Jean-Baptiste Dumas: A Life in Five Chapters

Chapter 1 · From an Apothecary's Counter to the Institut

Alais, Geneva, and Humboldt's letter

1800 – 1826 · Alais · Geneva · Paris

Jean-Baptiste André Dumas was born at Alais — now Alès — in the Cévennes in July 1800, the son of the town clerk. The family had no money for a professional education, and at fifteen he was apprenticed to a local apothecary.

He left for Geneva in 1816, aged sixteen, and worked in a pharmacy there while attending lectures at the Academy. Geneva at the time had a remarkable scientific community — Pictet, de Candolle, and the physicist Auguste de la Rive — and Dumas got himself noticed.

With the physician Jean-Louis Prévost he did work of real quality while still in his early twenties, including studies on the composition of blood and on the role of spermatozoa in fertilisation, showing that the sperm are the active agent and not, as some held, parasites.

In 1823 Alexander von Humboldt, passing through Geneva, met him and told him plainly that Geneva was too small for him and that he must go to Paris. Humboldt then wrote the letters that made it possible.

Dumas went, worked as an assistant, and rose quickly: lecturer at the Athénée, professor at the École Polytechnique, and by 1832 a member of the Académie des Sciences at thirty-two.

His early technical contribution was the *vapour density* method, published in 1826: vaporise a weighed sample in a bulb of known volume at a known temperature, and the density of the vapour gives the molecular weight relative to a standard. It was a genuine advance and gave him a route to atomic weights that was his own.

“The chlorine has entered and the hydrogen has gone.”

— Attributed to Jean-Baptiste Dumas, on the substitution reaction

Why this matters

Dumas's vapour-density method gave a route to molecular weights that depended on measurement rather than assumption, at a time when formulae were in dispute.

You have the apothecary's counter and Humboldt's letter. What would you ask?

Ask Dumas

• “What did Humboldt say to you in Geneva?”
• “How does vapour density give you a molecular weight?”
• “What did you establish about spermatozoa?”
• “Was an apothecary's apprenticeship a good training?”
• “Why did you have to leave Geneva?”

Chapter 2 · The Candles at the Ball

A complaint from the Tuileries

c. 1834 · Paris · The Tuileries

The story Dumas told, and which is repeated in every history of chemistry, is that a complaint reached him from the royal household. Candles supplied for a ball at the Tuileries had filled the room with acrid fumes that made the guests' eyes and throats sting, and the King's household wanted to know why.

Dumas investigated. The wax had been *bleached with chlorine*, a common commercial process for whitening tallow and wax.

He found that the chlorine had not simply been left behind as an impurity. Chlorine atoms had *entered the wax*, taking the place of hydrogen atoms — and the displaced hydrogen had combined with chlorine and left as *hydrogen chloride*, which is what the guests were breathing.

He followed it up systematically through the 1830s, passing chlorine over a range of organic compounds and analysing what resulted, and found the same pattern: hydrogen leaves, chlorine takes its place, atom for atom, and the substance that remains has broadly the *same general character* as the original.

The clearest case is acetic acid. Treat it with chlorine and successively replace one, two and three hydrogens, and you get mono-, di- and trichloroacetic acid. Each is still an acid. Each still forms the corresponding salts. The character survives.

This is *substitution*, and it is the reaction a fifteen-year-old now meets when shown what a halogen does to an alkane.

How much of the ball story is true is uncertain — Dumas told it years afterwards and it is a good story. The chemistry is not in doubt.

Why this matters

Substitution — one element replacing another atom for atom while the compound keeps its character — is the reaction every student meets when halogens react with alkanes.

You have the candles and what was in the smoke. What is your question?

Ask Dumas

• “What was actually making the guests cough?”
• “How do you show that chlorine went in and hydrogen came out?”
• “Why is trichloroacetic acid still an acid?”
• “How much of the ball story is true?”
• “What made you look for a general rule rather than one case?”

Chapter 3 · Berzelius Says It Is Absurd

A theory that could not survive a fact

1834 – 1840 · Paris · Stockholm

Substitution was not a small technical result. It destroyed the theory that organised the whole of chemistry.

Berzelius's *electrochemical dualism* held that a compound consists of an *electropositive* part joined to an *electronegative* part, held together by their opposite electrical characters. Hydrogen is strongly electropositive. Chlorine is strongly electronegative.

On that theory, taking a positive hydrogen out of a compound and putting a negative chlorine in its place is not a modification. It is an inversion. The compound should be transformed utterly, or should not form at all.

And trichloroacetic acid is still an acid.

Berzelius, the most authoritative chemist in Europe, said publicly that the result was absurd and must be wrong. He reinterpreted the products, then attacked Dumas personally, and fought it until his death in 1848.

A famous satire circulated — usually attributed to Auguste Laurent writing under a pseudonym, or to Friedrich Wöhler — purporting to report that by Dumas's method every atom in a substance could be replaced by chlorine, one by one, and the substance would remain itself; it described manganese acetate treated until nothing of the original remained but chlorine, still behaving as manganese acetate.

It was funny and it was aimed at a real weakness: Dumas had a rule and no account of *why* substitution preserves character.

But the fact stood, and dualism did not survive it. Dumas replaced it with the *theory of types*, classifying compounds by a fundamental skeleton into which substitutions can be made — which was better and was itself replaced within twenty years by structural formulae, which Dumas never really adopted.

