Oxygen, is a term invented by the French chemists, and at present employed to express the acidifying principle.
Oxygen is considered as an elementary something, utterly inca-pable of decomposition ; nor will it admit of being exhibited by itself, or of being produced in its simple state: for, at the moment of its becoming free, it unites with the light, and caloric, or heat of the surrounding medium, and thus forms what has been severally denominated vital-air, fire-air, de-phlogisticated or pure-air, and lastly, Oxygen-gas. The peculiar character of this elastic fluid was first developed by Dr. Priestley, whose experiments have been confirmed, and the properties of gas-oxygen fully explained, by Lavoisier, Cavendish, and other illustrious chemical philosophers.—-From their discoveries it appears, that this uncompounded invisible matter can be known only in its combinations ; that it forms a constituent part of the atmospheric air in which it exists in the proportion of 27 or 28 parts to 100.
Farther, oxygen may be separated not only from the atmosphere, but also from water; from all acids; and also from vegetables exposed to the rays of the sun. By this natural process, a considerable portion of it is evolved from the leaves of plants during their perspiration, in consequence of solar heat: thus, when oxygen is ca ried to their roots, by means of the circulating fluids, it is believed to promote their growth; though, if it be absorbed too copiously, and rapidly, it is unfavourable to vegetation. On the contrary, a very large proportion is requisite to conduce to the growth, and to nourish the vitality of animals.- Lastly, oxygen is supposed to exist in all bodies, whether of the vegetable, animal, or mineral kingdoms, and particularly in certain metallic calces or oxydes; such as ruddle, calamine, and burnt clay; which, on account of the large quantity of the acidifying principle they contain, are conjectured to be of considerable utility as manures.