PRESSURE ON RESISTANCE OF METALS. ()07 



purity, but not at all of the purity attainable by electrolytic'means. 

 Thus Jaeger and Diesselhorst ^ give for their nickel, with an analysis of 

 97.0 Ni, 1.4 Co, 0.4 Fe, 1.0 Mn, 0.1 Cu, and 0.1 Si, 0.00438 as the 

 temperature coefficient, but Fleming^* gives for electrolytic nickel 

 0.00618. It is probable that the temperature coefficient of nickel, 

 like that of iron, is excessively sensitive to slight impurities. The 

 initial value of the pressure coefficient at 0° as given graphically by the 

 deviation curve was — O.OslSS, against — O.O5I38 of Lisell^^. Lisell does 

 not give the temperature coefficient of his sample, but states that 

 chemical analysis showed no trace of impurity. 



The distinctive features of the behavior of nickel are shown when 

 the pressure-resistance curves are scaled so that the initial resistances 

 at different temperatures are the same. The curves at higher tem- 

 peratures are steeper, but with less curvature, the rate of decrease of 

 curvature being retarded at higher temperatures. The march of the 

 pressure of the maximum is very pronounced. Too much significance 

 should not be attached to any unusual features because of the lack of 

 perfect purity of this sample. 



Cobalt. I owe this material to the kindness of Dr. Herbert T. 

 Kalmus, who had prepared some samples of colbalt wire under the 

 direction of the Canadian government. His analysis showed Co 98.71, 

 Ni none, Fe 1.15, Si 0.14, Ca none, S 0.012, C 0.039, and P 0.010. The 

 number of the sample which he sent me was H 214; under tliis nimi- 

 ber some of its other physical properties have been described in a 

 publication of the Canadian government entitled "The Physical 

 Properties of the Metal Cobalt". It was furnished in the form of 

 wire 0.04 inch diameter. From this size it was most kindly swaged 

 and drawn down to 0.003 inch under the direction of Dr. W. D. 

 Coolidge of the General Electric Company. During the process of 

 reduction it was annealed at 540°, and after its final reduction I 

 further annealed it by heating to a cherry red for a few seconds in a 

 muffler, exposed to the air. These elaborate processes were necessary 

 because the wire cannot be drawn through dies like most metals. For 

 the measurements under pressure it was wound bare on a bone core; 

 at 0° its initial resistance was 71.9 ohms. Connections were made by 

 silver soldering. After winding it was further seasoned by heating 

 with the core to 135° for 2 hours. After the first application of 

 pressure there was a permanent increase of resistance of 0.2% of the 



14 J. A. Fleming, Proe. Roy. Soc. 66, 50-58 (1899-1900). 



