DEPARTMENT OF THE INTERIOR

UNITED STATES GEOLOGICAL SURVEY

GEORGE OTIS SMITH, DIRECTOR

BuxL/ETiisr 393

INCIDENTAL PROBLEMS

IN

GAS-PRODUCER TESTS

BY

R. H. FERNALD, C. D. SMITH, J. K. CLEMENT 

AND H. A. GRINE

WASHINGTON

GOVERNMENT PRINTING OFFICE

1909

CONTENTS.

Page.

Introduction J.....................i...................................... 5

Factors affecting proper length of tests..................................... 7

Practical importance of results!......................................... 7

Limitations of present experiments.................................... 8

Determination of fuel-bed thickness ................................... 8

Effect of error in measurement......... .............................. 9

Beginning and closing with equal fuel-bed depth ....................... 9

Division of tests into periods .........................................: 11.

Fluctuations of fuel-consumption rate.................................. 11

Estimate of proper test duration. ....................................... 13

Summary and table......................... .......................... 13

Temperature differences in fuel bed........................................ 15

Purpose and method of .experiments................................... 15

Temperature at different heights ...................................... 17

Different horizontal positions ......................................... 18

Causes of irregularities................................................ 20

Average results for each point......................................... 20

Process of gas formation .............................................. 22

Differences with distance from axis.................................... 24

Requisite temperature for formation of CO ............................. 26

Summary............................................................ 27

ILLUSTRATIONS.

Page. 

FIGURK 1. Cross section of gas-producer fuel bed............................ 10

2. Variation in coal consumption per brake horsepower hour......... 12

3. Cross section of gas producer.................................... 16

4. Pyrometer tube ................................................ 17

5. Gas-sampling tube.............................................. 17

6. Curves of temperature variation with height above base of fuel bed. 21

7. Variation of gas combustion temperature and British thermal units

with height above base of fuel bed............................. 23

8. Section of producer, showing temperature variation for height and

distance from sides of producer................................ . 25

INTRODUCTION.

By J. A. HOLMES.

As part of its investigation of methods of increasing the efficiency 

of fuel resources, the United States Geological Survey is .studying the 

general problems involved in the economic use of fuels in gas producers. In the course of this study many incidental problems of 

prime importance demand consideration. Among them is the determination, under practically constant conditions, of the duration of 

gas-producer tests necessary to reduce the possible error to a minimum. A discussion of this proper length of test period forms the 

first part of this bulletin.

An attempt to dispel some of the uncertainties that arise in an 

investigation or to account for some of the minor phenomena often 

necessitates a systematic and careful study of certain chemical, thermodynamic, or physical laws, or a combination of these, which in 

turn may result in information or conclusions of great value. Furthermore, seemingly unimportant observations often prove to bear 

directly upon the design, construction, or manipulation of the machine 

under test.

In attempts to improve the gas producer considerable attention has 

been given by manufacturers to such questions as fixing or isolating 

the combustible components of the tar, utilizing the waste heat of the 

producer for the generation of the steam required by the plant, applying the suction principle to bituminous coal and other tarry fuels, and 

many allied subjects. Little study, apparently, has been given to the 

physical-chemical conditions most suitable to the formation of hydrogen and of carbon monoxide, with a view to regulating the percentages 

of these gases in generators using fuels other than anthracite coal or 

charcoal.

An attempt was made to introduce such investigations when the 

operations of the government coal-testing plant began at the Louisiana Purchase Exposition in St. Louis in 1904, but owing to adverse 

conditions these problems were abandoned until the plant was transferred to Norfolk in 1907. The delay in beginning this line of investigations, together with the short testing season at Norfolk, limit the 

second part of this report to preliminary physical-chemical studies, 

which, however, are sufficiently significant to warrant careful examination pending more complete researches, which are to be carried on 

at the station recently located in Pittsburg.

5

INCIDENTAL PROBLEMS IN GAS-PRODUCER TESTS..

FACTORS AFFECTING PROPER LENGTH OF TESTS.

By R. H. FERNALD and C. D. SMITH.

PRACTICAL IMPORTANCE OF RESULTS.

The recent development of producer-gas as * an important element 

in power installations has led to a large number of tests of such 

plants within the past few years. Such tests have been conducted 

from several standpoints: (a) By the United States Geological Survey as a means of determining the economic value of different fuels 

when used in gas producers, and also the relative value of the fuels in 

the producer and under the steam boiler; (&) by the purchaser of 

such installations for a satisfactory verification of points in the contract; (c] by the gas-producer manufacturers to assist in determining 

questions of proper design, bases for guaranties in contracts, etc.; 

and (^), unfortunately, by.some promoters to obtain results purely 

for advertising purposes, at the same time conveying the impression 

that the absurd figures quoted have been obtained by carefully conducted tests by disinterested parties.

Some of the test results reported by certain gas-producer manufacturers are so absurd that no careful purchaser will be deceived; 

but, unfortunately, the alluring guaranties and special, inducements 

regarding the cost of the installation have caught enough unwary 

'buyers to injure seriously the business of reputable concerns. It is 

not uncommon to pick up advertising material that states a fuel consumption per horsepower per hour based on tests of two or three hours' 

duration only, in which the total coal charged during that period 

was from 20 to 30 pounds. The producers in such tests are of course 

of small sizes, but the principle is the same for all. The initial fuel 

bed built up before the test is started amounts to several times the 

quantity of fuel charged during short-interval tests, and the amount 

of gas that may be drawn from this foundation bed is an unknown 

quantity. It may be very small or may reach a large percentage of
8 PROBLEMS IN GAS-PRODUCER TESTS.

the total gas used during short tests, depending on the carelessness 

or cleverness of the superintendent of the test.

Of course the claim is made that at the end of the test the fuel bed 

is always brought to the same condition that it was in at the beginning, but experience in this direction need not be great to show that 

such conditions are practically impossible in tests of short duration. 

The error introduced by such an assumption may be sufficiently great 

to make the recorded results absurd. In fact, the percentage of possible error may be so large that it is only necessary to predetermine 

the desired fuel consumption per horsepower per hour and trust to 

the clever manipulation of the operator to secure that result.

It is no wonder, then, that tests showing a consumption of only 0.6 

pound of coal per horsepower per hour are often reported; and 

apparently it is only necessary for some daring'promoter to decide 

that a horsepower should be developed with a consumption of 0.25 

pound per hour for tests to be reported that show this figure.

