EFFECT OF TENSION ON CERTAIN ABNORMAL METALS. 47 



C. G. S. units. Take as the average 2.07 X 10" C. G. S., or 

 2.11 X 10^ tension in kg/cm-. Richards ^ has found for the cubic 

 compressibiHty 5.7 X 10^^^ Abs. C. G. S. Combined with Young's 

 modulus by the formula of elasticity gives for Poisson's ratio the 

 value 0.303. 



There is a very considerable range of tension above that of perfect 

 elastic behavior and below the breaking point where there are de- 

 partures from linearity and hysteresis. The immediate effect of 

 exceeding the elastic limit is to permanently increase the resistance. 

 The wire may be seasoned for any particular range of tension 

 beyond the elastic limit by repeated application and removal of the 

 load. After seasoning, the resistance, as a function of tension, de- 

 scribed hysteresis loops exactly similar in appearance to the familiar 

 hysteresis loops of the relation between tension and elongation. The 

 width of the loop in the extreme case of a tension just below the break- 

 ing point may amount to one third of the maximum change. This 

 maximum change of resistance was 1.73% for one specimen, and 2.43% 

 for the other. The average coefficient of resistance for the extreme 

 hysteresis loop was 20.5 X 10~® for one specimen, and 15.2 X 10~^ 

 for the other, against a coefficient in the elastic range of 8.4 X 10~^. 



Strontium. This material was from the same lot as the specimen 

 whose pressure coefficient of resistance was previously determined. 

 I am indebted for it to Dr. B. L. Glascock. The probable purity, and 

 some of its properties have been already discussed.^ The metal was 

 formed into wire by extrusion in the manner already described. Two 

 sizes were used, 0.035 and 0.019 inches in diameter. 



Two samples were used; the first was not geometrically perfect 

 and did not give as good results as the second. Two series of measure- 

 ments were made on the second. The diameter of this was 0.019 

 inches. The wire breaks without much preliminary yield at a load of 

 about 800 gm. At a load of 700 gm. there was a very small perma- 

 nent increase of resistance. The tension coefficient of resistance was 

 determined through a range of 400 gm., readings being made at eight 

 different loads within this range. The effect of tension is to decrease 

 the resistance. Within the limits of error the relation between tension 

 and decrease of resistance is linear. The maximum departure from 

 the straight line of any single observed point was 7% of the maximum 

 change. The maximum change of resistance was 0.14% of the initial 

 resistance. 



8 Reference 5, p. 96. 



