OXYGEN

(Gr. olv;, and yiwoiuv, to generate. )i This important element was discovered, in 1774, by Dr. Priest ley. It has been termed depklogisticatcd air, vital air, and e?npi/real air. As it forms a component part of many of the acids, it was termed, at the framing of the new nomenclature, oxi/gen gas. There are several compounds of oxygen which, when exposed to heat, are decomposed, and yield the gas in a state of purity: of these the best is chlorate of potash; but as that salt is expensive, we generally resort to black oxide of manganese, which, at a dull red heat, gives out a considerable quantity of tolerably pure oxygen gas. Oxygen gas is colourle , tastele , and inodorous; it is electro-negative, and therefore when compounds containing it are electrically decomposed, it always appears at the positive surface. It is a little heavier than atmospheric air, in the proportion, that is, of 1 1 to 10; ICO cubical inches weighing 346 grains. It is not absorbed by water, and is neither acid nor alkaline. It has a powerful attraction for most of the simple substances, especially for the electro-positive bodies: the act of combining with it is called oxidation. The compounds thus formed are divided into aa'ds and oxides: among the latter are the alkalis, and almost all salifiable bases. Oxidation is often attended with the evolution of heat and light, as in all proce es of combustion in atmospheric air: sometimes it is slow, and unattended with such phenomena, as in the gradual rusting of metals. Oxygen is a most powerful supporter of combustion; it constitutes one fifth of the bulk of the atmosphere, and is the principle which enables combustible bodies to burn in it. The product of combustion, that is, the oxide or acid, is sometimes itself gaseous, as when charcoal, by burning, is converted into carbonic acid; or it is liquid, as hydrogen, by combustion, produces water; or it is solid, as when iron, by burning, produces oxide of iron. Oxygen gas is also e ential to respiration; that is, to the evolution of carbonic acid from the blood. [s. 878]