sodium thiosulfate, Na₂S₂O₃, colorless crystalline compound that is more familiar as the pentahydrate, Na₂S₂O₃·5H₂O, an efflorescent, monoclinic crystalline substance also called sodium hyposulfite or "hypo." Sodium thiosulfate is readily soluble in water and is a mild reducing agent. Because it dissolves silver salts, its major use is in photography for developing film. It is also used in chrome-tanning leather and in chemical manufacture. Sodium thiosulfate is produced chiefly from liquid waste products of sodium sulfide or sulfur dye manufacture. It is also produced from sodium carbonate, sulfur dioxide, and sulfur by a process that involves several steps.

sodium tetraborate decahydrate: see borax.

sodium sulfate, chemical compound, Na₂SO₄. It is a white, orthorhombic crystalline compound at ordinary temperatures; above 100°C; it assumes a monoclinic structure, and above about 250°C; it assumes a hexagonal structure. Sodium sulfate is soluble in cold water and very soluble in hot water. It forms two hydrates; the decahydrate is Glauber's salt. Anhydrous sodium sulfate is found in nature as the mineral thenardite. The major commercial source of sodium sulfate is salt cake, a byproduct of the production of hydrochloric acid from sodium chloride (common salt) by treatment with sulfuric acid. It is obtained (with other chemicals) by evaporation of natural brines. It is also obtained as a byproduct of viscose rayon manufacture and in several other, less important ways. The principal use of sodium sulfate is in processing wood pulp for making kraft paper. It is also used in glass manufacture, textile dyeing, and synthetic detergents.

sodium silicate, any one of several compounds containing sodium oxide, Na₂O, and silica, Si₂O, or a mixture of sodium silicates. Sodium orthosilicate is Na₄SiO₄ (or 2Na₂O·SiO₂); sodium metasilicate is Na₂SiO₃ (or Na₂O·SiO₂); sodium disilicate is Na₂Si₂O₅ (or Na₂O·2SiO₂); sodium tetrasilicate is Na₂Si₄O₉ (or Na₂O·4SiO₂). All these compounds are transparent, glassy or crystalline solids that have high melting points (above 800°C;) and are water soluble. They are produced chiefly by fusing sand and sodium carbonate in various proportions. The product is commonly known as water glass. The greatest single use of sodium silicates is as a raw material for making silica gel.

sodium nitrate, chemical compound, NaNO₃, a colorless, odorless crystalline compound that closely resembles potassium nitrate (saltpeter or niter) in appearance and chemical properties. It is soluble in water, alcohol, and liquid ammonia. Sodium nitrate is also called soda niter or Chile saltpeter. It is found naturally in large deposits in arid regions of Chile, Peru, Argentina, and Bolivia as caliche, a crude, impure nitrate rock or gravel. Natural deposits are the major source of sodium nitrate; it is also obtained in small amounts as a byproduct of chlorine production by the nitrosyl chloride process, in which sodium chloride (common salt) is reacted with nitric acid. Sodium nitrate is used in making potassium nitrate, fertilizers, and explosives. It was formerly an important raw material for the production of nitric acid.

sodium hydroxide, chemical compound, NaOH, a white crystalline substance that readily absorbs carbon dioxide and moisture from the air. It is very soluble in water, alcohol, and glycerin. It is a caustic and a strong base (see acids and bases). Commonly known as caustic soda, lye, or sodium hydrate, it is available commercially in various solid forms, e.g., pellets, sticks, or chips, and in water solutions of various concentrations; both solid and liquid forms vary in purity. The major use of sodium hydroxide is as a chemical and in the manufacture of other chemicals; because it is inexpensive, it is widely used wherever a strong base is needed. It is also used in producing rayon and other textiles, in making paper, in etching aluminum, in making soaps and detergents, and in a wide variety of other uses. The principal method for its manufacture is electrolytic dissociation of sodium chloride; chlorine gas is a coproduct. Small amounts of sodium hydroxide are produced by the soda-lime process in which a concentrated solution of sodium carbonate (soda) is reacted with calcium hydroxide (slaked lime); calcium carbonate precipitates, leaving a sodium hydroxide solution.

sodium hydrogen carbonate: see sodium bicarbonate.

sodium hydrate: see sodium hydroxide.

sodium chloride, NaCl, common salt.

Properties

Sodium chloride is readily soluble in water and insoluble or only slightly soluble in most other liquids. It forms small, transparent, colorless to white cubic crystals. Sodium chloride is odorless but has a characteristic taste. It is an ionic compound, being made up of equal numbers of positively charged sodium and negatively charged chloride ions. When it is melted or dissolved in water the ions can move about freely, so that dissolved or molten sodium chloride is a conductor of electricity; it can be decomposed into sodium and chlorine by passing an electrical current through it (see electrolysis).

