a term adopted in the new chemical nomenclature to express the acidifying principle; from εύς "acid," and γενέσθαι "to generate." It is not found naturally in a separate state, but always combined or mixed with some other substance. In its aeriform or elastic state, it is called by the French chemists oxygenous gas, and is the same as the dephlogisticated air of... Priestley and Cavendish, the *empyreal* air of Scheele, the vital air and pure air of other modern chemists. It was called *dephlogisticated* by the followers of Stahl's doctrine, who imagined it to be air deprived of phlogiston; the epithet of *empyreal* was given to it by Mr Scheele, who first discovered it to be the only constituent part of the atmosphere which contributes to support inflammation or combustion. He made many curious experiments on inflammation, and was the first who completely analysed common air, showing it to consist of 27 parts of *empyreal*, 72 of foul, and 1 of fixed air. He found, that these 27 parts only were consumed by a burning body; and that these, during the act of combustion, were united and combined with the inflammable body burnt in them, so as to form a compound no longer combustible. Lavoisier extending these experiments, found that the body, thus produced by *empyreal* air, being combined with the matter of the inflammable body burnt in it, was, in many cases, an acid; in consequence of which property, he gave this air the name of *oxygen*, i.e. "the generator of acidity." He was perhaps too hasty in adopting this name; for the same air is found in combination with inflammable matter, forming compounds that are by no means acid, of which we shall content ourselves with producing only one example, namely water, which is the compound resulting from the combination of this air with inflammable air. See Water.

Common atmospheric air was found by Scheele to promote animal life in a manner somewhat similar to its promoting combustion. He extended his experiments to this subject also; and he concludes, that this *empyreal* air is the only part of the atmosphere which is capable of supporting animal life, and that no animal can exist a minute without it. In consequence of this property it has been called vital air. Since, however, it is absolutely necessary for the support both of combustion and of animal life, and since neither of these can exist without it, both the terms *empyreal* and *vital* are efficient, expressing only certain properties of this elastic fluid (which may be also said of the word *oxygen*); and hence some later chemists have suggested the propriety of designating it by the name of pure air. See Combustion, Inflammation, Chemistry, Air, Water.