30 



Agricultural Chemistry. 



a process of oxidation. These combine with the oxygen of the 

 air, in some cases with sufficient rapidity to produce a rise in 

 temperature causing spontaneous combustion. Destructive fires 

 occasionally result from such oxidations. 



Oxygen usually forms about 23.2 per cent of the air by weight. 

 "Where animal life is abundant or where much putrefaction is in 

 progress, the percentage of it in the air will be reduced. On 



Clover obtaining its necessary nitrogen from the air through the action 

 of certain bacteria. No. 5 contains these bacteria, while No. 6 

 does not (after Russell and Hastings). 



the other hand, being exhaled by plants, its proportion may in- 

 crease slightly where vegetation is abundant. 



Argon. This gas forms most of the remainder of the air. It 

 closely resembles nitrogen in its properties. Argon is not known 

 to be of any importance to agriculture. 



Carbon dioxide. Although usually forming a very small frac- 

 tion of the air 0.04 part, or less, by weight in 100 parts of air 

 this constituent is of great importance in agriculture. The aver- 

 age green corn crop of 12 tons per acre requires for its produc- 

 tion 4 tons of carbon dioxide, which necessitates the respiring of 

 10,000 tons of air, or about 14 the amount available over that 



