![]() These ideas were further developed and taught by Aristotle and remained influential for 2000 years. by Empedocles, who speculated that all matter consisted of combinations of earth, air, fire, and water. ![]() This had first been proposed in Greece during the fifth century B.C. Lavoisier did not originate the idea that certain substances (elements) were fundamental and all others could be derived from them. Because of this he suggested that oxygen must be an element-an ultimately simple substance which could not be decomposed by chemical changes. Lavoisier was able to decompose the red calx into mercury and oxygen, but he could find no way to break down oxygen into two or more new substances. Although oxygen combined with many other substances, it never behaved as though it were itself a combination of other substances. This principle is now called the law of conservation of mass.Īs Lavoisier continued his experiments with oxygen, he noticed something else. Lavoisier hypothesized that this should be true of all chemical changes, and further experiments showed that he was right. ![]() That is, there was no change in mass upon formation or decomposition of the calx. Lavoisier’s careful experiments also revealed that the combined masses of mercury and oxygen were exactly equal to the mass of calx of mercury. (A calx is the ash left when a substance burns in air.) At a higher temperature this calx decomposes into mercury and oxygen. In an important series of experiments he showed that when mercury is heated in oxygen at a moderate temperature, a red substance, calx of mercury, is obtained. Eventually he realized that this component was the dephlogisticated air which had been discovered by Joseph Priestly (1733 to 1804) a few years earlier. He became convinced that when a substance is burned in air, it combines with some component of the air. Much of Lavoisier’s work as a chemist was devoted to the study of combustion. The development of the atomic theory owes much to the work of two men: Antoine Lavoisier, who did not himself think of matter in terms of atoms but whose work laid organization groundwork for thinking about elements, and John Dalton, to whom the atomic theory is attributed.
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