Phlogiston theory

The phlogiston theory is an old scientific theory that was used to explain fire and combustion before modern chemistry and the discovery of oxygen. The concept was put forward in 1667 by Johann Joachim Becher, and many varieties of phlogiston theory were proposed by other 17th- and 18th-century chemists.

The theory put forward the belief that there was a fire-like element called phlogiston inside fuel which escaped when it burned, leaving behind a solid called calx. For a lot of solid fuels like coal, the ash after combustion weighs less than the fuel before, so this seemed logical from the information they had at the time.

Antoine Lavoisier was a major critic of the phlogiston theory. Careful experiments that measured the masses of gasses showed that the phlogiston theory was wrong. This led to the discovery of oxygen.

However, some scientists continued to believe in phlogiston, and continued to add more complexity to the theory to address the new discoveries. The explanations of phlogiston theorists began to contradict each other, which accelerated the decline of the theory even among scientists who supported it.