Potential- Difference, by Heating in Oil. 593 



u deflexion of 140 was observed. Oil sufficient to cover both 

 plates was then poured into the bath ; and, on again con- 

 necting and separating the plates several times, the deflexion 



averaged 110 divisions in the same direction as before. The 

 oil bath was then heated to about 145° C, after which the 

 connexion and separation gave no deflexion. The whole was 

 then allowed to cool and again tested, with the same result. 

 The "volta effect" had disappeared. Its disappearance is 

 apparently due to some effect of the heating since the mere 

 immersion in the oil did not cause it, and its absence is not 

 due to temperature merely, since this absence continued after 

 the oil had cooled. 



I take it that the volta effect ceased as soon as the condensed 

 films were evaporated. If the disappearance of the volta 

 effect had taken place immediately on immersion in the cold 

 oil, it might have been considered to be caused by some 

 conduction through the oil causing equalization of the 

 potentials observed on air, as happens when plates in air are 

 connected by a drop oil water. There is, in tact, some such 

 conduction of a very minute kind, the oil acting as an electro- 

 lyte and causing the combination to behave as a voltaic cell 



