From: SFPhysics <SFPhysics@aol.com>
Date: Thu, 16 Apr 1998 01:10:59 EDT
To: pinhole@exploratorium.edu
Subject: Re: Penny Cu/Zn Alloys
Hi Linda-
The new pennies are in fact zinc stampings with a copper plating. You did
indeed see a change as the copper went into the zinc by diffusion and created
an alloy called brass! One of the experiments in the Chemistry in the
Community Course by the American Chemical Society is to place an old solid
copper penny in a heated solution sodium hydroxide with mossy zinc. The penny
is then given a "hot-dipped" galvanized coating of zinc and becomes an
attactive silver. The penny is then heated over a bunsen burner until the
zinc amalgamates into the copper to form brass. Plunging the penny into water
stops the process and leaves you with a "gold" penny. This is a lot of fun
but what is more interesting is that pennies so treated change again since the
coating is only a few molecules thick and the zinc diffuses further into the
solid copper with time. Weird!
Al Sefl
SFPhysics@aol.com