560 COLLOIDAL BEHAVIOR OF PROTEINS 



III. 



What is the origin of these potential differences? Beutner^ has 

 shown that the potential differences at the boundary of water and 

 water-immiscible substances obey Nernst's well-known logarithmic 

 formula 



E = In - 



nF C2 



or at room temperature and iov n = 1 



0.058 log - 



Loeb and Beutner have found the same formula to hold for the po- 

 tential differences at the boundary of water and the skin of an apple, 

 a tomato, or the leaf of a rubber plant. 



It can be shown that the potential differences mentioned in Table 

 I follow Nernst's formula, if we assume that only the hydrogen ion 

 concentration need be considered for the potential difference. IfCi 

 is the concentration of free HCl in the gelatin solution, and d the con- 

 centration of HCl in the outside aqueous solution (without gelatin) 



r 

 the value log -^ becomes equal to (pH inside — pH outside) . 

 C2 



We measured the pH of the gelatin chloride solution (inside solu- 

 tion) and of the outside HCl solution (without gelatin) after the os- 

 motic and the Donnan equilibria were established. The surprising 

 result was noticed that the difference of pH inside the gelatin solution 

 minus the pH of the outside solution (without gelatin) becomes the 

 smaller the greater the concentration of the NaNOs, as shown in 

 Table II. 



We can calculate from this difference of pH inside minus pH out- 

 side the p.D. between inside and outside solution in millivolts by mul- 

 tiplying the differences by 58 or 59 (correcting for temperature of 

 24°C.). If the Nernst formula holds the values for p.d. thus calcu- 

 lated should be identical with the observed, values for p.d. Table 

 III show4S that this is true to a remarkable degree. 



^Beutner, R., Die Entstehung elektrischer Strome in lebenden Geweben, 

 Stuttgart, 1920. 



