Chapter VIII. 

 Nature of the Carriers in Electrolytic Solutions. 



1. Interaction between the Ions and Polar Molecules. The results 

 given in the preceding chapter indicate that an equilibrium exists between 

 the ions, and possibly the un-ionized fraction, of a dissolved electrolyte 

 and the molecules of an added non-electrolyte of the polar type. If 

 reactions of this type take place between a non-electrolyte and an elec- 

 trolyte, both of which are present in relatively small amounts in the 

 solvent medium, then there is all the more reason for believing that 

 reaction takes place between the electrolyte and the non-electrolyte when 

 the latter is present in large excess. Apparently, the ions in solution do 

 not consist merely of the charged groups present in the original salt, 

 but rather of these groups associated with the solvent. Where the ions 

 possess great tendency to form definite complexes with the solvent, as is 

 the case, for example, with the calcium ion in water and the silver ion in 

 ammonia, a portion of the solvent is present in the form of a definite 

 chemical compound. In addition to this, however, an ion may con- 

 ceivably be associated with a further amount of solvent as a result of the 

 charge on the ion and the electrical moment of the solvent molecules. 



2. Hydration of the Ions in Aqueous Solution. It has been defi- 

 nitely established that in aqueous solutions certain ions are hydrated ; * 

 that is, in passing through the solution they carry water with them. 

 Since the conductance values of all ions in water are of the same general 

 order of magnitude, it follows that all ions are in all likelihood hydrated, 

 save, perhaps, the highly complex ions. 



If the ions are hydrated, then, in the course of a transference experi- 

 ment, water will be transferred toward one electrode or the other. If 



N^ represents the number of molecules of water associated with the 

 anion and N the number of molecules of water associated with the 

 cation and if T is the fraction of the current carried by the anion, that 



1 Lobry de Bruyn, Rec. Trav. Ohim. 22, 430 (1903) ; Morgan and Kanolt, J. Am Chem 

 800. 28, 572 (1906) ; Bucbbock, Ztachr. f. phtfs. Chem. 55, 563 (1906) ; Washburn, J Am 

 Chem. Soc. 31, 322 (1909) ; Washburn and Millard, J. Am. Chem. /S'oc. 37, 694 (1915). 



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