Gold Essay Research Paper Antwan LucasGold

Gold Essay, Research Paper

Antwan Lucas

Gold

Gold, symbol Au , soft, dense,

bright yellow metallic element. Gold is one of the

transition elements of the periodic table (see Periodic

Law); its atomic number is 79.

Pure gold is the most malleable and ductile of all the

metals. It can easily be beaten or hammered to a

thickness of 0.000013 cm (0.000005 in), and 29 g (1.02

oz) could be drawn into a wire 100 km (62 mi) long. It

is one of the softest metals (hardness, 2.5 to 3) and is

a good conductor of heat and electricity. Gold is bright

yellow and has a high luster. Finely divided gold, like

other metallic powders, is black; colloidally suspended

gold ranges in color from ruby red to purple (see

Colloid).

Gold is extremely inactive. It is unaffected by air,

heat, moisture, and most solvents. It will, however,

dissolve in aqueous mixtures containing various halogens

such as chlorides, bromides, or some iodides. It will

also dissolve in some oxidizing mixtures, such as

cyanide ion with oxygen, and in aqua regia, a mixture of

hydrochloric and nitric acids. The chlorides and

cyanides are important compounds of gold. Gold melts at

about 1064. C (about 1947. F), boils at about 2808. C

(about 5086. F), and has a specific gravity of 19.3; its

atomic weight is 196.97.

Gold is found in nature in quartz veins and secondary

alluvial deposits as a free metal or in a combined

state. It is widely distributed although it is rare,

being 75th in order of abundance of the elements in the

crust of the earth. It is almost always associated with

varying amounts of silver; the naturally occurring

gold-silver alloy is called electrum. Gold occurs, in

chemical combination with tellurium, in the minerals

calaverite and sylvanite along with silver, and in the

mineral nagyagite along with lead, antimony, and sulfur.

It occurs with mercury as gold amalgam. It is generally

present to a small extent in iron pyrites; galena, the

lead sulfide ore that usually contains silver, sometimes

also contains appreciable amounts of gold. Gold also

occurs in seawater to the extent of 5 to 250 parts by

weight to 100 million parts of water. Although the

quantity of gold present in seawater is more than 9

billion metric tons, the cost of recovering the gold

would be far greater than the value of the gold that

could thus be recovered.

The metal has been known and highly valued from earliest

times, not only because of its beauty and resistance to

corrosion, but also because gold is easier to work than

all other metals. In addition, gold was easier to obtain

in pure form than the other metals. Because of its

relative rarity, gold became used as currency and as a

basis for international monetary transactions (see

Dollar; Gold Standard). The unit used in weighing gold

is the troy ounce; 1 troy ounce is equivalent to 31.1

grams.

The major portion of the gold produced is used in

coinage and jewelry (see Metalwork). For these purposes

it is alloyed with other metals to give it the necessary

hardness. The gold content in alloys is expressed in

carats (see Carat). Coinage gold is composed of 90 parts

gold to 10 parts silver. Green gold used in jewelry

contains copper and silver; white gold contains zinc and

nickel, or platinum metals.

Gold is also used in the form of gold leaf in the arts

of gilding and lettering. Purple of Cassius, a

precipitate of finely divided gold and stannic hydroxide

formed by the interaction of auric chloride and stannous

chloride, is used in coloring ruby glass. Chlorauric

acid is used in photography for toning silver images.

Potassium gold cyanide is used in electrogilding. Gold

is also used in dentistry. Radioisotopes of gold are

used in biological research and in the treatment of

cancer (see Isotopic Tracer).

The simplest process used for mining gold is panning,

using a circular dish often with a small pocket at the

bottom. The prospector fills the dish with gold-bearing

sand or gravel, holds it under a gentle stream of water,

and swirls it. The lighter parts of the gravel are

gradually washed off and the gold particles are left

near the center of the pan or in the pocket.

As gold mining developed, more elaborate methods were

introduced and hydraulic mining was invented. The

hydraulic method consists of directing a powerful stream

of water against the gold-bearing gravel or sand. This

operation breaks down the material and washes it away

through specially constructed sluices in which the gold

settles, while the lighter gravel is floated off. For

mining on rivers, elevator dredges are generally used.

The elevator dredge is a flat-b

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