A Substitute for Mercury Electrode Contacts Platinum electrodes used for potentiometry, eoulometry, and various types of eleetrolysir are usually mounted by sealing them in the ends of glass tubes. As shown in the diagram on the left, mercury is commonly used to make electrical contact between the platinum and the lead wire fmm the power supply or potentiometer. This practice has several disadvantages. Although platinum is not dissolved readily hy the mercury, the metal of the contact wire, often copper, does dissolve until eventually the contact is broken. Also, the use of a mercury contact requires that the electrode be oriented vertically with the platinum pointing downward. Although this orientation is usually used, there are situations in which the reverse orientation is needed. An example of such a situation occurs when demonstrating the electrolysis of water. Here the platinum electrodes need to stick up into the tubes where the gases are collected. Still another disadvantage relates to the toxic nature of mercurv which would be soilled and scattered if the electrode was broken or tilted too far toward the horizontal. A convenient substitute for mercury which is free of these disadvantages is to tightly pack steel wool, or preferably, fine copper turnings between the platinum and the lead wire (right diagram). If corrosion of the steel wool appears t o be a problem the tube can be sealed with wax or epoxy cement. Of course, if capper turnings are used, corrosion will not occur. ~~~~
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Abilene Christian University Abilene. TX 79601
U
J o h n L. Bradford
Volume 57. Number 2 February 1980 1 159
