﻿the Adsorption of Ions. 337 



The chemical adsorption of the anion is also not to be 

 neglected. The experimental data on this subject are meagre. 

 The various points raised here can be experimentally eluci- 

 dated. As shown above, the standpoint developed in this 

 paper can correlate all the observed tacts. Besides, it gives- 

 a definite idea of the electrical double layer. 



Adsorption of electrolytes. 



In the preceding sections the adsorption of ions has been 

 considered with reference to the electrical charge of surfaces- 

 in contact with aqueous solutions of a single electrolyte. 

 The electric effects accompanying the adsorption of ions have 

 enabled us to follow the total adsorption of ions of both signs. 

 In considering the adsorption of ions measured by chemical 

 means it is important to remember the influence of the ad- 

 sorption of the solvent pointed out by Arrhenius, Bancroft, 

 Williams, and others. 



The amount adsorbed is small and the analytical measure- 

 ment is difficult. For this reason, investigations have centred 

 round adsorbents with great adsorbing power and substances 

 which are strongly adsorbed. Often it happens, that if a sub- 

 stance is used in a satisfactorily pure state it does not have 

 the necessary specific surface to make the estimation of the 

 adsorbed amount possible. As a result adsorbents generally 

 contain small amounts of other substances. The importance- 

 of these impurities has been pointed out by some investigators. 



Michaelis and Freundlich and their co-workers have done 

 systematic work in this field. Their investigations have 

 brought out the following regularities : — 



(«) The electric charge of the solid influences the ad- 

 sorption, Thus Michaelis and Lachs (Z. Elektro-Cliem. xviL 

 pp. 1, 917 (1911)) ; Biochem. Zeitsch. xxv. p. 359 (1910) ) x 

 and Davidsohn, Biochem. Zeitsch. liv. p. 323 (1913)) found 

 that in contact with acid solutions chnrcoal adsorbs anions 

 strongly and does not adsorb cations. The reverse happens 

 in the case of cations. Freundlich and Poser [Koll. Cliem.. 

 Beihefte, vi. p. 297 (1914)) undertook an extensive investiga- 

 tion, and they agree with Michaelis as to the electro-chemical 

 nature of the adsorption. 



(l>) The chemical nature of the adsorbent has a specific 

 action. 



Michaelis and Rona {Biochem. Zeitsch. xcvii. pp. 57, 85 

 (1919)) believe that adsorption is due to chemical affinity. 

 They mention that charcoal has a great capacity for adsorbing 

 substances containing a chain of carbon atoms. (Cp. Abder- 

 halden and Fodor, Fermentforschuncj, ii. p. 74 (1917).) 

 Phil. Mag. S. 6. Vol. 44. No. 260. Aug. 1922. ^ Z 



