274 NATURE AND PROPERTIES OF SOILS 



The acidity of soils, which is a function not only of the soil 

 solution but of the solid portions also, is frequently attributed 

 to certain absorptive phenomena, one idea being that, due 

 to physical and chemical absorption of bases, a concentra- 

 tion of the hydrogen ion is produced and actual acidity re- 

 sults. Basic exchange seems to liberate iron and aluminum, 

 the salts of which easily hydrolize and yield acid solutions. 

 If, as some investigators maintain, the toxic principle of the 

 so-called acid soils is active aluminum, manganese or similar 

 elements, absorption may again be the activating phenomenon, 

 since an unsatisfied absorptive capacity, especially for cal- 

 cium and magnesium, seems to favor the presence of such 

 constituents in the soil solution. 



The absorptive power of the soil is a controlling factor as 

 far as the composition and concentration of the soil solution 

 is concerned. Any study of the dynamic relationships of the 

 water solution that exists in the soil interstices and in the col- 

 loidal complexes which coat the soil particles, must reckon 

 with absorption phenomena and all of the factors which tend 

 to influence them. 



