ON THE PHYSICAL VIEW OF NATURE. 



163 



dissociation of the electrolyte, was not the consequence, 40. 



Dissocia- 



but the accompanying feature or condition, of the exist- tion - 

 ence of an electric current in a solution. Clausius first 

 expressed this distinctly in 1857, and Helmholtz re- 

 peated it in 1880. The conception was thus intro- 

 duced that in certain (not in all) solutions of chemical 

 compounds dissociation might exist independently of an 

 electric current, and that the latter, if introduced, only 

 directed the already dissociated and wandering molecules 

 (ions), freeing them at the same time of their electric 

 charges. 1 This conception, though at first violently 



breaking-up of chemical compounds 

 not so much through the presence of 

 other chemical agencies as through 

 altered physical conditions, such, 

 notably, as heat, evaporation, and 

 condensation. "Deville's observa- 

 tions on dissociation . . . have a 

 very direct bearing on the kinetic 

 theory of gases, and it is a fact of 

 interest in the history of science 

 that Deville did not recognise the 

 validity of that theory. Our esti- 

 mate of the ingenuity, skill, and 

 patience shown in his experimental 

 work, and of the genius and sound 

 judgment which directed his theo- 

 retical conclusions, is perhaps raised 

 when we recollect that he was 

 neither led in the first nor biassed 

 in the second by ideas derived 

 from the kinetic theory, and his 

 hostile, or at least neutral, attitude 

 towards it gives perhaps greater 

 value to the evidence that his work 

 has contributed to its soundness" 

 (A. Crum Brown, ' Ency. Brit.,' 

 9th ed., article " Sainte Claire 

 Deville "). 



1 I have already mentioned (vol. 

 i. p. 435, note) that Clausius, when 

 introducing his kinetic theory and 

 distinguishing between molecules 

 and atoms, could refer to several 

 eminent chemists who had inde- 



pendently arrived at similar ideas 

 by quite different trains of reason- 

 ing. Again, when introducing, in 

 1857, his theory of dissociation by 

 solution, he~could refer to similar 

 anticipations. Williamson had said 

 already, in 1850 (Liebig's ' Annalen,' 

 vol. Ixxvii. p. 37), at the meeting 

 of the British Association in Edin- 

 burgh : " We are led to the conclu- 

 sion that in an aggregate of mole- 

 cules of every compound there 

 exists a continual exchange of the 

 elements contained in it. Suppose, 

 for instance, that a vessel with 

 hydrochloric acid were filled with 

 a great number of molecules of the 

 compound C1H, then the view at 

 which we have arrived would lead 

 us to the supposition that every 

 atom of hydrogen does not re- 

 main in quiet juxtaposition with 

 an atom of chlorine, with which it 

 is combined, but that there is a con- 

 tinual exchange of places with other 

 hydrogen atoms" (Clausius, 'Me- 

 chanische Wiirmetheorie,' vol. ii. p. 

 167, Braunschweig, 1879). For an 

 illustration of the theory of Clausius 

 modified to meet more recent con- 

 ceptions, see 0. Lodge's ' Modern 

 Views of Electricity,' 1892, p. 83, 

 &c. 



