chemical analysis indicates; the difference undoubtedly goes over into the combustion chamber and up the 

stack.

Item 32: Fixed carbon of proximate analysis.

Item 33: Volatile matter of proximate analysis.

The preceding two items are based on arbitrary methods of driving off the so-called 

"volatile matter" and weighing the remainder to get ash and fixed carbon. By 

varying the standard of conditions under which the distillation is effected very different results can be obtained, and thus it may be seen that care should be exercised 

in deducing results of practical trials from the purely arbitrary results obtained from 

proximate analyses of dry or moist coal. A greater number of ultimate analyses 

should customarily be made, inasmuch as they furnish absolute data. Coal molecules 

are probably complex,.and although little is known on the subject it is likely that the 

products and even the amounts of products of destructive distillation vary widely 

with the method followed, as to temperature, rapidity of heating, etc.

Item 34: Percentage of moisture in coal. This item is uncertain at best. It is 

probable that on warm, dry, and windy days the coal lost some moisture while being 

quartered on the floor of the boiler room, so that the coal fired was really lower in 

heating value than the chemical analysis indicates.

Items 37, 38, 39, 40, 41, and 42: Ultimate analysis of dry coal. Furnished by the 

chemical division.
COMPUTATIONS OF A STEAMING TEST. 151

Items 50 and 51: Furnished by the chemical division. These items were used in 

test calculations in preference to items 52 and 53.

Items 54 and 56: These items are untrustworthy in these tests; concordant results 

were never obtained. All the investigational work done on the matter pointed to the 

possibility that eddies vitiated the readings, because the vertical section of pipe in 

which the sampling nipples were placed was only 2 feet long. These items are probably not reliable within 50 per cent of the values given.

Item 77: Percentage of smoke. Dense black (so estimated) taken as1 100 per cent.

Item 81: Average thickness of fire. Only approximate, because of difficulties of 

measurement when flame is present. It also varies with the personal equation of the 

observer.

Items 84, 85, 86, 87, and 88: These items are somewhat in error, owing to air dilution.

Heat balance: Items 2 and 3, very nearly correct; item 4, usually doubtful, owing 

to inaccurate flue-gas temperatures; item 5, only approximate; item 6, doubtful 

results of. our tests show that the unaccounted-for loss and the flue-gas loss up the 

stack take and give reciprocally. (See fig. 35, p. 63.)

The chart shown in fig, 68 indicates that in general terms the unaccounted-for heat 

increases in percentage with the loss due to CO.

PER CENT C O LOSS

FIG. 68. Relation of unaccounted-for loss to CO loss (tests grouped on basis of per cent of CO loss). 

COMPUTATIONS OF A STEAMING TEST.

The data necessary for complete results of a steaming test come 

from three sources: (1) The boiler room, (2) the chemical laboratory, 

and (3) the United States Weather Bureau.

After a coal has been tested, from ten days to two weeks are required 

for the chemical work to be completed before definite results are 

known. The state of weather, the barometric pressure, and the 

relative humidity for the day of the test are obtained from the 

Weather Bureau.

The computed results given in this report have been calculated 

according to the methods indicated in the A. S. M. E. code for making 

boiler trials. However, it has been thought advisable to explain 

how several of the items were obtained or determined, and in doing 

this, for brevity, code numbers will be used.

Item 23: See explanation under " Average diameter of coal,", p. 45. 

Item 27=item 25X(100 item 34).

Item 28=total ash and refuse from test. This includes the coal which falls through 

the grate.
152 A STUDY OP FOUR HUNDRED STEAMING TESTS.

Item 29: In most tests the ash which was pulled from the grate when cleaning fires 

was called clinker unless the ash which formed on the grate was all free ash. Then 

the per cent of clinker is this weight figured as a percentage of item 28.

Item 30=item 27 item 28.

Item 30*=itein 25X(item 32+item 33) (item 28Xitem 44).

Item 31=item 28-r-item 27.

Item 32a=item 32-5-(item 32+item 33).

Item 33a=item 33-j-(item 32+item 33).

Items 37a, 38a, 39a, 40a, 41a are determined by dividing items 37, 38, 39, 40, and 

41 by (100 item 42).

Item 46=item 27^-item 2.

Item 47=item 30-r-item 2.

Item 47*=item 30*-j-item 2.

Item 48=item 46-^item 3.

Item 49=item 47-s-(item 7=2,031).

Item 49*=item 47*-=-(itein 7=2,031).

Item 51=item 50-s-(100 item 42).

Item 54, obtained by separating calorimeter.

Item 56, "quality of steam," found by subtracting item 54 from 100. In boiler 

use this value must be corrected, and it is the corrected value that we have used for 

this item.

Extract from the A. S. M. E. code for making boiler trials: "The factor of correction for quality of steam in a boiler test differs from the quality itself from the fact 

that the temperature of the feed water is lower than that of steam." In using quality 

of steam, as given by the calorimeter, therefore we lose the heat required to raise 

the temperature of the moisture in steam to steam temperature. The method of 

determining the factor of correction for quality of steam is given below:

Q=quality of moist steam as given by calorimeter.

P=the proportion of moisture in steam.

F=the factor of correction for the quality of the steam when the steam is moist.

H=the total heat of the steam due to the steam pressure.

Tt =the total heat in the water at the temperature due to the steam pressure.

,T 1 =the total heat in the feed water due to the temperature. 

F_Q (H-JQ+P (T.-Jt)

Item 57: This is corrected for iTiequality of water level and of steam pressure at 

beginning and end of test.

TT__1

Item 60= , in which H and hare, respectively, the total heat in steam of the

average observed pressure, and in water of the average observed temperature of the 

feed. The difference between H and h gives the heat absorbed. The 965.7 is the^ 

heat of vaporization at 212° F. Dividing H h by 965.7, we obtain a factor which 

we can use as a multiplier to reduce pounds of water fed to boiler to pounds of equivalent water.

Item 61=item 57 X item 56 X item 60.

Item 65=item 63-^-34.5 (34.5 pounds water evaporated per hour into dry steam from 

and at 212°, equals 1 boiler horsepower).

Item 68=itein 57-^-item 25.

Item 69=itein 61n-itern 25.

Item 70=item 61-s-item 27.

Item 71=item 61-r-itern 30.

Item 71*=item Gin-item 30*.

Item 72=item 71X965.7-^item 51. This is the efficiency of the furnace and boiler 

combined, figured from pounds of combustible apparently ascending from the grate.
CARBON DIOXIDE AND WATER VAPOE. 153

Item 72* item 7 1*X 965*7-7- item 51. This is the efficiency of the furnace and boiler 

combined, figured from pounds of combustible actually ascending from the grate.

Item 73=item 70x965.7-M.tem 50. This is the efficiency of the furnace, boiler, and 

grate. It is usually styled over-all efficiency.

Item 77: Smoke readings were taken by using the Ringelmann charts. To obtain 

this item the sum of the readings was multiplied by 20 and this result divided by the 

total number of readings.

Item 81: Estimated by expert in charge of fire.

Item 82: The fire was considered to be in normal condition from the start of the 

test until the close, except during cleanings. The time for cleaning is subtracted 

from the length of the test and the result divided by the number of firings.

Item 83: This is the interval between raking, slicing, and cleaning the fire.

The following items are from the heat balance or distribution of the heating value 

of the combustible:

Total heat value of 1 pound of "combustible," B. t. u. item 51.

Item 1= item 71*X 965.7 (evaporation from and at 212° F. per pound of " combustible-' 

ascending from the grateX965.7).

Item 2=item 34-i-(item 32+item 33)-s-100X[(212-t)+965.7+0.48 (T-212)]. This 

operation consists in referring the moisture to "combustible," raising the temperature 

to 21.2° F., evaporating it, and then superheating to stack temperature.- The specific 

heat of superheated steam was taken as 0.48. t=temperature of air in the boiler 

room, T=temperature of the flue gases.

Item 3= item 38a-^100X9X[(212-t)+965.7+0.48 (T-212)]. This operation assumes all the hydrogen burned to water. The temperature of the water is raised to 

212° F. and the water is evaporated and then superheated to stack temperature. 

,, HXitem. 84+8Xitem 85+7 (item 86+item 88) item37a

ltem4- 3 (item 84+item 86) X 100 X0.24X(l-t). 

t=temperature of air in boiler room; T=temperature of the flue gases. The above 

operation consists in figuring the pounds of dry chimney gases per pound of carbon ; this 

value, multiplied by the per cent of total carbon in the combustible, gives pounds of 

dry chimney gas per pound of combustible; this number of pounds of gas is then 

heated from the temperature of inside air .to stack temperature at a constant specific 

heat of 0.24.

Item .5= item 86-5-(item 84+item 86) X pX 10,150.- The quantity 10,150 is

the number of B. t. u. generated by burning to carbonic acid 1 pound, of carbon contained in carbonic oxide.

Item 6=100-(items 1+2+3+4+5).

DISSOCIATION CURVES OF CARBON DIOXIDE AND WATER VAPOR.

The curves of fig. 69 are probably self-explanatory. It should be 

stated that the data were experimentally obtained and calculated 

in 1905 or 1906 by Professors Nernst and Wartenberg, two men of 

the highest competency. As an example, using curve No. 1, 0.051 

per cent of water vapor (about 0.05 per cent) at atmospheric pressure is dissociated into hydrogen and oxygen. These data are 

probably the most reliable extant. They indicate that many fears 

heretofore widely held, as to limitations in high-temperature work 

due to dissociation, are almost groundless.

It will be -noticed that the per cent dissociation of CO2 increases 

more sharply at about 1 ; 300° C. than anywhere else. On referring 

to fig. 14 (p. 23), giving the percentage of CO as a function of com-
154 A STUDY OF FOUR HUNDRED STEAMING TESTS.

bustion-chamber temperature, it will be noticed that the sharpest 

curvature of the CO curve is at about 2,600° F. (about 1,420° C.), 

which is not far from 1,300° C.

Now comes in the vital factor of furnace practice. In order to 

get higher temperatures the air supply must be reduced; and less

77

PER CENT DISSOCIATION

FIG. 69. Dissociation curves of water vapor and carbon dioxide: Curve No. 1, H2 0 at atmospheric 

pressure; No. 2, CO2 at atmospheric pressure; No. 3, H2O at 0.1 atmospheric pressure; No. 4, CO2 

at 0.1 atmospheric pressure. Data from Zeitschrift fur physikalische Chemie, vol. 56, No. 5,1906.

oxygen means poorer combustion, as discussed under "Mass action" 

(p. 170). Thus high temperatures are .associated with incompleteness of combustion, shown in figs. 14 (p. 23) and 31 (p. 51).-

WATER-JACKETED GAS SAMPLER.

Fig. 15 (p. 24) shows a water-jacketed gas sampler, consisting of 

a IJ-inch pipe closed at each end with a cap and two J-inch pipes. 

The gas is drawn through one of the J-inch pipes, which passes 

through both the caps as indicated in the figure. The other £-inch 

pipe brings cold water into the large pipe. The |-inch nipple, fitted 

into the same end of the large pipe as that at which the water enters, 

serves as a water outlet. The water used for cooling the sampler is 

obtained from the city mains. The only difficulty ever experienced 

in the use of the sampler was when the city pressure was suddenly 

reduced.

Probably the gas drawn through this sampler would be more 

truly representative of the actual composition of the hot gases in 

the furnace if the opening from the furnace into the water-jacketed
COMPARISON OF READINGS OF CERTAIN GAS SAMPLERS. 155

passage were smaller. The internal diameter of a |-inch pipe is 

about three-eighths of an inch. Probably it would be better to use 

a brass pipe of very small bore, say |-inch. The object of having the 

gases enter a small-bore pipe would be to cool them suddenly so as to 

permit no combustion while they were being cooled. Still it is not 

likely that any serious error is introduced by using pipe of f-inch bore.

COMPARISON OF READINGS OF CERTAIN GAS SAMPLERS.

Fig. 70 shows the results of using simultaneously the code "multitubular sampler" at the base of the stack and a single small pipe a 

few inches above it, reaching across the stack base, and perforated

TIME. IN HOURS

FIG. 70. Comparison of readings of multitubular gas sampler (broken line) and of single tube in stack

(solid line); test 168.

with several small holes at intervals. It will be noticed that the 

multitubular sampler gave a more even line, on account of its containing a large storage space; the daily average for the two was 

the same within 0.1 per cent. But this excellent showing with the 

multitubular sampler was obtained only by constant care of it, for 

it gave a great deal of trouble from leakage.

The current of gas through the small sampling tubes is too slow, 

so that, the soot and small particles of ash settle in them and harden,, 

thus gradually stopping the openings. Tubes used in sampling 

from streams of gas carrying the most soot an.d ash become stopped 

sooner than others. Thus the multitubular sampler loses the apparent advantage, which led to its design, of drawing a sample from
156 A STUDY OF FOUB HUKDBED STEAMING TESTS.

every portion of cross section of the gas passage, and thereby loses 

also its value as a flue-gas sampler. It may be stated here that 

when the sampler was taken out, after two years of usage,-about 

three-fourths of the sampling tubes were found to be stopped up, 

although the sampler had been often blown out with steam. Its 

worst disadvantage lay in its leveling all readings considerably, so 

that the man running the fire could not depend on it for guidance so 

much as the single-tube sampler. For these reasons the A. S. M. E. 

multitubular sampler was permanently discarded.

The above-described faults of the multitubular sampler would not 

be so serious when using coals high in "fixed carbon."

FLUE-GAS SAMPLER.

Fig. 71 shows a design of a different form of flue-gas sampler which 

has been installed at the fuel-testing plant. The purpose of this 

design of collector is to obtain gas from various portions of the stack 

and- mix it before its temperature is taken and a sample drawn for 

analysis. This sampler is built of No. 16 sheet iron, and consists of 

a cylinder 5 inches in diameter to which are connected, by means of 

a double cone-shaped body, six scoops making an angle of 45° with 

the axis of the cylinder. The area of the cross se6tion of these 

scoops is 2.25 by 3 inches. In the bottom of each of the scoops is 

an opening which diminishes in width toward the center of the sampler, making the opening proportional at all points to the respective 

distances of the points from the center. The openings are shown in 

the bottom view of the sampler (fig. 71). The sampler is placed in 

the round portion of the stack about 2 feet below the damper, the 

ends of the scoops being about 4 inches above the top of the hood. 

The largest diameter across the scoops is about 6 inches smaller than

the diameter of the stack.

The sample of gas is drawn through a J-inch pipe, the end of which 

is inserted to the center of the 5-inch cylinder, as shown. The bulb 

of a flue-gas thermometer is also placed at the center of the cylinder 

near the £-inch pipe, so that the temperature of the flue gas and the 

sample of gas for analysis are taken at the same place. It is very 

probable that by this design of the sampler and location of the thermometer and sampling tube the average temperature and composition 

of the flue gas are obtained. To prevent the cooling of the gases by 

radiation after they have left the heating surface of the boiler the 

base of the stack was covered with asbestos. On close examination 

at the end of five months' constant use this sampler was found in perfect order in every respect and free from soot, both inside and out.

UNACCOUNTED-FOE PERCENTAGES PEOBABLY TOO HIGH.

Of late years the opinion has been gaining ground that all gases 

increase in specific heat as their temperatures are raised. If this is
UNACCOUNTED-FOB PEBCENTAGES PEOBABLY TOO HIGH. 157

true, more heat is lost up the flue than has been calculated on the 

basis that the specific heats of dry flue gases and steam were respectively constant at 0.24 and 0.48 under constant pressure.

If we assume, for instance, that the data given in E. Damour's 

Industrial Furnaces are correct, at an average flue temperature of 

662° F. (350° C.) the true amount of heat lost up the flue was roughly

FIG.'71. Flue-gas sampler installed to replace A. S. M. E. multitubular sampler.

5 per cent more than the amount regularly calculated about 1 per 

cent of the heating value of the fuel. This loss would be subtracted 

directly from the unaccounted-for heat; for instance, if the latter is 

given as 15 per cent it may really be about 14 per cent. But in consideration of the fact that in the last few years little work has been
158 A STUDY OF FOUR HUNDRED STEAMING TESTS.

done by physicists on the specific heats of gases at high temperatures 

the values given by Damour are probably not final, and so the calculations here given are subject to withdrawal.

PROBABILITY CURVES.

It is stated on pages 132 and 146 that when the calculated values of 

certain "constants" sought for are plotted according to the number 

of constants falling in each narrow group the free-hand curve drawn

through the points resembles 

a probability curve, and the 

peak is at a certain value of 

the constant. This relation 

makes it probable that the 

true value of the constant is 

the peak value, especially if 

the curve is narrow and 

symmetrical on the two sides 

and if the arithmetical average of all the points falls 

close to the peak of the 

curve. Perhaps the explanation can be best stated by 

reference to fig. 72.

When shot are dropped 

into the funnel they ought 

to fall into a vertical column 

the width of the funnel, but 

they will actually spread out, 

owing to obstructions. The 

curve drawn through the 

tops of the piles is a probability curve.

If a man were measuring 

a length carefully (as with a 

tape or with a micrometer), 

while very few of his readings would coincide if a large 

number of readings were 

used, the arithmetical aver-r 

age would be closely correct. 

