ABSORPTION BY SOILS 63 



theoretical and practical reasons alike, have uniformly failed. 

 A sufficient reason for this failure seems to lie in the fact that 

 most dissolved substances produce an appreciable effect on the 

 granulation or flocculation of the soil particles, which is pro- 

 gressive with the absorption so that a continual change of absorb- 

 ing or effective surface is taking place as the absorption proceeds. 1 

 Moreover, in the case of an absorption, with the formation of a 

 continuous film of the dissolved substance, a new kind of absorb- 

 ing surface is developed. Hence n is a function of so difficult 

 a character as to defy thus far any attempt at formulation. 2 



We cannot therefore predict in any quantitative way what 

 will be the distribution of a soluble substance such as salts in 

 commercial fertilizers, for instance, between the solid soil 

 particles and the soil solution. Empirical experiments show, 

 however, that with the amount of a soluble salt present under 

 normal conditions in a humid climate, or as used in fertilizer 

 practice, the absorption of ammonia, lime, potassium or phos- 

 phoric acid is relatively very great, and in a general way in about 

 the order named. 



Absorption is not an instantaneous process. However, the 

 rate at which a dissolved substance is absorbed is generally quite 

 rapid. That is, if a soil be stirred or mixed with an aqueous 

 solution, the absorption takes place very quickly, in the absence 



1 That mineral fertilizers have a decided influence on the granula- 

 tion of soils and the properties dependent thereon, and that this is of 

 practical importance, is gradually coming to be recognized; see, for 

 instance, Ein Beitrag zur Kenntnis der Wirkung kimstlicher Diinger auf 

 die Durchlassigkeit des Bodens fur Wasser, von Edwin Blanck, Landw. 

 Jahrb., 38, 863-869 (1909), and the literature there cited. Dr. R. O. E. 

 Davis in a yet unpublished investigation has shown that the addition of 

 soluble salts produces decided effects upon the soil-moisture relations 

 which affect crop production. The critical moisture content is displaced, 

 the penetrability, permeability, specific volume, vapor tension, etc., are 

 affected in measurable degree, and it appears that the physical functions 

 of mineral fertilizers are much greater in amount and importance than 

 has been popularly assumed. 



2 The distribution of solute between water and soil, by F. K. Cameron 

 and H. E. Patten, Jour. Phys. Chem., 11, 581-593 (1907). 



