254 MR. JOHN LEIOH ON THE CHEMICAL CHANGES 



the carbon of the manure, and supplying it with the carbonic 

 acid which constitutes its chief food. And hence it is, that 

 in stagnant water, the oxygen soon being removed by the 

 immersed plants, and a farther supply from the atmosphere 

 being prevented by the still water, the herbage is dark and 

 rank, sickly and unpalatable. 



We have seen, that by the absorbed oxygen of the water, 

 and we may add, by the action of the wind and waves, 

 dead plants, immersed in water, are not entirely, at least at 

 first, excluded fi-om contact with oxygen, but that this is sup- 

 pUed in very limited quantity. When the plants begin to 

 decompose, the water participates in the change, its ele- 

 ments unite with the decomposing matter, and the oxygen 

 which it held in solution is absorbed by the decaying vege- 

 table matter, carbonic acid being given off. It has been 

 stated above, that the composition of wood may be repre- 

 sented by carbon 36 ; hydrogen 22; oxygen 22. This is the 

 actual composition ofperfectlypurified, well-dried oak wood, 

 as determined by Gay Lussac and Thenard; and although 

 different varieties of wood may afford minute deviations from 

 these proportions, yet it may be assumed that these repre- 

 sent the empirical formula, and may be taken without much 

 risk of error as the groundwork of our reasoning and cal- 

 culations. When oak wood is decomposed under water, a 

 white mouldered matter is formed, which yields on analysis, 

 carbon 33, hydrogen 27, oxygen 24. Now, if to the 

 elements of oak wood, carbon 36, hydrogen 22, oxygen 22, 

 we add the elements of 5 atoms of water, with 3 atoms of 

 oxygen rz hydrogen 5, oxygen 5 -f- oxygen 3, and sub- 

 tract 3 atoms carbonic acid, carbon 3, oxygen 6, we have 

 the exact composition of the altered wood, or mouldered 

 oak. And this is what must really take place ; 5 atoms of 

 water or its elements, and 3 atoms of oxygen from the water 

 and air, unite with the decomposing woody matter, and 3 

 atoms of carbonic acid are given off and escape. 



