WEIGHT-NORMAL SYSTEM FOR SOLUTIONS. 103 



In view of the fact that van't Hoff had in mind volume-normal 

 solutions only, and referred the gas pressure of the solute always to 

 the volume of the solution, the author is unable to understand just how 

 the adoption of the weight-normal system and the practice of referring 

 the gas pressure of the solute to the volume of the solvent constituted a 

 return to "van't Hoff's original formulation." 



Furthermore, it is not clear what Professor Bancroft has in mind 

 when he says that Morse and Frazer have overlooked the fact that 

 their procedure "contains the tacit assumption that there is neither 

 expansion nor contraction when the two components are mixed." If he 

 means that the assumption in question is to the effect that the volume 

 of the solution is neither greater nor smaller than that of the solvent, 

 he has apparently again failed to apprehend the clear distinctions 

 between the weight-normal and the volume-normal systems for solutions, 

 and has imputed to Morse and Frazer an equal confusion of ideas. 

 If he means, on the other hand, that Morse and Frazer have overlooked 

 or ignored the fact that the volume of the solution is not exactly equal 

 to the sum of the volumes of solvent and solute separately, he is quite 

 misinformed as to the state of their knowledge of solutions, and as to 

 their attitude of mind toward the volume relations in question. 



It was realized in the beginning that the volume relations of solvent, 

 solute, and solution constitute an important phase of the subject under 

 investigation, and that they should be determined with the utmost 

 practicable precision. Accordingly, almost simultaneously with the 

 measurement of the osmotic pressure of cane-sugar and glucose, there was 

 begun a very careful parallel investigation of the volumes of the various 

 weight-normal solutions of those substances. The work at 0° was fin- 

 ished, but that at the higher temperatures is still incomplete. 



An example of the kind of information which was sought is given 

 in Tables 6 and 7. 



The important question — considered in its bearing upon the practice 

 of referring the gas volume of the solute to the volume of the solvent — 

 is not what is the total contraction which is observed when the com- 

 ponents of a solution are brought together, but to what extent does the 

 contraction modify the volume of the solvent itself? Any shrinkage or 

 expansion which may be due to the fact that the solute monopolizes 

 less or more space in the solution than in its previous separate state 

 does not necessarily involve the volume of the solvent. Contraction 

 due to the formation of hydrates in solution does involve the solvent, 

 and it undoubtedly diminishes its volume and concentrates the solution 

 in what may be called the weight-normal sense. This concentration 

 of the solution through hydration of the solute must express itself in 

 the form of an equivalent increase in osmotic pressure. An "ideal" 

 solution, in the "weight-normal sense" is one in which the solvent has 

 the same volume as in the separate state and is otherwise uninvolved. 



