Sodium chloride

</table> Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with formula Na Cl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms. It is commonly used as a flavour enhancer and preservative for food.

**Properties**
General
Name	Sodium chloride
Chemical formula	Na Cl
Appearance	White or clear solid
CAS-number	7647-14-5
Physical
Formula weight	58.4 amu
Melting point	1074 K (801 °C)
Boiling point	1738 K (1465 °C)
Density	2.2 ×10³ kg/m³
Crystal structure	f.c.c.
Solubility	35.9 g in 100g water
Thermochemistry
Δ_fH⁰_gas	-181.42 kJ/mol
Δ_fH⁰_liquid	-385.92 kJ/mol
Δ_fH⁰_solid	-411.12 kJ/mol
S⁰_{gas, 1 bar}	229.79 J/mol·K
S⁰_{liquid, 1 bar}	95.06 J/mol·K
S⁰_solid	72.11 J/mol·K
Safety
Ingestion	Dangerous in large quantities
Inhalation	May cause irritation
Skin	May cause irritation
Eyes	May cause irritation
More info	Hazardous Chemical Database (http://ull.chemistry.uakron.edu/erd/chemicals/10/9918.html)
SI units were used where possible. Unless otherwise stated, standard conditions were used. Disclaimer and references </font>

Contents

1 Biological importance

2 Salt throughout history

3 Production and use

3.1 Flavour enhancer
3.2 Biological uses
3.3 De-icing
3.4 Additives

Biological importance

Sodium chloride is essential to life on Earth. Most biological tissues and body fluids contain a varying amount of salt. The concentration of sodium ions in the blood is directly related to the regulation of safe body-fluid levels. Propagation of nerve impulses by signal transduction is regulated by sodium ions.

0.9% sodium chloride in water is called a physiological solution because it is isoosmotic with blood plasma. It is known medically as normal saline. Physiological solution is the mainstay of fluid replacement therapy that is widely used in medicine in prevention or treatment of dehydration.

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

Salt throughout history

Salt crystal

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 angels and looked back at the wicked city of Sodom.

Salt's preservative ability was also a foundation of civilisation. It eliminated dependency on the seasonal availability of food and allowed travel over long distances. By the Middle Ages, caravans consisting of as many as forty thousand camels traversed four hundred miles of the Sahara bearing salt, sometimes trading it for slaves.

Salt was once one of the most valuable commodities known to man. In the Roman Empire, salt was sometimes even used as a currency. Throughout much of history, it influenced the conduct of wars, the fiscal policies of governments, and even the inception of revolutions. Salt was taxed, from as far back as the 20th century BC in China. Merchants in 12th-century Timbuktu—the gateway to the Sahara Desert and the seat of scholars—valued salt as highly as books and gold. The Roman Republic and Empire controlled 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.

The empire of Mali, in Africa, 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 inflation in Europe, which was exporting the salt.

In later times, for instance during the British colonial period, salt production and transport were controlled in India as a means of generating enormous tax revenues. This ultimately led to a march led by Mahatma Gandhi in 1930 in which thousands of Indians went to the sea to produce their own salt in protest of the British tax on salt.

Production and use

Jordanian salt evaporation ponds at the south end of the Dead Sea

Nowadays, salt is produced by evaporation of seawater or brine from 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 manufacturing pulp and paper to setting dyes in textiles and fabric, to producing soaps and detergents.

Flavour enhancer

Salt is commonly used as a flavour enhancer for food and has been identified as one of the basic tastes. Ironically, 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 pressure in some, which in turn is associated with increased risks of heart attack and stroke.

Biological uses

Many microorganisms cannot live in an overly salty environment: water is drawn out of their cells by osmosis. For this reason salt is used to preserve some foods, such as smoked bacon or fish. It has also been used to disinfect wounds.

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 northern countries to de-ice roads in winter. This works because salt water has a lower freezing point than pure water: the ions prevent regular ice crystals from forming. Concerns are arising that this use may be harmful to the environment though, and, in Canada, norms were developed to minimise 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 1911 water was first added to salt to make it flow more freely. In 1924 trace amounts of iodine in form of ...., ..... or ..... were first added, creating iodide salt to decrease the incidence of simple gouter.

Crystal structure

Sodium chloride forms crystals with cubic symmetry. In these, the larger chloride ions are 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 halite structure.

Etymology

Salt has also had influence on the English language. Many of its effects can still be seen today. Words and expressions related to salt mostly come from the Roman and Greek civilizations when salt was still a valuable commondity.

The Latin word for salt, "sal," the French words "solde" (meaning pay) and "soldier", are all related. In Italian "soldi" means money, "soldato" is a soldier.

Roman soldiers were given a particular allowance to purchase salt (Latin: sal), salarium argentum, from which we take our English word "salary". The Romans also preferred salting of their greens, which led to the Latin word for salt being integrated in the word "salad".

Also the expression "He is not worth his salt" can be traced back to ancient Greece where salt was traded for slaves.

Random facts

Salty soil is generally unfit for agriculture, hence the practice of salting the earth in ancient times.

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’s famous painting.

Due to its high concentration of salt, the Dead Sea has such a high density that some objects which are not normally buoyant can float on its surface. Humans float easily, having a density slightly less than that of pure water.

The cities of Cincinnati and Detroit are on top of active salt mines.

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

External links

Salt Institute (http://www.saltinstitute.org) website
Salt Archive (http://salt.org.il/news_arch.htm) website