A wedge effect at amalgam/electrolyte surfaces

Abstract

When amalgams are formed by discharge of the ions Li + , Na + , K + , Ca ++ , Mg ++ , NH + 4 at a mercury cathode in a glass vessel, a wedge of electrolyte penetrates between the amalgam and the glass. The effect is not observed for the discharge of Ag + , Zn ++ , Cd ++ or OH + 3 ions. To elucidate the origin of the forces maintaining the wedge in equilibrium, the wedge thickness and the curvature of the mercury/electrolyte interface have been investigated in various ways. The apex of the wedge was studied by interferometry. Measurements have been made during electrolysis of the interfacial tensions mercury/electrolyte and mercury/gaseous nitrogen. Possible theoretical interpretations are discussed. A marked reduction of the surface tension which is observed at certain amalgam/electrolyte interfaces is attributed to strong surface adsorption of the metal especially when the atom is more readily polarized than mercury. The electro-positive character of the amalgams and this reduction of surface tension explain some of the phenomena of the wedge effect.