Recreate Physics History: Build a Voltaic Pile
In the late 1700s, Italian scientist Luigi Galvani stumbled across one of the most important discoveries of all time. He found that frog legs would contract when some of the muscles and nerves were connected – even when the frog was dead! Galvani attributed this phenomenon to the idea that animal and human brains produce electricity, which he referred to as "animal electricity." He surmised that this electricity was then stored in the animal's muscles after being transported to the muscles through the nerves, much like how electricity is stored in a Leyden jar. According to Galvani, when certain muscles and nerves were connected, animal electricity discharged and the muscles contracted.
An Italian scientist, Alessandro Volta, read about Galvani's work and through experimentation came to strongly disagree with Galvani's explanation of the phenomena, especially the idea that living beings produced "animal electricity." Volta instead believed that the electricity present in the frog was the result of the contact of the metal probes with the frog tissue. In 1791, Volta produced continuous electric current when he placed a cloth soaked in salt water between silver and zinc disks. In 1800, Volta discovered that the current increased when he stacked several pairs of these single electrochemical cells together. This device became known as the voltaic pile, and was the first electrochemical battery.
Voltaic Pile Materials
You can make your own voltaic pile out of simple and inexpensive materials. Although Volta used silver and zinc, it is more feasible – and inexpensive – to use copper and zinc for the metal disks. Even though pennies are no longer made of copper, their copper coating still makes them a great choice for copper disks, and zinc disks can be obtained by purchasing galvanized electrical boxes and punching out the holes. The electrical box seen on this page and in the video was purchased at a local home improvement store for only $0.74 and provides 17 zinc disks. Other materials needed include thick card stock, salt water, a voltmeter or multimeter, and scissors. Wooden dowel rods poked into modeling clay can provide vertical support for the pile as more and more cells are stacked on top of each other, and more closely replicates the design of the original Voltaic pile. You may also want to include an LED and connecting wires as your voltaic pile should generate enough power to light an LED.
To make the voltaic pile, cut out card stock disks the size of a penny and soak them in a cup of salt water. To make a single cell, place a card stock disk that was soaked in salt water on top of a zinc disk, and then place a penny on top of the card stock. Touch the positive probe of a voltmeter to the copper and the negative probe to the zinc and you will find that the electric potential difference, or voltage, of this simple electrochemical cell will likely be between 0.60 V and 0.80 V.
If you make another cell and stack, or pile, it on top of the other so that you essentially have two cells in series, you should find that the resulting electric potential difference is between 1.20 V and 1.60 V. If you continue to pile single cells made of a zinc-card stock-copper sandwich on top of each other, you will find that the voltage increases with each additional cell. Small wooden dowel rods poked into modeling clay can be used to keep the stack of electrochemical cells from falling over.
Voltaic Pile with Multiple Cells
The voltaic pile illustrated above was made of multiple zinc-card stock-copper cells and had an electric potential difference of 3.26 V at the time of the photo, although it had initially read larger. Unfortunately, you can expect to have fluctuations and inconsistencies in voltage readings, but readings should generally increase as additional cells are added.
You should be able to connect an LED to your voltaic pile and watch it light. LEDs are directional, which means that the positive lead (the longer of the two leads exiting the bottom of the bulb) must be connected to the positive (copper) terminal of your voltaic pile.