LIMITATIONS OF PRESENT EXPERIMENTS.

For accurate tests of gas producers and for a true determination 

of the fuel consumption, either (a) the conditions of the fuel bed. 

at the beginning and at the end of the test must be positively known, 

or (5) the test must be of sufficient duration to practically eliminate 

the uncertainties that arise from varying, conditions of the bed. 

Inasmuch as the first method is usually out of the question, it is 

necessary to resort to the second, at the same time securing as uniform 

conditions as possible in the fuel bed.

The exact relation between the size of producer and the proper 

length of test for measuring with a reasonable degree of accuracy 

the amount of coal consumed has not yet been fully determined at

the fuel-testing plant of the Geological Survey, but some light may 

be thrown upon this- important point by some of the results secured 

in the course of these tests.

During the tests at St. Louis very little information relating to 

the subject of this report could be obtained, because the average length 

of test was restricted to fifty hours or less by the limited supply of 

each variety of fuel furnished for the trial. At Norfolk, however, 

the conditions were more favorable in this respect, and four tests 

were of sufficient length to permit some study of the problem.

DETERMINATION OF FUEL-BED THICKNESS.

The producer used was of the pressure type. It was rated at 250 

horsepower and was 7 feet in internal diameter. The initial fuel bed, 

built up before the official start of each test, amounted to about 5,000 

pounds of coal.
FACTORS AFFECTING LENGTH OF TESTS. 9

The method of measuring the thickness of the fuel bed was as 

follows: Around the sides of the producer and located 90° apart 

were four sets of sight holes, designated A, B, C, and D. Each of 

these sets consisted of four holes placed vertically 6 inches apart, 

thus giving a vertical range of 18 inches for observation. During 

the operation of the plant the top of the ash bed was maintained 

within this range. The distance from the producer top to the top 

of the ash bed was taken as the average of the four -measurements 

at the points A, B, C, and D. In a similar manner the distance from 

the producer top to the top of the fuel bed was taken as the average 

of measurements at four corresponding points. The difference 

between these two measurements gave the thickness of the bed, and, 

with the weight of a given volume of the fuel known, the total weight 

of the fuel bed, on the basis of the assumptions noted, could be 

determined.

EFFECT OF ERROR IN MEASUREMENT.

The thickness of the fuel bed as determined by assumption, or even 

by measurement, in the producer used for these tests, may easily be 

in error from 4 to 6 inches. The error at the beginning may or may 

not be neutralized by an equal error at the close of the test period. 

The magnitude of the error depends on the state of the fuel at the 

time the measurements are taken. With a bed 7 feet in diameter it 

will amount to from 500 to 800 pounds if the fuel happens to be 

green coal (" coal as fired "); but as the uncertainty in measuring is 

at the bottom of the fuel bed, just above the ash line, where the fuel 

is not green coal but coke, an error in Aveight of fuel estimated from 

measurements of the depth of bed probably equals the weight of the 

corresponding volume of coke instead of green cpal. For the fuel 

used during these tests, the ratio of the weights of equal volumes of 

coke and coal is approximately 1 to 2. Hence, there may be an error, 

either positive or negative, due to the fuel-bed measurements alone, 

of 400 pounds of coke. .

It is readily seen that even if the essential conditions of the bed at 

the end of a test duplicate those at the beginning there is still considerable difficulty in determining the exact fuel consumption, owing 

to inaccuracy in the measurements indicated. It is evident, however, 

that a test may be continued to such length that this error of 800 

pounds of coal, or 400 pounds of coke, will be 'a small percentage of 

the total fuel consumed.

BEGINNING AND CLOSING WITH.EQUAL FUEL-BED DEPTH.

Although a test may continue so long that the error due to inaccurate measurement is eliminated, a second serious difficulty is 

encountered if the depth of bed at the end of the test does not equal
10 PBOBLEMS IN GAS-PRODUCER TESTS.

that at the beginning. For example, suppose the condition of the 

fuel bed to be practically the same at the beginning and end of the 

test, except in thickness. Let A, figure 1, represent the thickness of 

such a bed at the beginning and B its thickness at the close of the 

test; then the fuel consumed is the amount actually fired, plus some 

quantity represented by C. Again, the -fuel bed. at the beginning 

may be thicker by an amount C than at the close. It is evident that 

in either case -a correction must be made in the weight of fuel used 

equal to the weight of the volume C. But this volume may consist 

entirely of fresh coal, entirely of coke, or of a mixture of the two in 

any proportion.

In the producer used for these tests a layer of green coal 1 inch 

thick was equivalent to about 150 pounds; then if C is 10 inches and

the fuel in this 

volume is green 

coal the correction to be made 

amounts to 1,500 

pounds. If, however, the fuel occupying the volume C is assumed 

to be green coal, 

but is actually 

coke, an error of 

750 pounds is introduced. On the 

other hand, if the 

volume C is assumed to be filled

ir« V'/t*

Fuel i'n all stages * ^ifrom green coal "/- /' ^ 

to coke

Sight holesST ^-rFIGURE 1. Cross section of gas-producer fuel bed.

with coke and it is actually filled with green coal, there is still an 

error of 750 pounds, but in the opposite direction. The error may, 

therefore, vary between these two limits according to the assumption 

made and the character of the fuel actually in this volume C.

Owing to the lack of positive information on the subject, it was 

formerly the custom at the fuel-testing plant to allow for volumetric 

differences in the fuel bed, due to changes in the level, by adding 

or subtracting the weight of an equivalent volume of the green coal 

("coal as fired") used in the test; but during the Norfolk work 

special attention was given to closing each test with a fuel bed of the 

same thickness as at the start, so that the figures given for this series 

of tests for the average coal consumption per horsepower per hour 

for the entire test may be regarded as essentially, correct.
 FACTORS AFFECTING LENGTH OF TESTS. 11 

DIVISION OF TESTS INTO PERIODS.

In order to study conditions more carefully, each test was divided 

into several periods and the fuel consumed in the producer was calculated for each period. The desirability of having the fuel-bed level 

the same at the beginning and at the end of each of these short 

periods was not appreciated until the calculations had been made. 

This variation in depth (C, fig. 1) for some of the periods was as 

much as 10 inches, which, with a 7-foot producer, means a considerable volume.

