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was a French chemist, universally regarded as the founder of modern chemistry. His contributions to the science were wide ranging, but perhaps his most significant achievement was his discrediting and disproof of the phlogiston theory of combustion, which for so long had been a stumbling block to a true understanding of chemistry.

Lavoisier was born in Paris on 26 August 1743 into a well-off family. His mother died when he was young and he was brought up by an aunt. He received a good education at the Collège Mazarin, where he studied astronomy, botany, chemistry and mathematics. In 1768 he was elected an associate chemist to the Academy of Sciences; he eventually became its Director in 1785 and Treasurer in 1791.

Also in 1768 Lavoisier became an assistant to Baudon, one of the farmers- general of the revenue, and later he became a full member of the ferme générale, employed by the government as tax collectors. He married 14-year-old Marie Paulze, daughter of a tax farmer, in 1771 and the following year his father bought him a title. In 1775 he was made régisseur des poudres and improved the method of preparing saltpetre (potassium nitrate) for the manufacture of gunpowder. A model farm he set up at Frénchines in 1778 applied scientific principles to agriculture, and he drew up various agricultural schemes as secretary to the committee on agriculture, to which he was appointed in 1785. Two years later he became a member of the provincial assembly of Orléans, in which position he initiated many improvements for the community, such as workhouses, savings banks and canals. He was also a member of various other committees and commissions, including that formed in 1790 to rationalize the system of weights and measures throughout France, which ultimately led to the founding of the metric system.

During the French Revolution, Lavoisier came under suspicion because of his membership of the ferme générale (from which he derived a considerable income) and because of his marriage to one of its senior executives, although his wife acted as his scientific assistant, taking notes and even illustrating some of his books. Jean-Paul Marat, an extremist revolutionary whose membership of the Academy of Sciences had been blocked by Lavoisier, accused him of imprisoning Paris and preventing air circulation because of the wall he had built round the city in 1787. He fled from his home and laboratory in August 1792 but was arrested in the following November and sent for trial by the revolutionary tribunal in May 1794. At a cursory trial Lavoisier was one of 28 unfortunates sentenced to death. He was guillotined on 8 May 1794 and buried in a common grave. His widow later (1805) married the US physicist Benjamin Thompson (Count Rumford).

Among Lavoisier's early scientific work were papers of the analysis of the mineral gypsum (hydrated calcium sulphate), on thunder, and a refutation that water changes into 'earth' if it is distilled repeatedly. He helped the geologist J.E. Guettard to compile a mineralogical atlas of France.

But his most significant experiments concerned combustion. He found that sulphur and phosphorus increased in weight when they burned because they absorbed 'air', and reported these results in a note he left with the Academy of Sciences in 1772. He also discovered that when litharge (lead(II) oxide) was reduced to metallic lead by heating with charcoal it lost weight because it had lost 'air'. Then in 1774 Joseph Priestley produced 'dephlogisticated air' and Lavoisier grasped the true explanation of combustion, inventing the name oxygen (acid- maker) for the substance that combined with caloric and formed 'oxygen gas'. He coined the word azote for the 'non-vital air' (nitrogen) that remained after the oxygen in normal air had been used up in combustion. In June 1783 he published his finding that the combustion of hydrogen in oxygen produces water, although unknown to him this fact had already been announced by the British chemist Henry Cavendish. Lavoisier burned various organic compounds in oxygen and determined their composition by weighing the carbon dioxide and water produced - the first experiments in quantitative organic analysis. Lavoisier's findings were universally accepted after the publication of his clear and logical Traité élémentaire de chimiein 1789, in which he listed all the chemical elements then known (although some of these were in fact oxides).

After establishing that organic compounds contain carbon, hydrogen and oxygen, Lavoisier showed by weighing that matter is conserved during fermentation as with more conventional chemical reactions. From quantitative measurements of the changes during breathing, he discovered the composition of respired air and showed that carbon dioxide and water are both normal products of respiration.

Lavoisier also made many studies outside the field of chemistry. With Pierre Laplace he experimented with calorimetry and other aspects of heat. He began to use solar energy for scientific purposes as early as 1772 and observed that 'the fire of ordinary furnaces seems less pure than that of the sun'. He anticipated later theories about the interdependence of sequential processes in plant and animal life forms, as described in one of his papers discovered only many years after his death. His great contribution to science was summed up by Joseph Lagrange who said, on the day after Lavoisier was guillotined at the Place de la Revolution, 'It required only a moment to sever that head, and perhaps a century will not be sufficient to produce another like it.'

Author not available, Lavoisier, Antoine Laurent (1743-1794). , The Hutchinson Dictionary of Scientific Biography, 01-01-1998.

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