64 ASSIMILATION OF HYDROGEN. 



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 oxygen contained in the carbonic acid, 

 must be separated in a gaseous form. 



Each acre of land, which produces 8 centners or 

 cwts. of carbon, gives annually to the atmosphere 

 2600 Hessian Ibs. of free oxygen gas. The specific 

 weight of oxygen is expressed by the number 

 1*1026, hence 1 cubic metre of oxygen weighs 2*864 

 Hessian Ibs., and^ 2600 Ibs. of oxygen correspond 

 to 908 cubic metres or 58,112 Hessian cubic feet. 



An acre of meadow, wood, or cultivated land in 

 general, replaces, therefore, in the atmosphere as 

 much oxygen as is exhausted by 8 centners of 

 carbon, either in its ordinary combustion in the 

 air or in the respiratory process of animals. 



It has been mentioned at a former page that pure 

 woody fibre contains carbon and the component 

 parts of water, but that ordinary wood contains 

 more hydrogen than corresponds to this proportion. 

 This excess is owing to the presence of the green 

 principle of the leaf, wax, resin, and other bodies 

 rich in hydrogen. Water must be decomposed, in 

 order to furnish the excess of this element, and con- 

 sequently one equivalent of oxygen must be given 

 back to the atmosphere for every equivalent of 

 hydrogen appropriated by a plant to the production 

 of those substances. The quantity of oxygen, thus 



