Sodium chloride

For sodium in the diet, see Edible salt.

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compoundwith the formulaNaCl. Sodium chloride is the saltmost responsible for the salinity of the oceanand of the extracellular fluidof many multicellular organisms. As the main ingredient in edible salt, it is commonly used as a condimentand food preservative.

Crystal structure

Image:Sodium chloride crystal.png Sodium chloride forms crystalswith cubic symmetry. In these, the larger chloride ionsare arranged in a cubic close-packing, while the smaller sodium ions fill the octahedral gaps between them. Each ion is surrounded by six of the other kind. This same basic structure is found in many other minerals, and is known as the halitestructure.

Biological importance

Sodium chloride is essential to lifeon Earth. Most biological tissuesand body fluidscontain a varying amount of salt. The concentration of sodiumions in the bloodis directly related to the regulation of safe body-fluid levels. Propagation of nerve impulsesby signal transductionis regulated by sodium ions. (Potassium, a metalclosely related to Sodium, is also a major component in the same bodily systems).

0.9% sodium chloride in wateris called a physiological solution because it is isotonic with blood plasma. It is known medically as normal saline. Physiological solution is the mainstay of fluid replacementtherapy that is widely used in medicinein prevention or treatment of dehydration, or as an intravenous therapyto prevent hypovolemicshockdue to blood loss.

Humans are unusual among primatesin secreting large amounts of salt by sweating.

Salt throughout history

Image:SaltCrystaUSGOV.jpg Salt's preservative ability was a foundation of civilization. It eliminated dependency on the seasonal availability of food and allowed travel over long distances. By the Middle Ages, caravansconsisting of as many as forty thousand camelstraversed four hundred miles of the Saharabearing salt, sometimes trading it for slaves.

Until the 1900s, salt was one of the prime movers of national economies and wars. Salt has played a prominent role in determining the power and location of the world's great cities. Timbuktuwas once a huge salt market. Liverpoolrose from just a small Englishport to become the prime exporting port for the salt dug in the great Cheshiresalt mines and thus became the source of the world's salt in the 1800s.

Salt created and destroyed empires. The salt mines of Polandled to a vast kingdom in the 1500s, only to be destroyed when Germans brought sea salt(often, to most of the world, considered 'superior' to rock salt). Venicefought and won a war with Genoaover salt. Genoa, however, had the last laugh. Genovites Christopher Columbusand Giovanni Cabotodestroyed the Mediterranean trade by introducing the New Worldto the market.

Salt was once one of the most valuable commoditiesknown to man. Salt was taxed, from as far back as the 20th century BC in China. In the Roman Empire, salt was sometimes even used as a currency, giving us the term salary("salt money", see below for etymology). The Roman Republicand Empirecontrolled the price of salt, increasing it to raise money for wars, or lowering it to be sure that the poorest citizens could easily afford this important part of the diet. Throughout much of history, it influenced the conduct of wars, the fiscal policies of governments, and even the inception of revolutions.

In the empire of Mali, merchants in 12th-century Timbuktu—the gateway to the SaharaDesert and the seat of scholars—valued salt enough to buy it for its weight in gold; this trade led to the legends of the incredibly wealthy city of Timbuktu, and fueled inflationin Europe, which was exporting the salt.

In later times, for instance during the British colonial period, salt production and transport were controlled in Indiaas a means of generating enormous taxrevenues. This ultimately led to the Salt March to Dandi, led by Mahatma Gandhiin 1930in which thousands of Indians went to the sea to illegally produce their own salt in protest of the British tax on salt.

The salt trade was based on one fact — it is more profitableto sell salted foodstuffs than to sell just salt. Thus sources of food to salt went hand in hand with salt making. Before the salt mines of Cheshirewere discovered, a huge trade in British fishfor French salt existed. This was not a happy accord, for each nation did not want to be dependent on each other. The search for fishand salt led to the Seven Years Warbetween the two. With the British in control of saltworks in the Bahamasand North Americancod, their sphere of influence quickly covered the world. The search for oilin the late 1800sand early 1900sused the technology and methods pioneered by salt miners, even to the degree that they looked for oil where salt domes were located.

