Antoine-Laurent Lavoisier, the father of modern chemistry, was a French noble prominent in the histories of chemistry and biology. He stated the first version of the law of conservation of mass, recognized and named oxygen (1778) and hydrogen (1783), abolished the phlogiston theory, helped construct the metric system, wrote the first extensive list of elements, and helped to reform chemical nomenclature. He discovered that, although matter may change its form or shape, its mass always remains the same. He was also an investor and administrator of the "Ferme Générale" a private tax collection company; chairman of the board of the Discount Bank (later the Banque de France); and a powerful member of a number of other aristocratic administrative councils. All of these political and economic activities enabled him to fund his scientific research. Because of his prominence in the pre-revolutionary government in France, he was beheaded at the height of the French Revolution.

On the basis of his earliest scientific work, mostly in geology, he was elected in 1768—at the early age of 25—to the Academy of Sciences, France's most elite scientific society. In 1775, Lavoisier was appointed a commissioner of the Royal Gunpowder and Saltpeter Administration and took up residence in the Paris Arsenal. There he equipped a fine laboratory, which attracted young chemists from all over Europe to learn about the "Chemical Revolution" then in progress. He meanwhile succeeded in producing more and better gunpowder by increasing the supply and ensuring the purity of the constituents—saltpeter (potassium nitrate), sulfur, and charcoal—as well as by improving the methods of granulating the powder.

Characteristic of Lavoisier's chemistry was his systematic determination of the weights of reagents and products involved in chemical reactions, including the gaseous components, and his underlying belief that matter—identified by weight—would be conserved through any reaction. Among his contributions to chemistry associated with this method were the understanding of combustion and respiration as caused by chemical reactions with the part of the air he called "oxygen.” Lavoisier also demonstrated the role of oxygen in the rusting of metal, as well as oxygen's role in animal and plant respiration. Working with Pierre-Simon Laplace, Lavoisier conducted experiments that showed that respiration was essentially a slow combustion of organic material using inhaled oxygen. Lavoisier's explanation of combustion disproved the phlogiston theory, which postulated that materials released a substance called phlogiston when they burned. Lavoisier also discovered that Henry Cavendish's 'inflammable air', which Lavoisier had termed hydrogen (Greek for "water-former"), combined with oxygen to produce a dew which, as Joseph Priestley had reported, appeared to be water. 

With the French chemists Claude-Louis Berthollet, Antoine Fourcroy and Guyton de Morveau, Lavoisier devised a systematic chemical nomenclature. He described it in Méthode de nomenclature chimique (Method of Chemical Nomenclature, 1787). This system facilitated communication of discoveries between chemists of different backgrounds and is still largely in use today, including names such as sulfuric acid, sulfates, and sulfites.

His giving new names to substances was an important means of forwarding the Chemical Revolution, because these terms expressed the theory behind them. In the case of "oxygen," from the Greek meaning "acid-former," Lavoisier expressed his theory that oxygen was the acidifying principle. He considered 33 substances as "elements"—by his definition, substances that chemical analyses had failed to break down into simpler entities. Ironically, considering his opposition to phlogiston, among these substances was "caloric"—the unweighable substance of heat, and possibly light, that caused other substances to expand when it was added to them. To propagate his ideas, in 1789 he published a textbook, Traité Élémentaire de chimie, and began a journal, Annales de Chimie, which carried research reports about the new chemistry almost exclusively.

A political and social liberal, Lavoisier took an active part in the events leading to the French Revolution, and in its early years he drew up plans and reports advocating many reforms, including the establishment of the metric system of weights and measures. Despite his eminence and his services to science and France, he came under attack as a former farmer-general of taxes and was guillotined in 1794. A noted mathematician, Joseph-Louis Lagrange, remarked of this event, "It took them only an instant to cut off that head, and a hundred years may not produce another like it."

Sources

Chemical Heritage Foundation (Content Partner); Peter Saundry (Topic Editor). 2007. "Lavoisier, Antoine-Laurent." In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth September 15, 2006; Last revised February 19, 2007; Retrieved March 8, 2009]. 

Wikipedia Contributors, Lavoisier, Wikipedia The Free Encyclopedia, Accessed 8 March 2009.