296 Dandeno : Osmotic theories 



A 



theory 



sume ionization, though not inconsistent with it Physiological 

 investigation gives no support to the theory of dissociation, and 

 osmotic pressure need not assume it The strongest argument in 

 favor of dissociation is the electrical conductivity, but the very 



m 



current brought to bear upon the solution may actually induce the 

 condition which, by the ionization theory it is assumed exists there 



hefi 



It is not intended here to go 



into any discussion of the theory of dissociation further than to 

 state that osmosis, or osmotic pressure, does not furnish any data 

 for such theory. Osmosis and osmotic action can be explained 

 fully without the assumption of dissociation or ionization. And 

 these statements are made with full knowledge of the fact that 

 the relatively high pressure of such substances as KNO^ was 

 taken as one basis for the assumption of dissociation. 



The theory of surface tension to account for osmotic pressure 

 has been advanced, but, from the physiological side, it can receive 

 no support. Surface tension is something which depends upon 



r 



the attraction of the molecules of the solvent for one another, and 

 that only in the most minute distances; and is developed only in 

 a few layers of molecules on the extreme surface. It cannot ac- 

 count for osmotic pressure or other osmotic phenomena. 



More recently other theories, more or less directly connected 

 with the attraction theory, have been advanced in opposition to 

 van't Hoff's gas-pressure theory. 



Perhaps the most important of these is the discussion offered by 

 Kahlenberg * in which he opposes vigorously the gas-pressure 

 theory. So far, we agree with him thoroughly, but the main 

 point of difference between Kahlenberg's argument and that 

 offered in this discussion lies in the fact that Kahlenberg ascribes 

 to the membrane a large portion of that factor which the attraction 

 theory ascribes to the molecules of solute and solvent. 



Some of his experiments, notably that employing the three sub- 

 stances — chloroform, water, and ether — and which he calls a 

 "typical case of osmosis," can scarcely be considered osmosis at 

 all, for it is only a mixing of three liquids possessing varying 

 degrees of solubility for one another. Water in this case would 



♦Trans. Wisconsin Acad. 15 : 209. 1904, 



