BURGESS AND KELLBERG: ALLOTROPY OF COPPER 



659 



These experiments gave us negative results. A brief descrip- 

 tion of the methods used and a summary of the results obtained 

 may, nevertheless, be of some interest. 



The copper was in the form of hard drawn wire, of 0.005 cm. 

 diameter by about 35 cm. length, wound, together with a plati- 

 num wire of 0.015 cm. diameter, on a mica frame and enclosed 

 within a glass tube. This was immersed in a completely water- 

 jacketed and electrically-controlled calorimeter' the temperature 



D/ac^rams of Connections for Methods. 1,2 and 3 

 Fig. 1. Methods of resistance measurement. 



of which could be made to vary uniformly at any desired rate 

 between 0° and 95°C. 



Three methods of measurement were used, as illustrated in 

 figure 1 : 



1 . The resistance of the platinum and copper coils was measured 

 differentially and simultaneous observations of temperature were 

 taken with a mercury thermometer. The copper-platinum ther- 

 mometer was first annealed for 2 hours at 100° and then for 5 

 hours at 150°C. 



2. Using the same copper and platinum coils, a commutator 

 was inserted, as shown in figure 1, which permitted taking alter- 

 nate readings of the platinum resistance, which then served as a 

 thermometer, and of the platinum-copper resistance difference. 

 In this series of observations the glass container was evacuated, 

 to eliminate extraneous temperature influences caused by con- 

 vection down the containing tube. 



' H. C. Dickinson, Bulletin Bureau of Standards 11 : 210. 1915. 



