8 McBAIN 



the cation and anion respectively, x and y the number of g-mols 

 of water combined with one equivalent of each ion, A the 

 equivalent conductivity, and C the total concentration of the 

 electrolyte expressed as the number of g-equivs solute in one 

 g-mol water. Thus it is evident that if the transport num- 

 bers of the hydrated ions are to be very different from those of 

 Na" and CI', either the ions must differ widely in mobility and 

 have a large amount of combined water, or the difference in 

 hydration of the ions must be great. The numerical example 

 given in the paper quoted shows that in general the change in 

 the transport number caused by assuming that the ions are hy- 

 drated, is small. In very concentrated solutions, however, the 

 difference would be greater : and the h3^pothesis might be 

 checked by measuring the transport of some non-electrolyte 

 added to the solution, choosing one which will not react with 

 the electrolyte in question.^ 



Movement of Undissociaied Electrolyte. 

 The fact that transport numbers for simple electrolytes are 

 independent of the concentration discredits the hypothesis. The 

 movement of non-electrolytes measured by Nernst, Garrard and 

 Opperman^ and by Morgan and Kanolt '' corresponds to a 

 transport number of the order of magnitude of o.oi. This is 

 however a negligible quantity, being within the experimental 

 error of most measurements ; and the alternative assumption of 

 hydrated ions is from other considerations very plausible.* 



Complex Ions, Hydrolysis. 



Three methods have been worked out for dealing with elec- 

 trolytic solutions which are assumed to contain complex ions in 

 equilibrium with simpler ions and undissociated molecules ; the 

 first was developed and applied by Burgess and Chapman, the 

 other two by myself. The first and second methods are appli- 

 cable to special cases only ; the third is general, and may also 

 be employed in dealing with hydrolysis. 



(i) The method of Burgess and Chapman^ is based on the 



' Ibid., II, 961 (1905). 

 ^Nachr. Gott. Akad., 1900, 68. 

 *Zeit. phjs. Chem., 4S, 365 (1904). 

 *See Baur, Ahren's Saminhing, S (1903). 

 *Joiir. Clicm. Soc, 8^, 1305 (1904). 