If all his readings were 

sorted according to lengths 

as read and plotted with the 

vertical ordinate as the number of readings falling in each group and 

the horizontal ordinate as the average length of the readings in the 

groups a curve would result much like a probability curve. But

FIG. 72. Diagram illustrating probability curve.
EELATION OF TEMPEEATUEE TO POUNDS OF ATE USED. 159

suppose it was questionable whether or not the measured object 

changed length in unknown ways, if many measurements were taken 

the width of the curve would give a clew as to whether or not there 

really was any constant length. If a large number of readings formed 

a curve close to a theoretical probability curve the presumption of 

constant length would be nearly justifiable.

. Perhaps the best treatment of this subject for engineers is in J. W. 

Mellor's Higher Mathematics for Students of Chemistry and Physics, 

a very helpful book to the chemical engineer. 

The equation to this curve is

in which y = height of vertical ordinate at any point.

x = "horizontal distance of any point on the curve from the

center line passing up and down through the peak. 

e = base of hyperbolic system of logarithms, = 2.7183. 

h = a constant for each curve, which determines its width; 

the larger h the narrower .the curve, and hence the 

more reliable as an indicator of the probable value 

sought.

k = a constant for each curve, determining its height. 

The boiler division has plotted a number of curves of this equation, 

one or another of which is used to fit over any curve to which it bears 

a strong resemblance. But even if the fit is perfect no more is proved 

than that there is a strong probability that the figure sought is constant at the peak value. However, even this use of the equation and 

curves will serve to indicate whether a guess is along the right path, 

and in this way their use is sure to increase when they are generally 

known among engineers.

RELATION OF TEMPERATLRE OF PRODUCTS OF COMBUSTION TO POUNDS OF AIR

, USED.

Fig. 73 was prepared as a graphic illustration to show the different 

comparative temperature elevations attainable by completely burning various fuels, on the assumption that the specific heats of gases at 

constant pressure do not change with increase of temperature. It was 

thought that this assumption was wrong, but in the absence of more 

definite values it was decided to use constants. The general effect of 

this assumption is probably to make the temperatures with small air 

excesses too high; thus all the curves are somewhat too steep. In 

calculating the temperature the specific and latent heat of moisture 

in fuel and moisture formed by combustion have been considered.

The main object of the chart is to show that some Illinois coals 

are capable of use in high-temperature work, as in making malleableiron castings. In fact, by preheating the air used for combustion, 

Illinois coals are now burned in reverberatory furnaces in Chicago
160 A STUDY OF FOUR HUNDRED STEAMING TESTS.

and St. Louis. The curve shows that lignites could be used with 

preheating, especially as some lignites are very low in sulphur and 

burn freely with a long, hot flame.

POUNDS Of AIR PER POUND OF FUEL 

MAXIMUM ATTAINABLE TEMPERATURE. WHEN BURNING. FUELS WITH AIR

FIG. 73. Theoretical curves showing relation of temperature of products of combustion to pounds of 

air used per pound of various fuels.

CIRCULATION INDICATOR.

The construction of the circulation indicator is shown in fig. 74, 

which is a view of the instrument as mounted in the boiler. There 

are six essential parts which go to make up the indicator, as follows: 

The wheel or propeller, the contact strip, the brush that rests on it, 

the shaft, the supports or bearings of the shaft, and the receiving 

instrument (which may be a telephone).

The wheel is made up of four copper blades, secured to spokes by 

copper rivets and set at an angle of 30° with the axis of the shaft. 

The spokes are attached to a piece of brass tubing that acts as a 

hub and also as a support for the contact strip.

The contact strip is mounted on an insulating drum consisting of 

a glass tube about 1£ inches long slipped on the brass hub, which 

it fits tightly. A strip of copper about one-eighth inch wide and 

one thirty-second inch thick is bound to the glass tube with copper 

wire, and is electrically connected to the hub of the wheel by a 

copper-wire bond.
CIRCULATION INDICATOR. 161

The brush is a piece of watch spring, supported on a copper bar 

that is insulated from the remainder of the instrument by mica 

washers. It is arranged at right angles to the contact strip, with 

its end resting lightly thereon so as to make and break contact with 

the copper strip once every revolution of the wheel. A copper wire, 

that connects to a telephone receiver on the outside of the boiler 

through a 2-volt battery, is bonded to the brush support and insulated by means of rubber tubing at the point where it passes out of 

the boiler between the hand-hole cover and the water leg. The 

other wire from the telephone receiver is grounded to the boiler, as 

shown. By using a low voltage on the line the current is not short 

circuited much through the water in the boiler.

INSULATED FROM BOILER

FIG. 74. Circulation indicator mounted in boiler.

The shaft on which this instrument turns is a piece of brass wire 

about one-eighth inch in diameter and about 16 inches long. Two 

collars attached to the shaft close to the wheel, one on each side of 

the support, serve to keep the shaft from moving back and forth, 

and one of them, in conjunction Avith a cotter pin in the end of the 

shaft, holds the propeller in place.

One support for the shaft, at the end nearest the wheel, is a bar 

of brass with a hole in the center for the shaft and a slot on each 

end. These slots, which engage on the outside edge of the boiler 

tube, as shown, facilitate the centering of the instrument and changing from one tube to another. The other support for the shaft was 

8400 Bull. 325 07 11
162 A STUDY OF. FOUR HUNDRED STEAMING TESTS.

obtained by drilling a hole through, the center of a hand-hole cover 

and adding a small stuffing box made from the gland of a valve.

In the operation of this instrument the flow of water in any tube 

of the boiler in which the circulation indicator might be placed 

causes the wheel to rotate at a rate of speed proportional to the rate 

of flow. By placing the receiver to the ear a click is heard for each 

revolution, and one revolution of the indicator means the passage of 

approximately 1 foot of water. As the speed of rotation in all trials 

up to date has not been too high for an observer to count the clicks, 

no difficulty was encountered in keeping a record of the rate of flow 

in any boiler tube under observation under varying conditions of 

operation of the boiler.

Several instruments were built and tried before success was 

attained with this one. The instrument has lately been used to 

work an automatic counter through a couple of telegraph relays.

FIG. 75. Result of observations with circulation counter (propeller in back of boiler, middle tube, 

third row from bottom); test 379. Revolutions per minute calculated from averages of two readings of revolutions per fifteen seconds.

For information obtained see figs. 7 (p. 16) and 75 and pages 163 

and 164.

Fig. 75 shows the effect of cleaning fires, and of firing, on the 

speed of water circulation in a tube of the boiler, as measured relatively by the circulation indicator illustrated in fig. 74 and described 

on pages 160-2. The circulation is prompt in its changes and the 

values obtained vary considerably. The readings were taken by 

recording the number of revolutions in a fifteen-second interval 

opposite time figures, and from such data the temporary rate in 

revolutions per minute was calculated and plotted on this chart.

The curves of fig. 7 (p. 16) are based on readings taken for several 

days with the circulation indicator. The data from which the two 

curves were plotted were obtained by counting the total number of
CIRCULATION" INDICATOR. 163

revolutions of the indicator for each half-hourly period, and by 

calculating the percentage of builder's rated horsepower of boiler 

developed for each such period, respectively. The small circles give 

the positions of points and the numbers in the large circles near by 

give the number of half-hours fulfilling the coordinate values of the 

points. After plotting, the points were averaged in value in both 

horizontal and vertical strips, each point being included for averaging as many times as indicated by the number in the circle near by. 

Thus the two curves were determined. It will be noticed that they 

are very close together, indicating the reliability of the method of 

working up the data.

The important point is that the circulation rapidly drops behind 

the amount of steam made (per cent of rated capacity developed), 

especially at high rates of working. Thus at 70 per cent of rated 

capacity the average speed of rotation of the indicator was 80 revolutions per minute. At 105 per cent of rated capacity the rate of revolution was 102, whereas to be proportional it should have been 120; 

the speed of circulation fell about 15 per cent short.

This result is reasonable when we consider that, so far as one can 

make any speculations, the circulating forces are perhaps roughly 

proportional to the amount of steam which is generated and entrained 

with the rising water, whereas the frictional resistance to circulation 

is perhaps proportional to the square of the average velocity of 

circulation.

This failure of circulation to keep up proportionally with demands on 

it must decrease the efficiency of the boiler at higher rates of working, 

by allowing a proportionally larger percentage of the water-heating 

surface to be covered with steam bubbles, thus virtually reducing 

the heating surface. That this condition does supervene is indicated 

on a-number of charts, for instance those shown in figs. 5 (p. 14) and 

8 (p. 17), which.should be noted in this connection.

At a later date the circulation indicator was put in the middle 

tube of the lowest row of tubes, this being one of the tubes inclosed 

in clay tiles except at the rear end. The revolutions per minute for 

various capacities are given in the following table:

Readings of circulation indicator showing revolutions per minute for various capacities.

Capacity.

.58.2.

78 

217

01.4.

8 

257

118.2.

7 

273

. 92.2.

12 

291

The number of revolutions at any capacity is approximately three 

times as great as the number shown in fig. 7 for the second row of 

tubes just above.
164 A STUDY OF FOUR HUNDRED STEAMING TESTS.

In an earlier experiment the same circulation indicator was placed 

in the third row of tubes from the top of the boiler, and it was found 

that the rate of revolution was very slow indeed. This result indicates that the bottom row of tubes is doing far more work than any 

other row, and that as we go from the bottom row up the amount of 

work done decreases .very rapidly.

The probability that the bottom row of tubes absorbs so large a 

portion of the total heat, absorbed mostly on account of conduction 

through the clay tiles and radiation to the exposed portion of the 

tubes in the rear over the hot brickwork, makes it easy to realize that 

the efficiency of the boiler as a heat absorber may well rise far more 

rapidly with increasing furnace temperature than is indicated by the 

equation for heat absorption from the gases due to convection only, 

as developed on pages 129 and 130.

C-SHAPED v. FLAT-BOTTOMED TUBE TILES.

In boilers of the Heine furnace type the bottom row of tubes is 

incased in clay tiles. Such an installation is advantageous when coals 

break down, evolving gases difficult to burn, for the clay tiles serve 

a far better cause in protecting the burning gases from sudden cooling, and in acting as a small heat reservoir, than in protecting the 

tubes from burning. .

The first tiles used by the testing plant were of a C shape inside 

and out, and although they were made of excellent material they 

were so easily damaged by fire tools, and cracked so often from 

sudden temperature changes, that a new set had to be put in every 

two or three months. Later, both boilers were fitted with tiles which 

are flat on the bottom, giving the furnace roof the appearance of a 

ceiling. They are only 15 per cent heavier than the old C tiles, and 

could easily be made as light as the old tiles by cutting off the upper 

outside corners, above the tubes. The new tiles ha.ve withstood hot 

fires for over a year and are still good. They are among the most 

satisfactory parts of the boiler equipment. The difficulty referred to 

has been experienced at several power houses, and overcome in the 

same way, with equal satisfaction.

OBSAT TOTALS.

The sum of the percentages of C02 , 02 , and CO of an Orsat gas 

analysis is not at all constant. The sum is usually low at the start 

of a test and gradually rises during the first two hours. It also 

varies from day to day and from coal to coal. The first explanation 

suggested was that the available hydrogen of the coal burned to 

water that condensed before the gas sample arrived at the Orsat 

measuring tube, so. that out of every hundred volumes of air which 

entered the furnace one or two volumes might well be missing in the
ORSAT TOTALS. 165

Orsat measuring tube. On this assumption, when the same quantity of air is used to burn various fuels those highest in available 

hydrogen should give the lowest totals of Orsat analyses. To test 

this reasoning, a tabulation was made, headed "Classification of 

average flue-gas totals on basis of per cent of available hydrogen 

in dry coal." Many tests were grouped, first according to pounds of 

dry chimney gases per pound of "combustible." The tests of each of 

these groups were then reclassified according to per cent of available 

hydrogen in dry coal. For each subgroup the average was found for 

the Orsat totals of C02 , 02 , and CO. A glance along the horizontal 

rows of flue-gas totals shows but little relation between available 

hydrogen and flue-gas totals. This failure to connect per cent.of 

available hydrogen with shortage in Orsat totals suggests that other 

causes may be at work.

Perhaps the occurrence of low totals in the first part of ft test is 

due to the fact that an oxygen molecule may combine with carbon 

and form two CO molecules, which will occupy twice the space, 

thereby making the Orsat totals higher. During the first part of a 

test the CO is low, and later it rises. CO and available hydrogen 

have opposite effects on the totals. So it is, after all, not to .be 

expected that either taken alone will show anything. More work 

will be done on this problem.

Classification of average flue-gas totals on basis of per cent of available hydrogen in dry

coal.

Less than 18 pounds of dry 

chimney gases per pound of 

combustible:

Average per cent of available hydrogen in dry coal. 

Average of flue-gas totals 

(COz+Oa+'CO). ......... 

From 18 to 19 pounds of dry 

chimney gases per pound of 

combustible:

Average per cent of available hydrogen in dry coal. . 

Average of flue-gas totals 

(C02+O2+CO). .........

From 19 to 20 pounds of dry 

chimney gases per pound of 

combustible:

Average per cent of available hydrogen in dry coal . 

 Average of flue-gas totals 

(COa+Oa+CO)... .......

From 20 to 21 pounds of dry 

chimney gases per pound of 

combustible:

Average per cent of available hydrogen in dry coal. 

Average of flue-gas totals 

(COa+Os+CO)... .......

Per cent of available hydrogen in dry coal.

Under 

3.

2 

2.48 

19. 33

1 

2.31 

19.16

2 

2.49 

19.87

3 to 

3.2.o

o 3.4 to 

3.6.

1 

3.42 

18.92

2 

3.50 

19.25

3.6 to 

3.8.

1 

3.66 

19.38

2 

3.72 

18.71

4 

3.71 

19.42

3 

3.76 

18.91

3.8 to 

4.0.

2 

3.86 

18.55

2 

3.92 

19.15

7 

3.88 

19.01

2 

3.98 

19.79

4.0 to 

4.2.

8 

4.05 

19.16

6 

4.08 

19.04

14 

4.07 

19.07

12 

4.08 

19.48

4.2 to 

4.4.

8 

4.29 

18.60

11 

4.30

18.72

8 

4.30 

18. 92

11 

4.30 

19. 23

4.4 to 

4.6.

5 

4.56 

19.07

. 11 

4.54 

18.82

5 

4.52

9 

4.51 

18.89

4.6 to 

4.8.

3 

4.61 

18. 69

9 

4.67 

18. 62

5. 

4.68 

19.08

5 

4.72 

18. 98

4.8 to 

5.

No fuels in the 3.2 to 3.4 per cent class.
166 A STUDY OF FOUR HUNDRED STEAMING TESTS.

Classification of average flue-gas totals on basis of per cent of available hydrogen in dry

coal Continued.

From 21 to 22 pounds of dry 

chimney gases per pound of 

combustible:

Average per cent of available hydrogen in dry coal. 

, Average of flue-gas totals 

(COri-Oa+CO). ......... 

From 22 to 23 pounds of dry 

chimney gases per pound of 

combustible:

Average per cent of available hydrogen in dry coal . 

Average of flue-gas totals

From 23 to 24 pounds of dry 

chimney gases per pound of 

combustible:

Average per cent of availa 

ble hydrogen in dry coal. 

Average of flue-gas totals 

(COa+OH-CO).......... 

24 pounds or more of dry chimney gases per pound of combustible:

Average per cent of available hydrogen in dry coal. 

Average of flue-gas totals

Per cent of available hydrogen in dry coal.

Under 

3.

1 

2.89 

18.91

3 to 

3.2.

1 

3.17 

20.07

3.4 to 

3.6.

1 

3.56

19.29

1 

3.49

19.10

1 

3.47

18.92

' 3 

3.53 

19. 70

3.6 to 

3.8.

3 

3.70

19.23

3 

3.69

19.48

3 

3.71 

19. 67

3.8 to 

4.0.

. 1 

. 3.99

19. 65

1 

3.88

19. 59

2 

3.98 

19.45

4.0 to 

4.2.

7 

4.07

19. 52

5 

4.06 

19.82

3 

4.04

20.00

6 

4.08 

19.72

4.2 to 

4.4.

8 

4.27

19.17

3 

4.29 

19.19

5 

4.27

19. 58

4 

4.31 

19.45

4.4 to 

4.6.

3 

4.36

19. 36

8 

4.48 

19.17

10 

4.51

19.36

7 

4.52 

19. 43

4.6 to 

4.8.

5 

4.66

19.08

5 

4.69 

19.22

. 2 

4.68

19.25

2 

4.71 

18. 45

4.8 to 

5.

1 

4.85 

19.20

4 

4.85 

19.39

PEE CENT OF CO IN COMBUSTION CHAMBER.

Fig. 14 (p. 23) shows that when combustion-chamber temperatures 

are high, the per cent of CO in the rear of the combustion chamber is 

high and the totals of C02 , 02 , and CO are low. This concurrence of 

high CO and low totals of Orsat analyses has often been noticed. As 

a converse test, the classification tabulated below was made on per

cent of CO as a basis, to obtain the average of the Orsat totals. They 

are practically constant until the CO becomes high, when they drop 

at a comparatively rapid rate. This relation is of the same nature as 

that indicated in fig. 14 (p. 23). No explanation is given here, as 

several possible ones were found to be doubtful on investigation.

Classification of Orsat totals on basis of volumetric per cent of CO in combustion chamber

(tests 318-382).

Per cent of CO.

Number of readings.. . . 

Average of 100 (C0a+ 

CO+Os). ............

Oto 

0.10.

82 

18.5

0.10 to 

0.20.

31 

18.4

0.20 to 

0.30.

38 

18.5

0.30 to 

0.40.

