THERMO-ELECTRIC QUALITY UNDER PRESSURE. 



353 



The value given by Wagner up to 300 kg. between 0° and 100° is 

 + 18.6 X 10~'^2 volts per degree per kg. The values found above by 

 interpolation are 18.0 for the Heraeus, and 16.1 for Baker's platinum. 

 The agreement with the purer specimen is as good as could be expected. 

 ^^Molyhdenum. This was a fresh piece, obtained through the kind- 

 ness of Dr. W. D. Coolidge of the General Electric Company. The 

 piece whose resistance under pressure had been measured was not 



50° 60° 

 Temperature 



Molybdenum 



FiGTJRE 36. Molybdenum. Thermal E.M.F. of a couple composed of 

 one branch of uncompressed metal, the other compressed to the pressure in 

 kg./cm.2 indicated on the curves, the junctions being at 0°C and the tempera- 

 ture plotted as abscissae. 



large enough in diameter or long enough for use in this apparatus. 

 The new piece was 0.008 inch in diameter, with a resistance of 0.54 

 ohms per ft. when cold. A piece 18 inches long, the piece to be ex- 

 posed to pressure, was annealed by heating to a white heat with an 

 electric current in an atmosphere of hydrogen. The hydrogen was 

 not entirely free from oxj'gen, however, and there may have been 

 some chemical effect. The outer connecting piece of wire was left 



