THERMO-ELECTKIC Ql ALITY LNDEU PRESSURE. 



357 



used previously for the resistance measurements not being large 

 enough. This also was 0.008 inch in diameter. A piece long enough 

 for both inside and outside pieces was annealed at one time by heating 

 white hot with an electric current in an atmosphere of hydrogen under 

 reduced pressure. The hydrogen was not pure, however, and there 

 was appreciable formation of oxide. This treatment was successful 

 in keeping the permanent zero reading down to a normal value. 



o 



14 

 12 



2 10 

 o 

 > 



"<3 







10° 20° 30° 



40° 50° 60° 70° 



Temperature 



Tungsten 



80° 



90° 100" 



Figure 38. Tungsten. Thermal E.M.F. of a couple composed of one 

 branch of uncompressed metal, the other compressed to the pressure in kg./cm.^ 

 indicated on the curves, the junctions being at 0°C and the temperature 

 plotted as abscissae. 



At atmospheric pressure the average temperature coefficient of 

 resistance between 0° and 100° was 0.04317, the resistance being 

 sensibly linear with temperature. The coefficient of the resistance 

 specimen, which was only 0.0004 inch in diameter, was 0.00322. The 

 considerable difference may again be due to the difPerence of mechani- 

 cal treatment. 



