lo CELLULAR 



water will be twice as great. This follows from 

 the fact that the osmotic pressure is proportional 

 to the number of molecules present (since sugar 

 molecules do not split up in solution, as do mole- 

 cules of inorganic salts), de Vries found that a 

 5 per cent solution of raffinose had less osmotic 

 pressure than a 5 per cent solution of sugar, 

 hence it must contain fewer molecules and its 

 molecular weight must be greater than that of 

 cane sugar. His calculations gave a molecular 

 weight of 596, which differs by only a third of 

 I per cent from one of the molecular weights 

 (594) proposed by the chemists. 



Much of the work of de Vries in this field 

 preceded the investigations of van't Hoff and 

 Arrhenius and helped to lay the foundation for 

 them. This was particularly the case with regard 

 to the substances which produce unexpectedly 

 great osmotic pressure, de Vries rendered an in- 

 dispensable service by calling attention to these 

 cases and by carefully measuring the pressure 

 produced, thus paving the way for the work of 

 Arrhenius. 



About this time important studies on the 



