Element of the Day-- Gold

chemistry 100

Much of this material is derived from Gold Council Web site, Smithsonian Web Site (figures, minerals) and the book Metal Techniques for Craftsmen by Opi Untracht

Chemical Elements--

• there are about 100 known chemical elements
• fundamental materials, all other species are combinations of elements
• of these, about 40 are rare and have few if any applications
• of the 100, about 75 are metals
  • some are very important: iron, nickel, copper, aluminum
  • all but 13 are solids at room temperature

Gold-- the element known in pure form for the longest time

• it appears as nuggets and flakes of pure metal
  • placer gold
  • shiny and easy recognize, attracts interest
  • high density, easily separated from other solids
  • doesn't corrode (stays shiny)
  • soft, can be hammered into other shapes
    • that's different from all other minerals of antiquity
    • simple stones are useful tools
    • can hammer small pieces into bigger pieces
  • now we are more likely to melt and cast metals
    • but gold technology much older than casting technology
• gold was important to ancient civilizations
  • gold was known to stone age cultures
  • few if any tools of gold (too soft)
    • even having gold technology didn't change tools and vessels used
    • had no real social impact except perhaps, the concept of wealth
    • mostly decoration-- lots of artifacts
      • Egypt-- 3000-4000 BC
      • Central and South America-- 1200 BC
      • Africa
      • China-- before 1000 BC
      • Europe-- Britain / Celtic Gold, easily 1500 BC-- emerges from underground burials (barrows) as shiny as the day it was made

• gold also became unit of currency
  • rare enough and prized
  • could be traded for goods
  • initially -- wires and bars, change = cut off a piece
    • the metal itself had the value
  • gradually-- coinage had face value and a guarantee

• won't oxidize in air, even if heated, buried, immersed in sea

• gold is very soft -- too soft
  • alloys with copper used for most purposes
  • 24 K = pure gold, 18K = 18 parts of gold, 6 parts of copper (usually)
    • filled gold (gold on outside surface; silver or copper inside)
    • electroplate (thin surface layer of gold)
• gold can be
  • melted and cast
  • drawn into wires
  • hammered into extremely thin foil (gold leaf)
    • one ounce of gold leaf would cover about an acre of land
  • gilding-- glue and gold foil, burnished
  • electroplated
  • evaporated and condensed to form very thin films
    • useful as heat reflectors, also cheap decorative

Generally few deposits concentrated enough to be economical

• those that are can be exploited by one person, simple equipment
• most miners don't succeed but some get wealthy overnight
• (not generally true for other metals

Gold probably was found on the ground and used by prehistoric man as a tool. Highly sophisticated gold art objects and jewelry discovered by archaeologists in the Royal Tombs at Ur, in what is now Southern Iraq, date back to around 3000 BC. Similarly, goldsmiths of the Chavin civilization in Peru were making ornaments by hammering and embossing gold by 1200 BC.

• 4000 BC Gold first known to be used in parts of Central and Eastern Europe.
• 3000 Egyptians master the art of beating gold into gold leaf and alloying it with other metals.
• 1500 The Shekel (two-thirds gold) used as a standard unit of measure throughout the Middle East.
• 1091 Squares of gold are legalized in China as a form of money.
• 58 Julius Caesar seizes enough gold in Gaul (France) to repay Rome's debts.
• 1100 AD Venice secures its position as the world's leading gold bullion market due to its location astride the trade routes to the east.
• 1511 King Ferdinand of Spain sends explorers to the Western Hemisphere with the command to "get gold."
• 1717 Isaac Newton, Master of the London Mint, sets price of gold that lasts for 200 years.
• 1787 First US gold coin is struck by Ephraim Brasher, a goldsmith.
• 1803 North Carolina site of first US gold rush. The state supplies all the domestic gold coined for currency by the US Mint in Philadelphia until 1828.
• 1848 California gold rush begins when James Marshall finds specks of gold in tailrace of John Sutter's sawmill near the junction of the American and Sacramento Rivers.
• 1850 Edward Hammong Hargraves, returning from California, predicts he will find gold in Australia within one week. He discovers gold in New South Wales within one week of landing.
• 1886 George Harrison, while digging stones to build a house, discovers gold in South Africa.
• 1887 Glasgow doctors, Robert and William Forrest, and chemist John S. MacArthur patent the process for extracting gold from ore using cyanide.
• 1896 Two prospectors discover gold while fishing in the Klondike River in northern Canada, richer finds were rumored farther south in Alaska's Yukon, spawning the Alaska Gold Rush in 1898 -- the last gold rush of the century.
• 1900 US adopts the gold standard for its currency.
• 1903 The Engelhard Corporation introduces an organic medium to print gold on surfaces. First used for decoration, the medium becomes the foundation for microcircuit printing technology.
• 1922 King Tutankhamen's tomb (1352 BC) opened to reveal a 2,448 lb. gold coffin and hundreds of gold and gold-leafed objects (including the mask pictured at the beginning of this section).

modern crisis areas -- Gold mining

• use of cyanide to extract gold (cyanide is very poisonous)
• use of mercury to extract gold (large toxic areas in California and Yukon)
• Brazil (renegade mining, cyanide use wide spread, violence)

• Mining: can extract as little as ___ grams/ton and make a profit
  • newer technologies can rework old mine tailings (discarded materials)

Gold uses

• decorative: mostly jewelry
• dentistry
• electronics (plating, electrical contacts)
• coinage
• rare to use other than as the element
  • (few gold compounds of importance)
  • (a couple gold compounds used medically)

Lessons--

• Properties influence applications
  • properties can be modified
  • alloy can change physical properties (hardness, for example)
• Chemically, gold is very boring
  • for a metal, that's often very valuable property (non coroding)
• Resources
  • rarity and desirability = costly
  • scramble to acquire = serious social impact

Some Web Links (mostly Gold)

world gold council

gold history

inca gold, photographs

gold-- barrows of ancient England

More ancient England, bronze age references

photo--king tut gold burial mask