384 Conduction in Solutions and Gases, 



Interpreting the properties discovered by Kohlrausch* in the 

 light of the ideas of Williamson and Clausius regarding the 

 spontaneous dissociation of electrolytes, Arrhenius inferred that 

 in very dilute solutions the electrolyte is completely dissociated 

 into ions, but that in more concentrated solutions the salt is 

 less completely dissociated; and that as in all solutions the 

 transport of electricity in the solution is effected solely by the 

 movement of ions, the equivalent conductivityf must be pro- 

 portional to the fraction which expresses the degree of ionization. 

 By aid of these conceptions it became possible to estimate the 

 dissociation quantitatively, and to construct a general theory 

 of electrolytes. 



Contemporary physicists and chemists found it difficult 

 at first to believe that a salt exists in dilute solution only 

 in the form of ions, e.g. that the sodium and chlorine exist 

 separately and independently in a solution of common salt. 

 But there is a certain amount of chemical evidence in favour 

 of Arrhenius' conception. For instance, the tests in chemical 

 analysis are really tests for the ions ; iron in the form of a fer- 

 rocyanide, and chlorine in the form of a chlorate, do not respond 

 to the characteristic tests for iron and chlorine respectively, 

 which are really the tests for the iron and chlorine ions. 



The general acceptance of Arrhenius' views was hastened 

 by the advocacy of Ostwald, who brought to light further 

 evidence in their favour. For instance, all permanganates 

 in dilute solution show the same purple colour; and 

 Ostwald considered their absorption-spectra to be identical ;J 

 this identity is easily accounted for on Arrhenius' theory, by 

 supposing that the spectrum in question is that of the anion 

 which corresponds to the acid radicle. The blue colour 

 which is observed in dilute solutions of copper salts, even 

 when the strong solution is not blue, may in the same way be 



* Cf. p. 374. 



t I.e. the ohmic specific conductivity of the solution divided by the number of 

 gramme-equivalents of salt per unit volume. 



J Examination of the spectra with higher dispersion does not altogether 

 confirm this conclusion. 



