192 DISCUSSION OF EVIDENCE. 



to the present solvate theory of solution, it would differentiate it funda- 

 mentally from the older hydrate theory. 



The present theory is not simply a hydrate theory of aqueous solu- 

 tions. Evidence has been obtained, and is herein briefly discussed, 

 which shows that solvents other than water combine with the dis- 

 solved substance. This has been established for the alcohols by the 

 boiling-point method, and for the alcohols and many other solvents by 

 spectroscopic investigations. Indeed, enough evidence has already been 

 obtained to make it highly probable that solvation is not limited to 

 aqueous solutions, but is a general property of solutions. Solvents in 

 general have more or less power to combine with substances dissolved in 

 them in a word, we have the solvate instead of simply a hydrate theory. 



A method has been worked out in this laboratory for determining 

 the approximate composition of the hydrates existing in aqueous solu- 

 tions. This makes the present theory useful scientifically. We can 

 now determine approximately the amount of " combined" and the 

 amount of " free " water existing in any given aqueous solution. Thus, 

 our theory is placed upon a workable basis, and enables us to determine, 

 in any given case, how much of the liquid present is really playing the 

 role of solvent. 



The evidence pointing to the general correctness of the solvate theory 

 of solution is, then, so strong that it seems that this conception is in 

 accord with a fundamental condition in connection with the nature of 

 solution. 



Further, our solvate theory of solution is very different from the 

 earlier, unproved hydrate theory of Mendeleeff. 



The question now arises, of what scientific significance or value is the 

 establishing of the fact that there is more or less combination between 

 the dissolved substance and the solvent? 



SIGNIFICANCE OF THE SOLVATE THEORY OF SOLUTION. 1 



The evidence for the solvate theory of solution, which has been fur- 

 nished in this laboratory as the result of somewhat more than a dozen 

 years of investigation, has recently been brought together and briefly 

 discussed. 2 The evidence is so unambiguous and convincing, that ions 

 and some molecules combine with more or less of the solvent, that it 

 seems that it can now be accepted as a fact of science. 



This, however, raises a number of questions : What relation does the 

 solvate theory of solution bear to the theory of electrolytic dissociation? 



Does the solvate theory help us to explain any of the apparent dis- 

 crepancies in the theory of electrolytic dissociation? Does the solvate 

 theory help us to explain the facts of chemistry in general and of 

 physical chemistry in particular? Why is the nature of solution so 

 important, not only for chemistry but for science in general? 



1 This section is taken directly from my paper in the Journal of the Franklin Institute, Dec. 1913. 

 2 Zeit. phys. Chem., 74, 325 (1910). 



