ON THE CAUSE OF THE INFLUENCE OF IONS ON THE 



RATE OF DIFFUSION OF WATER THROUGH 



COLLODION MEMBRANES. II. 



By JACQUES LOEB. 



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



(Received for publication, February 28, 1920.) 



I. 



In this note it is intended to complete the proof that the influence 

 of the concentration of electrolytes on the transport of water through 

 a coUodion membrane is similar in the case of free and of electrical 

 endosmose. 



Fig, 1 gives the curves representing the influence of different con- 

 centrations of KCl, K2SO4, K3 citrate, and CaCl2 upon the initial rate 

 of diffusion of water, from pure water through a collodion membrane 

 into solution (free osmosis). The solution was inside a collodion bag 

 and the latter dipped into a beaker filled with distilled water. The 

 ordinates of the curves give the rise in the level of liquid after 20 

 minutes in a glass tube pushed through a rubber stopper into the col- 

 lodion flask. The curves show, as pointed out in a preceding publi- 

 cation,^ that the level rises at first with increasing concentration until 

 it reaches a maximum at about m/512 or m/256 and that it then drops 

 with a further rise in concentration until the latter is m/16 when a 

 second rise begins. The second rise is presumably the expression of a 

 prevalence of the gas pressure effect while the first rise and faU are 

 the effect of the electrostatic influence of the ions on the rate of dif- 

 fusion of water. As stated in the preceding publication, pure water 

 as well as water containing electrolytes is positively charged when in 

 contact with a collodion membrane while the latter is negatively 

 charged. Leaving aside the gas pressure effect on the rate of dif- 

 fusion, water will be driven through the pores or interstices of the 



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



563 



