320 



TABLE 398. — Resistance of Metals under Pressure (Brldgnun). 



The average temperature coefficients are per ° C between o° and ioo° C. The instantaneous pressure coefficients 

 are the values of the derivative {i/r)idr/dp}t, where r is the observed resistance at the pressure p and temperature /. 

 The average coenicient is the total change of resistance between o and 12,000 kg/cm' divided by 12,000 and the resist- 

 ance at atmospheric pressure and the temperature in question. Table taken from Proc. Nat. Acad. 3,0. 11, 1917. For 

 coefficients at intermediate temperatures and pressures, see more detailed account in Proc. Amer. Acad. 52, p. 573. 

 1917. Sn, Cd, Zn, Kahlbaum's "K " grade; Tl, Bi, electrolytic, high purity; Pb, Ag, Au, Cu, Fe, Ft, of exceptional 

 purity. Al better than ordinary, others only of high grade commercial purity. 



* 0° to 20°. t 0° to 24°. t Extrapolated from 50°. § Extrapolated from 75°. 



Additional data from P. Nat. Acad. .'=;c., 6, 505, ig2o. Data are 10,000 x mean pressure coefficient, o— 12,000 kg, 

 and 10,000 X instantaneous pressure coefficient at o kg. 1 = liquid ; s = solid. 



Mercury, pure and free from air and with proper precautions, makes a reliable secondary electric-resisttnce pres- 

 sure gauge. For construction and manipulation see " The Measurement of High Hydrostatic Pressure; a Secondary 

 Mercury Resistance Gaijge," Bridgman, Pr. Am. Acad. 44, p. 221, 1919. 



Pressure, kg/cm' 



R(P, -75°) 

 RiP,2S^).. 

 * 



R(P,' 125°). 



0.9186 



1 . 0000 

 I . 0000 



1.0970 



0.90SS 

 0.9836 

 o.'98s4 

 1.0770 



0.8930 



0.9716 

 1.0580 



0.8818 

 0.9535 

 0.9588 

 1 . 0400 



0.8714 

 0.9394 

 0.9462 

 1.0230 



0.8582 

 0.9258 

 0.9342 

 1.0070 



0.8478 

 0.9128 

 0.9228 

 0.9908 



0.8268 



0.9010 

 0.9614 



0.8076 

 0.8652 

 0.8806 

 0.9342 



6000 



0^7896 

 0.8438 

 0.8616 

 0.9086 



6500 



o. 7807 



0.833s 

 0.8527 

 0.8966 



* 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 mercurv freezes at 7500 kg/cm«. Man- 

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

 linear within 1/10 per cent of the change of resistance up to 13,000 kg/cm^. The coefficient varies slightly with the 

 sample. Bridgman s samples (German) had values of (AR/pRo) X 10' from 2295 to 2325. These are + instead of 

 — , as with most of the above metals. See "The Measurement of Hydrostatic Pressure up to 30,000 Kilograms per 

 Square Centimeter." Bridgman, Pr. Am. Acad. 47, p. 321, ign. 



Smithsonian Tables. 