If the periods into which these tests are divided are only eight 

hours, the fuel consumption for each period amounts to only 1,800 

pounds, approximately. If it so happens that an error of 750 pounds 

due to changes in the fuel-bed thickness is combined with a 400- 

pound error due to inaccurate measurement of the depth of bed, a

total error amounting to 1,150 pounds may result. The percentage 

of possible error in calculating fuel consumption for short periods 

is obviously great. With a period of twenty-four hours and a fuel 

consumption of about 5,400 pounds the percentage of possible error 

is much less, but is still over 20 per cent.

Of the tests used in studying this subject, No. 164 was divided into 

periods of eight hours each, while tests 165,166, and 168 were divided 

into periods of twenty-four hours. The table on page 14 gives the 

amount of coal actually charged into the producer during each period, 

and also the amount of coal consumed for each period as corrected 

(on the green-coal basis) for changes in the volume of the fuel bed, 

according to the methods indicated above.

FLUCTUATIONS OF FUEL-CONSUMPTION RATE.

It will be noted that the load carried, or brake horsepower, is very 

uniform except in one or tAvo instances, and for this reason a fairly 

uniform fuel consumption would naturally be expected. It will be 

seen from Table 1, however, that in the first three tests, Nos. 164, 165, 

and 166, the apparent fuel consumption per period and also per brake 

horsepower per hour for each period is far from uniform. The last 

column in the table gives the fuel consumption per brake horsepower 

per hour for the time from the start of the test to the end of each 

period. These values approach an average, and in general become 

more uniform as the test proceeds. It was expected that they would 

become so uniform as to practically determine the necessary duration 

of tests in plants of the given type and size, but of the four tests made 

only one, No. 168, was entirely satisfactory in this respect. In No. 

165, for example, the average fuel consumption per brake horsepower 

per hour at the end of the ninth period, or 216 hours, was 0.84 pound, 

and at the end of the tenth period, or 240 hours, it was 0.90 pound, an
12 PROBLEMS IN" GAS-PRODUCER TESTS.

increase of 7.1 per cent. These results are shown graphically by the 

curves in figure 2. The horizontal straight line indicates the average

1.401 

1.20 

1.00 

.80 

.60 

.40

3 

O

<D 

O

sh.oo

o

_c

o

-"i .so

-Q

<D

o.

g - 60

3

-a

g

a.

_c 

 o

V

El. 20

c 

o

-Si. 00

£ 

.80

.60

1.00 

.80 

.60

(

Hours 

) 25 50 75 100 125 150 175 200 225 25

-J

,\i

i i

o

-j r

4-

c ^

-r-

-V

D-

/

.

, >

^

^

\

1

^

 *.

Kii

/

i

*

1

 *

t-

_

 

-t

d

/

1

M

"1

1i

ts

"

'

-1

*=-vV

rf

"4

~

^.

^

/

-/

31

-P

/

^

t

\

--

-*

i

 3J

/

64-

f^

 1-

1

1

1

O

 f"

\

. '

F

i

;

/

/

"

\

/

t.±»

v

">

-T

_;

-T

V

?^

-T

^

-«

At

r.

&

K

\

\

H

,'

a

> <

>-

o

N

;

t

/-

at.

-6

^

M

^

-6

^

u

Bs

=7

X

<

^

^y

f

*

x^

=!> CN'

>.

X,

'

a

">,

oO

V

 \

*S

o-

 A

)

j

I

1

1

f--

/

^-g

For period. 

~rom beginning of test to end of period. 

Average for entire test.

1 1 1 1 1 II 1

/

"

-1

) 25 50 '75 100 125 . 150 175 '200 225 25 

Hours " - 

FIGURE 2. Variation in coal consumption per brake horsepower hour.

fuel consumption per brake horsepower per hour for the entire test; 

the points connected by a broken line give the fuel consumption for
FACTOES AFFECTING LENGTH OF TESTS. 13

each period and show a wide variation from one period to the next. 

The points connected by an unbroken line give the average fuel consumption from, the beginning of the test up to and including any 

period. In test 168 the results are very satisfactory. The average 

fuel consumption per brake horsepower per hour did not vary more 

than 1 per cent after the first 96 hours of the test; hence for this one 

test it is clear that 96 hours would have been .sufficient for securing 

reasonably accurate results.

ESTIMATE OF PROPER TEST DURATION.

From the table it may be seen that the lack of uniformity in quantity of fuel consumed per period is due, in a great measure, to the 

corrections made for thickness of fuel bed. The graphic logs* of 

these tests show that the thickness .of the fuel bed throughout test

No. 168 was comparatively uniform, although in tests 164, 165, and 

166 the fuel-bed thickness varied considerably, and frequently there 

was a change of 8 to 10 inches during one period. These observations led to a study of the effect of change in thickness of the fuel 

bed and of the error in the calculations for fuel consumption due to 

inaccurate measurements. With the results of test No. 168 as a 'basis 

for comparison, an inspection of the other curves strengthens che impression that, with proper precautions regarding uniformity of fuelbed depth, approximately 100 hours may be the required duration 

for tests on producers of this size and type, although this period may 

be infmenced^by the character of the fuel used.

SUMMARY AND TABLE.

From the above discussion it is evident: (a) That throughout a 

test the fuel bed should be maintained in uniform condition, with 

regard to both the character of the fire and the thickness of bed; 

(5) but that failing in this, special care should be exercised to see that 

the fuel bed is in the same condition and of the same thickness at the 

close of a complete test, or at the end of a test period, as at the beginning; (c) that a test should never be started when the producer has 

been standing idle for some time with " banked fires," as the fuel bed 

will not be in the average condition under which it will be required to 

work during the test; (d) that if, as the appointed hour for closing 

the test approaches, the fuel bed is not in the proper condition, the 

time of closing the test should be postponed until the bed naturally 

assumes the proper thickness and character! No forcing of conditions 

should be allowed simply to bring the test to an end at a previously 

determined hour.

0 These logs for tests 25-168 will appear in a bulletin entitled " Producer-gas tests, 

.1905-1907," now in preparation for publication by the United States Geological Survey. 

The logs for tests 1-124, made in 1904, appeared in Prof. Paper U. S. Geol. Survey No. 48, 

part 3.
14 PEOBLEMS GAS-PRODUCER TESTS.

TABLE 1. Results of gas-producer tests at Norfolk.

[Weights of coal in pounds.]

TEST No. 164."

No. of period.

1.......... ...................

2.............................

3.............................

4.............................

5.............................

G.... .........................

7.............................

9.............................

10.............................

11.............................

12.............................

13.............................

14.............................

Hi.............................

17.............................

