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Antoine Lavoisier: Joseph Priestley
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The son of a wealthy Parisian lawyer, Antoine-Laurent Lavoisier (1743–1794) completed a law degree in accordance with family wishes. His real interest... was in science, which he pursued with passion while leading a full public life. 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 the same year he bought into the Ferme Générale, the private corporation that collected taxes for the Crown on a profit-and-loss basis. A few years later he married the daughter of another tax farmer, Marie-Anne Pierrette Paulze, who was not quite 14 at the time. Madame Lavoisier prepared herself to be her husband's scientific collaborator by learning English to translate the work of British chemists like Joseph Priestley and by studying art and engraving to illustrate Antoine-Laurent's scientific experiments.
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Lavoisier brought a new understanding to these gases and ... 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.
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The "official" version of Lavoisier's Easter Memoir did not appear until 1778. In the intervening period Lavoisier had ample time to repeat some of Priestley's latest experiments and perform some new ones of his own. In addition to studying Priestley's dephlogisticated air, he studied more thoroughly the residual air after metals had been calcined. He showed that this residual air supported neither combustion nor respiration and that approximately five volumes of this air added to one volume of the dephlogisticated air gave common atmospheric air. Common air was then a mixture of two distinct chemical species with quite different properties. Thus when the revised version of the Easter Memoir was published in 1778, Lavoisier no longer stated that the principle which combined with metals on calcination was just common air but "nothing else than the healthiest and purest part of the air" or the "eminently respirable part of the air."
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Lavoisier's researches included some of the first truly quantitative chemical experiments. He carefully weighed the reactants and products in a chemical reaction, which was a crucial step in the advancement of chemistry. He showed that, although matter can change its state in a chemical reaction, the quantity of matter is the same at the end as at the beginning of every chemical change. These experiments supported the law of conservation of mass, which Lavoisier was the first to state,[2] although Mikhail Lomonosov (1711-1765) had previously expressed similar ideas in 1748 and proved them in experiments. Others who anticipated the work of Lavoisier include Joseph Black (1728-1799), Henry Cavendish (1731-1810), and Jean Rey (1583-1645).
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In Paris, the intrigued Lavoisier repeated Priestley's experiment with mercury and other metal calces. He eventually concluded that common air was not a simple substance. Instead, he argued, there were two components: one that combined with the metal and supported respiration and the other an asphyxiant that did not support either combustion or respiration. By 1777, Lavoisier was ready to propose a new theory of combustion that excluded phlogiston. Combustion, he said, was the reaction of a metal or an organic substance with that part of common air he termed "eminently respirable." Two years later, he announced to the Royal Academy of Sciences in Paris that he found that most acids contained this eminently respirable air. Lavoisier called it oxygène, from the two Greek words for acid generator.
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Lavoisier began working on the problem of combustion in 1773 with his friends Trudaine and Montigny. They became interested in combustion because of the similarities they saw between it and respiration. The prevailing view at the time was that the combustion of candles somehow decreased the volume of air. Mr. Priestley, a very prominent English chemist and a strong proponent of the phlogiston theory, considered this diminution to be a characteristic of the "goodness" of the air. Lavoisier and his friends decided to test the theory on their own. The first experiment they performed tested whether a candle would burn in the air left after a bird had been suffocated in a closed bell jar.
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Joseph Priestley