366 



BRIDGMAN. 



bone core. It had been previously seasoned by alternately heating 

 to 140° for 30 minutes, and slowly cooling to room temperature for 

 15 minutes, repeating three times. For the pressure measurements it 

 was seasoned by a single application of 12000 at room temperature. 

 After this first application of pressure there was a permanent decrease 

 of resistance amounting to 0.03% of the total resistance. The effect 

 of pressure is to increase the resistance very slightly, instead of to 

 decrease it, as for pure metals. Measurements were made at three 

 temperatures; 0°, 50°, and 97°. Within these limits the coefficient 



tO° 50° 60° 

 Temperature 

 Ojnstantcin 



Figure 42. Constantan. Thermal E.M.F. of a couple composed of one 

 branch of uncompressed metal, the other being at the pressure in kg./cm.^ 

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

 plotted as abscissae. 



is independent of temperature, and the relation between pressure 

 and resistance is linear up to 12000 kg. The pressure coefficient 

 between 0° and 100° up to 12000 kg. was found to be + 0.06409, 

 pressure measured in kg./cm.^. The smallest coefficient fovnid in the 

 previous work for a pure metal was that of tungsten, which was 

 -0.0b125. 



In contrast to the very small effect of pressure on resistance is its 

 very large effect on thermo-electric quality. The effect is positive. 



