( 



THERMO-ELECTRIC QUALITY UNDER PRESSURE. 365 



Co)ist(uitan. This was obtained from the Electrical Alloys Co. of 

 Morristown, N. J., and is sold by them under the trade name " Ideal." 

 The chemical analysis given by them is: Copper 55%, Nickel 44%, 

 Manganese 1%, and Iron 1.4%. The diameter of the wire was 0.010 

 inches. There is of course not a great deal of interest at the present 

 stage of affairs in the beha^•ior of a substance so complicated; the 

 study of alloys as such would begin with simpler ones. This alloy 

 is used extensively in electrical measurements, however, and there is 

 some practical interest in its behavior. I have not previously given 

 data for any of the electrical properties of this substance; the list here 

 given is composed of (1) the temperature coefficient of resistance at 

 atmospheric pressure, (2) thermal e.m.f. at atmospheric pressure 

 against lead, (3) pressure coefficient of resistance, (4) pressure effect 

 on thermo-electric quality. 



At atmospheric pressure the resistance passes through a maximum 

 with rising temperature near 12°. The values found for the resistance 

 were as follows: at 0°, 1.0000; at 25°, 1.0000; at 50°, 0.9998; at 76° 

 0.9994, and at 97°, 0.9989. The change is, therefore, as slight as that 

 of manganin for any small range, but the minimum of manganin is 

 more pronounced than the maximum of this, so that the total change 

 between 0° and 100° of "Ideal" is greater than of manganin. 



The thermo-electric behavior at atmospheric pressure against 

 lead is given by the formulas: 



E = (-34.76 f-0.0397f^) X lO'^ volts, 



P = (-34.76 -0.0794 f) {t + 273) X lO'^ volts, 



(T = -0.0794(i + 273) X lO'^ volts/°C. 



Its thermal e.m.f. against commercial copper is represented by 



E = -(38.50/ + 0.0445/2) X lO'^ volts. 



This may be compared with results of Johnston and Adams ^^ for 

 wire from the same source. They give their results in the form of a 

 table; the maximum discrepanc\' between their results and that above 

 is at 100°, where they give 4227 X 10"*^ volts against 4295 above. 

 The difference is not greater than one would expect in dift'erent speci- 

 mens with different handling. 



The pressure coefficient of resistance was measured by the method 

 described in the previous paper. The wire was wound bare on a 



13 J. Johnston and L. H. Adams, Amer. Jour. Sci. 31, 510, 1911. 



