229 



POLAETZATTON OP CADMIUM CELLS. 



By R. R. Ramsey. 



While working on another problem (Phys. Rev. Vol. 1G, p. 105) it 

 was noted that the E. M. F. of a cadmium cell was greatly decreased and 

 at times apparently reversed after a considerable quantity of electricity 

 had passed through it. 



To investigate the cause of this phenomenon the experiments de- 

 scribed below were undertaken. Work of a similar nature has been car- 

 ried out by F. E. Smith (Phil. Trans. Roy. Soc. Lon., Series A, Vol. 207, 

 p. 393) ; by S. J. Barnett (Phys. Rev. Vol. 18, p. 104, 1904), and by P. I. 

 Wold (Phys. Rev., Vol. 27, p. 132, 1909). However, in their experiments 

 the time of polarization was comparatively small, the attention of the 

 investigators being directed to the initial polarization or to the rate of 

 recovery. In my work I have attempted to find the cause of this polariza- 

 tion. 



Cells were constructed of the H type and according to the accepted 

 formula for cadmium cells. The chemicals used were C. P. chemicals of 

 commerce. With ordinary care a cell could be obtained whose E. M. F. 

 did not differ more than .001 volt from the standard value. Measurements 

 of E. M. F. were made by means of a potentiometer. At times where 

 rapid measurements were desirable and great accuracy was not necessary 

 a voltmeter was used, the readings being corrected for the internal re- 

 sistance of the cell. Current was measured with a milliameter and time 

 was measured with a watch. At first it was thought that the polarization 

 was a surface effect, that a relation existed between the area of the sur- 

 face of the electrode and the quantity of electricity required to polarize 

 a cell to some standard amount. Cells were made with electrodes of vari- 

 ous diameters. The current was noted at stated intervals, so that the 

 total quantity could be caluclated. This was found to differ in different 

 cells, but it appeared to depend more upon the past history of the cell 

 than upon the electrode surface exposed. 



It was found that after a cell has been polarized once and has re- 

 gained its normal E. M. F. again it required less quantity of electricity 

 to polarize it than it did during the first run. A cell with three legs was 



