Another Use For Broken Glass Electrodes Previously reported in this Journal are accounts of how broken glass electrodes can he put t o good use as indicator electrodes for potentiometric precipitation titrations,' and for the construction of ion selective e l e ~ t r o d e sAnother .~ use that can be made of slightly hroken glass electrodes or those that have stopped working is in the construction of metallic electrodes for potentiometry and eoulometry. For our undergraduate courses in quantitative analysis and instrumental analysis the metallic electrode which finds most frequent use is that of platinum. Platinum electrodes areusedas indicating electrodes for potentiametric redox titrations and as working and auxillaty electrodes in coul&etry. Their c&truction from broken glass electrodes is both simple and inexpensive and provides a desirable area of platinum surface along with an attached shielded lead and consolder venient insulated shank for mountine. epoxy Tn conat&ine the tio of the hroken elass electrode is ruhhed on ..~ " the metallic ele&des. ~~~,~ /platinum disc fine emery rluth until a flat m m t h surface is produred. During this operation thr small silwr hend~nc contact wire that normally dips into the internal filling solution is prorerwd hy rnrcf~~llg it up into the cavity of the electrode. A circle of platinum foil of suitable size is soldered to the cleaned contact wire and then sealed t o the glass shank with epoxy cement. The diameter of the platinum foil must be large enough t o cover the open end of the electrode, hut can extend several millimeters heyond the glass shank if an electrode of larger surface area is needed. The main expense involved is that of the platinum foil, however, a disc measuring 12 mm in diameter and having a thickness of 0.1 mm will cost Less than four dollars. ~~~
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Davidson, John E., J. CHEM. EDUC., 50,375 (1973). Olson, Virgil K., Hargens, Robert D., Catr, James D., and Larson, Robert D., J. CHEM. EDUC., 51,791 (1974). Abilene Christian University Abilene, Texas 79601
J o h n L. Bradford
Volume 55, Number 2 February 1978 / 129
