JACQUES LOEB 405 



Positively charged particles of water in the pores or interstices 

 of the membrane will be driven to that side of the membrane which 

 is more negatively charged. Since this is usually the solution side, 

 water will be driven from the side of pure water into the solution. 



When the collodion membrane has been treated with a protein, 

 it is also generally negatively charged when bounded by water except 

 when the solution contains hydrogen ions or simple trivalent or 

 tetravalent cations beyond a certain concentration (which for H is 

 10~^ n); in this case the membrane is positively and the watery 

 phase is negatively charged. If we add in this case an electrolyte 

 to the water, the charge on the membrane is increased by the 

 cations and diminished by the anions of the electrolyte. Whenever 

 the positive charge on the solution side of the membrane is greater 

 than on the opposite side, the negatively charged particles of water 

 will diffuse from the side of pure water to the side of solution. 



When the charge on the solution side of the membrane is dimin- 

 ished by the electrolyte so that the charge is smaller than on the 

 side of pure water, the liquid will flow through the membrane from 

 solution side to the side of pure water (negative osmosis) . 



Our experiments were made with collodion membranes only and it 

 is possible that Perrin's statement holds for other t3qDes of membranes. 

 It seems, however, that in the case of the influence of electrolytes on 

 the value of e at the boundary of oil drops and water the effect is also 

 an additive one of the oppositely charged ions. Powis^*^ has measured 

 this value from the velocity of the motion of oil drops through solu- 

 tions on the basis of the Helmholtz-Perrin formula for five electro- 

 lytes, KCl, BaCla, AICI3, ThCl4, and K4Fe(CN)6. The oil particles 

 are negatively charged and their charge is increased more by 

 K4Fe(CN)6 than by KCl. The charge is diminished with the increas- 

 ing valency of the cation. This indicates that the influence of elec- 

 trolytes on the value of the potential difference of the double layer 

 is in this case also an additive effect of the two kinds of ions. 



We have stated that in the case of free osmosis the rate of diffusion 

 of water from pure solvent to solution through a collodion membrane 

 increases at first with increasing concentration, reaches a maximum 



^° Powis, F., Z. physik. Chem., 1915, Ixxxix, 91. 



