Here is a short article for non-scientists, reprinted from the Joseph Priestley House Spring 2012 Newsletter:
For example: he showed that 'plants purify air made noxious by animals breathing', a discovery that demonstrated that we will not suffocate in the carbon dioxide ('fixed air') we produce; he discovered oxygen and many other gases, including nitric oxide and its antiseptic properties; the first recorded synthesis of water from hydrogen ('inflammable air') and oxygen ('dephlogisticated air') was at a meeting of the Lunar Society of Birmingham in 1781 (water is not an element!); he also showed, in 1791, while still at Birmingham, that blood absorbed oxygen, but, like many of his other discoveries, this was ignored (because of prejudices held against him for his political and religious views), holding up progress in respiratory physiology for a generation.
For an appreciation of Priestley's scientific work (from IBSN 1 85858 269 5):
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