2 Morris, Modem Theory of Solutions. 



between the internal pressure and the real osmotic 

 pressure, which, taking the ordinary estimate of the 

 internal pressure of water, gives a figure differing greatly 

 from the ordinary osmotic pressure, even when corrected 

 for the volume actually occupied by the molecules. For, 

 of course, the pressure actually exerted by a solute is not 

 the osmotic pressure, and consequently is not equal to the 

 theoretical gas pressure. If the solvent and solute were 

 associated in any way there would be no difficulty in the 

 explanation. 



An osmotic membrane seems to be only a method for 

 keeping two otherwise completely miscible liquids in 

 contact, in such a manner that their surface tension 

 effects can be observed. In discussing sucji membranes 

 it is essential to know whether the concentration of the 

 solute is the same at all heights of the column. 



The considerable differences that are found between the 

 theoretical and actual osmotic pressures are, on this theory, 

 due to self-combinations or decompositions of the molecules 

 of solute and not to interactions between solute and the 

 solvent. Auwcrs' has shewn that in many cases of associa- 

 tion the low osmotic pressure is probably due to interaction 

 with the solvent. 



The dissociation hypothesis is of much greater import- 

 ance. The use of the term " dissociation " is most 

 misleading, since it is impossible to separate finite 

 quantities of the ionized bodies without the application of 

 energy. The ions cannot be considered free, as the 

 products of gaseous dissociation are. The system of 

 electrical charges, supposed to account for the ions not 

 diffusing, has been shewn by Prof Fitzgerald to be 

 impossible. 



From a study of the distribution of picric acid between 



*K. Auwcrs, Zeit. Phys. Cheiii. 30 (1S99), p. 300 — 340. 