IS.............................

Coal 

actually 

charged in 

producer.

 1,200

1,200

1,500

1,500

1,650

1,800

2,250

1,800

1,050

1,650

1,650

1,500

1,650

1,650

1,500

1,800

1,500

1,350

Correction 

due to 

thickness 

of fuel bed.

+ 292

- 292

+ 876

+ 548

0

+ 844

-1,241

- 185

+ 591

- 211

+ 454

+ 621

- 840

+ 183

I K1 1

+ 73

- 91

+ 785

Coal consumed.

1,492

908

2,376

2,048

1,650

2,644

1,009

1,615

2,241

1,439

2,104

2,121

810

1,833-

2,011

1,873

1,409

2,135

Brake 

horsepower.

225.6

240.8

oo c o

233.2

235.0

237.4

234.1

236.0

237.1

931 fi

236.9

a 239.1

232.8

240.4

238.9

235.0

240.7

242.2

Coal per 

brake horsepower per 

hour.

0.83

.47

1.26

1.10

.88

1.39

.86

1.18

.78

1.11

1.11

.44

.95

1.05

1.00

.73

1.10

Coal per 

brake horsepower per 

hour from 

beginning 

of test.

0.83

.65

.85

.92

.91

99

09

.92

.95

ot

.95

.96

.92

.92

.93

.93

.92

.93

TEST No. 165. "

2.............................

3. .............................

6.............................

8.............................

9

10...........---.-......----...

6,750

4,950

5,250

4,800

5,250

4,800

' 6, 150

5,400

4,800

2,850

-2,646

+ 639

+ 165

+ 493

+ 292

- 402

- 621

- 876

-1,606

+5,001

4,104

5, 589

5,414

5,293

5,542

4,398

5,529

4,524

3,194

7,851

. 238.1

239.6

241.0

240.5

240.1

236.0

240.1

238.4

237.8

239.8

0.72

.97

.94

.92

.96

.78

.96

.79

.56

1.36

0.72

85

88

89

90

88

89

88

84

' 90

TEST No. 166. »

1..............................

2..............................

4..............................

5..............................

6..............................

8..............................

9..............................

4,350

4,800

4,800

4,800

5,100

4,950

5,100

+ 762

- 778

+ 1,424

- 563

+ 50

- 116

+ 547

- 431

5,112

4,022

6,224

4,237

5,150

5,434

5,497

4,669

235.9

235.9 OQI 7

236.2

235.5

235.3

233.5

237.7

0.90

.71

.81

1.10

.75

.91

1.08

.98

.82

0.90

.81

.81

.88

.85

.86

.89

.91

.89

TEST No. 168."

1.............................

2.............................

3. .............................

4.............................

5.............................

6.............................

7.............................

8............. ................

9.............................

10.............................

4,500

5,400

6,000

4,950

5,550

5,100

5,250

5,550

4,950

5,400

+ 795

- 116

- 447

- 398

- 331

+ 215

+ 149

- 530

+ 149

+ 116

5,295

5,284

5,553

4,552

5, 219

5, 315

5,399

5,020

5,099

 5,516

237.2

234.7

236.0

236.1

237.3

235.2

234.0

236.4

237.0

235.0

0.93

.94

.98

v .80

.92

.94

.96

.88

.90

.98

0.93

.94

.95

.91

.91

.92

.92

.92

.92

.92

Divided into periods of 8 hours. 6 Divided into periods of 24 hours.
TEMPERATURE DIFFERENCES IN FUEL BED.

By J. K. CLEMENT and H. A. GRINE.

PURPOSE AND METHOD OF EXPERIMENTS.

The object, of the experiments here described was to determine as 

nearly as possible the differences of temperature in the fuel bed of 

the gas producer, and the influence of such differences on the chemical 

reactions taking place within the producer.

To allow the introduction of the pyrometer and gas-sampling tubes 

required in making these observations, a number of holes large enough 

to receive l|-inch wrought-iron pipes were cut through the side of the 

producer, as shown in figure 3. The pipes projected about an inch 

beyond the outer shell of the producer and were provided with castiron caps.

Temperature measurements were made by means of a Le Chatelier 

platinum, platinum-rhodium thermocouple and a direct-reading semiportable galvanometer. The thermocouple was calibrated from time 

to time by determinations of the melting points of zinc and copper, 

and the correction required by the deviation of the temperature of 

the cold junction from zero was applied.

The arrangement of the thermocouple is shown in figure 4. The 

wires were insulated by tubes of porcelain or fused silica, and the 

couple was inclosed in a large tube of one or the other of these materials. The outer tube was incased in a protecting tube of extra 

heavy wrought-iron pipe.

To determine the temperature in the hotter portion of the producer 

proved to be no easy undertaking. Frequently, owing to the compactness of the fuel bed, the iron tube had to be driven through the 

bed with a sledge hammer. Ten minutes, or longer, was required for 

the pyrometer to assume the temperature of the surrounding fuel.

15
16 PROBLEMS IN GAS-PRODUCER TESTS.

FIGURE-3. Cross section of gas producer.
TEMPERATURE DIFFERENCES IN FUEL BED. 17

Water

At the higher temperatures this time Avas sufficient for the iron pipe 

to bend and, with the aid of the reducing gases, to slag and break both 

the" porcelain tube and the thermocouple.

When temperature observations Avere made, gas samples Avere usually taken. The sampling tube is shoAvn in figure 5. In order to 

eliminate as far as possible any variation in the composition of the 

gas through contact with 

a hot metallic surface, 

the tube Avas Avater jacketed to within 1^ inches 

from the end.

The method of procedure Avas as folloAvs: 

The pyrometer tube 

(fig. 4) was introduced

through one of the holes 

in the side of the producer (see fig. 3), and 

observations made at 

different elevations and 

at any desired distance 

from the axis of the producer. To make a series 

of observations at one 

test hole required half 

an hour or more. The 

pyrometer tube Avas then 

AArithdraAvn from the 

producer and the gassampling tube inserted 

in its place, and samples 

taken at several different 

places. When the desired number of observations had been made at one test hole, the pyrometer tube Avas removed 

to another hole and the process repeated.

TEMPERATURE AT DIFFERENT HEIGHTS.

The first series of observations are contained in Tables 2 and 3. 

These results shoAv that the temperature is highest, about 1,300° C., 

at a distance of 1 foot above the base of the hood. From this point 

upAvard the temperature falls gradually to 400° C. near the upper 

surface of the bed.

