Joseph Priestley isolated oxygen gas
On this day · 1 August 1774
On a sunny day in 1774, a clergyman aimed a giant lens at a lump of mercury rust and bottled the breath of life.
On August 1, 1774, the English clergyman and self-taught chemist Joseph Priestley ran his most famous experiment. Using a 12-inch glass “burning lens” to focus sunlight on reddish mercuric oxide sealed under mercury, he drove off a new gas and caught it in an inverted jar.
The results astonished him. A candle plunged into the gas blazed with a fierce, dazzling flame, and a mouse confined in it survived roughly four times as long as in ordinary air. Priestley even breathed some himself, finding his chest “peculiarly light and easy.”
A candle burned in it “with a remarkably vigorous flame.”
Clinging to the old phlogiston theory, Priestley called his discovery “dephlogisticated air.” It fell to Antoine Lavoisier to grasp its true nature and rename it oxygen. The Swedish chemist Carl Wilhelm Scheele had isolated the same gas earlier, but his findings appeared in print later, leaving Priestley the first to publish.
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