What is the Phogiston theory?

The Phlogiston theory was a historical scientific concept that posited a substance called "phlogiston" was released during combustion. According to this theory, all flammable materials contained phlogiston, which was emitted when they burned, leaving behind a residue called "calx." The theory was widely accepted in the 17th and 18th centuries but was eventually disproven by the discovery of oxygen and the development of modern chemistry, particularly through Antoine Lavoisier's work in the late 18th century. Lavoisier demonstrated that combustion involves a reaction with oxygen, fundamentally changing the understanding of chemical processes.