Estimation of Critical Constants T_c, ρ _c from the ρ(T) and T(ρ) Relations at Coexistence

The critical temperature T and the critical density ρ are estimated from new equations (1) for the double-valued ρ(T) relation, and (2) for the single-valued T(ρ) relation. For method (1) this report gives concise descriptions of the rectilinear diameter and of the densities of liquid oxygen. Calculated vapor densities agree well with experimental oxygen data over the wide range from triple-to critical-point. Method (2) is applied to hydrogen, oxygen, fluorine, and neon, giving the T(ρ) relation and estimates for T and ρ all in one step from the complete set of liquid and vapor data.