ATTEKDING THE FORMATION OF COAI^ &a 263 



mode of union, and the products of that union, being regu- 

 lated by the temperature. That, including in the consider- 

 ation the nitrogen, which, though not a constituent of the 

 woody tissue, is invariably found in the juices and in many 

 of the organs of a plant, and permeates every part of it, 

 when vegetables decompose with free access of air, the 

 products are carbonic acid, water, and ammonia; when 

 under water, with very limited access, or total exclusion of 

 air, carbonic acid, water, carburetted hydrc^en, ammonia, 

 sulphuretted hydrogen, phosphuretted hydrogen, &c. ; 

 with limited supply of water, and exclosicm of air, as in, 

 wood coal, carbonic acid, water, and a little carburetted 

 hydrc^en, till the process having nearly exhausted the 

 oxygen, as in truly fossilized coal, the carburetted hydrogen 

 exclusively takes the place of the carbonic acid ; and finally, 

 that when the divellent affinities are exalted by a high 

 temperature, other compounds are formed, in which some 

 of the elements are united with each other in increased 

 proportions, (olefiant gas, naphtha, petroleum, &c.) It ia 

 worthy of remark, that when olefiant gas is found in the 

 fire-damp of mines, when the coal is supposed to have been 

 subjected to heat, its proportion varies from 1*5 to 16 per 

 cent. The most usual proportion was about 6 per cent. 

 These numbers represent the whole amount of illuminating 

 gases existing in the gas here formed by nature's operations. 

 The analyst is BischofF; and nowhere but in Germany has 

 tliis gas hitherto been found in fire-damp. When vege- 

 table bodies, or bodies of vegetable origin, as coal, cannel, 

 &c., are subjected to distillation in close vessels, without 

 access of air, as in the process of gas-making, manufacture 

 of pyroligneous acid, &c., the products will vary with the 

 composition of the substance employed, and with the tempe- 

 rature. We have seen that all the elements participate in 

 the change, and form new combinations. The proportion 

 and relation of the elements of fresh wood, and of coal. 



