Background
Gold, recognizable by its yellowish cast, is one of the oldest metals used by humans. As far back as the Neolithic period, humans have collected gold from stream beds, and the actual mining of gold can be traced as far back as 3500 B.C., when early Egyptians (the Sumerian culture of Mesopotamia) used mined gold to craft elaborate jewelry, religious artifacts, and utensils such as goblets.
Gold's aesthetic properties combined with its physical properties have long made it a valuable metal. Throughout history, gold has often been the cause of both conflict and adventure: the destruction of both the Aztec and Inca civilizations, for instance, and the early American gold rushes to Georgia, California, and Alaska.
The largest deposit of gold can be found in South Africa in the Precambrian Witwatersrand Conglomerate. This deposit of gold ore is hundreds of miles across and more than two miles deep. It is estimated that two-thirds of the gold mined comes from South Africa. Other major producers of gold include Australia, the former Soviet Union, and the United States (Arizona, Colorado, California, Montana, Nevada, South Dakota, and Washington).
About 65 percent of processed gold is used in the arts industry, mainly to make jewelry. Besides jewelry, gold is also used in the electrical, electronic, and ceramics industries. These industrial applications have grown in recent years and now occupy an estimated 25 percent of the gold market. The remaining percentage of mined gold is used to make a type of ruby colored glass called purple of Cassius, which is applied to office building windows to reduce the heat in the summer, and to mirrors used in space and in electroscopy so that they reflect the infrared spectrum.
Physical Characteristics
Gold, whose chemical symbol is Au, is malleable, ductile, and sectile, and its high thermal and electrical conductivity as well as its resistance to oxidation make its uses innumerable. Malleability is the ability of gold and other metals to be pressed or hammered into thin sheets, 10 times as thin as a sheet of paper. These sheets are sometimes evaporated onto glass for infrared reflectivity, molded as fillings for teeth, or used as a coating or plating for parts. Gold's ability to be drawn into thin wire (ductility) enables it to be deposited onto circuits such as transistors and to be used as an industrial solder and brazing alloy. For example, gold wire is often used for integrated circuit electrical connections, for orthodontic and prosthetic appliances, and in jet engine fabrication.
Gold's one drawback for use in industry is that it is a relatively soft metal (sectile). To combat this weakness, gold is usually alloyed with another member of the metal family such as silver, copper, platinum, or nickel. Gold alloys are measured by karats (carats). A karat is a unit equal to 1/24 part of pure gold in an alloy. Thus, 24 karat (24K) gold is pure gold, while 18 karat gold is 18 parts pure gold to 6 parts other metal.
Extraction and Refining
Gold is usually found in a pure state; however, it can also be extracted from silver, copper, lead and zinc. Seawater can also contain gold, but in insufficient quantities to be profitably extracted—up to one-fortieth (1/40) of a grain of gold per ton of water. Gold is generally found in two types of deposits: lode (vein) or placer deposits; the mining technique used to extract the gold depends upon the type of deposit. Once extracted, the gold is refined with one of four main processes: floatation, amalgamation, cyanidation, or carbon-in-pulp. Each process relies on the initial grinding of the gold ore, and more than one process may be used on the same batch of gold ore.
Mining
In lode or vein deposits, the gold is mixed with another mineral, often quartz, in a vein that has filled a split in the surrounding rocks. Gold is obtained from lode deposits by drilling, blasting, or shoveling the surrounding rock.
Lode deposits often run deep underground. To mine underground, miners dig shafts into the ground along the vein. Using picks and small explosives, they then remove the gold ore from the surrounding rock. The gold ore is then gathered up and taken to a mill for refinement.
Placer deposits contain large pieces of gold ore (nuggets) and grains of gold that have been washed downstream from a lode deposit and that are usually mixed with sand or gravel. The three main methods used to mine placer deposits are hydraulic mining, dredging, and power shoveling. All methods of placer deposit mining use gravity as the basic sorting force.
In the first method, a machine called a "hydraulic giant" uses a high pressure stream of water to knock the gold ore off of banks containing the ore. The gold ore is then washed down into sluices or troughs that have grooves to catch the gold.
Dredging and power shoveling involve the same techniques but work with different size buckets or shovels. In dredging, buckets on a conveyor line scoop sand, gravel, and gold ore from the bottom of streams. In power shoveling, huge machines act like shovels and scoop up large quantities of gold-bearing sand and gravel from stream beds.
