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For gold bars.
(Sanskrit Jval; Anglo-Saxon gold; L. aurum, gold) Known and highly valued from earliest
times, gold is found in nature as the free metal and in tellurides; it is very widely
distributed and is almost always associated with quartz or pyrite.
It occurs in veins and alluvial deposits, and is often separated from rocks and other
minerals by mining and panning operations. About two thirds of the world's gold output
comes from South Africa, and about two thirds of the total U.S. production comes from
South Dakota and Nevada. The metal is recovered from its ores by cyaniding, amalgamating,
and smelting processes. Refining is also frequently done by electrolysis. Gold occurs in
sea water to the extent of 0.1 to 2 mg/ton, depending on the location where the sample is
taken. As yet, no method has been found for recovering gold from sea water profitably.
It is estimated that all the gold in the world, so far refined, could be placed in a
single cube 60 ft. on a side. Of all the elements, gold in its pure state is undoubtedly
the most beautiful. It is metallic, having a yellow color when in a mass, but when finely
divided it may be black, ruby, or purple. The Purple of Cassius is a delicate test for
auric gold. It is the most malleable and ductile metal; 1 oz. of gold can be beaten out to
300 ft2. It is a soft
metal and is usually alloyed to give it more strength. It is a good conductor of heat and
electricity, and is unaffected by air and most reagents.
It is used in coinage and is a standard for monetary systems in many countries. It is
also extensively used for jewelry, decoration, dental work, and for plating. It is used
for coating certain space satellites, as it is a good reflector of infrared and is inert.
Gold, like other precious metals, is measured in troy weight; when alloyed with other
metals, the term carat is used to express the amount of gold present, 24 carats being pure
gold. For many years the value of gold was set by the U.S. at $20.67/troy ounce; in 1934
this value was fixed by law at $35.00/troy ounce, 9/10th fine. On March 17, 1968, because
of a gold crisis, a two-tiered pricing system was established whereby gold was still used
to settle international accounts at the old $35.00/troy ounce price while the price of
gold on the private market would be allowed to fluctuate. Since this time, the price of
gold on the free market has fluctuated widely. The price of gold on the free market
reached a price of $620/troy oz. in January 1980. As of January 1990, gold was priced at
about $410/troy oz.
The most common gold compounds are auric chloride and chlorauric acid, the latter being
used in photography for toning the silver image. Gold has 18 isotopes; 198Au, with a
half-life of 2.7 days, is used for treating cancer and other diseases. Disodium
aurothiomalate is administered intramuscularly as a treatment for arthritis. A mixture of
one part nitric acid with three of hydrochloric acid is called aqua regia (because it
dissolved gold, the King of Metals). Gold is available commercially with a purity of
99.999+%. For many years the temperature assigned to the freezing point of gold has been
1063.0C; this has served as a calibration point for the International Temperature Scales
(ITS-27 and ITS-48) and the International Practical Temperature Scale (IPTS-48). In 1968,
a new International Practical Temperature Scale (IPTS-68) was adopted, which demands that
the freezing point of gold be changed to 1064.43C. The specific gravity of gold has been
found to vary considerably depending on temperature, how the metal is precipitated, and
Sources: CRC Handbook of Chemistry
and Physics and the American Chemical Society.
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