ON DEFINITION OF AN INTERNATIONAL PRACTICAL TEMPERATURE SCALE . INTERPOLATION OF DIFFERENCES IN RESISTANCE RATIOS OF PLATINUM THERMOMETERS BETWEEN 91-K AND 14-K

This study was made as a contribution to the information that was required to define an International Practical Temperature Scale between 90.2 K and 13.8 K by using a relation between the resistance ratio W(T) = R(T)/R (O°C) of platinum and the temperature. Three different methods for the interpolation of differences in resistance ratios (ΔW) have been applied to experimental data of 8 thermometers. Between the boiling point and the triple point of oxygen the accuracy of the interpolation is within 1 mK, between the triple point of oxygen and the boiling point of hydrogen interpolation within 2 mK is possible and between the boiling point and the triple point of hydrogen interpolation within 2 mK is possible if a calibration point near 17 K is indluded. The extrapolation below 13.8 K diverges rapidly. © 1969.