Interferometric Measurements of Isotherms of Sulfur Hexafluoride in the Critical Region

Abstract

Isotherms of sulfur hexafluoride in the critical region have been determined by interferometric measurements. A thin sample of pure fluid, compressed under its own weight, is placed in one arm of a Mach–Zehnder interferometer. The resulting interference pattern produced in the image plane of a lens yields horizontal fringes which relate fluid density to height in the sample. Isotherms giving density versus chemical potential or pressure are obtained from analysis of the interference patterns. Six sulfur hexafluoride isotherms for temperatures between 0.0018 K and 0.0281 K above the critical temperature are plotted.