Here’s how to to make a penny shell (using acid to dissolve the zinc core) –
Looking for something more interesting to do with that jar of pennies than just cash it in? One word: acid.
In most years before 1982, American pennies were 95 percent copper. Then the price of copper went up until you could get $100 worth of pennies at the bank, melt them down, and sell the metal for more than $100. So the government started using a core of cheap zinc with only a thin plating of copper.
The fact that pennies are made of two different metals opens up the interesting possibility of separating them.
GRAY MATTER Pretty Penny – Popular Science – Link.