Finally, something to do with those nasty modern penniesS

There are plenty of ways that pennies made before 1982 are superior to ones made afterwards: The pennies themselves are worth more, as they're made with solid copper. When flicked or dropped, they have a pleasing ring to them, while modern pennies thud. Finally, early pennies can be used in a bunch of fun science experiments... but now modern pennies have their day.

We're going to hollow them out and play with their skins. It does take a little work. For one thing, you need to get a bit of muriatic or hydrochloric acid at a local store — and that can take some doing. Next you have to very, very carefully read the safety instructions on that acid. And finally, you have to find a place outside where that acid can be undisturbed for six hours, giving off hydrogen gas and eating through a penny.

At least, it will eat through part of a penny. Modern pennies are coated in some copper, but filled with zinc. You need to pierce the outer shell of copper, either by clipping it with shears or just rubbing one part of the edge against sandpaper or rough concrete. Next, drop it in the acid and wait about six hours. Zinc reacts much more readily to the acid than copper does, so the acid slowly wears away the zinc filling. The zinc and the chlorine will team up as liquid while the hydrogen from the hydrochloric acid will bubble away as gas. After six hours, carefully pour away the acid, diluting it with a lot of water so it doesn't cause any more damage. Pour water into the container holding the pennies, and mix in some baking soda. The baking soda will neutralize the leftover acid and stop the reaction. After a while, rinse the pennies off and examine them. They should be eaten away to fragile copper foil, still in the shape of a penny.

[Via NGHS]