ELECTROLYTIC DISSOCIATION 31 



rather than upon the supporters of the hypothesis. An analy- 

 sis of this discussion, set forth in proper order, might prove 

 both lengthy and confusing, and I therefore relegate a chrono- 

 logical list of the original papers to the end of this review and 

 confine myself to a brief exposition of the hypothesis as it 

 stands at present, and of the chief objections which have 

 been raised to it. 



The fundamental idea is this: In electrical conductors of 

 the second class electricity can be transported only by elec- 

 trically "active" molecules, i.e., those in which the electro- 

 static charges are not neutralized within the molecule; the 

 ions are able to receive and transport charges, positive and 

 negative respectively, as long as they are separated, but not 

 when they are firmly knit into a neutral molecule. It follows 

 that there can be no conduction without a preexistent partial 

 dissociation of the molecules, which may be occasioned either 

 by heat or more generally by the presence of a foreign body, 

 such as water. It is, for instance, a well-known fact that some 

 of the best conductors, like the strong acids, become insula- 

 tors when freed from the last traces of water, while water 

 itself is classed among the poorest conductors when free from 

 impurities. The mechanism by which water, par excellence, 

 should produce electrolytic dissociation, while alcohol and 

 other solvents do not, has yet to be explained; it does seem 

 strange that such an effect should be produced without a cor- 

 responding dissociation of the water, an idea which Arrhen- 

 ius rejects or admits only to a minimal extent. However 

 that may be, electrolytic dissociation is assumed to be a phe- 

 nomenon closely corresponding to gaseous dissociation and 

 obedient to laws expressed by the same thermodynamic for- 

 mulae, with this difference, that "osmotic" pressure must 

 replace gas pressure. Consequently, dissociation must be 

 increased by dilution (increase of volume) and by heat; but 