869S9 Bull. 393 09 2

FIGURE 4. Pyrometer 

'tube.

FIGUUE 5.- Gas-sampling 

tube.
18 PROBLEMS IN GAS-PRODUCER TESTS.

TABLE 2. Temperatures at specified .points in, gas producer.

Date.

Do..............................................

Do.............!.........................'.......

Number 

of test 

hole.

3

2

1

2

2

Height 

above 

base of 

hood.

Ft. in. 

2 3

1 3

0 3

1 3

1 3

Item No.

1

 2 

3 

4 

5

6 

7

1 §

1 9 10

1 11

12 

13

14

15

Distance 

from 

axis of 

producer.

Inches. 

30

10 

16 

10 

22

28 

28 

34 

7 

10

28 7' 

10

7 

7

Temperature.

"C.

1,000

1,142 

1,140 

1,140 

1,170

1,000 

1,090 

1,015 

1,075 

1,100

425 

1,020 

1,140

1,070 

1,150

1,265

TABLE 3. Temperature at specified points in gas producer, with analyses and 

British thermal units of gas samples taken at different heights.

Date.

October 20.....

Do.........

Do.........

Do......... 

October 28.....

Do.........

Height 

above 

base of 

hood.

Ft. in. 

5 3

4 3 

3 3 

2 3 

2 3 

1 3

Item 

No.

1 

( 2

1- 3

1 

( ?

1 8 

( 9 

' 10 

11 

12 

13 

' 14 

15 16- 

17

18 

19

) 20 

I 21

Distance 

from axis 

of producer.

Inches. 

22 

7 

10 

22 

28 

7 

16 

22 

28 

7 

10 

22 

28 

7 

10 

22 

28 

7 

10 

22 

28

Gas analysis. '

C02 .

0.5

4.8

0.0

9.5

11.5

15.9

9.0

02 .

0

0

.2

.1

0

0

0

C2H4 .

0

.4

.1

.1

0

0

0

CO.

24.7

25.0

27.3

22.7

23.7

8.2

22.7

Hj.

14.0

17.4

11.4

8.0

7.4

3.2

8.2

CH4 .

1.8

2.4

.6

.9

1.5

.3

.9

N,.

53.0

49.4

54.4

58.7

55.9

72.4

59.2

British 

thermal 

units of 

gas per 

cubic 

foot.

154.1

182.1

138.8

123.8

122.4

43.1

117. 3

Temperature.

°C.

550 

580 

510

823 

744 

708

1,009 

972 

1,148 

1,150 

1,197 

1,117 

1,170 

1,160 

1,205 

1,230 

1,335 

1,200 

1,072

A rapid fall of temperature from the lower part of the producer, 

where combustion is taking place, to the freshly fired fuel at the 

surface of the bed was to be expected, as was also the corresponding 

increase in the amount of combustible gases exhibited by the analyses 

in Table 3. In addition to this vertical temperature gradient, however, an unlooked-for horizontal temperature variation was observed.

DIFFERENT HORIZONTAL POSITIONS.

Table 3 shows that running through the center of the fuel bed, 

along the axis of the producer, is a region whose temperature is 300° 

or 400° C. below that of the outer portion of the bed. It seemed not
TEMPEKATURE DIFFEBENCES IN FUEL BED. 19

unlikely that the low temperature of the inner portion of the fuel 

bed Avould result in the formation of a gas loAver in combustible constituents than the gas from, the outer part of the bed. In order to 

determine, if possible, the extent of variation of the quality of the 

gas from the axis toward the wall of the producer, in connection with 

further temperature observations, gas samples were taken at varying 

distances from the axis of the producer. The results of observations 

made in this manner are contained in Table 4.

TABLE 4. Temperatures at specified points in- gas producer, with analyses and 

British tJtcrmal units of yas samples taken at different li,eigli,ts and distances.

Date.

November 0.... 

Do........

November 7....

Do.........

November 8.... 

November 9....

Do.........

Height 

above 

base of 

hood.

Ft. in. 

4 3

3 3 

3 3

2 3

1 3 

4 3

3 3

Item 

No.

1 '

3

4 

5 

0 

7 

8 

. 9 

10 

11 

12 

13 

14 

15 

10 

17 

18 

« 19 

« 20 

21 

22 

23 

24 

25 

20 

27 

28 

29 

30 

31 

32 

33 

34 

35 

30 

37

Distance 

from 

axis of 

producer.

Inches. 

7 

10 

22 

 28 

34 

7 

13 

10 

22 

28 

31 34 

7 

10 

22 

28 

34 

7 

7 

7 

13 

10 

22 

28 

34 

. 7 

7 

10 

22 

28 

34 

34 

7 

10 

 22 

28 

34

Gas analysis.

C02 .

7.4

4.8 

10.5

5.2 

4.0

4.0

5.0 

5.0 

9.0 

5.9

0.5 

8.1 

0.5

5.0

7.0

Oj.

0

1.8 

0 

0 

0

0

6

0 

0 

0

0 

0 

0

.3

0

CsH<.

0

0 

0

6

0

0

0 

0 

0 

 0

0 

0 

0

6

0

CO.

22.4

21.4 

23.2

30.7 

18.8

21.4

20.1 

27.4 

24.3 

29.3

28.0 

24.4 

20.1

21.4

25.9

H>.

12.4

20.0 

10.8

12.8 

24.0

20.0

13.0 

17.8 

22.8 

12.0

10.0 

12.0 

20.0

24.4

10.4

CH4 .

4.2

3.3 

1.2

.0 

0.0

4.8

.0 

1.5 

0.0 

.0

.0 

.0

7.8

4.2

.0

Nj.

53.0

48.7 

48.3

50.7 

40.0

42. C

54.1 

48.3 

37.9 

51.6

54.3 

54.9 

45.0

44.7

50.1

British 

thermal 

units of 

gas per 

cubic 

foot.

100.1

179.4 

152.2

158.1 

215.1

218.4

144.8 

173.5 

224. 5 

152.1

 141. 0 

132.9 

224.9

204.3

133.0

Temperature.

°C. 

488 

488 

444 

597 

834 

039 

579 

505 

793 

913 

945 

949 

311 

355 

794 

1,038 

1,000 

512 

512

752 

909 

1,099 

1,174 

1, 109 

1,190 

260 

260 

278 

098 

845 

900 

390 

478 

911 

1, 096 

1,150

" Test 20 was made Immediately after test 19. 

water cooled and in test 20 it was uncooled.

