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Phlogiston was supposed to be a mysterious invisible substance (or, in the four element theory, type of earth) that was released when a substance burned. Hence, wood released its phlogiston when burned and hence had a corresponding decrease in weight.
Scientists in Europe widely accepted the theory for a few decades, and could explain some observations of matter with it. For example, Joseph Priestly considered the substance produced upon heating mercury(II) oxide (now known to be oxygen) to be to be "dephlogisticated air" in that substances burned more rapidly in it. Mice also lived longer in dephlogisticated air. Phlogisticated air (or nitrogen) prevented combustion.
Antoine Lavoisier falsified the concept on phlogiston in his article "Reflections on Phlogiston," basing the analysis on his and others' experiments. For example, metals heated in air gain mass despite also losing phlogiston. (The metals were really forming metal oxides.) While some scientists proposed "fixes" to the phlogiston theory, Lavoisier pointed out that phlogiston was never clearly defined and often had self-contradictory properties, and hence it was not a good theory.
Ideas about elements and notably oxygen replaced phlogiston, and the concept of the atom entirely supplanted it in the 1800s.
Not to be confused with: dark energy
- The information in this article is from Morris, Richard. The Last Sorcerers, The Path From Alchemy to the Periodic Table. John Henry Press: Washington, DC: 2003.