1179 



6. After having rigliHj pointed out that the discontinuity in tlie 

 tenfiperature coefficient of e.m.f. mentioned above cannot be ascribed 

 to anj abrupt change in the behaviour of the half saturated solution 

 of cadnnium sulphate, Getman continues as follows^): "That the 

 discontinuity cannot be ascribed to any nlianye in the amalgam has 

 been proven by the investigations of Bijl "), in which the e.m.f. of a 

 cell formed by connecting an 8 7o cadmium amalgam loith a standard 

 electrode was found to decrease regularly as the temperature tvas 

 raised from 25° to 75°." 



Consequently he ascribes this discontinuity to the transformation 

 of Cd-a into Cd-/i in the vicinity of 40^, calculating the transition 

 temperature t by equating the formulas (.4) and (/)): 



0.04742—0.000200 (^—25) = 0.04280 + 0.000170 (^—25), 

 from which he finds: 



t = 37°.49, 



that is to say, whereas Cohfn and Helderman found that Cd-« changes 

 into another modification (Cd-/?J in the vicinity of 60°, Getman con- 

 siders 37°. 49 to be the transition temperature of these modifications. 



7. In the first place 1 should like to call the reader's attention to 

 the mistake in that part of Getman's statement, which is given above 

 (^6) in italics. The contrary has been proven quantitatively by 

 Bltl '). This is evident from that part of Bijl's diagram which 

 describes the behaviour of the 8 "/« amalgam used by Getman in 

 his -cells. (Fig. 1.) 



This amalgam contains 13.4 atomic percents of cadmium and the 

 diagram shows that the amalgam passes in the vicinity of 40° from 

 the heterogeneous into the hoinogeneous liquid phase. Consequently, 

 cells with a constant negative electrode which contain below 40° the 

 heterogeneous 8 "/„ amalgam will show at this temperature an abrupt 

 change of their temperature coefficient '). 



These facts have been overlooked by Getman ; the temperature of 

 37°. 49 found by him consequently does not correspond to the transition 

 temperature of Cd-« into Cd-^i. • 



8. in order to prove this, it may be borne in mind that Getman 

 investigated some ^:f-cells between 0° and 35° in which Cd-;? had been 



I) The italics are mine (Cohen). 



») Zeitschr. f. physik. Chemie 41, 641 (1902). 



^) Ernst Cohen and H. R Kruyt, Zeitschr. f. physik. Chemie 72, 84 (1910). 



