Mercury (IPA: /ˈmɜːkjəˌɹi/), also called quicksilver, is a chemical element in the periodic table that has the symbol Hg (Latinized Greek: hydrargyrum, meaning watery or liquid silver) and atomic number 80. A heavy, silvery transition metal, mercury is one of five elements that are liquid at or near standard room temperature (the others are the metals caesium, francium, and gallium, and the nonmetal bromine). Mercury is used in thermometers, barometers and other scientific apparatus, although the use of mercury in thermometers has been largely phased out in clinical and scientific environments (in favor of alcohol-filled, digital or thermistor-based replacements) due to concerns about the element's toxicity. Mercury is still used in dental amalgam. Mercury is mostly obtained by reduction from the mineral cinnabar. Mercury, like lead, is a neurotoxin, and elevated blood mercury levels have led to retardation and deformities in children.

Mercury is used primarily for the manufacture of industrial chemicals or for electrical and electronic applications. It is used in some thermometers, especially ones which are used to measure high temperatures (In the United States, non-prescription sale of mercury fever thermometers is banned by a number of different states and localities). Other uses:

Mercury sphygmomanometers. Mercury barometers, diffusion pumps, coulometers, and many other laboratory instruments. As an opaque liquid with a very high density, it is ideal for this role. The triple point of mercury, -38.8344 °C, is a fixed point used as a temperature standard for the International Temperature Scale (ITS-90). In some gaseous electron tubes, mercury arc rectifier Gaseous mercury is used in mercury-vapor lamps and some "neon sign" type advertising signs and fluorescent lamps. Liquid mercury was sometimes used as a coolant for nuclear reactors. However, sodium is proposed for reactors cooled with liquid metal, because the high density of mercury requires much energy for circulating the coolant. Mercury was once used in the amalgamation process of refining gold and silver ores. This polluting practice is still used by the garimpeiros (gold miners) of the Amazon basin in Brazil. Mercury is still used in some cultures for folk medicine and ceremonial purposes which may involve ingestion, injection, or the sprinkling of elemental mercury around the home. It must be emphasized that the former two procedures, especially, are extremely hazardous and the latter is nearly as so because mercury evaporates easily resulting in a toxic vapor. Alexander Calder built a mercury fountain for the Spanish Pavilion at the 1937 World's Fair in Paris. The fountain is now on display at the Fundació Miró in Barcelona. Used in electrochemistry as part of a secondary reference electrode called the calomel electrode as an alternative to the Standard Hydrogen Electrode. This is used to work out the electrode potential of half cells. Used in Cold Cathode (also generalised under the Neon Sign Industry) lighting to increase the success of ionization and conductivity in Argon filled lamps, an Argon filled lamp without Mercury will have dull spots and will fail to light correctly. Lighting with Mercury in can only be bombarded (see bombarding)/oven pumped once. When added to Neon filled tubes the light produced will be inconsistent red/blue spots until the initial burning-in process is completed; eventually it will light a consistent dull off-blue colour.

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