The potential of the mercury+Fe(NO,), (500 mmolar) system was about +0.5 V (vs. the S.C.E.). However, as soon as cadmium or indium was mixed into the mercury and interfacial turbulence commenced, the potential decreased to about + 0.35 V (Cd) or + 0.39 V (In), and oscillated approx-imatelyf0.05
V about this mean value. It is apparent, then, that during turbulence, the mixed potential was dominated by the Fe3+/Fe2+ couple, although the Cd/Cd2+ or In/In3+ couple had a significant effect. This potential is quite far to the left of the electrocapillary maximum (approx.-0.5 V vs. a S.C.E.) in the region where small changes in potential produce large changes in interfacial tension.
Some observations made by Brimacombe and Richardson seem to agree with this mechanism as well. When an eddy of aqueous solution with a high concentration of ferric ions was projected from a syringe onto an interface between indium amalgam and an aqueous solution with a low concentration of ferric ions, a rapid outward movement of the interface away from the eddy was seen. According to Eq. ( 5), the potential at the region of the Fe3+ ion eddy would be undoubtedly higher than at the remainder of the interface where the Fe3+ ion concentration was less. The result would be a localized lowering of the interfacial tension and outward movement of the interface.