required to produce any given amount of mechanical energy, it follows that the greater the calorific value of the gas used in a gas engine the smaller the amount required per hour per horse power developed. If the gas engine were capable of using, with the same efficiency, gases of any calorific value, the respective amounts of the different gases required per hour per horse power would vary inversely as their calorific values. It is found, however, that for various reasons gas engines work a little more efficiently when using gas of comparatively low calorific value, 150 to 300 B. T. U. per cubic foot, than they do when using gas of higher calorific value, 500 to 1,000 B. T. U. per cubic foot, so that they require somewhat less of the low value, in comparison with the higher value gas, than is called for by the relation between the calorific values. In any case, the consumption of gas per horse power will vary with the condition in which the engine is kept and upon the proportion between the load it is carrying and that which it is capable of carrying, since when working at or near its full load the engine has a greater mechanical efficiency than when running under a small load. Under favorable conditions a 10-horse power gas engine can be run on a consumption of 20 cubic feet per brake horse power per hour when using gas of a calorific value of 650 B. T. U., but the average consumption under actual working conditions will be about 25 cubic feet per brake horse power per hour. (Trustees.) II. An instantaneous water heater burning gas at the rate of 81 cubic feet per hour will heat water from a temperature of 54° F. to one of 117° F. at the rate of 72 gallons per hour. The gas has a net calorific value of 650 B. T. U. per cubic foot. What is the efficiency of the heater? Ans. Under the conditions stated in the question the amount of heat developed in the heater per hour by the gas used is 81 (number of cubic feet of gas consumed per hour) × 650 (calorific value of a cubic foot) = 52,650 B T. U. The useful work done is measured by the amount of heat put into the water passing through the heater. The temperature of the water is raised 117 54 = 63° F. and the weight heated to this extent is 72 (number of gallons heated per hour) X 8.33 (weight of a gallon of water in pounds) = 599.76 lbs. Therefore, the gas consumed does an amount of useful work equal to 599.76 x 63 = 37,785 B. T. U. and the efficiency of 37785 the heater is 52650 = 71.7%. (Trustees.) SECOND SERIES OF QUESTIONS-SECTION OF 1906-PRACTICAL CLASS-AMERICAN GAS LIGHT ASSOCIATION. 1. What precautions should be taken to avoid spontaneous combustion in bituminous coal stored in a coal shed? 2. The furnaces employed for heating coal gas retorts may be divided into two general classes. What are these classes, what is the distinctive difference between them, and what advantages has either one over the other? 3. In the manufacture of carburetted water gas it is customary to have the water gas pick up the oil, in a state of vapor, at the entrance to the fixing vessels and carry this vapor and the resulting gas through these vessels, the oil gas being thus made in the presence of the water gas. What advantages has this method over that of making the oil gas entirely separate from the water gas? 4. Describe, with sketches if necessary, one or more forms of apparatus for removing heavy tar from gas, and state the position in the sequence of apparatus that should be occupied by the tar extractors, with your reason for such location. Define the term Specific Gravity of a Gas. Give the limits between which you would expect the Specific Gravity of Coal Gas to vary. Same for Carburetted Water Gas. How do you account for the difference in Specific Gravity between the two gases? 6. Give the weight of a cubic foot of each of the following gases when dry and at a temperature of 60° F. and a pressure of 30" of mercury: Describe the ordinary qualitative tests for the presence in gas of Tar, Ammonia (NH), Carbonic Acid (CO2), and Sulphuretted Hydrogen (H,S), and state at what points in the apparatus the test for each should be made in order to determine that the gas is being properly purified. Give your reason in each case. 8. What is the meaning of candle power" in the statement "this is a 20-candle power gas?" 9. Having provided drip pots at the proper points in the street main system what further precaution is necessary to prevent trouble from accumulation of condensation? IO. What principles govern the efficient combustion of gas for the production of light, and what details of construction have been adopted in the most improved forms of flat flame burners of the batswing or slit type to carry out these principles? II. Why are Bunsen or Atmospheric burners used in gas cooking stoves and incandescent gas lights? Why are they not used in the ordinary cylindrical gas heating stoves and gas radiátors? 12. What considerations would determine your choice between lime mortar and cement mortar for use in any given job of brick or stone masonry y? (Answers to these questions are due June 1st.) ANSWERS TO THE SECOND SERIES OF QUESTIONS-SECTION OF 1906-PRACTICAL CLASS-AMERICAN GAS LIGHT ASSOCIATION. Answers to all of these questions, except Nos. 3, 7 and 12, have been published in previous volumes of the Proceedings, and can be found there as follows: No. 1, Vol. XIX, page 189. No. 2, Vol. XVII, page 88. No. 4, Vol. XVII, page 91. The answers to Questions Nos. 3, 7 and 12 are as follows: 3. In the manufacture of carburetted water gas it is customary to have the water gas pick up the oil, in a state of vapor, at the entrance to the fixing vessels and carry this vapor and the resulting gas through these vessels, the oil gas being thus made in the presence of the water gas. What advantages has this method over that of making the oil gas entirely separate from the water gas? Ans. The principal advantage that is thought to be obtained by carrying on the manufacture of carburetted water gas so that the oil gas portion is made in the presence of the water gas instead of being made entirely separate from the water gas, is that the presence of the water gas shields the oil gas from the heat and renders it less subject to over-decomposition in case the temperature of the heated surfaces is too high or the exposure to the heat too prolonged. The effect upon the oil vapors and gas of exposure to heat of too great intensity or for too long a time is to produce hydrocarbon gases of low illuminating values, or hydrocarbon vapors, which, although they are of high illuminating value, can be carried by the gas only to a limited extent. By separating and sur rounding the molecules of the oil vapors and gas, the water gas reduces the extent to which they are exposed to the heat and so reduces the liability to over-decomposition. On the other hand, it is possible that an excess of water gas will exert so great an effect as to interfere with the complete gasification of the oil, and in cases where the amount of exposure is small or the intensity of the heat low, the presence of water gas during the decomposition of the oil may be detrimental. This, however, will not occur in an apparatus that is properly designed and handled. Another advantage of making the oil gas in the presence of the water gas is that the latter will pick up and carry oil vapors that escape gasification, and, if the water gas were not present, would be condensed and left behind when the oil gas was cooled. These vapors are of value as illuminants, and so the candle power of the carburetted water gas made in this way will be higher for an equal amount of oil used than will be that of carburetted water gas made by making the water gas and oil gas separately and mixing them cold. This advantage can, however, be obtained to a great extent even when the two gases are made separately by mixing them hot. This method of making carburetted water gas also makes it possible to conveniently arrange the apparatus so that the heat required for the gasification of the oil can be furnished very economically by the combustion, and partly by the sensible heat, of the producer gas formed in the generator while the fuel is being heated up to the temperature required for the manufacture of water gas. (Trustees.) 7. Describe the ordinary qualitative tests for the presence in gas of tar, ammonia (NH3), carbonic acid (CO2) and sulphuretted hydrogen (H,S), and state at what points in the apparatus the test for each should be made in order to determine that the gas is being properly purified. Give your reason in each case. Ans. The ordinary test for tar is made by allowing a jet of gas to impinge on a piece of white paper. If a dark stain appears on the paper, tar is present in the gas. A continuous test for tar can be made by passing a stream of gas through a |