What is Silver ?

Silver is a white, shiny corrosion resistant metal. It is able to conduct electricity, and heat very well. The atomic symbol for silver is Ag - it is a the abbreviation for the latin term "argentum" .

Sikverm was one of the metals popular among ancient civilizations, along with gold, copper, iron, tin, lead, and mercury. Pure silver is usually found in large masses, the metal is easily used without complex methods - and has been used since 3500 BC in ancient Egypt.

What is Silver Used for ?

 Silver has and is mainly used as a monetary unit - in both bullion and coin form. Sterling Silver and plated silver are widely used in tableware and in jewelry. About one third of the silver consumed is in the form of photosensitive silver halides, which are in photography. There are also many industrial applications of silver alloys. Corrosion resistant alloys are used as lining materials in vessels and pipes. Other alloys are used in brazing because of their low melting points and good workability. Alloys with high electrical conductivity are used in electrical contacts. Silver alloys are important in dentistry for bridgework, pins, and fillings. The bactericidal properties of colloidal silver make it useful medicine, and silver preparations are used as caustics, astringents, and antiseptics. Silver is also used as a catalyst in chemical reactions to promote the oxidation of organic compounds in the vapor state, such as oxidation of ethyl alcohol to acetaldehyde.

Properties of Silver

Silver is metal located in Group IB of the periodic table, along with copper and gold. Its atomic number is 47, and its atomic weight is 107.87. The isotopes of silver, including artificially produced radioactive isotopes, range in weight from 102 Ag to 117 Ag. The only naturally occurring isotopes are 107 Ag, which make 52% of the silver found in nature, and have a face centered cubic lattice structure. The element melts at 960.8°C (1774.4°F) and boils at about 1950°C (4010°F). Its specific gravity is 10.50 at 20°C (68°F). The most common valence of silver is +1, but the +2 state is also found.

  The electrical and thermal conductivities of silver are the highest of any element. It also has the highest optical reflectivity. When polished, silver will reflect about 95% of the light in the visible range of the spectrum. Silver is more malleable and ductile than any other element except gold. It is a relatively soft metal, and it scratches easily. Silver, which is intermediate in chemical reactivity between copper and gold, is a relatively inert metal that is resistant to common corrosive agents, such as oxygen, water, and dilute acids, however, it does combine readily with sulfur in the air or with hydrogen sulfide to form silver sulfide, Ag2S. Which is the black tarnish commonly seen on silverware. Silver is soluble in nitric acid, hot concentrated sulfuric acid, mercury, and fused alkali peroxides.

  An unusual property of silver is its ability when molten to absorb large quantities of oxygen, even up to 20 times its own volume. However, as the liquid silver cools, most of the oxygen is released.

Occurrence of Silver

Silver is a rare metal, making up less than a hundred-millionth of the earth’s crust. Although some silver is found as a native element, most occurs in compounds, such as sulfides, arsenides, antimonies, telluride, bismuthides, and halides. The most common of the silver minerals is argentite, AG2S, which when pure contains 87% silver. Argentite occurs alone or dissolved in galena, PbS. Copper ores containing silver are chalcopyrite, CuFeS2; chalcocite, Cu2S; and bornite, Cu5FeS4.

  More than two thirds of the silver produced is obtained as a by-product from ores of other metals, primarily lead and cooper ores, with small amounts from zinc and gold ores. Although only a few ounces of silver may be recovered per ton of ore, the great value of the metal makes working of low-grade mines profitable. The remainder ores, such as argentite ad cerargyrite, AgCl, which is commonly known as horn silver.

Extraction of Silver

Silver is extracted from its ores by direct smelting, amalgamation, leaching, or cyanidation. The most common method of obtaining silver directly from its ores is the high-recovery cyanidation process. In this process, silver is dissolved from the ore by treatment with sodium cyanide solution. The dissolved silver is then precipitated by the addition of zinc or aluminum and an alkali to the solution.

  In the leaching method, horn silver is dissolved in concentrated brine, and the silver is then precipitated out by the addition of copper. In the amalgamation process, horn silver is treated with mercury at room temperature. The ore is reduced to silver, which then dissolves in the mercury to form an amalgam. The mercury can be distilled off from the amalgam by heating.

