25(> !UR. W. R. ROrSFIKLD AND DR. T. M. LO\VRY ON THE ELECTRICAL 



(2.) Iiifluence of Viscosity on Conductivity. In the conventional, method of 

 deducing the coefficient of ionisation from the molecular conductivity by means of 

 the equation a = A/A a , it is assumed that the ionic mobility is independent of the 

 concentration. As, however, there is a marked difference (amounting to something 

 like 1 per cent.) between the viscosity of water and that of a decinormal salt solution, 

 it is clear that even at this small concentration some appreciable alteration must be 

 looked for in the ionic mobility, and the method is only strictly accurate at concen- 

 trations less than N/100. In order to correct for the variation of ionic mobility 

 produced by changes of viscosity, we have assumed as a first approximation that the 

 alterations of mobility are proportional to the alterations in the fluidity of the 

 solution. We have used the term " intrinsic conductivity" and the symbol I to 

 represent the ratio obtained by dividing the molecular conductivity by the fluidity of 

 the solution compared with that of water at the same temperature at unity, so that 

 whilst 1= A//, we have I x = A. The coefficient of ionisation is accurately given by 

 the relation a = A/(n-\-v) ; if (u-\- i")/f were constant it would also be given accurately 

 by the relation a = I/I. ; and with the help of this relation we believe that it will be 

 possible to extend the method of determining the coefficient of ionisation from the 

 conductivity to considerably greater concentrations than those within which the 

 validity of the relation =:A/A can be recognised. 



The possibility that the ionic mobility might be influenced by the dielectric 

 constant of the medium as well as its viscosity has been discussed by SUTHERLAND 

 (' Phil. Mag.,' 1902, (vi.), vol. 3, p. 161), but cannot be entered into here. 



(3.) Autolytic Conductivity of Dissolved Salts. All the acids behave as dielectrics 

 when pure, and only become electrolytes when associated with water or some other 

 " ionising solvent." The alkalies, on the other hand, like the majority of salts, are 

 excellent electrolytes when fused, and are believed to conduct the current quite 

 independently of any interaction with other substances. For the purpose of 

 convenience we propose, at Professor ARMSTRONG'S suggestion, to describe these two 

 classes of electrolytes as heterolytes and autolytes. It was conceivable that the 

 conductivity of dissolved salts was not wholly dependent on the ionising properties of 

 the solvent, but could be attributed in part to the mere presence of the liquified salt, 

 which could then conduct in the same way as when fused. An important result of 

 the present investigation has been to show that, when a correction for viscosity has 

 been applied, concentrated aqueous solutions of sodium hydroxide exhibit an 

 " intrinsic conductivity " which is too great to be accounted for by the direct 

 influence of the solvent, and which actually increases with the concentration of the 

 soda. This increase we attribute to the autolytic conductivity of the dissolved salt. 

 A similar effect is manifest in the isothermal conductivity-concentration curves for 

 50 C. and 100 C., which appear to indicate that the fused alkali would be an excellent 

 conductor if over-cooled to these temperatures, and that it contributes largely to the 

 conductivity of the more concentrated solutions. There can be little doubt that 



