In 1787, Lavoisier published a new nomenclature of chemistry, which contained 33 substances, such as zinc, sulphur and oxygen, which he called elements. Although the list included light as a chemical element, which Lavoisier believed was a measurable substance, this classification was widely accepted. The discovery was published in what is considered the first modern chemistry textbook. Lavoisier's fundamentals of chemical nomenclature and classification remain in use today.
Lavoisier was the first scientist to outline the law of conservation of mass, which says that matter is neither created nor destroyed, but remains constant after being transformed. Lavoisier demonstrated this principle with several chemical reactions, where every compound was accurately weighed. During one of these experiments, Lavoisier boiled a red mercury compound in a sealed apparatus. The result was the liberation of oxygen gas, while the red compound became silvery liquid. By weighing the apparatus, Lavoisier demonstrated that the chemical elements were the same in quantity and quality before and after the experiment.
Although known since ancient times, sulfur was not considered a chemical element, but a compound, which is a combination of two or more elements. However, through a series of experiments conducted in 1777, Lavoisier demonstrated to the scientific community that sulfur was in fact an element, not a compound. Sulfur is a component of many minerals, including gypsum, pyrite and galena.
Lavoisier studied oxygen in reaction with other elements and compounds. Using guinea pigs, he demonstrated that oxygen used in the respiration of plants and animals promoted the combustion of organic material, thus liberating energy and carbon dioxide. Lavoisier also discovered the role of oxygen in the rusting of iron. He found out that oxygen reacted with hydrogen forming a molecule of water.