In test 19 the gas-sampling tube was

In every case there is a rise of 300° or 400° C. from the interior to 

the exterior region of the fuel bed. Analyses of the gas samples fail 

to show any corresponding systematic variation in the amount of 

combustibles present. This can be explained, in part at least, by the 

circumstance that when the sampling tube was in position 'in the 

furnace, though an attempt was made to close the space between the 

sampling tube and the wall of the test hole, usually the excess pressure
20 PEOBLEMS IN GAS-PRODUCEE TESTS.

within the producer forced a passage between sampling tube and 

producer wall, through which poured a current of hot gasses. Consequently a current of gas, drawn from all parts of the producer, is 

continually flowing past the end of the sampling tube, and the gas 

drawn through the sampler probably does not represent the normal 

condition at the point of sampling.

CAUSES OF IRREGULARITIES.

A comparison of the temperature observations of Table 4 shows 

that there is a considerable deviation between observations made at 

the same points in the fuel bed but on different days. The temperature at any point in the producer is dependent on the depth of fuel 

bed, the draft, poking, and firing. As these conditions can not be 

maintained absolutely constant, the temperature varies accordingly. 

In order to obtain results which are strictly comparable, temperature 

measurements and gas sampling should take place simultaneously 

in various parts of the fuel bed. This is obviously impossible on 

account of the great amount of apparatus that would have to be 

handled and the rapidity with which the pyrometer and sampling 

tubes are attacked and destroyed in the hotter parts of the fuel bed. 

So much time was required for each observation that relatively few 

could be made in one day. Moreover, during a series of observations 

extending over a day, the condition of the fuel bed was continually 

changing, so that results obtained on the same day may disagree.

AVERAGE RESULTS FOR EACH POINT.

In Table 5 all the results in Tables 2, 3, and 4 have been combined 

by averaging the observations for each point in the producer. The 

observations are grouped with respect to their distance from the 

axis and in the order of their height above the hood.

TABLE 5. Average of observed temperatures and gas analyses for specified 

points in gas producer, grouped by distances from axis.

Distance from axis of producer.

Height 

above 

base of 

hood.

Ft. in.

{ 4 3 

3 3

2 3 

I 1 3 

I 4 3 

1 3 3 

1 2 3 

1 3

Gas analysis.

CO2.

7.0 

7.2 

6.4 

12.0

CO.

21.2 

21.0 

27.5 

16.3

H2.

16.5 

20.7 

16.4 

7.6

CH4 .

6.0 

3.6 

2.1 

.45

N2:

49.3 

47.4 47.3' 

63.6

British 

thermal 

units of 

gasper 

cubic 

foot.

195.5 

183.6 

175.5 

88.0

Temperature.

°C.

445 

521 

867 

1,151 

419 

526 

1,098 

1.220
TEMPERATURE DIFFERENCES IF FUEL BED. 21

TABLE 5. Average of observed temperatures and (/as analyses for specified 

points in gas producer, grouped l)y distance from axis Continued.

Distance from axis of producer.

S4 Indies

Height 

above 

base of 

hood.

Ft. in. 

f 4 3 

3 3 

\ 2 3 

1 3 

f 4 3 

1 3 3 

I 2 3 

I 1 3 

( 4 3 

1 3 3 

1 2 3 

I 1 3

Gas analysis.

C02.

4.8 

5.3 

10.5 

9.0

4.9 

5.9 

0.5

CO.

25.6 

 24.3 

23.2 

22.7

21.4 

27.6 

28.0

Ha.

17.4 

19.0

7.7 

8.2

22.2 

12.3 

10.6

CH<.

2.4 

2.7 

1.2 

.9

3.7 

.6 

.6

N2 .

49.4 

48.5 

57.3 

59.2

46.7 

53.6 

54.3

British 

thermal 

units of 

gas per 

cubic 

foot.

182.1 

178.6 

123.1 

117.3

191.8 

145.3 

141.0

Temperature.

°C. 

515 

877 

1, 140 

1,185 

706 

1,014 

1,144 

1,074 

840 

1,057 

1,169 

1,015

The variations both of temperature and of composition of gases 

are more marked than in the preceding tables. The temperature

1200

1000

o

°. 800

f, 600

400

200

100

334 from ax s of producer

is of producer 

of producer

2 3 

Height above base of hood, feet

FIGURE 6. Curves of temperature variation with height above base of fuel bed.

gradients along vertical lines located 7, 22, and 34 inches from the 

axis are illustrated graphically in figure 6. Here the curve for the 

temperatures nearest the axis (7 inches) falls rapidly from 1,150° to 

500° C. The middle curve of temperatures, midway between axis and 

wall, is flat for a distance representing a foot or more in height and 

then falls off as it approaches the top of the fuel bed. Finally the 

top curve for temperatures, near the furnace wall, rises gradually to 

a maximum and then falls off slowly. The low temperature at the
22 PROBLEMS IN GAS-PRODUCER TESTS.

lower part of the fuel bed and near the wall is due to the accumulation of ashes at that point.

These temperature variations are further illustrated-in figure 8, 

in which curves are drawn through points of equal temperature. 

The absolute temperature at any point in the fuel bed varies with, 

the conditions of operation for example, with the depth, draft, 

poking, and grinding of the bed. The curves in figure 8 have therefore a relative value only. They serve to show, however, that running 

through the center of the fuel bed is a region of low temperature, 

300° to 400° C. below the temperature of the outer zones.

PROCESS OF. GAS FORMATION.

In addition to combustion, the two principal reactions that take 

place in the producer are CO2+C=2CO and H2O+C=CO-f-H2 . 

The temperature in the central portion of the fuel bed is so low that 

these reactions can not take place there to an appreciable extent. 

Consequently a considerable proportion of the producer fuel bed is 

not effective in forming producer gas, and the producer is operating 

at a far lower capacity than if the temperature of the inner region 

were maintained equal to that of the outer zone.

Figure 8 furnishes an explanation of the irregular temperature 

distribution in the fuel bed. The current of air and steam proceeding from the mouth of the blower at a has two paths open to it, one 

straight ahead through c and one under the base of the hood at &. 

From the direction of the isothermal lines in figure 8, it seems likely 

that the greater portion of the incoming air passes out under the base 

of the hood and up through the outer part of the fuel bed. Either 

the opening at c is too small or it is clogged with ash and fuel.

