US Pennies used to be made out of 95% copper.  The mint has changed the composition of the cent because the value of copper in the penny is actually worth more than face value of the coin.  As of today, the value of the copper in one of these copper cents is actually worth 2.1 cents.  This has lead a lot of collectors to start hoarding these cents since one can obtain copper at roughly half price.  It is illegal to melt down these cents, however there is speculation that this ban might be lifted, allowing these collectors to obtain nice payday.  Currently in circulation there is a mixture of these copper and zinc cents, and one must do a little bit of work to sort out the far less valuable zinc cents.

When searching through rolls of cents, you should create three separate piles:

1. Pennies that are 1981 and below. (These are copper cents.)
2. Pennies that are 1983 and above. (These are zinc cents.)
3. Pennies that are 1982 (These can be either and require an additional step to sort.)

The US mint changed the composition of the cent during the year of 1982, so there are cents that are the 95% copper and 5% zinc (what we are looking for) and cents that are 97.5% zinc and 2.5% copper (what we want to discard).  We can sort between these two by their weight.  The copper pennies weigh 3.11 grams while the zinc pennies weigh 2.5 grams.  If you are fortunate enough to own a small scale that is able to detect the difference between a tenth of a gram, you can use this to simply weigh the pennies and sort appropriately.  If you do not own one of these scales, you can make a simple device that can detect the difference for you.

The equipment you will need are a wooden tongue depressor, a circular piece of wood for a fulcrum, a pre 1982 penny, and super glue.  Carefully balance the tongue depressor with the penny on the fulcrum and move it down the fulcrum until the penny's weight makes the depressor hit the ground.  When it does, mark lightly with a pencil where the fulcrum should be.

Carefully glue the stick between  your marked lines and wait to dry.  If your 1982 penny makes the scale hit the ground as follows, you have a copper cent.

If it does not make it hit the ground, you can discard it, as it is a zinc penny.