C()NIl'(TIVITV OF SODH'M HYIl:o\II|-; IN AQUKOUS SOLUTION. 293 



On correcting the conductivities shown in Table XIII. for the changes of viscosity 

 shown above, a series of values was obtained for the intrinsic conductivity, and these 

 are shown in contrast with the values for the molecular conductivity in the last 

 column of the same table. A graphical comparison of the two series of constants is 

 given in Diagram IX. The values for the intrinsic conductivity show a remarkable 

 increase of conductivity in concentrated solutions which is entirely masked in the 

 specific and molecular conductivities. The minimum value occurs at about 8 per cent. 

 NaOH, and in a 50-per cent, solution the intrinsic conductivity is nearly half as 

 great again as in the most dilute solutions. This increase of conductivity we 

 attribute to the fact that sodium hydroxide is an autolyte, that is to say, an 

 electrolyte when fused, and may therefore be able in concentrated solutions to 

 conduct the current quite independently of the ionising properties of the 

 solvent. 



Although it was obvious that the conductivity of concentrated aqueous salt 

 solutions might be in part autolytic, we had hitherto been able to obtain no direct 

 experimental evidence in support of this view. The case of sodium hydroxide is, 

 however, especially favourable for the observations of this property, since its high 

 solubility and low melting-point combine to produce in the concentrated solution a 

 condition approximating unusually closely to that of the fused salt. Thus the 

 minimum value in the intrinsic conductivity of zinc sulphate, to which attention has 

 been called by SUTHERLAND (' Phil. Mag.,' 1902, VI., voL 3, p. 171), is reached in a 

 normal solution for which I/I = 0'312, but the measurements of conductivity and 

 viscosity have only been carried as far as 5N, when the value of I/I rises to 0*443. 

 This small increase in the intrinsic conductivity might conceivably have been due, 

 not to the autolytic conductivity of the salt, but to some secondary cause, such for 

 instance as over-correcting for the influence of viscosity. Such an explanation can 

 scarcely be maintained in the case of sodium hydroxide, in which the value of I/I, 

 after falling to 0'0834 at 8 per cent. NaOH, rises again to T35 in a 50-per cent, 

 solution. 



These values apply to solutions at 18 C., a temperature at which the unconnected 

 specific and molecular conductivities give no indication of autolytic conductivity. 

 As the temperature rises, however, the extreme viscosity of the concentrated 

 solutions disappears, and the condition of the solutions approximates more and more 

 to that of the fused salt, so that at 50 C. and 100 C. evidence of autolytic 

 conductivity may be seen in the simple isothermal conductivity-concentration curves 

 of Diagram XIII. These are described in Part VII. of the paper. 



Clear indications having thus been obtained of autolytic conductivity in aqueous 

 solutions of sodium hydroxide, it was not difficult to find other cases in which the 

 abnormal properties of a solution could be referred to the same cause. This is 

 notably the case with the solutions of zinc sulphate, ammonium sulphate and calcium 

 chloride, for which SrTiiKKLAND found a minimum value of \jf. These minima were 



