Phlogiston

Phlogiston (from the Ancient Greek φλογιστόν phlogistón "burning up") was a fire-like element contained within combustible bodies and released during combustion. The air was thought to have a limited capacity to absorb the phlogiston released, this being the reason why combustion did not take place for long in an enclosed container.

The theory was first postulated in 1667 by Johann Joachim Becher as an attempt to explain processes of burning such as combustion, metabolism, and the rusting of metals, which are now collectively known as oxidation. Phlogiston remained the dominant theory until Antoine-Laurent Lavoisier (1743 – 1794) showed that combustion requires a gas that has weight (oxygen) and could be measured by means of weighing closed vessels.