PVTSurface ofHe4near Its Critical Point

Abstract

High-resolution measurements of the pressure coefficient ${\left(\frac{\partial P}{\partial T}\right)}_{\rho }$ of ${\mathrm{He}}^4$ are reported in both the one-phase and two-phase regions close to the critical point. The data consist of 29 isochores covering the density range $-0.2<\Delta \rho <0.2\mathrm{}$ and the temperature range $-0.020<t<\mathrm{}0.032\mathrm{}$, where $\Delta \rho =\frac{(\rho -{\rho }_c)}{{\rho }_c}$ and $t=\frac{(T-T_c)}{T_c}$. The intersections of the isochores with the coexistence curve locate 28 points on the coexistence curve. These points fit the equation $\left|\Delta \rho \right|=(1.395\mathrm{}\pm 0.020)t^{\beta }$, with $\beta =0.3554\mathrm{}\pm 0.0028$ and ${\rho }_c=69.580\mathrm{}\pm 0.020$ ${\mathrm{m}\mathrm{g}/\mathrm{c}\mathrm{m}}^3$. Parameters are reported for the best fit of the data to the "linear model" of Schofield, Litster, and Ho, in which the critical exponents have the values $\alpha =0.115\mathrm{}\pm 0.006$ and $\gamma =1.1743\mathrm{}\pm 0.0005$, and to a more accurate parametric model in which $\alpha =0.067\mathrm{}\pm 0.006$ and $\gamma =1.2223\mathrm{}\pm 0.0017$. The more accurate model does not have the symmetry required by the scaling hypothesis.