160 



TRANSFORMATION OF MINERAL SUBSTANCES 



filling the pore spaces. On the other hand, a relatively high tem- 

 perature and moisture content favor the production of carbon 

 dioxide, as shown in Table 39. Considering the amount of the 

 gas produced at the lowest temperature and moisture content cited 

 in the table as 1, increases in moisture and temperature raised the 

 production of carbon dioxide to 40. The numerous factors which 

 favor microbial development increase the rates of carbon dioxide 

 production, and factors lowering rates of diffusion tend to keep the 

 gas at a relatively high level in the soil air and consequently also 

 at a high level in the dissolved state as carbonic acid. 



TABLE 39 



Influence of Temperature and Moisture on Carbon Dioxide Content 

 OF SoiL.s (from Wollny) 



The action of carbonic acid may be exerted upon a great 

 variety of soil materials, forming carbonates of the basic sub- 

 stances, and if present in sufficient amount, producing bicar- 

 bonates from these carbonates: 



CaCOs + H2CO3 = Ca(HC0.3)2. 



In spite of the fact that most of the carbonic acid which is produced 

 in the soil is lost soon after its formation by volatilization of carbon 

 dioxide, some of the active acid reacts with the soil constituents 

 and may dissolve considerable amounts of those mineral substances 

 which are relatively insoluble in water alone. The reactions con- 

 cerned in these changes may be represented as follows: 



Ca2(HP04)2 + 2H2CO3 = Ca(H2P04)2 + Ca(HC03)2 



Di-calcium 

 phosphate 



Mono-calcium 

 phosphate 



Ca3(P04)2 + 4H2CO3 = Ca(HoP04)2 + 2Ca(HC03)2 



Tri-caleium 

 phosphate 



Mono-calcium 

 phosphate 



