Abstract: A hanging mercury drop electrode is described which makes use of a capillary tube with an inverted-U shape, removably fastened to an air-tight pressure-resistant cylindrical mercury reservoir. The capillary tube has a sufficiently thin inner diameter (0.35.times.10.sup.-2 to 0.5.times.10.sup.-2 cm) and a sufficient length (40 to 50 cm) such that the viscous forces prevent mercury from flowing through the capillary tube, once a height of the mercury head is selected (1 to 2 cm) which roughly counterbalances the back-pressure acting on the drop surface. To increase the drop size, a pressure higher than the atmospheric pressure is transmitted to the mercury reservoir from a pressure generator via an electromechanical valve, which is controlled by a timer or a microprocessor. The drop becomes stationary as soon as the mercury reservoir is connected with the outer atmosphere via another electromechanical valve.