Mercury is a metallic element with the atomic number 80 and the symbol Hg, from the Latin hydragyrus, which means “liquid silver.” On the periodic table of elements, it is found in Group 12, just below Cadmium, and in Period 6 between gold and thallium. It is referred to as a “transition metal.” Mercury is a heavy element that is liquid at room temperature. Described as silvery-white in color, it is poisonous.

Mercury’s discoverer is unknown. All that is known is that it was already recognized in ancient times. The extraction process was first described by the Greek philosopher Aristotle (384–322 B.C.). Its name, for the Roman god Mercury,

reflects that time period.

Most mercury is obtained from cinnabar ore. The process by which mercury vapor is extracted from cinnabar ore is called roasting. It is then condensed in order to collect it in liquid form. Mercury is found mainly in Europe — in Spain, Italy, and the area that was formerly Yugoslavia. About 8,400 tons (7,620 metric tons) per year are produced.

Mercury has a number of uses. It is the customary liquid in thermometers as well as barometers and sphygmomanometers, and is used in esophageal dilators, batteries, paint, plastics, and pesticides. Mercury vapor is also used in lamps, and mercury is used in the gold mining industry.

Mercury is highly toxic. It is associated with birth defects in children and with neurological damage, kidney damage, and blindness upon later exposure.

Today, contaminated fish is one of the main sources of mercury exposure outside of industry. In times past, mercury was used in the manufacture of felt hats, and mercury poisoning was thus an occupational hazard of a hatter, leading to the phrase “mad as a hatter,” and to the character of the Mad Hatter in Alice’s Adventures in Wonderland and Through the Looking-Glass by Lewis Carroll, the pen name of Charles Lutwidge Dodgson.

Mercury does have some health uses, however. Inorganic salts of mercury are components of some products that stem the growth of bacteria and fungi. It is also used in hospital labs in urine analysis and in fixatives.