PRESSURE COEFFICIENT OF RESISTANCE. 



157 



through a flat minimum, and then increased at the higher tempera- 

 tures. The departure from linearity of this new specimen is further- 

 more symmetrical about the mean pressure, so that it can be repre- 

 sented by a parabolic formula, whereas that of the former sample was 

 unsymmetrical, and there was a progressive shift of the pressure of 

 maximum deviation with rising temperature. 



Uranium. I am indebted to the kindness of Dr. A. W. Hull of the 

 General Electric Company for a sample of this metal. This had been 

 prepared with considerable difficulty for an investigation of its proper- 

 ties with a view to a possible commercial use. It turned out that its 

 properties were not promising, so that no more will be prepared. 

 This sample is probably unique, and I was most fortunate to obtain it. 

 It was furnished in the form of rolled sheet, about 0.05 cm. thick, 



40° 60° 

 Temperature 



1 00° 2 0° 

 Nickel 



40° 60° 

 Temperature 



Figure 2. Nickel. Results for the measured resistance. The deviations 

 from linearity are given as fractions of the resistance at kg. and 0° C. The 

 pressure coefficient is the average coefficient between and 12000 kg. 



0.7 cm. wide, and 4.5 cm. long. In this form the compressibility was 

 measured, and I am reporting the results in another place. There 

 were flaws in the specimen, which did not affect the compressibility 

 measurements, since it was exposed to pressure all over, but which 

 would have interfered with measurements of its electrical resistance. 

 A small homogeneous sliver was cut from the sheet about 0.79 cm. 

 wide and 2.2 cm. long. Uranium is very difficult to work, and the 

 sliver had to be cut with a steel disc charged with diamond powder; 

 I am indebted to the skill of Mr. David Mann for preparing the 

 specimen. 



The specimen was mounted for measurement with the potentio- 

 meter. It is not possible to solder leads to it. Fine grooves were 

 filed around each end of the specimen, and a special spring clamp 

 arrangement made by which the current and potential leads were 



