which are evolved in Coal-Mines. 325 



lysis which follows below of the pit-gas not decomposed by 

 heat, exhibits only a very inconsiderable amount of a foreign 

 gas ; but, if we consider that the gas submitted to the pre- 

 vious experiment remained nearly 24 hours* in contact with 

 a large quantity of water, it must be evident that a portion 

 of the gas must have been absorbed by the water, and, on the 

 other hand, that atmospheric air must have been given out 

 by the water. This must happen so much the more, because 

 the surface of contact between the water and the two gases 

 was great. The atmospheric air which, during the experi- 

 ment itself, was added to the gas, must naturally cause a par- 

 tial burning of the pit-gas in the porcelain tube, so that a 

 smaller increase of volume must have taken place than result- 

 ed from the above calculation. All these unavoidable circum- 

 stances must affect considerably the general accuracy of the 

 numerical results, and hence these can possess but a small 

 value. Besides, the following experiments shew that the de- 

 composition of the inflammable pit-gas is accompanied by other 

 peculiar phenomena. 



The empyreumatic smell which I had perceived in the por- 

 celain tube after the decomposition of the pit-gas, allowed it 

 to be supposed, that during the process, a peculiar hydro-car- 

 biu'etted compound might have been produced. As in the 

 earlier experiments only small quantities of pit-gas were con- 

 ducted through the heated porcelain tube, I repeated the ex- 

 periment with a larger quantity. The apparatus was some- 

 what altered. With the porcelain tube, which had a much 

 greater diameter (1 inch) than that employed in the previous 

 experiments, I united the previously described apparatus with 

 which I had collected the pit-gas in Gerhard's mine, and I 

 opened the cock so little, that only about a drop of water 

 flowed out in a second. The gas in the gasometer was there- 

 fore conducted through the chloride of calcium and the por- 

 celain tube with great slowness. In this manner nearly three 

 bottles of ^'A^ were conducted, but without being caused to 

 return as in the former experiments. 



* The experiment itself Instccl some hours, and as the gas could net be 

 measured until the nhole apparatus had cooled, it was neccseaiy to allow it 

 to itand orer night. 



