THE HYDRATE THEORY OF SOLUTIONS 217 



1904, 39, 359) in recognising the combination of the solvent with 

 both anion and kathion, but appears to differ from it in laying 

 greater stress on this property as the one efficient cause of ionisa- 

 tion. The formation of hydrated ions is regarded as the final 

 stage in the progressive hydration of the salt molecule, and has 

 been compared with the biological process of karyokinesis, where- 

 by the excessive growth of a cell results in the formation of two 

 separated individuals each with its own nucleus. The amount 

 of combined water may vary in the case of different ions, and 

 is probably very small indeed in the case of hydrogen and 

 hydroxyl ions ; this hypothesis accounts not only for the great 

 mobility of these ions, but also for the low coefficients of ionisa- 

 tion which are frequently observed in the case of acids and bases, 

 but are much less common in salts which contain neither of 

 these radicals ; there is no reason, however, for supposing that 

 the quantity of combined water is the sole factor in determining 

 the coefficient of ionisation of a salt. The (average) amount of 

 water in combination with the kathion or anion need not be an 

 exact whole number ; indeed, the (average) size of the ion may 

 vary both with the temperature and with the concentration of 

 the solution (Bousfield, Phil. Trans. 1906, 206, 127). It is, how- 

 ever, an essential characteristic of the theory that the solute 

 must be combined with a greater quantity of solvent in the 

 ionised than in the non-ionised condition, 1 since otherwise there 

 would be no force available for producing ionisation, and 

 dilution would favour the formation of the inactive rather than 

 the active form of the solute. 



Although primarily designed to explain the behaviour of 

 aqueous solutions, the hydrate theory of ionisation can readily 

 be modified so as to apply to any solvent which possesses the 

 property of forming compounds of greater stability {i.e. with 

 greater liberation of energy) when combined with a dissociated 

 than with an undissociated salt. It is also applicable to the 

 case of fused salts ; if it is supposed that these also consist 



of an active and an inactive part, the active part may consist of 



+ — 



complexes such as K(KC1) X and Cl(KCl) y , and the inactive part 



of molecules such as KC1 or (KC1) Z ; complexes of the former 



type may also exist in concentrated aqueous solutions which 



exhibit "autolytic " conductivity, i.e. conductivity which is due to 



1 An opposite conclusion has been arrived at by H. C. Jones and Stine {Amer. 

 CJiem. Journ. 1908, 39, 402). 



