466 Decline of the Hypothesis of Ionic Dissociation. 



conclusions arrived at by Acree and his co-workers and by 

 JBredig and Snethlage. On the other hand, if they do not 

 accept them, the equally grave difficulties which these in- 

 vestigators have attempted to remove still remain unexplained 

 on their hypothesis. 



The Arrhenius hypothesis undoubtedly owes its great 

 popularity to the remarkably simple picture it professes to 

 give of the nature of solutions of electrolytes and the pro- 

 cesses occurring in them. Unfortunately, the picture is a 

 great deal too simple. Of its various shortcomings, mention 

 may be made here of its almost complete disregard of the 

 part played in chemical interactions by the solvent, a defect 

 of the very greatest importance. Again, it expresses all 

 changes in activity as being due to changes in the mere 

 number of the active units, ignoring the possibility of altera- 

 tions in the degree of activity of the active units accompanying; 

 changes in dilution. This is the more remarkable now that 

 ionists recognize that if not hydrated, ions are at least sur- 

 rounded by spheres of attached water molecules and that the 

 amount of attached water is dependent on the dilution. The 

 part played in chemical change by this attached water is not 

 considered nor the fact that the condition of the water not so- 

 attached is altered by the presence of substances in solution. 

 Water, it must be remembered, is a complex equilibrated 

 mixture of different polymers of the simple molecule repre- 

 sented by the formula H 2 (hydrone) and the presence of 

 any dissolved substance is almost certain to disturb the 

 equilibrium. 



On the other hand, the accumulated evidence in favour of 

 chemical interaction being preceded by association of the- 

 interacting molecules is very great indeed. In the case of 

 hydrolysis effected by the agency of enzymes, there is little 

 doubt that the enzyme and the hydrolyte become intimately 

 associatecl before hydrolysis takes place. When acids are 

 the lrydrolytic agents, the phenomena observed under the 

 most varied conditions are apparently quite in accord with 

 the view: that hydrolysis is effected by the association and, 

 subsequent interaction of a molecule of the hydrated catalyst 

 with one of the hydrated hydrolyte: that the acid catalyst 

 presents water to the hydrolyte in much the same way as 

 does the enzyme. It is apparently only the water actually 

 attached to the interacting molecules that enters directly 

 into the hydrolytic change. The complexes which are formed 

 may break down in various ways and many of the cleavages 

 result in a return to the original components, only a fraction 

 being effective as far as hydrolysis is concerned. Decrease 



