Mercury (element)

Mercury (element)

Overview
Mercury is a chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

 with the symbol Hg and atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

 80. It is also known as quicksilver or hydrargyrum (from "hydr-" water and "argyros" silver). A heavy, silvery d-block
D-block
The d-block is the portion of the periodic table that contains the element groups 3-12. These groups correspond to the filling of the atomic d-orbital subshell, with electron configurations ranging from s2d1 to s2d10...

 element, mercury is the only metal that is liquid at standard conditions for temperature and pressure
Standard conditions for temperature and pressure
Standard condition for temperature and pressure are standard sets of conditions for experimental measurements established to allow comparisons to be made between different sets of data...

; the only other element that is liquid under these conditions is bromine
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...

, and metals such as caesium
Caesium
Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C , which makes it one of only five elemental metals that are liquid at room temperature...

, francium
Francium
Francium is a chemical element with symbol Fr and atomic number 87. It was formerly known as eka-caesium and actinium K.Actually the least unstable isotope, francium-223 It has the lowest electronegativity of all known elements, and is the second rarest naturally occurring element...

, gallium
Gallium
Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...

, and rubidium
Rubidium
Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group. Its atomic mass is 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other elements in group 1, such as very rapid...

 melt just above room temperature. With a freezing point
Freezing Point
Freezing Point is a news journal in the People's Republic of China which has been the subject of controversy over its criticism of Communist Party officials and the sympathetic ear it lent to a Chinese historian who had criticized official history textbooks...

 of −38.83 °C and boiling point
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

 of 356.73 °C, mercury has one of the narrowest ranges of its liquid state of any metal.

Mercury occurs in deposits throughout the world mostly as cinnabar
Cinnabar
Cinnabar or cinnabarite , is the common ore of mercury.-Word origin:The name comes from κινναβαρι , a Greek word most likely applied by Theophrastus to several distinct substances...

 (mercuric sulfide).
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Encyclopedia
Mercury is a chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

 with the symbol Hg and atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

 80. It is also known as quicksilver or hydrargyrum (from "hydr-" water and "argyros" silver). A heavy, silvery d-block
D-block
The d-block is the portion of the periodic table that contains the element groups 3-12. These groups correspond to the filling of the atomic d-orbital subshell, with electron configurations ranging from s2d1 to s2d10...

 element, mercury is the only metal that is liquid at standard conditions for temperature and pressure
Standard conditions for temperature and pressure
Standard condition for temperature and pressure are standard sets of conditions for experimental measurements established to allow comparisons to be made between different sets of data...

; the only other element that is liquid under these conditions is bromine
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...

, and metals such as caesium
Caesium
Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C , which makes it one of only five elemental metals that are liquid at room temperature...

, francium
Francium
Francium is a chemical element with symbol Fr and atomic number 87. It was formerly known as eka-caesium and actinium K.Actually the least unstable isotope, francium-223 It has the lowest electronegativity of all known elements, and is the second rarest naturally occurring element...

, gallium
Gallium
Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...

, and rubidium
Rubidium
Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group. Its atomic mass is 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other elements in group 1, such as very rapid...

 melt just above room temperature. With a freezing point
Freezing Point
Freezing Point is a news journal in the People's Republic of China which has been the subject of controversy over its criticism of Communist Party officials and the sympathetic ear it lent to a Chinese historian who had criticized official history textbooks...

 of −38.83 °C and boiling point
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

 of 356.73 °C, mercury has one of the narrowest ranges of its liquid state of any metal.

Mercury occurs in deposits throughout the world mostly as cinnabar
Cinnabar
Cinnabar or cinnabarite , is the common ore of mercury.-Word origin:The name comes from κινναβαρι , a Greek word most likely applied by Theophrastus to several distinct substances...

 (mercuric sulfide). The red pigment vermilion
Vermilion
Vermilion is an opaque orangish red pigment, similar to scarlet. As a naturally occurring mineral pigment, it is known as cinnabar, and was in use around the world before the Common Era began. Most naturally produced vermilion comes from cinnabar mined in China, and vermilion is nowadays commonly...

 is mostly obtained by reduction from cinnabar. Cinnabar is highly toxic by ingestion or inhalation of the dust. Mercury poisoning
Mercury poisoning
Mercury poisoning is a disease caused by exposure to mercury or its compounds. Mercury is a heavy metal occurring in several forms, all of which can produce toxic effects in high enough doses...

 can also result from exposure to water-soluble forms of mercury (such as mercuric chloride or methylmercury
Methylmercury
Methylmercury is an organometallic cation with the formula . It is a bioaccumulative environmental toxicant.-Structure:...

), inhalation of mercury vapor, or eating seafood contaminated with mercury.

Mercury is used in thermometer
Thermometer
Developed during the 16th and 17th centuries, a thermometer is a device that measures temperature or temperature gradient using a variety of different principles. A thermometer has two important elements: the temperature sensor Developed during the 16th and 17th centuries, a thermometer (from the...

s, barometer
Barometer
A barometer is a scientific instrument used in meteorology to measure atmospheric pressure. Pressure tendency can forecast short term changes in the weather...

s, manometers, sphygmomanometer
Sphygmomanometer
A sphygmomanometer or blood pressure meter is a device used to measure blood pressure, comprising an inflatable cuff to restrict blood flow, and a mercury or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just...

s, float valves, some electrical switches, and other scientific apparatus, though concerns about the element's toxicity have led to mercury thermometers and sphygmomanometers being largely phased out in clinical environments in favor of alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

-filled, galinstan
Galinstan
Galinstan is a family of eutectic alloys mainly consisting of gallium, indium, and tin, which are liquids at room temperature, typically freezing at . Due to the low toxicity and low reactivity of its component metals, it finds use as a replacement for many applications that previously employed...

-filled, digital, or thermistor
Thermistor
A thermistor is a type of resistor whose resistance varies significantly with temperature, more so than in standard resistors. The word is a portmanteau of thermal and resistor...

-based instruments. It remains in use in scientific research applications and in amalgam
Amalgam (dentistry)
Amalgam is an alloy containing mercury. The term is commonly used for the amalgam employed as material for dental fillings, which consists of mercury , silver , tin , copper , and other trace metals...

 material for dental restoration
Dental restoration
A dental restoration or dental filling is a dental restorative material used to restore the function, integrity and morphology of missing tooth structure. The structural loss typically results from caries or external trauma. It is also lost intentionally during tooth preparation to improve the...

. It is used in lighting: electricity passed through mercury vapor in a phosphor tube produces short-wave ultraviolet light which then causes the phosphor to fluoresce, making visible light.

Physical properties



Mercury is a heavy, silvery-white metal. As compared to other metals, it is a poor conductor of heat, but a fair conductor of electricity. Mercury has an exceptionally low melting temperature for a d-block metal. A complete explanation of this fact requires a deep excursion into quantum physics, but it can be summarized as follows: mercury has a unique electronic configuration where electrons fill up all the available 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, 5s, 5p, 5d and 6s subshells. As such configuration strongly resists removal of an electron, mercury behaves similarly to noble gas
Noble gas
The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity...

 elements, which form weak bonds and thus easily melting solids. The stability of the 6s shell is due to the presence of a filled 4f shell. An f shell poorly screens the nuclear charge that increases the attractive Coulomb interaction
Coulomb's law
Coulomb's law or Coulomb's inverse-square law, is a law of physics describing the electrostatic interaction between electrically charged particles. It was first published in 1785 by French physicist Charles Augustin de Coulomb and was essential to the development of the theory of electromagnetism...

 of the 6s shell and the nucleus (see lanthanide contraction
Lanthanide contraction
Lanthanide contraction is a term used in chemistry to describe the decrease in ionic radii of the elements in the lanthanide series from atomic number 58, Cerium to 71, Lutetium, which results in smaller than otherwise expected ionic radii for the subsequent elements starting with 72, Hafnium...

). The absence of a filled inner f shell is the reason for the somewhat higher melting temperature of cadmium
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...

 and zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

, although both these metals still melt easily and, in addition, have unusually low boiling points. Metals such as gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...

 have atoms with one less 6s electron than mercury. Those electrons are more easily removed and are shared between the gold atoms forming relatively strong metallic bonds.
At its freezing point (−38.86 °C), the density of mercury is 13.534 g/cm3.

Chemical properties


Mercury does not react with most acids, such as dilute sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

, although oxidizing acid
Oxidizing acid
An oxidizing acid is a Brønsted acid that is also a strong oxidizing agent . All Brønsted acids can act as moderately strong oxidizing agents, because the acidic proton can be reduced to hydrogen gas. Some acids contain other structures that act as stronger oxidizing agents than hydrogen....

s such as concentrated sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

 and nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...

 or aqua regia
Aqua regia
Aqua regia or aqua regis is a highly corrosive mixture of acids, fuming yellow or red solution, also called nitro-hydrochloric acid. The mixture is formed by freshly mixing concentrated nitric acid and hydrochloric acid, usually in a volume ratio of 1:3, respectively...

 dissolve it to give sulfate
Mercury sulfate
Mercury sulfate may refer to:*Mercurous sulfate , Hg2SO4*Mercuric sulfate , HgSO4...

, nitrate
Mercury nitrate
Mercury nitrate can refer to:*Mercury nitrate, Hg22*Mercury nitrate, Hg2...

, and chloride
Mercury chloride
Mercury chloride can refer to:*Mercury chloride or mercuric chloride *Mercury chloride or mercurous chloride...

salts. Like silver, mercury reacts with atmospheric hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

. Mercury even reacts with solid sulfur flakes, which are used in mercury spill kits to absorb mercury vapors (spill kits also use activated carbon
Activated carbon
Activated carbon, also called activated charcoal, activated coal or carbo activatus, is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions.The word activated in the name is sometimes replaced...

 and powdered zinc).

