CYTOPLASM 



203 



TABLE XXIII 

 DONNAN EQUILIBRIUM IN THE MOLECULAR FRAMEWORK 



K. H. Meyer combines this result with the velocity of ion migration in 

 a membrane possessing framework structure, in order to arrive at a quan- 

 titative expression for the permeability. Let U^ be the ion mobility of the 

 cation and U,^ that of the anion of the salt; further n^ the number of cations 

 and n^^ the number of anions of the migrated salt, defining these numbers 

 in such a way that always n^ + n^ = i (Meyer and Sievers, 1936). 



As the number of migrating ions is not only proportional to U but also 

 proportional to the ion concentration in the molecular framework (com- 

 pare Fig. 1 1 7), we have : 



Hk Uk (y + A) 



n, 



UA-y 



Since n^ + n^ = i, nj^ and n^ could be calculated if A and y were 

 known. This, however, is not the case and for this reason the known outer 

 concentration, c, is introduced. We have 



and therefore: 



y = y'c2 + A74 — A/2 



Hk Uk (a/4c^ + A^ + a) ^_ 

 Ha ~ Ua iV4c' + A2 - A) U, 



U 



K 



X. 



This relation is K. H. Meyer's starting point in his investigations on 

 permeability. The ratio n-^/ni^ can be determined potentiometrically. On 

 the other hand, the ratio Uk/U^ and the factor X are unknown. 



By carrying out measurements at different concentrations c, one ob- 

 tains several equations from which both unknown quantities can be derived. 

 Accordingly, the quantity A which Meyer designates as selectivity constant 

 can be determined, and thus an important property of the framework can 

 be expressed numerically. 



For instance, from the well-known potential measurements of the apple 

 skin by Loeb and Beutner (1912/1913), a selectivity constant A = 0.08 



