354 ELECTRICAL CHARGES OF COLLOIDAL PARTICLES 



cohesion between the protein ions constituting the gel, while both the 

 collodion membrane and the solid gel are permeable for crystalloidal 

 ions. We have already shown that when we separate a solution of 

 gelatin chloride from water by a collodion membrane, at equilibrium 

 the concentration of chlorine ions inside the gelatin solution is greater 

 than the concentration of chlorine ions in the outside solution, and the 

 concentration of the hydrogen ions inside the gelatin solution is 

 smaller than outside, as Donnan's theory demands.^ The concentra- 

 tion of the CI ions was determined by titration and it was shown 

 that the p.d. calculated with the aid of Nernst's formula from the 

 difference of concentration of chlorine ions inside and outside, was 

 within the limits of accuracy of the measurements, identical with 

 the P.D. directly observed between the gelatin chloride solution and 

 the outside solution with the aid of a Compton electrometer with 

 saturated calomel electrodes. In other words, it was found that 



c 



P.D. observed = 58 log ^ millivolts 



Cl inside 



or, since log Cci outside = pCl outside, and log Cci inside = pCl inside, 



P.D. observed = 58 . (pCl outside minus pCl inside) millivolts 



If Donnan's theory accounts quantitatively for the observed p. d., the 

 value 58 (pH inside minus pH outside) should also agree quantita- 

 tively with the observed p.d. 



The values of pH inside and pH outside were determined in our 

 experiments with the potentiometer {i.e. the hydrogen electrode), and 

 the value 58 (pH inside minus pH outside) was therefore also an 

 observed value. In order to avoid confusion of terms we call the 

 P.D. observed with the Compton electrometer the observed p.d., 

 since this gives us the empirical charge found 'in the micella or its 

 model, free from any theory. On the other hand, we will caU the 

 value 58 (pH inside minus pH outside) the calculated p.d. since we 

 could find this value by calculation from Nernst's formula if we 

 determined the hydrogen ion concentration of the inside and outside 

 solutions by titration instead of by the potentiometer. 



The detenninations of the value pH inside minus pH outside give 

 the following results already published in a preceding paper :^ (1) 



