252 Mr. F. E. Smith on Cadmium Amalgams 



If the temperature of an amalgam, containing the mixed 

 phases, is raised, the liquid phase is increased and the solid 

 phase diminished ; when stable, however, the E.M.F. of an 

 amalgam towards a solution of cadmium sulphate does 

 not depend on the relative amounts of the two phases. 

 Hence, stable amalgams containing different percentages of 

 cadmium, but possessing the two phases, have the same 

 E.M.F. towards a cadmium sulphate solution. With 

 amalgams all solid or all liquid, the E.M.F. varies with the 

 cadmium content. 



Bijl 6 determined the percentage composition of amalgams 

 possessing the 2-phase system from experiments on their 

 electromotive properties. His observations were made at 20°, 

 25°, 50°, and 75° C. Other experiments on the dilatation of 

 the amalgams, rate of cooling, <fec, were made at tempe- 

 ratures rano-ino- from —39° to 321°. 



The present investigation was commenced in October 1908. 

 The objects in view were : — (1) To trace the cause of the 

 electromotive difference, which sometimes existed and which 

 was sometimes absent, between 10 and 12^ per cent, amalgams. 

 (2) To determine the limits of temperature between which 

 amalgams of various concentrations could be usefully 

 employed. (Requests for information on this point had 

 on several occasions been received from India.) (3) To 

 explain the abnormal E.M.F/s of cells made by various 

 observers, when the amalgams contained from 12^ to 14 

 per cent, of cadmium. (4) As the recent International 

 Conference on Electrical Units and Standards (London, 

 1908) specify a 12J per cent, amalgam, it was important to 

 decide whether the limits of temperature (0° — 40° 0.) 

 specified, required amending or not. 



The Method . 



The method consisted in directly measuring the difference 

 o£ E.M.F. between two amalgams in contact with a saturated 

 solution of cadmium sulphate. The materials in contact with 

 the amalgams were identical with those used in the Weston 

 normal cell, and any amalgam could at any time be used as 

 the negative element of such a cell. 



The glass vessels used were of the form shown in fig. 1. 

 Each vessel has four vertical limbs connected by means of 

 a tubular cross-piece. A platinum wire is sealed through the 

 bottom of each of the limbs and passes into a narrow side- 

 tube containing mercury. A 10 per cent, amalgam was 

 placed in the bottom of one of the limbs, and amalgams of 

 different percentages of cadmium were placed in two of the 



