326 



TABLES 398-399. 

 TABLE 398. Resistance of Metals under Pressure. 



The average temperature coefficients are per C between o and 100 C. The instantaneous pressure coefficients 

 are the values of the derivative (i/r)\dr/dp\ t , where r is the observed resistance at the pressure /> and temperature /. 

 The average coefficient is the total change of resistance between o and 12,000 kg/cm 1 divided by 12,000 and the resist- 

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

 coefficients at intermediate te.nperatures 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, Pt, of exceptional 

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



* tO 20. 



t o to 24. 



J Extrapolated from 50. 



Extrapolated from 75. 



Additional data from P. Nat. Acad. Sc., 6, 505, 1920. 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. 

 Li, s, o +.0772 + .068 Ca. o 



Li, 1, 240 +.093 + .093 Sr, 



Na, s,o .345 .663 1I-, s,o 



Na, 1,200 .436 .922 Hg, 1 25 



K, s, 25 - .604 1.86 Ga, s, o 



K, 1, 165 .8o 9 a 1.68 Ga, 1, 30 



+ ..06 

 + .680 



.236b 



.219 



.0247 



0531 



+ .502 

 334 

 -.064 



Ti, o 

 Zr, o 

 Bi, 1, 275 

 W, o 

 La, o 

 P, black, o 



.00!? 



.0040 



.ioic 



0135 



-0331 



.81 



- .004 



-123 



.014 



-039 



2.OO 



a, o - 9,000 kg; b, 7,640 - 12,000 kg; c, o - 7,000 kg. The Ga, Na, K, Mg, Hg, Bi, W, P, of exceptional purity. 



TABLE 399. Resistance of Mercury and Manganin under Pressure. 



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

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

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



* 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 o C mercury freezes at 7500 kg/cm 2 . Man- 

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

 linear within i/io per cent of the change of resistance up to 13,000 kg/cm 2 . The coefficient varies slightly with the 

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

 , as with most of the above metals. See "The Measurement of Hydrostatic Pressure up to 20,000 Kilograms per 

 Square Centimeter." Bridgman, Pr. Am. Acad. 47, p. 321, 1911. 



SMITHSONIAN TABLES. 