In religion

There are thirty-two references to salt in the Bible, the most familiar probably being the story of Lot's wife, who was turned into a pillar of salt when she disobeyed the angelsand looked back at the wicked city of Sodom(Genesis19:26). Jesusalso referred to his followers as the "salt of the earth" (Matthew 5:13), a reference to salt's great value in the ancient world. Most of the time when talking about salt, the Bible is speaking of wisdom or age and wisdom combined.

In the native Japanese religion shinto, salt is seen as "pure" and can be used to purify (bless) locations and people, such as in Sumo Wrestling.

Production and use

Image:Dead-Sea---Salt-Evaporation-Ponds.jpg Nowadays, salt is produced by evaporationof seawateror brinefrom other sources, such as brine wells and salt lakes, and by mining rock salt, called halite.

While most people are familiar with the many uses of salt in cooking, they might be unaware that salt is used in a plethora of applications, from manufacturingpulp and paper to setting dyes in textiles and fabric, to producing soapsand detergents. In most of Canada and the northern USA, large quantities of rock salt are used to help clear highways of ice during winter, although "Road Salt" loses its melting ability at temperatures below -15°C to -20°C (5°F to -4°F).

Salt is also the raw material used to produce chlorinewhich itself is required for the production of many modern materials including PVCand pesticides.

Flavor enhancer

Main article: Edible salt

Salt is commonly used as a flavor enhancerfor foodand has been identified as one of the basic tastes. Unfortunately, given its history, this has resulted in large sections of the developed world ingesting salt massively in excess of the required intake, particularly in colder climates where the required intake is much lower. This causes elevated levels of blood pressurein some, which in turn is associated with increased risks of heart attackand stroke.

Biological uses

Many microorganismscannot live in an overly salty environment: water is drawn out of their cellsby osmosis. For this reason salt is used to preservesome foods, such as smoked bacon or fish. It has also been used to disinfect wounds.

Image:SaltMounds.jpeg

De-icing

While salt was a scarce commodity in history, industrialised production has now made salt plentiful. About 51% of world output is now used by cold countries to de-iceroads in winter, see Grit bin. This works because salt and water form a eutecticmixture that has about a 10°Clower freezing pointthan pure water: the ions prevent regular ice crystals from forming (below −10°C salt will not prevent water from freezing). Concerns are arising that this use may be harmful to the environment though, and, in Canada, norms were developed to minimize the use of salt in de-icing.

Additives

The salt one buys for consumption today is not purely sodium chloride as most people assume. In 1911Magnesium carbonatewas first added to salt to make it flow more freely. In 1924trace amounts of iodinein form of sodium iodide, potassium iodide or potassium iodate were first added, creating iodized salt to reduce the incidence of simple goiter.

Other facts

Image:SEM sodium chloride crystal (300x).jpg

• Salty soilis generally unfit for agriculture, hence the practice of salting the earth.

• The superstition that spilling salt brings bad luck is said to have originated with the overturned salt cellar in front of Judas Iscariot at the Last Supper, immortalised in Leonardo Da Vinci’sfamous painting.

• Due to its high concentrationof salt, the Dead Seahas such a high densitythat some objects which are not normally buoyant can float on its surface. Humansfloat easily, having a density slightly less than that of pure water. (Only 8% of the salt in the Dead Sea is sodium chloride; 53% is magnesium chloride, 37% is potassium chloride.)

• The cities of Cincinnati, Detroitand Hutchinsonare on top of active salt mines.

• The Third Reichstored vast amounts of money, paintings and artworks in salt minesand many important documents and items continue to be stored in former salt mines to this day. They are also used to store nuclear waste.

See also

• Biosalinity
• Black salt
• Edible salt
• Salinity
• Soap

External links

• Salt Institutewebsite
• Salt Archivewebsite
• Videoof rotating rock salt unit cell (divx, 378kb)bg:??????? ??????

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It uses material from the http://en.wikipedia.org/wiki/Sodium+chloride Wikipedia article Sodium chloride.