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(Anglo-Saxon, Seolfor siolfur; L. argentum) Silver has been known since ancient times.
It is mentioned in Genesis. Slag dumps in Asia Minor and on islands in the Aegean Sea
indicate that man learned to separate silver from lead as earl as 3000 B.C.
Silver occurs native and in ores such as argentite (Ag2S) and horn silver (AgCl); lead,
lead-zinc, copper, gold, and copper-nickel ores are principal sources. Mexico, Canada,
Peru, and the U.S. are the principal silver producers in the western hemisphere.
Silver is also recovered during electrolytic refining of copper. Commercial fine silver
contains at least 99.9% silver. Purities of 99.999+% are available commercially.
Pure silver has a brilliant white metallic luster. It is a little harder than gold and
is very ductile and malleable, being exceeded only by gold and perhaps palladium. Pure
silver has the highest electrical and thermal conductivity of all metals, and possesses
the lowest contact resistance. It is stable in pure air and water, but tarnishes when
exposed to ozone, hydrogen sulfide, or air containing sulfur. The alloys of silver are
Sterling silver is used for jewelry, silverware, etc. where appearance is paramount.
This alloy contains 92.5% silver, the remainder being copper or some other metal. Silver
is of the utmost importance in photography, about 30% of the U.S. industrial consumption
going into this application. It is used for dental alloys. Silver is used in making solder
and brazing alloys, electrical contacts, and high capacity silver-zinc and silver-cadmium
batteries. Silver paints are used for making printed circuits. It is used in mirror
production and may be deposited on glass or metals by chemical deposition, electrode
position, or by evaporation. When freshly deposited, it is the best reflector of visible
light known, but is rapidly tarnished and loses much of its reflectance. It is a poor
reflector of ultraviolet. Silver fulminate, a powerful explosive, is sometimes formed
during the silvering process. Silver iodide is used in seeding clouds to produce rain.
Silver chloride has interesting optical properties as it can be made transparent; it also
is a cement for glass. Silver nitrate, or lunar caustic, the most important silver
compound, is used extensively in photography. Silver for centuries has been used
traditionally for coinage by many countries of the world. In recent times, however,
consumption of silver has greatly exceeded the output.
While silver itself is not considered to be toxic, most of its salts are poisonous.
Exposure to silver (metal and soluble compounds, as Ag) in air should not exceed 0.01 mg/m3, (8-hour time-weighted
average - 40 hour week). Silver compounds can be absorbed in the circulatory system and
reduced silver deposited in the various tissues of the body. A condition, known as
argyria, results with a grayish pigmentation of the skin and mucous membranes. Silver has
germicidal effects and kills many lower organisms effectively without harm to higher
In 1939, the price of silver was fixed by the U.S. Treasury at 71 cents/troy oz., and
at 90.5 cents/troy oz. in 1946. In November 1961 the U.S. Treasury suspended sales of
nonmonetized silver, and the price stabilized for a time at about $1.29, the melt-down
value of silver U.S. coins. The coinage act of 1965 authorized a change in the metallic
composition of the three U.S. subsidiary denominations to clad or composite type coins.
This was the first change in U.S. coinage since the monetary system was established in
1792. Clad dimes and quarters are made of an outer layer of 75% Cu and 25% Ni bonded to a
central core of pure Cu. The composition of the one- and five-cent pieces remains
unchanged. One-cent coins are 95% Cu and 5% Zn. Five-cent coins are 75% Cu and 25% Ni. Old
silver dollars are 90% Ag and 10% Cu. Earlier subsidiary coins of 90% Ag and 10% Cu
officially were to circulate alongside the old coins; however, in practice they have
largely disappeared (Gresham's Law), as the value of the silver is now greater than their
exchange value. Silver coins of other countries have largely been replaced with coins made
of other metals. On June 24, 1968, the U.S. Government ceased to redeem U.S. Silver
Certificates with silver. Since that time, the price of silver has fluctuated widely. As
of January 1990, the price of silver was about $5.25/troy oz.; however, the price has
fluctuated considerably due to market instability.
Sources: CRC Handbook of Chemistry
and Physics and the American Chemical Society.
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