In seventeenth- and eighteenth-century chemistry, phlogiston was believed to be a fiery principle contained in combustible materials and lost during burning. The theory was later replaced by Antoine Lavoisier’s explanation of combustion through oxygen. In poetry, the word may evoke flame, heat, alchemy, Enlightenment-era Science, or the failure of once-trusted explanations.

The phlogiston theory is most closely associated with German chemist Georg Ernst Stahl in the early eighteenth century. The word comes from Greek phlogistos, meaning “burned” or “inflammable.” Historically, the theory struggled to explain why metals gain weight when heated to form oxides; oxygen theory resolved this problem. In literary writing, phlogiston can function as a learned or archaic scientific allusion rather than a literal scientific term. Related terms include combustion, oxidation, oxygen, alchemy, and ether, another obsolete scientific concept often used poetically.