Alessandro Volta (1745–1827) was born in Como, in northern Italy, and became professor of natural philosophy at the University of Pavia. He was a careful experimenter who had already invented a device for making static charge (the electrophorus, 1775) and discovered methane gas in marsh mud. His great invention came out of an argument.
Key idea
The problem: frogs' legs
In the 1780s Luigi Galvani, a doctor in Bologna, saw dissected frogs' legs twitch when touched with two different metals. In 1791 he published the idea that animals hold their own "animal electricity" in their nerves and muscles, and the metals only let it flow. Volta repeated the experiments, at first agreeing, then doubting. He suspected the electricity came from the two different metals touching through something wet, and the frog's leg was just a very sensitive detector.
What he tried
Volta tested pairs of metals in many combinations and ranked them by how strong an effect they gave. Zinc with silver or copper was among the best. He found that one pair gave only a tiny effect, so he tried adding more: cup after cup of salt water joined by metal strips (his "crown of cups"), and a pile of discs. The more pairs, the stronger the shock. On March 20, 1800, he described the pile in a letter to Sir Joseph Banks, President of the Royal Society in London.
The apparatus to which I allude, and which will, no doubt, astonish you, is only the assemblage of a number of good conductors of different kinds arranged in a certain manner.
In the same letter he lists the recipe: thirty, forty, sixty or more pieces of copper or silver, each against a piece of zinc, with layers of water, salt water, or card soaked in them between each pair, always in the same order.
Worked example: How tall a pile?
- Pairs add up: $n \times 0.8 = 12$.
- $n = 12 \div 0.8 = 15$.
Answer: 15 pairs.
Why it works
Who was right?
The argument between Galvani and Volta is a good example of two scientists each holding part of the truth. Volta was right that the pile's electricity comes from different metals and a liquid, not from the frog. Galvani was right that nerves and muscles use electricity: today we know nerve signals are electrical, and the science of bioelectricity grew from his work. Galvani died in 1798, before the pile was built.
| When | What happened |
|---|---|
| 1745 | Volta born in Como |
| 1775 | Invents the electrophorus |
| 1780s | Galvani's frog experiments in Bologna |
| 1791 | Galvani publishes on animal electricity |
| 1792–1799 | Volta tests metal pairs and argues for metallic electricity |
| 1800 | Volta describes the pile in a letter to the Royal Society |
| 1800 | Within weeks, William Nicholson and Anthony Carlisle use a pile to split water into hydrogen and oxygen |
| 1801 | Volta shows the pile to Napoleon in Paris |
| 1827 | Volta dies in Como |
| 1881 | The unit of voltage is named the volt |
Worked example: A long debate
- $1800 - 1791 = 9$.
Answer: 9 years.
What it led to
The pile gave scientists, for the first time, a current that kept flowing. Within a few years Humphry Davy used huge piles to discover sodium and potassium. Ørsted (1820) used one to find that a current moves a compass needle, and Faraday built his motor on that. Every battery today, from a flashlight cell to a car battery, follows Volta's plan.
Common mistake
Read more: Alessandro Volta and Voltaic pile.