Mercury (element)

I

Introduction

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. The atomic number of mercury is 80.

Mercury, once known as liquid silver and as quicksilver, was studied in alchemy. It was first distinguished as an element by the French chemist Antoine Laurent Lavoisier in his experiment on the composition of air.

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Properties and Occurrence

At ordinary temperatures mercury is a shining, mobile liquid, silvery-white in colour. Slightly volatile at room temperature, mercury becomes solid when subjected to a pressure of 7,640 atmospheres (5.8 million torrs), and this pressure is used as a standard in measuring extremely high pressures. The metal dissolves in nitric or concentrated sulphuric acid but is resistant to alkalis. Mercury melts at about -39° C (-38° F), boils at about 357° C (675° F), and has a relative density of 13.5. The atomic weight of mercury is 200.59.

Mercury ranks about 67th in natural abundance among the elements in crustal rocks. It occurs in its pure form or combined with silver in small amounts but is found most often in the form of the sulphide, the ore cinnabar. To obtain the metal from cinnabar, the ore is roasted with air, and the gases produced are passed through a condensing system.

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Uses

Mercury is used in thermometers because its coefficient of expansion is nearly constant; the change in volume for each degree of rise or fall in temperature is the same. It is also used in other types of scientific apparatus, such as vacuum pumps, barometers, and electric rectifiers and switches. Mercury-vapour lamps are used as a source of ultraviolet rays in homes and for sterilizing water. Mercury vapour is used instead of steam in the boilers of some turbine engines. Mercury combines with all the common metals, except iron and platinum, to form alloys that are called amalgams. In one method of extracting gold and silver from their ores, the metals are combined with mercury; the mercury is then removed by distillation.

Mercury forms monovalent and divalent compounds. Among the commercially important compounds of mercury are mercury(II) sulphide, a common antiseptic also used as the pigment vermilion; mercury(I) chloride, or calomel, used for electrodes, and formerly used as a cathartic; mercury(II) chloride, or corrosive sublimate; and medicinals such as Mercurochrome.

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Mercury Poisoning

Mercury is acutely hazardous as a vapour and in the form of its water-soluble salts, which corrode membranes of the body. Chronic mercury poisoning, which occurs when small amounts of the metal or its fat-soluble salts, particularly methylmercury, are repeatedly ingested over long periods of time, causes irreversible brain, liver, and kidney damage. Because of increasing water pollution, significant quantities of mercury have been found in some species of fish, which has aroused concern regarding uncontrolled discharge of the metal into the environment. See Occupational and Environmental Diseases.