﻿the Adsorption of Ions, 343 



force in the adsorption of ions can be multiplied (cp, Baur, 

 Z.Phijs. Chem. xcii. p. 81 (191(5) ; Michaelis and Davidsohn, 

 toe. cit.). 



Exchange of Bases in Soil and Soil- Acidity 



It is now easy to understand the nature of the exchange of 

 bases in soil-analysis and the cause of soil-acidity. A com- 

 plete reference to the older literature is given in the following- 

 papers : — 



(1) McCall, Hildebrandt, and Johnson, J. Phys. Chem. 

 191b", xx. p. 51. 



(2) Rxce; ibid. p. 214; (3) Truog, ibid. p. 457. 



Russell (Brit. Assoc. Rep. 1918, p. 70) has given an 

 excellent summary of the present position of the subject. 

 The facts are that — 



(a) Neutral solutions of salts like potassium chloride, if 

 treated with samples of soil, give acid extracts though the 

 extract with pure water is neutral. 



(//) In a large number of cases it has been shown that 

 there is a definite exchange of the cations. Equivalent 

 amounts of bases are exchanged in many cases. 



Two different views have been advanced to explain the 

 facts, The older chemical view regards the process as a 

 chemical interaction between definite acids (e. g., humus 

 acid) or complex salts {e.g., silicates) and salt solutions. 

 The other view begins with von Bemmelen, and regards it 

 as an adsorption process. Cameron suggested (cp. Russell's 

 Report) that the soil adsorbs the base more strongly than it 

 adsorbs the acid. 



The objections against the chemical view can be sum- 

 marized as follows : — The extract wich pure water being 

 neutral, the soil-acids must be insoluble. The acids must be 

 unusually strong, as they evidently decompose a neutral 

 salt solution combining with the base, liberating the strongest 

 known acids, like hydrochloric acid. 



Evidently such acids are unknown, and it is difficult to 

 conceive of such reactions. Regarding the exchange of 

 buses, the difficulty lies in the assumption that the basic ion 

 is taken up to form an insoluble salt. It is necessary to 

 postulate the existence of insoluble salts of alkali metals in a 

 large number ot' cases (cp. the remarks on Freundlich's 

 theory). 



That adsorption plays an important part is also evident 

 from the works of: Russell and Prescott (J. Agric. Sci. viii. 

 p. 05 (191G)) on the interaction of dilute acids and phos- 

 phates present in the soil. But the view of: Cameron does 



