260 MR. JOHN LEIGH ON THE CHEMICAL CHANGES 



retted hydrogen. The avidity with which the decomposing 

 vegetable mass seizes, even when converted into beds of 

 coal, on every available source of oxygen, was lately ob- 

 served in analysing the gas (consisting chiefly of fire-damp) 

 from the mines of Newcastle ; the nitrogen forming from 

 14 to 21 per cent, whilst scarcely any oxygen remained. 

 Now, the nitrogen -must have been derived from atmo- 

 spheric air, admitted by the mine to the coal, which had re- 

 moved the oxygen and combined with it. The constant pre- 

 sence of sulphuret of iron in coal, which originally must 

 have existed as sulphate of oxide of iron, and been converted 

 by the removal of its oxygen into sulphuret, also shows the 

 powerful deoxidizing power of the decomposing organic 

 mass. When, after a long lapse of ages, the oxygen had 

 been gradually' removed from the vegetable mass, in the 

 form of carbonic acid and water, until at length the wood 

 coal had lost its structure, and acquired the composition 

 possessed by our own beds of more perfectly formed coal, 

 in which 1 atom of oxygen only remains in union with 24 

 atoms of carbon and 13 atoms hydrogen, or approached this 

 composition, it is evident that a new series of results must 

 attend the changes going on witiiin the still altering coals; 

 oxygen no longer existing for the formation of carbonic acid, 

 the carbon and hydrogen now constituting almost the entire 

 mass of the coal, must of necessity unite, and escape as car- 

 buretted hydrogen. An analysis of the gas evolved in mines 

 from coal, shows it to consist almost exclusively of light car- 

 buretted hydrogen. The following analysis by Mr. Wiight- 

 son, made in the laboratory of the Museum of Economic 

 Geology, of the gas evolved from a seam in the Hebburn 

 colliery, will show this : — 



Light carburetted hydrogen 91"8 



Carbonic acid 07 



Nitrogen 6*7 



Oxygen ,.., 0-9 



1001 



