Burning substances release a fire-like material called phlogiston.

Not a fact anymore

Burning substances release a fire-like material called phlogiston.

What we know now

Combustion is a set of chemical oxidation reactions. In ordinary burning, a fuel reacts with oxygen and forms new products while releasing energy.

Why it changed

Careful weighing showed that many substances gain mass when burned rather than losing a material. Lavoisier's experiments identified oxygen's role in combustion and replaced phlogiston with a quantitative chemical account.

Status: Superseded
Category: Chemistry
Accepted approximately: Late 17th through the late 18th century
Changed approximately: 1770s–1790s

Phlogiston theory was not irrational for its time. It organized many observations and gave chemists a common language before gases and mass changes were properly understood.

Some early oxygen explanations were also incomplete. Modern combustion chemistry developed further through atomic theory, thermodynamics, and reaction kinetics.

Evidence

Sources and what they establish

Historical context

Antoine-Laurent Lavoisier Science History Institute
Explains the phlogiston theory and Lavoisier's quantitative reinterpretation of combustion.
The Science and Spectacle of the First Balloon Flights, 1783 Science History Institute
States that Lavoisier overturned the dominant phlogiston theory and laid foundations for modern chemistry.

Previous belief

Joseph Priestley Science History Institute
Describes Priestley's dephlogisticated air and how Lavoisier identified it as oxygen involved in combustion.