JACQUES LOEB 391 



membrane, a transport of water or of liquid occurs through the 

 membrane towards that electrode whose sign of charge is the opposite 

 of that of the watery phase of the double layer in the pores or inter- 

 stices of the membrane. This is the well known phenomenon of 

 electrical endosmose which was first investigated experimentally by 

 Quincke and Wiedemann and which was explained mathematically 

 by Helmholtz. The earlier workers found that the watery phase 

 of the double layer was generally positively electrified. Perrin^ 

 made the remarkable discovery that in the case of certain diaphragms, 

 such as powdered charcoal, carborundum, gelatin, etc., the sign of 

 charge can be reversed at will, chiefly with the aid of acid and of 

 alkali. In a slightly acid medium the liquid moves to the anode, 

 in a slightly alkaline medium it moves to the cathode. This has 

 been confirmed by every observer, and his deductions have been 

 generally accepted. 



It has been suggested by Girard, Bernstein, Bar tell and Hocker, 

 and Freundlich^ that the cases of so called negative osmosis where 

 liquid diffuses from acid into pure water instead of in the opposite 

 direction might be in reality manifestations of electrical endosmose. 

 The only difference between the case of free osmosis and electrical 

 endosmose being, according to these authors, the source of the 

 potential difference, which is an external one in the case of electrical 

 endosmose and an internal one — e.g. a diffusion or a boundary 

 potential — in the case of free osmosis. But this is thus far merely an 

 hypothesis which is not yet adequately supported by facts. 



The possibility of correlating the phenomena of free and electrical 

 osmosis meets at present with a difficulty. Our experiments on 

 collodion membranes leave no doubt that in the case of free osmosis 

 the influence of electrolytes on the velocity of diffusion of water from 

 pure solvent to solution through the collodion membrane is an addi- 



^ Perriii, J., /. chim. physique, 1904, ii, 601; 1905, iii, 50. 



^Gkavd, F.,Compt. rend. Acad., 1908, cxlvi, 927; 1909, cxlviii, 1047, 1186; 

 1910, cl, 1446; 1911, cliii, 401 ; La pression osmotique et le mecanisme de Tosmose, 

 Publications de la Societe de Chimie-physique, Paris, 1912. Bernstein, J., 

 Elektrobiologie, Braunschweig, 1912. Bartell, F. E., /. Am. Chetn. Soc, 1914, 

 xxxvi, 646. Bartell, F. E., and Hocker, C. D., /. Am. Chem. Soc, 1916, xxxviii, 

 1029, 1036. Freundlich, H., Kolloid-Z., 1916, xviii, 11. 



