B44 



following the method described by Mylius ^). In 100 gr. of this metal 

 we could oidj detect small traces of cadmium (lead and iron). We 

 think that the explanation of B. and A. which is based on the 

 presence of large amounts of impurities falls to the ground. 



9. That it is not the presence of foreign substances which give 

 rise to the strongly marked change of the mechanical properties of 

 zinc at higher temperatures (which fact has been the starting point 

 of Bknkdicks' in\estigations) is evident from the fact, that this change 

 may also be observed in the i)iirest zinc (Zink "Kahlbaum", comp. 

 § 5). We liave been able to confirm this result repeatedly on ivseh es. 



10. Finally some remarks, made in a note by Benedicks and Arpi 

 may be considered here. 



In the first place they believe, on account of an investigation con- 

 cerning the quenching velocities of metals, carried out by Benedicks *), 

 that "eine besonders grosse Abkühlungsgeschwindigkeit nicht zuerzielen 

 ist" when the method is followed which we used. (1 kilo of zinc 

 was chilled in a mixture of solid carbid dioxide and alcohol). It 

 may be pointed out that the velocity we used has been greatly exag- 

 gerated; we got the same results by using water or air of room tempe- 

 rature. We also carried out some experiments with carbon dioxide 

 and alco hoi in order to vary the external conditions of our experiments 

 as much as possible. In our researches on the allotropy of copper 

 and cadmium we also used water or air as a cooling medium. 



11. Secondly Benedicks and Arpi raise the question as to whether 

 there has not taken place an "Auflockerung der Oberflache" of our 

 preparations when we w^ashed them with dilute hydrochloric acid. 

 By this operation a change of density might have occurred. 



They have however overlooked two facts : in the first place the 

 recent investigations of Johnston and Adams ^), which prove that the 

 density of any substance is independent of its state of division. 

 Moreover they have not taken into account the results of our inves- 

 tigations on cadmium ^), where the same difficulties would have 

 occurred. The reproducibility and reversibility of the phenomena 

 prove that the disturbances, mentioned by Benedicks and Arpi really 

 do not occur. 



We hope to report shortly on the real transition points of zinc. 



Utrecht, September 1914. van 't Eoff- Laboratory. 



1) Zeitschf. f. anorg. Chemie 9. 144 ^895) ; Mylius, ibid. 74, 407 (-1912). 



2) Joiirn. of the Iron and Steel Institute 77, 153 (1908). 

 s) Journ. Americ. Ghem. Soc. 34, 563 (1912). 



^) Proceedings 16, 485 (1913). 



