194 DISCUSSION OF EVIDENCE. 



the Zeitschrift fur physikalische Chemie. 1 The amount of the solvent 

 combined with an ion is primarily a function of the nature of the ion 

 or ions in the solution. It is, however, conditioned very largely by the 

 dilution of the solution, and also by the temperature. 



The evidence, some of which is given in the paper referred to above, 

 and the remainder in other publications, of the results of investigations 

 carried out in this laboratory during the past fifteen years, shows 

 that the power of the ions to combine with the solvent is by no means 

 limited to water and aqueous solutions, but is a property of solutions 

 in general. The alcohols, acetone, glycerol, 2 etc., combine with certain 

 substances dissolved in them; and it seems more than probable that 

 all solvents combine with the dissolved substances to a greater or less 

 extent. In a word, we do not have simply a theory of hydration, but a 

 theory of solvation in general, which is an essential part of any general- 

 ization that would take into account the facts presented by solution. 



The solvate theory of solution has been regarded in some quarters 

 as a rival of the electrolytic dissociation theory of solution, if not 

 directly antagonistic to it. Such is not at all the case. The solvate 

 theory begins where the theory of electrolytic dissociation ends. The 

 latter gives us the ions from molecules, and the former tells us the con- 

 dition of the ions in the presence of a solvent after they are formed. 



The solvate theory of solution, then, simply supplements the theory 

 of electrolytic dissociation, and both must be taken into account if we 

 ever wish to understand the phenomena presented by solution. 



DOES THE SOLVATE THEORY HELP TO EXPLAIN ANY OF THE APPARENT 

 EXCEPTIONS TO THE THEORY OF ELECTROLYTIC DISSOCIATION? 



Given the theory of solvation in solution together with that of elec- 

 trolytic dissociation, the first question that arises is, does the former 

 really aid us in explaining the phenomena presented by solutions? 



Shortly after the theory of electrolytic dissociation was proposed, it 

 was recognized and repeatedly pointed out, that after all it is only a 

 theory of " ideal solutions," i. e., very dilute solutions. It was shown not 

 to be able to explain many of the phenomena presented by even fairly 

 concentrated solutions. Indeed, it frequently could not deal quanti- 

 tatively with the very solutions with which we work in the laboratory. 

 The explanation of this shortcoming was not fully seen, and an 

 analogy was resorted to. It was pointed out that the laws of Boyle 

 and Gay-Lussac for gases hold only for " ideal gases," i. e., dilute gases, 

 but do not hold for gases of any considerable concentration. 



It was stated that the gas laws when applied to solutions could not 

 be expected to hold more generally than when applied to gases, and 

 there the matter was allowed to rest. 



1 " Evidence obtained in this laboratory during the past twelve years for the solvate theory of 

 solution." Zeit. phys. Chem., 74, 325 (1910). 



2 " Conductivity and viscosity in mixed solvents," by H. C. Jones and co-workers, Carnegie 

 Inst. Wash. Pub. Nos. 80 and 180. 



