394 Prof. Johnston on the Composition of certain 



The elementary composition of these different substances, 

 therefore, is identical, and is the same as that of olefiant gas. 

 The ozocerite found in Urpeth Colliery must have had its 

 origin in the coal strata. Emitted, in the form of vapour, and 

 carried along by the lighter gas (fire damp), given off' at the 

 same time, it would pass through the trouble, on its way to 

 the surface, and be partly condensed in the cavities, and other 

 cool places it came in contact with. It is highly probable 

 that the other varieties of fossil wax may have been derived 

 from a similar source. 



In considering the inflammable and explosive substances 

 existing in coal mines it is usual to limit the attention solely 

 to the permanent gas given off", without adverting to the pos- 

 sibility of other substances, of a volatile nature, being also 

 emitted in the state of vapour. The occurrence of this variety 

 of Ozocerite, in Urpeth Colliery, shows us that the light 

 carbu retted hydrogen sometimes carries along with it other 

 volatile substances, and there is strong reason for believing 

 that the combustible portion of the atmosphere of our coal 

 mines rarely, if ever, consists wholly of this light gas. To 

 show the Proteus-like character of the compounds of carbon 

 and hydrogen, in the ratio of atom to atom, and how little che- 

 mical analysis can avail directly in determining the total abs- 

 ence of these substances, I subjoin a table, exhibiting the cha- 

 racteristic properties of the numerous bodies we are already ac- 

 quainted with, in which the elements exist in this proportion. 



