220 



ELECTROLYTES IN BIOLOGICAL SYSTEMS 



Whereas the data on potassium in skin do not fit the simple Langmuir iso- 

 therm equation, they do fit, however, an isotherm equation recently proposed 

 by Sips (64). Applied to the case under discussion, one has: 



Ki = 



Ki = 



Kr"-k-Ke 



(5«) 

 (56) 



[no*] = I 193 eq./l. 

 (K*)""' = .046 eq /kg 



006 01 015 005 .01 .015 019 



[k-],. eq./l 

 Fig. 10. Potassium isotherms (Sips) in frog skin (29). 



When n is unity, one arrives at Langmuir's isotherm. When n approaches the 

 value of 2, one deals, according to Sips, with adsorption characterized by a 

 Gaussian distribution of sites relative to the energy of adsorption. In figure lo, 

 the experimental data on potassium in frog skin are subjected to such a test, 

 using equation jb. The apparent success, however, does not warrant regarding 

 frog skin as a simple physico-chemical system. There are, probably, other 

 equations that could be used for the interpretation of the data. Sips' derivations 

 have been criticized (14, 65). Nevertheless, from the newer development of the 

 field of adsorption and chemisorption, one gains the impression that the data 

 on potassium in frog skin may be interpreted in terms of Langmuir's isotherm, 

 if one considers monolayer adsorption and sites for potassium adsorption of 

 varying activity and, eventually, repulsive interactions between adsorbed 



