362 Dr. James Walker on the 



Cliem. iv. p. 9(5), Arrhenins published a paper on this very 

 subject under the title " Ueber die Dissociationswarme und 

 den Einfluss der Teniperatar auf den Dissociationsgrad der 

 Elektrolyte ;" yet of the existence of this important memoir 

 Mr. Pickering is completely ignorant, although an abstract of 

 the results is contained in the Brit. Assoc. Report, 1890, 

 pp. 220-223. In it the whole subject is discussed in great 

 detail, numerical values being given for the heat of dissociation 

 in nearly thirty instances. Some of them are positive, some 

 negative, and mostly all are small. One of the most striking, 

 if not one of the main, points in this paper is the prediction 

 given by the dissociation theory of the existence of (hitherto 

 unknown) electrolytic solutions with negative temperature- 

 coefficients for the conductivity, and the perfect fulfilment of 

 the prediction in the cases investigated (Brit. Assoc. Report, 

 1890, p. 223 ; Sack, Wied. Ann. xliii. p. 212). 



A few paragraphs further on (p. 23) it is asked : — " How can 

 it be maintained that the positive electrification of the hydrogen 

 and the negative electrification of the chlorine would dissolve 



the union between them ? Further, if these so-called 



+ and — charges repel each other, why are they attracted 

 by the — and + charges respectively on electrodes during 



electrolysis ? On the new theory, the electric charges 



are the cause of decomposition." Here, again, there are put 

 into the mouths of the dissociation ists words which they 

 never uttered. No one has stated that the electrical charges 

 are the cause of dissociation, although they always accompany 

 the phenomenon ; nor has any one ventured to assert that the 

 + and — charges repel each other, — in fact, the assumption 

 that they attract each other as usual is the basis on which 

 Nernst has built his elegant theory of the diffusion &c. of salt- 

 solutions (Zeitsc/ir. pliysikal. Chem. ii. p. 617). In a com- 

 pletely dissociated solution — one of hydrochloric acid let us 

 assume — the positive and negative atoms are no longer paired 

 off together, but there is rather supposed to exist a complete 

 communism amongst the charged atoms. The positive ions 



(H) still attract the negative ions (CI), but one hydrogen ion no 

 longer exhausts all its attraction on one chlorine ion. There 

 is rather, now, attraction between it and all the chlorine ions in 

 its neighbourhood ; and, similarly, any one chlorine ion is 

 attracted in all possible directions by the hydrogen ions sur- 

 rounding it. It is only when the positive ions are separated 

 en bloc from the negative ions, that the electrostatic forces 

 between the opposite kinds of electricity become evident. 

 After discussing the Clausius-Williamson hypothesis from 