18 

18.5

0.40 to 

0.50.

' 17 

'18.5

0.50 to 

0.60.

7 

18.5

0.60 to 

0.70.

9 

18.3

0.70 to 

0.80.

4 

18.9

0.80 to 

0.90.

5

18.2

0.90 to 

1.00

2 

15.1

Over 

1.00.

7 

17.4

The following table was constructed to ascertain whether such conditions of poor combustion as permitted a high percentage of OO in
RELATION OF WIND TO EFFICIENCY. 167

the rear of the combustion chamber also conduced to smoke production. The finding is in the affirmative. See also the chart shown in 

fig. 33 (p. 56), based on per cent of black smoke, in which the per cent 

of CO rises rapidly with the per cent of smoke.

Classification of smoke production on basis of volumetric per cent of CO in combustion

chamber.

Average per cent of CO in combus:

Average per cent of black smoke. . . .

Per cent of CO.

Oto 

0.10.

9

0.03 

13.8

0.10 to 

0.20.

8

0.14 

19.9

0.20 to 

0.30.

4

0.23 

21.8

0.30 to 

0.40.

4

0.34 

18.1

0.40 to 

0.50.

4

0.44 

20.3

0.50 to 

0.60.

1

0.58 

38.5

0.60 to 

0.90.

1

0.83 

40.0

0.90 up.

1

1.10 

39.0

POUNDS OF DEY CHIMNEY GASES PEE POUND OF "COMBUSTIBLE."

The sub j oined tabulation of pounds of dry chimney gases per pound of 

"combustible" is based on intensity of draft under stack damper and 

difference of draft under stack damper and draft over fire. This table 

was made to ascertain whether the pounds of air used could be approximated by draft readings. As there was also air leakage, which varied 

with the amount of draft carried, it seemed best to average out the 

error by using separate readings for different values of stack draft. 

However, such a classification seems to be so greatly influenced by 

rate of combustion and air leakage as to make it of little value. The 

table shows a small increase of pounds of dry chimney gases per pound 

of "combustible/' as the difference of draft increases.

Classification of dry chimney gases per pound of "combustible" on basis of stack draft 

ana difference of draft under stack damper and draft over fire.

Average difference of stack draft and draft

Average pounds of dry chimney gases per

Average difference of stack draft and draft

Average pounds of dry chimney gases per

Stack draft. 

Under 

0.40.

18 

0.25 

19.75

0.40 to 

0.425.

23 

0.29 

19.04

0.425 to 

0.45.

12 

0.32 

18.25

0.45 to 

0.475.

25 

0.32 

19.79

0.475 to 

0.50.

23 

0.34 

20.02

0.50 to 

0.525.

17 

0.35 

19.52

0.525 to 

0.55.

14 

0.37 

21.09

Stack draft.

0.55 to 

0.575.

21 

0.38 

21.18

0.575 to 

0.60.

1C 

0.41 

22.08

O.GO to 

0.625.

28 

0.41 

22.16

0.625 to 

0.65.

18 

0.44 

22.92

0.65 to 

0.675.

10 

0.47 

21.86

0.675 

up.

32 

0.54 

21.91

EFFECT OF DIRECTION, VELOCITY, EELATIVE HUMIDITY, AND TEMPERATURE 

OF AIR ON EFFICIENCY 72*.

Inasmuch as the boilers stood in a poorly built wooden structure, 

near two large doors, which were always open in summer and sometimes in winter, it was thought that the cooling of the boiler room by
168 A STUDY OF FOUR HUNDEED STEAMING TESTS. -

winds might have some appreciable tendency to lower the efficiency 

72*. ,_ .

With the data from about 305 tests, the problem was attacked in 

several ways, as given below: .

1. The winds were classified in four groups, (a) from the north and 

northeast, (&) from the east and southeast, (c) from the south and 

southwest, (d) from the west and northwest and then all tests were 

classified according to the prevailing direction of the wind for that 

day, and the individual tests falling in each of the four wind groups 

were plotted by means of the two ordinates, efficiency 72* and velocity 

of wind in miles per hour. It was found that there was no appreciable 

effect on efficiency due to wind velocity. In the above-mentioned 

subdivisions the tests of all groups (a, I, c, and d) were arranged in 

subgroups according to the outside air temperatures for instance, 

the tests falling under wind from the east and southeast were divided 

into three subgroups, in which the ranges of outside air temperature 

were "below 40° F.," "40° to 50° F.," and "50° to 60° F."

2. With the same four groups of wind directions (a, Z>, c, and d) 

the item 72* (so-called " boiler efficiency") was plotted in each group 

with the items: (e) velocity of wind in miles per hour, (/) relative 

humidity of outside atmosphere, (g] outside air temperature, and 

(fi) average diameter of coal. In group 2 (e) the velocity of wind 

again had no noticeable effect. For all directions of wind excepting 

from the north and northeast, high relative humidity (/) of the outside atmosphere appeared to lower the efficiency, somewhat. A 

rise of outside-air temperature (g) appeared .to cause a slight rise in 

efficiency, but not any more than results from an equal reduction in 

stack temperature, so that the effect on radiation is not noticeable. 

The outside doors were generally closed in winter, however. The 

average diameter of the coal (Ji) varied only .slightly, and it apparently had no influence in disguising any of the other curves (e, f, 

and g).

The general conclusion is that calculations of radiation are not 

likely to be appreciably in error owing to changes in weather conditions, unless it is substantiated on further investigation that the 

relative humidity influences the amount of heat lost by convection 

or else retards the combustion of coal. Efficiency 72* was used 

because the* " unaccounted-for" item is not reliable.

RELATION OF UNACCOUNTED-FOE LOSS TO ASH PASSING OVER BRIDGE WALL.

It was thought that possibly all the coal which was blown up from 

the fuel bed and carried away with the gases did not burn, and that 

a clew to incomplete combustion might be obtained by comparing. 

the unaccounted-for items of the heat balance with the ash lost over
UNACCOUNTED-FOE LOSS. 169

the bridge wall. The opposite from the relation expected appears 

in the accompanying table, which shows that the greater the per 

cent of ash. carried away the less the unaccounted-for loss that a 

high percentage loss of ash does not mean a high unaccounted-for 

loss. As the average difference of draft under stack damper and 

. draft over fire increases the ash lost over the bridge wall increases, 

as might be expected.

The following is offered as an explanation of.the table: With higher 

draft there is an increased rate of combustion; the temperature of 

combustion^is increased; the pounds of dry chimney gases per pound 

of "combustible" are decreased; a higher initial temperature and 

increased rate of combustion will give a higher stack temperature, 

and this increased temperature will increase the loss up the stack 

and subtract almost directly from the unaccounted-for loss; and

with increased rate of combustion the per cent of radiation loss for 

each pound of coal burned will be less and this reduction will enter 

directly into the unaccounted-for loss. These factors tend to decrease 

the unaccounted-for loss. On the other hand, with higher rate of 

combustion and higher temperatures the gases are carried through 

the furnace faster and there is a greater amount of incomplete combustion owing to the fact that less time is taken in passing through 

the furnace. Moreover, as there is less excess of air and a higher 

temperature, the unaccounted-for loss will directly increase because 

hydrocarbon losses are not determined. There is necessarily a balancing of these losses and gains. The table shows their average 

effect only.

Three classifications showing relation between "unaccounted-for" loss and ash passing

over bridge wall.

Per cent of ash lost over 

bridge wall, referred to 

combustible burned ........

Average per cent of unaccounted-for loss from heat 

balance ..................... 

Average difference of draft 

under stack damper and 

draft over fire, inch of waAverage per cent of ash lost 

over bridge wall ............

Average per cent of unaccounted-for loss from heat

Average per cent of unacPer cent of ash lost over 

bridge wall, referred to

Average per cent of ash lost

0.27 

13

10.01

5. 69

20

3.81

3.04

0.58 

24

9.83 

0.35

0.79 

20

7.59

24

2.80

2.24

1.24 

26

11.74 

0.35

1.24 

34

12.12

8.54

22

3.10

2.45

1.73 

30

11.23 

0.34

.1.78 

29

10.78

9.48

29

2.64

2.10

2.26' 

28

 11.24 

0.36

2.25 

33

10.48

20

2.51

1.99

2.69 

19

9.73 

'0.38

2.80 

20

9.53

30

2.88'

2.26

3.26 

18

9.40

3.20 

23

9 08

19 ^

22

2:83

2.21

3.72 

20

10.49 

0.37

3.72 

14

9 40

13.38

12

2.81

2.19

4.42 

 25

9.52 

0.39

4. 50 

10

7.99

1.44

7.01 

19

8.45 

0.43

5.90 

9

9.01

10.70

15

2.10

1.75
170 A STUDY OF FOUR HUNDRED STEAMING TESTS. 

THE LAW OF MASS ACTION.

Although not yet very old, the law of mass action is already one 

of the most firmly established and useful of the laws of physical chemistry. Its operation is a matter of daily intuition in other fields; e.g., the 

more water one uses the easier it is to dissolve sugar, salt, etc. ' But 

only recently has the law been mathematically formulated in chemistry, and even yet it is often so hard to learn what the reactions are 

that one does not know which mass-action formula to use; still, 

the path of some reactions has been determined by finding what formula fitted the observed facts.

To take the simple case of combustion of carbon, it is an observation as old as the art of boiler practice that considerable excess of air is 

needed above the theoretical amount. Mathematically the situation is as follows:

As soon as some of the oxygen of the air has united with carbon 

or CO it is no longer available for oxidation of the remaining combustible; worse yet, the molecules formed are in the way, so that 

the combinations become less and less frequent. All this, of course, 

is on the supposition that the temperature is kept constant, so as to 

eliminate other variables. Now, as the above reaction proceeds the 

masses of oxygen and carbon, as compared with the total masses 

present, become less and less, whence the name, mass action; they, 

soon become nearly zero.

The above illustration is faulty in one respect it does not say in 

what terms the masses are to be measured. Elementary* chemistry 

states that CO and 0, for example, combine in just one proportion 

28 parts by weight of CO (its molecular weight) and 16 parts by 

weight of 0 (its atomic weight). The molecular weight of the 

oxygen is not taken (it is 32, as there are ordinarily two atoms in a

molecule) as the combining weight, because the molecule must first 

divide. Thus we should really consider 2 molecules of CO and 1 of 

O2 . For these reasons both combining substances must be considered according to the numbers of gram molecules present that is, the 

number of grams of each present divided by its respective molecular 

weight. Luckily this trouble disappears when working with gases 

analyzed volumetrically, as with an Orsat apparatus, because the 

volumetric weights of gases are directly proportional to their molecular weights, as all gases at the same temperature and pressure contain 

the same number of molecules per unit volume. Even dissociation, 

eijbher of molecules of H20 and C02 or of molecules of H2 and 02 and 

N2 into 2H, 2O, and 2N, would not trouble us, because volumes would 

increase proportionately. All we need to do is to substitute the 

volumetric percentages of 02 and of CO or CH4 , for example, of the 

analysis in the equation corresponding to the particular reaction and
THE LAW OF MASS ACTION. 171

obtain the relative indication of the rate of combustion, assuming, of 

course, the same temperature and pressure in every case.

Example: An analysis of gas from the rear of a combustion chamber through a small opening in a water-jacketed gas sampler showed 

the two following results, the combustion-chamber temperature in 

each case being 2,600° F. : (1) 02 , 4 per cent; CO, 0.5 per cent. 

(2) 02 , 7 per cent; CO, 0.4 per cent. The rest of the volume consisted of nitrogen, water vapor, carbon dioxide, and other gases foreign to this calculation. If the formula of the reaction is 2CO + 02 ^ 

2C02 ,° and if at 2,600° F. the dissociation of C02 is only about 0.01 

per cent, we may say with very close accuracy that the reaction is 

not a balanced one, but proceeds to a finish. It can be then written 

= 2C02 .

/7 'y*

If the rate of disappearance of CO in the gas is given by -=- = const.

(MI

(CO) 2 (O2 ), the rates of burning CO in the two cases given are'(l) 

4X(0.5) 2 = 1.00; (2) 7X (0.4) 2 = 1.12.

Thus the net velocity of combustion in the second case is considerably greater-^-with more oxygen. It would take an almost impossible rise in the CO percentage in the second case to neutralize the 

effect of 75 per cent more free oxygen. In such calculations care 

must be taken to include the volume of the steam gas present in the 

100 per cent total (not the 100 per cent total of the Orsat analysis). 

This volume can be roughly calculated, and is considerable in percentage and very variable.

It must be constantly borne in mind that calculations of velocity 

reactions based on the laws of mass action, are liable to be seriously 

in error owing to disturbing side reactions, catalysis, etc. ; but probably less is to be feared here with simple gases at high temperatures 

than with more complex substances at ordinary temperatures. At 

any rate, these laws of mass action are a very valuable guide in such 

problems, and if the facts do not fit proved formulas well we have 

applied too little theory; some refining corollaries must be added.

On page 61 is given a calculation based on actual data obtained, and 

the conclusion is reached that the velocity of combustion decreases 

enormously from the surface of the fire to the rear of the combustion 

chamber, where it is relatively very small; the practical application 

is that little is to be gained by adding further length of smooth combustion chamber, which would be commercially as poor an investment of capital as to add to the length of a Corliss engine cylinder 

and stroke; we must resort to thorough mixing.

o The sign ^ indicates that a chemical reaction and a reversing decomposition are going on side by 

side. The composition of the mixture changes according as combination or dissociation is the more 

rapid.
172 A STUDY OF FOUR HUNDRED STEAMING TESTS.

The question may arise, How are we to treat cases in which more 

than one combustible gas is present? Simply by adding the two 

effects together, as when we say that the pressure of a mixture of 

gases on the walls of a containing vessel is the sum of the pressures 

of the constituent gases; the two reactions go on independently side 

by side. Care must be taken not to add these velocity products 

without having first multiplied each by its proper reduction factor, 

which for most substances is imperfectly known at present for high 

temperatures. For the present, therefore, it is not feasible to get an 

expression for the comparative total velocities of combustion of all 

constituents taken together at several points along the flame.

Fig. 31 (p. 51) presents an excellent illustration of decrease of completeness of combustion because of decreasing oxygen mass action.

"Furnace efficiency" should more correctly be called "per cent 

of completeness of combustion," inasmuch as furnaces are usually 

fixed in size and shape, and so exert about the same mixing effect in 

all cases.

In the commercial combustion of fuels, where speed of coal consumption is important, so as to get high capacity, the operator must 

determine whether he will be most benefited by high temperatures 

or by a close approach to perfection of combustion. If he must put 

the heat into material at a high temperature, as in melting pig iron 

or clinkering cement, he must cut down the air supply even at the 

cost of a large fall in completeness of combustion due to decreased 

oxygen mass action, so as to have the temperature of the gases as 

far as possible above that of the material to be worked. If the temperature of his material is low, as is the water in a boiler, it will not 

make much difference how much air he uses so far as heat absorption 

is concerned, within reasonable limits; and larger porportions of air

mean larger oxygen mass action and more complete combustion. 

As a general rule the air supply per pound of fuel must be decreased, 

at a sacrifice of completeness of combustion, when the temperature 

of the material into which heat is to be put is high.

The only method of alleviating this condition is by making combustion chambers longer, or, much better yet, by putting some firebrick mixing structure in the path of the gases. As such a structure 

is damaged more by high than by low temperatures, it should be 

placed in the first part of the path of the gases to be mixed.

The most economical burning of various fuels for various purposes 

is largely dependent on proper adjustment of oxygen mass action, 

assisted by good stream-mixing structures.
DIMENSIONS OF BOILEES AND SETTINGS. 173

DIMENSIONS OF BOILEKS AND SETTINGS.

T*ne following is a statement of the dimensions of the boilers and 

settings at the fuel-testing plant:

,^i:.- Dimensions of Heine, water-tube boilers and settings used'in steaming tesls.^

Length of drum...................................................feet.. 21T|

Inside diameter of drum........................................ .inches.. 42

Number of tubes....:.................................................. 116

Internal diameter of tubes.'.....................................inches.. 3.26

Outside diameter of tubes.........................................do.... 3.5

Length of tubes exposed ..........................................feet.. 17-^

Plain grate:

Width of furnace..............................................do.... 6.16

Length .of furnace.............................................do.... 6.58

Mean height of furnace..................................... .inches.. 26

Air space..................................................per cent.. 45

Area of grate surface....................................square feet.. 40.55

Rocking grate:

Width of furnace.............................................feet.. 6

Length of furnace.............................................do.... 6.07

Area of grate surface....................................square feet.. 36.4

Depth of ash pit below grate....................................inches.. 25

Height of stack above grate.................................:...... .feet.. 113. 25

Diameter of stack...............................................inches.. 37.5

Area of gas passages:

Stack................................................square inches.. 1,104

Draft passage over bridge wall.................................do.... 888

Aggregate between lower entrance tubes to boiler..............do.... 1,070

Aggregate between tubes in boiler..............................do.... 1, 612

Aggregate between upper tubes from boiler....................do;... 640

Area of water-heating surface:

Tubes..................................................square feet.. 1, 897

Water legs....................................................do.... 91

Shell........................................................do.... 43

Total........................................................ do.... 2, 031

Superheating area....................................................... None.

