From: LindaNg01 <LindaNg01@aol.com>
Date: Tue, 14 Apr 1998 23:25:47 EDT
To: pinhole@exploratorium.edu
Subject: Magic pennies?
Hi everyone,
Today to illustrate conduction of heat, I placed a stack of 10 pennies on a
hot plate. A student then placed his finger on the top coin and left it there
until it was too hot to touch. The hot plate was set at medium high
temperature so the coins became too warm to the touch after 5 minutes. A few
minutes later I was just about to take the coins off the hot plate when I
noticed a couple of pennies became the color of shiny new dimes. When these
cooled, the colors became more pale yellow in color. (These pennies dated
1987 and later.)
Other than conjecturing that a chemical reaction occurred or that the heat
melted the copper coating and exposed the underlying alloy metal, we could not
come up with any other explanations. Do any of you know what happened?
Many thanks.
Linda Ng