316 Profs. J. A. Fleming and J. Dewar. On the Dielectric 



(i) Frozen electrolytes at low temperatures are capable of acting 

 as dielectrics even in the case of those substances which in 

 the liquid state and in aqueous solutions have relatively a 

 very high electrolytic conductivity. 



(ii) At temperatures not far removed below their freezing points, 

 these electrolytes have dielectric constants of large value, and 

 numerically of the order of that of ice or water at 0° C. or 

 in some cases much larger. 



(iii) The majority of these high dielectric values so far as observed 

 are reduced to very much lower values (near to 3) when the 

 dielectrics are cooled to, and below the temperature of, liquid 

 air. 



(iv) Certain aqueous solutions of potash retain their high dielectric 

 values to nearly the liquid air temperature, but give indication 

 of being reduced at lower temperatures to small values. 



(v) Frozen electrolytes at very low temperatures have very great 

 insulating power, but recover sensible conductivity with great 

 rapidity at temperatures far below their melting points. 



(vi) It appears probable that at the absolute zero of temperature 

 all electrolytes become perfect non-conductors of electricity or 

 have infinite resistivity, also that it is possible their dielectric 

 constants may all be reduced to, and represented by, a number 

 near to 2 or 3 at that temperature, that of a vacuum being 

 taken as unity. 



We are engaged in examining as many electrolytes as possible at 

 low temperatures to test the validity of the above last inference. In 

 conclusion, we have again to thank Mr. J. E. Petavel for much 

 valuable assistance in the laborious work of taking these observations, 

 a work which has necessitated frequently very considerable endurance, 

 in consequence of the fact that such series of observations, when once 

 begun, had to be continued often through the night without interrup- 

 tion until completed. 



" On the Dielectric Constants of Pure Ice, G-lycerine, Nitro- 

 benzol, and Ethylene Dibromide at and above the Tem- 

 perature of Liquid Air." By J. A. Fleming, M.A., D.Sc. 

 F.R.S., Professor of Electrical Engineering in University- 

 College, London, and James Dewar, M.A., LL.D., F.R.S., 

 Fullerian Professor of Chemistry in the Royal Institution, 

 &c. Received May 6, — Read June 3, 1897. 



In another communication we have described the instrumental 

 appliances we are at present using in investigations on dielectric 



