Alessandro Volta

Chapter 1 · The Boy Who Did Not Speak Until He Was Four

Como, and a career in static electricity

1745 – 1790 · Como · Pavia

Alessandro Giuseppe Antonio Anastasio Volta was born at Como in Lombardy in February 1745, into a noble but impoverished family. He did not speak until he was about four, and his family thought him slow. By seven he was reportedly ahead of his contemporaries.

His family intended him for the Church or the law. He was interested in electricity, and by his early twenties was corresponding with the leading electrical experimenters in Europe.

In 1775 he devised the *electrophorus*: a resin plate rubbed to charge it, and a metal plate with an insulating handle placed on it, touched briefly to earth, and lifted away carrying a charge. The crucial thing is that the process can be repeated *indefinitely* from a single charging of the resin, because the charge on the resin is not consumed — it induces charge in the metal plate again and again.

That is a machine for generating charge on demand, and it made him known.

He became professor of experimental physics at Pavia in 1779 and stayed for forty years.

He also, in 1776 and 1777, investigated the flammable gas rising from marshes near Lake Maggiore, isolated it, and showed it could be exploded by an electric spark in a closed vessel. That is *methane*.

And he improved the *electroscope*, adding a condenser arrangement that made it enormously more sensitive — able to detect charges far too weak for an ordinary instrument. That sensitivity turned out to matter for the argument that was coming.

“The apparatus of which I speak, and which will no doubt astonish you, is only an assemblage of a number of good conductors of different kinds arranged in a certain manner.”

— Alessandro Volta, letter to Sir Joseph Banks, 20 March 1800

Why this matters

Volta's condensing electroscope could detect charges far too weak for any other instrument, which is what let him win the argument with Galvani.

You have the electrophorus and the marsh gas. What would you ask him?

Ask Volta

• “How does the electrophorus keep producing charge?”
• “What did you find in the marshes at Maggiore?”
• “Why does a more sensitive electroscope matter so much?”
• “Is it true you did not speak until you were four?”
• “Why did your family want you in the Church?”

Chapter 2 · The Frog's Leg

Galvani's claim, and why it was reasonable

1791 – 1794 · Bologna · Pavia

*Luigi Galvani*, professor of anatomy at Bologna, published in 1791 a set of experiments on frogs.

He had found that a dissected frog's leg *twitches* when the nerve is touched with metal — particularly when *two different metals* are used, one touching the nerve and one the muscle, and brought into contact with each other.

His conclusion: the electricity resides in the *animal*. Living tissue generates its own electricity — *animal electricity* — stored in the muscle like a Leyden jar and discharged through the nerve, and the metals merely provide a path.

This was a sensation, and it was not an unreasonable conclusion. Electric fish were known and genuinely do generate electricity. Nerves plainly carry *something*. And Galvani had done careful work, including showing that the twitch occurs when a metal arc joins nerve to muscle with no external electrical source at all.

Volta initially accepted it, and then began to doubt.

His reasoning: the effect is much stronger with *two dissimilar metals* than with one. Why should the animal's own electricity care what the metals are made of? If the electricity comes from the frog, the metals are just wires — and any conductor should work equally.

He proposed instead that the electricity comes from the *contact of the two dissimilar metals*, with the moist tissue as a conductor between them. The frog is not a source. It is an extraordinarily sensitive *detector* — a galvanoscope, more sensitive than any instrument then existing.

That reframing is the important move, and it is a general one: a very sensitive detector is easily mistaken for a source of the thing it detects.

Why this matters

Volta's insight was that the frog was not producing the electricity but detecting it — and a very sensitive detector is easily mistaken for a source.

You have the twitching leg and two readings of it. What is your question?

Ask Volta

• “Why was Galvani's conclusion reasonable?”
• “What made you doubt it?”
• “How can a detector be mistaken for a source?”
• “Do animals generate electricity at all?”
• “How bitter did the argument get?”

Chapter 3 · Take the Animal Out

Silver, zinc and brine-soaked card, 1800

1799 – 1800 · Como · Pavia · London

The way to settle it is obvious once stated: *build the apparatus with no animal in it*. If it still produces electricity, the animal was never the source.

Volta stacked discs. A disc of *silver*, a disc of *zinc*, a disc of *card soaked in brine*. Then silver, zinc, brine again. And again, thirty or sixty times, into a column.

Touch a wire to each end and there is a current — *steady*, and *continuous*, and lasting as long as the pile holds together.

He described it in a letter to Sir Joseph Banks, President of the Royal Society, dated 20 March 1800, which Banks read out and published.

Two things about it are worth separating.

First, the argument was over. There is no frog. There is no tissue of any kind. The electricity does not require an animal.

Second — and this turned out to matter more — the pile was something *nobody had ever had*. Every previous source of electricity was *static*: a rubbed rod, an electrophorus, a Leyden jar, a friction machine. All of them give a large potential and a momentary discharge. You get a spark and a shock and then it is over.

The pile gives a *steady current*. It goes on. You can put it through a wire and leave it there for hours.

That is a completely different physical resource, and it opened a field that had not existed the week before.

Volta's *explanation* was wrong. He attributed the effect to the *contact of the two metals* itself — a contact potential — and regarded the brine as merely a conductor. The modern account is *chemical*: the current comes from a redox reaction, zinc dissolving and being oxidised, and the electrolyte is essential rather than incidental. That is why the pile runs down.

