(51) 



KoHNSTAMM the osmotic pressure in an isolated solution is established, 

 only ivhen he places semi-permeable walls or planes in it. But then 

 it is of course no isolated solution any more! What I demonstrate 

 is no more than this : Without semipermeable membrane no osmotic 

 pressure. And to this Kohnstamm will certainly not have any objection, 

 witness the cited question of Pupin how it is possible, that e. g. a 

 CaCl^-solution of no less than 53 atm. could be beld in a thin glass 

 vessel without bursting it ! I do not see very well, what objection 

 Kohnstamm can ha\'e to my assertion. For this is the core of the 

 question, with regard to which he proves to be quite of my opinion 

 in another place (cf. p. 742). 



4. What Kohnstamm further observes on pages 742 — 4 with 

 regard to the idea ''thermodynamic potential", and what he says on 

 "palpable conceptions" may be very well left undiscussed here. For 

 this is only a question of words, which does not affect the real 

 nature of the affair at all. Every one who works with the thermo- 

 dynamic potential, means with it the s-function of Gibbs, which 

 perfectly determines the condition of equilibrium, as it must be 

 minimum in this case. 



Finally I may only be allowed to point out that Dr. Kohnstamm 

 has evidently misunderstood me, where he says that he thinks the 

 request to supply something "as a substitute" for the osmotic pressure 

 and the kinetic conception of it less unreasonable than it seems 

 to me (p. 746). 



I, namel}^ spoke of the osmotic pressure m an isolated solution. 

 And I very distinctly added : nothing can be put in the place for 

 what does not exist. And I wrote further, that the usual (faulty) 

 kinetic conception of the osmotic pressure (i. e. where there ai-e semi- 

 permeable membranes) must be replaced by a perfectly ne^v kinetic 

 explanation, in which inter alia, the process of diffusion at the mem- 

 brane is put more into the foreground (Cli. Weekbl., 1905, N". 9). 



And where Kohnstamm himself has made a very laudable attempt 

 in this direction (1. c. p. 729 — 741) to explain the osmotic pressure, 

 I have after all reasons for satisfaction, though he has wisely aban- 

 doned the idea of drawing up an equation for non-diluted solutions 

 in this way. 



And as to the thermodynamic derivation, in this Kohnstamm has 

 been less fortunate in my opinion; where he has tried to substitute 

 for my perfectly exact, and yet so simple derivation an indirect, 

 elaborate derivation, the result of which on account of some neglections 

 cannot even lay claim to perfect accuracy. 



