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the brick work a one and a half inch iron pipe terminating in a tee, which carried on one branch a cap drilled with a one inch hole closed by a plate of glass. Through the other arm of the tee air was blown in just sufficient amount to keep the smoke back. This device proved very satisfactory. The Wanner pyronieter is unfitted for this work because of the small aperture of the peep hole. It is unsatisfactory also because it is inaccurate unless its storage battery is charged to the proper voltage.

The instrument we have come to rely on is the Morse Therniogage. This consists of a telescope in whose tube is a small incandescent electric lamp. A portable storage battery, a mille-ammeter, and a small rheostat, fastened to the telescope, complete the equipment. In operation the telescope is pointed at the retort, and the current flowing through the lamp is adjusted by the rheostat until the color of the filament blends with that of the furnace. The readings of the mille-ammeter give, by reference to the calibration table, the temperature. The telescope is made with a large objective, so that there is no trouble in locating the object desired, a feature which will be appreciated by those who have worked with the other forms of optical pyrometers. It is, of course, subject to the limitations of all optical pyrometers, the most important being that it can not be used where there are luminous flames, nor where there is a thick smoke. It is admirably adapted for taking the temperature of the interior of retorts after the charge has been drawn. Our observations indicate that, if the charge has been thoroughly burned off, the temperature of the inside of the retort, after the charge is drawn, is almost as high as that of the outside. Here are the results of a few observations. Exterior of Retort

Interior of Retort before Drawing Charge

after Drawing Charge 2010 degrees F.

1986 degrees F. 1914 degrees

1908 degrees It would thus seem that the temperature of the empty retort, as determined by an optical pyrometer, is a reliable indication of the furnace operation.

INFLUENCE OF RETORT TEMPERATURE. We can not detect any systematic effect of temperature in the figures for yield of gas, candle power, or heat value. This is probably, as explained previously, due to the disturbing influence of variations in pressure on the retort.

The values for the B. T. U. in the gas from one pound of coal are less liable to disturbance from variations in pressure. This value is obtained by multiplying the B. T. U. per cubic foot by the cubic feet of gas per pound. If we assume that the pressure within the retort is high, gas will be lost, but the heat value of the gas not lost will be inaffected. If there is suction on the retort, smoke gases will be pulled in, but it is not likely that any oxygen will get into the retort through the layer of carbon lining it. The effect of this smoke gas will be to lower the heat value of the gas by dilution, and to increase the volume of gas by the same proportion. The product of the two, which is the B. T. U. per pound of coal, will be unaffected by the dilution. Since the B. T. U. in the gas per pound of coal is unaffected by suction on the retort, and only one of the two factors used in its calculation is affected by pressure, the value thus obtained should be relatively independent of small variations in the retort pressure.

The figures for B. T. U. in the gas per pound of coal free from moisture and ash indicate a systematic variation with the retort temperature, imperfectly shown but nevertheless distinct. There are not so many tests available for this comparison since, on account of exasperating failures of thermocouples, there are some tests without temperature data. There are not enough points, nor are the data accurate enough to allow the curves to be drawn, but the general direction is shown by the following figures, which include all the tests for which temperature measurements are available.

Name of Coal
Harrisburgh,

Illinois

Table VII.

B. T. U. in gas

from one pound Test No. Retort Temp. coal, m. & a. free 1777

3120
1819

3330
1954
1979

3160

35

3220

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These figures indicate a maximum value for B. T. U. in gas from one pound of coal at a temperature between 1800 degrees and 1900 degrees F, the values decreasing for lower and higher temperatures. This general result would be expected from theoretical reasoning. At very low temperatures the yield of gas falls off rapidly without a correspondingly large increase in the heating value. At very high temperatures the heating value of the gas falls off without a corresponding increase in the quantity. Temperature can not be the only variable affecting this value, but it appears to be the important one. It must be emphasized that no quantitative significance can be attached to these figures. They are presented merely as indicating the general effect of change nf temperature.

SUMMARY. The present paper presents an analysis of the results of twenty-five tests on five coals. It is shown that the rate of gas production per hour from a retort is independent of the weight of the charge, or in other words that a given retort will yield a constant quantity of gas per day, irrespective of the weight of the charges, provided that the coke is drawn as soon as the gas is off, and that the retort is kept in continuous operation.

The rate of gas evolution is apparently a function of the rate of heat transmission through the walls of the retort, and this rate of heat transmission is more affected by the thickness of the skin of carbon on the inside of the retort than by ordinary variations in furnace temperature.

Systematic attempts were made to determine the effect of variation in the weight of the charge of coal by running consecutive tests on 300, 400 and 500 pound charges of these coals. There is no constant effect of the difference in weight of charge to be detected, either in quantity of gas, candle power, or heat value. The disturbing factor is believed to be variable retort pressure, causing leakage of gas through the wall of the retort. This variable is believed to have been important enough in our experiinents to have also masked the effect of temperature on the quantity of gas and on its candle power and heat value. The effect of temperature can be detected in the values for the B. T. U. in the gas from a pound of coal, which show an apparent maximum at moderate retort temperatures with decreasing values at higher and lower temperatures.

It is hoped that it will be possible during the coming year to exanıine more closely the iniportant subject of influence of retort pressure.

L'niversity of Michigan.
August, 1910.

DISCUSSION. Samuel Ball, Saginaw:

I am rather surprised at some of the constants and variables that have been brought out in this paper. Take for instance the coal from Hellier, Ky. I have always thought that weathering the coal would decrease the yield of gas. This of course would vary to a great extent for different coals but I think most of us have had this experience with coal that is stored outside for any length of time, but in the tests shown here the opposite results seem to have been obtained. The tests run this year give better results than those of last year.

Another remarkable thing is the increase yield with a decrease of nearly 200 degrees in retort temperature. A note attached to No. 21 indicates that the retort was badly coated with carbon at the time and it is possible that the charge was not a's completely burned off as for the tests run this year.

The average c.p. of tests No. 54 to 56 are higher than those of tests No. 21 and 30 which is what we would expect when we consider the difference for retort temperature. This, however, seems to hold good only with the Hellier coal, for when we come to the tests on the Harrisburg coal, we find that the higher the temperature the higher the c.p.

The fact brought out that the evolution of gas per hour per retort is a constant not affected by the size of the charge or the temperature of the retort within working limits, is a very interesting one. The papers show a large amount of good work done at the University during the past year and I think Professor White and Mr. Ferguson are to be congratulated on the results so far obtained in the study of Destructive Distillation of Coal.

Ernest F. Lloyd :

Discussion or criticism of this paper would seem to present difficulties. Its great value to me lies in two particulars. First, in the extent of the work participated in by students at the University, which necessarily carries an influence for good in the gas business far beyond the attention of the individual student collaborating with Prof. White.

And secondly, in its explanation of results obtained in commercial practice when working along the lines indicated in the

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