Absorption by Soils of Potassium. 



175 



potassium salt, with the result that the percolate is more concentrated 

 than the original solution. It should be borne in mind, however, that 

 we are probably not dealing with equilibrium conditions. The mech- 

 anism by which this negative absorption is effected, may be explained 

 by assuming that the solvent and the dissolved substance are capable 

 of being absorbed more or less independently and at different rates. 

 The rapid advance of the liquid through the fine pores of the soil results, 

 for a time, in the more rapid absorption of the water than of the salt, 



O.I 

 k 



o.z ,0.3 



Solution 



0.4 



0.5 0.6 



KLitersK- 



FIG. 21. 



0.7 



0.8 



Water 



0.9 



1.0 



leaving the liquid in the larger non-capillary spaces more concentrated. 

 This more concentrated solution then moves through the large spaces 

 and appears as the percolate. It is quite probable that after a few 

 hundred cubic centimeters have passed through, equilibrium will have 

 been established and the negative absorption will become positive. 

 This so-called negative absorption, therefore, may be considered as 

 a special case of selective absorption. 



From the work of Williams, to which reference has been made, it 

 appears that the absorption of the solute and the solvent is dependent 

 upon the relative masses present. With some electrolytes in water it 

 has been found experimentally that the absorption is at first positive, 

 increases to a maximum, decreases through zero, and finally becomes 

 negative, but there seems to be no case on record in which the initial 

 absorption effect is negative. 