Hydraulic mining and dredging are outlawed in many countries because they are environmentally destructive to both land and streams.
Grinding
Once the gold ore has been mined, it usually is washed and filtered at the mine as a preliminary refinement technique. It is then shipped to mills, where it is first combined with water and ground into smaller chunks. The resulting mixture is then further ground in a ball mill—a rotating cylindrical vessel that uses steel balls to pulverize the ore.
Separating the gold from the ore
The gold is then separated from the ore using one of several methods. Floatation involves the separation of gold from its ore by using certain chemicals and air. The finely ground ore is dumped into a solution that contains a frothing agent (which causes the water to foam), a collecting agent (which bonds onto the gold, forming an oily film that sticks to air bubbles), and a mixture of organic chemicals (which keep the other contaminants from also bonding to the air bubbles). The solution is then aerated—air bubbles are blown in—and the gold attaches to the air bubbles. The bubbles float to the top, and the gold is skimmed off.
Cyanidation also involves using chemicals to separate the gold from its contaminants. In this process, the ground ore is placed in a tank containing a weak solution of cyanide. Next, zinc is added to the tank, causing a chemical reaction in which the end result is the precipitation (separation) of the gold from its ore. The gold precipitate is then separated from the cyanide solution in a filter press. A similar method is amalgamation, which uses the same process with different chemicals. First, a solution carries the ground ore over plates covered with mercury. The mercury attracts the gold, forming an alloy called an amalgam. The amalgam is then heated, causing the mercury to boil off as a gas and leaving behind the gold. The mercury is collected, recycled and used again in the same process.
The carbon-in-pulp method also uses cyanide, but utilizes carbon instead of zinc to precipitate the gold. The first step is to mix the ground ore with water to form a pulp. Next, cyanide is added to dissolve the gold, and then carbon is added to bond with the gold. After the carbon particles are removed from the pulp, they are placed in a hot caustic (corrosive) carbon solution, which separates the gold from the carbon.
If the gold is still not pure enough, it can be smelted. Smelting involves heating the gold with a chemical substance called flux. The flux bonds with the contaminants and floats on top of the melted gold. The gold is then cooled and allowed to harden in molds, and the flux-contaminant mixture (slag) is hauled away as a solid waste.
The Future
Because gold is a finite resource, its long-term future is limited. In the short term, however, it will continue to find widespread use in jewelry and in industrial applications, especially in the electronics field.
In the last few years, several companies have focused on extracting gold from sulphide ore rather than oxide ore. Previous techniques made such extraction difficult and expensive, but a newer technique called bioleaching has made extraction more feasible. The process involves combining the sulphide ore with special bacteria that "eat" the ore or break it down into a more manageable form.
Where To Learn More
Books
Coombs, Charles. Gold and Other Precious Metals. Morrow Publishing, 1981.
Gasparrini, Claudia. Gold & Other Precious Metals: From Ore to Market. Springer-Verlag, 1993.
Green, Timothy. The World of Gold. Walker Publishing, 1968.
Hawkins, Clint. Gold & Lead. HarperCollins, 1993.
Lye, Keith. Spotlight on Gold. Rourke Enterprises, 1988.
McCracken, Dave. Gold Mining in the Nineteen Nineties: The Complete Book of Modern Gold Mining Procedure. New Era Publications, 1993.
Wise, Edmund, ed. Gold: Recovery, Properties, and Applications. Van Nostrand, 1964.
Periodicals
Abelson, Philip H. "Gold." Science. July 11, 1986, p. 141.
Dworetzky, Tom. "Gold Bugs." Discover, March, 1988, p. 32.
"Some Like It Hot." Economist. June 25, 1988, p.88.
"Mining with Microbes: A Labor of Bug." Science News. April 14, 1990, p. 236.
[Article by: Alicia Haley and; Blaine Danley]
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Gold BarsQuickly search merchant prices. 100,000 Stores. Deals. Reviews. shopping.yahoo.com
Sci-Tech Encyclopedia: Gold Top
Home > Library > Science > Sci-Tech Encyclopedia
A chemical element, Au, atomic number 79 and atomic weight 196.967, a deep yellow, soft, and very dense metal. Gold is classed as a heavy metal and as a noble metal; commercially, it is the most familiar of the precious metals. Copper, silver, and gold are in the same group of the periodic table of elements. The Latin name for gold, aurum (glowing dawn), is the source of the chemical symbol Au. There is only one stable isotope of gold, that of mass number 197. See also Periodic table.