Why this matters

Substitution destroyed electrochemical dualism because it showed that the electrical character of a substituted atom is not what holds a compound together.

You have the fact and the theory it broke. What would you ask?

Ask Dumas

• “Why can dualism not allow substitution?”
• “How did Berzelius attack you?”
• “Was the satire a fair criticism?”
• “Could you say why the character survives?”
• “What was the theory of types meant to do?”

Chapter 4 · Auguste Laurent

The blot on the record

1836 – 1853 · Paris · Bordeaux

Auguste Laurent had been Dumas's assistant, and he went further than Dumas was willing to go.

Laurent argued in the late 1830s that an organic molecule has a *nucleus* — a core structure — and that substitution replaces atoms within that structure while leaving it intact. He proposed representing molecules by geometrical figures, treated arrangement rather than composition as the thing to explain, and pressed toward what became structural chemistry.

Dumas's response was mixed and it does him no credit. He adopted parts of Laurent's thinking into his own theory of types, presenting it as his own development. When dualist opposition was fiercest, he publicly distanced himself from the more radical version and left Laurent exposed.

Laurent, who was outspoken, poor, and without patrons, was frozen out of Parisian scientific society. He could not get an appointment in Paris and was sent to a provincial chair at Bordeaux, which he regarded as exile. He worked in poor conditions, contracted tuberculosis — plausibly aggravated by an unheated and badly ventilated laboratory — and died in 1853, aged forty-five, in poverty. His major work was published posthumously.

Charles Gerhardt, his closest collaborator, died at forty-five as well, in 1856.

Both were substantially right, and both were dead before the structural chemistry they had argued for was accepted at Karlsruhe in 1860.

Dumas, meanwhile, prospered. Professor, dean of the faculty of sciences, member and later permanent secretary of the Académie, Master of the Mint, Senator under Napoleon III, and briefly Minister of Agriculture and Commerce.

He taught Louis Pasteur, who always spoke of him with gratitude.

He died at Cannes in April 1884, aged eighty-three, having been out of the laboratory for thirty years.

Why this matters

Auguste Laurent argued for structural chemistry, was frozen out of Paris, and died at forty-five in provincial poverty seven years before his position was accepted.

You have Laurent's exile and your own honours. What is your question?

Ask Dumas

• “What did Laurent see that you would not commit to?”
• “Did you use his ideas without helping him?”
• “Why was it so easy to freeze a man out of Paris?”
• “What did you owe an assistant?”
• “Would chemistry have moved faster if Laurent had been in Paris?”

Chapter 5 · A Chemist at the Mint

What happens when a scientist becomes a minister

1848 – 1884 · Paris · Cannes

From about 1848 Dumas was increasingly a public man rather than a working chemist.

He sat in the Legislative Assembly, became a Senator under Napoleon III, served briefly as Minister of Agriculture and Commerce, was president of the municipal council of Paris, and from 1868 was Master of the Mint — a chemist in charge of the national coinage, which is a reasonable appointment.

He was permanent secretary of the Académie des Sciences from 1868, one of the most powerful positions in French science, controlling what was read, published and funded.

That power is the thing to weigh. It let him support work he valued — he backed Pasteur consistently and effectively, and Pasteur was grateful for it all his life. It also meant that his coolness toward a man like Laurent was, in practice, career-ending.

His own scientific work largely stopped. He redetermined the atomic weight of carbon and of several other elements with care, and did some work on the composition of the atmosphere with Boussingault. But the laboratory years were behind him by his fifties.

He also, and this is worth recording, investigated *Prout's hypothesis* — the suggestion that all atomic weights are whole multiples of hydrogen's, implying the elements are built from a common unit. Dumas's own precise determinations showed some weights were not whole multiples, and he concluded the hypothesis was not exactly right while suspecting something like it might be true. Isotopes, discovered in the twentieth century, showed why: the weights are averages of mixtures.

He died at Cannes in April 1884.

Why this matters

Dumas ended as permanent secretary of the Académie, which meant his personal judgements about individuals had the force of career decisions.

You have the Mint, the Académie and the thirty years away from the bench. What would you ask?

Ask Dumas

• “What does a chemist do as Master of the Mint?”
• “Should a scientist take political office?”
• “What did being permanent secretary let you do?”
• “What did you conclude about Prout's hypothesis?”
• “Do you regret leaving the laboratory?”

What Dumas changed

Substitution is taught to every student who is shown what a halogen does to an alkane, and it broke the dualistic chemistry that had organised the subject for thirty years. Dumas also developed the vapour-density method for determining molecular weights and the theory of types that displaced dualism. He is a case study in how a theory can be right about a fact and wrong about everything underneath it.

A debate that continues

Dumas absorbed Auguste Laurent's ideas about molecular structure into his own theory of types while doing nothing to help Laurent's career, and Laurent died in provincial poverty at forty-five, seven years before his position prevailed.

Keep exploring — ask Dumas

• “What should Laurent be remembered for?”
• “Can a rule be worth having without an explanation?”
• “Which of your theories lasted longest?”

Related lives

• Jöns Jacob Berzelius — Who Gave Chemistry Its Alphabet
• August Kekulé — Who Gave Carbon Four Hands
• Louis Pasteur — Father of Germ Theory
• Justus von Liebig — Who Weighed What Burned Away

Related themes

Substitution reactions · Halogens and alkanes · Theories of bonding