salt, chemical compound (other than water) formed by a chemical reaction between an acid and a base (see acids and bases).

Characteristics and Classification of Salts

The most familiar salt is sodium chloride, the principal component of common table salt. Sodium chloride, NaCl, and water, H₂O, are formed by neutralization of sodium hydroxide, NaOH, a base, with hydrogen chloride, HCl, an acid: HCl+NaOH→NaCl+H₂O. Most salts are ionic compounds (see chemical bond); they are made up of ions rather than molecules. The chemical formula for an ionic salt is an empirical formula; it does not represent a molecule but shows the proportion of atoms of the elements that make up the salt. The formula for sodium chloride, NaCl, indicates that equal numbers of sodium and chlorine atoms combine to form the salt. In the reaction of sodium with chlorine, each sodium atom loses an electron, becoming positively charged, and each chlorine atom gains an electron, becoming negatively charged (see oxidation and reduction); there are equal numbers of positively charged sodium ions and negatively charged chloride ions in sodium chloride. The ions in a solid salt are usually arranged in a definite crystalline structure, each positive ion being associated with a fixed number of negative ions, and vice versa.

A salt that has neither hydrogen (H) nor hydroxyl (OH) in its formula, e.g., sodium chloride (NaCl), is called a normal salt. A salt that has hydrogen in its formula, e.g., sodium bicarbonate (NaHCO₃), is called an acid salt. A salt that has hydroxyl in its formula, e.g., basic lead nitrate (Pb[OH]NO₃), is called a basic salt. Since a salt may react with a solvent to yield different ions than were present in the salt (see hydrolysis), a solution of a normal salt may be acidic or basic; e.g., trisodium phosphate, Na₃PO₄, dissolves in and reacts with water to form a basic solution.

In addition to being classified as normal, acid, or basic, salts are categorized as simple salts, double salts, or complex salts. Simple salts, e.g., sodium chloride, contain only one kind of positive ion (other than the hydrogen ion in acid salts). Double salts contain two different positive ions, e.g., the mineral dolomite, or calcium magnesium carbonate, CaMg(CO₃)₂. Alums are a special kind of double salt. Complex salts, e.g., potassium ferricyanide, K₃Fe(CN)₆, contain a complex ion that does not dissociate in solution. A hydrate is a salt that includes water in its solid crystalline form; Glauber's salt and Epsom salts are hydrates.

Salts are often grouped according to the negative ion they contain, e.g., bicarbonate or carbonate, chlorate, chloride, cyanide, fulminate, nitrate, phosphate, silicate, sulfate, or sulfide.

Preparation of Salts

Salts are also prepared by methods other than neutralization. A metal can combine directly with a nonmetal to form a salt; e.g., sodium metal reacts with chlorine gas to form sodium chloride. A metal may react with a dilute acid to form a salt and release hydrogen gas; e.g., zinc reacts with dilute sulfuric acid to form zinc sulfate and hydrogen. A metal oxide may react with an acid to form a salt and water; e.g., calcium oxide reacts with carbonic acid to form calcium carbonate and water. A base can react with a nonmetallic oxide to form a salt and water; e.g., sodium hydroxide reacts with carbon dioxide to form sodium carbonate and water. Two salts may react with one another (in solution) to form two new salts; e.g., barium chloride and sodium sulfate react in solution to form barium sulfate (as an insoluble precipitate) and sodium chloride (which remains in solution). A salt may react with an acid to form a different salt and acid; e.g., sodium chloride and sulfuric acid react when heated to form sodium sulfate and release hydrogen chloride gas (which in solution forms hydrochloric acid). A salt undergoes dissociation when it dissolves in a polar solvent, e.g., water, the extent of dissociation depending both on the salt and the solvent.

rock salt: see sodium chloride.

Seignette salt: see Rochelle salt.

Salt, Sir Titus, 1803-76, English textile manufacturer and inventor. He invented a machine for making worsted from coarse wool and a process for spinning and weaving alpaca. In 1851 he started to build, on the Aire River, extensive textile works and a model manufacturing town, called Saltaire, in which he attempted to embody his conceptions of ideal factory conditions for workers.

Salt River valley, irrigated region around the lower course of the Salt River, which rises in mountain streams near the Mogollon Rim of the Mogollon Plateau and flows southwest to join the Gila River in S central Arizona. Phoenix is the main city of the latter Ariz. region. Native Americans used the Salt River for irrigation many centuries ago. In the 19th cent., American settlers began irrigated farming in the valley, and the Mormons used some of the old Native American canals at Mesa, Ariz. The Salt River project, the first large irrigation scheme undertaken under the Federal Reclamation Act of 1902, is one of the most economically successful projects in North America. It began in 1903 when construction started on the Roosevelt Dam in a canyon E of Phoenix. The dam, forming Roosevelt Lake behind it, impounds enough water to irrigate fields for about two years even if no rain falls. Other dams were built between 1922 and 1946 to supply water and power. The region is a rich producer of citrus fruits, lettuce, melons, and other crops. A major factor in the Salt River project's success is the long season without frost; the climate also makes this area an attractive winter resort.

