Compressibility of LiquidHe4as a Function of Pressure

The compressibility, $\beta =-\left(\frac{1}{V}\right){\left(\frac{\partial V}{\partial P}\right)}_T$, of liquid ${\mathrm{He}}^4$ was measured from 1 atm to the melting pressure and between 1.6 and 2.5°K. $\Delta V$ and $\Delta P$ were determined from deflections of the cell walls. The normal decrease of $\beta$ with increasing $P$ was observed except in an area below the $\lambda$ line. For an isotherm crossing the $\lambda$ line, $\beta$ showed a minimum at $P<\mathrm{}{P}_{\lambda }$ and a peak at $P_{\lambda }$. The minimum also occurred between the lowest $T_{\lambda }$ (1.76°K) and 1.70°K. The variation of $\beta$ with $P$ near $P_{\lambda }$, relative to $\beta$ at 2.20°K, followed an equation of the form ${\beta }_T-{\beta }_{2.2}=a-blog|P-P_{\lambda }|$, where $a$ and $b$ for $P<\mathrm{}{P}_{\lambda }$ are greater than $a$ and $b$ for $P>\mathrm{}{P}_{\lambda }$. Between the $T$ limits of the $\lambda$ line, ${\left(\frac{\partial \beta }{\partial T}\right)}_P$ was definitely negative for $P$ just above $P_{\lambda }$, but it approached zero for $P\gg P_{\lambda }$.