CHAPTER XVI 



THE ABSORPTIVE PROPERTIES OF SOILS 



If the brown water extract from manure is filtered 

 through a clay soil not containing soluble alkalieS;, the 

 filtrate will be nearly colorless. Many solutions of dye- 

 stuffs are affected in the same way. Solutions of alkali 

 or alkaline earth salts are more or less modified by this 

 operation^, the bases being retained by the soil to a greater 

 extent than are the acids. Thus, when a solution of 

 the nitrate, sulfate, or chloride of any one of these bases 

 is filtered through the soil, a part of the base is absorbed 

 by the soil, while most of the acid comes through in the 

 filtrate. If these bases are in the form of phosphates 

 or silicates, not only the base is absorbed, but the acid 

 as well. 



251. Substitution of bases. — Associated with the 

 absorption of the base from solution, there is liberation 

 of some other base from the soil, which combines with 

 the acid in the solution and appears in the filtrate as a 

 salt of that acid. 



When absorption takes place from solution, the base 

 is never entirely removed, no matter how dilute the solu- 

 tion may be. A dilute solution of potassium chloride 

 filtered through a soil will produce a filtrate containing 

 some calcium, magnesium, or sodium chloride, or all 

 these salts, and some potassium chloride. The more 

 dilute the solution, the larger will be the proportion re- 



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