352 MR. W. C. D. WHETHAM ON THE IONIZATION OF 



a continuous mark has been made ; where the curvature becomes appreciable, a dotted 

 line has been drawn. The divergences of individual observations from the smoothed 

 curves indicate the probable errors of experiment. 



Reasons have already been given for supposing that the ionization at the freezing 

 point differs from that at higher temperatures by an amount which varies as the con- 

 centration of the solutions changes. 



In order to directly compare the values of the ionization for different temperatures, 

 the equivalent conductivities as given by KOHLRAUSCH* for sulphuric acid, potassium 

 chloride, barium chloride and copper sulphate have been taken, and the ionizations at 

 different concentrations calculated from them. The results are placed on the 

 diagrams as crosses, X . It will be seen that the curves so obtained differ in each 

 case from those giving the results of the present work at 0, the ionization at 18 

 falling off more rapidly than at as the concentration increases. At the higher 

 temperature, too, the dilution must be carried further than at the freezing point, in 

 order to complete the ionization. This again is to be expected, for as we have seen 

 (p. 323), the general effect of heating a solution is to decrease its ionization. It 

 must be noticed that, although KOHLRAUSCH'S concentrations are expressed in 

 gramme-equivalents per litre of solution, while the present results are referred to a 

 thousand grammes of solution, the difference produced in the curves by this difference 

 in the method of reckoning is almost inappreciable ; in the case of sulphuric acid 

 where it would be greatest, the change is invisible on the diagram till the last two 

 solutions are reached. 



In order to obtain a more direct comparison, and to eliminate any error due to 

 difference of method, a series of measurements were made for copper sulphate at 18 

 in the present apparatus, the operations being conducted in precisely the same way 



as those at 0. The results are shown by the crosses within circles (>0 in the 



J v^y 



diagram for that salt ; these are connected by a second curve. 



It will be seen that, when this is done, the curves for and 18 are nearly coinci- 

 dent while the concentration varies from the smallest value used to about '001 

 (m* = O'lO). Beyond that value, the slant of the curve again becomes visibly greater 

 for the higher temperature. The results of KOHLRAUSCH'S measurements for this 

 substance (also at 18) are shown on the diagram by plain crosses. At very small 

 concentrations they differ from those made by the present method at the same 

 temperature by an appreciable amount ; but from about the point m = 2 X 10"' 

 (m l -124) onwards, the two sets of results practically coincide, giving a curve 

 much below that representing the ionization at the freezing point. 



* KOHLRAUSCH'S latest lists of conductivities ('Ann. der Physik und Chem.,' N.F., vol. 66, p. 811, 

 1898) give the values as far as a maximum dilution of -0001 normal only. This is not far enough to 

 directly estimate the value corresponding to complete ionization. The older numbers (' Wied. Ann.,' vol. 

 26, p. 195) are therefore used. They differ slightly in their absolute values from the new set, but this 

 will not affect the ionization. 



