THE NEW THEORY OF SOLUTIONS. 



23 



out, that if the membrane is really semi-permeable 

 its nature can have no influence on the value of the 

 osmotic pressure. It is concluded, therefore, that those 

 membranes giving the lower values were not quite firm, 

 or not quite impermeable to dissolved substance, and the 

 highest value of the osmotic pressure is regarded as being 

 nearest the truth. Even copper ferrocyanide does not 

 seem to be quite impermeable to sugar, as some of 

 Pfeffer's results are considerably lower than those given 

 in the table. The variations in the value of P/C may 

 be in part attributed to this cause. 



Evidence in support of Boyle's law, as applied to 

 solutions, is also furnished by the relative methods, as the 

 ratios of the concentrations of two isotonic solutions is in 

 general the same no matter what the absolute concen- 

 trations may be. From the nature of the methods, the 

 constancy of the ratio can only be investigated over 

 narrow limits of concentration. 



Gay Lussacs law for dilute solutions. — Pfeffer's ob- 

 servations on a one per cent, sugar solution, limited 

 though they are, supply the most extensive data for 

 testing the law. In the table are given the results of 

 three series of observations (a, 6, c), carried out in 

 different porous cells, t is the temperature of observa- 

 tion, P the pressure and R the ratio of P to the absolute 

 temperature. This ratio should be constant if the law is 

 obeyed. 



a 



14-2 



32-0 



6-8 

 i37 



22*0 



\ 36-0 



The ratios vary by some 4 per cent., and since the 



