EFFECT OF TENSION ON CERTAIN ABNORMAL METALS. 51 



temperature. The diameter of the wire was 0.028 inches, and the 

 range of tension 300 gm. The coefficients found were —4.65, —4.54, 

 and —4.78 X 10~^ respectively, the unit of tension being 1 kg/cm^. 



Measurements were made on one sample of the commercial electro- 

 lytic bismuth at two different temperatures. The dimensions of the 

 wire, and the range of tension were the same as for the commercial 

 material. At 31.1° the tension coefficient is —4.27 X 10~^ and at 

 0.0° 5.20 X 10~^. It is perhaps surprising that the coefficient should 

 be lower at the higher temperature, but this is also the case with the 

 pressure coefficient of resistance. 



One set of measurements was made on my own pure electrolytic 

 bismuth at 30°. The diameter of the wire was 0.0207 inches, and the 

 range of tension 100 gm. Within this range the effect is perfectly 

 linear, and no reading departs from the straight line by as much as 1%. 

 The total change of resistance under this load was 0.13%. The ten- 

 sion coefficient of this sample was —2.92 X 10~^. This is considerably 

 less than the coefficients of the other samples, but will be accepted in 

 the following as the best value for pure bismuth. 



Young's modulus of my pure electrolytic bismuth was determined 

 in the regular way by the bending experiments on two samples. The 

 diameter was as above, and the length about 6.5 cm. The maximum 

 load was 0.10 gm. The bending is linear with load within this range. 

 The two samples gave for Young's modulus 2.29 and 2.45 X 10^^ Abs. 

 C. G. S. units respectively. This is much less than the value given in 

 Kaye and Laby's tables, which is 3.19 X 10^^. It is of course possible 

 that this wire is not homogeneous, like antimony. Richards ^ has 

 found the compressibility to be 2.8 X 10~^-. Combined with my value 

 for Young's modulus this gives for Poisson's ratio 0.39 ; combined with 

 Kaye and Laby's value it gives 0.35. 



The phenomena beyond the elastic limit are complicated and would 

 be worth study for their own sake. In the first place, the resistance 

 increases beyond the elastic limit, and hence the change is in the same 

 direction as for other metals which are normal with respect to the elas- 

 tic effect of tension. The time effects are very large, and may con- 

 tinue for many days under loads which are much below the breaking 

 load and so small as to produce no marked change in the geometrical 

 dimensions. Under a fixed constant load, the resistance increases at a 

 time rate gradually becoming less, according to some law which I did 

 not attempt to discover. Commercial electrolytic bismuth showed 

 creep for two days under a load of 350 gm. whereas at 300 gm. the 

 effects were still elastic. In these two days the initial rate of creep 



