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(Gr. oxys, sharp, acid, and genes, forming; acid former) For many centuries, workers
occasionally realized air was composed of more than one component. The behavior of oxygen
and nitrogen as components of air led to the advancement of the phlogiston theory of
combustion, which captured the minds of chemists for a century. Oxygen was prepared by
several workers, including Bayen and Borch, but they did not know how to collect it, did
not study its properties, and did not recognize it as an elementary substance.
Priestley is generally credited with its discovery, although Scheele also discovered it
Its atomic weight was used as a standard of comparison for each of the other elements
until 1961 when the International Union of Pure and Applied Chemistry adopted carbon 12 as
the new basis.
Oxygen is the third most abundant element found in the sun, and it plays a part in the
carbon-nitrogen cycle, the process once thought to give the sun and stars their energy.
Oxygen under excited conditions is responsible for the bright red and yellow-green colors
of the Aurora.
A gaseous element, oxygen forms 21% of the atmosphere by volume and is obtained by
liquefaction and fractional distillation. The atmosphere of Mars contains about 0.15%
oxygen. The element and its compounds make up 49.2%, by weight, of the earth's crust.
About two thirds of the human body and nine tenths of water is oxygen.
In the laboratory it can be prepared by the electrolysis of water or by heating
potassium chlorate with manganese dioxide as a catalyst.
The gas is colorless, odorless, and tasteless. The liquid and solid forms are a pale
blue color and are strongly paramagnetic.
Ozone (O3), a highly
active compound, is formed by the action of an electrical discharge or ultraviolet light
Ozone's presence in the atmosphere (amounting to the equivalent of a layer 3 mm thick
under ordinary pressures and temperatures) helps prevent harmful ultraviolet rays of the
sun from reaching the earth's surface. Pollutants in the atmosphere may have a detrimental
effect on this ozone layer. Ozone is toxic and exposure should not exceed 0.2 mg/m#
(8-hour time-weighted average - 40-hour work week). Undiluted ozone has a bluish color.
Liquid ozone is bluish black and solid ozone is violet-black.
Oxygen, which is very reactive, is a component of hundreds of thousands of organic
compounds and combines with most elements.
Plants and animals rely on oxygen for respiration. Hospitals frequently prescribe
oxygen for patients with respiratory ailments.
Oxygen has nine isotopes. Natural oxygen is a mixture of three isotopes.
Natural occurring oxygen 18 is stable and available commercially, as is water (H2O with
15% 18O). Commercial oxygen consumption in the U.S. is estimated at 20 million short tons
per year and the demand is expected to increase substantially.
Oxygen enrichment of steel blast furnaces accounts for the greatest use of the gas.
Large quantities are also used in making synthesis gas for ammonia and methanol, ethylene
oxide, and for oxy-acetylene welding.
Air separation plants produce about 99% of the gas, while electrolysis plants produce
The gas costs 5 cents / ft3
in small quantities, and about $15/ton in large quantities.
Sources: CRC Handbook of Chemistry
and Physics and the American Chemical Society.