404 CAUSE OF INFLUENCE OF IONS. I 



Theoretical Remarks. 



According to the formula of Helmholtz for the transport of liquid 

 by a current through capillaries, modified by Perrin,^ we have 



q-t-E-D 



V = ■ 



4 TT. 17. / 



where v is the quantity of liquid carried electro-osmotically, e is the 

 potential difference between the two strata of the double layer, E the 

 external electromotive force, D the dielectric constant of the medium, 

 97 the coefficient of internal friction, and / the distance of the external 

 electrodes. Since in our experiments all quantities occurring in this 

 formula except v and e were kept approximately constant, we must 

 attribute the influence of electrotytes on the quantity of transport v 

 to an influence of the ions on e. We must therefore conclude that the 

 influence of electrolytes on the rate of free osmosis is due to the effect 

 of the ions of the electrolyte on the quantity of charge on the unit 

 area of the Helmholtzian double layer. Our experiments on both 

 free and electrical osmosis show that this influence is an additive 

 effect of the two oppositely charged ions of the electrolyte at least 

 in the case of collodion membranes. Since the quantity of trans- 

 port V increases with the value of e we must further conclude that 

 the ion with the same sign of charge as the watery phase of the 

 double layer diminishes the value of e since this ion diminishes 

 transport in both free and in electrical osmosis ; while the ion with the 

 opposite sign of charge as this watery phase increases the value of e 

 in both forms of osmosis. Both effects increase with the valency and 

 with the second constitutional quantity of the ion (Table III). The 

 total effect of the two oppositely charged ions of an electrolyte on the 

 rate of diffusion of water through a collodion membrane is therefore 

 the difference between the opposite effects of its ions on the value of 

 e. These statements give the theoretical basis of what we called in 

 our former papers the apparent electrostatic action of the ions on the 

 rate of diffusion of the electrified particles of water from pure water 

 into solution through a collodion membrane (free osmosis). 



^ Freundlich, H., Kapillarchemie, Leipsic, 1909, 226. 



