MEMBRANE POTENTIALS 135 



the ratio of cubic centimeters of 0.1 N HC1 and 0.1 N H 2 SO 4 

 in 100 c.c. of liquid. The rest of the table requires no further 

 explanation. As in all gelatin-acid salt experiments, the agree- 

 ment between observed and calculated P.D. is good. 



Both P.D. and osmotic pressure are depressed the more the 

 more HC1 is replaced by H 2 S0 4 , but the depressing effect is 

 greater in the case of osmotic pressure than in the case of P.D. 

 The result of interest to us is the following: The value of pH inside 

 minus pH outside was, for gelatin chloride of pH 3.64, = 0.49, and 

 for gelatin sulphate of pH 3.64, = 0.31. The ratio of the two 

 values is as nearly 3:2 as the accuracy of the measurements 

 permits us to expect. The values for the observed P.D. agree 

 with the values of the calculated P.D. within the limits of ac- 

 curacy of the measurements. 



This quantitative agreement between the observed P.D. and 

 the P.D. calculated on the basis of the Donnan theory leaves 

 little doubt that the observed P.D. is exclusively determined by 

 the Donnan equilibrium. 



HYDROGEN ION AND CHLORINE ION POTENTIALS 

 If we write the equation for the equilibrium condition between 

 gelatin chloride solution and water in the form 



y _ x 

 x y +z 



where x is the concentration of H and Cl ions in the outside 

 solution, y the concentration of the H and Cl ions of the free HC1 

 inside the gelatin chloride solution, and z the concentration of 



the Cl ions in combination with the gelatin, - is the ratio of 



x 



hydrogen ion concentration inside to the hydrogen ion concen- 



/> 



tration outside; and - - the ratio of the concentre 



y -f a 



chlorine ion outside to the chlorine ion inside. Since, 

 and 



tration outside; and ^r the ratio of the concentration of the 

 > 



log = pH inside minus pH outside 

 x 



log j = pCl outside minus pCl inside 



it follows that 



pH inside minus pH outside = pCl outside minus pCl inside (2) 



