186 



the corresponding non-ideal gas state. (Cf. Seclis Vortrage p. 29^30, 

 and tlie cited paper in Tiiese Proc, p. 57 et seq ). 



Already from this we are led to surmise that the so-called osmotic 

 pressure has an entirely different ground from what the analogy of 

 the behaviour of the dissolved sid)stanoe to that of tiie same sub- 

 stance in the corresponding gas state would lead us to suspect, and 

 that there is iiere no close relation, only analog;/. Particularly tiie 

 occurrence of the term — log (1 — x) (which only i)asses into .v at 

 X = 0) in the expression (1) for the osmotic pressure should have 

 admonished to caution. This term continues to exist in the most 

 dilute solutions. 



Thesis V. If actually the osmotic pressure was caused by the 

 pressure of the dissolced substance fihe old theory revived !), as 

 Ehrenfest also assumes again, the pressure of the "sugar" molecules 

 against the semi-permeable membrane would cause the reverse of wliat 

 is actually observed. Then there would namelj' no water pass from 

 the side of the pure solvent through the membrane into the solution, 

 and give rise to the hydrostatic counterpressure = .t in the 

 ascension tube of the osmometer — but this water would on the 

 contrary be checked, since the pressure in the so/utioii would be 

 greater from the outset than in the pure water ! 



Thesis VI. In reality the osmotic pressure is caused by the water, 

 penetrating through the semi-permeable membrane into the sugar 

 solution, which gives rise to a hydrostatic pressure, which prevents 

 the further intrusion of the water. 'This excess of pressure -t =: /^ — p, 

 is the so-called "osmotic pressure" of the solution. 



Thesis VII. Every theory, whicli would try to interpret the occur- 

 rence of the osmotic pressure kineticalli/, should be based on the 

 diffusion of the water molecules on both sides of the membrane. 

 Quite generally one- can assume then two solutions of different con- 

 centration A'l and ./■, on both sides of the membrane. If one confines 

 oneself to a soluiion of the conceuti-ation .c and pure water, one 

 has what follows : In the unity of time there diffuse a certain 

 numl»er of water molecules of the |)ure water towards the solution, 

 and another number from the solution towards the water. But on 

 account of the solution containing less water than the pure water, 

 there will go — parallel with the prevailing diffusion pressure — 

 more panicles of the waier to the solution than the reverse. 



In ordinary circiimstaiices the dissolved substance (sugar) would 



