Coexisting densities and critical asymmetry between gas and liquid

•Coexistence-curve diameter data support complete scaling of pure-fluid criticality.•Dielectric-constant data and calorimetric data prove highly valuable.

We assess currently available experimental data of the diameter of the coexistence curve for the gas-liquid phase transition of pure fluids. Various approaches, including the direct evaluation of dielectric-constant data and the analysis of calorimetric experiments, are found to support a leading |T-Tc|2β singular term in the diameter, with β≅0.326 and Tc the critical temperature. This is consistent with the predictions from “complete scaling” formulation of asymmetric fluid criticality.