THE ORIGIN OF THE POTENTIAL DIFFERENCES RESPON- 

 SIBLE FOR ANOMALOUS OSMOSIS. 



By JACQUES LOEB. 

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



(Received for publication, September 19, 1921.) 



/. Potential Diferences in Collodion Membranes Coated with Protein. 



In a series of papers^ the writer has published the results of experi- 

 ments showing the peculiar influence of electrolytes on the rate of 

 diffusion of water through collodion membranes. When a collodion 

 membrane separates a solution of an electrolyte (of not too high a 

 concentration) from pure warer, the water diffuses from the side of 

 pure water to the solution side, but the initial rate at which this dif- 

 fusion occurs does not obey van't Hoff's law. The initial rate of diffu- 

 sion was measured by the rise of level of liquid in a glass tube inserted 

 through a rubber stopper in a closed collodion bag containing the 

 solution, the collodion bag dipping into a beaker filled with pure water. 

 When the membrane was merely a collodion membrane, the following 

 rules expressed the influence of electrolytes on the initial rate of diffu- 

 sion of water through the membrane from the water side to the side 

 of the solution. 



1 . Water diffuses into the solution of an electrolyte through a col- 

 lodion membrane as if the particles of water were positively charged 

 and as if they were attracted by the anion and repelled by the cation 

 of the electrolyte in solution with a force increasing with the valency. 



2. In the case of certain electrolytes the "attracting force" of 

 the anion for water increraes at first more rapidly with increasing 

 concentration than the "repelling force" of the cation, until a point 

 is reached where with a further increase in concentration the "repell- 

 ing force" of the cation increases more rapidly than the "attractive 

 force" of the anion. Finally, a concentration is reached where the 



'Locb, J., Science, 1921, liii, 77; J. Gen. Physiol, 1918-19, i, 717; 1919-20, 

 ii, 173, 387, 577. 



213 



