For more than a century, some of the best chemists in the world accepted that a substance leaving a metal during burning could make the metal heavier. This episode traces the rise and fall of phlogiston, from Johann Joachim Becher’s oily earth in 1667 and Georg Ernst Stahl’s 1703 rebranding to Antoine Lavoisier’s sealed-jar experiments.

Along the way we look at how the theory unified combustion, metallurgy, plant growth, and breathing; how the weight gain seen in calcination forced defenders to propose negative mass or buoyancy; how Daniel Rutherford and Joseph Priestley named nitrogen and oxygen through the phlogiston lens; and how Elizabeth Fulhame’s water experiments, Giovanni Antonio Giobert’s 1792 prize paper, and Pierre Macquer’s desperate patches marked the end.

• Why the four-element model of Empedocles and Aristotle could not explain why coal burns and limestone does not
• How Stahl’s framework made forge observations, from disappearing charcoal to purified metal, seem to confirm the theory
• The Archimedes’ principle calculation showing buoyancy could not account for the weight gain of burning magnesium
• Johann Heinrich Pott’s shift of phlogiston into an unmeasurable universal essence that explained everything and nothing
• Lavoisier’s conservation of mass and why 10 plus 2, not 10 minus 2, equals 12