Oxygen
was first discovered as a separate gas in 1774, when it was produced by
heating red oxide of mercury and was given its present name by the famous
chemist, Lavoisier.
Oxygen is prepared in the laboratory by various methods, these including
the heating of chloride of lime and peroxide of cobalt mixed in a retort,
the heating of chlorate of potash, and the separation of water into its
elements, hydrogen and oxygen, by the passage of an electric current. While
the last process is used on a large scale in commercial work, the others
are not practical for work other than that of an experimental or temporary
nature.
This gas is a colorless, odorless, tasteless element. It is sixteen times
as heavy as the gas hydrogen when measured by volume under the same
temperature and pressure. Under all ordinary conditions oxygen remains in
a gaseous form, although it turns to a liquid when compressed to 4,400
pounds to the square inch and at a temperature of 220 below zero.
Oxygen unites with almost every other element, this union often taking
place with great heat and much light, producing flame. Steel and iron will
burn rapidly when placed in this gas if the combustion is started with a
flame of high heat playing on the metal. If the end of a wire is heated
bright red and quickly plunged into a jar containing this gas, the wire
will burn away with a dazzling light and be entirely consumed except for
the molten drops that separate themselves.
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