PRESSURE ON RESISTANCE OF METALS. 



627 



TABLE XX. 

 Resistance of Bismuth. 



It is evident from a comparison of the data for the different grades 

 of bismuth that the effect of impurity on the temperature coefficient 

 is much greater than on the pressure coefficient. The temperature 

 coefficient of the impurest bismuth above was on the average negative 

 (= — 0.00039) over the range 0° to 100°; its resistance passed through 

 a minimum at 75°. The coefficient of grade " K" was 0.00332 between 

 0° and 100°, and the instantaneous coefficient at 0°, was about 0.0027. 

 The average temperature coefficient of the electrolytic bismuth above 

 may be found from an extrapolation of the data of Table XX to be 

 0.00438, and the instantaneous coefficient at 0° 0.00381. Another 

 sample from the same piece of wire, which had not been subjected to 

 pressure at all, gave 0.00441 between 0° and 100°, and 0.00389 at 0°. 

 These latter values may be accepted as more probably correct for 

 this material in a state of ease. 



The mean temperature coefficient of pure bismuth between 0° and 

 100° is given by Jaeger and Diesselhorst ^ as 0.00454, but as already 

 explained, their value was obtained by an extrapolation, assuming 

 linearity. If we assume that their deviation from linearity was the 

 same as that found above, their temperature coefficient between 0° 

 and 100° corrects to 0.00438, slightly less than the best value above. 



