ON THE CONVERSION OF THERMODYNAMIC PROPERTIES TO THE BASIS OF THE INTERNATIONAL TEMPERATURE SCALE OF 1990

The basis and application of the Douglas equations for the adjustment and calculation of differences in thermodynamic properties due to a ch ange in the temperature scale are reviewed. When higher-order terms in the general Douglas equations are discarded, the simplified Douglas e quations are obtained. These simplified equations together with the re cently revised set of differences between values of temperatures on th e International Temperature Scale of 1990 (ITS-90) and the correspondi ng values on the International Practical Temperature Scale of 1968 (IP TS-68) for 903.765 K < T-90 < 1337.33 K have been used to calculate ap proximate differences in thermodynamic properties for synthetic sapphi re (alpha-Al2O3). Tables of differences (T-90-T-68)/K and the derivati ves d(T-90-T-68)/dT are given as a function of T-68/K. (C) 1996 Academ ic Press Limited