«U3 



only contained 0,0047»/., of' Cd., 0.0033"/,, of Ph., 0,00045»/,, F«>,Cn). 

 But working with the same material to which 0.52 per cent by 

 weight of Cd, resp. 0,5 per cent of Ph. or 0,5 per cent of Cd-[-0,5 

 per cent of Pb had been added, he found sevei-al transition points 

 which grosso modo agreed with those found formerly by Benkdicks a.o. 

 On account of these results Benedicks and Arpi conclude that the 

 transition points found by LJenedicks in his first investigation are to 

 be attributed to impurities in the metal used and that zinc which 

 is pure does not show transition points. 



6. In the first place it may be pointed out that the curves which 

 form the basis of the authors' conclusions, are so roughly defined, 

 that it is almost impossible to conclude anything from them. For 

 example, from a consideration of the curve 2 in Fig. 2 (which refers 

 to pure zinc), one might arrive at the conclusion that a break ^) 

 exists at 150°. 



7. However, a more serious objection to the method followed, 

 may be pointed out. Our recent investigations on the allotropy of 

 metals have shown that the changes in these substances take place 

 very slowly even at high temperatures. These retardations can only 

 be removed by special means (inoculating in contact with an electro- 

 lyte, repeated changes of temperature etc.). We may call to nnnd the 

 fact that we were able to heat cadmium 95 degrees above one of 

 its transition points without any changes occurring. It will be necessary 

 to give special attention in future to these phenomena, which play 

 also a role in "thermal analysis" and which may falsify its results. 



Benedicks and Arpi did not make any provision to eliminate these 

 pfienomena. Ou account of what we know^ now^ about these hyste- 

 resis phenomena it w^as to be expected that any transition point, if 

 it really existed, would only be found under favourable circumstances, 

 or by a systematic elimination of the retardations mentioned above. 



8. Moreover it may be pointed out that Benedicks and Arpi ??z^7(/(^ 

 the supposition "dass die betreffenden Metalle nicht genügcnd rein 

 waren" (viz. the zinc, puriss. Merck, used by Benedicks in his first 

 investigations and by Le Chatelier among others). We think that the 

 opinion put forward by Benedicks in his first paper (see above § 3) "dass 

 die Menge von Fremdkörpern zu vernachlassigen ist", is the just one. 

 As we were told by Messrs. Merck at Darmstadt their "Zinc, puriss. 

 Merck (garantiert frei von Eisen und Arsen in Stiiben)" contains only 

 small traces of cadmium. We carried out an analysis of this material 



') Whether this point i-ealiy exists or not may be left open for the moment. 