Salt River Bay National Historical Park and Ecological Preserve: see National Parks and Monuments (table).

Salt Lake City, city (1990 pop. 159,936), alt. c.4,330 ft (1,320 m), state capital and seat of Salt Lake co., N central Utah, on the Jordan River and near the Great Salt Lake, at the foot of the Wasatch Range; inc. 1851. The largest city in the state, it is a great regional center, world headquarters of the Church of Jesus Christ of Latter-day Saints, and the processing point for products of an irrigated farm region that is rich in minerals. Major industries include tourism; medical research; food processing; silver, lead, copper, zinc, and iron smelting; the manufacture of computers and electronic equipment; oil refining; and warehousing. The city's outlying suburbs grew rapidly in the 1980s.

Founded in 1847 by Brigham Young as the capital of the Mormon (see Latter-day Saints, Church of Jesus Christ of) community, the city achieved greatness as its economic hub. The prominence of the gigantic Temple (built 1853-93) on Temple Square at the city's heart reflects the Mormon nature of Salt Lake City; nearby are the Mormon Tabernacle (opened 1867) and Conference Center (opened 2000). After 1849, Salt Lake City was a supply point for overland travel to California and was connected with the first transcontinental railroad by a line built (1869-70) by Brigham Young to Ogden. It is the seat of the Univ. of Utah, Westminster College, and a campus of Brigham Young Univ. Of interest are the state capitol (1914), Brigham Young's home (the "Beehive House," 1877), and the Brigham Young Monument (1897). Home to the Utah Jazz of the National Basketball Association, the city hosted the 2002 Winter Olympic games.

SALT, Strategic Arms Limitation Talks: see disarmament, nuclear.

Rochelle salt, colorless to blue-white orthorhombic crystalline salt with a saline, cooling taste. It is also called Seignette salt after Pierre Seignette, an apothecary of La Rochelle, France, who was the first to make it (c.1675). Chemically, it is potassium sodium tartrate, KNa (C₄H₄O₆)·4H₂O. It is soluble in water and slightly soluble in alcohol, melts at about 75°C;, has specific gravity 1.79, and exhibits double refraction. It is used in medicine as a mild purgative, often in the form of Seidlitz powders. It is an ingredient of Fehling's solution. It is used in silvering mirrors. Crystals of Rochelle salt are easily grown and are used in piezoelectric devices, e.g., crystal microphones and phonograph pickup cartridges (see piezoelectric effect).

Great Salt Plains Dam, on Salt Fork, a tributary of the Arkansas River, NW Okla., near Enid. The dam was authorized in 1936 as a federal project and completed in 1941. In a salt-encrusted plains area, it provides flood control and impounds a large reservoir that is part of a national wildlife refuge.

Great Salt Lake, shallow body of saltwater, NW Utah, between the Wasatch Range on the east and the Great Salt Lake Desert on the west; largest salt lake in North America. Fed by the Weber, Jordan, and Bear rivers, the lake varies greatly in size and depth according to weather changes. Its average depth ranges from 13 to 24 ft (4 to 7.3 m). From 1,000 sq mi (2,590 sq km) in the period between 1955 and 1975, the lake expanded to its modern maximum of almost 2,500 sq mi (6,477 sq km) by the mid-1980s. Storage of spring run-off in reservoirs to meet domestic and industrial demands for water have contributed to seasonal lake shrinkage. The salt content, nearly 10% at its greatest size, increases as the water level decreases. Magnesium chloride, potash, and common table salt have been commercially extracted from the lake. The heavy brine supports no life except brine shrimp and colonial algae. The Great Salt Lake is a remnant of prehistoric Lake Bonneville, which covered an extensive area of the Great Basin and was once c.1,000 ft (305 m) deep. Its various levels are marked by former beachlines on the mountains and by rich soil deposits on the terraces to the east, where irrigated farming is practiced. Antelope and Fremont islands are the largest islands in the lake; the smaller islands are rookeries for sea gulls and other birds. Promontory Point, a mountainous peninsula 20 mi (32 km) long, extends into the lake from the north; a railroad cutoff on a causeway passes through the neck as it crosses the lake and the Great Salt Lake Desert from Ogden to Lucin, Utah. The Bonneville Salt Flats, in the western part of the desert, is a world-famous automobile racing ground. In 1845 the U.S. explorer John Frémont became the first person to cross the salt desert.

Glauber's salt, common name for sodium sulfate decahydrate, Na₂SO₄·10H₂O; it occurs as white or colorless monoclinic crystals. Upon exposure to fairly dry air it effloresces, forming powdery anhydrous sodium sulfate. Johann Glauber was the first to produce the salt (from Hungarian spring waters). The naturally occurring salt is called mirabilite. Glauber's salt is water soluble, has a salty, bitter taste, and is sometimes used in medicine as a mild laxative; it is also used in dyeing.

