Gold has been prized since ancient times; in fact, the first coins containing gold were minted and used around 700 B.C. in Lydia, a kingdom in modern-day Turkey. From the time of Aristotle through the medieval era in Europe, alchemists sought to turn base materials into gold, and more recently, the discovery of gold deposits sparked a frenzy that led to the development of cities in Alaska and California. The metal, which bears the chemical symbol Au and has the atomic number 79, is a stable, nonreactive element that is an excellent conductor of electricity. Its atomic weight is 196.966569, and its boiling point is 2,836 degrees Celsius. The purity of gold is measured in karats, with 24-karat gold being the most pure. 24-karat gold is very expensive because of its purity, but it is also very soft; although it is often used in jewelry in Asia, most jewelry made in the West contains harder alloys such as 18-karat or 14-karat gold.
The mining of silver started around 3000 B.C. in modern-day Turkey, but while it was mined and used as a commodity and for jewelry for thousands of years, mining of this precious metal grew by leaps and bounds with the discovery of the New World and its resources. In more recent times, the discovery of Nevada's Comstock Lode made the United States a prominent player in the silver trade. Further discoveries of this metallic element and the expansion of mining in other countries coupled with the development of new mining technologies have led to further grown in the industry. Silver, which bears the symbol Ag on the periodic table and has the atomic number 47, is the lightest in weight of the precious metals. It has an atomic weight of 107.8682 and a boiling point of 2,162 degrees Celsius. It is also the most reactive precious metal; for example, the chemical reaction between silver and sulfur causes silver to tarnish. In addition, silver has anti-microbial properties and was used before antibiotics to prevent illness. However, one should take care not to ingest silver in significant quantities, as this can cause discoloration of the body tissues, a condition called argyria, as well as serious health problems such as kidney damage and seizures.
Platinum, which has the symbol Pt on the periodic table and the atomic number 78, was first discovered in South America in 1735, and it is the most valuable of the precious metals. It has an atomic weight of 195.084 and a boiling point of 3,825 degrees Celsius. This element is primarily used in jewelry, but it is also used in some scientific and engineering applications due to its failure to corrode in air and its high melting point. In fact, platinum is often used to coat and protect things such as the tips of missiles and fuel nozzles for jet engines. The chemistry of platinum also has some everyday, mundane uses: It is often found in catalytic converters used on automobiles, and its reaction with methyl alcohol has been used to create hand-warmers.
Palladium was discovered in 1803 by British chemist William Hyde Wollaston while he was studying a sample of platinum ore. This element, which has the symbol Pd on the periodic table, has the atomic number 46 and an atomic weight of 106.42. Its boiling point is 2,963 degrees Celsius. Like platinum, palladium can be used as a catalyst in chemical reactions. It can be found in catalytic converters, and it is also used in jewelry, surgical instruments, and spark plugs for airplanes. Palladium is also combined with gold to make white gold.