16 Mr Vegard, On the Free Pressure in Osmosis. 



Discussion of the Experiments. 



4. The relation between the friction pressure and the velocity 

 is represented in Fig. 1 B curve II, corresponding to Exp. 2, Table I. 

 We see that as far as the observations go the points are distributed 

 round a straight line. Consequently we have 



Q=AV (1) 



where J. is a constant characteristic of the membrane and the 

 fluid, and dependent on the temperature. We shall call it the 

 Specific Resistance of the system. 



The law for the motion through the membrane is the same as 

 that for the motion of a viscous fluid through narrow tubes. This 

 fact is simplest explained by assuming that the liquid also during 

 the passage through the membrane maintains the character of a 

 liquid. Then in points inside the tubes of the membrane the 

 fluid should possess a certain hydrostatic pressure and the cause 

 of the motion at each point should be found in the pressure 

 gradient at the point. 



The values of the specific resistance corresponding to the two 

 experiments are — using the method of least squares — found 

 to be: 



Exp. 1. A= 0-0463 or A' = 1-02 . 10^^ [dyn. cm.-i sec.-^]. 



Exp. 2. A= 0-0492 or ^' = 1-OS . lO^^ 



A corresponds to the units given in the table, A' to absolute 

 units. 



We see that we get nearly the same value for the specific 

 resistance in the two cases and that in spite of the fact that the 

 maximum electric resistance in the last experiment was not half 

 of that in the first one, where the frictional resistance even is 

 somewhat smaller. Thus the maximum electric resistance seems 

 to give a very delicate test for the permeability of the membrane. 

 When the membrane first is well formed the mechanical resistance 

 against the water flow will be very little altered for very con- 

 siderable changes in the maximum electric resistance. 



5. In Fig. 1 A the measurements given in Table II are 

 represented by curves giving the velocity as a function of time 

 reckoned from the time when the solution was brought into 

 contact with the membrane. This time was not exactly observed 

 so there may be a fault of a few minutes in the time of beginning. 



We see that the velocity begins with a rather large value, but 

 falls very rapidly until at a certain value the curve makes a very 

 sudden bend. In the case of the three lowest concentrations the 

 curve assumes a horizontal direction showing that the osmosis 

 has reached a steady state. In the case of the highest concen- 



