Table 21 5 239 



THE INTERNATIONAL TEMPERATURE SCALE 



(Adapted from G. K. Burgess, Bur. Standards Journ. Res., 1, 635, 1928.) 



The Thermodynamic Centigrade Scale, on which the temperature of melting 

 ice, and the temperature of condensing water vapor, both under the pressure of 

 one standard atmosphere, are numbered o° and ioo°, respectively, is recognized 

 as the fundamental scale to which all temperature measurements should ulti- 

 mately be referable. 



The experimental difficulties incident to the practical realization of the 

 thermodynamic scale have made it expedient to adopt for international use a 

 practical scale designated as the International Temperature Scale. This scale 

 conforms with the thermodynamic scale as closely as is possible with present 

 knowledge, and is designed to be definite, conveniently and accurately repro- 

 ducible, and to provide means for uniquely determining any temperature within 

 the range of the scale, thus promoting uniformity in numerical statements of 

 temperature. 



Temperatures on the international scale will ordinarily be designated as 

 " °C," but may be designated as " °C (Int.) " if it is desired to emphasize the 

 fact that this scale is being used. 



The International Temperature Scale is based upon a number of fixed and 

 reproducible equilibrium temperatures to which numerical values are assigned, 

 and upon the indications of interpolation instruments calibrated according to a 

 specified procedure at the fixed temperatures. 



The basic fixed points and the numerical values assigned to them for the 

 pressure of one standard atmosphere are given in the following table, together 

 with formulas which represent the temperature (t p ) as a function of vapor 

 pressure (/>) over the range 680 to 780 mm of mercury. 



Basic Fixed Points of the International Temperature Scale 



°C 



(a) Temperature of equilibrium between liquid and gaseous oxygen 



at the pressure of one standard atmosphere (oxygen point). —182.97 



t P = t 760 + 0.0126 (p — 760) — 0.0000065 (P — 760) 2 



(b) Temperature of equilibrium between ice and air-saturated water 



at normal atmospheric pressure (ice point) 0.000 



(f ) Temperature of equilibrium between liquid water and its vapor 



at the pressure of one standard atmosphere (steam point) . . 100.000 



^p = ^760 + + 0.0367 (p - 760 ) - 0.000023 ( p - 760 ) 2 



(d) Temperature of equilibrium between liquid sulphur and its 



vapor at the pressure of one standard atmosphere (sulphur 



point) 444.60 



* P = / 7 go + 0.0909 (£ — 760) — 0.000048 (p — 760) 2 



(e) Temperature of equilibrium between solid silver and liquid 



silver at normal atmospheric pressure (silver point) 960.5 



(/) Temperature of equilibrium between solid gold and liquid gold 



at normal atmospheric pressure (gold point) 1,063 



Smithsonian Tables 