  Silver-bearing lead and copper ores are treated by direct smelting. When the ore is fused, the silver is absorbed by either the lead or the copper. Silver is extracted from lead by the Parke process, in which 1% zinc is added to the molten crude lead. The zinc reacts with silver to form alloys with melting points and lower densities than the lead bath. Thus, these alloys float to the surface and are skimmed off. Zinc is removed from the alloys by dilation. Any lead remaining with the silver is removed by cupellation, a process in which the molten metal is heated in a blast of air on a cupel, or hearth, made of bone ash. The lead is converted to litharge, PbO, which flows over the edge of the cupel, leaving pure silver.

  Silver is extracted from copper by the Betts process, in which copper is electrolytically refined. In this process silver is obtained from the sludge, or anode slime, deposited in the baths. Silver is dissolved out of the sludge with nitric acid and is then obtained in pure from by cathodic reduction.

Silver Alloys.

Other metals are alloyed with silver to improve its mechanical strength and its resistance to wear and tarnish. The silver content of metals is expressed in terms of “fineness”, or parts of silver per 1,000 parts of total metal. For example, sterling silver, which is the most familiar of the silver alloys, is 925 fine- that is, it contains 92.5% silver; the other 7.5% is copper. The addition of the copper to the silver increases the mechanical strength of the metal and lowers its melting point. Sterling silver is widely used for tableware, jewelry, and decorative articles.

  Antimony and arsenic are alloyed with silver to improve its tarnish resistance. Cadmium is alloyed with silver to lower its melting point. These low-melting substances are used as brazing alloys as jewelry solders. They are also used in electrical contacts. Copper-silver alloys can be worked and are used in the brazing of metals.

  Iron-silver alloys are important because silver has a grain-refining and deoxidizing action on stainless steel, and consequently the stainless steel suffers less pit corrosion. Silver is alloyed with lead because it improves the resistance of lead to deformation. These alloys are used in soft solders and as anodes in the electrolytic refining of zinc. Silver-lead alloys containing 3% to 5% lead have excellent antifriction properties.

  An alloy of tin and silver is used to form a dental amalgam, which is plastic for a short time before setting into a hard mass that is resistant to corrosion. Palladium and platinum increase the tarnish resistance of silver, and these alloys are also used in dental work because of their corrosion resistance.

 Tin-silver alloys are used in valves in refrigeration equipment. Zinc-silver alloys are used for electrical contacts and in brazing. Alloys of silver and copper and zinc have low melting points, good flow characteristics, high strength, and good malleability, ductility and corrosion resistance. These alloys are used in brazing.

Silver Compounds

The most important compound of silver is silver nitrate, AgNO3, which is used as the starting compound and in the manufacture of mirrors. The major use of silver nitrate is in the production of silver halides for photosensitive emulsions for films and papers in the photographic industry. Silver nitrate is a colorless salt that is very soluble in water. It is prepared by dissolving silver in nitric acid and then evaporating the solution. Traces of silver nitrate will blacken the skin as a result of the reduction of silver ions to metallic silver by proteins.

  Silver carbonate, AG2CO3, is a light yellow salt produced by the addition of carbonic acid to silver oxide. It is useful in the synthesis of organic compounds. Silver chromate, Ag2Cro4, is a dark red powder that is also used in organic synthesis.

  Silver bromide, AgBr, and silver chloride, AgCl, are the silver halides used in photosensitive emulsions. Silver bromide is a yellowish white solid, and silver chloride is white. Both are insoluble in water and soluble in sodium thiosulfate, which is commonly known as photographers. Silver iodide, AgI, has a crystalline structure that very closely resembles that of ice, and it has been used in seeding clouds to furnish nuclei for ice formation in attempts at rainmaking.

  In the compounds discussed previously the valence of silver is +1. Silver compounds in which the valence of the element is +2 are not stable in solution except in the form of complex ions. However, there are stable solid compounds, such as AgF2 and AgO, in which the valence of silver is +2.

Silver Plating

Silver is one of the most commonly used metals for electroplating either metallic or nonmetallic materials. Plating is done to increase the reflectivity of the material or for decorative purposes. Silver is plated on metals from a sodium cyanide bath containing silver nitrate. Plastics can be silvered by the chemical reduction of a complex silver ion to metallic silver or by the deposition of silver by vacuum evaporation.

