JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. V DECEMBER 19. 1915 No. 21 



PHYSICAL CHEMISTRY.— On a supposed allotropy of copper. 

 G. K. Burgess and I. N. Kellberg, Bureau of Standards. 



Some dilatometric experiments have been carried out recently 

 by Professor Ernst Cohen and W. D. Hulderman^ which have led 

 them to the conclusion that copper exists in two allotropic (enan- 

 tiotropic) forms, having a transition point at 71 ?7 C. to 69?2 C. 

 under varying conditions of fineness and previous contact with an 

 electrolyte. The copper was in the form of metal chips turned 

 from sticks that had been cast in asbestos from Kahlbaum re- 

 melted electrolytic copper. The metal therefore probably con- 

 tained some cuprous oxide. 



Messrs. Cohen and Hulderman also consider the change in 

 the zero value of electrical resistance of copper after heating to 

 100°C. an a priori indication of the probability of allotropic modi- 

 fications between 0° and 100°C. This phenomenon of shift of 

 zero is, however, common to all metals and is known to be re- 

 lated to the degree of hardness of the metal. It is very per- 

 sistent, being removed only by complete annealing and freedom 

 from strains.- 



In Table I are given a comparative series of measurements at 

 0° and 100° for copper and platinum wire resistance thermome- 

 ters, wound on the same frame. It will be seen that the plati- 



1 Proc. Amsterdam Acad. 16: Dec. 27, 1913; 17: May 30, 1914; Phys. Chemie 

 87:419. 1914. 



2 See for example the behavior of Pt and Pd resistance thermometers, Waidner 

 and Burgess, Scientific Paper No. 124, Bureau of Standards. 



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