Absorption of ions to the surface of dilute electrolyte solutions: The Jones-Ray effects revisited

The controversial observation of a minimum in the surface tension of dilute aqueous electrolyte solutions by Jones and Rays in the 1930s is confirmed by resonance-enabled second harmonic generation experiments. The experiments show that the quadruply charged ferrocyanide, Fe(CN)6(super 4-), anion is not surface active at high concentration, as expected, but at dilute concentrations, the anion is strongly attracted to the interface with a Gibbs free energy of adsorption of -6.8 kcal/mol.