Ice as an Electrolyte. 



119 



servations given below. When the temperature had fallen to 

 — 13°'5 C, we stopped the resistance-tests to take the capacity 

 of the ice. We charged for ten seconds with an electromotive 

 force of 0*174 volt, and short-circuiting the ice for fifteen 

 seconds after each discharge, exactly as was done with the 

 water. We now found, however, that when using the one- 

 thonsandth shunt there was no visible motion of the spot of 

 light on discharging ; and when no shunt was employed the 

 swings only reached 25. Now, disregarding the error pro- 

 duced by varying the shunt in capacity-testing (a correction 

 for which could be made in the way explained by Mr. Latimer 

 Clark, Journ. Soc. of Teleg. Engineers, vol. ii. 1873, p. 16), 

 and also neglecting the frictional resistance of the air, it fol- 

 lows that the capacity of ice at — 13°'5 0. is to the capacity 

 of water at +8°-7 C. as 25 to 79,000, or as unity to 3160. 

 This result, however, has to be corrected for the effects of an 

 opposing electromotive force due to some slight oxidation of 

 the copper on the sides of the ice, and which equalled 0*053 

 volt. Applying this correction, we find the ratio of the ca- 

 pacities to -be as unity is to 2240. This makes the capacity 

 per cubic centimetre of ice at — 13°*5 C. to be 0*002 micro- 

 farad, and the specific inductive capacity 22,160, that of air 

 being called unity. 



Substance. 



Approximate ca- 

 pacity per cubic 

 centimetre in 

 microfarads. 



Specific Inductive 

 capacity approxi- 

 mately. 



Air 



8831x10-^^ 

 196x10-^ 



4-384 



I 

 22160 



50xl0« 



Ice at — 13°-5 C 



Distilled water at +8°7 0. 



This furnishes an additional example of the principle re- 

 cently pointed out by us, that low specific resistance is asso- 

 ciated with high specific inductive capacity. 



For further experiments on the capacity of the ice at differ- 

 ent temperatures &c., see further on. 



At 12 hours 30 J minutes the current produced by 2*61 

 volts was passed between the copper plates, the ice being at a 

 temperature of — 13°*6 C. The temperature was allowed to 

 rise very gradually ; and time-readings of the galvanometer 

 deflection were taken. From these the cuives ABODE, 

 F Gr, HI, J K (fig. 2) have been constructed, horizontal dis- 

 tances representing time on such a scale that from the point 

 A to the point E the time was 207^ minutes, and vertical 



