The Physical Character of Soils 39 



Action of It has been well said that the chemistry 



Organic ^^ carbon is the chemistry of life, for its 



Agents in . -^ ' 



Soils presence m the soil is evidence of living 



forms having been there and died there. 



In like manner it has been said that the chemistry of 



the rocks is the chemistry of silicon, of which rocks are 



so largely composed, and which in their decay they 



have furnished in many complex compounds to the 



soils of the earth. In fact bio-chemistry, the study of 



chemical changes made in the soil through the action 



of living forms, is becoming more and more a matter of 



investigation from which great results are being had and 



greater are still to be obtained. 



We know that the breaking down of organic matter 



in the soil is the work of microscopic plant Hfe. The 



ammonia thus released in turn becomes the food of other 



micro-organisms, which reduce it to nitrites. Then still 



another form feeds on nitrites and makes nitric acid, which 



at once unites with some base in the soil, such as lime or 



potash, and in this form, a nitrate, the nitrogen becomes 



food for the green-leaved plants. We know, too, that while 



the green-leaved plants are dependent for their carbon on 



the carbon dioxide in the air, these microscopic forms, 



which make no green and cannot thus get carbon from 



the air, have the power that green-leaved plants do not 



possess of getting carbon from the carbonate of lime in 



the soil, and that thus the presence of lime carbonate in 



the soil aids in the process of nitrification or the change of 



organic nitrogen into the readily available nitrates. But 



the soil still offers innumerable problems to the chemist, 



and many a question is yet to be worked out there in the 



