Mercury

Mercury is the only metal that is liquid at common temperatures and has an almost linear coefficient of expansion.   Therefore, it is widely used in thermometers, barometers, diffusion pumps, and other measuring instruments, although replacements are being made to restrict its use because of its high toxicity.   Mercury is used to make mercury-vapor lamps, which emit ultraviolet radiation.   Mercury is used as an electrode in the production of chlorine and sodium hydroxide, NaOH.   It is used in advertising signs, mercury switches, pesticides, and dental preparations (an amalgam of mercury, silver and tin), antifouling paint, batteries, and catalysts.   Important mercury chemical salts are mercuric chloride, HgCl₂, an extremely toxic poison used to kill rats and insects, mercurous chloride, Hg₂Cl₂, (calomel, an antiseptic), mercury fulminate, Hg(ONC)₂, an explosive detonator, and mercuric sulfide, HgS (vermillion, a high-grade paint pigment).   Methyl mercury is a dangerous pollutant found in lakes and rivers.   Mercury ingested by sea animals poisons humans when eaten. ^{Lide 4-18}

Mercury was known by the ancients.   Its amalgam with gold was and is used to extract gold from its ores.   The main mercury ore is cinnabar, MgS, mined mainly in Spain and Italy.   The metal is obtained by heating cinnabar in a current of air and then condensing the vapor. ^{Lide 4-18}