Total water space............................................ cubic feet.. 287

Steam space. .................................................... .do.... 73

Ratio of heating surface to grate surface.................................. 50.1 to 1

Ratio of smallest draft area to grate area................................. 1 to 9.1

The boilers were erected by the Heine Boiler Company, and were 

similar to those in commercial use. a When the water stood at 3 

inches in the gage glass, boiler No. 1 contained 16,850 pounds of 

water, and boiler No. 2, 16,755 pounds of water, at 75° F. Each inch 

of water, as shown by the glass, represented 340 pounds in the boiler. 

This figure was determined by calibrating the boilers with cold 

water at about 75° F., by noting the height of water in the gage 

glass as the water was drawn from the blow-off and weighed.

oFor further description of apparatus see Prof. Paper U. S. Geol. Survey No. 48,1906, pp. 302-314.
174 A STUDY OF FOUR HUNDRED STEAMING TESTS. 

TRUE BOILEE EFFICIENCY.

In confirmation of the ideas on boiler efficiency and heat absorption 

advanced in this study, and of the probability of being able so to 

construct boilers as to evaporate several times as much water per 

unit .of heating surface, the boiler division has recently begun some 

accurate experiments on heat transmission through the tubes of

small multitubular boilers and finds that the results answer to 

Professor Perry's theory very closely.

An account of the first few experiments will be found in a paper 

read by Prof. L. P. Breckenridge before the Western Society of Engineers, Chicago, March 20, 1907.
A STUDY OF FOUE HUNDRED STEAMING TESTS. 175

GENERAL CONCLUSIONS.

All the tests that are discussed in this bulletin were made under a 

Heine boiler with a hand-fired furnace. The principal object of 

these tests was to determine the relative value of coals for steaming 

purposes. With this in view each coal was burned to its best advantage for hand firing.

All the tests were made^.at about the rated capacity of the boiler, 

carrying a steam pressure of about 80 pounds. The average length 

of a test was about ten hours. The only variable conditions were 

thickness of fire and intensity of draft.

While the average efficiencies are fairly high, better efficiency could 

be obtained with furnaces and other conditions more especially 

adapted to particular coals. The average efficiency obtained at the 

fuel-testing plant is about 10 per cent higher than is obtained in good 

commercial plants. This is true for all coals.

The efficiency used as a basis for comparison of coal tests under a 

boiler is code item 72*. This is the ratio of the heat carried away in 

the steam to the calorific value of the " combustible." In determining the amount of "combustible" burned it was considered that the 

coal which fell through the grate was never fired. This efficiency 72* ' 

is the product of boiler and furnace efficiencies.

Per cent of completeness of combustion is the ratio of heat evolved 

in the furnace to the potential heat in the coal ascending from the 

grate.

The efficiency of the boiler proper is the ratio of the heat absorbed 

by the boiler to the heat evolved in the furnace. Efficiency 72* is not 

commonly subdivided into furnace and boiler efficiency on account 

of the difficulty of determining the actual heat evolved in the furnace.

The true boiler efficiency is the ratio of the heat absorbed by the 

boiler to the heat available for absorption. This is the true measure 

of the ability of a boiler to absorb heat.

Inasmuch as efficiency 72* is the product of furnace and boiler efficiency, it increases with an increase of furnace efficiency, which 

means that efficiency 72* is higher with coals which are more easily 

and completely burned. Except in extreme cases it is very little 

affected by the temperature of combustion. High C02 content in the 

gas analysis is not a definite indication of high efficiency, although 

some high 72* efficiencies were obtained with high C02 content in the 

gas. The best efficiencies of tests recorded in this paper were obtained 

with about 10 per cent of C02 . High CO is always an indication of 

low 72* efficiency. It does not by itself account for all of the incomplete combustion, but merely indicates poor conditions in the furnace. The other combustible gases which probably pass up the 

stack, though occurring in very small quantities, will account for heat 

loss many times as great as the CO loss.
176 A STUDY OF FOUR HUNDRED STEAMING TESTS.

The true boiler efficiency (E4 ) is not of constant value in commercial boilers, but varies somewhat with temperature of combustion 

and capacity. This variation with temperature is due to the heat 

absorbed by radiation from the fire and the hot brick walls. To 

increase capacity there must be a proportionate increase in temperature difference between the first layer of water and the film of gas 

adhering to the tube. Since the temperature of the water is in 

most cases constant, the temperature of the adhering film of gases 

will be raised and the flue gases will leave the boiler at a higher 

temperature.

In general the efficiency is affected by the formation of soot and 

scale on the heating surface and by defective circulation of water in 

the boiler. These conditions cause poor absorption of heat and higher 

flue-gas temperature.

The rate of combustion is affected by the chemical composition of 

the coal, the size of the coal, the intensity of the draft, and to some 

extent by the thickness of the fire 'and the formation of clinker. 

Bituminous coals high in "volatile matter" burn more quickly than 

those high in "fixed carbon." Coals ranging in size from one-fourth 

inch to H inches burn much more rapidly than either very small or 

very large sizes. This is undoubtedly due to a better distribution of 

air with these sizes. Fine coal, the formation of clinker, and thick 

fires hinder the passage of air and reduce the rate of combustion. By 

increasing the draft, more air is drawn through the fuel bed, causing 

the coal to' burn more rapidly.

With higher rates of combustion less air is used per pound of combustible, the temperature of combustion rises, the gases pass through 

the boiler faster, and after a certain rate of combustion is reached 

black smoke is produced. Capacity varies almost directly with the 

rate of combustion. Extremely high or low rates of combustion 

reduce efficiency.

The presence of ash in dry coal up to about 15 per cent has very 

little effect on efficiency and capacity. Above this percentage, however, the efficiency drops.

Moisture reduces efficiency and capacity, perhaps, by hindering 

combustion.

The presence of sulphur in coal is not detrimental to the value of 

coal as fuel for steaming purposes except where it exists in certain 

combinations with other constituents of the ash so as to form fusible 

clinker which may adhere to the grate.

If there are no other reasons for washing coal than for efficient 

burning, coal need not be washed, as the efficiency of the furnace 

and boiler are not increased by washing except with coals of high 

ash or considerable free pyrites. Washed coal can usually be 

burned at a higher rate of combustion. The washing of coal does 

not decrease the per cent of black smoke produced.
COMMERCIAL CONSIDERATIONS. 177'

Most coals when briquetted can be burned at a higher rate'of 

combustion. As a rule briquetted coals burn with little or no 

smoke.

Bituminous coal should be fired in small quantities every three or 

four minutes. It is best to fire only on one-half of the grate area 

at a' time. When burning bituminous coal, up to a medium rate of 

combustion, the production of smoke may be entirely avoided by 

leaving the furnace doors partly open for a short time immediately 

after firing. The best thickness of fire ranges from 5 to 10 inches, 

varying with the intensity of draft of 0.5 to 0.7 inch under the stack 

damper.

Most of the eastern semibituminous coals, especially the small 

sizes, cake badly in the fire. When using these coals the fire must 

be raked frequently. Coal of this class can be fired every five or six 

minutes and more can be fired at a time than of bituminous coal. 

Either the spreading or alternate method of firing, may be used. 

Owing to its tendency to crumble, coal of this class usually reaches 

the boiler room as fine as slack, which reduces its value as a. steaming coal. It can be improved for steaming purposes by briquetting.

Good results can be obtained with lignites if a difference of draft 

of 1£ to 2 inches of water is carried between the ash pit and the 

stack. With this draft these fuels may be fired in large quantities 

every six or eight minutes, the spreading method of firing being 

\ised. Rocking grates may be used to good advantage in burning 

lignites.

For hand firing a furnace with a tile roof and large combustion 

chamber containing good mixing structures is well adapted for burning bituminous and lignitic coals. The mixing structures cause 

resistance to the passage of furnace gases, and consequently a higher 

stack draft must be carried to maintain capacity.

COMMERCIAL CONSIDERATIONS.

General. Inasmuch as the boiler plant is at present the expensive portion of a steaming outfit, and as it probably is possible to 

cut its cost down to a fraction of the present cost and at the same 

time obtain a higher efficiency, it is felt that there is good ground 

for anticipating an enormous improvement in the production of 

steam power within the next few years. If so, it will not be the 

first time that a new arrival in a field has spurred on older forms of 

enterprise to a higher prosperity than they ever dreamed of before. 

The competition of the gas engine may be the best thing that ever 

happened to steam engines and turbines.

The statements, theories, and proposals made in this study are 

widely scattered and may not have been plain because they are 

mathematically involved. For this reason a short summary wi!l be 

8400 Bull. 325 07 12
178 A STUDY OF FOUR HUNDRED STEAMING TESTS.

made here of the possibility of so improving the system of working 

steam-turbine plants that they may be permanently kept above 

commercial competition from gas-producer and engine plants in 

large powers. Of course there is little doubt that a great field 

immediately awaits the gas engine in smaller plants, say under 5,000 

horsepower. All these suggestions are tentative only.

Boilers. The authors see no reason why boilers can not be constructed, and probably operated with entire satisfaction, which will 

produce about ten times the amount of steam now obtained per 

square foot of heating surface, and with no difficulty in obtaining 

dry steam. The efficiency from coal to steam should easily be made 

considerably higher than that of- a good performance of to-day. Such 

a plant would require only a fraction of the present investment in 

steam plants, buildings, and real estate. Perry states in his book, 

The Steam Engine and Gas and Oil Engines, that he thinks boilers 

should be made to do ten and possibly twenty times the work 

they do at present.

Furnaces. It will probably be found on attempting this reduction of dimensions and cost that the limit will be not in the boiler 

as such, but in the combustion chamber. Burning a large amount 

of coal on a small grate area is largely a question of draft and continual riddance of ash, but the rate of travel of gases, through a. 

combustion chamber is dependent, practically, only on the amount 

of carbon burned per unit of time, the rate being about the same 

no matter what the air supply per pound of carbon. As combustion chambers are now constructed for western coals they are too 

small, but "small" is a word not to be understood in this connection as referring to volume or length alone. By a "small combustion chamber" is meant a chamber in which either the time spent 

by the gas in traveling from the front to the rear of the boiler is 

short or the mixing devices are inefficient or absent. In the discussion of mass action it was stated that mere length of combustion 

chamber counts for little that mixing is what counts and thus 

there is. a possibility of enormously increasing the efficiency of a combustion chamber as a burner of volatile matter. Effort in completing a steam-generating outfit of small dimensions must be largely 

concerned with the construction of a combustion chamber containing many gas-mixing appliances.

Turbines. The work on turbines is provisional only, but it is 

believed that all the assumptions made are on the side of safety; 

that is, that the over-all efficiency of the turbines working with 

high superheat and low pressure would probably be greater than 

estimated.
A STUDY OF FOUR HUNDRED STEAMING TESTS. 179

BIBLIOGRAPHY.

BARR, William M. Combustion of coal and the prevention of smoke. The Norman 

W. Henley Publishing Company, New York. 

A practical catechism for engineers.

BARRUS, George H. Boiler tests. D. Van Nostrand, New York.

BOOTH, William H., and KERSHAW, John B. C. Smoke prevention and fuel economy.

The Norman W. Henley Publishing Company, New York. 

DAMOTJR, E. Industrial furnaces and methods of control. Translated by A. L.

Quereau, 1906. Eng. and Min. Jour.

DUHEM, P. Thermodynamics and chemistry. Translated by George K. Burgess. 

Should receive careful study by the chemical engineer.

HOFF, Dr. J. H. van't. Lectures on theoretical and physical chemistry. Translated by'Dr. R. A. Lehfeldt. Part 1, chemical dynamics; part 2, chemical 

statics. Edward Arnold, 37 Bedford street, Strand, London.

JONES, Harry C. Elements of physical chemistry. Macmillan Company.

KENT, William. Steam boiler economy. John Wiley & Sons, New York.

KERSHAW, John B. C., and BOOTH, William H. Smoke prevention and fuel economy. 

The Norman W. Henley Publishing Company.

MELLOR, J. W. Chemical statics and dynamics. Longmans, Green & Co., New York, 

1904.

MELLOR, J. W. Higher mathematics for students of physics and chemistry. Longmans, Green & Co.

An exceedingly helpful book to engineers, but very poorly indexed. Deserves much deep study 

by applied scientists. . "

MEYER, Dr. Oskar Ernil. The kinetic theory of gases. Translated' by Robert E. 

Baynes, M. A. Longmans, Green & Co.

A simple and clearly written book on an intricate subject, by an authority. Should be carefully 

studied by every engineer who deals with gases in any way.

NERN'ST, Dr. Walther. Theoretical chemistry from the standpoint of Avogadro's 

rule and thermodynamics. Translated from fourth German edition. Macmillan Company.

NERNST, W., and WARTENBERG. H. v. Die Dissociation von Wasserdampf. Zeitsch. 

f. prakt. Chemie, vol. 56, No. 5, 1906.

NERNST, W., and WARTENBERG, H. v. Ueber die Dissociation der Kohlensaure. 

Zeitsch. f. prakt. Chemie,'vol. 56, No. 5, 1906.

PARR, S. W. The classification of coals. Jour. Am. Chern. Soc., vol. 28, No. 10, 1906.

PARSONS, H. de B. Steam boilers, their theory and design. A. C. McClurg & Co., 

Chicago.

PENNSYLVANIA RAILROAD COMPANY. Locomotive tests and exhibits of Pennsylvania 

Railroad system at Louisiana Purchase Exposition, St. Louis, 1904. Published 

by the company, Philadelphia, Pa.

PERRY, John. The steam engine and gas and oil engines. Macmillan Company, 1902. 

A splendid book; chapters 26, 30. and 33, concerning boilers, are especially good; gist of most 

matter on true boiler efificiency in footnote of page 591.

ROWAN, F. J. The practical physics of the modem steam boiler. A. C. McClurg &

. Co., Chicago. 

SMITH, Robert H. Commercial economy in steam and other thermal power plants.

J. B. Lippincott Company', Philadelphia, Pa. 

VAN DEVENTER, Dr. Charles M. Physical chemistry for beginners. Translated by

Dr. R. A. Lehfeldt. Edward Arnold, 37 Bedford street, Strand, London. 

WALKER, James. Introduction to physical chemistry. Macmillan Company. 

WARTENBERG, H. v., and NERNST, W. Die Dissociation von Wasserdampf. Zeitsch.

f. prakt. Chemie, vol. 56, No. 5, 1906. 

WARTENBERG, H. v., and NERNST, W. Ueber die 'Dissociation der Kohlensaure.

Zeitsch. f. prakt. Chemie, vol. 56, No. 5, 1906.
180 A STUDY OF FOUR HUNDRED STEAMING TESTS.

GLOSSARY.

ABSOLUTE TEMPERATURE. The temperature of a substance reckoned from that temperature 461° below the zero on the Fahrenheit scale and 273° below the zero 

on the centigrade scale at which all heat is supposedly absent.

AIR-DRIED COAL. A term applied to coal that has been prepared for chemical analysis. 

The coal is dried at a temperature somewhat above that of the room in which 

it is to be analyzed, in the atmospheric conditions prevailing in the room, so that 

the sample will not vary in weight while being handled. No coal has a constant 

air-drying loss, since its loss in weight varies according to conditions, such as size 

of coal analyzed, air currents, and weather conditions. Air-drying results are of 

value only to the chemist who figures them back to coal as received and to dry coal.

AVAILABLE HEAT. The portion of the heat supplied to the boiler over and above the 

amount required to raise the gases from atmospheric to steam temperature.

AVAILABLE HYDROGEN. The excess of hydrogen in coal over and above that which is 

required to unite completely with the oxygen in the coal to form water (H/)). 

It is found by subtracting one-eighth of the total oxygen from the total hydrogen.

AVOGADRO'S LAW. The temperature and pressure being the same, the number of 

molecules in a unit volume is the same for all gases.

BAFFLE. A term applied to partitions designed to change the course of moving gases 

in the combustion chamber or among the boiler tubes.

BASE VALUES. A term used to designate the abscissa value of any point on a curvethat is, the horizontal distance of that point from the left side of the chart.

BLACK BODY, A term used to designate a hollow body whose walls are all at the 

same temperature. If an extremely small hole were made in such a body, heat 

would be radiated through the hole in proportion to the difference of the fourth 

powers of the absolute temperatures of the black body and the surrounding 

objects.

BOLTZMANN AND STEFAN'S LAW. See Stefan and Boltzmann's law.

BRITISH THERMAL UNIT. That quantity of heat which is required to raise the temperature of 1 pound of pure water through 1° F. at or near 39.1° F., the temperature of maximum density of water. The abbreviation B. t. u. is used in this 

volume.

CAKING COAL. A term applied to coal which fuses together when burning a coal 

that is not free burning.

CAPACITY. A term rather loosely used to denote the percentage of steam made, taking 

as the basis (100 per cent) the rated evaporation designated by the boiler builder.

CARBON AVAILABLE-HYDROGEN RATIO. The total carbon content of coal divided 

by the available hydrogen (q. v.).

CARBON, FIXED. See Fixed carbon.

CARBON HYDROGEN RATIO OF DRY COAL. The total carbon content divided by the 

total hydrogen content.

CARBON HYDROGEN RATIO OF COAL "AS FIRED," OR "AS RECEIVED" (MOIST COAL). 

The total carbon content divided by the total hydrogen content, including the 

hydrogen of the free moisture present.

CATALYZER. A substance whose presence, among the substances participating in a 

chemical reaction, hastens or retards the speed of the reaction, although the 

nature and total amount of catalyzer present is always the same at the end as at 

the beginning of the reaction, so far as can be detected.