Amalgams



Mercury dissolves to form amalgams
Amalgam (chemistry)
An amalgam is a substance formed by the reaction of mercury with another metal. Almost all metals can form amalgams with mercury, notable exceptions being iron and platinum. Silver-mercury amalgams are important in dentistry, and gold-mercury amalgam is used in the extraction of gold from ore.The...

 with gold, zinc and many other metals. Because iron is an exception, iron flasks have been traditionally used to trade mercury. Other metals that do not form amalgams with mercury include tantalum, tungsten and platinum. Sodium amalgam
Sodium amalgam
Sodium amalgam, commonly denoted Na, is an alloy of mercury and sodium. The term amalgam is used for alloys, intermetallic compounds, and solutions involving mercury as a major component. Sodium amalgam is often used in reactions as strong reducing agents with better handling properties compared...

 is a common reducing agent in organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

.

Mercury readily combines with aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 to form a mercury-aluminium amalgam when the two pure metals come into contact. Since the amalgam reacts with air to give aluminium oxide, small amounts of mercury corrode aluminium. For this reason, mercury is not allowed aboard an aircraft under most circumstances because of the risk of it forming an amalgam with exposed aluminium parts in the aircraft.

Isotopes



There are seven stable isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

s of mercury with being the most abundant (29.86%). The longest-lived radioisotopes are with a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...

 of 444 years, and with a half-life of 46.612 days. Most of the remaining radioisotopes have half-lives that are less than a day. and are the most often studied NMR
Nuclear magnetic resonance
Nuclear magnetic resonance is a physical phenomenon in which magnetic nuclei in a magnetic field absorb and re-emit electromagnetic radiation...

-active nuclei, having spins of and respectively.

History



Mercury was found in Egyptian
Ancient Egypt
Ancient Egypt was an ancient civilization of Northeastern Africa, concentrated along the lower reaches of the Nile River in what is now the modern country of Egypt. Egyptian civilization coalesced around 3150 BC with the political unification of Upper and Lower Egypt under the first pharaoh...

 tombs that date from 1500 BC.

In China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 and Tibet
Tibet
Tibet is a plateau region in Asia, north-east of the Himalayas. It is the traditional homeland of the Tibetan people as well as some other ethnic groups such as Monpas, Qiang, and Lhobas, and is now also inhabited by considerable numbers of Han and Hui people...

, mercury use was thought to prolong life, heal fractures, and maintain generally good health, although it is now known that exposure to mercury leads to serious adverse health effects. One of China's emperors, Qín Shǐ Huáng Dì
Qin Shi Huang
Qin Shi Huang , personal name Ying Zheng , was king of the Chinese State of Qin from 246 BC to 221 BC during the Warring States Period. He became the first emperor of a unified China in 221 BC...

 — allegedly buried in a tomb that contained rivers of flowing mercury on a model of the land he ruled, representative of the rivers of China — was killed by drinking a mercury and powdered jade
Jade
Jade is an ornamental stone.The term jade is applied to two different metamorphic rocks that are made up of different silicate minerals:...

 mixture formulated by Qin
Qin Dynasty
The Qin Dynasty was the first imperial dynasty of China, lasting from 221 to 207 BC. The Qin state derived its name from its heartland of Qin, in modern-day Shaanxi. The strength of the Qin state was greatly increased by the legalist reforms of Shang Yang in the 4th century BC, during the Warring...

 alchemists (causing liver failure
Liver failure
Acute liver failure is the appearance of severe complications rapidly after the first signs of liver disease , and indicates that the liver has sustained severe damage . The complications are hepatic encephalopathy and impaired protein synthesis...

, mercury poisoning
Mercury poisoning
Mercury poisoning is a disease caused by exposure to mercury or its compounds. Mercury is a heavy metal occurring in several forms, all of which can produce toxic effects in high enough doses...

, and brain death
Brain death
Brain death is the irreversible end of all brain activity due to total necrosis of the cerebral neurons following loss of brain oxygenation. It should not be confused with a persistent vegetative state...

) who intended to give him eternal life.

The ancient Greeks
Ancient Greece
Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...

 used mercury in ointments; the ancient Egyptians and the Romans
Roman Empire
The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

 used it in cosmetics
Cosmetics
Cosmetics are substances used to enhance the appearance or odor of the human body. Cosmetics include skin-care creams, lotions, powders, perfumes, lipsticks, fingernail and toe nail polish, eye and facial makeup, towelettes, permanent waves, colored contact lenses, hair colors, hair sprays and...

 which sometimes deformed the face. In Lamanai
Lamanai
Lamanai is a Mesoamerican archaeological site, and was once a considerably sized city of the Maya civilization, located in the north of Belize, in Orange Walk District...

, once a major city of the Maya civilization
Maya civilization
The Maya is a Mesoamerican civilization, noted for the only known fully developed written language of the pre-Columbian Americas, as well as for its art, architecture, and mathematical and astronomical systems. Initially established during the Pre-Classic period The Maya is a Mesoamerican...

, a pool of mercury was found under a marker in a Mesoamerican ballcourt
Mesoamerican ballcourt
A Mesoamerican ballcourt is a large masonry structure of a type used in Mesoamerica for over 2,700 years to play the Mesoamerican ballgame, particularly the hip-ball version of the ballgame. Over 1,300 ballcourts have been identified, 60% in the last 20 years alone...

. By 500 BC mercury was used to make amalgams
Amalgam (chemistry)
An amalgam is a substance formed by the reaction of mercury with another metal. Almost all metals can form amalgams with mercury, notable exceptions being iron and platinum. Silver-mercury amalgams are important in dentistry, and gold-mercury amalgam is used in the extraction of gold from ore.The...

 (Medieval Latin amalgama, "alloy of mercury") with other metals.

Alchemists
Alchemy
Alchemy is an influential philosophical tradition whose early practitioners’ claims to profound powers were known from antiquity. The defining objectives of alchemy are varied; these include the creation of the fabled philosopher's stone possessing powers including the capability of turning base...

 thought of mercury as the First Matter from which all metals were formed. They believed that different metals could be produced by varying the quality and quantity of sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

 contained within the mercury. The purest of these was gold, and mercury was called for in attempts at the transmutation of base (or impure) metals into gold, which was the goal of many alchemists.

Hg is the modern chemical symbol
Chemical symbol
A chemical symbol is a 1- or 2-letter internationally agreed code for a chemical element, usually derived from the name of the element, often in Latin. Only the first letter is capitalised...

 for mercury. It comes from hydrargyrum, a Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

ized form of the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 word Ύδραργυρος (hydrargyros), which is a compound word meaning "water-silver" (hydr- = water, argyros = silver) — since it is liquid like water and shiny like silver. The element was named after the Roman god Mercury
Mercury (mythology)
Mercury was a messenger who wore winged sandals, and a god of trade, the son of Maia Maiestas and Jupiter in Roman mythology. His name is related to the Latin word merx , mercari , and merces...

, known for speed and mobility. It is associated with the planet Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...

; the astrological symbol for the planet is also one of the alchemical symbol
Alchemical symbol
Alchemical symbols, originally devised as part of alchemy, were used to denote some elements and some compounds until the 18th century. Note that while notation like this was mostly standardized, style and symbol varied between alchemists, so this page lists the most common.-Three primes:According...

s for the metal; the Indian word for alchemy is Rasavātam which means "the way of mercury". Mercury is the only metal for which the alchemical planetary name became the common name.

The mines in Almadén
Almadén
Almadén, Spain, is a town and municipality in the province of Ciudad Real, within the autonomous community of Castile-La Mancha. The town is located at 4° 49' W and 38° 46' N and is 589 meters above sea level. Almadén is approximately 200 km south of Madrid in the Sierra Morena...

 (Spain), Monte Amiata
Monte Amiata
Mount Amiata is the largest of the lava domes in the Amiata lava dome complex located about 20 km NW of Lake Bolsena in the southern Tuscany region of Italy.-Geology:...

 (Italy), and Idrija
Idrija
Idrija is a small town and municipality in the Goriška region of Slovenia. It is known for its mercury mine and lace....

 (now Slovenia) dominated the mercury production from the opening of the mine in Almadén 2500 years ago until new deposits were found at the end of the 19th century.

Occurrence



Mercury is an extremely rare element in the Earth's crust
Crust (geology)
In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...

, having an average crustal abundance by mass of only 0.08 parts per million (ppm). However, because it does not blend geochemically
Geochemistry
The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks, water, and soils, and the cycles of matter and energy that transport the Earth's chemical components in time and space, and...

 with those elements that constitute the majority of the crustal mass, mercury ores can be extraordinarily concentrated considering the element's abundance in ordinary rock. The richest mercury ores contain up to 2.5% mercury by mass, and even the leanest concentrated deposits are at least 0.1% mercury (12,000 times average crustal abundance). It is found either as a native metal (rare) or in cinnabar
Cinnabar
Cinnabar or cinnabarite , is the common ore of mercury.-Word origin:The name comes from κινναβαρι , a Greek word most likely applied by Theophrastus to several distinct substances...

, corderoite
Corderoite
Corderoite is an extremely rare mercury sulfide chloride mineral with formula Hg3S2Cl2. It crystallizes in the isometric crystal system. It is soft, 1.5 to 2 on the Mohs scale, and varies in color from light gray to black and rarely pink or yellow....

