A Convenient Method for Refurbishing Laboratory Clamps Frequently laboratory damps are discarded due to excessive mrmsion that renders them unsightly a t best and inoperative a t worst. Such corrosion results in the familiar unsightly green residue that accumulates on the metal surfaces and in the deposits that gradually "freeze" the thumbscrews. When this happens, attempts to free the thumbscrews by force usually result in either breaking the screws or stripping the threads. As laboratory clamps are becoming increasingly expensive even for simple ones ($12-16 apiece), and their replacement is wasteful of budget and resources, we sought a way to restore such clamps. We have found that nonferrous laboratory clamps,' particularly the popular Castalloy clamps, may be easily and safely restored by treatment with citric acid solution. After removing the Fiherglas jaw covers'(vinyl jaw covers may be left on), the corroded clamps are simply allowed to stand immersed in a steaming hot solution of 125 g of citric acid in 3 L of water.2 The solution is contained in a vessel such as a large beaker or even a large pan, preferably of Stainless Steel to prevent accidental breakage, on a hot plate. Usually 30 minis more than enough to remove all of the corrosion, free "frozen" thumbscrews, and restore the metal surfaces to a dean, if not polished, surface. The clamps may be soaked in the hot solution a s long a s is necessary, a s it does not rapidly attack the metal surfaces.The clamps are then rinsed, brushed with soap and water, rinsed again, and dried in a warm location. The thumbscrews are lubricated with a few drops of penetrating ail. The refurbished clamps are then ready to he returned to use. Occasional lubrication of the thumbscrews with oil will keep them operating freely indefinitely. 'Imn rings and other steel laboratory ware such as tongs and forceps may be cleaned with the cit"c acid solution;however, the solution will anack the metal upon pmlonged heating. Dibasic ammonium citrate is preferred in this case and may be inexpensively prepared by the addition of 87 mL of concentrated ammonium hydroxide to the above solution of citric acid. Alternatively, the more expensive mmmercial ammonium citrate may be used (Cohen, S. H., J. Chem. Educ.. 1982,59,670).Phosphoric acid solutions may also be used to remove rust fmm imn ware; this reaoent suners from the disadvantaae of beino verv corrosive. 21ne;pensive 99t %citric acid may b; purchask frdm Lancaster Synthesis (X4238,$18.901 kg)
Stephen W. Wright The Du Pont Merck Pharmaceutical Comoanv -~ ~~
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DU Pont Experimental ~tLtio;l Wilmington, DE 19880 J. Stephen Teeter Danrno~thCollege rlanover. NH 03755
322
Journal of Chemical Education
