Lambda Curve of LiquidHe4

Abstract

We have measured the pressure ${P}_{\ensuremath{\lambda}}$ and the derivatives ${(\frac{\mathrm{dP}}{\mathrm{dT}})}_{\ensuremath{\lambda}}$ and ${(\frac{d\ensuremath{\rho}}{\mathrm{dT}})}_{\ensuremath{\lambda}}$ of the lambda curve of ${\mathrm{He}}^{4}$ as a function of temperature from the upper lambda point to the lower lambda point, using an apparatus of very high resolution. Empirical equations for ${P}_{\ensuremath{\lambda}}$ and ${\ensuremath{\rho}}_{\ensuremath{\lambda}}$ are presented which represent our data very well and agree generally with previous measurements. These equations define the position and slope of the lambda curve in the $\ensuremath{\rho}$, $P$, $T$ space to a higher order of accuracy and detail than has been possible before.