AUREM....or GOLD, if you prefer!
Most metals are metallic grey or silvery white whereas gold is
characteristically a metallic yellow colour, in other words gold-coloured.
Cesium is also gold coloured. The gold colour seems related to relativistic
effects of the outermost gold orbitals.
Small amounts of other metals alloyed with gold change the colour as well as mechanical properties such as hardness. White gold
for jewelry is formed by mixing palladium, silver, or nickel with gold,
although the result is green gold with certain proportions of silver. White
gold is commonly used for wedding rings in the USA. Addition of some copper
gives "rose gold", a soft pink colour. Remarkably other colours such
as purple (a gold:aluminium alloy), blue (a gold:indium alloy) and even black
(a gold:cobalt alloy) may be formed.
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.
Gold is readily available commercially and its price (see the UtiliseGold
directory if you wish to track it) changes day by day and is one of the most
widely tracked commercial prices.
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.
•Name: Gold
•Symbol: Au
•Atomic number: 79
•Atomic weight: 196.966569 (4)
•Standard state: solid at 298 K
•CAS Registry ID: 7440-57-5
•Group in periodic table: 11
•Group name: Coinage metal
•Period in periodic table: 6
•Block in periodic table: d-block
•Color: yellow colored; gold
•Classification: Metallic
Historical information
Gold had been known since the ancient times, and I couldn't find a
specific discoverer. Origin of name is from the Anglo-Saxon word
"gold" (the origin of the symbol Au is the Latin word
"aurum" meaning "gold"). Gold has always fascinated people
and gold is certainly one of the very first metals known. Nobody knows who
picked up a gold nugget first but it would have been because it was shiny. Gold
was highly valued from from the earliest recorded times in history. It seems
that the Egyptians developed gold smelting some 5600 years ago (about 3600 BC)
using clay blowpipes to heat the smelter contents. Egyption inscriptions dating
back to 2600 BC describe gold. Gold workers from Mesopotamia (known now as Iraq)
made one of the earliest known pieces of gold jewellery in about 2600 BC. Gold
is mentioned several times in the Old Testament. Tutankhamun's funeral mask is
one of the most iconic gold pieces known. It was made around 1223 BC and is a
stunning piece of ancient gold craftsmanship.
The first use of gold in dentistry as the Etruscans (an ancient Italian
civilisation from an area corresponding now to Tuscany) begin securing
substitute teeth with gold wire, and with astonishing skill. This was as early
as 700-600 BC. Apparently Etruscan craftsmen made gold dental bridges for women
so that they could show display their wealth and status. Some women had their
incisors removed so that they could be fitted with the gold prosthetics. The
Etruscans probably learned dentistry from the Egyptians, Phoenicians, and
Greeks but took the art much further. Many specimens of Etruscan dental
fittings are to be found in Italian and other museums.
Gold loops were fitted over the remaining natural teeth, set in place,
and maintained by solder. The patient's missing teeth were replaced by either
the teeth of human beings and on occasion the tooth of an ox.
Bio-compatibility, malleability and corrosion resistance make gold
valuable even today in dental applications, and is often used as a chelating
agent for treatments in some autoimmune diseases, like rheumatoid arthritis.
Colloidal gold has been used since Roman times to colour glass shades of
yellow, red, or violet. Melting gold powder into glass diffuses gold
nanoparticles into the glass, these refract light, giving the glass a luminous
red glow. THe precise colour depends upon the form of the colloidal gold.
Faraday (1857) recognised that the colour is due to the minute size of the gold
particles and called the sample he made 'activated gold'. In 1898 Richard Adolf
Zsigmondy prepared the first colloidal gold in dilute solution. Today,
colloidal gold is made by the addition of reducing agents to dilute solutions
of Au(III) (the auric ion). One famous form is that made by the use of tin
dichloride (SnCl2) as reducing agent. This is a very stable form of colloidal
gold and is known as the "Purple of Cassius". It is suitable for
colouring ceramics and glasses, and in addition is a good test for Au(III). The
form that Faraday studied was made using phosphorus to reduce gold chloride.
Gold is one of the elements which has an alchemical symbol, a circle with
a dot in the center.
Hallmarking practice established The world's first
"hallmarking" system was established at Goldsmith's Hall in London in
1300 AD. London's Assay Office is still there. THe purpose of the hallmarking
system is to determine and guarantee the quality of precious metals such as
gold.
Sometime prior to the autumn of 1803, the Englishman John Dalton was able
to explain the results of some of his studies by assuming that matter is
composed of atoms and that all samples of any given compound consist of the
same combination of these atoms. Dalton also noted that in series of compounds,
the ratios of the masses of the second element that combine with a given weight
of the first element can be reduced to small whole numbers (the law of multiple
proportions). This was further evidence for atoms. Dalton's theory of atoms was
published by Thomas Thomson in the 3rd edition of his System of Chemistry in
1807 and in a paper about strontium oxalates published in the Philosophical
Transactions. Dalton published these ideas himself in the following year in the
New System of Chemical Philosophy.
Gold has been the basis of many currencies over the centuries and so for
economic reasons, among others, the possession of gold was or is restricted in
some countries. Notably, private ownership of gold (apart from as jewellery and
coins) was banned between 1933 and 1975. In 1422 the Venice Mint made
("struck") 1.2 million gold ducats using 4.26 metric tonnes of gold.
These small coins (each about 3.5 g) were popular perhaps because they were
easy to make and are highly transportable. In 1717 Great Britain moved to a
pure gold standard. The British government linked the currency to gold at a
fixed rate (77 shillings, ten and a half pennies per ounce of gold).
The Californian Gold Rush of 1848 and 1855 started on 24 January 1848
when gold was found by James W. Marshall at Sutter's Mill, in Coloma,
California. Although attempts were made to keep the discovery quiet, news
leaked out and the result was the migration of 300,000 people to California
from the United States and beyond. The New York Herald was the first East Coast
newspaper to report the discovery of gold and on 5 December 1848, President
James Polk confirmed the discovery in an address to Congress. The gold-seekers
were called the "Forty-niners" and often had a very hard time.
Prospectors retrieved the gold from streams and riverbeds using low-technology
methods such as panning. More sophisticated methods of gold recovery were
eventually developed. Gold worth tens of billions of US dollars (2010
equivalent price) was extracted. Some became wealthy but many finished with
little profit and a lot of heartache. Today, the forty-niners name lives on in
the name of the San Francisco 49ers, an American football team in California.
Some years later in 1885 the South African Gold Rush began. An Australian
miner, George Harrison, found gold on Langlaagte farm near Johannesburg while
digging to build a house. South Africa became the source of almost one-half of
the world's gold.
