The ITS-90 is defined in the ranges 0,65 K to 3,2 K and 1,25 K to 5,0 K by the vapour-pressure/ temperature relations of 3 He and 4 He, respectively. An apparatus has been constructed at the National Institute of Standards and Technology (NIST) for realizing the ITS-90 below 84 K which includes cells for realizing the ITS-90 through vapour-pressure thermometry with 3 He and 4 He. We present here the results of our realizations with He vapour pressures. The expanded uncertainties () of the ITS-90 temperature realizations are 0,12 mK or less over 97 % of the ranges of the ITS-90 definitions. In the lower 3 % of each range, the uncertainties of the realizations increase to 0,14 mK for 3 He and 0,16 mK for 4 He because of the growing size of the thermomolecular pressure correction. Comparisons are made with the previous wire scale of the NIST, which is traceable to the and NPL-75 scales. Also presented are the results from direct comparisons of 3 He and 4 He realizations between 1,25 K and 3,2 K ; these show the non-uniqueness of the ITS-90 in this region to be less than 0,3 mK.

Ill 41 6. Appendix 1. Thermodynamic functions for copper (in calories) 7. Appendix 2. Thermodynamic functions for silver (in calories). 8. Appendix 3. Thermodynamic functions for gold (in calories) V

fhe literature sources of heat-capacity data on ruthenium, rhodium, palladium, osmium, iridium, and platinum have been compiled and the data critically analyzed. Except for osmium where data arc lacking, best .... o.luee of thermodynamic properties have been evaluated between 0 and 300 K fro~ the analyses. The literature values of heat capacity, the electronic coefficient of heat capacity 6,), and the zero K limiting Debye characteristic temperature <6JO»)"are compared. The sources of data are tabulated chronologically along with the temperature range of measurements, purity of sample, and the pertinent experilnental procedures used. A bibliography of the references is listed.

Erratum: Equation (22) contains an error. It should read 100 ɛ(t, 0 °C) = 8.79 × 10 −4 t + 0.805 × 10 −7 t 2 .

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