ft5 1^' Tiiomspii on a spcyiitanemis emission of Gas. 



ciajfburettied hydrogen gas. The slate- clay, from being always 

 soaked with moisture, would be impervious to this gas, so that 

 i% had been accumulating for some time, and existed in the 

 cavity in a state of condensation. It is easy to see how the 

 draining process would occasion a shrinking in the bed of 

 slate-clay ; cracks would be formed in it through which the gas 

 would find its way to the surface. If this explanation be the 

 jlrue one, the escape of gas will continue till the gas in the ca- 

 vity has reduced itself to the same state of elasticity as the 

 external air. It will then stop or will only appear occasionally, 

 and will become gradually diluted with common air, so as at 

 last to lose the property of inflaming. To enable the evolu- 

 tion of gas to be perpetual, it is obvious that it would require 

 to be formed as fast as it escapes. 



I collected a quantity of the inflammable gas, and subjected 

 it to a chemical examination. It is destitute of all smell, and 

 possesses all the mechanical properties of common air. It con- 

 tained not the least trace of carbonic acid gas, which is always 

 present when this gas is formed at the bottom of stagnant 

 pools of water. As the gas which I collected ascended through 

 the rivulet, flowing at the time with considerable velocity, it 

 may be supposed that carbonic acid gas might have been mix- 

 ed with the gas in its original repository ; but that it was 

 all washed away while the mixture passed up through the wa- 

 ter. But from the great violence with which it issued, I do 

 not think that this could have been the case. For if you mix 

 carbonic acid and carburetted hydrogen gases, and pass the 

 mixture through a column of water several feet long, a consi- 

 derable portion of the carbonic acid will still continue in the 

 mixture. 



The gas was not quite free from common air. A careful 

 set of experiments varied in different ways satisfied me that 

 the volume of common air in the gas was exactly 12.5 per 

 cent, or the gas was a mixture of 



Carburetted hydrogen, 87.5 volumes 



Common air, 12.5 



100 

 The carburetted hydrogen gas which constituted so great a 



