Is there any better way to spend an idyllic summer afternoon in Toronto's Kew Gardens than dissolving pennies in acid? If there is, I haven't heard about it!

For over 100 years (1858-1996, to be exact), Canadian pennies were at least 95% copper. But the pennies minted since then are only a few per cent copper - they have thin copper plating over a zinc (1997-99) or steel (2000-present) core. If you take a file to the edge of a recently minted penny, you'll see a silvery glint from the core metal!

Copper is a great metal to use in coins because, like nickel, it is highly unreactive. Zinc and the iron found in steel are another matter, especially in the presence of hydrochloric acid.

We put this to the test on the street (where else?). Many metals react with acids, but copper is relatively acid-resistant. Zinc, on the other hand, reacts like crazy with hydrochloric acid. The solid metal is rapidly consumed in the reaction and hydrogen gas is released.

We simply filed away the protective copper coating around the edge of post-1997 pennies and dropped them into the acid. The exposed zinc or steel immediately begin to react, as evidenced by the vigorous bubbling of hydrogen gas! After just a few minutes, the core is gone and all that is left are two thin sheets of copper veneer, with the head and tail relief of the penny perfectly preserved.

And if you try this, remember: BE CAREFUL! Hydrochloric acid is highly corrosive and must be handled and disposed of properly. It will hurt you badly if you're not careful!