461 Prof. F. P. Worley on the Decline of the 



Thus Stieglitz * writes — 



" In the case of the catalysis of the esters we are certain 

 of three main facts which have been proved experimentally r 

 the action is accelerated in proportion to the concentration o£ 

 the hydrogen ions present ,„,.,. " 



Acree and Johnson f, in reference to their explanation of 

 hydrolytic change, say — 



"The assumption explains , t why the velocity of sapo- 

 nification and esteritication increases directly in proportion 

 to the concentration of the hydrogen ions." 



The fact, however, has Jong been patent that this is by no 

 means the case. The entirely opposite effects of dilution on 

 the molecular hydrolytic activity and the degree of presumed 

 ionic dissociation of hydrogen chloride in aqueous solution 

 is clearly shown in Table I. On applying Acree's method 

 to this case, in which cane-sugar was the hydrolyte, we 

 arrive at the conclusion (see Table II.) that the undissociated 

 molecule of hydrogen chloride is as much as twelve times 

 as active as the hydrogen ion. The experiments were not 

 carried out for this purpose and the changes of concentration 

 are not great enough to give smooth results : but there can 

 be no doubt that on Acree's assumption the molecule is- 

 far more active w T hen non-dissociated than when dissociated 

 into ions. 



The molecular hydrolytic activity of the stronger acids 

 generally in aqueous solutions decreases with dilution; and 

 if we assume that the divergence from the course followed 

 by the degree of ionic dissociation is due to the fact that the 

 molecules and ions are both active, we are driven to admit a 

 degree of activity for the acid molecule greater than that of 

 the presumed hydrogen ion. 



Now it is the close connexion that exists between chemical 

 activity, especially as exhibited by precisely the above hydro- 

 lytic activity and the degree of ionic dissociation measured 

 electrically, that has appeared to form so strong an argument 

 in favour of the ionic dissociation hypothesis; and, indeed,, 

 if it could be maintained, as most supporters of the hypothesis 

 have believed to be the case, that the chemical activity of 

 acids is proportional to the concentration measured electro- 

 lytically of the dissociated ions, presumed to be alone 

 responsible for the acidity, there would undoubtedly be con- 

 siderable support for the ionic dissociation hypothesis. The 

 admission, however, that the hydrogen ions and the undis- 

 sociated acid molecules are both active chemically undermines- 



* Amer. Chem. Journ. xxxix. p. 30 (1908). 

 t Ibid, xxxviii. p. 341. 



