New Theories of Solution. 361 



and with the principle of the conservation of energy." It is 

 a curious fact, and one not without a certain significance, that 

 it has been left to chemists to discover that the dissociation 

 theory is at variance with the fundamental principles of 

 energy, while physicists, on the other hand, have preferred to 

 base their objections on more or less purely chemical grounds. 

 Prof. Oliver Lodge, for example, refers to " that extreme 

 state of dissociation which physically seems to be so satisfac- 

 tory and chemically so abhorrent " (Brit. Assoc. Report, 1890, 

 p. 331). Surely if the theory is such as to satisfy so eminent 

 an authority as Prof. Lodge on the physical side, Mr. Picker- 

 ing need not concern himself to show that it is in contradic- 

 tion to the fundamental laws of energy. What it contradicts 

 is Mr. Pickering's preconceived ideas of the nature of atoms 

 and molecules and the energy associated with them*. 



In his criticism in the July number of this Magazine 

 (p. 21) Mr. Pickering lays great stress on the fact that the 

 supporters of the dissociation theory sometimes speak of the 

 heat of electrolytic dissociation as being positive, sometimes 

 as being negative. Arrhenius, in his original paper (1884), 

 stated that heat was absorbed on dissociation ; whereas " they 

 now hold, I believe, that the decomposition of molecules into 

 ions evolves heat/' " This change of front must rather be 

 inferred directly from the writings of dissociationists than 

 from any definite retraction which they have published ; nor 

 does it appear to have been followed by all the supporters of 



the theory It may also be remarked that up to July 



1889 Ostwald seems to have held both views, and to have 

 adopted either just as the exigencies of the case suggested. . . . 

 The first point, therefore, on which the dissociationists should 

 give us definite information is whether dissociation of a 

 molecule into its ions is supposed to evolve or to absorb heat." 

 If Mr. Pickering had not been more zealous to criticise the 

 dissociation theory than to properly comprehend it, he would 

 scarcely have written these sentences. Two years ago, in the 

 recognized organ of the " dissociationists " {Zeitsclir. physikal. 



* That Mr. Pickering is occasionally liable to mistake divergencies 

 from his own opinions for contradictions to the u recognized principles of 

 science " may also be seen in his paper " On Chemical Action " (' Nature,' 

 xliii. p. 165), where he accuses thennochemists of implying that " physical 

 changes are not subservient to the law of the conservation of energy." 

 He assumes that all chemical reactions must be accompanied by evolution 

 of heat, and explains the known exceptions to this arbitrary principle by 

 introducing dissociation as an accessory process in endothermic reactions. 

 This explanation, given by Berthelot (Mecanique Chimique, ii. p. 452), is 

 rejected by Horstmaun (Physikalische Chemie, vol. i. part 2 of Graham- 

 Otto's LehrbucK) and others as unnecessary. 



