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



conveying the current and these ions also were supposed to 

 be the sole cause of chemical interactions. According to 

 this view, dissociation is the immediate antecedent of every 

 chemical interchange, an interpretation which is in opposi- 

 tion to the view, first definitely expressed by Kekule and 

 since advocated by a small school of chemists, notably by 

 Armstrong in England and Michael in America, that asso- 

 ciation of the molecules concerned is the necessary antecedent. 

 The activity of acids has always been attributed by Arrhenius 

 and his followers to their hydrogen ions and a great deal of 

 work has been done with the object of showing the close 

 connexion between such chemical activity and the presumed 

 concentration of the hydrogen ions deduced from measure- 

 ments of electrolytic conductivity. Ostwald's early research 

 on the subject showed that the hydrolytic activity of acids 

 was in the order of the degree of assumed ionic dissociation; 

 and a vast amount of investigation has since been carried 

 out with the object of showing that the one is exactly pro- 

 portional to the other. This object has not been realized 

 and very serious discrepancies have been shown to exist 

 which the supporters of the Arrhenius hypothesis have failed 

 to explain and have frequently been very loath to recognise. 

 One is the influence above referred to which neutral salts 

 exercise upon hydrolytic phenomena. The hydrolytic 

 activity of any strong acid is considerably increased by the 

 addition of a neutral salt of the acid : for instance, when 

 caue-sugar is hydrolysed by an aqueous solution of hydrogen 

 chloride, the rate of hydrolysis is very much increased by the 

 addition of sodium chloride and still more by calcium 

 chloride. The effect produced is entirely opposite to that 

 demanded by the dissociation hypothesis, as instead of in- 

 creasing the concentration of the hydrogen ions the salt 

 should, in fact, diminish it. This " neutral salt action " has 

 received considerable attention, especially from Arrhenius 

 himself; but it has not been satisfactorily explained on the 

 basis of his hypothesis. 



Another difficulty is the fact that the molecular hydrolvtic 

 activity of an acid, at least of a strong acid, decreases as 

 dilution is increased, instead of increasing as it should if its 

 activity were proportional to the degree of ionic dissociation. 

 The acid itself appears to have a " neutral salt action/' This 

 difficulty, which is perhaps the most formidable of all, has 

 been constantly avoided and, as will be shown later, has 

 apparently been entirely overlooked by some of the chief 

 workers on this branch of the subject. 



