Effect of Bacteria on Minerals of the Soil. 183 



Calcium. This important element is present in the 

 soil in the form of calcium carbonate or lime stone, which 

 is insoluble in pure water, but owing to the presence of 

 carbon dioxide and organic acids in the soil, the water 

 percolating through the soil carries with it more or less 

 calcium carbonate. The water which comes in contact 

 with beds of lime stone is called "hard' 7 water because 

 it carries in solution such large quantities of calcium car- 

 bonate. The greater the amount of organic matter 

 added to the soil, the greater will be the quantity of cais 

 bon dioxide and organic acids formed by bacterial action 

 and the more rapidly will the lime be removed from the 

 soil. 



On account of this constant solution of lime, the soil 

 tends to become acid, which condition becomes unfavor- 

 able for bacterial action and the soil is no longer fertile. 

 The farmer finds it necessary to correct this acid condi- 

 tion by adding lime to the soil in the form of crushed 

 lime stone. 



The dissolved lime passes off in the drainage water to 

 the sea, where it is used by marine animals in forming 

 their shells. As these organisms die they gradually sink 

 to the bottom of the sea, forming beds of lime stone. In 

 some great movement of the crust of the earth these are 

 raised above the surface, and are subjected to the action 

 of weathering and influence of biological changes. Thus 

 the movement of lime from land to sea and sea to land 

 goes on. 



Phosphorus. The phosphorus of the soil is largely 

 in the form of calcium phosphate, which, like calcium 

 carbonate, is insoluble in pure water but which is easily 

 dissolved in water which is acid in reaction. Even car- 

 bonic acid will change it to a soluble form in the same way 



