OXYGEN. 0=8. (Greek ovc sharp, yevretv to produce.) An elementary gas, the name of which is derived from its property of pro ducing acids. The atmosphere contains about one-fifth part, by volume, of oxygen gas, in a state of mixture ; and 'water eight-ninths, by weight, in combination with hydrogen.
Oxygen is the great supporter of life and combustion. Animals, by breathing, withdraw it from the air and return carbonic acid in exchange. Vegetables, during the action of light in the day time, absorb carbonic acid and return oxygen; hence the balance is main tained.
Oxygen is rather heavier than air, and when pure is tasteless, colourless, and inodorous. Its chief use to the photographer is for affording a brilliant light for exhibiting photographic magic lantern slides, or when a powerfully actinic artificial light is required in any of his operations. (See the following article.) The readiest mode of obtaining oxygen for this purpose is as follows : A copper retort, containing a mixture of about 3 parts of chlorate of potass and 1 part of black oxide of manganese, (thoroughly well mixed together,) is placed upon a common fire. In a short time
oxygen gas is evolved. This is conveyed by an india-rubber tube attached to the nozzle of the retort into a bottle of water, called the purifier, which may stand upon the ground. After passing through the water, which cools and purifies it, the gas passes along another india-rubber tube into a large wedge shaped india-rubber bag, which is capable of containing sufficient gas for an evening's entertainment. This bag may be filled in about half an hour, from half a pound, or less, of the mixed manganese and chlorate. When required for use the gas bag, filled with oxygen, is placed upon the ground between two boards hinged together, and upon the upper one weights are laid sufficient to force the gas out at the required rate, along a tube, either to the spirit lamp of the oxycalcium light apparatus, or to the point where it unites with the hydrogen jet of the Bude light, Perfectly pure oxygen is obtained from chlorate of potass alone, and collected over mercury after having been passed through a tube containing fused chlmide of calcium.