Constants of Pure Ice, tyc, at Low Temperatures. 32S) 



pentine all have such a direction as to show that their dielectric 

 constants decrease with rise of temperature between +10° C. and 

 + 80° C. We find that the constant for glycerine increases from 

 — 185° C. to —lOO C, and hence it follows that it has a maximum 

 value for a certain temperature. 



This fact makes it necessary to be very cautious in drawing con- 

 clusions as to the complete form of the dielectric curve from 

 observations made over a limited range of temperature. A some- 

 what hasty generalisation of this kind has been made by R. Abegg 

 (see Wiedemann's 'Annaien,' 1897, No. 1, p. 59). He measured by 

 Nernst's method the dielectric constants of water, alcohol, and other 

 bodies from +10° C. down to —80° C. with such results as 

 follows : — 



Water. 



Temperature. 



+ io-o° 



+ 20*0 

 -40-0 

 -60-0 

 -80-0 



Dielectric constant 

 (Abegg). 



83-8 



101-0 



112-0 



127-0 



1370 



Ethyl Alcohol. 



+ 14-0 

 -330 

 -616 

 -86-6 



26-4 

 339 

 38-8 

 44-3 



He concludes that the dielectric constant of water would be 372 at 

 the absolute zero of temperature, and that of alcohol would be 80 at 

 —196°. As a matter of fact, both these constants have a value not far 

 removed from 3*0 at the temperature of liquid air, and it is highly 

 improbable that they increase again on further cooling. 



Thus at 15° C. and at —185° C. we have the following dielectric 

 constants for four definite compounds containing molecular groups 

 OH and N0 2 . 



Dielectric constants. 



t * i 



Atl5°C. At -185°C. 



Water, H(OH) 80 2-4 to 2-9 



Ethyl alcohol, C 2 H 5 (0H) 25 31 



Glycerine, C 2 H 3 (0H) 3 56 3'2 



Mononitrobenzol, C 6 H 5 (NO a ). . . . 32 2 6 



VOL. LXI. 



