Happy birthday, Alessandro Volta! The inventor of the first electrochemical battery was born on this day in 1745. In 1800, he demonstrated a device built out of alternating discs of copper and zinc, which were separated by saltwater-soaked cloth or paper, could supply steady electrical current through a circuit.

His discovery that produced electricity out of nothing more than a collection of metallic coins, paper and brine must have seemed like magic to those who witnessed it. In fact, it generated so much interest that the Italian physicist was called on to demonstrate it to Napoleon Bonaparte. It also energized a flood of experimentation and discoveries in chemistry and electricity.

Though it wasn’t clear at the time exactly how the battery worked, research in the intervening years has shown that chemical reactions allow electrons to flow. Each of the two metals reacts differently to contact with the conductive saltwater-soaked material, called an electrolyte, that separates them. Zinc sheds positively charged zinc ions into the electrolyte, which leaves behind negatively charged electrons in the disc. Meanwhile, the copper reacts with positively charged hydrogen ions in the saltwater by giving up electrons at its surface to form neutral hydrogen gas.

So, over time, the copper becomes more positively charged while the zinc becomes more negatively charged. These dissimilar electric charges between the two metal discs is called the potential difference, or voltage. In the analogy that equates electrical phenomena to water moving through pipes, voltage is described as the difference in water pressure between two points in the pipe. The two different points are the surfaces of the two different metal discs separated by the saltwater electrolyte. This potential difference causes electrons to flow through the circuit, the phenomenon we call electrical current.

You can make your own battery just like Alessandro Volta did centuries ago. You might have most of the equipment rattling around in your pocket to make a coin voltaic pile.

Top Image: Voltaic pile on display at the Science Museum in the UK.

Bottom image: An early voltaic pile. A. Volta. On the electricity excited by the mere contact of conducting substances of different kinds, 1800. Courtesy MIT.