Antoine Lavoisier (1743 to 1794) is one of the forerunners to modern chemistry. In addition to formulating the theory of combustion, history credits Lavoisier with putting together one of the first list of elements, as well as helping create the metric system. Lavoisier proved his various theories through a variety of experiments.
Disproving the Phlogiston Theory
Until Lavoisier's time, one of the prevailing notions of chemistry was the "Phlogiston Theory," which postulated there was a substance known as phlogiston in material, and that phlogiston released when a material burned. Lavoisier disproved the existence of phlogiston when he heated mercury so that it became mercury calx (HgO), a substance phlogiston allegedly released. However, when Lavoisier heated the calx even further, it reverted into mercury and oxygen gas, for which the phlogiston theory could not account.
Further Experiment to Disprove Phlogiston
Lavoisier further disproved phlogiston when he performed an experiment that broke water down into two gases -- hydrogen and oxygen -- and then subsequently was able to recombine them into water, thus making Lavoisier one of the first to show that water is a combination of two other elements. A similar experiment involved Lavoisier burning pyrophor -- a distilled substance found in fecal matter -- and he discovered that it would gain weight when it burned because of sulfur that was released, not because of phlogiston.
Lavoisier summarized his conclusions in his "Oxygen Theory," also known as the "Theory of Combustion." Lavoisier showed that an attribute of the atmosphere, not phlogiston in a material, was responsible for the various effects explained by the phlogiston theory -- such as corrosion and the added weight found in burned substances. Lavoisier was the first to coin the word "oxygen" to describe the element in air that caused these conditions. Lavoisier identified more than 30 elements in his work "Traite Elementaire de Chemie" -- "Elementary Treatise on Chemistry" -- published in 1789.
While experiments that disproved the phlogiston experiment are an important part of Lavoisier's work, he also engaged in several other experiments, including experiments in biology. Lavoisier proved that respiration is combustion. He ran an experiment that found a guinea pig exhales carbon dioxide and produces heat at a rate that is similar to burning carbon to make carbon dioxide. He measured the amount of heat given off by the guinea pig using a calorimeter, which he designed with the help of the mathematician Pierre Simon de Laplace.
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