OXYGEN, a term adopted in the chemical nomenclature to express the acidifying principle, and formed from ἔξω, acid, and γενεσι, to generate. It is not found naturally in a separate state, but always in combination with some other substance. In its aeriform or elastic state it is called oxygenous gas, and is the same as the dephlogisticated air of Priestley and Cavendish, the empyrean air of Scheele,
and the vital or pure air of other chemists. See CHEMISTRY.