106 ELECTRIFICATION OF WATER AND OSMOTIC PRESSURE 



tion of gelatin and of hydrogen ions. Apparently negatively charged 

 water diffuses also with less rapidity through a collodion membrane 

 into a solution of gelatin sulfate than into a solution of gelatin chloride 

 or nitrate of the same concentration of gelatin and of hydrogen ions. 

 3. If we define osmotic pressure as that additional pressure upon 

 the solution required to cause as many molecules of water to diffuse 

 from solution to the pure water as diffuse simultaneously in the 

 opposite direction through the membrane, it follows that the osmotic 

 pressure cannot depend only on the concentration of the solute but 

 must depend also on the electrostatic effects of the ions present and 

 that the influence of ions on the osmotic pressure must be the same 

 as that on the initial velocity of diffusion. This assumption was 

 put to a test in experiments with gelatin salts for which a collodion 

 membrane is strictly semipermeable and the tests confirmed the 

 expectation. 



