142 The Osmotic Pressure of Solutions. 



dissolved substance in 100 gr. solvent, and M = molecular 

 weight of the dissolved substance. 



We have accordingly n = — ^p and writing ^r = ^ = 

 heat of fusion for 1 gr. solvent and ^- = C = difference of 

 the sp. heats of liquid and solid solvent, and also calling 



J 1 



jp 2 we get 



•02 [T F 2 F 2 Ft dw\ 



M* 



In the special case when j^ = ^ and kn=l this equation 



becomes 



C i\ 



2 F 2 / 



iL=jy w 



M* •02\T o F 



and when the solutions are dilute this may be written 



m _ -02 T 2 

 9 W 



This is the expression for the molecular depression of 

 the freezing point, which was first given by Van 't Hoff in 

 1885* 



• Van 't Hoff, loc, cit. p. 47. 



