OXYGEN (symb. 0. equiv. 8; new system. 16; sg. gr. 1.1056) is a colorless, inodorous, tasteless gas, long regl,rded as a " permanent " gas, but liquefied by Pietet of Geneva for the first lime in 1877. Its Chemical affinities for other elementary substances are very powerful; with most of them it is found in combination, or may be made to Com bine, in more than one proportion; with several in 4, 5, or proportions; and there is only one element (fluorin•) with which it does not enter into any combintition• Owing to time intensity with which many of these combinations take place, this gas has the power of supporting combustion (q.v.) in an eminent degree. Of all known sub stances. it exerts the smallest refracting power on the rays of light. It possesses weak but decided mmnetie properties, like those of iron, and like this substance, its susceptibility to magnetization is diminished or even suspended by a certain elevation of temperature. It is only slightly soluble in water; 100 cubic inches of that liquid dissolving 4.11 clbie inches of gas at 32°, and only 2.99 inches at 59°.
Oxygen gas is not only respirable, but is essential to the support of animal life; and hence it was Old air by some of the older chemists. A small animal placed Mn it bell-glass containing pure oxygen will not be suffocated so soon as if it were placed in the sane glass tilled with atmospheric air. For further details on this property of oxygen, the reader is referred to the article REsentATioN.
Oxygen is the most abundant and the most widely distributed of all the elements. its free slate (rm:•ed but not combined with nitrogen), it constitutes about a fifth of the bulk, and considerably more than a fifth of the weight, of the atmosphere. In corabina• lion with hydrogen, it forms eight-nintlis of all the water on the globe; and in combina tion with silicon, calcium, aluminium, etc., it enters largely into all the solid constituents of the earth's crust; silica in its various forms of sand, common quartz, flint, etc.— chalk, limestone, and marble—and all the varieties of clay, containing about half their weight of oxygen. It is, moreover, found in the tissues and fluids of all forms of animal and vegetable life, none of which can support existence independently of this element. • There are various modes of obtaining oxygen. the simplest of which consists in the exposure of certain metallic oxides to a high temperature. It was originally obtained by its discoverer, Dr. Priestley, from the red oxide of mercury, which, when heated to about 750°, resolves itself into metallic mercury and oxygen gas. It may be similarly obtained from red oxide and peroxide of lead, the resulting products in these cases being protoxide of lead and oxygen. The following are the chief methods now employed: (1.) The black oxide (or hinoxide) of manganese is much employed as a source of this The mineral is reduced to small pieces of about the size of a.pea, and intro
duced into an iron bottle, with a pipe through which the gas may escape. When the bottle is placed in a furnace, and attains a red heat, the mineral parts with one third of its oxygen, and the red oxide of manganese remains behind; the reaction being explained by the equation: Black oxide of Manganese. Red oxide of Manganese. Oxygen.
3Mn + 20 (2.) A very pure and abundant supply of oxygen may be obtained by heating chlorate of potash which yields up all its oxygen (amounting to 39.16 per cent), and leaves a residue of chloride of potassium. One ounce of this salt yields nearly two gal lons of oxygen gas. It is found by experiment, that if the chlorate of potash is mixed with about a fourth of its weight of black oxide of copper, or of binoxide of manganese, the evolution of the gas is greatly facilitated, although the oxides do not seem to undergo any change during the process. (3.) Oxygen is readily obtained by heating strong sul phuric acid with about half its weight of powdered black oxide of manganese, or chlorate of potash, in a glass retort; the reaction in the former case being expressed by the equation: Black oxide of Manganese. Sulphuric acid. Sulphate of Manganese. Water. Oxygen.
HO, Mn 0, SO, + HO + 0 and in the latter case, being of a more complicated character. (4.) Various processes have been proposed for obtaining the gas' on a large scale. of which the following, recommended by St. Claire Deville and Debray, is perhaps the best: The vapor of hydrated sulphuric acid is passed over red-hot platinum, by which it is decomposed into oxygen and sulphurous acid, the latter of which may easily be separated (and made available for the formation of sulphites) by its solubility in water or alkaline solutions. It has been calculated that a cubic meter (35.375 cubic ft.) of oxygen costs 8s. 4d. when obtained from chlorate of potash; nearly 4s. ld. when obtained from manganese; and only 10d. when obtained from sulphuric acid.
Of the compounds of oxygen, it is unnecessary to speak here, as they are described in the articles on the other chemical elements.
Oxygen was discovered almost simultaneously, in the year 1774, by Priestley and by Scheele, the English chemist having the precedence by a few weeks. Priestley gave it the name of dephlogi8tkoted cdr; Seneele termed it empyreal air; Condowet shortly after ward suggested rital air, as its most appropriate designation; and in 1789, Lavoisier, who, by a series of carefully conducted and very ingenious experiments, proved that the combustion of bodies in the air consisted in their chemical combination with oxygen, and thus overthrew the phiogiston. (q.v.) theory, gave it the name which it now retains, in consequence of his (erroneously) believing that it possessed a certain property which is described in the article OXYACIDS.