Mercury: The Element

Mercury, a chemical element with the atomic number 80 is a transition metal. The most interesting fact about mercury is that though it is a heavy metal, it can exist in liquid form at room temperature and pressure. It is a rare element found in the crust of the Earth, naturally occurring as cinnabar or mercuric sulfide. Sometimes, it also occurs as livingstonite, corderoite and other minerals, but rarely is it found as a native metal. In chemistry, mercury is represented by the symbol Hg, which comes from the Latin word hydrargyrum, which in turn is said to be derived from the Greek word hydrargyros, which means water and silver. The name suits the metal, as it occurs as a liquid with a silvery shine.

No single scientist can be credited for discovering mercury, as it was familiar to many civilizations including those of China and India, since the ancient times. However, French chemist Antoine-Laurent de Lavoisier is accredited with distinguishing mercury as an element. Mercury has also been found in some Egyptian tombs which are almost 3500 years old. For people in China and Tibet, mercury was an element which was supposed to prolong life and heal fractures and was associated with good health. For the ancient Greeks, it was an essential ingredient in many ointments, while the ancient Egyptians and Romans used it in cosmetics. At one point, it also captivated the minds of the alchemists, who considered it as the First Matter, from which all other matters could be obtained, simply by varying the quality and the quantity of the sulfur content.

Mercury is known to have seven stable isotopes. It can easily dissolve, to form amalgams with many metals, including gold and zinc. However, it does not form amalgams with iron, due to which it can be stored in an iron flask. It is also not a very active element, in the sense that it does not react easily, and for this reason is considered to be a noble metal along with gold, silver and platinum. But, when heated, it reacts with oxygen to produce mercuric oxide.

Mercury and many of its compounds have been used traditionally for varied purposes. For example, mercury (I) chloride and mercury (II) sulfide were (and still are) used in medicines and as vermilion (a red pigment). Another traditional use of mercury in extracting gold and silver, has declined substantially nowadays. Mercury (II) chloride was also used in the past to treat syphilis.

Mercury has been used in thermometers, barometers, sphygmomanometers, manometers and many scientific instruments. However, because of its toxicity, some of these apparatuses are now being replaced with alcohol-filled or digital instruments. Mercury is also used as an amalgam in dentistry, while mercury fulminate is used as a detonator in explosives. Thiomersal is a mercury compound, which is used in manufacturing mascara and as a preservative in vaccines. Merbromin is another mercury compound, which is used as an antiseptic for topical use. Besides, mercury is also used in fluorescent lamps, mercury vapor lamps, gaseous electron tubes, batteries, liquid-mirror telescopes, etc.

Almost half of the atmospheric mercury is contributed by volcanoes when they erupt, while the rest is from human activities like coal power plants, gold production, production of non-ferrous metals, caustic soda production, disposal of wastes, mercury production mainly for use in batteries, pig iron and steel production, etc.

Mercury is a highly toxic metal, when inhaled or ingested into the body. Many compounds of mercury are also poisonous, out of which dimethyl mercury and methyl mercury are the most toxic of all. Methyl mercury, which is soluble in water, is assimilated in high concentrations by many fishes and shellfishes. If these fishes are consumed, it can increase the level of mercury in the body and eventually lead to mercury poisoning. This compound has the potential to cause permanent damage to the brain and kidneys. It has been found to be harmful for fetal development. Ingestion of mercury is also supposed to weaken the immune system. Therefore, considering all the health and environmental hazards associated with mercury and mercury compounds, their use has been brought under the control of various regulations in many countries, including the United States and the European Union countries.