Gold

History and Uses:

An attractive and highly valued metal, gold has been known for at least 5500 years. Gold is sometimes found free in nature but it is usually found in conjunction with silver , quartz (SiO2), calcite (CaCO3), lead , tellurium , zinc or copper . There is roughly 1 milligram of gold dissolved in every ton of seawater, although extracting it currently costs more than the gold is worth. It has been estimated that all of the gold that has currently been refined could be placed in a cube measuring 20 meters on a side. Gold is the most malleable and ductile of all known metals. A single ounce of gold can be beaten into a sheet measuring roughly 5 meters on a side. Thin sheets of gold, known as gold leaf, are primarily used in arts and crafts for gilding. One sheet of gold leaf can be as thin as 0.000127 millimeters, or about 400 times thinner than a human hair. Pure gold is soft and is usually alloyed with other metals, such as silver, copper, platinum or palladium , to increase its strength. Gold alloys are used to make jewelry, decorative items, dental fillings and coins. The amount of gold in an alloy is measured with a unit called a carat. One carat is equal to one part in twenty-four, so an 18 carat gold ring contains 18 parts pure gold and 6 parts alloy material. Gold is a good conductor of heat and electricity and does not tarnish when it is exposed to the air, so it can be used to make electrical connectors and printed circuit boards. Gold is also a good reflector of infrared radiation and can be used to help shield spacecraft and skyscrapers from the sun's heat. Gold coated mirrors can be used to make telescopes that are sensitive to infrared light. A radioactive isotope of gold, gold-198, is used for treating cancer. Gold sodium thiosulfate (AuNa3O6S4) is used as a treatment for arthritis. Chlorauric acid (HAuCl4) is used to preserve photographs by replacing the silver atoms present in an image.

Availability: gold is available in many forms including wire, foil, and bars. Small and large samples of gold foil, wire, and teflon coated wire (and gold alloy in wire form) can be purified.

Gold is usually alloyed in jewellery to give it more strength, and the term carat describes the amount of gold present (24 carats is pure gold). 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. It is metallic, with a yellow colour when in a mass, but when finely divided it may be black, ruby, or purple.

It is the most malleable and ductile metal; 1 ounce (28 g) of gold can be beaten out to 300 square feet. 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.

The most common gold compounds are auric chloride (AuCl3) and chlorauric acid (HAuCl4). A mixture of one part nitric acid with three of hydrochloric acid is called aqua regia (because it dissolved gold, the King of Metals). It is unaffected by air and most reagents. It is found free in nature and associated with quartz, pyrite and other minerals. Two thirds of the world's supply comes from South Africa, and 2/3 of USA production is from South Dakota and Nevada. Gold is found in sea water, but no effective economic process has been designed (yet) to extract it from this source

Here is a brief summary of the isolation of gold.

It would not normally be necessary to make gold in the laboratory as it is readily available commercially. The most romantic way to extract gold is by panning it out from a stream in some pleasant valley but most such sources are now depleted. Panning relies upon the density of gold (which is very high) being much greater than that of the sand and other particulates. It therefore settles to the bottom of the pan.

Today, more often than not, gold is extracted from ores. These ores often contain relatively little gold. Some of these processes cause environmental concern. The ore is crushed to a powder so as to expose the small gold particles. These are dissolved by treatment of the rock with cyanide solution in air. The result of this is a gold cyanide complex. Addition of zinc powder to the resulting solution precipitates out the gold.

In 1837, under pressure of a bad drought, Thomas Learmonth and a group of squatters explored the area to the north of their settlement near Geelong in search of better watered regions. On this journey they reached and climbed Mt. Bonan Yowing (now Buninyong) and were thus the first to see the Ballarat area. In March 1838, two squatters, Yuille and Anderson, settled with their flocks on the banks of an area known as Black Swamp, now Lake Wendouree.

Star of the East Gold Mine

During the next 13 years, shepherds and their flocks