CELLULOSE. A substance represented chemically by the expression C6H1005 . It is 

the basis of wood structure, excluding a slight amount of mineral ash in the cell 

walls.

CLINKER. A term used herein to designate the more or less molten portions of ash 

(including some carbon) drawn from the grate and ash pit.

CO. Abbreviation for carbon monoxide.
GLOSSAEY. 181

C02 . Abbreviation for carbon dioxide.

COAL, AIR-DRIED. See Air-dried coal. 

COAL, DRY. See Dry coal.

COAL, FREE-BURNING. See Free-burning coal.

COMBUSTIBLE. A loose expression and misnomer for the phrase "coal free from moisture and ash," sometimes called "pure coal." The pounds of "combustible" 

used in every steam test have been computed in two ways, as follows: '

1. Item 30: Obtained by subtracting from the total pounds of dry coal fired 

the pounds of ash and combustible drawn out of the ash pit and through the fire 

doors in cleaning the fire.

2. Item 30*: The weight of the coal fired is corrected for moisture and ash as 

given by the proximate analysis, thereby giving the pounds of "combustible" 

fired. From this amount is subtracted the pounds of "combustible" lost in the 

refuse, giving the total pounds of "combustible" actually ascending from the 

grate during the test.

Two efficiencies have been figured from these weights of "combustible" 

items 72 and 72*.

In this bulletin there are many references to '' code item 72*.'' In reality there 

is no such item. This 72* item is the one given in the code as item 72, and is the 

comparable efficiency, because with different grates different amounts-of coal 

might drop into the ash pit and in figuring 72* corrections have been made for this 

loss. (See 72* under "Computations of a steaming test," p1 . 151.)

Whenever the word "combustible" in this bulletin is in quotation marks it 

means "coal free from moisture and ash." Quotation marks are employed 

because the word used in this sense is a misnomer, inasmuch as the oxygen and 

nitrogen, and -perhaps part of the sulphur, do not burn.

COMBUSTION CHAMBER. Strictly, the entire space between the surface of the fuel 

bed and the area at which the gases enter the boiler; term usually applied, however, to designate the space between the bridge wall and that area.

CONDUCTION. The process of transferring heat by direct contact; as when heat travels 

along a rod, or from a hot stove lid to a flatiron resting on it.

CONVECTION. The addition to, or removal from, .a body of heat, by gases or liquids 

circulating in direct contact with the body; as the removal of heat from a steam 

radiator by the circulation of air.

CONES, SEGER. See Seger cones.

DISSOCIATION. The state of separation of the molecules of a substance into two or 

more parts. A term used herein to denote effects due to high temperatures.

DRY CHIMNEY GASES. In all calculations in this bulletin this term includes C02, 

02 , CO, and N2 gases.

DRY COAL. Coal which has been dried in a very finely powdered condition for one 

hour at a constant temperature of 105° C. In the expression "B. t. u. per pound 

of dry coal as fired," however, the "dry coal" is computed from a determination 

of the moisture in the coal sample.

EFFICIENCIES:

Boiler and grate ("over-all"} efficiency, code item 73, denoted by E1; is the ratio 

of the heat absorbed by boiler to the potential heat of dry coal fired.

Boiler efficiency, code item 72*, denoted by E2 , is the ratio of the heat absorbed 

by the boiler to the potential heat of combustible ascending from grate. The 

combustible in this item is equal to the total dry coal fired, minus the ash by 

analysis of dry coal, minus the combustible in refuse.

Boiler efficiency, code item 72 (seldom referred to in this bulletin), is the same 

as 72*, except that the combustible is taken to be equal to total dry coal fired 

minus the total refuse determined by actual weighing, this total refuse being 

combustible and ash.

Furnace efficiency, or per cent of completeness of combustion, denoted by E3 , is 

the ratio of the heat actually evolved in the furnace to the potential heat of the 

combustible ascending from the grate.
182 A STUDY OF FOUK HUNDRED STEAMING TESTS.

EFFICIENCIES Continued.

True boiler efficiency, denoted by E4 , is the ratio of the heat absorbed by the 

boiler to the heat in the gases which is available to the boiler, counting only 

that part of the heat in the gases as available to the boiler which remains after 

subtracting from the total heat actually generated the amount which is used in 

heating the gases from atmospheric to steam temperature.

Boiler efficiency corrected, denoted by E5 , is the ratio of the heat absorbed by 

the boiler to the heat actually evolved in the furnace.

Tliermodynamic furnace efficiency is the ratio of the heat made available to the 

boiler to the potential heat of coal fired.

Thcrmodynamic efficiency of boiler is the ratio of the heat made available for 

engine or turbine to the heat available to the boiler.

EMPIRICAL FORMULA. A formula expressing the actual relations between two or more 

variables and constants, but not founded on known laws. Cf. " Rational formula.''

ENDOTHERMIC. An adjective describing a chemical reaction which can take place 

only by absorbing heat from the surroundings or by reducing the temperature of 

the reacting matter. The opposite of exothermic.

EXOTHERMIC. An adjective describing a chemical reaction which evolves heat. The 

opposite of endothermic. 

FIXED CARBON. A term applied to that portion of the carbon in a coal left after the 

"volatilization" process of the proximate analysis. It is obtained by subtracting 

from 100 the percentages of ash, moisture, and volatile matter.

FREE-BURNING COAL. A term applied to coal which when thrown in the'fire burns 

without the separate pieces of coal fusing together. A noncaking coal.

"FREE" MOISTURE. Moisture which is driven off from coal when subjected to a 

temperature of 105° C. (221° F.) for one hour. t

GRAM MOLECULE. An amount of a substance, in granis, numerically equal to the 

molecular weight of the substance. For instance,'a gram molecule of water is 

18 grams, the molecular weight of water being 18 (2 of hydrogen and 16 of oxygen).

HEAT, AVAILABLE. See Available heat:

HOOD. The inverted funnel, usually about 4 feet high, between the top of the brick 

setting and the bottom of the cylindrical smokestack. The flue temperatures 

and gas samples are taken at the top of the hood, and the stack damper is just 

above this point.

HYDROGEN, AVAILABLE. See Available hydrogen.

HYDROCARBON GASES (HYDROCARBONS). Gases which are distilled from coal when 

it is heated. They are high in heating value, approximately 1£ times as high in 

B. t. u. per pound as pure carbon. They usually occur in three forms, expressed 

by the formulas: C,,Hn , CnH2n , and GnH2n+2 .

IGNITION TEMPERATURE. The ignition temperature of a substance is that temperature to which it must be raised in the presence of oxygen to cause the two to unite 

by combustion. This temperature is rather indefinite, as extremely, slow union 

begins far below the point of rapid union. For any one substance there are generally two temperatures, within perhaps 200° F. 'of each other, at the lower of 

which the rate of combustion is inappreciable and at the higher of which it is 

almost infinite. " '

KINETIC THEORY OF GASES. This theory postulates that gases consist of immense 

numbers of individual molecules moving among each other with enormous 

velocities. The sum of the molecular impacts against the sides of a containing 

vessel constitutes the pressure of a gas. Raising the temperature of a gas increases 

the molecular speed, and consequently the force of impact.

MASS ACTION., LAW OF. The speed of a chemical reaction is-proportional to the product of the weights of reacting substances present, in unit volume, the weight of 

each substance being expressed in gram molecules.

MOISTURE, "FREE." See "Free" moisture.
GLOSS AEY. 183

O2 . Abbreviation for oxygen (one gaseous molecule).

ORSAT APPARATUS. An instrument for determining the percentages of carbon dioxide, 

oxygen, and carbon monoxide by absorbing them successively in certain solutions. 

(See text-books on gas analysis.)

POTENTIAL HEAT. A. term applied to the heat in coal as determined by a calorimeter.

PROBABILITY CURVE. The graphic plotting of a certain mathematical equation 

expressing the likelihood of a quantity being more or less different from what it 

"ought" to be. (Seep. 158.)

PROXIMATE ANALYSIS OF COAL. An empirical method of determining the percentage 

of "free" moisture, of "volatile matter," of "fixed carbon," and of ash in coal. 

The method of determination varies somewhat with different chemists.

PYROMETER. An instrument for measuring high temperatures.

RADIATION. The process of transferring heat through space from one body to another 

without the aid of tangible substance for example, the transfer of heat from the 

sun to the earth.

RATIONAL FORMULA. A formula deduced from fundamental laws, as of physics. Of. 

"Empirical formula."

REFUSE. Clinker, ash, and unconsumed coal taken from the ash pit and pulled out of 

the furnace when cleaning fire.

SEGER CONES. Small pyramids made of various chemicals variously mixed. The 

temperatures of softening of the different cones are fairly well known. Sdveral 

of them are put into a furnace in a row, each having a melting point intermediate 

between its neighbors. By watching the curling over of the tips one.can form a 

fairly correct estimate of the average temperature.

STEFAN AND BOLTZMANN'S LAW. The amount of energy radiated by a black-body 

surface to another body is proportional to the difference of the fourth powers of 

their absolute temperatures.

STRAIGHT-LINE FUNCTION. A value changing directly or inversely with a variable, so 

that if simultaneous values are plotted on coordinate paper the points would lie 

in a straight line.

TEMPERATURE, ABSOLUTE. See Absolute temperature.

TEMPERATURE, IGNITION. See Ignition temperature.

TEMPERATURE GRADIENT. As used in this bulletin, any continuous change of temperature along a body actively conducting heat.

ULTIMATE ANALYSIS OF COAL. A chemical analysis^so made as to give, in percentages, 

the amounts of carbon, hydrogen, oxygen, nitrogen, and ash in a dry coal. The 

sulphur is separately determined.

"UNACCOUNTED-FOR LOSS." That percentage of the potential heat of a combustible 

which, remains after deducting all the known expenditures of heat.

VELOCITY. A term loosely applied to the speed of a chemical reaction for example, 

combustion. It is proportional at any instant to the rate of formation of new substance by the reaction. ' VOLATILE MATTER FROM PROXIMATE ANALYSIS, or "volatile combustible matter," as it 

is often incorrectly termed, is the mixture of gases, together with some particles 

of carbon, driven off when a sample of finely ground coal is heated in a closed 

vessel. This is an arbitrary determination, dependent on the operator and the 

conditions under which it is made. A committee from the American Chemical 

Society has suggested a method of volatilization which is generally followed. 

This method gives fairly concordant results when the same operator, using the 

same apparatus, makes duplicate determinations on the same sample of coal.

VOLATILE CARBON. A. name given to that part of the carbon in coal which is expelled 

 in the process of volatilization by the "standard method" of proximate analysis. 

It exists in the "volatile matter" resulting from distillation, largely in combination with hydrogen as gaseous hydrocarbons.

WATER OF COMPOSITION. A fictitious value determined by uniting the total oxygen 

in dry coal with such a part of the hydrogen as would be required to form water.

INDEX.

A. Page.

Absorption. See Boiler, absorption

by.

Absolute temperature, definition of_ 180 

Acknowledgments to those aiding _ 7-8 

Air-dried coal, definition-of_____ 180

See also Coal, air-dried. 

Air leakage, data on__________ 67-68 

Air supply. See Draft. 

Alabama coal, smoke test of____ 57 

No. 3, smoke test of__________ 58

No. .4, carbon-hydrogen ratio of_ 72, 77 

smoke test of__________ 58 

Arkansas coal, smoke test of____ 57 

No. 7, smoke test of ___ __ 58 

No. 7 A, carbon-hydrogen ratio of_ 71, 77 

No. 8, carbon-hydrogen ratio of_ 71, 77 

smoke test of___-______ 58 

No. 10, smoke test of_______ 58 

Ash, amount of, carried over wall, relation of, to unaccounted for loss______ 168-169 

discussion of _______ 31-33, 38-44 

distribution of __________ 29, 36 

fusing point of, determination of_ 29 

relation of, to method of burning .____________ 43

to carbon-hydrogen ratio _ 42 

figure showing ____ 41 

to combustion-chamber temperatures ______ 42 

figure showing ____ 41 

to completeness of combustion__________ 42

figure showing _ _ 41 

to dry-chimney-gas evolution____________ 42 

figure showing_____ 41 

to efficiency 72*_______ 41-42 

figure showing_ __ 41 

to flue-gas temperatures__ 42 

figure showing.____ 41 

to rated capacity_____ 42 

figure showing_ _ 41 

relation of clinkers and____ 36, 39 

figure showing ____ . 40

relation of efficiency 72* to__ 31,

32-33, 176

figure showing________ 33

relation of efficiency 73 and__ 39, 176 

relation of size of .coal to__ 42-43, 49 

figure showing_.._____ 48 

See also Coal, dry, ash plus sulphur in. 

Ash-sulphur ratio, relation of, to

clinkering ________ 38-39 

relation of efficiency 72* and__ 93-94

Page.

Available hea't, definition of_____ 180 

Available hydrogen, definition .of__ 180 

See also Coal, hydrogen in ; Hydrogen. 

Avogadro's law, statement of ___ 110-180

B.

Baffle, definition of__________ 180 

description of_____ ___ 62

figure showing _ 62

use of ____________ 20,62-63

Barker, Perry, work of__ _ 10

Base values, definition of__ _ 180

Bibliography ______ _________ 179

Bird, F. J., work of __ - 10 

Black body, definition of_______ 180

Boiler and grate efficiency Ei, definition of__________ 181 

Boiler efficiency E4 , calculation of__ ISO136, 143,147-149, 174 

conclusions on_ __ 176 

constant-capacity curves of__ 143- 

144,147-149

figure showing-__ ' 144 

curve of_ _ 146-149 

figure showing. _ __ .147 

definition of ________ 95,141,182 

relation of, to initial temperature __________ 112-113 

relation of efficiency 72* and__ 147 

figure showing _______ 147

relation of probability curve

to ____.______ 146-149^ 

figure showing _______ 147

Boiler efficiency corrected Er,, calculation of __ 130-132, 142-143 

constant-capacity curves of___ 141- 

143, 147-149

figure showing__ ___ 141

definition of ______ 95, 138, 140, 182

discussion of ____________ 95-99,

103-109, 134-149

relation of, to ratio of velocity / 

of gas to combustionchamber temperature 140-141 

figure showing________ 14.1

relation of carbon-hydrogen ratio to_______ 73-74, 78-79 

figures showing ______ 37, 71 

relation of combustion-chamber

temperature and ___ 51

relation of heat evolution to__ 93-94-

figure showing _ _______ 93

relation of smoke to______ 56

figure showing :__ 56
186 INDEX.

Page. 

Boiler efficiency 72, definition of____ 181

Boiler efficiency 72,* classification by 40 

conclusions on__________ 175

definition of ______ 137-138, 181

relation of, to ash______ 31, 32-33

to ash, figure showing___ 33

to ash-sulphur basis_____ 93, 94

to carbon dioxide in flue

gases _:___1__ 26-27, 35 

figure showing_ _ 27 

to carbon monoxide in flue

gases _______ 26-27, 65

figure showing ____ 27

to clinker in refuse____ 28,

29, 31, 35, 44

figure showing_____ - 30

to sulphur_________ 28-31,44

figure showing_____ 30

to unaccounted for loss_ 139

figure showing __ 138

relation of ash to______ 41-42, 176

figure showing-_______ 41

relation of ash plus sulphur to_ 94, 95 

relation of ash-sulphur ratio to_ 94 

relation of carbon available

hydrogen ratio to_____ 83-84

figure showing________ 84 

relation of carbon (volatile)- 

carbon (total) ratio 

to ______________ 83-85' 

figure showing_______- 86 

relation of carbon-hydrogen

ratio to __ 70-76, 79-83, 88 

figure showing _ 37,

 69, 71, 74, 75, 76,

 79, 80, 81, 82, 83 

.relation of carbon monoxide in

flue gases to_____ 27, 65 

figure showing ________ 28 

relation of clinker in refuse to_ 44 

relation of combustion-chamber

temperature to___- 22-24, 50 

figure showing __.______ 25 

relation of fixed carbon to__ 90 

figure showing ___ _ 91 

relation of hydrogen to____ 83 

 figure showing _ 84 

relation of hydrogen-available hydrogen ratio to_ 85-86 

figure showing ___ 87 

relation of iron-ash ratio to__ 34-35,

'37-38

figure showing ______ 35 

relation of moisture to_____ 32,176 

figure showing _ _ 33 

relation of nitrogen in flue gases

to ____________ 64-65 

figure showing.____ -. 28 

relation of oxygen in combustible and ________ 92-93 

figure showing ______ 92 

relation of probability curve and

146-149 

figure showing ____ 147

Page. 

Boiler efficiency 72*, relation of rate

of combustion to___ 16-17 

relation of rate of combustion

to, figure showing__ 17 

relation of rate of heat evolution to _________ 15-17 

figure showing _______ 14

relation of rated capacity to__ 52

relation of size of coal to___ 46 51

figure showing ________ 46, 48

relation of sulphur in coal to_ 43-44,

176

figures showing __ 43 

relation of true boiler efficiency

(E4 ) and ________ 147

figure showing ________ 147

relation of volatile matter to__ 89-90

figure showing _________ 90

relation of washing to_____ 176 

relation of wind to______ 167-168 

test of ______________ 26-32 

Boiler efficiency 72* at about rated 

capacity, relation of 

carbon-hydrogen ratio 

to_____________ 70 

figure showing ______ 69

Boiler efficiency 73, definition of__ 181 

relation of ash and_____ 39-40, 176 

figure showing ______ 40 

Boiler tubes. See Tubes. 

