Melting curve thermometry

FIGURE 19 (a) The entropy Sof liquid and solid He (upper diagram) measured in units of the gas constant R, plotted as functions of temperature T and the melting pressure Pm of He as a function of T. It may be noted that the minimum in the melting curve occurs at the temperature where the difference between the solid and liquid entropies changes sign. [From values tabulated by Betts, D. S. (1976). Refrigeration and Thermometry Below One Kelvin, Sussex Univ. Press, London.]... 

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