THE REVERSAL OF THE SIGN OF THE CHARGE OF 

 MEMBRANES BY HYDROGEN IONS. 



By JACQUES LOEB. 



(From the Laboratories of The Rockefeller Institute for Medical Research.) 

 (Received for publication, March 13, 1920.) 



I. INTRODUCTION. 



The similarity between the influence of ions on free and on electrical 

 endosmose through collodion membranes leads to the conclusion that 

 this influence is due to an alteration of the density of the electrical 

 charge of the membrane by the ions.^ This conclusion rests on the 

 assumption that the Helmholtzian theory of the double layer and the 

 formula connecting the volume of transport of liquid with the den- 

 sity of charge is correct. We have seen that on this assumption the 

 observations lead to„the conclusion that the ions with the same sign 

 of charge as the membrane increase and the ions with the opposite 

 sign of charge diminish the density of charge of the membrane. 

 Whether, therefore, a given ion increases or diminishes the density 

 of charge of the membrane depends upon the sign of the charge of the 

 membrane, and, hence, the sign of the charge precedes the influence 

 of ions on the density of charge. One of the problems in the theory 

 of the double layer at the boundary of membrane and watery solution 

 is therefore the origin of the sign of the charge of membranes in 

 contact with water. 



Chemists consider the double layer at the boundary of membrane 

 and water as ionic in character and as due to the preferential adsorp- 

 tion of one kind of ions by the membrane, while the watery phase of 

 the double layer is formed by the ions with the opposite charge from 

 those adsorbed. This view has been developed with remarkable lu- 

 cidity and consistency by Perrin^ who assumes that the H and OH 



1 Loeb, J., J. Gen. Physiol., 1919-20, ii, 387, 563. 



^Perrin, J., /. chim. physique, 1904, ii, 601; 1905, lii, 50; Notice sur les 

 titres et travaux scientifiques de M. Jean Perrin, Paris, 1918. 



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