, livingstonite
Livingstonite
Livingstonite is a mercury antimony sulfosalt mineral. It occurs in low-temperature hydrothermal veins associated with cinnabar, stibnite, sulfur and gypsum....

 and other mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

s, with cinnabar (HgS) being the most common ore. Mercury ores usually occur in very young orogenic belts where rock of high density are forced to the crust of the Earth, often in hot springs or other volcanic
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 regions.

Beginning in 1558, with the invention of the patio process
Patio process
The patio process was a process used to extract silver from ore. The process was invented by Bartolomé de Medina in Pachuca, New Spain , in 1554. The patio process was the first process to use mercury amalgamation to recover silver from ore. It replaced smelting as the primary method of extracting...

 to extract silver from ore using mercury, mercury became an essential resource in the economy of Spain and its American colonies. Mercury was used to extract silver from the lucrative mines in New Spain
New Spain
New Spain, formally called the Viceroyalty of New Spain , was a viceroyalty of the Spanish colonial empire, comprising primarily territories in what was known then as 'América Septentrional' or North America. Its capital was Mexico City, formerly Tenochtitlan, capital of the Aztec Empire...

 and Peru
Peru
Peru , officially the Republic of Peru , is a country in western South America. It is bordered on the north by Ecuador and Colombia, on the east by Brazil, on the southeast by Bolivia, on the south by Chile, and on the west by the Pacific Ocean....

. Initially, the Spanish Crown's mines in Almaden in Southern Spain supplied all the mercury for the colonies. Mercury deposits were discovered in the New World, and more than 100,000 tons of mercury were mined from the region of Huancavelica
Huancavelica
Huancavelica is a city in Peru. It is the capital of the Huancavelica region and has a population of approximately 40,000. Indigenous peoples represent a major percentage of the population. It has an approximate altitude of 3,600 meters; the climate is cold and dry between the months of February...

, Peru, over the course of three centuries following the discovery of deposits there in 1563. The patio process and later pan amalgamation
Pan amalgamation
The Pan amalgamation process is a method to extract silver from ore, using mercury. The process was widely used from 1609 through the 19th century; it is no longer used....

 process continued to create great demand for mercury to treat silver ores until the late 19th century.
Former mines in Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

, the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 and Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

 which once produced a large proportion of the world supply have now been completely mined out or, in the case of Slovenia
Slovenia
Slovenia , officially the Republic of Slovenia , is a country in Central and Southeastern Europe touching the Alps and bordering the Mediterranean. Slovenia borders Italy to the west, Croatia to the south and east, Hungary to the northeast, and Austria to the north, and also has a small portion of...

 (Idrija
Idrija
Idrija is a small town and municipality in the Goriška region of Slovenia. It is known for its mercury mine and lace....

) and Spain (Almadén
Almadén
Almadén, Spain, is a town and municipality in the province of Ciudad Real, within the autonomous community of Castile-La Mancha. The town is located at 4° 49' W and 38° 46' N and is 589 meters above sea level. Almadén is approximately 200 km south of Madrid in the Sierra Morena...

), shut down due to the fall of the price of mercury. Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...

's McDermitt Mine, the last mercury mine in the United States, closed in 1992. The price of mercury has been highly volatile over the years and in 2006 was $650 per 76-pound (34.46 kg) flask.

Mercury is extracted by heating cinnabar in a current of air and condensing the vapor. The equation for this extraction is
HgS + O2 → Hg + SO2


In 2005, China was the top producer of mercury with almost two-thirds global share followed by Kyrgyzstan
Kyrgyzstan
Kyrgyzstan , officially the Kyrgyz Republic is one of the world's six independent Turkic states . Located in Central Asia, landlocked and mountainous, Kyrgyzstan is bordered by Kazakhstan to the north, Uzbekistan to the west, Tajikistan to the southwest and China to the east...

. Several other countries are believed to have unrecorded production of mercury from copper electrowinning
Electrowinning
Electrowinning, also called electroextraction, is the electrodeposition of metals from their ores that have been put in solution or liquefied. Electrorefining uses a similar process to remove impurities from a metal. Both processes use electroplating on a large scale and are important techniques...

 processes and by recovery from effluents.

Because of the high toxicity of mercury, both the mining of cinnabar and refining for mercury are hazardous and historic causes of mercury poisoning. In China, prison labor was used by a private mining company as recently as the 1950s to create new cinnabar mercury mines. Thousands of prisoners were used by the Luo Xi mining company to establish new tunnels. In addition, worker health in functioning mines is at high risk.

The European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

 directive calling for compact fluorescent bulbs to be made mandatory by 2012 has encouraged China to re-open deadly cinnabar mines to obtain the mercury required for CFL bulb manufacture. As a result, environmental dangers have been a concern, particularly in the southern cities of Foshan
Foshan
Foshan is a city in central Guangdong province in southern China. The prefectural area under the city's jurisdiction over an area of about 3,840 km² and a population of 5.4 million of which 1.1 million reside in the city proper ....

 and Guangzhou
Guangzhou
Guangzhou , known historically as Canton or Kwangchow, is the capital and largest city of the Guangdong province in the People's Republic of China. Located in southern China on the Pearl River, about north-northwest of Hong Kong, Guangzhou is a key national transportation hub and trading port...

, and in the Guizhou
Guizhou
' is a province of the People's Republic of China located in the southwestern part of the country. Its provincial capital city is Guiyang.- History :...

 province in the south west.

Abandoned mercury mine processing sites often contain very hazardous waste piles of roasted cinnabar calcines. Water run-off from such sites is a recognized source of ecological damage. Former mercury mines may be suited for constructive re-use. For example, in 1976 Santa Clara County, California
Santa Clara County, California
Santa Clara County is a county located at the southern end of the San Francisco Bay Area in the U.S. state of California. As of 2010 it had a population of 1,781,642. The county seat is San Jose. The highly urbanized Santa Clara Valley within Santa Clara County is also known as Silicon Valley...

 purchased the historic Almaden Quicksilver Mine
Almaden Quicksilver County Park
Almaden Quicksilver County Park is a 4,147 acres park that includes the grounds of former mercury mines adjacent to south San Jose, California, USA...

 and created a county park on the site, after conducting extensive safety and environmental analysis of the property.

Chemistry



Mercury exists in two main oxidation states, I and II. Higher oxidation states are unimportant, but have been detected, e.g., mercury(IV) fluoride
Mercury(IV) fluoride
Mercury fluoride, HgF4, is the first mercury compound to be discovered with the metal in the oxidation state IV. Mercury, like the other group 12 elements , has an s2d10 electron configuration and generally only forms bonds involving its s orbital...

  but only under extraordinary conditions.

Compounds of mercury(I)


Different from its lighter neighbors, cadmium and zinc, mercury forms simple stable compounds with metal-metal bonds. The mercury(I) compounds are diamagnetic and feature the dimeric cation, Hg. Stable derivatives include the chloride and nitrate. Treatment of Hg(I) compounds complexation with strong ligands such as sulfide, cyanide, etc. induces disproportionation to and elemental mercury. Mercury(I) chloride
Mercury(I) chloride
Mercury chloride is the chemical compound with the formula Hg2Cl2. Also known as calomel or mercurous chloride, this dense white or yellowish-white, odorless solid is the principal example of a mercury compound...

, a colorless solid also known as calomel, is really the compound with the formula Hg2Cl2, with the connectivity Cl-Hg-Hg-Cl. It is a standard in electrochemistry. It reacts with chlorine to give mercuric chloride, which resists further oxidation.

Indicative of its tendency to bond to itself, mercury forms mercury polycations
Mercury polycations
Mercury polycations are polyatomic cations that contain only mercury atoms. The best known example is the ion, found in mercury compounds...

, which consist of linear chains of mercury centers, capped with a positive charge. One example is Hg32+(AsF6)2.

Compounds of mercury(II)


Mercury(II) is the most common oxidation state and is the main one in nature as well. All four mercuric halides are known. The form tetrahedral complexes with other ligands but the halides adopt linear coordination geometry, somewhat like Ag+ does. Best known is mercury(II) chloride
Mercury(II) chloride
Mercury chloride or mercuric chloride , is the chemical compound with the formula HgCl2. This white crystalline solid is a laboratory reagent and a molecular compound. It is no longer used for medicinal purposes Mercury(II) chloride or mercuric chloride (formerly corrosive sublimate), is the...

, an easily sublimating white solid. HgCl2 forms coordination complexes that are typically tetrahedral, e.g. HgCl42–.

Mercury(II) oxide
Mercury(II) oxide
Mercury oxide, also called mercuric oxide or simply mercury oxide, has a formula of HgO. It has a red or orange color. Mercury oxide is a solid at room temperature and pressure...

, the main oxide
Oxide
An oxide is a chemical compound that contains at least one oxygen atom in its chemical formula. Metal oxides typically contain an anion of oxygen in the oxidation state of −2....

 of mercury, arises when the metal is exposed to air for long periods at elevated temperatures. It reverts to the elements upon heating near 400 °C, as was demonstrated by Priestly in an early synthesis of pure oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

. Hydroxides of mercury are poorly characterized, as they are for its neighbors gold and silver.

Being a soft metal, mercury forms very stable derivatives with the heavier chalcogens. Preeminent is mercury(II) sulfide, HgS, which occurs in nature as the ore cinnabar and is the brilliant pigment vermillion
Vermilion
Vermilion is an opaque orangish red pigment, similar to scarlet. As a naturally occurring mineral pigment, it is known as cinnabar, and was in use around the world before the Common Era began. Most naturally produced vermilion comes from cinnabar mined in China, and vermilion is nowadays commonly...

. Like ZnS, HgS crystallizes in two forms
Polymorphism (materials science)
Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...

