What Is Phlogiston?

Phlogiston is a now obsolete scientific theory that stated that combustible materials released a fire-like element called phlogiston during the process of combustion. Johann Joachim Becher first proposed the theory in 1667.

The theory stated that all flammable substances contained the material that had no color, smell, taste or mass. When the substance containing phlogiston was burned, it would be released. The dephlogisticated material was thought to be in its true form.

It is now known that combustion is a process of oxidation in which hydrocarbons are oxidized in the air. Phlogiston theory believed the fact that a fire stopped burning in an enclosed space simply meant that the air in the space was able to absorb only a certain amount of phlogiston. When air became too full of phlogiston, nothing could burn in it, and it could no longer support life. In fact, the theory believed that respiration was the process through which the body removed phlogiston.

Becher first set forth the theory in his book "Physical Education." In the book, he called the element "terra pinguis" and described it as having sulphurous, oily or combustible properties. Georg Ernst Stahl renamed "terra pinguis" as "phlogiston" in 1703. This later version of the theory most likely resulted in it greatest level of influence.