This is a great experiment that can be done inexpensively and usually wows the kids. This experiment will only work if you use a penny that was minted after nineteen eighty two. Pennies were originally made of copper. Starting in nineteen eighty two the mint began using zinc inside our nations pennies and simply coating them with copper. While copper can withstand pool acid, pool acid dissolves the zinc leaving you with a copper shell. Make sure the children at no time come in contact with the pool acid. Make sure you rinse the copper shell thoroughly before the children examine it.