Abstract
A single-crystal cerous magnesium nitrate (CMN) paramagnetic salt thermometer has been set up and used for therometry between 0.4 K and 3.1 K in a cryostat also equipped for the measurement of the vapour pressures of 3He and 4He. Two temperature scales, TX 1 and TX 2, have been derived in experiments with samples of CMN obtained from different sources. They are in agreement to ± 0.2 mK with the NPL-75 gas thermometry scale above 2.6 K, with the TXISU (1975) magnetic thermometry scale down to 1.3 K and with each other down to 1 K. There are appreciable differences between the two scales below 1 K for an unidentified reason. The scales are retained in terms of calibrations of 5 rhodium-iron resistance thermometers which also carry NPL-75. Vapour pressure data for 3He and 4He obtained with these thermometers have contributed to the derivation of values for the differences between EPT-76 and the established vapour pressure scales, T58 and T62, and also are intended for use in the complete revision of T58 and T62 which is envisaged by the Comité Consultatif de Thermometrie. The relationships between these various scales and other thermometric data in the range 0.5 K to 5.2 K are discussed.

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