SURFACE-CHARGE DENSITY-MEASUREMENTS WITH A CONTROLLED GROWTH MERCURY-ELECTRODE

The surface charge density of the mercury-electrolyte interface is est imated using chronocoulometry at a controlled growth mercury electrode . After initial formation and equilibration the mercury drop is expand ed by further addition of mercury. Direct measurement of the charge re quired as new area is formed is used to estimate the surface charge de nsity. The mercury drop is modeled as a step-wise expanding sphere. Th e capillary noise continuously produced by stationary drops under pote ntial control was investigated and characterized. Spectral analysis of the noise reveals that the electrode is particularly sensitive to vib rations near the resonant frequency of the suspended drop. Ambient vib rations in the laboratory environment produce alternating currents at the electrode which vanish al the point of zero charge and so mark its position.