The Voltaic Pile

Late in the 19th century, an Italian physicist, Alessandro Volta, created a remarkable device, an invention that had a profound impact on the evolution of science and technology. Volta was a professor of experimental physics at the University of Pavia. He had become involved in a debate with his colleague Luigi Galvani about the nature of electricity. Galvani was a doctor and scientist. His experiments with different metals and frog muscles led him to believe that electricity originated in living organisms, like frogs. He called this animal electricity. Volta was unconvinced. He didn't believe that frogs could create electricity. He suspected that the metals used in Galvani's experiments somehow produced electricity, and he set about trying to prove that. Volta spent years experimenting, eventually demonstrating that electricity could be produced using two metals. He accomplished this by creating a unique electrochemical cell. He produced a detectable electric current with disks of copper and zinc, separated by fabric that had been soaked in salt water. Volta then took this simple cell further. Piling cells on top of each other, he created a device with an increased electrical output. Called the voltaic pile, Volta had created a practical battery consisting of multiple cells. No one at the time could imagine how important this invention would become. It is not difficult to create a working voltaic pile. We will start by creating a single cell with a copper penny, some filter paper soaked in salt water, and a zinc washer. The salt water is the electrolyte in this cell. The copper penny is the positive terminal, and the zinc washer creates the negative terminal. We will assemble a number of these cells together, connecting copper to zinc. This is called a series connection. Make sure before you start that your pennies are actually copper pennies, and that your washers are galvanized. Galvanized means they're coated in zinc, and galvanized washers are available from most hardware stores. Start by creating a salt water solution. Mix one tablespoon of salt with 100 milliliters of hot water. This is the electrolyte. You may want to pour this solution into a petri dish or saucer. It makes it easier to soak the paper inserts. Cut some absorbent paper to the same size as a penny. I used coffee filter paper. Paper towels also work. Start by laying a strip of aluminum foil on the table. We will use this as one terminal of our cell. This aluminum foil is only being used as a conductor, connecting to the copper penny. It does not contribute to the output of the cell. We could have used any metal. Lay a penny on one end of the foil strip. Soak one of the paper circles in the salt water solution. Remove any excess solution. Lay the wet paper carefully on the penny. Next, lay a zinc plated washer on the wet paper. This is a completed cell. We set our digital meter to read direct current volts. That is DCV on the rotary dial. Touching the red positive lead to the aluminum foil and the black negative lead to the zinc washer, we get a reading of between 0.7 and 0.8 volts. Incidentally, the term volt, a measure of electromotive force, is derived from Voltas last name in recognition of his contributions to our knowledge of electricity. Now to start building the voltaic pile. Lay a penny on the galvanized washer, then a wet paper. This is the electrolyte, followed by a galvanized washer. Be careful when putting the next wet papers on each cell. It is important that no excess electrolyte spills down the side of your battery. This can create a short circuit, reducing the output. Now we have two cells connected in series, negative to positive. Reading our voltage again, we now have over 1.5 volts, twice the voltage of a single cell. A third cell triples the voltage reading. Let's take a look at the current that this battery is producing. I'll switch the meter to read current, and we see this battery produces only 1.3 milliamperes, a very tiny current. Even though that is a small current, I think it is enough to light a high efficiency LED. Remember that LEDs are polarized. Touch the positive lead to the aluminum and the negative lead to the galvanized washer. We get a dim glow. We can produce more current by adding another battery in parallel. To do this, just assemble a second battery beside the first one, both standing on the aluminum strip. Join the top of each battery with another piece of aluminum. When completed, the voltage remains the same, but the current has almost doubled. We are now getting 2.5 milliamps, and our LED is now a bit brighter. Four batteries in parallel yield the same voltage as a single battery, but the current has now increased to 4.7 milliamps. The LED glows brightly. As we have discovered, individual cells can be organized to create any voltage or current requirement. Assembling cells in series increases voltage. Assembling cells in parallel increases current. The battery cells in hybrid electric cars, like this Prius, are connected in series and parallel. Custom versions of these batteries can be configured to produce over 200 volts with 80 amps of current. The cells in these batteries use exotic materials and sophisticated chemistry, but we can trace their origins to the basic metals and salt water of that first voltaic pile. Volta's invention revolutionized the use of electricity. If you're interested in learning more about electricity and battery technology, check out our website, hileroad.com. Follow the project's link.