dephlogistication

Dephlogistication is a term used in the history of science to describe the gradual abandonment of the phlogiston theory of combustion in favor of an oxygen-based explanation. The phlogiston theory, developed in the 17th and early 18th centuries by Becher and Stahl, posited that a fire-like substance called phlogiston was released during burning. Fire and oxidation were interpreted as the expulsion of phlogiston from materials, with later refinements attempting to account for observed mass changes.

The shift began in the 1770s with experiments by scientists such as Joseph Priestley and Carl Wilhelm Scheele, who produced gases that supported combustion and respiration. Priestley called one of these gases dephlogisticated air, reflecting the then-prevailing idea that removing phlogiston from air enhanced its properties for supporting burning. Antoine Lavoisier, building on these findings, proposed a different interpretation: combustion involves a specific component of air that is consumed during burning, which he later named oxygen. He demonstrated that mass is conserved in combustion by showing that metals fuse with this component of air to form oxides, a view that contradicted the notion of phlogiston release.

Dephlogistication culminated in a new chemical framework in which oxidation is viewed as a reaction with oxygen, rather than the loss of phlogiston. This transformation, central to the Chemical Revolution, led to revised nomenclature, the development of quantitative chemistry, and a modern understanding of oxidation-reduction processes. The term is used by historians to capture this epistemic shift in late 18th‑century chemistry.