XIII 



JOSEPH PRIESTLEY 



1733-1804 



'Joseph Priestley, born in Yorkshire, England, March 13, 1/33, was 

 a Unitarian minister. In iJ'/4 he discovered oxygen, which he called 

 ''dephlogisticatcd air." Because of his liberal political ideas he was 

 persecuted by his countrymen, and in 1/P4 emigrated to Northumber- 

 land, Pennsylvania, where he lived until his death, February 6, 1804. 



THE DISCOVERY OF OXYGEN * 



Presently, after my return from abroad, I went to work upon the 

 mercurius calcinatus, which I had procured from Mr. Cadet ; and, 

 with a very moderate degree of heat, I got from about one-fourth of 

 an ounce of it, an ounce-measure of air, which I observed to be not 

 readily imbibed, either by the substance itself from which it had been 

 expelled (for I suffered them to continue a long time together before 

 I transferred the air to any other place) or by water, in which I suf- 

 fered this air to stand a considerable time before I made any experi- 

 ment upon it. 



In this air, as I had expected, a candle burned with a vivid flame ; 

 but what I observed new at this time (November 19), and which sur- 

 prised me no less than the fact I had discovered before, was, that, 

 whereas a few moments agitation in water will deprive the modified 

 nitrous air of its property of admitting a candle to burn in it; yet, 

 after more than ten times as much agitation as would be sufficient to 

 produce this alteration in the nitrous air, no sensible change was pro- 

 duced in this. A candle still burned in it with a strong flame ; and it 



* From Experiments and Observations on Different Kinds of Air, Vol. II, 



(1775). 



96 



