JACQUES LOEB 89: 



the remnants of the solution. The initial treatment of the mem- 

 branes with gelatin apparently modified the collodion permanently 

 since after weeks of daily use these membranes, treated once with 

 gelatin, behaved differently from membranes not treated with gelatin. 

 We shall return to this fact in another publication. An investiga- 

 tion of the influence of electrolytes on the rate of diffusion of water 

 through such collodion membranes previously treated with gelatin 

 has shown that all the phenomena observed can be explained on the 

 basis of the following two rules. 



"1. Solutions of neutral salts possessing a univalent or bivalent cation influence 

 the rate of diffusion of water through a collodion membrane, as if the water 

 particles were charged positively and were attracted by the anion and repelled 

 by the cation of the electrolyte; the attractive and repulsive action increasing 

 with the number of charges of the ion and diminishing inversely with a quantity 

 which we will designate arbitrarily as the "radius" of the ion. The same rule 

 applies to solutions of alkalies. 



2. Solutions of neutral or acid salts possessing a trivalent or tetravalent cation 

 influence the rate of diffusion of water through a collodion membrane as if the 

 particles of water were charged negatively and were attracted by the cation and 

 repelled by the anion of the electrolyte. Solutions of acids obey the same rule."^ 



These two rules allow us to predict in which sense the nature of the 

 electrolyte in solution should modify the osmotic pressure of a solu- 

 tion calculated on the basis of van't Hoff's law. Suppose pure water 

 is separated by a collodion membrane from a watery solution of 

 an electrolyte. When the electrolyte is one of those mentioned in 

 Rule 1, i.e. possessing a monovalent or bivalent cation, water is 

 attracted by the solution and diffuses from the side of pure water 

 into the solution, as if the particles of water were positively charged. 

 They should therefore be attracted by the anion and repelled by the 

 cation of the electrolyte and the more so the higher the valency of 

 these ions. Hence water should diffuse more slowly into a solution 

 of m/192 CaCl2 than into a solution of m/128 NaCl, and more slowly 

 into m/128 NaCl than into m/192 Na2S04, and considerably more 

 slowly into m/128 NaCl than into m/256 Na3P04or m/320 Na4Fe(CN)6. 

 If, however, the water particles are negatively charged everything 

 is reversed, the water diffusing more rapidly into m/192 CaCla than 



» Loeb, J., J. Gen. Physiol., 1918-19, i, 720. 



