Cadmium Amalgams and the Weston formal Cell. 251 



that it was not wise to use such an amalgam at low tempe- 

 ratures (0° (J.) but that an 8 per cent, amalgam could be so 

 used. A few experiments were subsequently made with 10 

 and 12}, per cent, amalgams, but the results were incon- 

 sistent. However, an amalgam of* less cadmium content 

 than 12h was preferred for low temperatures and in con- 

 sequence most of the Weston normal cells at the National 

 Physical Laboratory 12 contain 10 per cent, amalgams. 

 Pending further investigation it was thought wise not to 



o ~ o 



specify the limits of temperature between which a cell con- 

 taining 12\ per cent, cadmium amalgam might be used, and 

 in preliminary specifications 11 for the standard cell, issued 

 in 1908, no limits of temperature are fixed. 



Tinsley 13 , in 11>08, obtained some results with Weston 

 cells which led him to believe that cells containing 12^ per 

 cent, amalgam should be used with caution below 10° 0. 

 However, the cell with 12^- per cent, amalgam had the lower 

 E.M.F. at the lower temperatures, which is not in accordance 

 with the author's observations. 



Janet and Jouast 15 , 10 obtained results which were opposed 

 to those of Tinsley. They found a 12^- per cent, amalgam 

 cell to be normal at low temperatures (0°'5 C.) and a 10 per 

 cent, amalgam cell to behave abnormally. This conclusion 

 also is directly opposed to our own experience. 



Wolff 14 at the National Bureau of Standards, Washington, 

 used 200 Weston cells to determine the relation between 

 E.M.F. and temperature, the range being 0° C. to 40° C. 

 All of these cells were set up with 12tt per. cent, amalgams 

 and only a few behaved abnormally. 



Jn November 1908, Cohen and Kruvt 17 found differences 

 of 0-04, 0'23, 0-13, 0*16, 0'20, and 0'20 millivolt between 

 amalgams of 10 and 12^ per cent, of cadmium when the 

 electrolyte was a solution of cadmium sulphate and the tem- 

 perature was maintained at 0° C. : the E.M.lYs of the cells 

 containing the 12J per cent, amalgam- were the greater. 

 Cohen suggests the use of an 8 per cent, amalgam for 

 general use. 



The exact constitution of cadmium amalgams is doubtful 

 and is not discussed in the present paper, but there is no 

 doubt that the electromotive properties of the amalgam- 

 depend on whether one or two phases are present. When, 

 by increasing the temperature a solid amalgam is converted 

 into a mixture of liquid and solid phases, there is an im- 

 mediate change in the electromotive temperature coefficient 

 of the amalgam, and a similar change results when the 

 coexisting phases are changed entirely into the liquid state. 