Uses
Consumption of gold in jewelry accounts for about three-fourths of the world's production of gold. Industrial applications, especially electronic, consume another 10–15%. The remainder is divided among medical and dental uses, coinage, and bar stock for governmental and private holdings. Gold coins and most decorative gold objects are actually gold alloys, because the metal itself is too soft (2.5–3 on Mohs scale) to be useful with frequent handling.
Radioactive 198Au is used in medical irradiation, in diagnosis, and in a number of industrial applications as a tracer. Another tracer use is in the study of movement of sediment on the ocean floor in and around harbors. The properties of gold toward radiant energy have led to development of efficient energy reflectors for infrared heaters and cookers and for focusing and retention of heat in industrial processes.
Occurrence
Gold occurs widely throughout the world, but usually very sparsely, so that it is quite a rare element. Sea water contains low concentrations of gold, on the order of 10 μg per ton (10 parts of gold per trillion parts of water). Somewhat higher concentrations accumulate on plankton or on the ocean bottom. At present, no economically feasible process is visualized for extracting gold from the sea. Native, or metallic, gold and various telluride minerals are the only forms of gold found on land. Native gold may occur in veins among rocks and ores of other metals, especially quartz or pyrite, or it may be scattered in sands and gravel (alluvial gold).
Properties
The density of gold is 19.3 times that of water at 20°C (68°F), so that 1 ft3 of gold weighs about 1200 lb (1 m3, about 19,000 kg). Masses of gold, like those of other precious metals, are measured on the troy scale, which counts 12 oz to the pound. Gold melts at 1064.43°C (1947.97°F) and boils at 2860°C (5180°F). It is somewhat volatile well below its boiling point. Gold is a good conductor of heat and electricity. It is the most malleable and ductile metal. It can easily be made into translucent sheets 0.0000039 in. (0.00001 mm) thick or drawn into wire weighing only 0.00005 oz/ft (0.5 mg/m). The quality of gold is expressed on the fineness scale as parts of pure gold per thousand parts of total metal, or on the karat scale as parts of pure gold per 24 parts of total metal. Gold readily dissolves in mercury to form amalgams. Gold is one of the least active metals chemically. It does not tarnish or burn in air. It is inert to strong alkaline solutions and to all pure acids except selenic acid.
Compounds
Gold may be either unipositive or tripositive in its compounds. So strong is the tendency for gold to form complexes that all the compounds of the 3+ oxidation state are complex. The compounds of the 1+ oxidation state are not very stable and tend to be oxidized to the 3+ state or reduced to metallic gold. All compounds of either oxidation state are easy to reduce to the metal.
In its complex compounds gold forms bonds most readily and stably with halogens and sulfur, less stably with oxygen and phosphorus, and only weakly with nitrogen. Bonds between gold and carbon are fairly stable, as in the cyanide complexes and a variety of organogold compounds.
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Dental Dictionary: gold Top
Home > Library > Health > Dental Dictionary
n
A precious or noble metal; yellow, malleable, ductible, nonrusting; much used in dentistry in pure and alloyed forms.
Sponsored Links
Gold BarsSearching for Gold Bars? Online listings and info. www.OnlyGoldBars.com
Gold vs. U.S. DollarsHow safe is your money? Free Reports & Info www.goldiras.com
Britannica Concise Encyclopedia: gold Top
Home > Library > Miscellaneous > Britannica Concise Encyclopedia
.content{clear:both;}
Metallic chemical element, one of the transition elements, chemical symbol Au, atomic number 79. It is a dense, lustrous, yellow, malleable precious metal, so durable that it is virtually indestructible, often found uncombined in nature. Jewelry and other decorative objects have been crafted from gold for thousands of years. It has been used for coins, to back paper currencies, and as a reserve asset. Gold is widely distributed in all igneous rocks, usually pure but in low concentrations; its recovery from ores and deposits has been a major preoccupation since ancient times (see cyanide process). The world's gold supply has seen three great leaps, with Christopher Columbus's arrival in the Americas in 1492, with discoveries in California (see gold rush) and Australia (1850 – 75), and discoveries in Alaska, Yukon (see Klondike), and South Africa (1890 – 1915). Pure gold is too soft for prolonged handling; it is usually used in alloys with silver, copper, and other metals. In addition to being used in jewelry and as currency, gold is used in electrical contacts and circuits, as a reflective layer in space applications and on building windows, and in filling and replacing teeth. Dental alloys are about 75% gold, 10% silver. In jewelry, its purity is expressed in 24ths, or karats: 24-karat is pure, 12-karat is 50% gold, etc. Its compounds, in which it has valence 1 or 3, are used mainly in plating and other decorative processes; a soluble chloride compound has been used to treat rheumatoid arthritis.
