Coexistence Curve of Sulfur Hexafluoride

The coexistence curve of sulfur hexafluoride has been determined by interferometric measurements for the temperature range 10^-5<(Tc-T)Tc<10^-1. The refractive index difference nₗ-nᵥ is fitted by a power law. The difference Δn is proportional to (ΔT)^β, where β=0.346±0.001 for the temperature range 10^-2<(Tc-T)Tc<10^-1. The exponent β decreases to 0.339 ±{} 0.003 as (Tc-T)Tc decreases to the lower limit of the data at 10^-5.