Mercury, or quicksilver, is one of the elements known to antiquity. It was used in cosmetics and medicines in various cultures, although we now know mercury is quite toxic.
As the only room-temperature liquid metal, mercury was important to the medieval alchemists. Mercury was considered to be the fundamental metallic principal that could be infused into other substances. As a crude example, if yellow sulfur could be made metallic, it might be turned into gold.
During the Age of Discovery, mercury was crucial to extracting silver and gold from ore. Mercury sources in Spain and later Peru supplied the mercury for processing Spanish silver mined in the New World. This is still a process in use, with precautions, although mercury has a variety of other chemical uses as well.
Mining and Production
Mercury comes primarily from heating the mineral cinnabar, which is mercury sulfide. Mercury is not very common in the Earth's crust, but it concentrates in ore deposits that are economical to mine. Also, simple heating is a very cheap refining process if the resulting mercury vapors can be handled safely.
The production of mercury has shifted from country to country over the decades and centuries. China is the biggest current producer. The 1,600 tons that China produced in 2014 may represent 75% of the world total, although not all production is reported. Mining and refining of mercury is nasty and dangerous because of the health risk.
Properties and Uses
Mercury is famous as a very dense silvery liquid that can be held in the hands and played with (not by itself a dangerous activity). It amalgamates with (dissolves) many solid metals, including gold and aluminum, but can be stored in iron flasks. A gold-mercury amalgam was for a long time the favorite choice for dental fillings.
Mercury is a good conductor of electricity (though poor conductor of heat). A drop of mercury closes the circuit in older light switches. Mercury expands considerably with heat, which is why mercury thermometers work well. The metal freezes near -40 Celsius, though, and so thermometers in very cold weather use alcohol instead.
Mercury-vapor street lights can be identified by their slightly bluish color (right).
Mercury has numerous uses in industrial chemistry. Many traditional consumer uses are being phased out, however, because mercury is such a toxic heavy metal.