Analysis of 1982 Pennies
tory.
In 1981 (and the preceding 20 years) pennies were composed of a copper-zinc alloy of about 94% copper. When the surface of these coins is examined by energy dispersive X-ray Iluorescenre (XRF),this composition is easily confirmed without destruction of the coin. We were surprised, therefore, to discover that a similar analysis of a 1982 penny did not indicate less copper, but instead, pure copper. Our disbelief was removed when we discuvered that the method of manufacture has changed, and that the new pennies have asurface coalingof pure copper on a core of zinc. By stripping off the copper surface, with dilute acid. the zinc core was revealed. XRF showed that i l wasmainlvzinc (about 99%) with a trace of copwer and some
of copper has been reduced fiom 94% tu abnut 2.4% We were also surprised to find that only about half of the 1982 pennies which have come into our possession are of the "new" type. As far as we are aware, all pennies made in Denver are of the old type, but other unmarked pennies cannot he classified without analysis. This uncertainty can provide the motivation for the analysis of 1982 pennies. There is a simpler method of distinguishing the pennies. however, if they are in relatively good rundition. The older type weigh approximately 3.1g while the new ones weigh only 2.5 g. We would like to express appreciation to the class of sophomores who participated in this study. James M. Miller Drew University Madison. NJ 07940
142
Journal of Chemical Education
