Heat Capacity and Freezing Curves of Fluid<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">He</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">He</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">He</mml:mi></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>Mixtures

The heat capacity at constant volume, ${C}_{v}$, and the freezing curves, $p\ensuremath{-}T$ and $p\ensuremath{-}V$, have been measured for ${\mathrm{He}}^{3}$-${\mathrm{He}}^{4}$ fluid mixtures of ${\mathrm{He}}^{3}$ concentration, $X=0.17, 0.51, 0.79, \mathrm{and} 0.95$, between 50 and 150 atm and up to 4.5\ifmmode^\circ\else\textdegree\fi{}K. Some measurements of ${C}_{v}$ for pure ${\mathrm{He}}^{3}$ and ${\mathrm{He}}^{4}$ were also made in the same range. It is found that the freezing pressure is linear in $X$, $p(X, T)=X{{p}_{3}}^{0}(T)+(1\ensuremath{-}X){{p}_{4}}^{0}(T)$, within 1 atm; and that the excess volume at freezing, ${V}^{E}$, is smaller than \ifmmode\pm\else\textpm\fi{}0.04 ${\mathrm{cm}}^{3}$/mole. The specific heat ${C}_{v}$ can be fitted by a linear interpolation between ${C}_{v}$ at the same volume and temperature for the pure isotopes. Calculations of the discontinuous change in ${C}_{v}$ on freezing, based on these linear interpolations, are in fair agreement with experimental values.

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