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X. The Normal Weston Cadmium Cell 



By F. E. SMITH, A.R.C.Sc. 

 (From the National Physical Laboratory.) 



Communicated by R. T. GLAZEBROOK, F.R.S. 



Received July 13, Read November 21, 1907. 



[PLATE 5.] 



THE experimental investigations described in this communication had as their 

 primary object the improvement of the Clark and Weston Cadmium Cells as 

 standards of electromotive force. 



The older investigations of RAYLEIGH,* KAHLE.t and GLAZEBKOOK and SKINNER^ 

 proved the Clark cell to be very trustworthy, and only within the last few years has 

 any serious attempt been made to displace it from the premier position in which it 

 was placed in 1894. In 1892 WESTON introduced the cell bearing his name. This 

 cell contains a solution of cadmium sulphate instead of zinc sulphate, as in the Clark, 

 and an alloy of cadmium and mercury forms the negative pole. ' As originally 

 specified, the solution was saturated at 4 C., and no crystals of cadmium sulphate 

 were inserted in the cell ; under normal conditions there was therefore no change in 

 the concentration for small variations in temperature. When the solution is saturated 

 at all temperatures, i.e., when solid cadmium sulphate is always present in the cell, 

 the name " Cadmium Cell " has been frequently assigned to it in order to distinguish 

 it from the original form. In this communication the latter cell is the type experi- 

 mented with, and since it is referred to as the Westou Cadmium Cell in the reports 

 of the International Conference the same name has been adopted by the author. 



* Lord RAYUUGH, ' Phil. Trans.,' 175, p. 412, 1884, and 176, p. 781, 1886. 

 t K. K.UII.K, 'Zeitech. f. Instnimentenk.,' 12, p. 117, 1892, and 13, p. 293, 1893. 

 ; R. T. GLAZBBROOK and S. SKINNER, ' Phil. Trans.,' 183, p. 567, 1892. 

 WKSTON, ' The Electrician,' voL 30, p. 741, 1892. 

 VOL. CCV1I. A 422. 3E 16.1.08 



