gold & silver | gold | silver
Atomic weight: 196.967
Melting point: 1,064 degrees C
Specific gravity: 19.3 when pure
Hardness: 2.5-3
Gold is 19.3 times heavier than an equal volume of water.
Gold is a rare, noble metal, with the chemical symbol Au, derived from Aurora or dawn. The purity of gold is described by its 'fineness' (parts per 1,000) or by the carat scale. The word 'carat' derives from the Italian carato, Arabic qirat or Greek keration, all meaning the fruit of the carob tree. Ancient traders used carob seeds as the means to balance the scales in oriental bazaars. Pure gold is 24 carat (or 1,000 fine), and because pure gold is soft and liable to wear, it is often alloyed with other metals.
While gold is known for its resistance to corrosion, it can be dissolved by cyanide or aqua regia (a mixture of nitric acid and hydrochloric acid). For information on how aqua regia is used in the assaying process click here.
Gold is noted for its malleability and ductility. It can be beaten into leaves only 0.00001 mm thick. The leaves can be so thin that light can pass through them. One ounce can be drawn into a piece of wire 80 km long.
Decoration
Gold has been used for ornamental purposes and as a medium of exchange for over 5,000 years. Gold leaf has been used for decoration of tombs and statues, cathedrals and temples, fine books, and picture frames since Egyptian times. Many Egyptian burial cases, including King Tutankhamun's (1352 BC), were overlaid with beaten gold. Gold leaf is still often preferred for adorning the domes or ceilings of public buildings (such as the Metropolitan Opera House in New York) because its resistance to corrosion means that it will outlast paint by many years. Liquid gold painted on tableware and containers and fired in a kiln produces a lustrous decoration at a very low cost.
Gold was made into jewellery long before it was used as currency. The earliest gold jewellery dates from the Sumeric civilisation around 3,000BC. The jewellery was worn by both men and women. Goldsmith’s skills that were understood and mastered at that time are still used today, although some of the techniques have been lost. Gold wedding rings, used in marriage ceremonies since the 9th century, date back to the ancient Egyptians. The ring is placed on the third finger of the left hand because it was believed that this finger carried an artery leading directly to the heart.
Gold Reflective Glass.
Gold's ability to reflect heat has led to the increasing use of glass coated with a thin gold film in modern buildings. One ounce of gold is enough to cover 93 square metres (approximately 1000 square feet) of glass, which not only reflects heat in summer, but helps to retain warmth in winter. The use of reflective glass has reduced cooling and heating costs by as much as 40% in some buildings.
Electronics.
Gold is used in electronics because of its high electrical conductivity, its ductility and its total freedom from corrosion or tarnishing at either high or low temperatures. It is the gold plating of contacts for switches, relays and connectors that accounts for most of the 120 to 140 tonnes of gold required annually by the electronics industry for the circuitry of calculators, television sets, computers, telephones and a host of other products. In telecommunications, especially satellites, and in computers, gold is indispensable.
above: Gold reflective glass. The Royal Bank of Canada building in Toronto has 77.7 kilograms of gold in its windows, cutting cooling and heating costs.
below: Gold plated contacts and connectors are an essential part of modern electronics.
Satellites and Communications
Satellites send information about weather patterns around the world, useful for tracking the paths of tropical storms. Satellites take photos of agricultural changes, such as diseases affecting crops, to predict production each year and help countries plan what they grow for food or trade. Satellites carry 50% of New Zealand’s international toll calls. The rest travel by submarine cable. News agencies use satellites to send and receive news all over the world. Many television companies transmit news, sports and entertainment programmes direct to viewers via satellite. For navigational purposes, ships and aircraft carry equipment that use satellite tracking to enable them to show their position.
above and right: Radar and satellite communications rely on the properties of gold. Gold plated contacts and connectors are an essential part of modern electronics in everything from computers to televisions.
Aerospace
The success of the United States space programme depends heavily on the clean, non-corroding electrical performance of gold. The metal’s ability to reflect heat protects astronauts, satellites and critical electronic components from damage by hazardous x-rays and solar radiation found in space.
Medicine
Recent medical research has demonstrated the healing powers of gold. Compounds of gold were first used experimentally in 1927 in the treatment of rheumatoid arthritis and are now the basis of a successful form of therapy. Radioactive gold is used in the treatment of several types of cancer. Gold leaf is used to treat chronic ulcers as well as in surgery to patch damaged blood vessels, nerves, bones and membranes.
Dentistry
Dentists in the United States alone, use about 30 tonnes of gold annually. Because of their high resistance to corrosion, tarnish and other properties, gold alloys are used for crowns, bridges, gold inlays and dentures.
above left: An antique gold pocket watch.
above right: An Indian bride adorned with the customary 22 carat gold ornaments.
Reference: Green T, and Russell R. The Gold Companion - The A-Z of Mining, Marketing, Trading and Technology. Rosendale Press Ltd, 1991, Great Britain.
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