Relative Molar Volume and Limiting Solubility ofHe3in SuperfluidHe4

The relative fractional molar volume $\alpha$ of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in a ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ solution has been determined by a capacitance-measurement technique with a solution which remained in a single phase down to the lowest temperature of measurement, 31.7 mK. The observed temperature dependence at saturated vapor pressure is in excellent agreement with theory. Accounting for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ kinetic and interaction effects, we deduce that ${\alpha }_0$, the fractional molar volume of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ at zero (concentration, temperature, and pressure) is 0.286 ± 0.001. Measurements on more concentrated solutions permitted redetermination of the limiting solubility at zero temperature, with the result $x_0=0.0660\mathrm{}\pm 0.0006$.