In Table 5 the process of formation of producer gas may be traced

roughly in each of the three groups of samples. The proportion of 

C02 and nitrogen decreases in each group from the level of test 

hole No. 2, which is a foot above the hood, to the surface of the fuel 

bed. There is a marked increase in the percentage of hydrogen and 

methane (CHJ from the lower to the upper test hole. A corresponding increase in the amount of carbon monoxide (CO) might 

be expected. The CO values in Table 5, however, exhibit no systematic variation.

The variations are more clearly shown in Table 6, in which the 

means of all the values for each height, irrespective of distance from 

the axis, are arranged in the order of .the height of the points of 

observation above the hood.
TEMPERATURE DIFFERENCES IN- FUEL BED. 23

TABLE 6. Average of observed temperatures and gas analyses for specified 

heights, irrespective of distance, in gas producer.

Height above base of hood.

Gas analysis.

C02.

7.2 

5.6 

0.1 

7.8 

10.5

CO.

22.9 

22.7 

24.3 

26.2 

19.5,

Ha.

15.0 

18.7 

17.3 

11.6 

7.9

CH4 .

1.8 

4.0 

2.3 

1.3

.7

 N2 .

53.1 

48.5 

49.8 

53.0 

61.4

British 

thermal 

units of 

gas per 

cubic 

foot.

152.9 

189.8 

169.2 

146.5 

102.6

Temperature.

°C.

585 

799 

1,084 

1,129

The values of Table 6 are represented graphically by the curves, in 

figure 7. The vertical line at the right of the figure (abscissa=5 feet

2 3 .4 

Height above base of hood, feet

FIGURE 7. Variation of gas combustion temperature and British thermal units with 

height above base of fuel bed.

6 inches) represents the approximate level of the surface of the fuel 

bed. The points lying on this line and connected with the appropriate 

curves by means of dotted lines are the mean values of the percentage 

of the various gases and of the calorific values in British thermal
PROBLEMS IN GAS-PRODUCER, TESTS.

units for the gas leaving the producer. The data are taken from the 

official gas analyses. The temperature is that of the gas just above 

the fuel bed.

The conclusions or results shown by Table 6 and figure 7 are of 

interest only as a confirmation of the generally accepted theory of 

the gas producer and offer nothing novel.

DIFFERENCES WITH DISTANCE FROM AXIS.

In Table 7 the results of Table 5 have been grouped in accordance 

with their height above the base of the hood, to permit a comparison 

of gas samples taken from the same height in the producer but at 

different distances from the axis.

TABLE 7. Average of observed temperatures and gas analyses for specified 

points in gas producer, grouped l>y heights.

Height above base of hood.

3 feet 3 inches ...................

2 feet 3 inches ...................

Distance 

from 

axis of 

producer.

Inches. 

7 

16 

22 

28 

34

7 

16

22 

28 

34 

7 

16 

22 

28 

34 

7

16

22 

28 

34

Gas analysis.

CO2 .

7.0

4.8

4.9 

7.2

5.3

5.9 

6.4

10.5

6.5 

12.0

9.0

CO.

21.2

25.6

21.4 

21.0

24.3

27.6 

27.5

23.2

28.0 

16.3

22.7

Hj.

16.5

17.4

22.2 

20.7

19.0

12.3 

16.4

7.7

10.6 

7.6

8.2

CEU.

6.0

2.4

3.7 

3.6

2.7

.6 

2.1

1.2

.6 

.45

.9

N2.

49.3

49.4

46.7 

47.4

48.5

53.6 

47.3

57.3

54.3 

63.6

59.2

British 

thermal 

units of 

gas per 

cubic 

foot.

195.5

182.1

191.8 

183.6

178.6

145.3 

175.5

123.1

141.0

88.0

117. 3

Temperature.

"C. 

445 

419 

515 

706 

840 

521 

526 

877 

1,014 

1,057 

867 

1,098 

1, 140 

1,144 

1,169 

1, 151 

1,220 

1, 185 

1,074 

1,015

It has been shown above (p. 22 and fig. 8) that the low temperature of the interior of the producer is not favorable to the formation 

of CO and H2 . It was to be expected, therefore, that samples taken 

in the outer portions of the fuel bed would show a higher percentage 

of H2 and CO and a lower percentage of CO2 than those taken along 

the same radius nearer the axis of the producer. 

Assuming that the temperature distribution in the producer is 

represented correctly by the curves of figure 8, and assuming further 

that the lines of flow of the gas are approximately vertical, then 

samples from the same level, up to the level of test hole No. 3, should 

not be expected to show any great variation.

Above the level of hole 3 the temperature of the interior of the 

bed is below the temperature necessary for the formation of appreci-
TEMPERATURE DIFFERENCES IN FUEL BED. 25

able quantities of CO and EL A marked difference might therefore 

be expected between samples from the inner and outer portions of 

the bed taken through test hole 4 or 5. Table 7 does not show any 

such systematic difference. Whereas at an elevation of 4 feet 3 inches 

above the base of the hood (hole 5) the hydrogen content is appreciably higher near the wall of the producer than near the axis, the

FIGURE 8. Section of producer showing temperature variation for height and distance

from sides of producer.

samples taken a foot lower (hole 4) show a variation in the opposite 

direction. The methane content alone shows a systematic variation, 

being higher in samples from the inner portion of the bed. This is 

probably because methane, being readily liberated at relatively low 

temperatures, is mostly given off before the coal reaches the hot region 

of the outer zone.
26 PEOBLEMS IN GAS-PRODUCER TESTS.

REQUISITE TEMPERATURE FOR FORMATION OF CO.

The experiments show a gradual increase in the amount of combustible constituents and a corresponding decrease in the amount of 

CO2 from the level of test hole 2 to the surface of the bed. While 

the percentage of hydrogen is more than doubled between holes 2 and 

5, the increase in CO is less than a fourth as great. Apparently the 

formation of CO from CO2 takes place for the most part below hole 

2, in the lower part of the bed.

The analyses of gas samples offer no evidence to confirm the supposition that the lower temperature of the inner portion of the bed 

would give rise to a gas lower in CO and EL, than that of the outer 

regions. These facts especially made it desirable to determine, if 

possible, the temperature requisite for the formation of gas rich in 

CO and H2J or in. other words to determine at what temperatures 

the reaction CO2+C=2CO and H,O+C=CO+H2 may be complete.

