TABLE 392.— THERMAL ELECTROMOTIVE FORCE OF NICKEL 3§9 

 VERSUS PLATINUM l43 



Temperature versus emf 



143 Nat. Bur. Standards Journ. Res., vol. 5, p. 1291, 1930. 



TABLE 393.— AVERAGE PRESSURE COEFFICIENTS* OF ELECTRICAL 

 RESISTANCE UP TO 7000 kg/crr. 2 AS A FUNCTION OF TEMPERATURE 1 " 



Temperatures 



* xio« 



144 Undgman, P. W., Proc. Amer. Acad. Arts and Sci., vol. 67, p. 342, 1932. 

 t Maximum pressure 4300. 

 t On a less pure sample. 



TABLE 394.— RESISTIVITY OF MERCURY AND MANGANIN UNDER PRESSURE 



Pressure, kg/cm 8 500 1003 1500 2000 2500 3000 4000 5000 6000 6500 



R(P, -75°) Hg.. .9186 .9055 .8930 .8818 .8714 .8582 .8478 .8268 .8076 .7896 .7807 



R(p, 25°) Hg.... 1.0000 .9836 .9682 .9535 .9394 .9258 .9128 .8882 .8652 .8438 .8335 



*Hg 1.0030 .9854 .9716 .9588 .9462 .9342 .9228 .9010 .8806 .8616 .8527 



Rip, 125°) Hg... 1.0970 1.0770 1.0583 1.0400 1.0230 1.0070 .9908 .9614 .9342 .9086 .8966 



* This line gives the specific mass resistance at 25°, the other lines, the specific volume resistance. 



The use of mercury as above has the advantage of being perfectly reproducible so that at any time a pressure 

 can be measured without recourse to a fundamental standard. However, at 0°C mercury freezes at 7500 kg/cm 2 . 

 Manganin is suitable over a much wider range. Over a temperature range to 50°C the pressure resistance 

 relation is linear within Vio percent of the change of resistance up to 13,000 kg/cm 2 . The coefficient varies 

 slightly with the sample. Dridgman's samples (German) had values of (AR/pR<,) X 10 9 from 2295 to 2325. 

 These are + instead of — , as with most of the above metals. 



SMITHSONIAN PHYSICAL TABLES 



