Mercury
. Mercury (element) (Latin, hydrargyrum, “liquid silver”), symbol Hg, metallic element that is a free-flowing liquid at room temperature. Mercury is one of the transition elements of the periodic table (see Periodic Law ). The atomic number of mercury is 80. Mercury, once known as liquid silver and as quicksilver, was studied by the alchemists (see Alchemy ). It was first distinguished as an element by French chemist Antoine Laurent Lavoisier , who burned mercury and other substances in his experiments to determine the composition of air. PROPERTIES AND OCCURRENCE At ordinary temperatures mercury is a shining, mobile liquid, silvery-white in color. Slightly volatile at room temperature, mercury becomes solid when subjected to a pressure of 7,640 atmospheres (7.7 million millibars), and this pressure is used as a standard in measuring extremely high pressures. The metal dissolves in nitric or concentrated sulfuric acid but is resistant to alkalis. When cooled to sufficiently low tempera