PHENOMENA OF MOTION 



61 



NaCl which diffuses depends on the concentration of the solutions 

 in space (1) and space (2). If the concentration in space 2 (C 2 ) is 

 high in proportion to that in space 1 (Ci) much NaCl will pass from 

 (1) to (2) and, if the conditions are reversed, only a little will do so. 

 Mathematically represented (assuming complete electrolytic dis- 

 sociation) we have the following equation, where Ci or C 2 represent 

 the molar ion concentration in the respective spaces and X the frac- 

 tion of the molar ion concentration which diffuses from (2) to (1) : 



C 2 - X Ci + C 2 



X C 2 



\r si 



If C 2 is small in comparison with Ci we may express it: 77- = TT* 



C 2 Ci 



X 1 



If d is very small the equation becomes TT = o' 



2 



The following table taken from DONNAN'S work illustrates the dis- 

 tribution of NaCl. 



Though we might assume d priori that the NaCl would distribute 

 itself equally in both spaces in the presence of a membrane absolutely 

 permeable for it, this table shows that the colloid electrolyte has a 

 remarkable influence as soon as the concentration of NaCl falls. To 

 a certain extent the colloid electrolytes drive the NaCl out of the 

 cell. If Ci = 1 only about 11 per cent of a physiological salt solu- 

 tion (C 2 = 0.145) could penetrate the cell; or if it were already in 

 the cell it was reduced to about 11 per cent. Apparently the mem- 

 brane is permeable only from one side for the readily diffusible NaCl. 

 (c) Finally we must consider the case when the colloid electrolyte 

 in the membrane is opposed to an electrolyte without an ion in com- 

 mon, as for instance : 



Initial condition 



Equilibrium 



Na 



R 



(D 



K 

 CI 



(2) 