, the reddish cubic form and the black zinc blende form. Mercury(II) selenide
Mercury(II) selenide
Mercury selenide is a chemical compound of mercury and selenium. It is a grey-black crystalline solid semi-metal with a sphalerite structure. The lattice constant is 0.608 nm....

 (HgSe) and mercury(II) telluride
Mercury(II) telluride
Mercury telluride is a binary chemical compound of mercury and tellurium. It is a semi-metal related to the II-VI group of semiconductor materials. Alternative names are mercuric telluride and mercury telluride....

 (HgTe) are also known, these as well as various derivatives, e.g. mercury cadmium telluride and mercury zinc telluride
Mercury zinc telluride
Mercury zinc telluride is a telluride of mercury and zinc, an alloy of mercury telluride and zinc telluride. It is a narrow-gap semiconductor material....

 being semiconductors useful as infrared detector
Infrared detector
An infrared detector is a photodetector that reacts to infrared radiation. The two main types of detectors are thermal and photonic.The thermal effects of the incident IR radiation can be followed through many temperature dependent phenomena....

 materials.

Mercury(II) salts form a variety of complex derivatives with ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

. These include Millon's base (Hg2N+), the one-dimensional polymer (salts of HgNH2+)n), and "fusible white precipitate" or [Hg(NH3)2]Cl2. Known as Nessler's reagent
Nessler's reagent
Potassium tetraiodomercurate is an inorganic compound containing potassium cations and the tetraiodomercurate complex anion. It is mainly used as Neßler's reagent, a 0.09 mol/L solution of potassium tetraiodomercurate in 2.5 mol/L potassium hydroxide, used to detect ammonia.-Nessler's...

, potassium tetraiodomercurate(II) (HgI42–) is still occasionally used to test for ammonia owing to its tendency to form the deeply colored iodide salt of Millon's base.

Mercury fulminate
Mercury(II) fulminate
Mercury fulminate, or Hg2, is a primary explosive. It is highly sensitive to friction and shock. It is mainly used as a trigger for other explosives in percussion caps and blasting caps...

, (a detonator
Detonator
A detonator is a device used to trigger an explosive device. Detonators can be chemically, mechanically, or electrically initiated, the latter two being the most common....

 widely used in explosives);

Organomercury compounds



Organic mercury compounds
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 are historically important but are of little industrial value in the western world. Mercury(II) salts are a rare examples of simple metal complexes that react directly with aromatic rings. Organomercury compounds are always divalent and usually two-coordinate and linear geometry. Unlike organocadmium and organozinc compounds, organomercury compounds do not react with water. They usually have the formula HgR2, which are often volatile, or HgRX, which are often solids, where R is aryl
Aryl
In the context of organic molecules, aryl refers to any functional group or substituent derived from an aromatic ring, be it phenyl, naphthyl, thienyl, indolyl, etc....

 or alkyl and X is usually halide or acetate. Methylmercury
Methylmercury
Methylmercury is an organometallic cation with the formula . It is a bioaccumulative environmental toxicant.-Structure:...

, a generic term for compounds with the formula CH3HgX is a dangerous family of compounds that is found in some a polluted
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...

 water. They arise by a process known as biomethylation.

Applications



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. A still increasing amount is used as gaseous mercury in fluorescent lamps, while most of the other applications are slowly phased out due to health and safety regulations and is in some applications replaced with less toxic but considerably more expensive Galinstan
Galinstan
Galinstan is a family of eutectic alloys mainly consisting of gallium, indium, and tin, which are liquids at room temperature, typically freezing at . Due to the low toxicity and low reactivity of its component metals, it finds use as a replacement for many applications that previously employed...

 alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

.

Medicine





Mercury and its compounds have been used in medicine, although they are much less common today than they once were, now that the toxic effects of mercury and its compounds are more widely understood. The element mercury is an ingredient in dental amalgams
Amalgam (dentistry)
Amalgam is an alloy containing mercury. The term is commonly used for the amalgam employed as material for dental fillings, which consists of mercury , silver , tin , copper , and other trace metals...

. Thiomersal
Thiomersal
Thiomersal , and commonly known in the US as thimerosal, is an organomercury compound. This compound is a well established antiseptic and antifungal agent....

 (called Thimerosal in the United States) is an organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

 used as a preservative
Preservative
A preservative is a naturally occurring or synthetically produced substance that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes....

 in vaccine
Vaccine
A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins...

s, though this use is in decline. Another mercury compound Merbromin
Merbromin
Merbromin is a topical antiseptic used for minor cuts and scrapes. Merbromin is an organomercuric disodium salt compound and a fluorescein...

 (Mercurochrome) is a topical antiseptic used for minor cuts and scrapes is still in use in some countries.

Since the 1930s some vaccine
Vaccine
A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins...

s have contained the preservative thiomersal
Thiomersal
Thiomersal , and commonly known in the US as thimerosal, is an organomercury compound. This compound is a well established antiseptic and antifungal agent....

, which is metabolized or degraded to ethyl mercury. Although it was widely speculated
Thiomersal controversy
The thiomersal controversy describes claims that vaccines containing the mercury-based preservative thiomersal contribute to the development of autism and other brain development disorders...

 that this mercury-based preservative can cause or trigger autism
Autism
Autism is a disorder of neural development characterized by impaired social interaction and communication, and by restricted and repetitive behavior. These signs all begin before a child is three years old. Autism affects information processing in the brain by altering how nerve cells and their...

 in children, scientific studies showed no evidence supporting any such link. Nevertheless thiomersal has been removed from or reduced to trace amounts in all U.S. vaccines recommended for children 6 years of age and under, with the exception of inactivated influenza vaccine.

Mercury in the form of one of its common ores, cinnabar, is used in various traditional medicines, especially in traditional Chinese medicine
Traditional Chinese medicine
Traditional Chinese Medicine refers to a broad range of medicine practices sharing common theoretical concepts which have been developed in China and are based on a tradition of more than 2,000 years, including various forms of herbal medicine, acupuncture, massage , exercise , and dietary therapy...

. Review of its safety has found cinnabar can lead to significant mercury intoxication when heated, consumed in overdose or taken long term, and can have adverse effects at therapeutic doses, though this is typically reversible at therapeutic doses. Although this form of mercury appears less toxic than others, its use in traditional Chinese medicine has not yet been justified as the therapeutic basis for the use of cinnabar is not clear.

Today, the use of mercury in medicine has greatly declined in all respects, especially in developed countries. Thermometers
Mercury-in-glass thermometer
A mercury-in-glass thermometer, also known as a mercury thermometer, was invented by German physicist Daniel Gabriel Fahrenheit in 1724 and is a thermometer consisting of mercury in a glass tube. Calibrated marks on the tube allow the temperature to be read by the length of the mercury within the...

 and sphygmomanometer
Sphygmomanometer
A sphygmomanometer or blood pressure meter is a device used to measure blood pressure, comprising an inflatable cuff to restrict blood flow, and a mercury or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just...

s containing mercury were invented in the early 18th and late 19th centuries, respectively. In the early 21st century, their use is declining and has been banned in some countries, states and medical institutions. In 2002, the U.S. Senate passed legislation to phase out the sale of non-prescription
Medical prescription
A prescription is a health-care program implemented by a physician or other medical practitioner in the form of instructions that govern the plan of care for an individual patient. Prescriptions may include orders to be performed by a patient, caretaker, nurse, pharmacist or other therapist....

 mercury thermometers. In 2003, Washington and Maine
Maine
Maine is a state in the New England region of the northeastern United States, bordered by the Atlantic Ocean to the east and south, New Hampshire to the west, and the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast. Maine is both the northernmost and easternmost...

 became the first states to ban mercury blood pressure devices. Mercury compounds are found in some over-the-counter drug
Over-the-counter drug
Over-the-counter drugs are medicines that may be sold directly to a consumer without a prescription from a healthcare professional, as compared to prescription drugs, which may be sold only to consumers possessing a valid prescription...

s, including topical antiseptics, stimulant laxatives, diaper-rash
Diaper rash
Irritant diaper dermatitis is a generic term applied to skin rashes in the diaper area that are caused by various skin disorders and/or irritants.Generic rash or irritant diaper dermatitis is characterized by joined patches of erythema and...

 ointment, eye drops
Eye Drops
Eye Drops was a television program on TechTV that showcased short computer animation movies and clips made using off the shelf 3D animation software. The show claimed to showcase all different types of animation, but only a very small number of shorts featured non-CG animation...

, and nasal spray
Nasal spray
Nasal sprays come in a variety of forms. Medicated such as Astelin, Afrin and Nasonex and natural such as Sinusoothe and Sterimar. Although delivery methods vary, most nasal sprays function by instilling a fine mist into the nostril by action of a hand-operated pump mechanism.-Antihistamine nasal...

s. The FDA
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...

 has "inadequate data to establish general recognition of the safety and effectiveness", of the mercury ingredients in these products. Mercury is still used in some diuretics, although substitutes now exist for most therapeutic uses.

Production of chlorine and caustic soda


Chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

 is produced from sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...

 (common salt, NaCl) using electrolysis
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...

 to separate the metallic sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 from the chlorine gas. Usually the salt is dissolved in water to produce a brine. By-products of any such chloralkali process
Chloralkali process
The chloralkali process is an industrial process for the electrolysis of sodium chloride solution . Depending on the method several products beside hydrogen can be produced. If the products are separated, chlorine and sodium hydroxide are the products; by mixing, sodium hypochlorite or sodium...

 are hydrogen (H2) and sodium hydroxide (NaOH), which is commonly called caustic soda or lye
Lye
Lye is a corrosive alkaline substance, commonly sodium hydroxide or historically potassium hydroxide . Previously, lye was among the many different alkalis leached from hardwood ashes...

