WEIGHT-NORMAL SYSTEM FOR SOLUTIONS. 105 



osmotic pressure. They have never made any claim to the discovery 

 of this system, as has been intimated by one critic of their work. Such 

 a claim would have been absurd in the light of the fact that the "weight- 

 normal" system was the obvious and the already known alternative of 

 the "volume-normal," or more usual, system of making up solutions. 



The question now to be answered is whether the experimental data, 

 as far as they have been acquired up to the present time, do, or do not, 

 appear to justify the wisdom of the choice which was made and to 

 call for its continuance in use. The strongest evidence which could 

 be adduced in favor of any system would be the fact that, under it, 

 the osmotic pressures of the solutions appear to conform to a definite 

 temperature coefficient and to bear some definite relation to concen- 

 tration. It is not at all necessary, in order to give weight to the 

 evidence, that the relations in question shall be found to conform to 

 the laws of Gay-Lussac and of Boyle for gases. Evidence pointing 

 equally clearly to the existence of other laws than these would be 

 quite as convincing. The facts are, however, that, under the weight- 

 normal system, all the reliable osmotic evidence thus far gathered 

 points emphatically either to a substantial conformity with the laws 

 of Gay-Lussac and of Boyle for gases, or to a species of non-conformity 

 which is rationally and adequately explainable on the supposition that, 

 at moderate temperatures, some of the solutes are hydrated. A brief 

 resume is given below of the established facts which bear upon the 

 question of the obedience of osmotic pressure in aqueous solutions to 

 the laws of Gay-Lussac and of Boyle. 



(1) It has been shown that in all solutions of cane sugar, from 0.1 

 to 1.0 weight-normal, the ratio of the observed osmotic to the estimated 

 gas pressure of the solute is constant for each concentration between 

 0° and 25°. This proves that, between the specified limits of concentra- 

 tion and temperature, the osmotic pressure of cane-sugar solutions 

 obeys the law of Gay-Lussac for gases. 



(2) The ratio in question exceeds unity in every instance. This 

 suggests, of course, a concentration of the solutions through a with- 

 drawal of some of the solvent for the purpose of hydrating the solute. 

 If hydration exists, it must be constant in quantity for each concen- 

 tration of solution within the given limits of temperature; for, other- 

 wise, the law of Gay-Lussac could not hold. 



(3) The osmotic pressure of cane-sugar solutions, between 0° and 25°, 

 are not proportional to the quantities of the solute. In other words, the 

 ratio of osmotic to gas pressure varies from concentration to concentra- 

 tion, though, as stated under (1), it is strictly constant for any given 

 concentration. This leaves the applicability of Boyle's law in doubt, 

 but does not demonstrate its inapplicability; for the phenomenon may 

 be due to differences among the various concentrations of solution in 

 respect to the degree of hydration which they have severally suffered. 



