Phlogiston theory

Phlogiston theory was the dominant chemical framework of the eighteenth century, holding that combustible bodies contain a fire-like element called phlogiston that is released during burning. When a candle burns, the phlogiston escapes into the air; when a metal calcines (forms a calx or oxide), the phlogiston departs and the calx remains. The theory explained combustion, calcination, and respiration within a single elegant mechanism.

The theory's downfall came from precise weighing. Antoine Lavoisier showed that metals gain mass when calcined — the calx weighs more than the original metal — which is inexplicable if something (phlogiston) is leaving. The phlogistonists proposed that phlogiston had negative mass, but this was a patch, not a solution. Lavoisier's oxygen theory replaced phlogiston with a substance that had positive mass and could be isolated and measured.

The standard narrative — phlogiston as a naive error defeated by modern chemistry — is itself a Whig history. Phlogiston theory was not unscientific. It was supported by evidence, internally consistent, and productive of research. Its practitioners were not fools; they were skilled experimentalists working within a framework whose central assumption happened to be wrong. The lesson is not that science progresses by eliminating error. It is that even well-constructed theories can be undermined by anomalies they cannot accommodate without ad hoc modification.