CHAPTER XX. 



EFFECT OF BACTERIA ON MINERALS OF THE 



SOIL. 



The water that falls on the soil in the form of rain 

 contains no mineral matter in solution. If the water 

 from a well or that which runs from a drain is exam- 

 ined, it will be found to contain a varying amount of ma- 

 terial that has been dissolved from the soil through 

 which the water has passed. Most of the mass of the 

 soil is insoluble in pure water, hence there should be 

 found but a very small amount of mineral matter in the 

 drainage water unless there are factors at work in the 

 soil, changing the insoluble minerals into soluble com- 

 pounds. It has been seen that the bacteria render the 

 various kinds of organic matter soluble, and that the prod- 

 ucts formed by. their action are water, ammonia, and car- 

 bon dioxide together with some less important products. 

 Many intermediate pro<ducts are formed in the decomposi- 

 tion of organic matter that have a great effect on the 

 mineral part of the soil. 



In the decomposition of such organic substances as 

 sugars, starches, and related compounds, acids are 

 formed, as lactic, acetic, and butyric. Carbon dioxide 

 when dissolved in water acts as a weak acid. All of 

 these acids have a solvent effect on the different minerals 

 of the soil. In the process of nitrification a strong acid 

 is formed, nitric acid, which also has an effect on the soil 

 particles. 



