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XXIV. On Cadmium Amalgams and the Weston jS^ormal CelL 

 By F. E. Smith, AJl.C.Sc* 



(From the National Physical Laboratory.) 



[Plate III.] 



XTTTITHIN the past few years a number of researches 

 1 t have been made on the electromotive properties ofc' 

 mercurous sulphate, and as a result the standard cell is now 

 reproducible with a very high degree of accuracy. How- 

 ever, there are many instances of abnormal behaviour of such 

 cells both with regard to constancy of E.M.F. and with 

 respect to change of E.M.F. with varying temperature. The 

 want of constancy has been attributed by Hulett to slow 

 hydrolysis of the mercurous sulphate, and by Steinwehr 1 * 

 to a change in the size of the mercurous sulphate crystals. 

 Irregular behaviour with changing temperature has been 

 observed by Tinsley 13 , by Janet 15 and Jouast 1516 , and more 

 recently by Cohen and Kruyt 17 , and all of these attribute the 

 observed differences to the cadmium amalgam. 



Dearlove 1 first showed in 1893 that attention must be 

 paid to the percentage of cadmium in the amalgam, and from 

 1808 to 1900, Cohen 3 , Kerp and Boettger 4 , BijF, Puschin 8 , 

 and Jaeger 2 made independent investigations on such 

 amalgams. 



The research of BijFs was especially complete and its value 

 appears to have been overlooked in much of the recent work 

 on the standard cell. Possibly the reason is that the electro- 

 motive properties of the amalgams were examined at 20°, 25 c y 

 50° and 75° C. only. However, from other data given by 

 Bijl — as pointed out by Cohen and Kruyt — the conclusion 

 may be drawn that a 12^ per cent, amalgam cannot be 

 usefully employed below about 14° C. 



Jaeger made observations at room temperature (20° C- 

 approx.) on amalgams varying in content from 1 to 20 per 

 cent, of cadmium, and showed that at that temperature all 

 amalgams containing from 5 to 14 per cent, of cadmium 

 could be used in the anode limb of the Weston cell with the 

 same resulting E.M.F. In a note on Bijl's work Jaeger 7 

 emphasizes the fact that the cells made by Lindeck 5 and 

 himself with amalgams containing 12 and 13 per cent, of 

 cadmium showed no irregularities when cooled. 



No objection appears to have been raised against the 12J 

 per cent, amalgam until 1905, when the author 10 stated 



* Communicated by the Physical Society : read October 22, 1909. 



