CHAPTER IX 



THE ACTION OF BACTERIA ON THE MINERALS OF 

 THE SOIL 



The mineral portion of the soil consists almost wholly of 

 carbonates, sulphates, phosphates, chlorides, and silicates, 

 which are, of course, relatively insoluble, otherwise they 

 would be removed by the percolating water. The water 

 that falls on the soil in the form of rain contains no mineral 

 matter, or at most only traces; but drainage or well water 

 contains considerable quantities of mineral matter in solu- 

 tion. It is thus apparent that processes are at work in the 

 soil by which some of the minerals of the soil are being con- 

 verted into soluble compounds. In all ground waters will be 

 found carbonates, sulphates, nitrates, and chlorides of cal- 

 cium, magnesium, potassium and sodium. 



Probably none of the minerals of the soil is absolutely 

 insoluble in pure water, but most of them are so slightly af- 

 fected by the water as to be classed as insoluble. As has 

 been shown, various organic acids are formed in the decom- 

 position of organic matter. A strong acid, nitric acid, is 

 also the final product in the decomposition of nitrogenous 

 compounds. Ultimately all the carbon of organic matter 

 appears as carbonic acid. These various acids are dissolved 

 in the soil water, and influence its action on the minerals 

 of the soil, which by their fine state of division present an 

 enormous surface to it. 



Calcium. The limestone that is found in the soil was re- 

 moved from the water of the sea by the action of the shell- 

 forming animals. At the death of the animal the shell 



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