Priestley isolates oxygen

On 1 August 1774, the English clergyman and chemist Joseph Priestley focused sunlight with a large lens on red mercuric oxide in a closed vessel and collected a gas in which a candle burned with a dazzling flame and in which a mouse lived longer than in ordinary air. He called it 'dephlogisticated air'. The Swedish apothecary Carl Wilhelm Scheele had made the gas earlier, but published later. The French chemist Antoine Lavoisier, whom Priestley visited in Paris in October, explained that it was a new element and named it oxygen, overthrowing the phlogiston theory and founding modern chemistry.

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