THE ABSORPTIVE PROPERTIES OF SOILS 271 



other bases from the soil, which appear in the filtrate as ions 

 and in combination with acid radicals. Such phenomena may- 

 be considered as mere basic exchange, pushed forward by the 

 mass action of the ion absorbed, and is called substitution of 

 bases. The change may be illustrated as follows: 

 KC1 + X n Silicate ^ X n Cl + K Silicate 



It is unlikely that this reaction actually takes place to any 

 extent in fertilizer practice. 1 It is more probable that the 

 acid produced by the selective absorption liberates the bases 

 from their loose union with the hydrated aluminum silicate 

 complexes. 



HC1 + X n Silicates ?± X n Cl + H Silicates 



A dilute solution of potassium chloride filtered through a 

 soil will produce a filtrate containing some calcium, mag- 

 nesium, or chloride or all of these salts and some potassium 

 chloride. The more dilute the solution, the larger will be the 

 proportion retained, but the less the total quantity absorbed. 

 Peters 2 treated 100 grams of soil with 250 cubic centimeters 

 of a solution of potassium salts, and found that the potassium 

 of separate salts was retained in different proportions, and 

 that the more concentrated solutions lost relatively less than 

 the weaker ones, although more actual potassium was re- 

 moved from the former. 



Table LIX 



1 Parker, E. G., Selective Absorption by Soils; Jour. Agr. Kes., Vol. 1, 

 No. 5, p. 180, 1913. 



2 Peters, E., vber die Absorption von Kali durch Aclcererde; Landw. 

 Vers. Stat., Band 2, Seite 113-151, 1860. 



