Joseph Priestley *
Illustration: Ellen Sharples * 1774: Oxygen gas is discovered for at least the third time. This one sticks, however, when its latest discoverer, Joseph Priestly, publishes a paper on the subject that appears to predate the claims of priority made by Carl Wilhelm Scheele and Antoine Lavoisier.
In any case, Priestly did isolate the element oxygen, reportedly on this date, calling it "dephlogisticated air" and describing it as "five or six times better than common air for the purpose of respiration." He tested the pure oxygen on a couple of mice and when they did not die as expected, he tried it out himself:
"The feeling of it to my lungs was not sensibly different from that of common air, but I fancied that my breast felt peculiarly light and easy for sometimes afterwards. Who can tell but that, in time, this pure air may become a fashionable article in luxury. Hitherto, only two mice and myself have had the privilege of breathing it."
Priestly delivered his oxygen paper the following year and then included it as part of his Experiments and Observations on Air, published in 1776. It's largely on the basis of this paper and this book that Priestly's claim of priority lies. Since then, Priestly's status has been challenged by others arguing that Polish alchemist Michael Sendivogius described oxygen as early as 1604.
Whether he was or wasn't the true discoverer of oxygen, Priestly's place in history is secure. Tinkering with air was only one of his pursuits. In the realm of political science and theology, Priestly will be remembered as a fervent humanist, an influential advocate of religious tolerance and civil rights.
Which, in the end, makes breathing the air a lot sweeter.
(Source: Various)
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