188 



d'i fusion phenomenon, as was indicated by ine already more than 

 20 years ago, and was further worked out by me ten years ago 

 (Seclis Vortrage I. c.)- 



OBSERVATIONS. Thongli I wish a long otium cum dignitate to 

 all incorrect kinetic theories, I would by no means be considered a 

 personal foe to the osmotic pressure — the significance of which for 

 the theory of the dilute solutions was set forth by van 't Hoff in 

 the" ingenious way characteristic of him. 



My earlier and later opposition was only directed against two 

 later introduced abuses (with which Prof. Ehrenfest of course entirely 

 agrees), nainely : 



1. Against the extension of the idea {thouyht as realiti/) to isolated 

 homogeneous solutions (i. e. wlieu no semipermeable membrane is 

 thought to exist), in which of course no real pressure of 24 atms. 

 for every dissolved gr. mol. occurs. 



2. Against the practical application of the idea to non-diluted 

 solutions, which application I thought undesirable in view of the 

 inaccuracies which then occur and which are not to be ascertained 

 — which can give rise to very erroneous conclusions (and have 

 indeed done so !). Then the general theory of tlie thermodynamic 

 potential (or free energy) is the obvious and sure way. 



The existence of the osmotic pressure has never been called in 

 question by me. One does not give calculations and interpretations 

 of something that does not exist! But it exists only in a solution 

 that is separated by a semi pervieahle membrane ïvom{\\Q\mve?,o\\ ent 

 (or from a solution of slighter concentration) — and manifests itself 

 then through a diffusion pressure from, the pure solvent toioards 

 the solution (so just the reverse of what the kinetic interpreters 

 imagine). 



That the above described osmotic diffusion pressure for exceed- 

 ingly diluted solutions has a value as if the sugar molecules in the 

 sugar solution in the corresponding ideal gas state exert this pres- 

 sure, is a mere coincidence, only owing to the term — log (1 — x) 

 of the so-called Gibbs' paradox ; which term, as we know, is kine- 

 lically in connection with the diifusion tendency of the components 

 of the mixture. 



Only a kinetic theory of the osmotic pressure which starts from 

 the diifusion phenomenon, arrives at the term in question (Sechs 

 Vortrage, S. 20 — 21); all other theories, which imagine the pressure 

 in ihe stigai' soluiion, only come to non-logaritkmical expressions 

 \v ;i - ' ilv (' (i«^|>- c, '/. 7— /• etc.), which owing to their deri- 



