PRESSURE ON RESISTANCE OF METALS. 



617 



The average temperature coefficient between 0° and 100° is 0.004336. 

 This is to be compared with the value 0.0034 given by Somerville.^^ 

 In the tables of Kaye and Laby, the value is given as 0.0050, with no 



i 



.0,2 



a .Osi 



20° 40" 60" 80" 100° 

 Temperature 



a:;3.0,123| 



Temperature 

 Molybdenum 



80° 100" 



Figure 18. Molybdenum, results for the measured resistance. The devia- 

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

 Since the deviations are symmetrical about the mean pressure, there is no need 

 of giving the detailed curves. The pressure coefficient is the average coefficient 

 between and 12000 kg. 



reference except the year 1910. Since I have been able to find no 

 other reference for the temperature coefficient of molybdenum, and 

 the work of Somerville was published in 1910, it seems plausible to 

 suppose the value of Kaye and Laby is a misprint. The amount of 

 impurity in my specimen was stated by Dr. Coolidge to be of the order 

 of 0.2%. There are no previous measurements of the pressure coeffi- 

 cient for comparison over any range. 



When the resistance-pressure curves are scaled to the same initial 

 resistance for all temperatures the curves for higher temperatures are 

 found less steep and less curved. This is like platinum. 



Tantalum. This was obtained from the General Electric Co. 

 through the kindness of Mr. MacKay. It is bare, 0.0022 inch diam- 

 eter. It was subjected to the same seasoning as the molybdenum, 

 and was wound bare on a core of bone with an initial resistance at 0° 

 of 82.1 ohms. A perfectly satisfactory method of connection was not 

 found. Neither gold nor silver solder will stick to the surface. Con- 

 nection may be made to platinum by arcing in hydrogen, but the 

 tantalum becomes excessively brittle in places where it has been 

 subjected to a high heat, and the connection is very likely to drop off. 

 Connection was finally made with a simple spring clip, consisting of a 

 tightly wound helix of small piano wire. The spring is stretched, and 

 the tantalum wire dropped between the extended spires. The results 



16 A. A. Somerville, Phys. Rev. 31, 261-277 (1910). 



