WEIGHT-NORMAL SYSTEM FOR SOLUTIONS. 



107 



or utility, or, least of all, the character of a general equation. It has 

 still remained — despite its more impressive appearance in mathematical 

 dress — simply a rule, the question of whose validity was to be strictly 

 limited to the already known and fully accredited facts, and which, 

 therefore, was subject to modification as the number of established facts 

 increased. The direct measurement of osmotic pressure is a task of 

 supreme difficulty, and those who would undertake it effectively should 

 qualify themselves for the enterprise by discarding all convictions as 

 to whither their labors may lead them. 



Probably it will be generally conceded that the weight-normal is the 

 simpler and more rational system for the statements of the freezing- 

 point depressions of aqueous solutions. We have determined these in 

 all of the concentrations of solution of cane sugar and glucose which 

 have been employed for the measurement of osmotic pressure, and 

 they are given in Table 8, together with the corresponding molecular 

 depressions of the freezing-points. 



Table 8. — Cane sugar and glucose. — Depression of the freezing-points 



of weight-normal solutions. 



Table 9 is added in order to illustrate and emphasize the limitations 

 of the freezing-point method as a means for the determination of 

 osmotic pressure in aqueous solutions. 



The direct measurement of osmotic pressure is often deprecated on 

 account of the great difficulties which are encountered; and it is fre- 

 quently asserted, with an air of thorough conviction, that there are other 

 methods available which are more accurate and much easier. If this 

 were really true, we should have emerged long ago from our present 

 lamentable state of ignorance with regard to the osmotic pressure of 

 solutions. The very fact that we can not yet make a safe prediction as 

 to the magnitude of osmotic pressure in any aqueous solution which has 

 not been extensively investigated by the direct method is proof enough 

 that these other "more accurate and easier methods" have failed to render 

 the service of which they are said to be capable. 