For more information on gold, visit Britannica.com.
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English Folklore: gold Top
Home > Library > Literature & Language > English Folklore
Thought to have healing properties, especially for sore eyes and styes, which should be rubbed with a wedding ring (the only gold object most families were likely to possess). Gold earnings were also thought to strengthen the eyes, and, among sailors and fishermen, to prevent one from drowning. Aubrey says some people of his time tied gold coins to ulcers and fistulas; he wonders whether the cure worked because ‘gold attracts mercury’ or because older gold coins ‘were printed with St Michael the Archangel, and to be stamped according to some Rule Astrological’ (Aubrey, 1688/1880: 206). Similarly, a letter written during the Plague of 1665 advices: ‘Friend, get a piece of angell gold, if you can of Eliz. coine (yt is ye best) wch is phylosophicall gold, and keepe it allways in yor mouth when you walke out or any sicke persons come to you’ (Opie and Tatem, 1989: 175). In such cases, the power resides both in the metal and in the symbolism of its design.For good luck at sea, sailing boats often had a gold sovereign set in the socket under the mast; the custom was common till about 1914, and is still sometimes followed. It has precedents from ancient Rome (Smith, FLS News 26 (1997), p. 12). Lovett found that fishermen from several towns used to ram a coin into the cork float of a drift-net, to break a run of bad luck in fishing, and held that ‘in the old days’ it would have been a gold one (Lovett, 1925: 54-5).
Gold, recognizable by its yellowish cast, is one of the oldest metals used by humans. As far back as the Neolithic period, humans have collected gold from stream beds, and the actual mining of gold can be traced as far back as 3500 B.C., when early Egyptians (the Sumerian culture of Mesopotamia) used mined gold to craft elaborate jewelry, religious artifacts, and utensils such as goblets.
Gold's aesthetic properties combined with its physical properties have long made it a valuable metal. Throughout history, gold has often been the cause of both conflict and adventure: the destruction of both the Aztec and Inca civilizations, for instance, and the early American gold rushes to Georgia, California, and Alaska.
The largest deposit of gold can be found in South Africa in the Precambrian Witwatersrand Conglomerate. This deposit of gold ore is hundreds of miles across and more than two miles deep. It is estimated that two-thirds of the gold mined comes from South Africa. Other major producers of gold include Australia, the former Soviet Union, and the United States (Arizona, Colorado, California, Montana, Nevada, South Dakota, and Washington).
About 65 percent of processed gold is used in the arts industry, mainly to make jewelry. Besides jewelry, gold is also used in the electrical, electronic, and ceramics industries. These industrial applications have grown in recent years and now occupy an estimated 25 percent of the gold market. The remaining percentage of mined gold is used to make a type of ruby colored glass called purple of Cassius, which is applied to office building windows to reduce the heat in the summer, and to mirrors used in space and in electroscopy so that they reflect the infrared spectrum.
Physical Characteristics
Gold, whose chemical symbol is Au, is malleable, ductile, and sectile, and its high thermal and electrical conductivity as well as its resistance to oxidation make its uses innumerable. Malleability is the ability of gold and other metals to be pressed or hammered into thin sheets, 10 times as thin as a sheet of paper. These sheets are sometimes evaporated onto glass for infrared reflectivity, molded as fillings for teeth, or used as a coating or plating for parts. Gold's ability to be drawn into thin wire (ductility) enables it to be deposited onto circuits such as transistors and to be used as an industrial solder and brazing alloy. For example, gold wire is often used for integrated circuit electrical connections, for orthodontic and prosthetic appliances, and in jet engine fabrication.
Gold's one drawback for use in industry is that it is a relatively soft metal (sectile). To combat this weakness, gold is usually alloyed with another member of the metal family such as silver, copper, platinum, or nickel. Gold alloys are measured by karats (carats). A karat is a unit equal to 1/24 part of pure gold in an alloy. Thus, 24 karat (24K) gold is pure gold, while 18 karat gold is 18 parts pure gold to 6 parts other metal.
