OF WOODY FIBRE. 309 



carbonic acid, which contains 3 parts, by weight, of 

 carbon; while the weight of the sawdust is di- 

 minished by 15 parts. Hence 12 parts, by weight, 

 of water, are at the same time separated from the 

 elements of the wood. 



It has already been mentioned, that pure woody 

 fibre contains carbon and the elements of water. 

 Humus, however, is not produced by the decay of 

 pure woody fibre, but by that of wood which con- 

 tains foreign soluble and insoluble organic sub- 

 stances, besides its essential constituent. 



The relative proportion of the component ele- 

 ments are, on this account, different in oak wood 

 and in beech, and the composition of both of these 

 differs very much from woody fibre, which is the 

 same in all vegetables. The difference, however, is 

 so trivial, that it may be altogether neglected in 

 the consideration of the questions which will now 

 be brought under discussion ; besides, the quantity 

 of the foreign substances is not constant, but varies 

 according to the season of the year. 



According to the careful analysis of Gay-Lussac 

 and Thenard, 100 parts of oak wood, dried at 212 

 (100 C.), from which all soluble substances had 

 been extracted by means of water and alcohol, con- 

 tained 52*53 parts of carbon, and *47'47 parts of 

 hydrogen and oxygen, in the same proportion as 

 they are contained in water. 



Now it has been mentioned that moist wood acts 

 in oxygen gas exactly as if its carbon combined 



