Mr. Vegard, On the Free Pressure in Osmosis. 23 



TTo is the osmotic pressure and q the corresponding free pressure in 

 the steady state. From equation (3) follows Lim ( ° " ) = 0. 



Ao=0 V_ -A A,o / 



This gives an explanation to the fact that the osmosis for small 

 concentrations immediately assumes a velocity very near to that of 

 the steady state. 



11. When the pressure on the solution is augmented, the 

 properties are no longer so simple as they are when tt = 0. The 

 degree of semipermeability begins to play a more important part 

 as regards the velocity. As stated in the earlier paper the 

 absolute value of the velocity for pressures less than the reversion 

 pressure and when other circumstances are the same is greater 

 for a more perfect membrane. The increase of pressure was 

 accompanied by a sudden decrease in the velocity, and this 

 decrease is the greater the less perfect the membrane is. If the 

 membrane was quite stable for pressures and quite semipermeable 

 we should expect that an increase of the pressure on the solution 

 with an amount tt would have the same effect on the velocity as 

 if the concentration was diminished to a value G corresponding to 

 an osmotic pressure ttq — tt. As a consequence of this the velocity 

 curve in the interval < tt < ttq would be 



TTo — TT = r- 



where A and X,^ should have the same values as before if we 

 assume the qualities of the membrane and the temperature to be 

 the same. The direction of the tangent at the reversion point 

 should be that of the friction line. In general we find at this point 



-J— >A, only if the characteristic point lies near to the reversion 



point we find -j- nearly equal to A. This seems to be a special 



case of the more general rule that the direction of the velocity 

 curve* just before reaching the characteristic point at least for 

 more perfect membranes is very near to that of the friction line 

 corresponding to the same membrane and temperature. 



12, From the preceding considerations we see that the experi- 

 ments are very well explained by the assumption of a hydrostatic 

 pressure inside the membrane which leads to the theory of the 

 Free Pressure. This theory, however, gives no explanation of the 

 manner in which the semipermeability is brought about in the 

 layer next to the solution. The effect of the membrane is 

 equivalent to a very great resistance against the flow of solution 

 in bulk whatever .may be the manner in which this resistance is 

 brought about. 



* See L. Vegard, loc. cit., Exp. I, II, III. 