Extraction and Refining
Gold is usually found in a pure state; however, it can also be extracted from silver, copper, lead and zinc. Seawater can also contain gold, but in insufficient quantities to be profitably extracted—up to one-fortieth (1/40) of a grain of gold per ton of water. Gold is generally found in two types of deposits: lode (vein) or placer deposits; the mining technique used to extract the gold depends upon the type of deposit. Once extracted, the gold is refined with one of four main processes: floatation, amalgamation, cyanidation, or carbon-in-pulp. Each process relies on the initial grinding of the gold ore, and more than one process may be used on the same batch of gold ore.
Mining
In lode or vein deposits, the gold is mixed with another mineral, often quartz, in a vein that has filled a split in the surrounding rocks. Gold is obtained from lode deposits by drilling, blasting, or shoveling the surrounding rock.
Lode deposits often run deep underground. To mine underground, miners dig shafts into the ground along the vein. Using picks and small explosives, they then remove the gold ore from the surrounding rock. The gold ore is then gathered up and taken to a mill for refinement.
Placer deposits contain large pieces of gold ore (nuggets) and grains of gold that have been washed downstream from a lode deposit and that are usually mixed with sand or gravel. The three main methods used to mine placer deposits are hydraulic mining, dredging, and power shoveling. All methods of placer deposit mining use gravity as the basic sorting force.
In the first method, a machine called a "hydraulic giant" uses a high pressure stream of water to knock the gold ore off of banks containing the ore. The gold ore is then washed down into sluices or troughs that have grooves to catch the gold.
Dredging and power shoveling involve the same techniques but work with different size buckets or shovels. In dredging, buckets on a conveyor line scoop sand, gravel, and gold ore from the bottom of streams. In power shoveling, huge machines act like shovels and scoop up large quantities of gold-bearing sand and gravel from stream beds.
Hydraulic mining and dredging are outlawed in many countries because they are environmentally destructive to both land and streams.
Grinding
Once the gold ore has been mined, it usually is washed and filtered at the mine as a preliminary refinement technique. It is then shipped to mills, where it is first combined with water and ground into smaller chunks. The resulting mixture is then further ground in a ball mill—a rotating cylindrical vessel that uses steel balls to pulverize the ore.
Separating the gold from the ore
The gold is then separated from the ore using one of several methods. Floatation involves the separation of gold from its ore by using certain chemicals and air. The finely ground ore is dumped into a solution that contains a frothing agent (which causes the water to foam), a collecting agent (which bonds onto the gold, forming an oily film that sticks to air bubbles), and a mixture of organic chemicals (which keep the other contaminants from also bonding to the air bubbles). The solution is then aerated—air bubbles are blown in—and the gold attaches to the air bubbles. The bubbles float to the top, and the gold is skimmed off.
Cyanidation also involves using chemicals to separate the gold from its contaminants. In this process, the ground ore is placed in a tank containing a weak solution of cyanide. Next, zinc is added to the tank, causing a chemical reaction in which the end result is the precipitation (separation) of the gold from its ore. The gold precipitate is then separated from the cyanide solution in a filter press. A similar method is amalgamation, which uses the same process with different chemicals. First, a solution carries the ground ore over plates covered with mercury. The mercury attracts the gold, forming an alloy called an amalgam. The amalgam is then heated, causing the mercury to boil off as a gas and leaving behind the gold. The mercury is collected, recycled and used again in the same process.
The carbon-in-pulp method also uses cyanide, but utilizes carbon instead of zinc to precipitate the gold. The first step is to mix the ground ore with water to form a pulp. Next, cyanide is added to dissolve the gold, and then carbon is added to bond with the gold. After the carbon particles are removed from the pulp, they are placed in a hot caustic (corrosive) carbon solution, which separates the gold from the carbon.
If the gold is still not pure enough, it can be smelted. Smelting involves heating the gold with a chemical substance called flux. The flux bonds with the contaminants and floats on top of the melted gold. The gold is then cooled and allowed to harden in molds, and the flux-contaminant mixture (slag) is hauled away as a solid waste.
The Future
Because gold is a finite resource, its long-term future is limited. In the short term, however, it will continue to find widespread use in jewelry and in industrial applications, especially in the electronics field.
