It is to Joseph Priestley that one attributes the discovery of oxygen or more exactly the element of 'l'air vital' for the animal kingdom. In 1772, he discovered that the air in a closed chamber where candles had burned until extinction could be regenerated by growing plants inside. He also reported that an atmosphere in which mice had died was regenerated by plants. He had discovered that plants resupplied with oxygen an atmosphere in which a candle had burned or animals had breathed. Thus, Priestley had the genius to gather under the same concept the combustion of a candle and animal's breathing. In 1774 Priestley isolated a new gas from mercury (II) oxide, and called it "air dephlogistique", which was in fact oxygen.

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