Boilers, air leakage of, data on___ 67-68 

cost of ______________ 177 

dimensions of ___________ 173 

figure showing ______ 174 

efficiency of. Sec Boiler efficiency.

heat absorption by__-.___ 105-112 

factors of, relation of, to furnace temperature- 113-114 

relation of, to furnace 

temperature, figureshowing ______._ 15

Perry's theory of ____ 109-112 

test of ________ 132-134 

relation of, to physical attributes ______ 112-113 

to total available heat 130- 

131,137

figure showing __ 131 

relation of carbon-hydrogen

ratio to ________ 37 

figure showing _ 37 

relation of density of gas

to ________ 109, 113-114

figure showing _____ 15

relation of gas velocity to 109-

110,113-118, 130-132

figure showing ___ 131

relation of specific heat of

gases to __ 110-112,132-137. 

relation of water circulation and _______ 120-121 

theoretical curves of____ 27-28 

figure showing ___ 29
INDEX. 187

"Page. 

Boilers, heat absorption by, theory

of _______ 109-112 

heat absorption by, theory of,

application of__ 118-120 

theory of, modifications of- 125- 

132,134-137 

variation in, along a fire

tube _______ 121-125 

along a fire 'tube, figures showing _ 123-124 

See also Heat balance, 

heat losses of _______ 99 

improvement of ____ ____ 177 

insulation of, by soot, etc___ 125-132 

low pressure in, effect of, on

economy _____ _ 102-105 

parts of ______________ 95 

rated capacity of. See Capacity,

rated.

type of :_____________ 8 

water circulation in, effect of 

firing and cleaning fires 

on _____________ 162 

effect of. firing and cleaning fires on, figure 

showing _________ 162 

indicator for, description

of___________ 160-162 

figure showing ______ 161 

rate of, relation of rate of

steaming to______ 16, 163 

figure showing ___ 16 

relation of heat absorption

and __________ 120-121 

Boltzman and Stephan's law, statement of _______ 112, 183 

Brazil coal, smoke test of______ 57 

No. 1, clinker in_________'_. 34 

smoke test of_____,_____ 58 

Brcckenridge, L. P., work of____ 10,174 

Briquetting, effects of________ 50, 177 

British thermal units, definition of__ 180 

See also Heat.

Caking, definition of _________ 180 

Calcium sulphate, occurrence of _ 38

Sea also Sulphur. 

Campbell, M. R., carbon-hydrogen

classification by_:__ 68 

Capacity,'rated, definition of____ 180 

discussion of__________ 51 52 

relation of, to combustion-chamber temperature ___ 52 

to efficiency.________ 52 

to ratio of combustionchamber temperature 

minus steam to flue 

gas minus steam__ 137 

figure showing____ 136 

relation of ash to__'______ 42 

figure showing _ _ 41 

relation of carbon-hydrogen ratio to ___________ 69, 73

Page.

Capacity, rated, relation of ^arbondrogen ratio to, figure 

showing _____ _ 37, 69, 

71, 74, 75, 76,79, 80, 81, 82 

relation of .clinker in refuse to,

figure showiug_!_________ 36

relation of combustion-chamber

temperature to__20-21, 25-26

figures showing____ _ 21, 25

relation .of fixed carbon to_ 90

figure showing ___ --- 91

relation of heat evolution to___ 15, 94

figure showing ____ 14, 93

relation of hydrogen-available

hydrogen ratio to___ 86 

figure showing.________ 87

relation of rate of combustion

.to_____________ 17,176 

figure showing _______ 17 

relation of revolutions per minute and___.___ _ 1G, 103 

figure showing ^._________ 16

relation of size of coabto_:_ _ 46, 48

figure showing _-__:__ ___ 46, 48

Carbon, fixed, classification by____ 87-88

definition of -- - _____________ 180

nature of______:___ __ 59

relation -of, 'to completeness of

combustion ___ _ _ 92 

to completeness of combustion, figure showing__ 91 

to combustion-chamber temperature _________ 90-91 

figure showing 91 

to efficiency 72*______ 90 

figure showing ____ 91 

to flue-gas temperature___ 91 

figure showing _____ 91

to gas evolution___ ___ 92 

figure showing ____ 91 

to rated capacity______ 90 

figure showing _ 9.1 

relation of-smoke to_______ 57 

figure showing ________ _ 56 

Carbon, volatile, definition of____ 59,183 

Carbon (volatile) total carbon ratio, 

relation of, to efficiency 

72* __!__________ 83-85 

relation of, to efficiency 72*,

figure showing_____ 86 

CarbonTavailable hydrogen ratio,

definition of _1_____ 180 

Sec also Coal, dry; Coal as rei. ceived. 

Carbon dioxide. See Gases, carbon

dioxide in.''

Carbon-hydrogen ratio, basis of___ 68-69 

classification by__________ 68-81 

definition of__________.__ 180 

Sec also Coal as received ; Coal,

dry.

Carbon monoxide, definition of___ 180 

Sec also Gases, carbon monoxide 

in.
188 INDEX.

Page.

Carbon monoxide loss, relation of 

carbon-hydrogen ratio 

to __________ 73, 74-80 

relation of carbon-hydrogen ratio to, figures showing ________ 37, 71, 74, 75, 

76, 79, 80, 81, 82

relation of clinker and__: __ 35 

relation of hydrogen available

hydrogen ratio to____ 86 

figure showing- _ . 87 

relation of rate of combustion

to _____________ 12 

figure showing . 12 

relation of heat evolution to 14-15 

figure showing _ . 13 

Catalyzer, definition of_________ 180 

Cellulose, definition of________ 180 

Chimney gases. See Gases. 

Circulation, water. See Boiler, water circulation in. 

Cleaning fires, effect of, on water

circulation _______ 162 

effect of, on water circulation,

figure showing . 162

time required for________ 38, 39

Clinker, definition of__________ 180

See also Refuse, clinker in. 

CO. See Carbon monoxide. 

C02 . See Carbon dioxide. 

Coal, ash in. See Ash.

ash-sulphur ratio of, relation of

efficiency and ____ 93-94 

burning of, relation of ash and

clinkers to_______ 43 

classification of ________ 17, 68-94 

clinker from. See Refuse, clink- .

ers in.

combustion of, forecasting of__ 10 

crushing of, advantage .of____ 50-51 

distillation of___________ 58-59 

iron in, relation of, to clinkers- 35, 38

nature of______________ 58

size of, effects of________.__ 45-51

relation of ash and_____ 42 43

relation of clinkers and__ 35 37,

40-41, 47

relation of nitrogen in flue

gases to _______ 65 

figure showing____ 28 

See also Coal, dry. 

sizing of _______________ 45-46 

sulphur in. See Sulphur, 

washing of, relation of, to efficiency 72*_______ 176 

See also Combustible. 

Coal, air dried, classification of, on

carbon-hydrogen ratio. 68-70 

definition of ____________ 180 

Coal as received, ash in. See Ash. 

carbon-available- carbon ratio

' of, definition of ___ 180 

relation of, to efficiency

72* ___________. 83 

figure showing_____ 84

Page. 

Coal as received, carbon-hydrogen

ratio of ________ 70-72

carbon-hydrogen ratio of, relation of, to CO lossrelation of, to CO loss, figure showing ___ _ 

71, 74,

to combustion-chamber

temperature-_____

figures showing-__

74,

to completeness of combustion________ 

to efficiency 72*_____

figures showing___ 

69, 71, 74, 75,

73, 

74-77

37,

75, 76

75-76

71,

75, 76

82

70-76, 

82-83

37, 

76,83

to efficiency 72* at

about rated capacity 70

figure showing__ 69

to gases evolved _ 73

figures showing._ 37,

71, 74, 75, 76

to heat evolved____ 73 

figures showing __ 71 

to rated capacity---_ 69, 73 

figures showing__ 69, 

71, 74, 75, 76 

to hydrogen-available 

hydrogen ratio 76-77 

figures showing-_ 76 

to theoretical boiler

efficiency _______ 73-74 

figures showing__ 71 

See also Carbon-hydrogen

ratio; Coal, dry.

classification of __________ 70-77 

hydrogen in. See Hydrogen, 

hydrogen - available hydrogen 

ratio of, relation of, to 

carbon-hydrogen ratio _ 76-77 

relation of, to carbon-hy- 

. drogen ratio, figure

showing ____ _ 76

moisture in ____________ 32

relation of efficiency and__ 32,176

figure showing ____ 33

Coal, dry, ash in. - See Ash.

ash plus sulphur in, relation of,

to efficiency 72* ___ 95 

ash-sulphur ratio of, relation of

efficiency 72* and__ 93, 94 

carbon-hydrogen ratio of____ 77-78 

relation of, to CO loss_^__ 79-80 

to CO loss, figure showing ____ 37, 79, 80, 81, 82 

to chimney-gas evolution___________79-81 

figure showing __ 37, 

79, 80, 81, 82

to clinker in refuse___ 78 

figure showing__ 37
INDEX. 189

Page.

Coal, dry, carbon-hydrogen ratio of, 

relation of, to combustion-chamber temperature _____i___ 79-80, 88 

carbon-hydrogen ratio of, relation of, to combustionchamber temperature, figures showing.. 37, 79, 80, 81, 82 

relation of, to efficiency

72*________ 79-81, 88 

to efficiency 72', figures

showing __ ___ 87, 

79, 80, 81, 82 

to gases,- evolved, ' figures showing ___ 79, 

80, 81, 82 

to hydrogen - available

hydrogen ratio___ 77 81

figures showing-. 79, 80,

81, 82

to rated capacity, figures showing 37, 

79, 80, 81, 82 

to theoretical boiler efficiency ________ 78-79 

figure showing__ 37 

relation of ash to_ __ 42 

figure showing. ___ 41 

relations of size of coal

and________ 46-48, 78 

figure showing___ 37, 46, 48 

See also Carbon-hydrogen 

ratio ; Coal as received, 

classification of, on carbon-hydrogen ratio 77-82 

on efficiency basis_____ 40 

definition of ____________ 181 

hydrogen in. See Hydrogen, 

hydrogen - available hydrogen

ratio of __________ 85-88 

relation of, to CO loss___ 86 

to CO loss, figure showing __________ 87 

to combustion-chamber

temperature __ 85-86 

figure showing __ 87 

to rated capacity 86 

figure showing __ 87 

to efficiency 72*____ 85-86 

figure showing __ 87 

to carbon-hydrogen ratio ________ 79-81 

figure showing __ 37. 

80, 81, 82 

iron-ash ratio of, relation of,

to efficiency__ 34-35, 37-38 

relation of, to efficiency, figure showing _____ 35 

oxygen in, relation of smoke to_ 57 

relation of smoke to, figure

showing _________ 56 

size of,-relation of, to ash____ 49 

relation of, to ash, figure

showing-_______ 48 

to carbon - hydrogen

ratio_______ 46-48 

'figures showing __ 46, 48

Page.

Coal, size of, relation of, to chimneygas evolution ___ 46, 48-49 

size of, relation of, to chimneygas evolution, figure 

showing ___J____ 46, 48 

relation of, to combustionc h a m b e r temperature _._______ .46, 47, 50 

to combustion-chamber 

temperature, figure 

showing ______ 46 

to completeness of combustion __ ____ 46 

figure showing ___ 46 

to draft_________ 48, 176 

figure showing _ 48 

to efficiency 72*_____ 46-51 

figure showing _:._ 46, 48 

to flue-gas temperature 40 

figure showing _ 46 

to rated capacity___ 46, 48 

figure showing. 48 

to rate of combustion- 48, 176 

figure showing___ 46, 48 

See also Coal, 

sulphur in. See Sulphur. 

Coal, pulverized, burning of- ___ 50-51 

Combustible, computation of____ 181 

definition of ___________ 181 

hydrogen in. See Hydrogen, 

oxygen in. See Oxygen, 

relation of, to gas evolution__ 167 

volatile matter in, classification

by ______'_____ 87-90 

relation of, to combustion-

. chamber temperature 90 

to combustion-chamber 

temperature, figure 

showing ______ 89 

relation of, to efficiency

72*___________ 89-90 

figure showing ___ 89 

Combustible in refuse, relation of

clinkers to___i___ 38 

Combustion, completeness of, definition of_________ 172,181 

completeness of. _ _ _ 10 

relation of ash to __ 42 

figure showing___ 41 

relation of COo in flue gases

to ___________ 65-66 

figure showing _____ 51 

relation of carbon-hydrogen

ratio to__________ 82-

relation of draft and____ 172

relation of fixed carbon to^ 92

figure . showing ____ 91

relation of heat evolution

to ___________ 94 

figure showing __ 93 

relation of size of coal to_ 46 

figure showing___ 46 

relation of sulphur to____ 44 

figure showing _____ 43 

relation of-temperature and- 172 

See also Furnace efficiency 

' E3.
190 INDEX.

Page. 

Combustion, products of, relation of,

to draft__________ 15-16 

products of, relation of, to draft,

figure showing _____ 15 

temperature of, relation of,

to draft______ 159-160 

figure showing _____ 160 

rate of__-__________ 60-61,176 

relation of, to draft____ 176 

to rated capacity- 16-17,176 

figure showing___ 17 

to flue-gas temperature 11 

figure showing __ 12 

to various losses--__ 11-13 

figure showing _ 12 

relation of combustiouchamber temperature 

to____________ 19-20 

figure showing_____ 20 

relation of size of coal to_ 48,176 

figure showing_____ 48 

results of, forecasting of__ 10 

temperatures of, calculation of-:-_________ 9-10 

relation of draft and 

completeness of combustion and_____ 172

Combustion chamber, baffle wall in.

Sec Baffle.

carbon monoxide in_______ 166-167

relation of smoke and__ 166-167

definition of___________ 181

description of___________ 59

gases in, analyses of_______ 59-60

volumetric composition of_ 61

See also Gases.

temperature of, discussion of__ 18-26 

relation of, to carbon dioxide in flue gas___ 24-25 

to carbon dioxide in 

flue gas, figure showing 25 

to efficiency 72*____ 20-21, 

23-24, 50, 51

. figures showing__ 21,25

to flue-gas temperature- 22-23

figure showing__ 24

to heat balance_____ 63

figure showing^ 63

to losses ______ 20-21,'63

figure showing__ 21, 63

to rate of combustion- 19-20

figure showing-__ 20

to rated capacity___ 20-21,

25-26

figure showing __ 21, 25 

to theoretical heat evolution_________ 19-20 

figure showing 20 

. relation of ash to_l_____ 42 

figure showing_____ 41 

relation of CO2 to_____ 21-22 

figure showing _____ 22, 23

Page.

Combustion chamber, temperature of, 

relation of carbon- , 

hydrogen ratio to _ 75- 

76, 79, 80, 88

temperature of, relation of carbon-hydrogen ratio 

to, figure'"showing_ 37,71, 

74, 75, 76, 79, 80, 81, 82 

relation of CO to____ 21-22, 65 

figure showing___ 22, 23 

relation of clinkers in refuse to________ 44 

figure showing ____ 36- 

relation of fixed carbon to_ 90-91 

figure showing_____ 91 

relation of flue-gas composition to_______ 21-22 

figures showing-____ 22,23 

relation of heat evolution to,

figure showing____ 93. 

relation of hydrogen-available hydrogen ratio 

to __________ 85-86 

figure showing _____ 87 

relation of oxygen in flue

gas to_________ 21-22 

figures showing ____ 22, 23 

relation of rated capacity

to _______ __'_ 52

relation of size of coal to_ 46,

 ' 47, 50

figure showing : 46

relation of smoke to_ _ 57

figure showing __ _ 56

relation of sulphur to___ . 44

figure showing _____ 43

relation of volatile matter

. to ____________ 90 

figure showing _ 89 

temperature of, minus steam,

relation of, to flue gas 

minus steam ____ 132-134 

minus steam, relation of, to 

flue gas minus steam, 

figure showing ___ 133 

relation of, to flue gas 

 minus steam, modifications of_____ 134-137 

Combustion space, description of 59 

function of__ _____ 59 

Conduction, definition of__ __ 181 

Cones, Seger, definition of 183 

Convection, definition of^___ 181

D.

Data, reliability of _________ 149-153 

Density. See Gases, density of.' 

Dissociation. See Gases, dissociation 

of.
INDEX. 191

Page. 

Draft, In stack, relation of, to gas

evolution____:____ 167 

in stack and over fire, difference

of_____________ 167 

relation of, to chimney-gas .

evolution _______ 66-68 

to chimney-gas evolution, figure showing. 6G 

to size of coal_____ 48 

figure showing__ 48 

over fire, relation of availability

of heat to_______ 137 

relation of availability of

heat to, figure showing. 138 

relation of completeness of

combustion and ____ 172 

relation of products of combustion to _____-__ 15-16 

figure showing.______ 15 

relation of rate of combustion and__.______ 176 

relation of temperature of 

products of combustion to_ 159-160, 172 

figure showing 160 

Dry chimney gases, definition of__ 181

See also Gases. 

Dry coal. See Coal, dry.

Efficiencies, thermodynamic, definition of _______ 95-97, 182 

definition of, figure illustrating- 96 

Empirical formula, definition of _ 182 

Endothermic, definition of______ 182 

Exothermic, definition of_______ 182

F.

Fire tubes, absorption of heat by,

. increase in ___ 124 125 

absorption of heat by, variations in________ 121-125 

variations in, figures showing ___________ 123,124 

incasing of_____ _-_ 164 

See also Boilers.

