Removal of Silver Nitrate Stains Chemical laboratory students are often informed that clean hands on the day following an experiment utilizing silver nitrate or Tollen's reagent is a sign of good technique. Those students lacking in such technique are distinguished by the inexorable development of black stains on their skin and/or elothing, a visible indictment of their shortcomings, with a permanence reminiscent of Cain or Hester Prinn. Anxious students are little consoled when informed that the stains are no more permanent than the skin itself and will wear off in a week or two. T h e recent staining of this writer's hands prompted a successful search for available methods to remove silver stains. Since the results were not generally well known, these methods are offered here. Method 1': Silver stains are effectively removed from clothing and skin, even after darkening, by treatment with an aqueous solution of potassium iodide, followed by soap and water. Removal of the stain is usually not immediate but takes several hours. T h e skin is sometimes left with a pale white discoloration which also fades in a day or so. Removal of stains from clothing appears complete. Method Z2: Solution A-potassium ferricyanide (lo%,wlv) in water; Solution B-sodium thiosulfate (1090,w/v) in 1%("1") aqueous ammonia. Equal parts of Solutions A and B are mixed and applied to the stain followed by soap and water. Method 3? Solution A-copper sulfate or chloride (1090,wlv) in water; Solution B-sodium thiosulfate (45% wlv) in water. Equal parts of Solutions A and B are mined with 2 parts of water immediately before use and applied as above.
' Hayes, Jr., Daniel J., Corning Glass Works, Central Falls, RI, personal communication.
Schweis, Bruno, "Mirrors, A Guide to the Manufacture of Mirrors and Reflecting Surfaces", Pelham Books, London, 1973, p. 76. Clair J. C h e e r
University of Rhode Island Kingston, RI 02881
Volume 58
Number 2
February 1981
201
