Lavoisier and the beginning of Chemistry

Antoine Lavoisier was a French aristocrat in the mid-1700's. Lavoisier worked as a tax collector for Louis XVI, a deeply unpopular occupation that resulted in his death on the guillotine during the French Revolution.

Portrait of Antoine-Laurent de Lavoisier and his wife, 

chemist Marie-Anne Pierrette Paulze by Jacques-Louis David

Before his death, however, Lavoisier used his wealth to build a chemical laboratory in his home and, in that laboratory, transformed chemistry from a qualitative science into a quantitative one.

Lavoisier is credited with the discovery of oxygen, and for proving that sulfur was an element, not a compound. Most important for our purposes, Lavoisier did a series of experiments that demonstrated quantitatively, the conservation of mass - the idea that reactions involve the rearrangement of material but not the destruction or creation of material.