Hypothesis of Ionic Dissociation. 461 



An important change o£ front has been made independently, 

 in the same direction, by Bredig and Snethlage* in Germany 

 and by Acreef and his co-workers % in America. These 

 ardent supporters o£ the Arrhenius hypothesis have come to 

 the remarkable conclusion that an electrolyte in solution 

 may enter into chemical interactions both by means of its 

 ions and also by means of its undissociated molecules — that 

 the catalytic action of acids, for instance, is due both to the 

 hydrogen ions and to the undissociated molecules. Such a 

 conclusion is of vital importance but it cannot fail to breed 

 confusion in the ionic camp, as it involves the sacrifice of 

 the very important connexion between electrical and chemical 

 phenomena which has been the mainstay of the dissociation 

 hypothesis. 



Bredig and Snethlage arrived at their conclusion from an 

 investigation of the change in the catalytic activity of an 

 acid produced by the addition of a neutral salt of the acid. 

 The interaction investigated was that between ethylic diazo- 

 acetate and absolute alcohol in the presence of either picric 

 or some other weak acid as catalyst : — 



N 2 HC . COOCW5+ C 2 H 5 OH=C 2 H 5 . H 2 C . CQOC 2 H 5 + N 2 , 



Snethlage found that the hydrolytic activity could be re- 

 duced to a limiting value by adding a sufficient amount of 

 a salt of the acid. He supposes that under these conditions 

 the ionic dissociation of the acid is almost completely sup- 

 pressed and that the observed catalytic activity is due to 

 the non-ionized acid molecules alone. From his results 

 he deduced the ratio of the activities of the undissociated 

 molecules of the acids used to that of the hydrogen ion. 



Acree's conclusion has been arrived at from the study of 

 the effect of dilution on such changes as the interaction 

 of ethyl halides and ethylates or phenolates of the alkali 

 metals dissolved in absolute alcohol, by which change the 

 alkaline halide and an ether are produced, e. g. 



C 2 H 5 I + NaOC 2 H 5 == (C 2 H 5 ) 2 + Nal. 



Constants are obtained expressing the velocity with which 

 the interaction would proceed if the concentration of the 

 ethylate or phenolate were reduced to unity and the deoree 

 oE ionic dissociation at the different dilutions were unchanged. 

 In other words, these constants express the molecular activity 



* Chemiker Zeitwuj, May 25, 1912, p. 087 ; Zeits. Eleldroehem. xviii. 

 p. 839 (1912). 



t Ainer. Chem. Journ. xlviii. p. 352 (1912). 



X Robertson and Acree, ibid. xlix. p. 474 (1913). 



Phil. Mag. S. 6. Vol. 27. No. 159. March 1914. 2 I 



