which are Evolved in Coal-Mines. 135 



Carbon, . . 3.322 or 74.99 



Hydrogen, . . 1.111 or 25.01 



100.00 



This agrees very nearly with the composition of carburetted 

 hydrogen gas, but differs somewhat from the results of the 

 analysis in the detonation-tube, according to which, owing to 

 the mixed olefiant gas, the carbon ought to have turned out 

 somewhat greater ^in amount. Probably this proceeds from 

 the circumstance, that the dry and heated gas, which escaped 

 unconsumed, vaporised some of the water of the solution of 

 potash, so that the carbonic acid was estimated at too small 

 a quantity. If the analysis were to be repeated, it would be 

 necessary to connect a chloride-of-calcium tube with the ab- 

 sorbing apparatus. I satisfied myself, however, with the ap- 

 proximative result, as it was only intended "as a check on the 

 analysis of the pit-gas in the detonation-tube. 



§ 11. Determination of the Specific Gravity of the Pit-Gas. 



The gas was conducted into the exhausted balloon from a 

 gasometer through a tube, which was filled with chloride of 

 calcium, and was four feet long. The balloon was again ex- 

 hausted, and new gas was in like manner very slowly intro- 

 duced. In order to convince myself that the gas was perfectly 

 dry, I put in the balloon, immediately before the first pump- 

 ing out, a small tube filled with chloride of calcium. It pre- 

 sented, however, no increase of weight upon taking it out..after 

 the weighing of the balloon. The cock of the balloon closed it 

 quite securely ; for even after twenty-four hours the exhausted 

 balloon presented no increase of weight.' In communication 

 with the balloon on the air-pump there stood a receiver, under 

 which there was a thermometer and a small barometer, in 

 order to admit of the determination of the tension of the gas, 

 which still remained behind. In order, finally, to enable a 

 correction to be made for the unequal aerostatic influence du- 

 ring the different weighings, the external volume of the bal- 

 loon with its cock was determined by weighing it under pure 

 water. The loss of weight of the balloon, filled with water, 

 amounted in the water to 87672.5 grains at 51° F. At 32° F. 



