phlogitone

Phlogitone is a hypothetical substance proposed in the early 18th century by German chemist Georg Ernst Stahl. He suggested that phlogitone was a fire-like element present in combustible bodies and released during combustion. The theory posited that when a substance burned, it released its phlogitone into the air, leaving behind a dephlogistigated residue. This residue, in some interpretations, was thought to be the pure essence of the element, while air, capable of absorbing phlogitone, was considered "phlogiston-rich" or "dephlogistigated."

The phlogitone theory was influential for several decades, providing a seemingly coherent explanation for various phenomena related to burning, rusting, and respiration. For instance, it explained why metals turned to "calx" (metal oxide) when heated in air, suggesting the calx was the dephlogistigated form of the metal, and that the released phlogitone could be recaptured by heating the calx with charcoal, a substance rich in phlogitone.

However, the phlogitone theory eventually faced significant challenges. Antoine Lavoisier, through his quantitative experiments in the late 18th century, demonstrated that combustion was actually a process of oxidation, involving the combination of a substance with oxygen, a gas that was previously unknown or misunderstood. Lavoisier’s work showed that the mass of the substance increased during combustion, not decreased as the phlogitone theory predicted, and that air was consumed, not produced. This led to the eventual abandonment of the phlogitone theory in favor of Lavoisier's more accurate oxygen theory of combustion.