﻿396 Mr. Rollo Appleyard on Dielectrics. 



salt in different solvents. Some numbers have already been 

 given in the July number of l Science Progress, 5 but for the 

 sake of convenience they are reproduced here. The values of 

 the specific inductive capacities of water and ethyl alcohol 

 have been determined by several observers; but apparently the 

 only number for methyl alcohol is one given by Teneschin, 

 so his values for all three liquids are taken, viz. water 83*7, 

 methyl alcohol 32*65, ethyl alcohol 25'8. Correcting these 

 numbers for the viscosities (100; 63; 120) we get the fol- 

 lowing values, which should, if our assumptions are correct, 

 be proportional to the molecular conductivities of a salt in the 

 three solvents :— 



Water = 100; Methyl Alcohol 63; Ethyl Alcohol 26. 



Since these are measured for the pure solvent, they should 

 give the relative molecular conductivity of an infinitely dilute 

 solution. An investigation on the conductivities of very 

 dilute solutions of calcium chloride in ethyl and methyl 

 alcohols is now being made by Mr. Fitzpatrick and the 

 present writer. There are not for these cases such definite 

 limiting values as for water solutions, but the following rela- 

 tive numbers (that of the infinitely dilute aqueous solution 

 being taken as 100) correspond to the greatest dilutions 

 reached : — 



Water 100; Methyl Alcohol 70; Ethyl Alcohol 23. 



The approximation of these numbers to those given above 

 suggest that the specific inductive capacity and the viscosity 

 are at all events the chief factors in determining the u relative 

 ionization power " of a solvent. 



Trinity College, Cambridge, 

 August 15, 1894. 



XLVI. On Dielectrics. By Rollo Appleyard *. 



MOST dielectrics, when submitted to the ordinary " insu- 

 lation " test, show an apparent increase of resistance 

 under the action of the testing-current. That is to say : 

 from the moment the current has been applied, the galvano- 

 meter-spot, having reached its maximum position, falls 

 gradually towards zero with time. The rate of this dimi- 

 nution, at any instant, is a measure of the so-called u electri- 

 fication " of the dielectric at that instant. For commercial 

 purposes the " electrification " is usually computed between 

 the first and second minutes from the moment of charge ; 

 the value thus determined is an excellent confirmatory guide 

 * Communicated by the Physical Society : read May 11, 1894, 



