CHAPTER X. 



THE ABSORPTION BY SOILS OF POTASSIUM FROM AQUEOUS SOLU- 

 TIONS OF POTASSIUM CHLORIDE. 



BY A. G. McCALL, WITH THE COOPERATION OF F. M. HlLDEBRANDT, F. S. HOLMES, 



E. S. JOHNSTON, AND S. F. TRELEASE. 



As early as 1866 Frank 1 studied the retention of potassium chloride 

 by the soil, using metal cylinders 3 inches in diameter and varying in 

 length from 3 to 6 feet. His solution contained 1 gram of potassium 

 chloride per liter of water. He found that the first foot of soil retained 

 91 per cent of the potassium chloride, while the first 18 inches removed 

 95.5 per cent of the salt. The solution appearing at the bottom of his 

 6-foot columns had lost all but 2 per cent of their original salt content. 

 The addition of sodium chloride to the solution diminished the absorp- 

 tion of the potassium chloride. 2 



As the result of his experiments with potassium salts Treutler 3 con- 

 cluded that the deeper penetration of the potassium into the soil was 

 to be secured by the use of potassium chloride rather than by the appli- 

 cation of potassium sulphate as a fertilizer. 



Peat and preparations of the humic acids were found by Heiden, 4 to 

 have the power of removing a part of the salt, when brought into con- 

 tact with solutions of potassium chloride. The greater part of the 

 salt was readily recovered by the use of a small quantity of water. 

 Liebermann 5 reported that aqueous solutions of potassium chloride 

 showed no change as to acidity or alkalinity after passing through 

 animal charcoal, but that the concentration was decreased. 



More recent work on absorption has not only confirmed these earlier 

 observations, but has brought out the fact that finely divided sub- 

 stances exercise a selective action with respect to the solutions with 

 which they are brought in contact. In some cases the effect of this 

 selective action is to remove one ion of the salt more rapidly than the 

 other, leaving the solution acid or alkaline, depending upon which ion 

 is absorbed to the greater extent. Cameron and Bell 6 found that 

 absorbent cotton has the power of removing the potassium ion from a 

 solution of potassium chloride more rapidly than the chlorine, leaving 

 the solution decidedly acid to ordinary indicators. Previous to this 



J Landw. Vers.-Stat,, 8, 45 (1866). 



2 In this paper the terms "absorption" and "adsorption" are used, the former to denote the 

 removal of material from solution regardless of whether the act is essentially chemical or physical , 

 and the latter to designate the same process when the act appears to be clearly physical, that is, 

 dependent upon the extent of surface alone. 



3 Landw. Vers.- Stat., 12, 184 (1869); 15, 371 (1872). 



4 Hoffman's Jahresb., 1866, p. 29. 



6 Wien. Akad. Ber., 74, 331 (1877). 



U. S. Dept. Agriculture, Bureau of Soils, Bulletin 30 (1905). 



167 



