﻿Conductivity of Sulpliated Accumulator Plates. 743 

 through the cell, recorded. The curves so obtained are the 



continuous curves of fig. 2. 



Fig-. 2. 



Variation or Potential Difference 



WITH J /MF.. 



(Current not constant) 



4 



If V denote the potential measured by the voltmeter, we 

 have 



V=CR-E', 



where E' is any back e.m.f. that may arise in the cell. No 

 evidence could be found of a larger back e.m.f. than the two 

 volts which develops when the cell is charged. Cook* has 

 suggested the presence of a back e.m.f. to explain the 

 properties of the aluminium anode-film, but this is not now 

 generally accepted. Accordingly the variation of lv with t 

 may be found by keeping constant the current through the 

 cell, or by dividing values of V by simultaneous values of 0. 



* Cook, Phys. Rev. xviii. p. 23 (1904) 



