688 



DONNAN EQUILIBRIUM AND MEMBRANE POTENTIALS 



was determined in two different ways in the two experiments; in one 

 experiment it was determined with the potentiometer, in the other 

 it was determined in the gelatin chloride solution by titration with 

 NaOH according to the method described in a preceding paper. ^ 

 Both methods of determining the pCl led to the result that the values 

 pCl outside minus pCl inside were for the same solution at the point 

 of equilibrium equal to the value pH inside minus pH outside (within 

 the limits of accuracy of the experiments). The pCl outside was 

 identical with the pH outside, since the outside solution contained 

 only free HCl. The values of pH were all determined potentio- 

 metrically. 



TABLE XI. 



Experiment 1. pCI determined by titration. 



pH of gelatin chloride solution at 



equilibrium 



pH inside minus pH outside 



pCl outside minus pCl inside 



4.13 

 0.56 

 0.48 



3.69 



0.58 

 0.51 



3.30 

 0.50 

 0.59 



3.10 

 0.49 

 0.44 



2.92 



0.44 

 0.44 



2.78 

 0.44 

 0.38 



2.46 

 0.33 

 0.35 



2.26 

 0.23 

 0.22 



2.01 

 0.15 

 0.15 



1.76 

 0.10 

 0.11 



Experiment 2. pCl determined electrometrically. 



pH of gelatin chloride solution at 



equilibrium 



pH inside minus pH outside 



pCl outside minus pCl inside 



4.04 

 0.60 

 0.55 



3.92 

 0.62 

 0.60 



3.78 

 0.66 

 0.57 



3.61 

 0.55 

 0.50 



3.46 3.16 



0.50 

 0.53 



0.43 

 0.38 



2.73 

 0.30 

 0.32 



2.36 2.04 

 0.200.12 

 0.170.12 



1.73 

 0.07 

 0.07 



Nernst's formula leads therefore to the same theoretical p.d. regard- 

 less of the fact whether we calculate the p.d. on the basis of the 

 difference pH inside minus pH outside or pCl outside minus pCl 

 inside. It is also obvious that both assumptions lead to the same 

 sign of charge of the gelatin chloride solution. If we assume that 

 the P.D. is determined by differences in the hydrogen ion concentra- 

 tion the outside solution is concentrated and the inside solution 

 dilute; if the p.d. is determined by differences in the concentration of 

 the CI ions the inside solution is concentrated and the outside solu- 

 tion dilute. Since the common ion is positive in the former and nega- 

 tive in the latter case, the gelatin solution becomes positive in both 

 cases. 



» Loeb, J., /. Gejt. Physiol., 1918-19, i, 559. 



