THE NEW THEORY OF SOLUTIONS. 



25 



The isotonic coefficients of the four substances as 

 found by the different methods are approximately equal. 



Tamman by his optical method obtains results for six 

 indifferent substances. He uses potassium ferrocyanide 

 as standard. If n be the gram molecular weights of 

 this salt dissolved in 1000 gr. of water he finds for n = 1 

 and for n = 3 the ratios R of the isotonic molecular 



concentrations of the indifferent substances, 

 are as follows : — 



His results 



In general, the above results support the idea that equal 

 volumes of indifferent isotonic solutions are equimolecular. 

 In order to test the validity of Avogadro's hypothesis 

 in the case of the absolute measurements on sugar the 

 osmotic pressures have to be compared with the corre- 

 sponding gaseous pressures. The following table gives 

 the comparisons of the osmotic pressure P at different 

 temperatures /, with the gaseous pressure P' calculated by 

 the equation P' = 49/27 (1 + -00367/). This equation 

 gives the pressures which would be exerted by a volume 

 of gas equal to that of the solution and containing the 



