Lambda Curve of LiquidHe4

Abstract

We have measured the pressure $P_{\lambda }$ and the derivatives ${\left(\frac{\mathrm{dP}}{\mathrm{dT}}\right)}_{\lambda }$ and ${\left(\frac{d\rho }{\mathrm{dT}}\right)}_{\lambda }$ 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 $P_{\lambda }$ and ${\rho }_{\lambda }$ 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 $\rho$, $P$, $T$ space to a higher order of accuracy and detail than has been possible before.