Constants of Electrolytic Solutions. 813 



VII. Dielectric Constants of Solutions. 



Four substances were chosen for investigation : — 



Sugar : a typical non-electrolyte. 

 Potassium chloride : a uni-uni-valent electrolyte. 

 Copper sulphate : a bi-bi-valent electrolyte. 

 Tetraethylammonium napthalene-/3-sulphonate : a uni- 

 uni-valent electrolyte with comparatively large ions. 



(a) Sugar Solutions. — Three concentrations were used ; 

 the traces of saline impurity in commercial sugar gave the 

 solutions an appreciable conductivity (the 20-per-cent. 

 solution had a conductivity comparable with that of 0*001 

 normal KC1 solution). 



Table IX. — Dielectric Constants of Sugar Solutions. 

 Wave-length in air = 45*5 metres. K = 38*4. 



Percentage of sugar 684 11'92 20'6 



Temperature (° C.) 13 14 16 



D for solution 81*2 69'8 (79 c.) 



D for water 82'8 82'45 81*75 



Eatio 0-985 085 



The last horizontal row gives the ratio of D for the 

 solutions to that of water at the same temperature. Inter- 

 polation of Harrington's results 30 gives 0*975 and 0*96 for 

 the corresponding ratios; Drude 17 , using waves of 2 metres 

 length in air, found for the square of the refractive index of 

 a 40-per-cent. solution the value 67*5. He noted " strong- 

 absorption " equivalent to that of a solution having con- 

 ductivity 3 x 10 ~ 7 , though the actual conductivity, as tested 

 by the ordinary methods, was only 6 x 10 -10 . 



(b) Potassium chloride. — In the case of the more con- 

 centrated solutions the maximum current was so small that 

 accuracy in adjusting the condenser was very poor. The 

 necessary corrections are large and depend on a number of 

 observations, and hence the values obtained for D are 

 untrustworthy and are not quoted. It will be seen that 

 very fair agreement was obtained between values of the mole- 

 cular conductivity (A) and those obtained by Kohlrausch*. 



* As the apparatus was designed with a view to making- the effects 

 due to conductivity as small as possible, the accuracy with which A nmv 

 be determined is also small. 



