Lavoisier and the Chemical Revolution (1789): Modern Chemistry

The Chemical Revolution was the transformation of chemistry in late eighteenth-century France led by Antoine-Laurent Lavoisier. Through precise weighing, he showed that combustion and respiration involve oxygen, overturned the old phlogiston theory and, with colleagues, gave chemistry a new language. His Traité élémentaire de chimie of 1789, the year the French Revolution began, became the first modern chemistry textbook.

Background: chemistry before Lavoisier

In the mid-eighteenth century most chemists explained burning through phlogiston, a theory developed by the German chemist Georg Ernst Stahl. Burnable materials were thought to contain phlogiston, which escaped into the air as they burned. A metal turning into a powdery “calx” when heated was likewise said to be losing phlogiston.

The theory had a problem: many metals gained weight when they formed a calx. Meanwhile British and Swedish chemists, studying different “airs”, were discovering new gases, including fixed air (carbon dioxide) and inflammable air (hydrogen), the latter isolated by Henry Cavendish in 1766.

Lavoisier the man

Lavoisier was born in Paris on 26 August 1743 into a wealthy family. He trained in law but turned to science and was elected to the Academy of Sciences in 1768. The same year he bought a share in the Ferme générale, the private company that collected indirect taxes for the crown, which gave him the fortune to equip a superb laboratory.

In 1771 he married Marie-Anne Pierrette Paulze, the 13-year-old daughter of a fellow tax farmer. She became his closest collaborator, learning English to translate chemical works, keeping laboratory records and drawing the plates for his books. From 1775 he also directed the national gunpowder administration and lived at the Paris Arsenal, where he did much of his research.

In 1788 the painter Jacques-Louis David portrayed the couple together, Lavoisier at a table covered with scientific instruments and Marie-Anne standing beside him. The large double portrait, now in the Metropolitan Museum of Art in New York, is one of the best-known images of eighteenth-century science. After her husband’s death, Marie-Anne kept his memory alive and arranged the publication of his collected Mémoires de chimie.

Oxygen and combustion

In 1772 Lavoisier showed that phosphorus and sulphur gain weight when burned, absorbing something from the air. In 1774 the English chemist Joseph Priestley, who had isolated a gas in which candles burned brightly, described his work to Lavoisier during a visit to Paris. The Swedish apothecary Carl Wilhelm Scheele had prepared the same gas independently a few years earlier.

Both men interpreted the gas within phlogiston theory. Lavoisier instead concluded that it was a distinct element that combined with substances when they burned or formed calxes. He named it oxygène, from Greek words meaning “acid-former”, because he wrongly believed it was present in all acids.

In 1783, working with the mathematician Pierre-Simon Laplace, Lavoisier showed that water is a compound of oxygen and the gas he named hydrogen (“water-former”). With Laplace he also built an ice calorimeter to measure heat and argued that animal respiration is a slow form of combustion.

A new language and the 1789 Traité

In 1787 Lavoisier, Louis-Bernard Guyton de Morveau, Claude-Louis Berthollet and Antoine-François Fourcroy published the Méthode de nomenclature chimique. It replaced traditional names such as “oil of vitriol” with systematic ones such as sulphuric acid, so that a name described a substance’s composition. Names like oxide, sulphate and carbonate come from this reform.

The Traité élémentaire de chimie of 1789 brought everything together. It defined an element as a substance that could not be broken down further by analysis and listed 33 “simple substances”. Most are still recognised as elements, though the list also included light and caloric, a supposed heat fluid. The book clearly stated that in every operation the quantity of matter is the same before and after, the principle now called the conservation of mass. In the same year Lavoisier and his allies founded the journal Annales de chimie.

Reception: the end of phlogiston

The new chemistry did not win overnight. In 1787 the Irish chemist Richard Kirwan published an Essay on Phlogiston defending the old theory. Madame Lavoisier translated it into French in 1788, and Lavoisier and his colleagues added critical notes answering it point by point. Kirwan himself eventually accepted the new system.

Younger chemists in France were won over quickly, and the clarity of the Traité, which was soon translated into English, German, Italian and other languages, spread the new ideas across Europe. By the late 1790s most leading chemists had abandoned phlogiston. A notable exception was Joseph Priestley, who never accepted Lavoisier’s theory and defended phlogiston until his death in 1804.

Lavoisier’s method mattered as much as his conclusions. He insisted on weighing all the substances that entered and left an experiment, including gases, using balances made to unusual precision. He treated chemistry as a balance sheet, in which nothing could appear or disappear without being accounted for. This approach made results comparable between laboratories and became standard practice.

Public service and the tax farm

Lavoisier spent much of his time on public work. As head of the gunpowder administration he improved the quality and supply of French saltpetre and powder, which helped France and its allies during the American War of Independence. On his farm at Fréchines he ran agricultural experiments, and he wrote on public finance, hospitals and prisons.

His role as a tax farmer, however, linked him to the most resented institution of the old regime. In the 1780s he supported the building of a customs wall around Paris, the Wall of the Farmers-General, to stop the smuggling of taxed goods into the city. The wall was deeply unpopular with Parisians and was attacked by crowds in July 1789.

Revolution and execution

Lavoisier supported reform in the early years of the French Revolution and served on the commission that prepared the metric system. Earlier, in 1784, he had sat on the royal commission that tested Mesmer’s animal magnetism.

His role in the Ferme générale proved fatal. The tax farmers were widely hated, and in November 1793 they were arrested. On 8 May 1794 Lavoisier was guillotined in Paris with 27 other tax farmers, among them his father-in-law, during the Reign of Terror. The mathematician Joseph-Louis Lagrange is reported to have remarked that it took only a moment to cut off that head, and a century might not produce another like it.

Myths and facts

The claim that the judge declared “the Republic has no need of scientists” is almost certainly apocryphal. It is also wrong to say Lavoisier discovered oxygen single-handedly; his achievement was to explain it. And while he stated the conservation of mass clearly, earlier thinkers, including the Russian scientist Mikhail Lomonosov, had expressed similar ideas.

Timeline

• 1743, 26 August: Antoine-Laurent Lavoisier is born in Paris.
• 1768: Elected to the Academy of Sciences; joins the Ferme générale.
• 1772: Shows that phosphorus and sulphur gain weight on burning.
• 1774, October: Priestley describes his new gas to Lavoisier in Paris.
• 1783: With Laplace, shows that water is a compound of hydrogen and oxygen.
• 1787: The Méthode de nomenclature chimique is published.
• 1789: The Traité élémentaire de chimie appears.
• 1794, 8 May: Lavoisier is guillotined in Paris.

Why it matters

Lavoisier turned chemistry into a quantitative science based on the balance and on clear definitions of elements and compounds. His oxygen theory, naming system and conservation principle form the foundation on which later chemists, from Dalton to Mendeleev, built the modern understanding of matter.