In the last few years, several companies have focused on extracting gold from sulphide ore rather than oxide ore. Previous techniques made such extraction difficult and expensive, but a newer technique called bioleaching has made extraction more feasible. The process involves combining the sulphide ore with special bacteria that "eat" the ore or break it down into a more manageable form.
Where To Learn More
Books
Coombs, Charles. Gold and Other Precious Metals. Morrow Publishing, 1981.
Gasparrini, Claudia. Gold & Other Precious Metals: From Ore to Market. Springer-Verlag, 1993.
Green, Timothy. The World of Gold. Walker Publishing, 1968.
Hawkins, Clint. Gold & Lead. HarperCollins, 1993.
Lye, Keith. Spotlight on Gold. Rourke Enterprises, 1988.
McCracken, Dave. Gold Mining in the Nineteen Nineties: The Complete Book of Modern Gold Mining Procedure. New Era Publications, 1993.
Wise, Edmund, ed. Gold: Recovery, Properties, and Applications. Van Nostrand, 1964.
Periodicals
Abelson, Philip H. "Gold." Science. July 11, 1986, p. 141.
Dworetzky, Tom. "Gold Bugs." Discover, March, 1988, p. 32.
"Some Like It Hot." Economist. June 25, 1988, p.88.
"Mining with Microbes: A Labor of Bug." Science News. April 14, 1990, p. 236.
[Article by: Alicia Haley and; Blaine Danley]
Sponsored Links
4 Top Gold Stocks of 2009Discover how to get rich investing in gold. Free report reveals how... www.SmartProfitsReport.com/Gold2009
Gold BarsQuickly search merchant prices. 100,000 Stores. Deals. Reviews. shopping.yahoo.com
Sci-Tech Encyclopedia: Gold Top
Home > Library > Science > Sci-Tech Encyclopedia
A chemical element, Au, atomic number 79 and atomic weight 196.967, a deep yellow, soft, and very dense metal. Gold is classed as a heavy metal and as a noble metal; commercially, it is the most familiar of the precious metals. Copper, silver, and gold are in the same group of the periodic table of elements. The Latin name for gold, aurum (glowing dawn), is the source of the chemical symbol Au. There is only one stable isotope of gold, that of mass number 197. See also Periodic table.
Uses
Consumption of gold in jewelry accounts for about three-fourths of the world's production of gold. Industrial applications, especially electronic, consume another 10–15%. The remainder is divided among medical and dental uses, coinage, and bar stock for governmental and private holdings. Gold coins and most decorative gold objects are actually gold alloys, because the metal itself is too soft (2.5–3 on Mohs scale) to be useful with frequent handling.
Radioactive 198Au is used in medical irradiation, in diagnosis, and in a number of industrial applications as a tracer. Another tracer use is in the study of movement of sediment on the ocean floor in and around harbors. The properties of gold toward radiant energy have led to development of efficient energy reflectors for infrared heaters and cookers and for focusing and retention of heat in industrial processes.
Occurrence
Gold occurs widely throughout the world, but usually very sparsely, so that it is quite a rare element. Sea water contains low concentrations of gold, on the order of 10 μg per ton (10 parts of gold per trillion parts of water). Somewhat higher concentrations accumulate on plankton or on the ocean bottom. At present, no economically feasible process is visualized for extracting gold from the sea. Native, or metallic, gold and various telluride minerals are the only forms of gold found on land. Native gold may occur in veins among rocks and ores of other metals, especially quartz or pyrite, or it may be scattered in sands and gravel (alluvial gold).
Properties
The density of gold is 19.3 times that of water at 20°C (68°F), so that 1 ft3 of gold weighs about 1200 lb (1 m3, about 19,000 kg). Masses of gold, like those of other precious metals, are measured on the troy scale, which counts 12 oz to the pound. Gold melts at 1064.43°C (1947.97°F) and boils at 2860°C (5180°F). It is somewhat volatile well below its boiling point. Gold is a good conductor of heat and electricity. It is the most malleable and ductile metal. It can easily be made into translucent sheets 0.0000039 in. (0.00001 mm) thick or drawn into wire weighing only 0.00005 oz/ft (0.5 mg/m). The quality of gold is expressed on the fineness scale as parts of pure gold per thousand parts of total metal, or on the karat scale as parts of pure gold per 24 parts of total metal. Gold readily dissolves in mercury to form amalgams. Gold is one of the least active metals chemically. It does not tarnish or burn in air. It is inert to strong alkaline solutions and to all pure acids except selenic acid.
