414 



MR. F. E. SMITH ON THE NORMAL WESTON CADMIUM CELL. 



more than 6 hours. Twenty-four hours afterwards, however, its E.M.F. was normal 

 within 2 parts in 10,000, and it completely recovered within 6 weeks. 



In 1884 Lord RAY LEIGH made some experiments on the polarisation of Clark cells 

 and conclusively showed that the effect of short-circuiting for a few minutes rapidly 

 passed away. 



E.M.F. 



roisso 



I'OI780 



TOI730 



8 



12 



IS 2O 



N/1 1 NOTES 



24 



28 



32 



Fig. 14. Recovery curve of cell short-circuited for 5 minutes. 



Recovery curves for the Clark cell have been published by FISHER,* for a large 

 type of cadmium cell by TINSLEY,* and for the Calomel or Hibbert cell by HIBBEKT.* 

 An analysis of such curves leaves little doubt that short-circuiting is only temporarily 

 injurious. 



Charging the Cell. 



In practice, a standard cell is usually placed in a circuit in which a very small 

 current alternates in direction. These small charging and discharging currents can 

 have no immediate serious effect on the cell, as is amply proved by many cadmium 

 cells in use at the National Physical Laboratory which are frequently checked in the 



* W. C. FlBHEK, " The Potentiometer and its Adjuncts," ' Electrician ' Series ; W. HIBBERT, ' The 

 Electrician,' vol. 37, p. 32, 1896; H. TINSLEY, "The Electrician,' vol. 47, p. 991, 1901. 



