Mercury Electrodes

Three examples of mercury electrodes are illustrated here: (a) hanging mercury drop electrode, or HMDE; (b) dropping mercury electrode, or DME; and (c) static mercury drop electrode, or SMDE.

Figure11.34

In the hanging mercury drop electrode, or HMDE, a drop of Hg is extruded by rotating a micrometer screw that pushes the mercury from a reservoir through a narrow capillary tube.

In the dropping mercury electrode, or DME, mercury drops form at the end of the capillary tube as a result of gravity. Unlike the HMDE, the mercury drop of a DME grows continuously—as mercury flows from the reservoir under the influence of gravity—and has a finite lifetime of several seconds. At the end of its lifetime the mercury drop is dislodged, either manually or on its own, and replaced by a new drop.

The static mercury drop electrode, or SMDE, uses a solenoid driven plunger to control the flow of mercury. Activation of the solenoid momentarily lifts the plunger, allowing mercury to flow through the capillary and forming a single, hanging Hg drop. Repeatedly activating the solenoid produces a series of Hg drops. In this way the SMDE may be used as either a HMDE or a DME.

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