BY THE DECOMPOSITION OF WATER. 81 



expressed by the number 1*1026; hence 1 cubic me- 

 tre of oxygen weighs 3-157 lbs., and 2866 lbs. of 

 oxygen correspond to 908 cubic metres, or 32,007 

 cubic feet. 



An acre of meadow, wood, or cultivated land in 

 general replaces, therefore, in the atmosphere as 

 much oxygen as is exhausted by 10 cwts. 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 hy- 

 drogen than corresponds to this proportion. This 

 excess is owing to the presence of the green princi- 

 ple 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 consequently 

 one equivalent of oxygen must be given back to the 

 atmosphere for every equivalent of hydrogen appro- 

 priated by a plant to the production of those sub- 

 stances. The quantity of oxygen thus set at liberty 

 cannot be insignificant, for the atmosphere must re- 

 ceive 547 cubic feet of oxygen for every pound of 

 hydrogen assimilated. 



It has already been stated, that a plant, in the 

 formation of woody fibre, must always yield to the 

 atmosphere the same proportional quantity of oxy- 

 gen ; that the volume of this gas set free would be 

 the same whether it were due to the decomposition 

 of carbonic acid or of water. A little consideration 

 will show that this must be the case. It has repeat- 

 edly been stated, that woody fibre contains carbon 

 in combination with oxygen and hydrogen in the 

 same proportion in which they exist in water. Water 

 contains 1 equivalent of each element, whilst carbon- 

 ic acid consists of 1 equivalent of carbon, united to 

 2 equivalents of oxygen. In the formation of woody 

 fibre, 2 equivalents of oxygen must therefore be lib- 

 erated. The woody fibre can only be formed in one 

 of two ways : either the carbon of carbonic acid 