An extensive series of investigations on the relative proportions of 

CO2 and CO in equilibrium with carbon at different temperatures 

has been carried out by Boudouard.a He found the respective percentages of CO2 and CO in equilibrium with carbon at 650° C. to be 

61 and 39; at 800° C., 7 and 93; and at 925° C., 4 and 96. 

1 These results of Boudouard have been used by writers on the theory 

of the gas producer to demonstrate the temperature in the fuel bed 

necessary for the formation of rich CO gas. Boudouard's results apply to mixtures of C02 and CO which have been in contact with hot 

carbon for a considerable length of time until equilibrium has been 

reached. In his experiments at 650° and 800° C. sealed glass tubes 

containing carbon and CO2 were heated for a period of several hours.

Since for the reaction CO2 -|-C=2CO an appreciable amount of

time is required that is, the reaction does not take place instantaneously the direct application of Boudouard's results to the process 

in the gas producer, in which the gas rushes through the fuel bed at a 

high velocity is not justifiable. Recent experiments under the direction of one of the authors of this report, the results of which will be 

'published in forthcoming bulletins, have established that, with the 

rate of flow of gas and the depth of fuel bed which obtain in a gas 

producer a temperature of 1,100° C. or more is required for the formation of 90 per cent CO gas from CO, and charcoal, and 1,300° for 

the same percentage from C02 and coke and from CO2 and anthracite 

coal. With a temperature 100° C. lower than these the resultant gas 

will contain about 50 per cent CO. It follows that the temperature of 

the fuel bed of the gas producer must be at least 1,300° C. in.order to 

yield the highest possible percentage of CO.

<*Boudouard, Compt. Rend. Acad. Sci. Paris, vol 28, 1890, pp. 824, ,1542; vol. 130, 

1000, p. 132; vol. 131, 1000, p. 1204. See also Haber, Thermodynamics of technical gas 

reactions, London, 1908, p. 311.
TEMPERATURE DIFFERENCES IN FUEL BED. ' 27 

SUMMARY.

1. Temperature observations were made and gas samples taken in 

different parts of the fuel bed of the gas producers. The temperature 

was found to be highest at the bottom of the fuel bed and to decrease 

from this point to the top of the bed.

2. The temperature of the inner region of the fuel bed was found 

to be 300° or 400° lower than that of the outer layers. A corresponding inferiority in the quality of the gas in the center of the producer 

could not be established; probably on account of the defective method 

of sampling.

3. It has been suggested that by an improvement in the method of 

admitting the draft to the fuel bed a more uniform distribution of 

temperature, and consequently a gain in the capacity of the producer 

and in the quality of the gas, might be obtained.

4. Reference has been made to recent experiments by one of the 

authors which have established 1,300° C. as the lower limit of temperature for the formation of a gas rich in CO.
SURVEY PUBLICATIONS ON FUEL TESTING.

A classified list of Survey papers dealing with coal is given in Bulletin 316, and in an abstract from that bulletin, pp. 439 to 532, published separately.

The following publications on fuel testing, except those to which a 

price is affixed, can be obtained free by applying to the Director, 

Geological Survey, Washington, D. C. The priced publications can 

be purchased from the Superintendent of Documents, Government 

Printing Office, Washington, D. C.

BULLETIN 261. Preliminary report on the operations of the coal-testing plant 

of the United States Geological Survey at the Louisiana Purchase Exposition, in 

St. Louis, Mo., 1904; E. W. Parker, J. A. Holmes, M. R. Campbell, committee 

in charge. 1905. 172 pp. 10 cents.

PROFESSIONAL PAPER 48. Report on the operations of the coal-testing plant 

of the United States Geological Survey1 at the Louisiana Purchase Exposition, 

St. Louis, Mo., 1904; E. W. Parker, J. A. Holmes, M. R. Campbell, committee in 

charge. 1906. In three parts. 1492 pp., 13 pis. $1.50.

BULLETIN 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. 20 cents.

BULLETIN 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. 10 cents.

BULLETIN 325. A study of four hundred steaming tests, made at the fuel-testing plant, St. Louis, Mo., 1904, 1905, and 1Q06, by L. P. Breckenridge. 1907. 

196 pp. 20 cents.

BULLETIN 332. Report of the United States fuel-testing plant at St. Louis, 

Mo., January 1, 1906, to June 30, 1907; J. A. Holmes, in charge. 1908. 299 pp.

BULLETIN 334. The burjiing of coal without smoke in boiler plants; a preliminary report, by D. T. Randall. 1908. 26 pp. 5 cents.

BULLETIN 336. Washing and coking tests of coal and cupola tests of coke, by 

Richard Moldenke, A. W. Belden, and G. R. Del.amater. 190S. 76 pp. 10 cents.

BULLETIN 339. The purchase of coal under government and commercial specifications on the basis of its heating value, with analyses of coal delivered under 

government contracts, by D. T. Randall. 1908. 27 pp. 5 cents.

BULLETIN 343.'Binders for coal briquets, by J. E. Mills. 1908? 56 pp.

BULLETIN 362. Mine sampling and chemical analyses of coals tested at the 

United States fuel-testing plant, Norfolk, Va., in 1907, by J. S. Burrows. 

1908. 23 pp. 5 cents.

BULLETIN 363. Comparative tests of run-of-mine and briquetted coal on locomotives, by W. F. M. Goss. 1908. 57 pp.

BULLETIN 366. Tests of coal and briquets as fuel for house-heating boilers, by 

D. T. Randall. 1908. 44 pp.

28
SURVEY PUBLICATIONS ON FUEL TESTING. 29

BULLETIN 367. Significance of drafts in stearn-boiler practice, by W. T. Ray 

and Henry Kreisinger. 1909. 61 pp.

BULLETIN 368. Washing and coking tests of coal at Denver, Colo., by A. W. 

Belden, G. R. Delamater, and J. W. Groves. 1909. 54 pp., 2 pis.

BULLETIN 373. The smokeless combustion of coal in boiler plants, by D. T. 

Randall and H. W. Weeks. 1909. 188 pp.

BULLETIN 378. Results of purchasing coal under government specifications, 

by J. S. Burrows; Burning the small sizes of anthracite for heat and power 

purposes, by D. T. Randall. 1909. 44 pp.

BULLETIN 385. Briquetting tests at Norfolk, Va., by C. L. Wright. 1909. 41 

pp., 9 pis. ' '

BULLETIN 392. Gasoline and. alcohol tests on iuternal-combustion engines, by 

R. M. Strong. 1909.

O