nihich are evolved in Coal- Mines. 327 



sides, products of dry distillation (solid or liquid carburetted 

 hydrogen compounds) are formed, as in the decomposition of 

 organic substances. 



In order to ascertain somewhat more exactly the nature of 

 these carburetted hydrogen compounds, I repeated the pre- 

 ceding experiment with this difference, that between the col- 

 lecting appai'atus and the porcelain tube, the well-known ab- 

 sorbing apparatus of Professor Liebig, filled with concentrated 

 sulphuric acid, was introduced, and was carefully united to 

 both, the whole being made air-tight. Six bottles of pit-gas 

 were conducted through, and the experiment lasted from five 

 to six hours. 



After the passage of the gas through the heated porcelain 

 tube had commenced, there appeared in the first ball of the 

 absorbing apparatus, white vapours, which soon rendered the 

 sulphuric acid brown. There then appeared in the glass tube 

 of this apparatus, which was united with the porcelain tube, 

 yellow drops which gradually flowed down into the ball. Af- 

 terwards, greenish drops were condensed over the sulphuric 

 acid in the first ball. The acid in the three remaining balls 

 also gradually assumed a brown tint, and, after the termina- 

 tion of the experiment, it became deep brown in colour. I 

 allowed the apparatus to remain at rest until the porcelain 

 tube was entirely cooled. 



The decomposed gas burned with the same flame as the for- 

 mer, only with this difference, that the yellow portion was 

 somewhat smaller, and that the flame afforded less light. It 

 thus seems to follow, that the substances, which, in this ex- 

 periment, were absorbed by the sulphuric acid, but which, in 

 the former, at least partially, remained mixed with the gas in 

 the form of vapour, increased the burning power of the flame. 

 The gas had, moreover, still an empyreumatic smell, which, 

 however, seemed to be feebler than in the preceding experi- 

 ment. Hence it results that the sulphuric acid did not absorb 

 all the products of the decomposition. 



On the following day I separated the apparatus ; I was much 

 surprised at finding in the porcelain tube only some triflino- 

 little spangles of carbon, whereas, in the former experiment, 

 with a smaller quantity of gas, there was a considerable quan- 

 tity of carbon. There was likewise a coating, which, however, 



