Antoine Lavoisier

Antoine Lavoisier (1743-1794), French chemist, usually considered the founder of modern chemistry. Among his many achievements he advanced the use of quantitative chemical methods, was largely responsible for developing the modern conception of a chemical element, and revealed the true nature of combustion.

Lavoisier was born on August 26, 1743, in Paris, the son of a prosperous lawyer. When he was five, his mother died and he was looked after by a maiden aunt. He attended an outstanding school, the Collège Mazarin, where he acquired a sound classical and literary training. One year was devoted to mathematics and science, but chemistry only came later, when he attended a course given by Guillaume François Rouelle at the Jardin du Roi. Although he had an early interest in science, this provided few career opportunities, so he studied law, gaining his licentiate in 1764. He also purchased a share in the Company of General Farmers, responsible for collecting several indirect taxes. This system of taxation was quite profitable for the tax-farmers, the private individuals who were its managers, but it involved Lavoisier in numerous trips to the provinces to inspect the local collection of taxes.

Lavoisier undertook a geological expedition in the provinces in 1767. He wrote a memoir on gypsum, which he submitted to the Academy of Sciences. He also attracted the attention of the Academy by winning a prize for an essay on the street lighting of Paris, and in May 1768 was elected as a junior member of the Academy in the chemistry section, at the unusually early age of 24. His first memoir as an Academician was a careful quantitative study to disprove the idea that water could be transmuted into “earth” by prolonged boiling in a glass vessel. He showed that the small solid residue consisted of material from the glass, which had been dissolved by the water and then precipitated.

As early as 1766 Lavoisier had begun to speculate on the nature of the four so-called “elements” of Aristotle, still then accepted by most chemists: water, earth, fire, and air. It was the study of air that was to be crucial, a subject that had been pioneered by a succession of British workers. The study of air (1727) by Stephen Hales was followed by the discovery by Joseph Black (1754) that, apart from ordinary air, there was another type of air, which he called “fixed air”, and we now call carbon dioxide. This led to the discovery of other gases, including “inflammable air” (hydrogen) by Henry Cavendish (1766) and many other gases by Joseph Priestley in the 1770s. These included a gas that Lavoisier was later to call “oxygen”.

Lavoisier brought a new understanding to these gases and also to the related subject of combustion. According to the theory of Georg Ernst Stahl, all combustible bodies and metals contained a common principle called phlogiston, which was given off when these bodies were strongly heated. If this were true, the product should have weighed less than the original substance. By careful use of the balance, however, Lavoisier showed in 1772 that when either sulphur or phosphorus was burnt, the product weighed more than the original substance. He began to suspect that the air played some part in this and predicted that his experiments were “destined to bring about a revolution in physics and chemistry”. One of his experiments (1775) involved heating “red mercury calx” (oxide of mercury) and finding that the gas evolved allowed a candle to burn more brightly in it. This had already been discovered by Priestley in 1774 but the British chemist had interpreted his findings in terms of the phlogiston theory. When Lavoisier repeated the experiment in 1775 he was unwilling to do the same, and described the gas simply as “eminently respirable air”. He claimed that it was this gas that combined with most metals when they were strongly heated in the air, resulting in an increase in weight. Yet it was to be several years before Lavoisier was ready to launch a full attack on the phlogiston theory.

Lavoisier’s understanding of the new gas was to be increased by his study of acids, particularly nitric acid, which he showed was one of the constituents of saltpetre (potassium nitrate). In 1775 he was appointed Commissioner of the Royal Gunpowder Administration, since the French government needed his expertise in the manufacture of gunpowder, of which saltpetre was the principal constituent. Lavoisier took up residence in the Paris Arsenal, where he set up a fine laboratory. He was helped by his wife, who took notes, translated foreign publications, and drew his apparatus.

Lavoisier claimed that his research vastly improved the quality of French gunpowder. As far as science was concerned, his research led him to conclude that not only nitric acid but all acids contained “eminently respirable air”, which he now proposed to call oxigène, from the Greek words for “acid” and “generate”. Lavoisier’s great ambition to reform chemistry had here led him to an invalid generalization. A further error was to suppose that heat was a material substance, which he called “caloric” and which he used to explain the difference between solids, liquids, and gases; the latter, he claimed, contained the most caloric.

Lavoisier was able to show that combustion normally involves combination with oxygen in the atmosphere. He was also able to demonstrate that the atmosphere contains a mixture of “azote” (nitrogen) and oxygen in the approximate proportion of 4 to 1. He offered a chemical explanation of respiration, which he saw as analogous to the slow combustion of a candle: both gave out carbon dioxide and heat. He was thus able to reduce a process belonging to physiology to the more basic science of chemistry. Turning to another of Aristotle’s “elements”, he showed that water is not a simple substance but a compound of hydrogen and oxygen. He demonstrated this both by analysing water into these gases and by synthesizing it from them.

Lavoisier collaborated with three French colleagues—Guyton de Morveau, Claude Louis Berthollet, and Antoine François de Fourcroy—to produce their Méthode de Nomenclature Chimique (Method of Chemical Nomenclature, 1787). Previously used “trivial” names, such as “oil of vitriol” and “Epsom salts”, were replaced by systematic ones, so that the names of compounds reflected their constituents. Thus “red mercury calx” became “oxide of mercury”. Lavoisier won new converts with his textbook, Traité Élémentaire de Chimie, (Elementary Treatise on Chemistry, 1789), in which he drew up a list of simple substances, or elements, which were essentially the building blocks of the new chemistry. They included metals, such as iron and lead, and non-metals, such as sulphur and carbon. Finally, he collaborated with several other chemists to launch a journal based on the new chemistry, which he called Annales de Chimie (Annals of Chemistry, 1789). This effectively completed the “chemical revolution”. Chemistry was now held up as a model science, having made enormous progress and gained new coherence over a single generation.

Lavoisier was much involved in administration. He attempted to introduce reforms in the French monetary and taxation systems and in farming methods. He was sympathetic to the early stages of the French Revolution, but in the later stages he was imprisoned, together with other unpopular tax-farmers, and on May 8, 1794, was tried, condemned, and executed by guillotine. The story that the presiding judge said, “The Republic has no need of scientists” is apocryphal. Yet it is surprising that Lavoisier’s distinction as the greatest French scientist of his age was not sufficient to save him.