This Invention Report describes a measurement of density and velocity of sound with only reflection of ultrasound from the solid-liquid interface. One novel feature is that the passage of ultrasound through a liquid (or slurry) is NOT required. This means that the measurement can be carried out even though the slurry can be very attenuative. It also means that the vessel can be very large. If the solid material is quartz the measurement uncertainty is about 0.05%. If the solid is stainless steel, the measurement system is more rugged and a clamp-on sensor may be feasible.