Compounds
Gold may be either unipositive or tripositive in its compounds. So strong is the tendency for gold to form complexes that all the compounds of the 3+ oxidation state are complex. The compounds of the 1+ oxidation state are not very stable and tend to be oxidized to the 3+ state or reduced to metallic gold. All compounds of either oxidation state are easy to reduce to the metal.
In its complex compounds gold forms bonds most readily and stably with halogens and sulfur, less stably with oxygen and phosphorus, and only weakly with nitrogen. Bonds between gold and carbon are fairly stable, as in the cyanide complexes and a variety of organogold compounds.
Sponsored Links
Investing In Gold 2009Learn How You Can Make a Fortune in the 2009 Gold Boom www.DailyWealth.com/Gold_Report
Buy US Gold Coins2008 American Eagle Gold Coins. from Coast To Coast Coins www.CoastCoin.com
Dental Dictionary: gold Top
Home > Library > Health > Dental Dictionary
n
A precious or noble metal; yellow, malleable, ductible, nonrusting; much used in dentistry in pure and alloyed forms.
Sponsored Links
Gold BarsSearching for Gold Bars? Online listings and info. www.OnlyGoldBars.com
Gold vs. U.S. DollarsHow safe is your money? Free Reports & Info www.goldiras.com
Britannica Concise Encyclopedia: gold Top
Home > Library > Miscellaneous > Britannica Concise Encyclopedia
.content{clear:both;}
Metallic chemical element, one of the transition elements, chemical symbol Au, atomic number 79. It is a dense, lustrous, yellow, malleable precious metal, so durable that it is virtually indestructible, often found uncombined in nature. Jewelry and other decorative objects have been crafted from gold for thousands of years. It has been used for coins, to back paper currencies, and as a reserve asset. Gold is widely distributed in all igneous rocks, usually pure but in low concentrations; its recovery from ores and deposits has been a major preoccupation since ancient times (see cyanide process). The world's gold supply has seen three great leaps, with Christopher Columbus's arrival in the Americas in 1492, with discoveries in California (see gold rush) and Australia (1850 – 75), and discoveries in Alaska, Yukon (see Klondike), and South Africa (1890 – 1915). Pure gold is too soft for prolonged handling; it is usually used in alloys with silver, copper, and other metals. In addition to being used in jewelry and as currency, gold is used in electrical contacts and circuits, as a reflective layer in space applications and on building windows, and in filling and replacing teeth. Dental alloys are about 75% gold, 10% silver. In jewelry, its purity is expressed in 24ths, or karats: 24-karat is pure, 12-karat is 50% gold, etc. Its compounds, in which it has valence 1 or 3, are used mainly in plating and other decorative processes; a soluble chloride compound has been used to treat rheumatoid arthritis.
For more information on gold, visit Britannica.com.
Sponsored Links
Sell Gold Jewelry OnlineAs Seen on TV. Cash in 24 Hrs. Free Shipping. Top Payment Guarantee! www.GoldPaq.com
Gold BarsThe Ultimate Guide to Gold Bars GoldBars-Direct.com
English Folklore: gold Top
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Thought to have healing properties, especially for sore eyes and styes, which should be rubbed with a wedding ring (the only gold object most families were likely to possess). Gold earnings were also thought to strengthen the eyes, and, among sailors and fishermen, to prevent one from drowning. Aubrey says some people of his time tied gold coins to ulcers and fistulas; he wonders whether the cure worked because ‘gold attracts mercury’ or because older gold coins ‘were printed with St Michael the Archangel, and to be stamped according to some Rule Astrological’ (Aubrey, 1688/1880: 206). Similarly, a letter written during the Plague of 1665 advices: ‘Friend, get a piece of angell gold, if you can of Eliz. coine (yt is ye best) wch is phylosophicall gold, and keepe it allways in yor mouth when you walke out or any sicke persons come to you’ (Opie and Tatem, 1989: 175). In such cases, the power resides both in the metal and in the symbolism of its design.For good luck at sea, sailing boats often had a gold sovereign set in the socket under the mast; the custom was common till about 1914, and is still sometimes followed. It has precedents from ancient Rome (Smith, FLS News 26 (1997), p. 12). Lovett found that fishermen from several towns used to ram a coin into the cork float of a drift-net, to break a run of bad luck in fishing, and held that ‘in the old days’ it would have been a gold one (Lovett, 1925: 54-5).
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