Measurements on a cast sample and an extruded sample are reported. There is no significant difference in behaviour. No anomaly of the type reported by Dauphinee et al. (1954) was found. A thermal study of the martensitic transformation showed a large specific-heat anomaly in the reversion region and a specific heat dependent on thermal history in the two-phase region. The heat of transformation from hexagonal close-packed to body-centred cubic sodium is deduced to be about 10 cal/g atom and the Debye temperatures of the two phases at 20$^\circ$K to be 160 and 153$^\circ$K respectively. The entropy at 298.15$^\circ$K is 12.24$\pm$0.12 cal/$^\circ$K g atom.