That has been explained many times here. Basically you are making a balance beam thing. You simply place a flat stick on a pencil so it balances. Using a pencil with those sort of flat sides makes it easier. Once you have made a balance beam thing, you place a previous to 82 cent on one side, it is Copper, and a 82 Cent on the other side of the stick. If it balances, the 82 is Copper. If not, the 82 cent is the Zinc stuff.
Or you can start with a later than 82 cent on one side and then any you put on the other side either is heavier, it is the Copper one, or is the same and balances.