Constants of Pare Ice, §c, at Loiv Temperatures. 323 



constant in cooling ice from 0° C. to —185° C, it follows that there 

 is unquestionably some temperature at which ice-water has a maximum 

 value for its dielectric constant. This temperature may, and probably 

 does, vary with the presence of slight impurities in the water, and 

 with the frequency of the electromotive force reversals. 



On examining the carves for perfectly pure water and for ordinary 

 distilled water, it will be seen that minute impurities, as well as 

 change of frequency, evidently have a considerable effect upon the 

 dielectric constant at any given temperature. 



This was additionally shown as follows : — 



Being desirous of trying the effect of varying the frequency of the 

 contact breaker, two sets of experiments were made with the care- 

 fully purified distilled water, the condenser being reduced in tem- 

 perature to —79° C. by the aid of solid carbonic acid and alcohol. 



The following values were obtained : — 



Dielectric Constant of Ice from Pure Distilled Water. 

 Frequency of contact maker 120. Charging volts 1*43. 



Temperature in platinum 



Dielectric 



degrees. 



constant. 



-78-0 



353 



-75-1 



40-7 



-711 



49-8 



-66-5 



55-0 



-60-2 



58-2 



-50-7 



63-8 



It will be seen that the dielectric values are all higher than those 

 given in the former table for the corresponding temperatures. 



We are disposed to attribute the differences between the values 

 obtained in the last set of observations and the first set to the fact 

 that the water became slightly contaminated with alcohol during the 

 process of freezing down the condenser in the carbonic acid and 

 alcohol. This view was confirmed by the observations taken with a 

 mixture of alcohol and water, which showed that such a mixture 

 rises in dielectric value as temperature increases more rapidly than 

 does the pure distilled water. 



Similar observations were taken with a double frequency of 250 

 and a charging voltage of 1*434. 



Temperature in platinum Dielectric 



degrees. constant. 



-71-8 61-0 



-71-5 53-2 



-69-8 57-4 



-69-0 61-0 



-68-7 61-4 



