noun
a substance once believed to exist in all combustible materials and to be released during combustion
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The theory of phlogiston, an outdated concept in chemistry, posited that all combustible objects contained a substance called phlogiston.
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Back in the day, scientists actually believed in this thing called phlogiston that they thought was responsible for combustion.
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Phlogiston was like the OG fire juice according to old-school chemists.
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Her passion for the project burned like the phlogiston fueling an ancient alchemical experiment.