Tables 275-277. 

 TABLE 276. — Platinum Resistance Thermometers. 



247 



Callendar has shown that if we define the platinum temperature, pt, by pt = 100 ■{ (R — Ro) 

 /(Rioo— Ro) } , where R is the observed resistance at t° C, Rq that at 0°, Rioo at 100°, then the re- 

 lation between the platinum temperature and the temperature t on the scale of the gas thermo- 

 meter is represented by t — pt ;= 5-{ t/ 100 — i ^ t/ 100 where S is a constant for any given sample 

 of platinum and about 1.50 for pure platinum (impure platinum having higher values). This holds 

 good between — 23° and 450° when 5 has been determined by the boiling point of sulphur (445°-) 

 See Waidner and Burgess, Bui. Bureau Standards, 6, p. 149, 1909. 



TABLE 276. —Thermodynamic Temperature of the Ice Point, and Reduction to Thermodynamic Scale. 



Mean = 273.10° C. (ice point) 



For a discussion of the various values and for the corrections of the various gas thermometers to 

 the thermodynamic scale see Buckingham, Bull. Bureau Standards, 3, p. 237, 1907. 



Scale Corrections for Qas Thermometers. 



See Burgess, The Present Status of the Temperature Scale, Chemical News, 107, p. 169, 1913. 



TABLE 277. — Standard Points for the Calibration of Thermometers. 



♦ Thermoelectric extrapolation, t Optical extrapolation. 

 (Day and Sosman, Journal de Physique, 1912. Mesure des temperatures elevees.) A few additional points are: H, 



boils— 252.7°; O, boils — 182.9°; Hg. freezes 

 Smithsonian Tables. 



•37.7°; Alumina melts 2000° ; Tungsten melts 3000°. 



