Mercury, also called quicksilver, is the only common metal which is a liquid at room temperature. Heavy and silvery-white in appearance, mercury rarely occurs free in nature, and is found mainly in cinnabar ore from Spain and Italy. The metal is extracted by heating cinnabar in a current of air and condensing the vapor.
Mercury is a poor conductor of heat as compared with other metals, but it is a fair conductor of electricity. It is so heavy that objects such as bricks, cannonballs, and lumps of lead will float on its surface.
Mercury easily forms alloys with many metals, such as gold, silver, and tin and as such, has been used to make amalgams since 500 BC, and is also useful in recovering gold from its ores. In addition, the ancient Greeks used mercury in ointments and the Romans used it in cosmetics. The expression “mad as a hatter" is said to have referred to hatters who suffered brain damage as a result of the use of mercury in felt hat-making; mercury nitrate aided the removal of fur from animal skins.
Today, mercury is used for the manufacture of industrial chemicals and for electrical and electronic applications. It can be found in meteorological equipment like thermometers and barometers. Gaseous mercury is used in mercury-vapor lamps which light highways at night. Mercury batteries, dental amalgams, and even mirrors can make use of mercury.
But although mercury has such widespread use, it has long been known to be highly toxic in both liquid and gaseous forms, causing brain and/or liver damage if ingested, or with prolonged exposure. In its pure metal form, mercury is not deadly, but in compounds such as mercuric chloride, it is lethal. Many organic mercury compounds are also quite important — and quite dangerous.
Among the most lethal of these is methylmercury, a pollutant found in rivers and lakes and fish. Salts released into the environment are converted by anaerobic bacteria into such compounds. There are two types of mercury poisoning: acute and chronic. As explained on ExtoxNet:
Acute mercury poisoning results from the ingestion of soluble mercury salts, which violently corrode skin and mucous membranes. Although cases have occurred in which persons have ingested elemental mercury without suffering permanent damage, mercury vapor aspirated into the lungs can cause severe pneumonia and death.
The federal government limits the level of inorganic mercury in rivers, lakes, and streams, as well as bottled water; regulates the release of mercury metal into the environment; and protects workers by keeping the amount of inorganic mercury vapor in workroom air to safe levels.
Chronic mercury poisoning occurs through the regular absorption of small amounts of mercury. This condition is often a disease of workers in mercury mines, laboratories, and industries that use mercury.
In addition, there is pending legislation that address mercury use and emissions.