. By far the largest use of mercury in the late 20th century was in the mercury cell process (also called the Castner-Kellner process
Castner-Kellner process
The Castner–Kellner process is a method of electrolysis on an aqueous alkali chloride solution to produce the corresponding alkali hydroxide, invented by American Hamilton Castner and Austrian Karl Kellner in the 1890s....

) where metallic sodium is formed as an amalgam
Amalgam (chemistry)
An amalgam is a substance formed by the reaction of mercury with another metal. Almost all metals can form amalgams with mercury, notable exceptions being iron and platinum. Silver-mercury amalgams are important in dentistry, and gold-mercury amalgam is used in the extraction of gold from ore.The...

 at a cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...

 made from mercury; this sodium is then reacted with water to produce sodium hydroxide. Many of the industrial mercury releases of the 20th century came from this process, although modern plants claimed to be safe in this regard. After about 1985, all new chloralkali production facilities that were built in the United States used either membrane cell or diaphragm cell technologies to produce chlorine.

Laboratory uses


Some medical thermometers, especially those for high temperatures, are filled with mercury; however, they are gradually disappearing. In the United States, non-prescription sale of mercury fever thermometers has been banned since 2003.

Mercury is also found in liquid mirror telescopes. The mirror is formed by rotating liquid mercury on a disk, the parabolic form of the liquid thus formed reflecting and focusing incident light. Such telescopes are cheaper than conventional large mirror telescopes by up to a factor of 100, but the mirror cannot be tilted and always points straight up.

Liquid mercury is a part of popular secondary reference electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...

 (called the calomel electrode
Mercury(I) chloride
Mercury chloride is the chemical compound with the formula Hg2Cl2. Also known as calomel or mercurous chloride, this dense white or yellowish-white, odorless solid is the principal example of a mercury compound...

) in electrochemistry
Electrochemistry
Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor and an ionic conductor , and which involve electron transfer between the electrode and the electrolyte or species in solution.If a chemical reaction is...

 as an alternative to the standard hydrogen electrode
Standard hydrogen electrode
The standard hydrogen electrode , is a redox electrode which forms the basis of the thermodynamic scale of oxidation-reduction potentials...

. The calomel electrode is used to work out the electrode potential
Electrode potential
Electrode potential, E, in electrochemistry, according to an IUPAC definition, is the electromotive force of a cell built of two electrodes:* on the left-hand side is the standard hydrogen electrode, and...

 of half cell
Half cell
A half-cell is a structure that contains a conductive electrode and a surrounding conductive electrolyte separated by a naturally occurring Helmholtz double layer. Chemical reactions within this layer momentarily pump electric charges between the electrode and the electrolyte, resulting in a...

s. Last, but not least, the triple point
Triple point
In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases of that substance coexist in thermodynamic equilibrium...

 of mercury, −38.8344 °C, is a fixed point used as a temperature standard for the International Temperature Scale (ITS-90).

Niche uses




Gaseous mercury is used in mercury-vapor lamp
Mercury-vapor lamp
A mercury-vapor lamp is a gas discharge lamp that uses an electric arc through vaporized mercury to produce light. The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger borosilicate glass bulb...

s and some "neon sign
Neon sign
Neon signs are made using electrified, luminous tube lights that contain rarefied neon or other gases. They are the most common use for neon lighting, which was first demonstrated in a modern form in December, 1910 by Georges Claude at the Paris Motor Show. While they are used worldwide, neon signs...

" type advertising signs and fluorescent lamps. Those low-pressure lamps emit very spectrally narrow lines, which are traditionally used in optical spectroscopy for calibration of spectral position. Commercial calibration lamps are sold for this purpose; however simply reflecting some of the fluorescent-lamp ceiling light into a spectrometer is a common calibration practice. Gaseous mercury is also found in some electron tubes
Gas filled tube
A gas-filled tube, also known as a discharge tube, is an arrangement of electrodes in a gas within an insulating, temperature-resistant envelope. Although the envelope is typically glass, power tubes often use ceramics, and military tubes often use glass-lined metal...

, including ignitron
Ignitron
An ignitron is a type of controlled rectifier dating from the 1930s. Invented by Joseph Slepian while employed by Westinghouse, Westinghouse was the original manufacturer and owned trademark rights to the name "Ignitron"....

s, thyratron
Thyratron
A thyratron is a type of gas filled tube used as a high energy electrical switch and controlled rectifier. Triode, tetrode and pentode variations of the thyratron have been manufactured in the past, though most are of the triode design...

s, and mercury arc rectifiers. It is also used in specialist medical care lamps for skin tanning and disinfection (see pictures). Gaseous mercury is added to cold cathode
Cold cathode
A cold cathode is a cathode used within nixie tubes, gas discharge lamps, discharge tubes, and some types of vacuum tube which is not electrically heated by the circuit to which it is connected...

 argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...

-filled lamps to increase the ionization
Ionization
Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...

 and electrical conductivity. An argon filled lamp without mercury will have dull spots and will fail to light correctly. Lighting containing mercury can be bombarded/oven pumped only once. When added to neon
Neon
Neon is the chemical element that has the symbol Ne and an atomic number of 10. Although a very common element in the universe, it is rare on Earth. A colorless, inert noble gas under standard conditions, neon gives a distinct reddish-orange glow when used in either low-voltage neon glow lamps or...

 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 color.

Cosmetics


Mercury, as thiomersal
Thiomersal
Thiomersal , and commonly known in the US as thimerosal, is an organomercury compound. This compound is a well established antiseptic and antifungal agent....

, is widely used in the manufacture of mascara
Mascara
Mascara is a cosmetic commonly used to enhance the eyes. It may darken, thicken, lengthen, and/or define the eyelashes. Normally in one of three forms—liquid, cake, or cream—the modern mascara product has various formulas; however, all contain the same basic components of pigments, oils, waxes, and...

. In 2008, Minnesota became the first state in the US to ban intentionally added mercury in cosmetics, giving it a tougher standard than the federal government.

A study in geometric mean urine mercury concentration identified a previously unrecognized source of exposure (skin care products) to inorganic mercury among New York City
New York City
New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...

 residents. Population-based biomonitoring also showed that mercury concentration levels are higher in consumers of seafood and fish meals.

Historic uses




Many historic applications made use of the peculiar physical properties of mercury, especially as a dense liquid and a liquid metal:
  • In Islamic Spain, it was used for filling decorative pools. Later, the American artist Alexander Calder
    Alexander Calder
    Alexander Calder was an American sculptor and artist most famous for inventing mobile sculptures. In addition to mobile and stable sculpture, Alexander Calder also created paintings, lithographs, toys, tapestry, jewelry and household objects.-Childhood:Alexander "Sandy" Calder was born in Lawnton,...

     built a mercury fountain
    Mercury fountain
    A mercury fountain is a fountain constructed for use with mercury rather than water.The most noted example is a modern sculpture designed by the American artist Alexander Calder and commissioned by the Spanish Republican government for the 1937 World Exhibition in Paris...

     for the Spanish Pavilion at the 1937 World Exhibition in Paris
    Exposition Internationale des Arts et Techniques dans la Vie Moderne (1937)
    The Exposition Internationale des Arts et Techniques dans la Vie Moderne was held from May 25 to November 25, 1937 in Paris, France...

    . The fountain is now on display at the Fundació Joan Miró
    Fundació Joan Miró
    The ' is a museum of modern art honoring Joan Miró and located on the hill called Montjuïc in Barcelona, Catalonia.-History:...

     in Barcelona
    Barcelona
    Barcelona is the second largest city in Spain after Madrid, and the capital of Catalonia, with a population of 1,621,537 within its administrative limits on a land area of...

    .
  • Mercury was used inside wobbler lures. Its heavy, liquid form made it useful since the lures made an attractive irregular movement when the mercury moved inside the plug. Such use was stopped due to environmental concerns, but illegal preparation of modern fishing plugs has occurred.
  • The Fresnel lens
    Fresnel lens
    A Fresnel lens is a type of lens originally developed by French physicist Augustin-Jean Fresnel for lighthouses.The design allows the construction of lenses of large aperture and short focal length without the mass and volume of material that would be required by a lens of conventional design...

    es of old lighthouses used to float and rotate in a bath of mercury which acted like a bearing.
  • Mercury sphygmomanometer
    Sphygmomanometer
    A sphygmomanometer or blood pressure meter is a device used to measure blood pressure, comprising an inflatable cuff to restrict blood flow, and a mercury or mechanical manometer to measure the pressure. It is always used in conjunction with a means to determine at what pressure blood flow is just...

    s (blood pressure meter), barometer
    Barometer
    A barometer is a scientific instrument used in meteorology to measure atmospheric pressure. Pressure tendency can forecast short term changes in the weather...

    s, diffusion pump
    Diffusion pump
    Diffusion pumps use a high speed jet of vapor to direct gas molecules in the pump throat down into the bottom of the pump and out the exhaust. Presented in 1915 by Wolfgang Gaede and using mercury vapor, they were the first type of high vacuum pumps operating in the regime of free molecular flow,...

    s, coulometers
    Mercury coulometer
    Mercury coulometer is an electroanalytical chemistry device using mercury to determine the amount of matter transformed during the following reaction:...

