Dandeno : Osmotic theories 291 



that in the former case there must be a greater number of solvent 

 particles per unit volume than in the pure solvent. Hence if the 

 above explanation can be retained, there should be no osmotic 

 pressure developed in such solution ; indeed, it should appear on 

 the side of the pure solvent/' 



Livingston gives in the book already named a more detailed 

 argument than that quoted above to show the fallacy of the theory 

 offered as explanation of osmotic pressure. 



Now Livingston himself offers a theory which is objectionable 

 perhaps to the same degree as that which he so thoroughly refutes. 

 He says, p. 26, the pressure is " due to the bombardment of the 

 walls by the solute particles/' and, p. 3f, ''If there were available 

 a membrane permeable to the solute but impermeable to the 

 solvent, this diffusion tension of the solvent might be directly 

 measured. It would be an osmotic pressure similar to that occa- 

 sioned by the solute molecules, but of much greater magnitude 

 and in the opposite direction." From this it appears as though 

 both solute and solvent exerted osmotic pressure, and this is due 

 to the ** bombardment of the walls." But he says, p. 28, *' Osmotic 

 pressure is independent of the solvent and dependent only upon the 

 number of particles of solute." Now the bombardment of the 



r 



walls otitzvard does not account for an injlozv of water ; in fact, it 

 . would, if anything, oppose the inflow- But he speaks of an 

 osmotic pressure of the pure solvent. Now if this be so, the in- 

 flow would be due to this pressure and not to the bombardment of 

 the walls in the opposite direction. He says, p. 30, " Water mole- 

 cules pass i . . in both directions " and also "particles of solute 

 hinder the escape of the solvent molecules." Yet, if the solute mole- 

 cules were bombarding outzvard^ there would be a greater tendency 

 ■ for a free course without hindrance for solvent molecules outward. 

 From the above, the gist of the idea is that the pressure is- due to 

 the bombardment of the walls by the solute, and that water is 

 forced in owing to the bombardment from within, because " The 

 pressure produced by the solvent on one side of the membrane is 

 practically equalled by that on the other side." Yet the crucial 

 point is to account for the inflow of water, and it is not easy to 

 see how water enters when there is no force exerted except a 

 bombardment in the opposite direction. 



