26 SCIENCE PROGRESS. 



same number of molecules as there are of dissolved 

 sugar. 



In no case is the difference between observed and 

 calculated numbers considerable. 



Now it has been shown by the relative methods that 

 solutions of indifferent substances which at the same tem- 

 perature have the same osmotic pressure as a sugar solution 

 contain, per unit volumes, the same number of dissolved 

 molecules as the sugar solution. Hence it follows that 

 these substances as well as cane sugar conform to Avo- 

 gadro's hypothesis as applied to solutions. Equimolecular 

 solutions of each at the same temperature exert the same 

 osmotic pressure, and this pressure is the same as that 

 which the dissolved substance would exert if it were gasi- 

 fied and if it occupied at the same temperature a volume 

 equal to that of the solution. 



J. W. Rodger. 



(To be continued.) 



