Phlogiston

• Although the process of combustion was speculated on by philosophers such as Aristotle, little was understood. In the mid-17th century, early chemists proposed the existence of a substance that enables material to be burned. As the substance burned, this substance --- called "phlogiston" --- was released, revealing a material's true identity, known as the calx.
  
  

Phlogisticated Air

• According to the idea of phlogiston, as phlogiston entered the air, the substance became dephlogisticated (the phlogiston was removed) while the air became phlogisticated (saturated with phlogiston). Phlogisticated air could no longer support combustion or animal life.
  
  

Joseph Priestley

• In 1774, Joseph Priestly performed a series of experiments involving mice, combustion and oxidized metals in which the air could be phlogisticated and then dephlogisticated. He found that his dephlogisticated air was better able to support life and combustion than normal air.
  
  

Antoine Lavosier

• Building on the research of Priestly and other chemists, French chemist Antoine Lavosier identified the dephlogisticated air as oxygen, eventually disproving phlogiston theory. Lavosier argued that when a substance burned, it combined with oxygen from the air rather than releasing the mysterious, hypothetical substance phlogiston.