which are evolved in Coal-Mines. 143 



ingly, in the first experiment to 0.16, and in the second to 

 0.15. 



This increase amounts, therefore, to somewhat more than 

 that of the pit-gas of JFellesweiler Stollen ; but the difference 

 is not great. When we consider that the results of these expe- 

 riments depend on circumstances which we have not under 

 our control, this difference will not appear surprising. Indeed, 

 it is very probable that the increase of volume which the car- 

 buretted hydrogen undergoes when exposed to a red-heat is a 

 constant quantity, and that it does not exceed 0.2. What is 

 true of the carburetted hydrogen gas, is probably true as re- 

 gards the olefiant gas. Hence the latter gas, which, according 

 to the analysis, is contained in both the pit-gases, was not 

 taken into consideration. 



The carbon which was deposited in the porcelain tube was 

 quite of the same nature as in the Wellesweiler pit-gas, and 

 the same empyreumatic smell was perceptible. 



The analysis, by the detonation-tube, of the pit-gas from 

 Gerhard's Stollen, was conducted in the same manner as in § ix. 

 After it had been purified, by being washed with solution of 

 potash, it was mixed with three times its volume of oxygen, 

 which was likewise washed in the same way. 



The following are the results of the experiments, after sub- 

 tracting the watery vapour, and after reduction to 32° F. and 

 28 in. 



We might already reckon on the presence here of a consi- 

 derable quantity of a foreign gas, from the comparatively small 

 absorption by detonation and by potash. Therefore I agitated 

 the residue, after the absorption of the carbonic acid, for twenty 

 minutes, with sulphuret of potassium, and in the same way 1 

 determined also the amount of nitrogen in the oxygen em- 

 ployed for detonation. 



The following is the result of Experiment II. 



Residue after absorption of the carbonic acid, . . 1.4234 vol. 



Residue after agitation with a solution of sulphuret of potas- 

 sium, ...... 0.2830 ... 



