which are evolved in Coal-Mines. 139 



gravity of carburetted hydrogen, assumed above, as calcu- 

 lated from the experiments of Berzelius and Dulong. As 

 the specific gravity of the olefiant gas was calculated from the 

 same experiments, we must put faith in the previous calcula- 

 tion. On the other hand, I can also answer for the accuracy 

 of my determinations of the specific gravity of the pit-gas. 

 The difference between the specific gravities calculated ac- 

 cording to the analysis, and that found by direct experiment 

 (which of course becomes still a little greater when we take 

 into consideration the small admixture of atmospheric air, 

 which was mingled with the pit-gas), therefore still remains 

 somewhat puzzling. 



As, according to § viii., the sulphuric acid took up no pit-gas, 

 there can be no vapour contained in it, which, as in the deto- 

 nation of the oil-gas used for gas-light, could cause the formation 

 of a greater quantity of carbonic acid gas than belongs to the 

 carburetted hydrogen and olefiant gas. Can we suppose that 

 the pit-gas contains a very small quantity of a carburetted 

 hydrogen compound, which is not absorbed by sulphuric acid, 

 and likewise not by chlorine in the dark ? It is possible that 

 the phenomena mentioned in § vi. (vol. xxix. p. 322), the for- 

 mation of a peculiar oil-like combination during the passage 

 of the pit-gas through a red-hot porcelain tube, might arise 

 from such a vapoury hydro-carbon, and not from the carbu- 

 retted hydrogen or olefiant gas. The disagreeable smell, like- 

 wise, which pit-gas, kept for a long time in well-closed bottles, 

 acquires, and which resembles that of sulphuretted hydrogen, 

 may perhaps arise from the decomposition of such a substance. 



Chemical Analysis of the Pit-Gas of Gerhard's Stollen. 



This investigation was conducted in the same manner as 

 the preceding, and therefore I shall merely communicate the 

 results. 



Nitric oxide gas indicated no determinable quantity of oxy- 

 gen. 



Caustic potash indicated 0.039 vol. of carbonic acid gas. 



Chlorine-gas afforded such small absorptions, that, accord- 

 ing to these experiments, the existence of olefiant gas remains 

 somewhat doubtful. Should it be present, it con, at all events, 