  In the production of mirrors, silver is chemically deposited on one surface of the glass to increase its reflectivity. The silvering preparations consist of two solutions. One is an moniacal solution of silver nitrate, Ag(NH3)2NO3, which also contains some potassium hydroxide. The other solution is a reducing agent, such as sugar, Rochelle salt, or formaldehyde. The reducing agent, when mixed with the silver solution, converts the silver-ammonia complex ion to metallic silver. The glass to be silvered is first thoroughly cleaned, and then the solutions are poured on it. If the ammonical silver solution is allowed to evaporate on standing, it can deposit a silver azide that is sensitive and explosive.

  Silver has been used as money since the time of ancient Babylonia. For centuries it was the primary from of money. In the United States, bimetallism was officially adopted in 1792, when the mint was authorized to coin as much gold and silver as were offered. The silver dollar contained 371.25 grains and the gold dollar 24.75 grains, a ratio of 15 to 1.

Silver in the 19^th century.  

The bimetallic standard depended on a ratio of market prices of the two metals equal to their official mint ratio. In fact, however, the market price ratio was near 15.5:1 by 1803, when France adopted a 15.1:1 dual metal standard. The market ratio continued to creep up toward 16:1 by 1816, when England adopted this ratio for coinage. In 1834, after an extensive flow of gold to England, The U.S congress lowered the gold content of the dollar to 23:2 grains. Thus the mint ratio was increased to 16:1.

  Rich gold discoveries in the mid-1800’s led, however, to lowered gold prices and high silver prices. As the discrepancy widened between official mint prices and market prices, bimetallism ceased to work. Silver was sold in the market for a higher price than it commanded at the mint. Silver coin was driven from circulation during the Civil War, and further coinage of silver dollars was prohibited by the Coinage Act of 1873. Europe and Latin America also abandoned the free coinage of silver in the 1970’s. Silver circulated as money only in the form of subsidiary coinage. This was possible only because silver’s value in subsidiary coins was considerably debased. The American half dollar, for example, contained 172.8 grains of silver instead of 185.625.

  In the United States, silver shortly became involved in a contest between easy-money and tight-money adherents. In 1873 the relative prices of silver and gold shifted again. Discoveries of silver in Nevada lowered its price below the old mint price of $1.293 an ounce. Silver-mine owners, farmers, and debtors, who wanted to increase the supply of money is circulation and thus bring about higher prices, began a campaign to restore bimetallism.

  In 1878 and again 1890, Congress voted to require substantial open-market silver purchases and to authorize treasury noted backed by silver.  In 1896, however, sound-money forces won a decisive political victory over the advocates of “free silver.” In 1900, Congress officially adopted a gold-coin monetary standard, eliminating silver from the defintition.

Silver in the 20^th century.

The silver-mine owners and their representatives continued to carry on the fight for silver early in the 20^th century, and in World War I, when the price of silver again to soar, they brought back silver dollars.

  The great depression of the 1930’s reawakened interest in silver. As a result of the London Monetary Conference of 1933, the United States agreed to buy 24 million ounces at 64.64 cents an ounce- half the traditional price but 50% more than the prevailing market price. Throughout the 1930’s, senators favoring silver and congressional proponents of cheap money succeed in having the government artificially maintain the price of silver by buying quantities of it, ostensibly for coinage but mostly for burial in the vaults of West Points.

  During World War II the rationale for silver as a monetary metal again disappeared. As silver-using industries operated at full capacity, the price of silver rose rapidly. The public began to hoard silver coins in anticipation of the day when the market price of the silver content would exceed their face value. When this finally occurred in the early 1960’s, the U.S government took steps to eliminate silver from the money system.

  The Treasury ceased to issue silver certificates- the paper money secured silver. However, the reduced supply of $1 and $2 bills was filled by Federal Reserve notes. In 1965 the silver content of newly minted quarters and dimes was eliminated, and quarters and dimes there after consisted of a layer of copper between two layers of cupronickel. The Silver content of the half dollar was reduced to 40%, and by 1970 it was eliminated entirely.

  Silver became simply a precious metal, traded by industrial and commercial users and speculators. The market price soared to unprecedented heights in late 1979, reaching $50.35 per ounce in January 1980. Two months later the price had dropped to $10.80 per ounce. Silver prices has risen up to over $47 in 2011 - and is currenly moving around the $40 range.