22 



SOIL PHYSICS AND MANAGEMENT 



feet beneath the surface will crumble or " slake " upon exposure 

 to the air. 



(f) Solution. Water is a universal solvent, but its power is 

 greatly increased by the presence of substances in solution so that 

 it becomes a very active agent in breaking down rocks. Its efficiency 

 is greatly increased by the presence of carbon dioxide which is 

 absorbed by rain water from the atmosphere and still more from 

 the soil air as it percolates through the soil, the air of which con- 

 tains large amounts of carbon dioxide. The water thus becomes a 

 very active solvent (see table, page 20). 



Effect of Decomposition on Loss of Constituents from Rocks B 



In 1848 Rogers Brothers 7 carried on. some experiments to show 

 the power of carbonated water in dissolving minerals of different 

 kinds. The minerals were powdered and digested for 48 hours in 

 carbonated water, and from 0.4 to 1 per cent of the whole mass was 

 dissolved. When 40 grains of powdered hornblende were digested 

 for 48 hours in carbonated water at a temperature of GO degrees F., 

 the following peicentages were dissolved: Silica, 0.08; oxide of 

 iron, 0.095 ; lime, 0.13 ; and magnesia, 0.095. It is to be under- 

 stood that this process will not take place so rapidly under natural 

 conditions because the minerals are more massive, but at the same 

 time the process is going on constantly. Richard Miiller has shown 

 that during seven weeks of treatment of minerals with carbonated 



