570 CAUSE OF INFLUENCE OF IONS. H 



tube in order to, bring about a rise in the level of water in the tube. 

 It is obvious from Fig. 4 that the electro-endosmotic transport of the 

 negatively charged liquid rises at first with increasing concentration 

 of the electrolyte and then falls again; and the initial rise increases 

 with increasing valency of the cation and diminishes with increasing 

 valency of the anion. The turning point varies for different elec- 

 trolytes, probably on account of secondary chemical reactions at the 

 electrodes, especially acid formation at the anode. The curves if 

 interpreted on the basis of Helmholtz's theory prove that when the 

 membrane is positively charged its positive charge is raised in low 

 concentrations of electrolytes more considerably by the cation than 

 it is depressed by the anion of the electrolyte, while when the con- 

 centration of the electrolyte exceeds a certain limit the depressing 

 effect of the anion increases more rapidly with further increase in 

 concentration than the opposite effect of the cation; thus supporting 

 the explanation offered for the phenomena of free osmosis in Fig. 3. 



in. 



Fig. 5 is a repetition of a figure pubUshed in a preceding paper* 

 showing the difference of influence of AI2CI6 on the rate of diffusion of 

 water when the collodion membrane has been treated with a protein 

 and when it has not been treated. When the membrane has been 

 treated with a protein, water is powerfully attracted by a solution of 

 AI2CI6 and the attraction increases with the concentration (upper 

 curve); when the membrane has not been treated with a protein, 

 water is not attracted by the solution except when the concentration 

 becomes so high that the gas pressure effect of the solution shows itself 

 (lower curve). The explanation offered by the writer was as follows. 

 When we separate AI2CI6 solutions of sufficiently low concentration 

 from pure water by a membrane treated with gelatin, the water dif- 

 fuses through the membrane in the form of negatively charged par- 

 ticles which are attracted powerfully by the Al ion and repelled weakly 

 by the CI ion; or, in other words, the Al ion increases the positive 

 charge of the membrane considerably and the CI ion depresses the 

 same charge less. As a consequence the density of the positive 

 charge of the membrane on the solution side of the membrane must 



5 Loeb, J., J. Gen. Physiol, 1919-20, ii, 255. 



