The Vapour Pressure Curve of Liquid Potassium up to the Critical Point

The vapour pressure curve of liquid potassium was measured up to the critical point which was found at Tcrit = 1925 °C ± 30 and Pcrit = 155 ± 15 bar. Using these vapour pressure data and existing density data of the vapour and liquid at saturation pressure the vaporization entropy of potassium as a function of temperature was determined. The vapour pressure was determined by the observation of the drastic change in the electrical conductivity and the thermoelectric power when the liquid metal is evaporated. Since no electrically insulating container material compatible with alkali metals is available, metallic tungsten‐rhenium container were used as conductors in parallel with the fluid metal sample. This newly developed method can also be applied to other corrosive liquid metals.