Natural Occurrence and Commercial Preparation

Nearly all chemical compounds that contain either sodium or chlorine are ultimately derived from salt. Salt is widely and abundantly distributed in nature. It makes up nearly 80% of the dissolved material in seawater, and is the greater part of dissolved matter in the Dead Sea, the Great Salt Lake, and in salt wells in various parts of the world. It is also widely distributed in solid form. The mineral halite is pure salt. Rock, or mineral, salt is usually less pure; it is found in large deposits in the United States, notably in New York, Michigan, Ohio, Kansas, Texas, and Louisiana, and also in Great Britain, France, Germany, Russia, China, and India.

The manufacture and use of salt is one of the oldest chemical industries. Salt is mined from deposits or is obtained as a brine by introducing water into the deposits to dissolve the salt and then pumping the solution to the surface. Salt is also obtained by evaporation of seawater, usually in shallow basins warmed by sunlight; salt so obtained was formerly called bay salt, and is now often called sea salt or solar salt. Most salt for table use is obtained from seawater. It is usually not pure sodium chloride—it may contain natural impurities that provide dietary minerals, or small amounts of other substances (e.g., magnesium carbonate, hydrated calcium silicate, or tricalcium phosphate) may be added to prevent lumping.

Biological Importance and Uses

Salt is important in many ways. It is an essential part of the diet of both humans and animals and is a part of most animal fluids, such as blood, sweat, and tears. It aids digestion by providing chlorine for hydrochloric acid, a small but essential part of human digestive fluid. Persons with hypertensive heart disease often must restrict the amount of salt in their diet.

Salt is widely used as a seasoning for foods and is used in curing meats and preserving fish and other foods. Iodized table salt usually contains small amounts of potassium iodide, sodium carbonate, and sodium thiosulfate. As a chemical salt is used in making glass, pottery, textile dyes, and soap. It is used in large amounts to melt ice and snow on streets and highways. The major use of salt is as a raw material for the production of chlorine, sodium metal, and sodium hydroxide; it is also used in large amounts in the Solvay process for making sodium carbonate. Historically, salt has been used as money; a high tax on salt was a contributing cause of the French Revolution.

sodium carbonate, chemical compound, Na₂CO₃, soluble in water and very slightly soluble in alcohol. Pure sodium carbonate is a white, odorless powder that absorbs moisture from the air, has an alkaline taste, and forms a strongly alkaline water solution. It is one of the most basic industrial chemicals. Sodium carbonate decahydrate, Na₂CO₃·10H₂O, is a colorless, transparent crystalline compound commonly called sal soda or washing soda. Because seaweed ashes were an early source of sodium carbonate, it is often called soda ash or, simply, soda. The Solvay process provides most sodium carbonate for industrial use. It is found in large natural deposits and is mined in Wyoming; it is also recovered (with other chemicals) from lake brines in California. The principal uses of sodium carbonate are in the manufacture of glass and the production of chemicals. It is also used in processing wood pulp to make paper, in making soaps and detergents, in refining aluminum, in water softening, and in many other applications. The Leblanc process, the first successful commercial process for making soda, is no longer used in the United States but played a major role in the Industrial Revolution.

sodium bicarbonate or sodium hydrogen carbonate, chemical compound, NaHCO₃, a white crystalline or granular powder, commonly known as bicarbonate of soda or baking soda. It is soluble in water and very slightly soluble in alcohol. It evolves carbon dioxide gas when heated above about 50°C;, a property made use of in baking powder, of which it is a component. It is also decomposed by most acids; the acid is neutralized and carbon dioxide is given off. The major use of sodium bicarbonate is in foods, e.g., baked goods. It is used in effervescent "salts" and is sometimes used medically to correct excess stomach acidity. It is also used in several kinds of fire extinguishers. Although it is an intermediate product in the Solvay process for making sodium carbonate, it is more economical to prepare it from purified sodium carbonate than to purify the intermediate. Because the bicarbonate is less soluble than the carbonate, carbon dioxide gas is bubbled into a saturated solution of pure carbonate, and the bicarbonate precipitates out to be collected and dried.

sodium benzoate or benzoate of soda, chemical compound, C₆H₅CO₂Na, colorless or white crystalline, aromatic compound; the sodium salt of benzoic acid. It is soluble in water and is used as a preservative in foods and beverages; because it is poisonous, the concentration is limited by law to 0.1%.