Why this matters

Every source of electricity before the pile gave a momentary discharge; the pile gave a steady current, which is a different physical resource entirely.

You have the stack of discs and no frog. What would you ask?

Ask Volta

• “Why does taking the animal out settle the argument?”
• “What is the brine actually doing?”
• “How is a steady current different from a spark?”
• “Why does a pile eventually stop working?”
• “Why write to the Royal Society rather than publish at home?”

Chapter 4 · Within Months

Water split, and six elements out of the ground

1800 – 1808 · London · Europe

The speed of what followed is the measure of what the pile was.

Banks showed the letter around before publishing it. Within about six weeks, in May 1800, *William Nicholson* and *Anthony Carlisle* in London had built a pile and used it to pass a current through water — and obtained *hydrogen at one wire and oxygen at the other*, in the volume ratio of two to one.

Water, decomposed by electricity, into its elements. That is *electrolysis*, and it happened within two months of the announcement.

*Humphry Davy* at the Royal Institution then took it much further. He had the largest battery in the world built by subscription, and reasoned that if electricity can decompose water it might decompose anything — that chemical combination is itself electrical in nature.

In 1807 he electrolysed molten potash and obtained *potassium*, a metal that had been locked inside a compound nothing could open. Sodium followed within days, then calcium, magnesium, strontium and barium in 1808.

Six new elements in two years, from an instrument that had not existed in 1799.

Michael Faraday later worked out the quantitative laws of electrolysis. Berzelius built a whole theory of chemical bonding on electrical attraction. The entire field of electrochemistry dates from the letter of March 1800.

Volta himself demonstrated the pile before *Napoleon* in Paris in 1801, and Napoleon — who took a real interest — awarded him a medal, made him a count and a senator of the Kingdom of Italy, and had him decorated.

Galvani had died in 1798, two years before the pile was announced, stripped of his professorship for refusing an oath to the Cisalpine Republic, still defending animal electricity.

And he was partly right. Nerve impulses *are* electrical. Bioelectricity is real, and the field is called *galvanism* in his honour.

Why this matters

Within two months of the pile's announcement water had been split into its elements, and within eight years six new elements had been isolated with it.

You have two months to electrolysis and eight years to six elements. What is your question?

Ask Volta

• “What did Nicholson and Carlisle do six weeks later?”
• “How did Davy get metals out of salts with it?”
• “What was it like demonstrating before Napoleon?”
• “Was Galvani right about anything?”
• “Did you expect any of this to follow?”

Chapter 5 · The Volt

A quiet retirement, and a unit

1801 – 1827 and after · Como · Pavia

Volta did comparatively little of importance after 1800. He was fifty-five when the pile was announced, and he had been working on the problem for a decade; he seems to have regarded it as finished.

He continued at Pavia, was showered with honours, and retired to Como in 1819, where he lived quietly with his family until his death in March 1827, aged eighty-two.

He was, by every account, a modest and courteous man. He remained generous about Galvani personally throughout the dispute — praising the quality of his experiments while rejecting his conclusion entirely — which is not the usual conduct of a scientific quarrel.

In 1881, at the International Congress of Electricians in Paris, the unit of electric *potential difference* was named the *volt*.

That is worth thinking about, because a unit is a peculiar kind of memorial. Volta had no concept of potential difference as a measurable quantity. He had no notion of resistance, or of current as a rate of flow of anything, or of what was flowing. He could tell that a bigger pile gave a bigger effect and that is about the limit of the quantitative account he could offer.

The quantity named after him was defined by people who came later, using a framework he did not have.

What he actually contributed was an *instrument* — and instruments are how physics moves. The pile is the ancestor of every battery on Earth: the cell in a torch, in a phone, in an electric car. All of them are two dissimilar materials with an electrolyte between them, which is the arrangement Volta stacked in 1800.

And the general lesson from the frog is durable: when an effect appears in a complicated system, ask whether the complicated part is producing it or merely revealing it.

Why this matters

Every battery on Earth is two dissimilar materials with an electrolyte between them — the arrangement Volta stacked in 1800.

You have the unit, the batteries and the quiet retirement. What would you ask?

Ask Volta

• “Did you understand what a volt would come to mean?”
• “Why did you stop working after 1800?”
• “Why stay courteous about Galvani?”
• “What is inside a modern battery that was in your pile?”
• “Is an instrument worth more than a theory?”

What Volta changed

Every battery on Earth is a descendant of the pile, and the volt is named after him. He also supplied the instrument that made chemistry electrical: within a decade of 1800 the pile had split water and produced sodium, potassium, calcium and magnesium. The whole field of electrochemistry dates from a letter written in March 1800.

A debate that continues

Volta's own explanation — that the effect arises from the contact of dissimilar metals — was wrong; the current is produced by a chemical reaction, and the electrolyte is essential rather than incidental. Galvani was also partly right, since bioelectricity is real.

Keep exploring — ask Volta

• “What would you have built next with a better pile?”
• “How do you argue with someone whose experiments you admire?”
• “What is actually flowing in your column?”

Related lives

• Humphry Davy — Who Prised New Metals Out of Salt
• Michael Faraday — Discoverer of Electromagnetic Induction
• Georg Ohm — Whose Proportion Was Called A Fancy
• Napoleon Bonaparte — Emperor of the French

Related themes

Cells and batteries · Electrolysis · Current electricity