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CHAPTER IV. 

 THE REACTIONS OCCURRING IN SOILS. 



THE chemical changes occurring in a soil are numerous and 

 complex. To acquire a general knowledge of their nature and 

 direction is difficult, especially as they are greatly influenced 

 by circumstances, e.g., temperature, strength of the solution 

 with which the soil is moistened, free or difficult access of air, 

 and a number of other constantly varying conditions. It is 

 therefore only possible to indicate some of the actions which 

 take place and to describe, to some extent, the effect thereon of 

 variations in conditions. 



The inorganic portion of the soil is subjected to the same 

 actions of the air and water as gave rise to its formation from 

 the original rock and which have been already considered. It 

 is to be noted, however, that the changes probably proceed at 

 an accelerated rate because of the larger quantity of carbon 

 dioxide provided by the decomposing organic matter of the 

 soil. Fragments of felspar, mica, and other minerals are thus 

 exposed to the action of air and of water rich in carbonic acid. 

 Their disintegration and the solution of the potash, lime, and 

 magnesia which they contain thus proceed rapidly. 



The reactions which occur are probably of a type which may 

 be thus represented : 



Al. 2 8 -K. 2 0.6Si0. 2 + CO, + 10H. 2 



Orthodase. 



= AlA.2SiO a .2H a O + K a CO + 4H,Si0 4 



Kaolin. Potassium carbonate, silk-ic acid. 



Also 



the CaCOg acting as a carrier of C0 2 ; or if lime or mag- 

 nesia be present, as, e.g., in anorthite, proportionately more 

 carbon dioxide is required : 