    , and many other laboratory instruments. As an opaque liquid with a high density and a nearly linear thermal expansion, it is ideal for this role.
  • As an electrically conductive liquid, it was used in mercury switch
    Mercury switch
    A mercury switch is a switch whose purpose is to allow or interrupt the flow of electric current in an electrical circuit in a manner that is dependent on the switch's physical position or alignment relative to the direction of the "pull" of earth's gravity, or other inertia.Mercury switches...

    es (including home mercury light switches installed prior to 1970), tilt switches used in old fire detectors, and tilt switches in many modern home thermostats,
  • Owing to its acoustic properties, mercury was used as the propagation medium in delay line memory devices used in early digital computers of the mid-20th century.
  • Experimental mercury vapor turbines were installed to increase the efficiency of fossil-fuel electrical power plants. The South Meadow power plant in Hartford, CT employed mercury as its working fluid
    Working fluid
    A working fluid is a pressurized gas or liquid that actuates a machine. Examples include steam in a steam engine, air in a hot air engine and hydraulic fluid in a hydraulic motor or hydraulic cylinder...

    , in a binary configuration with a secondary water circuit, or a number of years starting in the late 1920s in a drive to improve plant efficiency. Several other plants were built, including the Schiller Station in Portsmouth, NH, which went online in 1950. The idea did not catch on industry-wide due to the weight and toxicity of mercury, as well as the advent of supercritical
    Supercritical fluid
    A supercritical fluid is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist. It can effuse through solids like a gas, and dissolve materials like a liquid...

     steam plants in later years.
  • Similarly, liquid mercury was used as a coolant
    Coolant
    A coolant is a fluid which flows through a device to prevent its overheating, transferring the heat produced by the device to other devices that use or dissipate it. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, and chemically inert, neither causing nor...

     for some nuclear reactor
    Nuclear reactor
    A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

    s; however, sodium
    Sodium
    Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

     is proposed for reactors cooled with liquid metal, because the high density of mercury requires much more energy to circulate as coolant.
  • Mercury was a propellant for early ion engines in electric space propulsion systems. Advantages were mercury's high molecular weight, low ionization energy, low dual-ionization energy, high liquid density and liquid storability at room temperature
    Room temperature
    -Comfort levels:The American Society of Heating, Refrigerating and Air-Conditioning Engineers has listings for suggested temperatures and air flow rates in different types of buildings and different environmental circumstances. For example, a single office in a building has an occupancy ratio per...

    . Disadvantages were concerns regarding environmental impact associated with ground testing and concerns about eventual cooling and condensation of some of the propellant on the spacecraft in long-duration operations. The first spaceflight to use electric propulsion was a mercury-fueled ion thruster developed by NASA Lewis and flown on the Space Electric Rocket Test "SERT-1" spacecraft launched by NASA
    NASA
    The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

     at its Wallops Flight Facility
    Wallops Flight Facility
    Wallops Flight Facility , located on the Eastern Shore of Virginia, is operated by NASA’s Goddard Space Flight Center, primarily as a rocket launch site to support science and exploration missions for NASA and other U.S. government agencies...

     in 1964. The SERT-1 flight was followed up by the SERT-2 flight in 1970. Mercury and caesium
    Caesium
    Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C , which makes it one of only five elemental metals that are liquid at room temperature...

     were preferred propellants for ion engines until Hughes Research Laboratory performed studies finding xenon
    Xenon
    Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...

     gas to be a suitable replacement. Xenon is now the preferred propellant for ion engines as it has a high molecular weight, little or no reactivity due to its noble gas
    Noble gas
    The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity...

     nature, and has a high liquid density under mild cryogenic storage.
  • Mercury has been used to produce liquid mirror telescopes.


Others applications made use of the chemical properties of mercury:
  • Mercury was used for preserving wood, developing daguerreotype
    Daguerreotype
    The daguerreotype was the first commercially successful photographic process. The image is a direct positive made in the camera on a silvered copper plate....

    s, silvering
    Silvering
    Silvering is the chemical process of coating glass with a reflective substance. When glass mirrors first gained widespread usage in Europe during the 16th century, most were made of an amalgam of tin and mercury, but by the 19th century mirrors were commonly made through a process by which silver...

     mirror
    Mirror
    A mirror is an object that reflects light or sound in a way that preserves much of its original quality prior to its contact with the mirror. Some mirrors also filter out some wavelengths, while preserving other wavelengths in the reflection...

    s, anti-fouling paints (discontinued in 1990), herbicide
    Herbicide
    Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...

    s (discontinued in 1995), handheld maze games, cleaning, and road leveling devices in cars. Mercury compounds have been used in antiseptic
    Antiseptic
    Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction...

    s, laxatives, antidepressant
    Antidepressant
    An antidepressant is a psychiatric medication used to alleviate mood disorders, such as major depression and dysthymia and anxiety disorders such as social anxiety disorder. According to Gelder, Mayou &*Geddes people with a depressive illness will experience a therapeutic effect to their mood;...

    s, and in antisyphilitics
    Syphilis
    Syphilis is a sexually transmitted infection caused by the spirochete bacterium Treponema pallidum subspecies pallidum. The primary route of transmission is through sexual contact; however, it may also be transmitted from mother to fetus during pregnancy or at birth, resulting in congenital syphilis...

    .
  • It was allegedly used by allied spies
    Western Allies
    The Western Allies were a political and geographic grouping among the Allied Powers of the Second World War. It generally includes the United Kingdom and British Commonwealth, the United States, France and various other European and Latin American countries, but excludes China, the Soviet Union,...

     to sabotage Luftwaffe planes: a mercury paste was applied to bare aluminium
    Aluminium
    Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

    , causing the metal to rapidly corrode
    Corrosion
    Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...

    ; this would cause structural failures.
  • Chloralkali process
    Chloralkali process
    The chloralkali process is an industrial process for the electrolysis of sodium chloride solution . Depending on the method several products beside hydrogen can be produced. If the products are separated, chlorine and sodium hydroxide are the products; by mixing, sodium hypochlorite or sodium...

    : The largest industrial use of mercury during the 20th century was in electrolysis for separating chlorine and sodium from brine; mercury being the anode
    Anode
    An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....

     of the Castner-Kellner process
    Castner-Kellner process
    The Castner–Kellner process is a method of electrolysis on an aqueous alkali chloride solution to produce the corresponding alkali hydroxide, invented by American Hamilton Castner and Austrian Karl Kellner in the 1890s....

    . The chlorine was used for bleaching paper (hence the location of many of these plants near paper mills) while the sodium was used to make sodium hydroxide for soaps and other cleaning products. This usage has largely been discontinued, replaced with other technologies that utilize membrane cells.
  • As electrode
    Electrode
    An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...

    s in some types of electrolysis
    Electrolysis
    In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...

    , batteries
    Battery (electricity)
    An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...

     (mercury cells
    Mercury battery
    A mercury battery is a non-rechargeable electrochemical battery, a primary cell. Due to the content of mercury, and the resulting environmental concerns, the sale of mercury batteries is banned in many countries. Both ANSI and IEC have withdrawn standards for mercury batteries...

    ), sodium hydroxide and chlorine
    Chlorine
    Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

     production, handheld games, catalysts, insecticide
    Insecticide
    An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...

    s.
  • Mercury was once used as a gun barrel bore cleaner.
  • From the mid-18th to the mid-19th centuries, a process called "carroting" was used in the making of felt
    Felt
    Felt is a non-woven cloth that is produced by matting, condensing and pressing woollen fibres. While some types of felt are very soft, some are tough enough to form construction materials. Felt can be of any colour, and made into any shape or size....

     hats. Animal skins were rinsed in an orange solution (the term "carroting" arose from this color) of the mercury compound mercuric nitrate, Hg(NO3)2·2H2O. This process separated the fur from the pelt and matted it together. This solution and the vapors it produced were highly toxic. The United States Public Health Service
    United States Public Health Service
    The Public Health Service Act of 1944 structured the United States Public Health Service as the primary division of the Department of Health, Education and Welfare , which later became the United States Department of Health and Human Services. The PHS comprises all Agency Divisions of Health and...

     banned the use of mercury in the felt industry in December 1941. The psychological symptoms associated with mercury poisoning are said by some to have inspired the phrase "mad as a hatter". Lewis Carroll
    Lewis Carroll
    Charles Lutwidge Dodgson , better known by the pseudonym Lewis Carroll , was an English author, mathematician, logician, Anglican deacon and photographer. His most famous writings are Alice's Adventures in Wonderland and its sequel Through the Looking-Glass, as well as the poems "The Hunting of the...

    's "Mad Hatter
    Mad Hatter
    Hatta, the Hatter is a fictional character in Lewis Carroll's Alice's Adventures in Wonderland and the story's sequel, Through the Looking-Glass. He is often referred to as the Mad Hatter, though this term was never used by Carroll...

    " in his book Alice's Adventures in Wonderland
    Alice's Adventures in Wonderland
    Alice's Adventures in Wonderland is an 1865 novel written by English author Charles Lutwidge Dodgson under the pseudonym Lewis Carroll. It tells of a girl named Alice who falls down a rabbit hole into a fantasy world populated by peculiar, anthropomorphic creatures...

    was a play on words based on the older phrase, but the character himself does not exhibit symptoms of mercury poisoning.
  • Gold and silver mining. Historically, mercury was used extensively in hydraulic gold mining in order to help the gold to sink through the flowing water-gravel mixture. Thin mercury particles may form mercury-gold amalgam and therefore increase the gold recovery rates. Large-scale use of mercury stopped in the 1960s. However, mercury is still used in small scale, often clandestine, gold prospecting. It is estimated that 45,000 metric tons of mercury used in California for placer mining
    Placer mining
    Placer mining is the mining of alluvial deposits for minerals. This may be done by open-pit or by various surface excavating equipment or tunneling equipment....

     have not been recovered. Mercury was also used in silver mining.