Fires, cleaning of, time of_______ 38, 39 

Firing, effect of, on water circulation ____________ 162 

.effect of, on water circulation,

figure showing-__ 162 

method of, recommendation

of______________ 177 

Fixed carbon. See Carbon, fixed. 

Fletcher, C. J., work of- ___ 10 

Florida coal, smoke test cf 57 

Flue gases. See Gases. 

Free-burning coal, definition of__ 181 

Free moisture, definition of__ 182 

Fuel adaptation, principles of__ _ 10

Page. 

Furnace, adaptation of, to burning

slack___________ 50 

gases of. See Gases, furnace, 

heat evolution in, calculation of 137 

heat losses in__l_________ 99 

improvement of __________ 178 

initial temperature of, modifications due to_-__ 134-137 

relation of, to economy ___ 100-102 

parts of___ _________ 59 

temperatures of__________ 26 

Furnace efficiency E3, definition of_ 138,

172,181

discussion of______ 95-99, 137-14& 

figure showing ________ 96 

See also Combustion, completeness of.

G.

Gait, Ralph, work of_________ 10

Gas sampler, description of_ 154-155,156

figure Showing__________ 24, 157

readings of-^ ________ 155-156

Gases, analyses of________ 59-60, 100

carbon dioxide in, dissociation

of ___________ 153-154 

dissociation of, figure showing______^______ 154 

relation of, to combustionchamber temperature 21-22 

to combustion-chamber 

temperature, figures 

showing _______ 22, 23 

to completeness of

combustion __ 65-66 

figure showing _ _ 51 

 to efficiency 72*____ 27'. 35 

figure showing__ '27 

relation of combustionchamber temperature to_________ 24-25 

figure showing ____ 25 

relation of efficiency 72* to 26-27 

figure showing ____ 27 

C02 + O2 + CO in, relation of

available hydrogen to 165-166 

variation of________ 164-166 

See also Orsat apparatus, 

carbon monoxide in, relation of, 

to combustion-chamber temperature _ 21-22, 65 

relation of, to combustionchamber temperature, figures showing __"________ 22, 2* 

to efficiency 72*__ 26-27, 65 

figure showing __ 27, 28 

to smoke _______ 57, 167 

figure showing __ 5ft 

relation of efficiency 72*

to__________ 26-27,65

figure showing ___ 27

relation of size of coal to_ 49, 50

. significance of_____ __ 65
192 INDEX.

Page.

Gases, composition of_____ 61,100-101 

composition of, relation of, to 

combustion-c h a m b e r 

temperature ______ 21 22 

relation of, to combustionchamber temperature, 

figures showing ____ 22, 23 

density of, relation of heat absorption to___ 109, 113-114 

relation of heat absorption

to, figure showing ___ 15 

dislodgment of from boiler surface __________ 109-111 

figure showing ___ _ ^_ 110 

dissociation of, definition of__ 181 

processes of____I___ 153-154 

figure showing_.____ 154 

evolution of, relation of ash to_ 42 

relation of ash to, figure

showing _______ 41 

relation of carbon-hydrogen

ratio to ______ 73, 79-81 

figure showing_____ 37, 71, 

74, 75, 76, 79, 80, 81, 82 

relation of clinker in refuse

to ____________ 44

figure showing_ . 36

relation of draft to__ 66-68, 167

figure showing___ _ 66

relation of fixed carbon to_ 92

figure showing_____ 91

relation of heat evolution

to ___________ 94 

figure showing 93 

relation of, rate of combustion to ___ .

figure showing___ 

relation of rate of

evolution to _______

figure showing________

relation of size of coal to_

11

12

heat

.___ 14 

_____ 13

46, 

48-49

figure showing_____ 46, 48 

relation of sulphur to___ 44 

figure showing_____ 4.3 

losses in__ ___ _____ 142 

relation of, to initial temperature____.__ 100-102 

to initial temperature,

figure showing___ 102 

See also CO loss; C02 loss, 

mixing of. See Mass action, law

of.

nitrogen in, relation of, to efficiency ________ 64-65 

relation of, to efficiency,

figure showing ___ 28 

to size of coal_____ 65 

figure showing ^__ 28 

oxygen in, relation of, to combustion - chamber temperature _________ 21-22

Page.

Gases, oxygen in. relation of, to combustion-chamber temperature, figures showing_____________ 22, 23 

specific heat of, relation of, to

heat absorption___ 110-112 

temperature-gradients of__ 126-127 

figure showing_______ 127 

temperature of, relation of, to

heat absorption__ 110-112, 

132-137

relation of ash to______ 42 

figure showing_____ 41 

relation of combustionchamber temperature 

to __________- 22-23 

figure showing_____ 24 

relation of fixed carbon to_ 91 

figure showing_____ 91 

relation of rate of combustion to, figure showing ___________. 12 

relation of rate of heat 

evolution to, figure 

showing _________ 13 

relation of size of coal to_ 46 

figure showing.____ 46 

temperature ofj minus steam, 

ratio of combustionchamber temperature 

to __ _________. 132-134 

figure showing___ 133 

modification of 134-137 

minus steam, relation of,

to rated capacity___ 137 

velocity of, ratio of, to combustion-chamber temperature, relation of, 

efliciency E5 to___ 141-142 

ratio of, to combustionchamber temperature, 

relation of efficiency E5 

to, figure showing__ 141 

relation of, to heat absorption _________ 109-110, 

113-118, 130-132 

to heat absorption, figure showing_:__ 131 

volumetric composition of___ 61 

Glossary ________________ 180-183 

Gram molecule, definition of____ 182 

Grate, function of________.__ 59 

Green, C. I-L, work of_________ 10

H.

Heat, absorption of__ ______ 95-149 

absorption of. See also Boiler, 

absorption-of heat by; 

Boiler efficiency, 

availability of, relation of, to

draft __________ 139 

relation of, to draft, figure

. showing ________ 138
INDEX. 193:

Page.

Heat, evolution of___________ 93-94 

rate cf_____________ 13-18 

relation of, to efficiency

72* _______,_ 15-17 

to efficiency 72*,

figure showing 14 

to flue-gas temperature ____ 14 

figure showing 13 

to various losses_ 13-15 

figure showing 13 

to rated capacity- 13 

figure showing 14 

relation of combustionchamber temperature to_____ 10-20 

figure showing__ 20 

relation of carbon-hydrogen .ratio to_ 73 

figure showing__ 7.1 

relation of, to completeness

of combustion____ 04 

to completeness of combustion,'figure showing _______ ___ 93 

Sec also Cornbus- 

. tion, completeness of; Furnace 

efficiency E3. 

to combustion-chamber 

temperature, figure

showing ___ 93 

to efficiency 72*____ 93-94 

figure showing-_ 9;} 

to gas evolution____ 94 

figure showing__ 93 

to rated capacity___ 94 

figure showing___. 03 

loss of. unaccounted for, definition of_________ 183 

unaccounted for, estimation

of _________ 156-158 

explanation of _ 64 

relation of, to ash

passing over wall- 168-160 

relation of combustionchamber temperature 

to_____-______ 63 

figure showing__ 63 

relation of . efficiency

72* to_________ 137 

figure showing__ 138 

relation of rate of 

combustion to__:_ 12 

figure showing__ 12 

relation of rate of 

heat evolution to__ 14 

figure showing__ 13 

relation of smoke to_ 56-57 

figure showing- 56 

plus loss up stack, relation of combustion-chamber temperature to______ 20-21. 63

Page..

Meat, loss of, unaccounted for, plus 

loss up stack, relation 

of combustion-chamber 

temperature to, figure 

showing_________ 21-6.".. 

loss of, unaccounted for, plus

loss up stack, relation 

of heat evolution to_ 14 

unaccounted for, plus loss 

up stack, relation of 

heat evolution to, 

figure showing___ 13'. 

up stack, relations of, to

rate of combustion. 11-13. 

relations of, to rate of 

combustion, figure 

showing _______ 12- 

to rate of heat 

evolution____ 14-15- 

figure showing _______ .1.",

relation of combustionchamber temperature 

to ___________ 63: 

figure showing- 63. 

relation of rate of heat

evolution to _____ 14-15. 

figure showing__ .13. 

transmission of. See Boilers, 

absorption of heat by.

Meat, available, definition of____ ISOHeat balance, forms of________ 139-

forms of, discussion of____ 139-141 

Hood, definition of_____._______ 182;

Hydrogen, available, definition of__ ISO, 

relation of, to efficiency 72*__ 8-".: 

to efficiency 72*, figure

showing _______ 84

to flue-gas total_____ 165-166.

relation of smoke to______ 57

figure showing________ 56; 

iS'cc also Coal as received ; Coal, 

dry.

Hydrogen-available hydrogen ratip. . 

K<x Coal, as . received ; 

Coal, dry.

I.

Ignition temperature, definition of_ 182: 

Illinois coal, smoke test of_I_____ 57 

tests on_ _________ 49-50' 

use of, in high - temperature

work __________ 159-160- 

No. OB, smoke test of________ 58: 

No. 7C, carbon-hydrogen ratio of_ 72, 78. 

No. 7D, carbon-hydrogen .ratip.of- JJ'2. 78, 

No. 9B, carbon-hydrogen ratio of- 7-2; .78: 

No. 11 A, carbon-hydrogen ratio of- 72, 77 

No. 11C, smoke test of _!___'___ 5$. 

No. 12, carbon-hydrogen ratio of_ 72, 78: 

No. 13, carbon-hydrogen ratio of-- .72,-77'

8400 Bull. 325 07- -13
194 INDEX.

	Page.

Illinois coal, No. 14, carbon-hydrogen ratio of______ 72, 78 

No. 15, carbon-hydrogen ratio of__ 72, 78 

No. 16, carbon-hydrogen ratio of _ 72, 77 

AT o. 18, carbon-hydrogen ratio of_ 72, 78 

No. 19A, carbon-hydrogen ratio of_ 72, 77 

No. 19B, carbon-hydrogen ratio of_ 72, 77 

No. 20, carbon-hydrogen ratio of_ 72, 78

smoke test of _-_ ______ 58

No. 21, carbon-hydrogen ratio of_ 72, 78

smoke test of ________.___ 58

No. 22A, carbon-hydrogen ratio of_ 72, 78

No. 23A, carbon-hydrogen ratio of_ 72, 78

smoke test of __________ 58

No. 24B, carbon-hydrogen ratio of_ 72, 78

No. 25, carbon-hydrogen ratio of _ 72, 78

smoke test of ___________ 58

No. 26, carbon-hydrogen ratio of _ 72, 78

No. 27, carbon-hydrogen ratio of_ 72, 78

Indiana coal, smoke test of_____ 57

tests on __ _ ____ _ 49-50

No. 3,-carbon-hydrogen ratio of _ 72,78

No. 4, carbon-hydrogen ratio of _ 72, 78

No. 5, carbon-hydrogen ratio of__ 72, 78

No. 6, carbon-hydrogen ratio of __ 72, 78

No. 7A, carbon-hydrogen ratio of_ 72, 78

No. 7B, carbon-hydrogen ratio of _ 72, 78

smoke test of ___ _______ 58

No. 8, carbon-hydrogen ratio of __ 72, 78

No. 9, carbon-hydrogen ratio of___ 72, 78

No. 9B, carbon-hydrogen ratio of_ 78

No. 10, carbon-hydrogen ratio of_ 72, 78

No. 11, carbon-hydrogen ratio of_ 72

No. 12, carbon-hydrogen ratio of _ 72, 78

Initial temperature, definition of__ 140

Sec Furnace, initial temperature

of.

Iron in coal, cliukeriug due to _ 34

See also Coal, iron in.

K.

Kansas coals, clinkering of______ 38-39

smoke test of--__--________ 57

No. 6, carbon-hydrogen ratio of__ 72, 77

Kentucky coal, smoke test of____ 57

tests on__________-.____ 49-50

No. 1C, carbon-hydrogen ratio of_ 72, 77

No. 5, carbon-hydrogen ratio of___ 72, 77

No. 6, carbon-hydrogen ratio of__ 72, 77

No. 7, carbon-hydrogen ratio of___ 77

Kinetic theory, statement of____ 182

Kreisinger, Henry, work of_-__---_ 7, 10

Kuss, R. II., work of ____ 10

1,.

Lignites, firing of _ __ 177 

Lord, N. W., work in charge of ___ 7, 29 

Loss unaccounted for, definition of_ 183 

Sec also Heat, loss of, unaccounted for. 

Loss up stack. Sec Heat, loss of, up

stack. 

Low-pressure steam, use of____ 102-104

Page.

M.

Maryland coal, smoke test of____

No. 1, carbon-hydrogen ratio of__

smoke test of_________________

Mass action, law of______ 170-17 

Missouri coal, smoke test of____._ 

No. 5, carbon-hydrogen ratio of___ 

smoke test of___________ 

No. 6, carbon-hydrogen ratio of_lNo. 7, carbon-hydrogen ratio of__ 

Moisture. Sec Coal, moisture in : 

Free moisture.

Negative results, value of_______.

Nerst, Walther, on dissociation__.

New Mexico coal, smoke test of__. 

No. 3A, clinker in_________ 

No. 3B, clinker in________ 

No. 4A, clinker in_________

No. 5, clinker in________. 

smoke test of ____________

Nitrogen. .Sec Gases, nitrogen in.

North Dakota coal, smoke test of_- 

No. 3, smoke .test of ____________

1,77

58

2.182

72, 78

58

72, 78

72,78

9-10 

153 

57 

34 

34 

34 

34 

58

57

58

O.

18

72,77

Observations, reliability of____ 149-153 

Ohio coal, smoke test of_______ 57 

No. 1, carbon-hydrogen ratio of _ 72, 78 

No. 2, carbon-hydrogen ratio of_ 72, 78 

No. 3, carbon-hydrogen ratio of_ 72, 77 

No. 4, carbon-hydrogen ratio of 72, 77 

No. 5, carbon-hydrogen ratio of_ 71,

72, 77

No. 6, carbon-hydrogen ratio of__ 72 

No. 7, carbon-hydrogen ratio of 72, 78 

No. 8, carbon-hydrogen ratio of 72, 78 

No. 8, test of, temperature of, figure showing__________

No. 9A, carbon-hydrogen ratio of_ 

No. 9B, carbon-hydrogen ratio of_ 72, 78 

Optical pycijmeter. See Pyrometer. 

Orsat apparatus, definition of____ 183 

totals in_____________ 164-166 

Oxygen in coal, relation of efficiency

72* and__________ 92-93 

relation of efficiency 72* and,

figure showing ____ 93 

relation of smoke to_______ 57 

figure showing________ 56 

See also Gases, oxygen in.

P.

Pahmeyer, F. 0., work of-_____ 10

Park, W. W., work of________ 10

Pennsylvania coal, smoke test of_ 57

No. 4, carbon-hydrogen ratio of__ 71,77

No. 5, carbon-hydrogen ratio of-_ 72, 77

No. 6, carbon-hydrogen ratio of_- 71, 77

No. 7, carbon-hydrogen ratio of_ 71, 72, 77

clinker in_____________ 33, 34
INDEX. 195

Pennsylvania coal No. 8, carbouhydrogeu ratio of _ 71,77

smoke test of___ _.. _ 58

No. 10, carbon-hydrogen ratio of_ 72, 77

Perry, -John, formulas of._____ 108-112

formulas of, temperature test

of ___________ 132-184 

Pope, G. S.,. work of ___^____ 10 

Post, U. H., work of__________ 10 

Potential heat, definition of_____ 183 

Probability curves, definition of___ 158-

159,183

figure showing . _ 158 

relation of, to efficiency 72*__ 146-149 

to. efficiency 72*, figure

showing ________ 147

to true boiler efficiency

E4 __________ 140-149 

figure showing____ _ 147

Proximate analysis, definition of 183 

Pyrites, nature and occurrence of 38

Sec also Sulphur.

Pyrometer, optical, check by___ 132-134 

check ou_____ 1_ 9

description of________ 52-53, 183 

figure showing__.__ _______ 19

temperatures by, check on____ 55, 106

check on, figure showing__ 55 

Pyrometry, discussion of ._ _ _ 52, 55

K.

Radiation, definition of________ 183 

estimation of__^________ 143-146 

Kandall, D. T., work of________ 7 

Rated capacity developed. Sec Capacity, rated.

Rational formula, definition of____ 183 

Ray, W. S., introduction by._____ 9-11 

work of____-__________ 7,30-11 

Refuse, clinker and combustible in,

relations of _ ___ 38

clinker in__.__ ____ 28-38, 40-41

causes of____________ 34

prevention of, by method of

burning ________ 43

by limestone_______ 39

by steam jet__.____ 38-39 

relation of, to chimney

gases produced.!--_ 44 

to chimney gases produced, figure showing ___________ 36 

to combustion-chamber

temperature __ 44 

figure showing__ 36 

to efficiency 72*____ 44 

to rated capacity, figure showing..___ 30 

to size of coal____ 40-41 

relation of ash and____ 36, 39

relation of ash-sulphur ra-

-tio to _________ 38 

relation of carbon-hydrogen ratio to, figure 

showing _ 37

Pasrc. 

