Density Measurements and Solid Helium/3

This report describes the density measurements as a function of temperature and pressure PVT relations made on solid He4. The isothermal compressibility and the volume changes at the phase transitions have been accurately measured in the region of the body-centered-cubic solid phan estimate is made of the isobaric thermal expansion coefficient. The data suggest that thermodynamic relations predicting a negative thermal expansion coefficient in the solid might be altered by the fact that the compressibility of the solid at the melting curve is greater than at higher pressures. Calculations were made on the data of several experiments studying the flow of superfluid helium. There is ample evidence that a dissipative interaction can exist between the superfluid and the boundaries of the flow system when the superfluid velocity is greater than a certain critical value.