Equation of state and melting properties ofHe4from measurements to 20 kbar

We measured simultaneously the pressure, volume, temperature, and ultrasonic longitudinal velocity in fluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ from 75 to 300 K and 2 to 20 kbar. The data were fitted to a Benedict-type equation of state from which various thermodynamic quantities were calculated. From 75 to 97 K the measurements extended into the solid region, yielding values of the melting properties and new constants for the Simon melting equation. We used the Lindemann relation to determine a Debye temperature from which the ultrasonic transverse velocity of solid. ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ was estimated. The melting entropy was analyzed to determine the contribution due to disordering of the atoms.