. JACQUES LOEB 183 



from pure water the attraction of the sohition for water diminishes with 

 increasing concentration for concentrations between m/256 to about m/32 

 or above, according- to the nature of the electrolyte. This is exactly the 

 reverse of what we should expect on the basis of van't Hoff's law which 

 demands that the attraction of the solution for water should increase 

 with the concentration. Such a reversal occurs only in the case of 

 electrolytes and we assume provisionally that it is due to the fact 

 that the repelHng action of the cation of the electrolyte upon the posi- 

 tively charged particles of water increases inside the critical range of 

 concentrations more rapidly with the concentration than the attrac- 

 tive action of the anion upon the same particles of water. 



It will be necessary to test this assumption by further experiments. 



We have shown in the first paper that water particles diffuse through 

 collodion membranes in the form of positively charged particles from 

 pure solvent to solutions of electrolytes with monovalent or bivalent 

 cation when the solution is neutral or alkaline in reaction. When, how- 

 ever, the solution is rendered sufficiently acid the water particles dif- 

 fuse through the membrane as if they were negatively charged, being 

 attracted by the cation and repelled by the anion of the electrolyte 

 with a force increasing with the valency of the ions. We will now con- 

 sider the influence of the concentration of electrolytes upon the 

 rate of diffusion of negatively charged particles of water through the 

 membrane. 



We have stated in a former paper' that the collodion membranes 

 were suspended for 1 night in a 1 per cent gelatin solution before being 

 used; after this they were used sometimes for a week or more without 

 any further gelatin treatment. The membranes were, of course, 

 rinsed a large number of times in warm water after the gelatin treat- 

 ment to remove all the gelatin that could be removed by rinsing. 

 This gelatin treatment is not necessary to obtain the results with 

 neutral solutions of electrolytes described in the preceding chapter. 

 The gelatin treatment of the membrane is, however, necessary to 

 obtain the results with negatively charged particles of water to be 

 described in this chapter. We intend to return to this fact in a later 

 paper. 



2 Loeb, J., J. Gen. Physiol., 1919-20, ii, 87. 



