Density of liquid potassium on the saturation line: A brief $50$-year history

This article considers a unit of a unique design created at the Joint Institute for High Temperatures of the Russian Academy of Sciences, which implements the method of a pycnometer of constant volume and variable mass. The data are obtained on the density of liquid potassium on the saturation line and on the $100$ atm isobar in the temperature range $336$–$2030$ K. The relationship between the results of the methodology implemented at the Joint Institute for High Temperatures, Russian Academy of Sciences (JIHT RAS) and measurements of the compressibility of water and steam carried out at the Moscow Power Engineering Institute (MPEI), starting with the work of V.A. Kirillina $1953$, is noted. The reliability of the experimental data on the density of liquid potassium in $1976$–$1977$ is analyzed in comparison with the results of the new, independent measurements in $1990$. The position of the ideal, as in a rarefied gas, coefficient of thermal expansion of the liquid on the saturation line and on the potassium isobar is found. The experimental data on density, compressibility, and ideal thermal expansion coefficients are used to estimate the position of the unit compressibility factor line and the inversion line of the Joule–Thomson effect for dense potassium in the temperature range $\sim1600$–$2300$ K and pressures up to $\sim2$ kbar. The considered data on the thermodynamic surface of liquid potassium require new experimental and theoretical work and expansion of the list of analyzed properties.