302 



MR. W. R. BOUSFIELU AND DR. T. M. LOWRY ON THE ELECTRICAL 



it was of interest to determine the character of the change produced by alterations 

 of temperature in the isothermal conductivity-concentration curve of Diagram VII. 

 The curves for C., 18 C., 50 C., and 100 C. are shown in Diagram XIII., and the 

 data are tabulated in Table XV. The most striking features are : 



(1.) The great increase in the maximum specific conductivity and the gradual 

 shifting of the maximum in the direction of the more concentrated solutions ; this 

 is shown in Table XVI. 



TABLE XVI. 



(2.) A remarkable holding up of the conductivity of the most concentrated 

 solutions. Thus the conductivity of a 50-per cent, solution at C. is 5 per cent, 

 of the maximum, at 18 C. 24 per cent., at 50 C. 47 per cent., and at 100 C. 

 84 per cent. 



(3.) It is noteworthy that the isothermal curves for 50 C. and 100 C. give clear 

 indications that at these temperatures liquid (over-cooled) sodium hydroxide would 

 possess a very considerable conductivity. The power to conduct in the fused state is 

 necessary, in order to explain the form of the two isothermal curves referred to, and 

 the fact that this effect can already be detected in solutions containing less than 50 per 

 cent. NaOH affords very strong confirmatory evidence of the view arrived at from the 

 study of the intrinsic conductivity in Part VI. of the paper, that in concentrated 

 aqueous solutions the conductivity of sodium hydroxide is to a large extent indepen- 

 dent of the ionising power of the solvent, and depends on the self-ionising properties 

 of the liquid alkali. If reference be made to the curves in Diagram XIII., it will be 

 seen that whilst the curve for C. leads down almost to zero value for the conduc- 

 tivity at concentrations above 50 per cent. NaOH, the curves for 50 C. and 100 C. 

 cannot be brought down to the axis of concentration, except by introducing an 

 additional point of inflexion in the curve, which there is no reason to suppose exists. 



Form of the Curves. Cubic Formula. Hitherto the conductivity-temperature 

 relations have been expressed exclusively by linear or parabolic formulae, but these 

 are obviously incapable of representing a curve containing a point of inflexion. The 

 normal solution of sodium hydroxide, which shows the inflexion very clearly, formed 

 the starting-point of the investigation of the form of the curves which is now 

 described. The series of values given in Table XVII. having been obtained, a curve 

 was plotted of the approximate values of dx/dt at different temperatures obtained by 



