80 ON THE ASSIMILATION OF HYDROGEN 



CHAPTER IV. 



ON THE ASSIMILATION OF HYDROGEN. 



The atmosphere contains the principal food of 

 plants in the form of carbonic acid, in the state, 

 therefore, of an oxide. The solid part of plants 

 (woody fibre) contains carbon and the constituents 

 of water, or the elements of carbonic acid, together- 

 with a certain quantity of hydrogen. It has former- 

 ly been mentioned that water consists of the two 

 gases, oxygen and hydrogen. The range of affinity 

 possessed by both these elements is so extensive, that 

 numerous causes occur which effect the decomposi- 

 tion of water. Indeed, there is no compound which 

 plays a more general or more important part in the 

 phenomena of combination and decomposition. We 

 can conceive the wood to arise from a combination 

 of the carbon of the carbonic acid with the elements 

 of water, under the influence of solar light. In this 

 case, 72-35 parts of oxygen, by weight, must be sep- 

 arated as a gas for every 27*65 parts of carbon, 

 which are assimilated by a plant ; for this is the 

 composition of carbonic acid in 100 parts. Or, what 

 is much more probable, plants, under the same cir- 

 cumstances, may decompose water, the hydrogen of 

 which is assimilated along with carbonic acid, whilst 

 its oxygen is separated. If the latter change takes 

 place, 8-04 parts of hydrogen must unite with 100 

 parts of carbonic acid, in order to form woody fibre, 

 and the 72*35 parts by weight of oxygen, which was 

 in combination with the hydrogen of the water, and 

 which exactly corresponds in quantity with the oxy- 

 gen contained in the carbonic acid, must be separ- 

 ated in a gaseous form. 



Each acre of land, which produces 10 cwts. of 

 carbon, gives annually to the atmosphere 2865 lbs. of 

 free oxygen gas. The specific weight of oxygen is 



