﻿the Adsorption of Ions. 345 



gels, and that probably the surface is saturated with anions. 

 As crystalloids (insoluble) are also present, the type of 

 exchange considered by Paneth (loc. cit.) is also possible. 



It is needless to point out that in this discussion only the 

 theoretically simple case has been considered. Complications 

 due to simultaneous primary adsorption of different ions and 

 their mutual displacement are not always negligible. Besides, 

 the changes may not be restricted to the surface ; formation 

 of solid solutions, etc., are not excluded. Considering all 

 these complex influences, it is interesting to note that most 

 of the observed regularities correspond to the theoretically 

 simple case. 



Adsorption of Ions in its Relation to Permeability of 

 Membranes and to Negative Osmosis. 



In conclusion, a few remarks will be made on the funda- 

 mental interest that a study of the adsorption of ions has for 

 biological phenomena. Cell activity is greatly conditioned 

 by the permeability of its "walls" or the cell-substance to 

 the contents of the liquid with which it is in contact. The 

 connexion between the rate of osmotic flow through mem- 

 branes and even the direction of the flow, and the potential 

 differences existing on the two sides of the membranes, has 

 been clearly established (Girard, C.R. cxlvi. p. 927 (1908), 

 and following authors : Bartell, J. Amer. Chem. Soc. 

 xxxvi. p. 6±6 (19.14) ; Hamburger, Z. Pliys. Chem. xcii. 

 p. 385 (1917)). The origin of the potential difference 

 is generally assumed to be due to the fact that the rate of 

 diffusion of the electrolytic ions in the membrane substances 

 is different from that in water. That the membrane potential 

 is due to a selective permeability of ions was first suggested 

 by Ostwald (Z. Phys. Chem. vi. p. 71 (1890)) ; Donnan (Z. 

 Elektrochem. xvii. p. 572 (1911)) has discussed the origin 

 of the potential differences theoretically, and has given it a 

 quantitative form based on thermodynamic considerations. 

 In collaboration with others he has carried out a number of 

 investigations which have established the validity of this 

 view. 



The simpler case of a potential difference between two 

 interfaces when an immiscible liquid is placed between 

 two aqueous solutions has also attracted a good deal of 

 attention. The work of Loeb and bis co-workers on cell- 

 permeability and origin of the membrane potential is of 

 fundamental importance (Loch and Beutner, Biochetn. Zeit. 

 li. p. 295 (1913) ; Beutner, Z. Phys. Chem. lxxxvii. p. 385 



