Vapor-Liquid Equilibria inHe3—He4Solutions

Recent measurements of the vapor pressures of ${\mathrm{He}}^3$—${\mathrm{He}}^4$ liquid solutions by Daunt and Heer and by Sommers are used to evaluate the solution non-ideality, for the calculation of which the large deviations of the vapor from ideality are taken into account. Estimation of the standard chemical potential of normal ${\mathrm{He}}^4$ at temperatures below the lambda-point is discussed. Agreement of excess chemical potentials of ${\mathrm{He}}^4$ above the lambda-point and the values obtained from the simple theory demonstrates the usefulness of the theory in discussions of effect of nonideality on the shift of the lambda-point with ${\mathrm{He}}^3$ concentration.