360 ELECTRICAL CHARGES OF COLLOIDAL PARTICLES 



Hence the p.d. of gelatin sulfate solution should be two-thirds of 

 the p. D. of a gelatin chloride solution of the same pH and the same 

 concentration of originally isoelectric gelatin. 



1 gm. of isoelectric gelatin was dissolved in 100 cc. of water con- 

 taining in one case 5 cc. of 0.1 N HCl, in the other, 5 cc. of 0.1 n 

 H2SO4. One collodion bag with a volume of 50 cc. was filled with 

 the gelatin chloride solution and this bag was dipped into a beaker 

 containing 350 cc. n/1000 HCl. A second collodion bag was filled 

 with the gelatin sulfate solution and this bag was dipped into 350 cc. 

 n/1000 H2SO4. The solutions were kept for 24 hours at 24°C. and 

 the pH inside, and pH outside were measured. The pH of the two 

 gelatin solutions was identical, namely 3.64, but the value pH inside 

 minus pH outside was for the gelatin chloride solution 0.49 and for 

 the gelatin sulfate solution 0.31, which is as near 3:2 as the accuracy 

 of the measurements permits. A confirmation of this result can be 

 found in the experiments published in a preceding paper where this 

 relation had not yet been recognized.^ Thus it was found that for 

 gelatin phosphate of pH 3.98 the value of pH inside minus pH out- 

 side was 0.58, while for gelatin sulfate of pH 3.98 the value of pH 

 inside minus pH outside was 0.38, which is again the ratio of 3:2. 

 For pH 4.31 the value pH inside minus pH outside was 0.53 for 

 gelatin chloride while it was for pH 4.34, 0.35 for gelatin sulfate, 

 which is again as 3:2. The p.d. observed directly with the Compton 

 electrometer agreed quantitatively with the value 58 (pH inside 

 minus pH outside). 



Quantitative results, such as these, leave little doubt that the 

 p. d. between solutions of gelatin-acid salts and outside watery solu- 

 tions when separated by a collodion membrane are determined entirely 

 by the Donnan equilibrium; and that there can be no other source 

 of the charge of this micella model. 



IV. The p. D. of Solutions of Crystalline Egg Albumin. 



The experiments published thus far had all been done on gelatin. 

 It was of importance to make sure whether or not these results can 

 be confirmed with crystalline egg albumin. This was found to be 

 the case, and the experiments on the membrane potentials of the 



