56 BRIDGMAN. 



The value found for Young's modulus was 1.35 X 10^^ Abs, C. G. S. 

 or 1,39 X 10^ when the unit of tension is 1 kg/cm^. Neither the 

 coefficient of cubic compressibility nor any other of the elastic con- 

 stants of manganin seem to have been determined. I shall assume 

 in the following that a probable value of Poisson's ratio is f . 



Therlo. This alloy is made by the Driver Harris Co., and is much 

 like manganin in its properties. Its pressure coefficient of resistance 

 is also positive/* and is very close numerically to that of manganin. 



Measurements were made on both hard drawn and annealed wire, 

 as for manganin. Two samples of hard drawn wire were used. The 

 range of tension was 250 gm. The diameter of the wire was 0.005 

 inches. Within this range the relation between change of resistance 

 and tension is sensibly linear; the departure from linearity shown by 

 the manganin was not in evidence here. One run was made on the 

 first sample; the coefficient found for it was + 4.32 X 10~^ for a 

 tension of 1 kg/cm'. Three runs were made on the second sample, 

 giving 5.19, 4.80, and 4.84 for the coefficient. I take as the most 

 probable value for the coefficient + 4.8 X 10~^. 



A piece was annealed by heating to redness. Readings were made 

 of the resistance during a long series of applications of tension, through 

 a maximum range of 320 gm. The breaking load of the annealed 

 wire is about 350 gm.; that of the hard drawn is over 1 kg. The 

 initial coefficient for small loads immediately after annealing was 

 4.22 X 10"^. After seasoning as above, this coefficient had risen to 

 4.60 X 10""^. There seemed to be considerably less hysteresis in the 

 relation between tension and resistance than in the case of annealed 

 manganin. 



Young's modulus was measured in the same way as that of man- 

 ganin. There was considerably greater departure from linearity and 

 more hysteresis than was shown by manganin, and much more of 

 both than was shown by the resistance measurements.- Seasoning 

 was by the application and removal of 500 gm., and the modulus was 

 measured over a cycle of 400 gm. 



The hysteresis loop for this range of tension had an extreme width of 

 12% of the extreme extension. If we take the initial slope of this loop 

 as giving Young's modulus, we find 1.41 X 10^^ Abs. C. G. S., or 1.46X 

 10^ in kg/cni'. As in the case of manganin, I shall assume that 

 Poisson's ratio is \. 



The behavior of the resistance beyond the elastic limit is compli- 



14 Reference 5, p. 135. 



