ANALYSIS OF THE OSCILLATIONS IN BEATING MERCURY HEART SYSTEMS

A column of mercury whose top surface is covered with aqueous acid or base undergoes periodic changes in height when the surface is brought into contact with a corroding metal electrode. The voltage between the mercury and the corroding electrode also undergoes periodic changes which we have followed on an oscilloscope. Wc present here a thorough analysis of a mechanism for these oscillations which is based on the effect of voltage and adsorption on the surface tension of mercury. Oscillations in sulfuric acid solutions of strong oxidants, such as Cr2O72-(aq), apparently are associated with a film of Hg2SO4 on the mercury. The reduction of this film by the corroding electrode-or, in the absence of strong oxidants, the reduction of electron acceptors such as O2(aq)-modifies the surface tension of mercury. For an appropriate placement of the corroding electrode and the mercury, the altered surface tension switches the direction in which the surface moves. This effect breaks electrical contact between the mercury and the corroding electrode, so that the voltage of the mercury is free to rise as the oxidation or reduction process proceeds. The increasing voltage, in turn, modifies the surface tension in such a manner as to bring the mercury and electrode back into contact, completing the oscillation. We support this mechanism with quantitative measurements of the oscillations under a variety of conditions. Finally we show that the limit-cycle oscillations which occur in a simple mathematical model of this mechanism are in close correspondence to the observed oscillations. © 1979, American Chemical Society. All rights reserved.