Dielectric Properties of Solid Glycerine. 



241 



" Some Dielectric Properties of Solid Glycerine." By Ernest 

 Wilson, Professor of Electrical Engineering, King's College, 

 London. Communicated by Sir William Pkeece, K.C.B., 

 F.B.S. Received January 7,— Read January 22, 1903. 



At high frequency, obtained by resonance, Thwing gives 56*2 for 

 the specific inductive capacity of glycerine at 15° C* The specific 

 inductive capacity of pure liquid glycerine at 8° C. was found to be 

 about 60, whether the frequency of experiment was of the order 

 2 million or 100. f At a frequency of 120 the specific capacity of 

 glycerine varies from about 60 to 4*6, as the temperature is varied 

 from - 50° to - 100° in platinum degrees. % The present paper deals 

 with the specific capacity of glycerine at temperatures varying from 

 about + 10° to - 80° C. The methods of experiment and the apparatus 

 are those described in connection with the earlier experiments.! The 

 platinum plates forming the electrodes of a condenser were placed in 

 pure glycerine, supplied by Messrs. Hopkins and Williams, and after a 

 preliminary experiment, made to find its conductivity (see table), the 

 glycerine was frozen by aid of carbonic acid snow. The temperature 

 of the glycerine was observed by aid of a platinum thermometer. 

 At - 48° C. the specific capacity at about 2 million periods per second is 

 3*97. At - 44° C. the specific capacity at about 100 periods per second 

 is 54, which is of the same order of magnitude as that given by Fleming 

 and Dewar. The conductivity of this condenser at - 59° C, and with 

 times of contact varying from 0-00002 to 0*009 second, was found and 

 is shown by the curve No. 1 in the accompanying figure. If K be the 

 instantaneous capacity and C the electric resistance, then the total 

 capacity of the condenser at time t is 



Now the capacity of this condenser at - 48° C. at about 2 million 

 periods per second is '00032 micro-farad, and the value of 



;'0-009 



— ,H t, as given by the curve, will only account for 



J 0-00002 C Coo 



•0*00018 micro-farad. Assuming that it will be the residual charge 

 which comes out in one-sixth of the period which produces the effect 

 on the capacity, a large proportion of the residual charge comes out 

 between the times T V x 10 _l5 and 20 x 10 _0 second. If the refractive 

 index of the glycerine when frozen is taken to be 1*47 for short times, 

 then Maxwell's law would indicate a specific capacity of 2*17 ; and 



* ' Zeitsclirift for Pkysikalische Cheniie,' vol. 14, p. 293. 

 f Hopkinsonand Wilson, 'Phil. Trans.,' A, vol. 189 (1897), pp. 109—136. 

 X Fleming and Dewar, ' Proc. Roy. Soc.,' vol. 61, p. 316. 

 VOL. LXXI. T 



