JACQUES LOEB 225 



with a diminishing pH until a maximum is reached at a pH of about 

 4.2, and diminishing with a further diminution of the pH. 



These experiments then lead to the result that the anomalous os- 

 mosis discussed in this paper is determined by a potential difference 

 between the opposite sides of the membrane, and that this p.d. seems 

 to have a double source; namely, the Donnan equilibrium and 

 diffusion potentials. 



In addition to these two sources of p.d. between the opposite sides 

 of the membrane there may be others, as, e.g., the Coehn effect due 

 to the difference in the dielectric constant between liquid and mem- 

 brane. If such a P.D. plays a role in our experiments it can be only 

 of minor importance. 



The experiments suggest the possibility that the establishment 

 of a Donnan equilibrium between membrane and solution is one of 

 the factors determining the. Helmholtzian electrical double layer, at 

 least in the conditions of our experiments. 



SUMMARY AND CONCLUSION. 



1. Collodion bags coated with gelatin on the inside were filled 

 with a m/256 solution of neutral salt (e.g., NaCl, CaCl2, CeCls, or 

 Na2S04) made up in various concentrations of HNO3 (varying from 

 n/50,000 to n/100). Each collodion bag was put into an HNO3 

 solution of the same concentration as that inside the bag but contain- 

 ing no salt. In this case water diffuses from the outside solution 

 (containing no salt) into the inside solution (containing the salt) 

 with a telative initial velocity which can be expressed by the fol- 

 lowing rules: (a) Water diffuses into the salt solution as if the par- 

 ticles of water were negatively charged and as if they were attracted 

 by the cation and repelled by the anion of the salt with a force increas- 

 ing with the valency of the ion. (b) The initial rate of the dift'usion 

 of water is a minimum at the hydrogen ion concentration of about 

 n/50,000 HCl (pH 4.7, which is the point at which gelatin is not ion- 

 ized), rises with increasing hydrogen ion concentration until it reaches 

 a maximum and then diminishes again with a further rise in the 

 initial hydrogen ion concentration. 



2. The potential differences between the salt solution and the 

 outside solution (originally free from salt) were measured after the 