Bonneville Salt Flats, desert area in Tooele co., NW Utah, c.14 mi (22.5 km) long and 7 mi (11.2 km) wide. The smooth salt surface of the Flats is ideal for auto racing, and several world land speed records have been set there. The Flats are part of Great Salt Lake Desert, NW Utah, the former bed of Lake Bonneville, whose area once covered c.19,500 sq mi (50,500 sq km). The lake expanded during the late Cenozoic era, then shrank rapidly at the end of the Pleistocene epoch. Six terraces indicate different lake levels. Great Salt Lake, Lake Sevier, and Utah Lake are remnants of Lake Bonneville, which was named for U.S. explorer Benjamin de Bonneville.

Water that makes up the oceans and seas. Seawater is a complex mixture of 96.5percnt water, 2.5percnt salts, and small amounts of other substances. Much of the world's magnesium is recovered from seawater, as are large quantities of bromine. In certain parts of the world, sodium chloride (table salt) is obtained by evaporating seawater. In addition, desalted seawater can theoretically furnish a limitless supply of drinking water, but the high processing costs are prohibitive. Large desalination plants have been built in dry areas along seacoasts in the Middle East and elsewhere to relieve shortages of fresh water.

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or pan or flat or dry lake

Flat-bottomed depression that is periodically covered by water. Playas occur in interior desert basins and adjacent to coasts in arid and semiarid regions. The water that periodically covers the playa slowly filters into the groundwater system or evaporates into the atmosphere, causing the deposition of salt, sand, and mud along the bottom and around the edges of the depression.

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Largely subsurface geologic structure that consists of a vertical cylinder of salt embedded in horizontal or inclined strata. In the broadest sense, the term includes both the core of salt and the strata that surround and are “domed” by the core. Major accumulations of oil and natural gas are associated with salt domes in the U.S., Mexico, the North Sea, Germany, and Romania; domes along the Gulf Coast contain large quantities of sulfur. Salt domes are also major sources of salt and potash on the Gulf Coast and in Germany, and they have been used for underground storage of liquefied propane gas. Storage “bottles,” made by drilling into the salt and then forming a cavity by subsequent solution, have been considered as sites for disposal of radioactive wastes.

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Chemical compound formed when the hydrogen of an acid is replaced by a metal or its equivalent, such as ammonium (NH₄). Typically, an acid and a base react to form a salt and water. Most inorganic salts ionize (see ion) in water solution. Sodium chloride—common table salt—is the most familiar salt; sodium bicarbonate (bicarbonate of soda), silver nitrate, and calcium carbonate are others.

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Naturally occurring sodium chloride (NaCl), common or rock salt. Halite occurs on all continents, in beds that range from a few feet to more than 1,000 ft (300 m) in thickness. Termed evaporite deposits because they formed by the evaporation of saline water in partially enclosed basins, they characteristically are associated with beds of limestone, dolomite, and shale. Halite is found in large deposits in New York and in Russia, France, India, and Canada.

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Negotiations between the U.S. and the Soviet Union aimed at curtailing the manufacture of strategic nuclear missiles. The first round of negotiations began in 1969 and resulted in a treaty regulating antiballistic missiles and freezing the number of intercontinental ballistic missiles and submarine-launched ballistic missiles. It was signed by Leonid Brezhnev and Richard Nixon in 1972. A second round of talks (1972–79), known as SALT II, addressed the asymmetry between the two sides' strategic forces and ended with an agreement to limit strategic launchers (see MIRV). Signed by Brezhnev and Jimmy Carter, it was never formally ratified by the U.S. Senate, though its terms were observed by both sides. Subsequent negotiations took the name Strategic Arms Reduction Talks (START). Seealso intermediate-range nuclear weapons; Nuclear Test-Ban Treaty.

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City (pop., 2000: 181,743), capital of Utah, U.S. Located on the Jordan River, near the southeastern end of Great Salt Lake, it was founded in 1847 by Brigham Young and a group of 148 Mormons as a refuge from religious persecution. It was known as Great Salt Lake City until 1868. It prospered from rail connections to become a hub of western commerce and became the state capital in 1896. The largest city in the state, it lies at an altitude of 4,390 ft (1,338 m). It is a commercial centre for nearby mining operations and has diversified manufacturing industries. It is the headquarters of the Mormon Church of Jesus Christ of Latter-day Saints, which influences the social, economic, political, and cultural life of the state and region. It is the site of the Mormon Temple and Tabernacle. It was the host city of the 2002 Winter Olympic Games.

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Lake, northern Utah, U.S. It is the largest inland body of salt water in the Western Hemisphere and one of the most saline in the world. It fluctuates greatly in size, depending on rates of evaporation and the flow of the rivers into it. Its surface area has varied from about 2,400 sq mi (6,200 sq km) at its highest levels in 1873 and the mid 1980s to about 950 sq mi (2,460 sq km) at its low level in 1963. At times of median water level, it is generally less than 15 ft (4.5 m) deep. Surrounded by stretches of sand, salt land, and marsh, the lake remains isolated, though in recent years it has become important as a source of minerals, as a beach and water-sports attraction, and as a wildlife preserve.

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