390 CAUSE OF INFLUENCE OF IONS. I 



basis for the explanation of the phenomena of abnormal osmosis. 

 For this latter purpose we must express the facts in the following 

 form. When we separate a solution of an electrolyte from pure water 

 by a collodion membrane the oppositely charged ions of the electro- 

 lyte influence the initial velocity of diffusion of water through the 

 membrane into the solution in an opposite sense; the ion with the 

 opposite sign of charge from that of the electrified water (or the 

 watery phase of the double layer) increasing the velocity, the ion with 

 the same sign of charge as the watery phase of the double layer 

 diminishing the velocity. The accelerating and retarding effects of 

 ions were found to increase with the valency and with that other 

 constitutional quantity which was designated as the radius of the 

 ion but which requires further definition. 



In passing we may remark that the relative retarding and acceler- 

 ating effect of oppositely charged ions of an electrolyte on the rate 

 of osmosis of water into the solution was not found to be the same for 

 all concentrations of a solution. ^ At the lowest concentrations the 

 effect of that ion usually (and possibly always) prevails which has 

 the opposite sign of charge from that of the watery phase of the double 

 layer, at a higher concentration the effect of that ion prevails which 

 has the same sign of charge as the watery phase. Hence in the 

 lower concentrations the accelerating effect of the electrolyte pre- 

 vails over the retarding effect and for the higher concentrations the 

 reverse is true. For a number of solutions, e.g. salts of monovalent 

 cations, the turning point lies at a concentration of about m/256. 

 The anomalous osmosis ceases at that concentration of the solution 

 where the retarding and accelerating effects of the oppositely charged 

 ions become equal. From then on the solutions of electrolytes 

 seem to behave like those of non-electrolytes. This group of facts 

 has been described in a preceding paper- and will not be discussed 

 here. 



In our experiments on free osmosis the collodion membrane was 

 bounded on one side by pure water and on the other by the solution. 

 When both sides of the membrane are bounded by identical solu- 

 tions the rate of diffusion of water and of electrolyte in opposite 

 directions is equal, and no change occurs. When, however, an 

 external difference of potential is produced on the two sides of the 



