44 



SCIENCE 



[N. S. Vol. XXXI. No. 785 



solves the camphor or the camphor the 

 antimony trichloride is clearly an idle 

 question. "We may regard either the one or 

 the other as the solvent, for this is ob- 

 viously a purely arbitrary matter. Let us 

 now raise the following question: In the 

 syrupy liquid that has been formed by the 

 action of antimony trichloride and cam- 

 phor on each other, how much of the cam- 

 phor present is combined with the anti- 

 mony trichloride that has been employed^ 

 The answer is perfectly obvious, for clearly 

 all of the antimony trichloride is combined 

 with all of the camphor in the syrupy 

 liquid that has been formed. One might 

 as well ask the question: When mercury 

 and oxygen unite to form mercuric oxide, 

 how much of the oxygen present is united 

 with the mercury that the oxide contains? 

 Clearly here too all of the oxygen is united 

 with all of the mercury present. When 

 the solution of antimony trichloride and 

 camphor is heated, the vapor obtained 

 contains both of the ingredients. Simi- 

 larly when we heat mercuric oxide the 

 vapor contains mercury and oxygen. We 

 see thus that the cases are essentially simi- 

 lar in character, the only difference being 

 that in the case of the solution in question 

 we have a compound according to variable 

 proportions, whereas in the mercuric oxide 

 we have a compound according to definite 

 proportions. 



Now when ice acts on sodium chloride is 

 not the ease quite similar to that of cam- 

 phor and antimony trichloride? Suppose 

 we knew of no temperature above 0° C, 

 would any one argue that the solid ice dis- 

 solved the solid salt in the process of form- 

 ing the brine? Certainly not, we should 

 say that the brine has been formed by the 

 union of the ice with the salt. And here 

 similarly the question as to how much of 

 the salt in the brine is united with how 

 much of the water in the latter is quite 

 idle, for obviously all of the salt used has 



united with all of the ice. The ease would 

 clearly not be altered if we started with 

 liquid water and solid salt and formed the 

 brine by the interaction of the two sub- 

 stances. This view, that in a solution all of 

 the substances present are united with 

 one another just as all of the elements 

 in a definite compound are combined with 

 one another, is to my mind the only ra- 

 tional view we can take of the matter. It 

 is not new ; on the contrary, it is quite old. 

 It has been held quite generally by scien- 

 tists prior to 1887, when the physical theo- 

 ries came upon the stage and diverted at- 

 tention into other channels, as already 

 stated, with the result that the true nature 

 of solutions has been thoroughly obscured. 

 If now we dilute the brine with more water, 

 does the water added combine further with 

 the salt present? Most assuredly, for is 

 not the vapor tension of a brine, however 

 dilute, lower than that of pure water, and 

 does not this show that the water in the 

 brine experiences greater difBculty in 

 evaporating because of the mutual attrac- 

 tion between the salt and the water? 

 Were any of the latter uneombined with 

 the salt of the brine, this uneombined 

 water would show the same vapor tension 

 as pure water; but a brine of the same 

 vapor tension as pure water of the same 

 temperature does not exist. 



The phase rule of Willard Gibbs marks 

 a great advance in the study of hetero- 

 geneous equilibrium. Through the prac- 

 tical work of Bancroft, Roozeboom and 

 numerous other able chemists, the phase 

 rule has borne rich fruits. In all of this 

 work the composition of the phases that 

 are in equilibrium with one another under 

 given conditions of temperature and pres- 

 sure was carefully determined. This work 

 has revolutionized solubility determina- 

 tions, placing them upon an accurate 

 scientific footing. Nowadays when the 

 solubility of a compound is to be thor- 



