Most people are under the impression that pennies are made of copper. This is only partially true. Before 1982, pennies were made of 95% copper and 5% zinc. Because the price of copper was rising, the U.S. Mint had to change the penny’s composition to keep the cost of the coin under one cent.
Now pennies are 97.5% zinc and 2.5% copper. This changes the outcome of the experiment when you melt down a penny from both time periods and makes the experiment much more interesting.
Copper has a melting point of 1984.32 °F (1084.62 °C), and zinc has a melting point of 787.15 °F (419.53 °C). Because of this major difference in melting points, you can heat up a penny, and the zinc will melt long before the copper does. The problem with this is that the zinc is contained inside the copper that surrounds it, so you have to create a way to allow the zinc to escape.
Take a regular car battery and attach a piece of copper to both the positive (+) and the negative (-) posts of the battery. Make sure that the pieces of copper don’t touch, but rather have about a ¼” gap, in between them, so that you can touch the penny to both ends of the copper to make the connection. Hold the penny in a pair of pliers that have rubber handles to avoid shock. Next hold each penny to both pieces of copper, making the connection long enough to get the full effect.
Melting a penny with a car battery
Since the metal composition has changed in the penny over time the results will also be different when you use a car battery to try and melt them. An older penny, minted before 1982, will glow red all the way across in a uniformed manner when heated up. When you remove the penny from the battery the outside will blacken, also across the whole area of the coin. This is known as oxidation, and since the older older penny is composed of mostly copper it will be more prevalent.
When you do the same experiment with a penny which was minted after 1982 you will wind up with different results. Your penny won’t glow and there will be very little oxidation on the penny and not in a uniformed manner as in the case of the older penny. You will also be able to see the silver colored zinc showing from the center of the penny where chunks of it have melted away.