Density, Coefficient of Thermal Expansion, and Entropy of Compression of LiquidHe4under Pressure Below 1.4°K

The density of liquid ${\mathrm{He}}^4$ at pressures up to 24.5 atm and at temperatures between 0.5 and 1.4°K has been measured by the dielectric-constant method. From the density data we derive the coefficient of thermal expansion, the entropy of compression, and the compressibility as a function of temperature and pressure. The results are discussed in terms of the Landau theory for liquid ${\mathrm{He}}^4$, and the parameters $\Delta$, $\mu$, and $p_0$ of the roton excitation spectrum are determined at several pressures and compared with previous determinations.