Antoine-Laurent Lavoisier conducts an experiment on human respiration in this drawing made by his wife, who depicted herself at the table on the far right. Image provided by Edgar Fahs Smith Memorial Collection, Department of Special Collections, University of Pennsylvania Library. Antoine-Laurent Lavoisier (1743–1794) Antoine-Laurent Lavoisier was in some ways the Batman of chemistry, practicing science after hours while living the respectable life of a wealthy Parisian financier during the day. Despite working all day in both government and private business, the French chemist was legendary for his hard work in the lab and meticulous experimental style. With precise measurements of the masses of the reactants and products (including those elusive gaseous products), he was able to establish the law of conservation of mass, which holds that matter is never gained or lost during chemical reactions. He also showed that combustion was the chemical combination of substances with oxygen; reduction, the release of oxygen from oxides. Moreover, he systematized inorganic nomenclature, naming compounds based on their component elements for the first time. His work revolutionized chemistry and laid the groundwork for people like John Dalton, Amadeo Avogadro, and Joseph-Louis Gay-Lussac. He has rightfully been called the father of modern chemistry. In addition to his chemical work, he studied respiration, agriculture, and economics, and he helped develop the metric system. While a brilliant scientist, skilled businessman, and competent bureaucrat, he seems to have been somewhat naïve in some areas concerning human nature. Early in his career, he became a major shareholder in the private corporation that collected taxes for the French crown, a decision that would have dire consequences. After the French Revolution, Lavoisier had many opportunities to flee the country but chose to remain in France, seemingly unaware of the danger. He was ultimately beheaded during the Reign of Terror. A sympathizer remarked that while it took only an instant to sever his head, a hundred years may not produce another like it.