570 



SCIENCE PROGRESS 



after direct measurements of osmotic pressure and of vapour 

 pressure had been made. Here again then practice has served 

 as a guide to theory and direct measurements have alone proved 

 adequate to justify the validity of the formula in which the 

 thermodynamic relationships find expression. 



In the paper on weak solutions of calcium ferrocyanide direct 

 measurements of osmotic pressure were correlated with measure- 

 ments of electrical conductivity. Once again the conditions 



(c) Galactose. 



(a) Cane sugar. 



fi u 

 U-C 



l a 



o_./> 



o 



3 IS 



ty 



Concentrations in grammes per 

 litre of solution. 



150 300 450 



Concentrations , n grammes per 

 litre of solution. 



750 



o 150 yx> +50 600 



Concentrations in grammes per 

 litre_ of solution. 



40 "So 120 160 



Concentrations m grammes per 

 litre of solution. 



(i) Dextrose. (d) Mannitol. 



Fig. 8. — Influence of concentration on equilibrium pressure. 



were too complex to be expressed by the simple formulae 

 usually applied to such solutions ; but with the help of the new 

 observations it was possible to find suitable assumptions by 

 means of which the experimental results could be expressed and 

 formulated. 



F. Theoretical Considerations 



On comparing the exact measured values of the osmotic 

 pressures, as recorded by Morse and by the Earl of Berkeley, 

 with those calculated from van't Hoffs equation, the latter is 



