Commentary on “Correlation of solubility of hexamethylene-1,6-bisthiosulphate disodium salt dihydrate versus dielectric constants of water + ethanol mixtures”

Apelblat model equation coefficients reported by Song and coworkers [Fluid Phase Equilib. 384 (2014) 143-149] are found to give calculated mole fractions that exceed unity for the solubility of hexamethylene-1,6-bisthiosulphate disodium salt dihydrate dissolved in binary aqueous-ethanol solvent mixtures. The calculated mole fraction solubilities are approximate ten thousand times the experimental values. A polemic is also given regarding the authors' interpretation of an observed mathematical relationship between the experimental mole fraction solubility data and the dielectric constant of the binary solvent mixture. The authors' interpreted one of the curve-fit equation coefficients as the free energy of solute at the thermodynamic equilibrium state. An unit analysis examination shows that the unit of the curve-fit equation coefficient must be J/(mol K) which is inconsistent with free energy.