Historic medicinal uses


Mercury(I) chloride (also known as calomel or mercurous chloride) has been used in traditional medicine
Traditional medicine
Traditional medicine comprises unscientific knowledge systems that developed over generations within various societies before the era of modern medicine...

 as a diuretic
Diuretic
A diuretic provides a means of forced diuresis which elevates the rate of urination. There are several categories of diuretics. All diuretics increase the excretion of water from bodies, although each class does so in a distinct way.- Medical uses :...

, topical disinfectant, and laxative
Laxative
Laxatives are foods, compounds, or drugs taken to induce bowel movements or to loosen the stool, most often taken to treat constipation. Certain stimulant, lubricant, and saline laxatives are used to evacuate the colon for rectal and/or bowel examinations, and may be supplemented by enemas under...

. Mercury(II) chloride
Mercury(II) chloride
Mercury chloride or mercuric chloride , is the chemical compound with the formula HgCl2. This white crystalline solid is a laboratory reagent and a molecular compound. It is no longer used for medicinal purposes Mercury(II) chloride or mercuric chloride (formerly corrosive sublimate), is the...

 (also known as mercuric chloride or corrosive sublimate) was once used to treat syphilis
Syphilis
Syphilis is a sexually transmitted infection caused by the spirochete bacterium Treponema pallidum subspecies pallidum. The primary route of transmission is through sexual contact; however, it may also be transmitted from mother to fetus during pregnancy or at birth, resulting in congenital syphilis...

 (along with other mercury compounds), although it is so toxic that sometimes the symptoms of its toxicity were confused with those of the syphilis it was believed to treat. It is also used as a disinfectant. Blue mass
Blue mass
Blue mass was the name of a medicine prescribed, made, and sold in the United States in the 19th century.-Description:Blue mass was recommended as a remedy for such widely varied complaints as tuberculosis, constipation, toothache, parasitic infestations, and the pains of childbirth...

, a pill or syrup in which mercury is the main ingredient, was prescribed throughout the 19th century for numerous conditions including constipation, depression, child-bearing and toothaches. In the early 20th century, mercury was administered to children yearly as a laxative and dewormer, and it was used in teething powders for infants. The mercury-containing organohalide merbromin
Merbromin
Merbromin is a topical antiseptic used for minor cuts and scrapes. Merbromin is an organomercuric disodium salt compound and a fluorescein...

 (sometimes sold as Mercurochrome) is still widely used but has been banned in some countries such as the U.S.

Toxicity and safety




Mercury and most of its compounds are extremely toxic and must be handled with care; in cases of spills involving mercury (such as from certain thermometers
Mercury-in-glass thermometer
A mercury-in-glass thermometer, also known as a mercury thermometer, was invented by German physicist Daniel Gabriel Fahrenheit in 1724 and is a thermometer consisting of mercury in a glass tube. Calibrated marks on the tube allow the temperature to be read by the length of the mercury within the...

 or fluorescent light bulbs), specific cleaning procedures are used to avoid exposure and contain the spill. Protocols call for physically merging smaller droplets on hard surfaces, combining them into a single larger pool for easier removal with an eyedropper, or for gently pushing the spill into a disposable container. Vacuum cleaners and brooms cause greater dispersal of the mercury and should not be used. Afterwards, fine sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

, zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

, or some other powder that readily forms an amalgam (alloy) with mercury at ordinary temperatures is sprinkled over the area before itself being collected and properly disposed of. Cleaning porous surfaces and clothing is not effective at removing all traces of mercury and it is therefore advised to discard these kinds of items should they be exposed to a mercury spill.

Mercury can be inhaled and absorbed through the skin and mucous membranes, so containers of mercury are securely sealed to avoid spills and evaporation. Heating of mercury, or of compounds of mercury that may decompose when heated, is always carried out with adequate ventilation in order to avoid exposure to mercury vapor. The most toxic forms of mercury are its organic compounds, such as dimethylmercury
Dimethylmercury
Dimethylmercury is an organomercury compound. This colorless liquid is one of the strongest known neurotoxins. It is described as having a slightly sweet smell, although inhaling enough vapor to detect its odor would be hazardous....

 and methylmercury
Methylmercury
Methylmercury is an organometallic cation with the formula . It is a bioaccumulative environmental toxicant.-Structure:...

. However, inorganic compounds, such as cinnabar
Cinnabar
Cinnabar or cinnabarite , is the common ore of mercury.-Word origin:The name comes from κινναβαρι , a Greek word most likely applied by Theophrastus to several distinct substances...

 are also highly toxic by ingestion or inhalation. Mercury can cause both chronic and acute poisoning.

Releases in the environment



Preindustrial deposition rates of mercury from the atmosphere may be about 4 ng /(1 L of ice deposit). Although that can be considered a natural level of exposure, regional or global sources have significant effects. Volcanic eruptions can increase the atmospheric source by 4–6 times.

Natural sources, such as volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

es, are responsible for approximately half of atmospheric mercury emissions. The human-generated half can be divided into the following estimated percentages:
  • 65% from stationary combustion, of which coal-fired power plants are the largest aggregate source (40% of U.S. mercury emissions in 1999). This includes power plants fueled with gas where the mercury has not been removed. Emissions from coal combustion are between one and two orders of magnitude higher than emissions from oil combustion, depending on the country.
  • 11% from gold production. The three largest point sources for mercury emissions in the U.S. are the three largest gold mines. Hydrogeochemical release of mercury from gold-mine tailings has been accounted as a significant source of atmospheric mercury in eastern Canada.
  • 6.8% from non-ferrous metal
    Non-ferrous metal
    In metallurgy, a non-ferrous metal is a metal that is not ferrous, that is, any metal, including alloys, that does not contain iron in appreciable amounts...

     production, typically smelters.
  • 6.4% from cement
    Cement
    In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...

     production.
  • 3.0% from waste disposal, including municipal and hazardous waste
    Hazardous waste
    A hazardous waste is waste that poses substantial or potential threats to public health or the environment. According to the U.S. environmental laws hazardous wastes fall into two major categories: characteristic wastes and listed wastes.Characteristic hazardous wastes are materials that are known...

    , crematoria, and sewage sludge incineration. This is a significant underestimate due to limited information, and is likely to be off by a factor of two to five.
  • 3.0% from caustic soda production.
  • 1.4% from pig iron
    Pig iron
    Pig iron is the intermediate product of smelting iron ore with a high-carbon fuel such as coke, usually with limestone as a flux. Charcoal and anthracite have also been used as fuel...

     and steel
    Steel
    Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

     production.
  • 1.1% from mercury production, mainly for batteries.
  • 2.0% from other sources.

The above percentages are estimates of the global human-caused mercury emissions in 2000, excluding biomass burning, an important source in some regions.

Current atmospheric mercury contamination in outdoor urban air is (0.01–0.02 µg/m3) indoor concentrations are significantly elevated over outdoor concentrations, in the range 0.0065–0.523 µg/m3 (average 0.069 µg/m3).

Mercury also enters into the environment through the improper disposal (e.g., land filling, incineration) of certain products. Products containing mercury include: auto parts, batteries
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...

, fluorescent bulbs, medical products, thermometers, and thermostats. Due to health concerns (see below), toxics use reduction
Waste management
Waste management is the collection, transport, processing or disposal,managing and monitoring of waste materials. The term usually relates to materials produced by human activity, and the process is generally undertaken to reduce their effect on health, the environment or aesthetics...

 efforts are cutting back or eliminating mercury in such products. For example, most thermometers now use pigmented alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

 instead of mercury, and galinstan
Galinstan
Galinstan is a family of eutectic alloys mainly consisting of gallium, indium, and tin, which are liquids at room temperature, typically freezing at . Due to the low toxicity and low reactivity of its component metals, it finds use as a replacement for many applications that previously employed...

 alloy thermometers are also an option. Mercury thermometers are still occasionally used in the medical field because they are more accurate than alcohol thermometers, though both are commonly being replaced by electronic thermometers and less commonly by galinstan thermometers. Mercury thermometers are still widely used for certain scientific applications because of their greater accuracy and working range.

The United States Clean Air Act, passed in 1990, put mercury on a list of toxic pollutants that need to be controlled to the greatest possible extent. Thus, industries that release high concentrations of mercury into the environment agreed to install maximum achievable control technologies (MACT). In March 2005 EPA rule added power plants to the list of sources that should be controlled and a national cap and trade
Emissions trading
Emissions trading is a market-based approach used to control pollution by providing economic incentives for achieving reductions in the emissions of pollutants....

 rule was issued. States were given until November 2006 to impose stricter controls, and several States are doing so. The rule was being subjected to legal challenges from several States in 2005 and decision was made in 2008. The Clean Air Mercury Rule was struck down by a Federal Appeals Court on February 8, 2008. The rule was deemed not sufficient to protect the health of persons living near coal-fired power plants. The court opinion cited the negative impact on human health from coal-fired power plants' mercury emissions documented in the EPA Study Report to Congress of 1998.

Historically, one of the largest releases was from the Colex plant, a lithium-isotope separation plant at Oak Ridge. The plant operated in the 1950s and 1960s. Records are incomplete and unclear, but government commissions have estimated that some two million pounds of mercury are unaccounted for.

