Priestley Discovers Oxygen: Chemistry's Breakthrough
Joseph Priestley heated mercuric oxide with a magnifying glass on August 1, 1774, and collected the gas released. He noticed a candle burned more brightly in this gas and a mouse survived longer in a sealed jar of it. Priestley called it "dephlogisticated air," still clinging to the phlogiston theory of combustion. Antoine Lavoisier later identified the gas as oxygen and used it to demolish phlogiston theory entirely, establishing modern chemistry. Carl Wilhelm Scheele in Sweden had actually isolated oxygen two years earlier but didn't publish in time. Priestley's experiment provided the public demonstration that forced the scientific community to abandon a century of wrong thinking about combustion and respiration.
August 1, 1774
252 years ago
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