ON THE CAUSE OF THE INFLUENCE OF IONS ON THE 



RATE OF DIFFUSION OF WATER THROUGH 



COLLODION MEMBRANES. I. 



By JACQUES LOEB. 



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

 (Received for publication, January 23, 1920.) 



When we separate a watery solution from pure water by a collodion 

 membrane water will diffuse into the solution and solute will diffuse 

 out. We will call this diffusion free osmosis to distinguish it from 

 osmosis due to an outside force; e.g., electrical endosmose. The free 

 diffusion of solute into pure water occurs at a rate proportional to the 

 concentration of the solution^ (with the possible exception of very 

 low or very high concentrations) and need not occupy our interest 

 in this paper. The diffusion of water into the solution has a different 

 character when the solute is a non-electrolyte than when it is an 

 electrolyte. When the solute is a non-electrolyte, the initial rate of 

 diffusion of water into the solution is (within the limit of moderate 

 concentrations) practically a linear function of the concentration of 

 the solute, as it should be according to the law of van't Hoff. When 

 the solution is an electrolyte, anomalies occur which are a character- 

 istic function of the oppositely charged ions of the electrolyte and 

 these anomalies were described for collodion membranes in a series of 

 papers which have appeared recently.^' 2. 3, 4 'pjjg anomahes seem to 

 occur only in the lower concentrations of electrolytes, below m/8 or 

 less; above these values the osmosis seems to occur in a way similar 

 to that observed in solutions of non-electrolytes, though this point 



' Loeb, J., /. Gen. Physiol., 1918-19, i, 717. 

 2Loeb, J., /. Gen. Physiol, 1919-20, ii, 173. 



3 Loeb, J., /. Gen. Physiol, 1919-20, ii, 255. 



4 Loeb, J., Proc. NaL Acad. Sc, 1919, v, 440. 



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