A serious industrial disasters
Industrial disasters
This article lists notable industrial disasters, which are disasters caused by industrial companies, either by accident, negligence or incompetence. They are a form of industrial accident where great damage, injury or loss of life are caused....

 was the dumping of mercury compounds into Minamata Bay, Japan. It is estimated that over 3,000 people suffered various deformities, severe mercury poisoning symptoms or death from what became known as Minamata disease
Minamata disease
', sometimes referred to as , is a neurological syndrome caused by severe mercury poisoning. Symptoms include ataxia, numbness in the hands and feet, general muscle weakness, narrowing of the field of vision and damage to hearing and speech. In extreme cases, insanity, paralysis, coma, and death...

.

Occupational exposure


Due to the health effects of mercury exposure, industrial and commercial uses are regulated in many countries. The World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...

, OSHA
Occupational Safety and Health Administration
The United States Occupational Safety and Health Administration is an agency of the United States Department of Labor. It was created by Congress of the United States under the Occupational Safety and Health Act, signed by President Richard M. Nixon, on December 29, 1970...

, and NIOSH
National Institute for Occupational Safety and Health
The National Institute for Occupational Safety and Health is the United States’ federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness. NIOSH is part of the Centers for Disease Control and Prevention within the U.S...

 all treat mercury as an occupational hazard, and have established specific occupational exposure limits. Environmental releases and disposal of mercury are regulated in the U.S. primarily by the United States Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...

.

Case control studies have shown effects such as tremors, impaired cognitive skills, and sleep disturbance in workers with chronic exposure to mercury vapor even at low concentrations in the range 0.7–42 μg/m3. A study has shown that acute exposure (4 – 8 hours) to calculated elemental mercury levels of 1.1 to 44 mg/m3 resulted in chest pain, dyspnea
Dyspnea
Dyspnea , shortness of breath , or air hunger, is the subjective symptom of breathlessness.It is a normal symptom of heavy exertion but becomes pathological if it occurs in unexpected situations...

, cough, hemoptysis
Hemoptysis
Hemoptysis or haemoptysis is the expectoration of blood or of blood-stained sputum from the bronchi, larynx, trachea, or lungs Hemoptysis or haemoptysis is the expectoration (coughing up) of blood or of blood-stained sputum from the bronchi, larynx, trachea, or lungs Hemoptysis or haemoptysis ...

, impairment of pulmonary function, and evidence of interstitial pneumonitis
Pneumonitis
Pneumonitis or pulmonitis is a general term that refers to inflammation of lung tissue.Pneumonia is pneumonitis combined with consolidation and exudation...

. Acute exposure to mercury vapor has been shown to result in profound central nervous system effects, including psychotic reactions characterized by delirium, hallucinations, and suicidal tendency. Occupational exposure has resulted in broad-ranging functional disturbance, including erethism
Erethism
Erethism or erethism mercurialis is a symptom complex of mercury poisoning, presenting with excessive shyness, timidity and social phobia. This was common among hat makers of old England who used mercury to stabilize the wool in a process called felting...

, irritability, excitability, excessive shyness, and insomnia. With continuing exposure, a fine tremor develops and may escalate to violent muscular spasms. Tremor initially involves the hands and later spreads to the eyelids, lips, and tongue. Long-term, low-level exposure has been associated with more subtle symptoms of erethism, including fatigue, irritability, loss of memory, vivid dreams and depression.

Treatment


Research on the treatment of mercury poisoning is limited. Currently available drugs for acute mercurial poisoning include chelators N-acetyl-D, L-penicillamine
Penicillamine
Penicillamine is a pharmaceutical of the chelator class. It is sold under the trade names of Cuprimine and Depen. The pharmaceutical form is D-penicillamine, as L-penicillamine is toxic...

 (NAP), British Anti-Lewisite (BAL), 2,3-dimercapto-1-propanesulfonic acid
2,3-Dimercapto-1-propanesulfonic acid
2,3-Dimercapto-1-propanesulfonic acid and its sodium salt are chelating agents that form complexes with various heavy metals. They are related to dimercaprol, which is another chelating agent....

 (DMPS), and dimercaptosuccinic acid
Dimercaptosuccinic acid
Dimercaptosuccinic acid , is the organosulfur compound with the formula HO2CCHCHCO2H. This colorless solid contains two carboxylic acid and two thiol groups, the latter being responsible for its mildly unpleasant odour. It occurs in two diastereomers, meso and the chiral dl forms...

 (DMSA). In one small study including 11 construction workers exposed to elemental mercury, patients were treated with DMSA and NAP. Chelation therapy
Chelation therapy
Chelation therapy is the administration of chelating agents to remove heavy metals from the body. For the most common forms of heavy metal intoxication—those involving lead, arsenic or mercury—the standard of care in the United States dictates the use of dimercaptosuccinic acid...

 with both drugs resulted in the mobilization of a small fraction of the total estimated body mercury. DMSA was able to increase the excretion of mercury to a greater extent than NAP.

Fish



Fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 and shellfish
Shellfish
Shellfish is a culinary and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater environments, some kinds are found only in freshwater...

 have a natural tendency to concentrate mercury in their bodies, often in the form of methylmercury
Methylmercury
Methylmercury is an organometallic cation with the formula . It is a bioaccumulative environmental toxicant.-Structure:...

, a highly toxic organic compound of mercury. Species of fish that are high on the food chain
Food chain
A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...

, such as shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

, swordfish
Swordfish
Swordfish , also known as broadbill in some countries, are large, highly migratory, predatory fish characterized by a long, flat bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood...

, king mackerel
King mackerel
The king mackerel is a migratory species of mackerel of the western Atlantic Ocean and Gulf of Mexico. It is an important species to both the commercial and recreational fishing industries.-Description:...

, albacore tuna, and tilefish
Tilefish
Tilefishes, also known as blanquillo, are mostly small perciform marine fish comprising the family Malacanthidae.They are usually found in sandy areas, especially near coral reefs....

 contain higher concentrations of mercury than others. As mercury and methylmercury are fat soluble, they primarily accumulate in the viscera, although they are also found throughout the muscle tissue. When this fish is consumed by a predator, the mercury level is accumulated. Since fish are less efficient at depurating than accumulating methylmercury, fish-tissue concentrations increase over time. Thus species that are high on the food chain
Food chain
A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...

 amass body burdens of mercury that can be ten times higher than the species they consume. This process is called biomagnification
Biomagnification
Biomagnification, also known as bioamplification or biological magnification, is the increase in concentration of a substance that occurs in a food chain as a consequence of:* Persistence...

. Mercury poisoning
Mercury poisoning
Mercury poisoning is a disease caused by exposure to mercury or its compounds. Mercury is a heavy metal occurring in several forms, all of which can produce toxic effects in high enough doses...

 happened this way in Minamata
Minamata, Kumamoto
is a city located in Kumamoto prefecture, Japan. It is on the west coast of Kyūshū. The city was founded on April 1, 1949.As of 2008, the city has an estimated population of 27,856 and the density of 171 persons per km²...

, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, now called Minamata disease
Minamata disease
', sometimes referred to as , is a neurological syndrome caused by severe mercury poisoning. Symptoms include ataxia, numbness in the hands and feet, general muscle weakness, narrowing of the field of vision and damage to hearing and speech. In extreme cases, insanity, paralysis, coma, and death...

.

Regulations


In the United States, the Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...

 is charged with regulating and managing mercury contamination. Several laws give the EPA this authority, including the Clean Air Act, the Clean Water Act
Clean Water Act
The Clean Water Act is the primary federal law in the United States governing water pollution. Commonly abbreviated as the CWA, the act established the goals of eliminating releases of high amounts of toxic substances into water, eliminating additional water pollution by 1985, and ensuring that...

, the Resource Conservation and Recovery Act
Resource Conservation and Recovery Act
The Resource Conservation and Recovery Act , enacted in 1976, is the principal Federal law in the United States governing the disposal of solid waste and hazardous waste.-History and Goals:...

, and the Safe Drinking Water Act
Safe Drinking Water Act
The Safe Drinking Water Act is the principle federal law in the United States intended to ensure safe drinking water for the public. Pursuant to the act, the Environmental Protection Agency is required to set standards for drinking water quality and oversee all states, localities, and water...

. Additionally, the Mercury-Containing and Rechargeable Battery Management Act
Mercury-containing and Rechargeable Battery Management Act
In the United States, the Mercury-Containing and Rechargeable Battery Management Act was signed into law on May 13, 1996...

, passed in 1996, phases out the use of mercury in batteries, and provides for the efficient and cost-effective disposal of many types of used batteries. North America contributed approximately 11% of the total global anthropogenic mercury emissions in 1995.

In the European Union
European Union
The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

, the directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment (see RoHS
Restriction of Hazardous Substances Directive
The Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment 2002/95/EC was adopted in February 2003 by the European Union. The RoHS directive took effect on 1 July 2006, and is required to be enforced and become law in each member state...

) bans mercury from certain electrical and electronic products, and limits the amount of mercury in other products to less than 1000 ppm. There are restrictions for mercury concentration in packaging (the limit is 100 ppm for sum of mercury, lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

, hexavalent chromium
Hexavalent chromium
Hexavalent chromium refers to chemical compounds that contain the element chromium in the +6 oxidation state. Virtually all chromium ore is processed via hexavalent chromium, specifically the salt sodium dichromate. Approximately of hexavalent chromium were produced in 1985...

 and cadmium
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...

) and batteries (the limit is 5 ppm). In July 2007, the European Union also banned mercury in non-electrical measuring devices, such as thermometers and barometers. The ban applies to new devices only, and contains exemptions for the health care sector and a two-year grace period for manufacturers of barometers.
Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...

 enacted a total ban on the use of mercury in the manufacturing and import/export of mercury products, effective January 1, 2008. In 2002, several lakes in Norway were found to have a poor state of mercury pollution, with an excess of 1 mg/g of mercury in their sediment.

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