sodium, a metallic chemical element; symbol Na [Lat. natrium]; at. no. 11; at. wt. 22.98977; m.p. 97.81°C;; b.p. 892.9°C;; sp. gr. 0.971 at 20°C;; valence +1. Sodium is a soft, silver-white metal. Extremely reactive chemically, it is one of the alkali metals in Group 1 of the periodic table. Like potassium, which it closely resembles, it oxidizes rapidly in air; it also reacts violently with water, liberating hydrogen (which may ignite) and forming the hydroxide. It must be stored out of contact with air and water and should be handled carefully. Sodium combines directly with the halogens. The metal is usually prepared by electrolysis of the fused chloride (the Downs process); formerly, the chief method of preparation was by electrolysis of the fused hydroxide (the Castner process). Metallic sodium has limited use. It is used in sodium arc lamps for street lighting; pure or alloyed with potassium, it has found use as a heat-transfer liquid, e.g., in certain nuclear reactors. It is used principally in the manufacture of tetraethyl lead (a gasoline antiknock compound) and of sodamide, NaNH₂, sodium cyanide, NaCN, sodium peroxide, Na₂O₂, and sodium hydride, NaH. Sodium compounds are extensively used in industry and for many nonindustrial purposes. Among the most important compounds are chloride (common salt, NaCl), bicarbonate (baking soda, NaHCO₃), carbonate (soda ash, or washing soda, Na₂CO₃), hydroxide (caustic soda, or lye, NaOH), nitrate (Chile saltpeter, NaNO₃), thiosulfate (hypo, Na₂S₂O₃·5H₂O), phosphates, and borax (Na₂B₄O₇·10H₂O). Sodium hydroxide is used wherever a cheap alkali is needed, for example, in making soap. Substances containing sodium impart a characteristic yellow color to a flame. Because of its activity sodium is not found uncombined in nature. It occurs abundantly and widely distributed in its compounds, which are present in rocks and soil, in the oceans, in salt lakes, in mineral waters, and in deposits in various parts of the world. Sodium compounds are found in the tissues of plants and animals. Sodium is an essential element in the diet, but some people must limit the amount of sodium in their food for medical reasons. Discovery of sodium is usually credited to Sir Humphry Davy, who prepared the metal from its hydroxide in 1807; its compounds have been known since antiquity.

Atomic Number:	Atomic Number: 11
Atomic Symbol:	Atomic Symbol: Na
	Name of Element: Sodium
Atomic Weight:	Atomic Weight: 22.98977
Electron Configuration:	Electron Configuration: 2 · 8 · 1

or tincal

Sodium tetraborate decahydrate (Na₂B₄O₇ ·10H₂O), a soft, light, colourless crystalline mineral used as a component of glass and pottery glazes in the ceramics industry, as a solvent for metal-oxide slags in metallurgy, as a flux in welding and soldering, and as a fertilizer additive, a soap supplement, a disinfectant, a mouthwash, and a water softener. About 50percnt of the world's supply comes from southern California deserts, including Death Valley.

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White crystalline substance, a sodium salt of the amino acid glutamic acid. MSG is used to intensify the natural flavour of meats and vegetables. It elicits a unique taste, called in Japan umami, different from the four basic tastes. Originally derived from seaweed and first used in Japan in 1908, it has become a common ingredient in Chinese and Japanese cooking. MSG in large amounts may have physical effects, including an allergic reaction commonly called “Chinese restaurant syndrome.”

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Chemical element, one of the alkali metals, chemical symbol Na, atomic number 11. A very soft, silvery white metal, the sixth most abundant element on Earth, it occurs mainly as halite, never free. Extremely reactive, it is used as a chemical reagent and raw material, in metallurgy, as a heat exchanger (in nuclear power generators and certain types of engines), and in sodium-vapour lamps (see electric discharge lamp). Sodium is essential for life but rarely deficient in diets; high intake is linked to hypertension. Sodium in compounds, many of great industrial importance (including bicarbonate of soda, caustic soda, sodium nitrate [Chile saltpetre], and sodium chloride), has valence 1. Sodium carbonate, one of the four most important basic chemical commodities, is used in making glass, detergents, and cleansers. Sodium hypochlorite, familiar as household bleach, is also used to bleach paper pulp and textiles, to chlorinate water, and in some medicines. The sulfate is used in the kraft process and also used to make paperboard, glass, and detergents. The thiosulfate (hyposulfite, or “hypo”) is used to developed photographs.

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