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



"On the Dielectric Constants of Metallic Oxides dissolved or 

 suspended in Ice cooled to the Temperature of Liquid 

 Air." By James Dewar, M.A., LL.D., F.R.S., Fullerian 

 Professor of Chemistry in the Royal Institution, and J. A. 

 Fleming, M.A., D.Sc, F.R.S., Professor of Electrical 

 Engineering in University College, London. Received 

 June 29, 1897. 



By the aid of the cone condenser and the method described by us 

 in another communication,* we have studied the changes produced 

 in the dielectric constants cf ice at and above the temperature of 

 liquid air when the ice has suspended in it insoluble metallic oxides 

 or else has dissolved in it soluble metallic oxides or hydrates. We 

 have also examined the dielectric properties of some of these oxides 

 and hydrates when dissolved in other menstrua frozen and reduced 

 to very low temperatures. 



The experiments were conducted exactly as described in the com- 

 munication above mentioned, and the frequency of the electromotive 

 force reversals was, as before, 120. 



In the following tables the four columns of figures give respec- 

 tively the platinum temperature of the dielectric, the scale deflection 

 of the galvanometer, representing the capacity of the condenser with 

 the selected dielectric, when corrected for voltage and capacity of 

 the leads and vibrator ; the deduced dielectric constant, and the 

 electromotive force at which the charging of the condenser was con- 

 ducted. 



The figure given at the head of each table as the corrected galva- 

 nometer deflection with air as dielectric, represents the capacity of the 

 condenser with gaseous air at normal pressure and temperature as its 

 dielectric. 



The hydrates dissolved in water or other media, or the oxides in a 

 very fine state of division, suspended in water, were introduced by 

 means of a pipette, as the dielectric into the cavity of the cone con- 

 denser. This liquid dielectric was then frozen and reduced to the 

 temperature of liquid air by lowering the whole condenser into a 

 large vacuum vessel holding several litres of liquid air. As soon as 

 the dielectric was reduced to the temperature of —188° C. the 

 observations for capacity and temperature began. 



In all cases an observation was taken for electric conductivity and 

 the dielectric measurements were stopped the moment any sensible 

 conductivity made its appearance. 



* See Fleming and Dewar, " On the Dielectric Constants of Certain Frozen 

 Electrolytes at and above the Temperature of Liquid Air," 1 Eoy. Soc.Proc.,' vol. 61, 

 p. 299. 