Refuse, clinker in, relation of carbon

monoxide and._____ 35 

clinker in, relation of efficiency

to _____________ 28-29, 

31,35

relation of efficiency to, figure showing______ l>0 

relation of iron to_____ .'55, 38 

relation of size of coal and- 35- 

30, 47

. figure showing_____ 

relation ot sulphur to___ 39, 44 

combustible in, relation of clinkers to__________ 38 

 definition of ____________ 1X.°> 

Re-volutions per minute, relation of

rated capacity and 10, 103 

.relation of rated capacity and,

figure showing___. _ 163

Rhode Island coal, smoke test of___ 57

No. 1, smoke test of__ _.__ 58

Ryder, G. E., work of__., ______ 10

Scale, insulation of water in boiler

by ________.___ 325-126 

Seger cones, definition of--____ 183 

Slack coal, utilization of_______ 50-51 

Smith, L. H. H., on clinkers_____ 38 

Smoke, discussion of_______ 50-58

relation of, to efficiency 72*__ f>0 

to efficiency 72*, figure

showing _ ___ 50 

to CO in combustion chamber ____________._ 107 

to CO in flue gases____ 57 

figure showing _____ 56 

to combustion-chamber temperature------ _ 57

figure showing-___ 56 

to fixed carbon______ 57

figure showing__.__ 56

to hydrogen in combustible 57

figure showing 56

to oxygen in coal________ 57

figure showing____ 50

to rate of combustion__ .176

to unaccounted-for loss__ 50-57

figure showing _.___ 50

Soot, insulation by____.__ 125-126,170.

Stack loss. Sec Heat, loss of, up

stack.

Steam, bubbles of, formation _ of, 

effect of, on heat 

transmission _____ 125-120 

Steam, low pressure, use of____'_ 102-105

Steam jet, prevention of clinkers by_ 38-39 

Steaming, rate of, effect of, on circulation of water____ 10. 103. 

rate of, effect of, on circulation 

of .water, figure showing______--____ 10 

-Stephan and Bolzmann's law, statement of_________. 112. IS.",

Stowe, L. K., work of___________ 1O

Straight-Hue function, definition of_ 183.
196 INDEX.

Page. 

Sulphur, relation of, to chimney-gas

evolution________ 44 

relation of, to chimney-gas evolution, figure showing__ 43 

relation of, to clinkering__ 38-89, 44 

to combustion-chamber temperature-__-____ 44 

figure showing.___. _ 37 

to completeness of combustion____________ 44 

figure showing--____. 43 

relation of efficiency 72* and 28-31, 

43-44, 176 

figure showing.______:__ 30, 43

T.

Temperature. Sec Furnace; Combustion c h a m her; 

Gases; etc.

Temperature, absolute, definition of_ .1.80 

Temperature, ignition, definition of_ 182 

Temperature, initial. See Furnace, 

initial temperature of.

'Temperature gradient, definition of 183 

'Tennessee coal, smoke test of_____ 57

No. 1, carbon-hydrogen ratio of_ 72, 78 

No. 2, carbon-hydrogen ratio of_ 72, 77 

No. 3, carbon-hydrogen ratio of__ 72, 78 

No. 4, carbon-hydrogen ratio of__ 72, 78 

No. 5, carbon-hydrogen ratio of_ 72, 77 

smoke test of______ ______ 58

No. 6, carbon-hydrogen ratio of__ 72, 77

smoke test of___________ 58

No. 7 A, carbon-hydrogen ratio of_ 72, 78

No. 8 A, smoke test of_______ 58

No. 8 B, smoke test of______ 58

No. 0, carbon-hydrogen ratio of_ 72 ; 77 

smoke test of_______ 58

Tests, data of, relations'of _____ .11-58 

object of__________________ 7

repetition of, effect of^_______ 31-32

unreliability of__-__^.______ 0

Texas coal, smoke test of_______ 57

No. 4, clinker in___________ 34 

smoke test of____l___________ 58

Thermodynamic efficiencies, definition

of_:_________. 05-07, 182 

figure showing. _________ OG 

Thermoelectric couple, description

of ________1_J__ 5.3-55 

Tiles, tube, forms of_____ __ 164

Tubes, boiler, absorption of heat by,

increase in_________ 124-125

absorption of heat by, variation

in___________. 121-125 

variation in, figures showing_____"___ ____. 123, 124

incasing of___i_________ 164

Sec also Boilers. 

Turbines, low-pressure steam in____ 103-

105, 178

Turbines, low-pressure steam in.

figure showing ______

True boiler efficiency. Sec Boiler

efficiency E4 .

U.

Ultimate analysis, definition of_____ 

Unaccounted for loss. Sec Heat, loss

of, unaccounted for. 

Utah coal, smoke test of_________

183

V.

Velocity, definition of_________ 183

Virginia coal, smoke test of_____ 57

No. 1 B, carbon-hydrogen ratio-_ 72

No. 2, carbon-hydrogen ratio of_ 72,77

No. 3, carbon-hydrogen ratio of__ 71, 77

No. 4, carbon-hydrogen ratio__ 72

clinkering of____________ 38-39

Volatile carbon, definition of____ 50, 183 

Volatile matter, definition of____ 183 

nature of___^__________ 59 

See also CaVbon, volatile ; Combustible.

W.

Wanner pyrometer. Sec Pyrometer. 

Wartenberg, Doctor, on dissociation

of gases_______ 153-154

Washington coal, smoke test of___ 57

No. 1 B, carbon-hydrogen ratio of- 78

clinker in_____________ 34

No. 2, carbon-hydrogen ratio of__ 72. 78

Water circulation. Sec Boilers, water

circulation in.

Water of composition, definition of__ 183

Weeks, H. W., work of________ 7, 10

West Virginia coal, smoke test of__ 57

No. 13. carbon-hydrogen ratio of__ 72. 77

No. 14, carbon-hydrogen ratio of__ 71, 77

clinkering of __ __________ 38-39

No. 15, carbon-hydrogen ratio of__ 72, 77

clinkering of____________ 38-39

No. 17, carbon-hydrogen ratio of_ 71, 77

No. 18, carbon-hydrogen ratio of__ 71, 77

No. 19, carbon-hydrogen ratio of _ 71, 77

test of, temperature of, figure

showing_____ _______ IS

smoke test of___________ 58 

No. 20, carbon-hydrogen ratio__ 

No. 21, carbon-hydrogen ratio of_

smoke test of_________ 58

Wind, effect of, on efficiency 72*_ 107-108

Wyoming coal, smoke test of____ 57

No. 2 B, clinker in__________ 34

carbon-hydrogen ratio of ___ 72. 78

smoke test of ___________ 58

No. 3, carbon-hydrogen ratio___ 72, 78

smoke test of__________. 58
CLASSIFICATION OF THE PUBLICATIONS OF THE UNITED STATES GEOLOGICAL.

SURVEY.

[Bulletin No. 325.1

The ^publications of the United States Geological Survey consist of (1) Annual 

Reports, (2) Monographs, (3) Professional Papers, (4) Bulletins, (5) Mineral 

Resources, (6) Water-Supply and Irrigation Papers, (7) Topographic Atlas of United 

States folios and separate sheets thereof, (8) Geologic Atlas of United Statesfolios thereof. The classes numbered 2, 7, and 8 are sold at cost of publication; the 

others are distributed free. A circular giving complete lists can be had on application.

Most of the above publications can be obtained or consulted in the following ways:

1. A limited number are delivered to the Director of the Survey, from whom they 

can be obtained, free of charge (except classes 2, 7, and 8), on application.

2. A certain number are delivered to Senators and Representatives in Congress 

or distribution.

3. Other copies are deposited with the Superintendent of Documents, Washington, 

D. C., from whom they can be had at prices slightly above cost.

4. Copies of all Government publications are furnished to the principal public 

libraries in the large cities throughout the United States, where they can be consulted 

by those interested.

The Professional Papers, Bulletins, and Water-Supply Papers treat of a variety of 

subjects, and the total number issued is large. They have therefore been classified 

into the following series: A, Economic geology; B, Descriptive geology; C, Systematic geology and paleontology; D, Petrography and mineralogy; E, Chemistry and 

physics; F, Geography; G, Miscellaneous; H, Forestry; I, Irrigation; J, Water storage; K, Pumping water; L, Quality of water; M, General hydrographic investigations; N, Water power; 0, Underground waters; P, Hydrographic progress reports, 

Q, Fuels; R, Structural materials. This paper is the fifty-third in Series E, and 

the fifth in Series Q, the complete lists of which follow (PP=Professional Paper; 

B=Bulletin):

SERIES E, CHEMISTRY AND PHYSICS.

B 0. Report of work clone in the Washington laboratory during the fiscal year 1883-8-1, by P. W. Clurke

and T. M. Chatartl. 1884. 40pp. (Out of stock.) 

B 14. Electrical and magnetic properties of the iron carburets, by Carl Barns and Vincent Strouhal.

1885. 238pp. (Out of stock.) 

K 27. Report of work done in the Division of Chemistry and Physics, mainly during the year 1884-85.

1886. 80pp. 

B ;J2. Lists and analyses of the mineral springs of the United States (a preliminary study), by Albert

C. Peale. 18S6. 235pp. (Out of stock.)

B 35. Physical properties of the iron carburets, by Carl Barus and Vencent Strouhal. 188C. 62 pp. 

B 36. Subsidence of fine solid particles in liquids, by Carl Barus. 1886. 58 pp. (Out of stock.) 

B 42. Report of work done in the Division of Chemistry and Physics, mainly during the fiscal year

1885-86, by F. W. Clarke. 1887. 152 pp., 1 pi. (Out of stock.) 

B47. Analyses of waters of the Yellowstone National Park, with an account of. the methods of

analyses employed, by F. A. Gooch and J. E. Whitfield. 1888. 84pp. (Out of stock.) 

B 52. Subaerial decay of rocks and origin of the red color of certain formations, by I.' C. Russell.

1889. 65 pp., 5 pis. (Out of stock.) 

Bf>.|. On the thermoelectric measurement of high temperatures, by Carl Barus. 1889. 313 pp., 11

pis. (Out of stock.) 

B 55. Report of work done in the Division of Chemistry and Physics, mainly during the fiscal year

1886-87, by F. W. Clarke. 1889. 96pp. (Out of stock.)
II SERIES LIST.

B 60. Report of work done in the Division of Chemistry and Physics, mainly during the fiscal year

1887-S8. 1890. 174pp. (Out of stock.) 

B 64. Report of work done iu the Division of Chemistry und Physics, mainly during the fiscal year

1888-89, by F. \V. Clarke. 1890. 60 pp.

B 68. Earthquakes iri California in 1889, by J. E. Keeler. 1890. 25 pp. 

B 73. The viscosity of solids, by Carl Barus. 1891. xii, 139pp., 6 pis. 

.B 78. Report of work done in the Division of Chemistry and Physics, mainly during the fiscal year

1889-90, by F. W. Clarke. 1891. 131pp. (Out of stock.) 

B 90. Report of work done in the Division of Chemistry and Physics, mainly during the fiscal year

1890-91, by F. W. Clarke. 1892. 77 pp.

B 92. The compressibility of liquids, by Carl Barus. 1892. 96 pp., 29 pis. 

B 94. The mechanism of solid viscosity, by Carl Barus. 1892. 138 pp.

B 95. Earthquakes in California in 1890 and 1891, by E. S. Holden. 1892. 31 pp. I 

B 96. The volume thermodynamics of liquids, by Carl Barus. 1892. 100 pp. 

B 103. High temperature work in igneous fusion and ebullition, chiefly in relation to pressure, by

Carl Barus. 1893. 57 pp. ,9 pis.

B 112. Earthquakes in California in 1892, by C. D. Perrine, 1893. 57 pp. 

B 113. Report of work done in the Division of Chemistry and Physics during the fiscal years 1891-92

and 1892-93, by F. W. Clarke. 1893. 115 pp.

B 114. Earthquakes in California in 1893, by C. D. Perrine. 1894. 23 pp. 

B 125. The constitution of the silicates, by F. W. Clarke. 1895. 100pp. (Out of stock.) 

B 129. Earthquakes in California in 1894, by C. D. Perrine. 1895. 25 pp. 

B 147. Earthquakes in California in 1895, by C. D. Perrine. 1896. 23 pp. 

B 148. Analyses of rocks, with a chapter on analytical methods, laboratory of the United States

Geological Survey, 1880 to 1896, by F. W. Clarke and W. F. Hillebrand. 1897. 306 pp. (Out

of stock.)

B 155. Earthquakes in California in 1896 and 1897, by C. D. Perrine. 1898. 47 pp. 

Bid. Earthquakes in California in 1898, by C. D. Perrine. 1899. 31 pp., 1 pi. 

B 167. Contributions to chemistry and mineralogy from the laboratory of the United States Geological Survey; F. W. Clarke, Chief Chemist. 1900. 166 pp. 

B 168. Analyses of rocks, laboratory of the United States Geological Survey, 1880 to 1899, tabulated by

F. W. Clarke. 1900. 308pp. (Out of stock.) 

B 170. Some principles and methods of rock analysis, by \Y. F. Hillebrand. 1900. 114 pp. (Out of

stock.)

B 186. On pyrite and marcasite, by H. N. Stokes. 1900. 50 pp. 

B 207. The action of ammonium chloride upon silicates, by F. W. Clarke and George Steiger. 1902

57pp. (Out of stock.) 

PP14. Chemical analyses of igneous rocks published from 1884 to 1900, with a critical discussion of

the character and use of analyses, by H. S. Washington. 1903. 495 pp. 

PP 18. Chemical composition of igneous rocks expressed by means of diagrams, with reference to

rock classification on a quantitative chcmico-mineralogical basis, by J. P. Iddings. 1903.

98pp., 8 pis. 

B 220. Mineral analyses from the laboratories of the United States Geological Survey, 1880 to 1903,

tabulated by F. W. Clarke, Chief Chemist. 1903. 119 pp. 

B 228 Analyses of rocks from the laboratory of the United States Geological Survey, 1880 to 1903,

tabulated by F. W. Clarke, Chief Chemist. 1904. 375 pp. 

PP 28. The superior analyses of igneous rocks from Roth's tabellen, 1869 to 1884, arranged according to 

the quantitative system of classification, by H. S. Washington. 1904. 68 pp. 

B 239. Rock cleavage, by C. K. Leith. 1904. 216 pp., 27 pis.

B 241. Experiments on schistosity and slaty cleavage, by G. F. Becker. 1904. 34 pp., 7 pis. 

B 253. Comparison of a wet and crucible-fire method for the assay of gold telluride ores, with notes

on the errors occurring in the operations of fire assay and parting, by W. F. Hillebrand and

E. T. Alien. 1905. 33 pp. 

B 261. Preliminary report of the operations of the coal-testing plant of the United States Geological

Survey at the Louisiana PurchaseExposition, St. Louis, Mo., 1904; E. W. Parker, J. A. Holmes,

M. R. Campbell, committee in charge. 1905. 172 pp. 

B 262. Contributions to mineralogy from the United States Geological Survey, by F. W. Clarke, W. F.

Hillebrand, F. G. Ransome, S. L. Penfield, Waldemar Lindgren, George Steiger, and W. T.

Schaller. 1905. 147pp. 

PP 48. Report on the operations of the coal-testing plant of the United States Geological Survey at the

Louisiana Purchase Exposition, St. Louis, Mo., 1904; E. W. Parker, J. A. Holmes, M. R. Campbell, committee in charge. 1906. 3 parts. 1,492 pp., 13 pis. 

B 290. Preliminary report on the operations of the fuel-testing plant of the United States Geological

Survey at St. Louis, Mo., 1905, by J. A. Holmes. 1906. 240 pp.

B 305. The analysis of silicate and carbonate rocks, by W. F. Hillebrand. 1906. 200 pp. 

B 312. The*interaction between minerals and water solutions, with special reference to geologic phenomena, by E. C. Sullivan. 1907. 69 pp.
SEEIES LIST. Ill

B 316. Contributions to economic geology, 1906, Part II: Coal, lignite, and peat; M. R. Campbell

geologist in charge. 1907. pp., 23 pis. 

B 323. Experimental work conducted in the chemical laboratory of the United States fuel-testing

plant at St. Louis, Mo., January 1,1905, to July 31,1906, by N. W. Lord. 1907. 49 pp. 

B 325. A study of four hundred steaming tests made at the fuel-testing plant, St. Louis, Mo., in 1904,

1905, and 1906, by L. P. Breckenridge, 1907. 190 pp.

SERIES Q, FUELS.

B 261. Preliminary report of the operations of the coal-testing plant of the United States Geological 

Survey at the Louisiana Purchase Exposition, St. Louis, Mo., 1904; E. W. Parker, J. A.Holmes, 

M. R. Campbell, committee in charge. 1905. 172 pp.

PP 48. Report on the operations of the coal-testing plant of the United States Geological Survey at the 

Louisiana Purchase Exposition, St. Louis, Mo., 1904; E. W. Parker, J. A. Holmes, M.R. Campbell, committee in charge. 1906. 3 parts. 1,492 pp., 13 pis.

B 290. Preliminary report on the operations of the fuel-testing plant of the United States Geological 

Survey at St. Louis, Mo., 1905, by J. A. Holmes. 1906. 240 pp.

B 323. .Experimental work conducted in the chemical laboratory of the United States fuel-testing 

plant at St. Louis, Mo., January 1,1905, to July 31,1906, by N. W. Lord. 1907. 49 pp.

B 325. A study of four hundred steaming tests made at the fuel-testing plant, St. Louis, Mo., in 1904, 

1905, and 1906, by L. P. Breckenridge, 1907. 196 pp.

Correspondence should be addressed to

THE DIRECTOR,

UNITED STATES GEOLOGICAL SUKVKY,

WASHINGTON, I). G. 

OCTOBER, 1907.

o