18 Mr. W. Sutherland on Weak Electrolytes and 



chemistry fix attention on this successful verification, and 

 proceed to discuss the whole of electrolysis and related 

 phenomena as if ionization were ordinary dissociation un- 

 complicated with any electrical phenomenon. I have sought 

 to show in i( Ionization in Solutions and Two New Tvpes 

 of Viscosity" (Phil. Mag. [6] xiv. p. 1, 1907) that with 

 ordinary electrolytes the ionizing action of the solvent is so 

 powerful that it holds the tendency of the ions to recombine 

 quite in check notwithstanding the strong electric attrac- 

 tions between them. But these electric forces introduce 

 two sorts of viscous resistance which make the mobility of 

 the ions a function of their concentration. This change of 

 mobility is what the prevalent theory interprets as change of 

 degree of ionization in strong electrolytes. In reality 

 ionization is always complete in strong electrolytes at all 

 concentrations. On these grounds it is plain why the 

 current theory of physical chemistry fails to account for the 

 variation of the conductivity of ordinary solutions with 

 concentration, since the law of mass action is not in opera- 

 tion, being suppressed by the ionizing action of the solvent. 

 The '''dilution law " of Ostwald for the electric conductivity 

 of aqueous solutions of acetic acid and similar w r eak electro- 

 lytes must have a different interpretation from that given to 

 it in the text-books of physical chemistry, and seemingly 

 accepted by a theoretical physicist like Planck {Acht Vorles- 

 ungen fiber Tlieoretisclie Physik, S. Hirzel, Leipzig 1910). 

 I have already suggested that in the case of such a weak 

 electrolyte as acetic acid, the double molecules (CH H COOH) 2 

 are partly dissociated in water into CH 3 COOH, all of which 

 is entirely ionized in accordance with the general principle 

 stated above. On this view, the dilution law of Ostwald 

 would express the equilibrium between the ions H# and 

 CH 3 COOt> acting as CH 3 COOH ; on the one hand, and 

 (CH 3 COOH) 2 on the other. 



Here it may be objected, as by Walker at the Faraday 

 Society's Discussion on the Constitution of Water (Trans. 

 Faraday Soc. vi. 1910), that the molecular lowering of the 

 freezing-point of water brought about by acetic acid shows that 

 in dilute but only slightly ionized solutions of acetic acid the 

 acid exists as CH 3 COOH and not as (CH 3 COOH) 2 . Here, 

 again, I think we have to do with the application of an induc- 

 tion to a case which lies outside of its limits. It is easy to see 

 that there are limits to the applicability of the lowering of 

 freezing-point to the measurement of molecular mass. For 

 instance, a little of a solvent added to itself does not lower the 

 freezing-point. Consider next the case in which to a solvent 



