Oxygen

oks'i-jen, an elemental gas, without color, taste, or odor. Its most prominent characteristic is its power to burn up many substances, that is to say, to unite with them and give off heat and light during the process. Substances which burn or unite with oxygen are said to be combustible. Burning bodies obtain oxygen usually from the air. If the air is shut off burning ceases. Oxygen was discovered by Priestley in 1774, and was named by the chemist Lavoisier. It is the most abundant element in the world. It forms one-fifth of the air, eight-ninths of the water, and from forty-four to forty-eight hundreths of the solid crust of the earth. It enters into combination with other elements to make up the structure of all plants and animals. Animals breathe air that the blood may absorb oxygen. Animal heat and energy are supplied by the action of oxygen. A combination of oxygen with another element is called an oxide. Thus we have mercuric oxide, zinc oxide, silver oxide, oxide of iron, etc. A dioxide is a compound with a double quantity of oxygen. Carbon dioxide, for instance, is a union of carbon with a double quantity of oxygen. The rusting of iron is the slow formation of an iron oxide. It is interesting to know that under a pressure of fifty atmospheres and a temperature of--119 degree. C., oxygen becomes a pale, steel-blue liquid, and that it may be frozen into a white solid. See Ozone; Water; Air; Sand; Sugar; Fire