DECAY OF WOODY FIBRE. 331 



wood with the oxygen of the atmosphere, and that during the 

 process of oxidation carbon and oxygen escape from the wood 

 of carbonic acid. 



It has already been mentioned, that pure woody fibre con- 

 tains carbon and the elements of water. Humus, however, is 

 not produced by the decay of pure woody fibre, but by that of 

 wood which contains foreign soluble and insoluble organic 

 substances, besides its essential constituents. 



The relative proportions of the component elements are, on this 

 account, different in oak wood and in beech, and the composition 

 of both of these again differs 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 quan- 

 tity 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, contained 52-53 parts of carbon, and 47-47 parts of hy- 

 drogen 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 directly with oxygen, and that 

 the products of this action are carbonic acid and humus. 



If the action of the oxygen were confined to the carbon of the 

 wood, and if nothing but carbon were removed from it, the re- 

 maining elements would necessarily be found in the humus, un- 

 changed, except in the particular of being combined with less 

 carbon. The final result of the action would therefore be a com- 

 plete disappearance of the carbon, whilst nothing but the ele- 

 ments of water would remain. 



But when decaying wood is subjected to examination in dif- 

 ferent stages of decay, the remarkable result is obtained, that 

 the proportion of carbon in the different products augments. 

 Consequently, if we did not take into consideration the evolution 

 of carbonic acid under the influence of the air, the conversion 



