Synthetic uses
Salt is also the raw material used to produce chlorine which itself is required for the production of many modern materials including PVC and pesticides. Industrially, elemental chlorine is usually produced by the electrolysis of sodium chloride dissolved in water. Along with chlorine, this chloralkali process yields hydrogen gas and sodium hydroxide, according to the chemical equation
Sodium chloride is used in other chemical processes for the large-scale production of compounds containing sodium or chlorine. In the Solvay process, sodium chloride is used for producing sodium carbonate and calcium chloride. In the Mannheim process and in the Hargreaves process, it is used for the production of sodium sulfate and hydrochloric acid.
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 and can also be used to detach leeches that have attached themselves to feed. It has also been used to disinfect wounds.
Optical uses
Pure NaCl crystal is an optical compound with a wide transmission rage from 200nm to 20um. It was often used in the infrared spectrum range and it is still used some time.
NaCl crystal is soft, hygroscopic and cheap. This limits its application to protected environment or for short term uses ( prototyping ). Exposed to free air NaCl optics will "rot".
Today other crystals much more tough like ZnSe has overcome NaCl (for the IR spectral range).
Household uses
Since at least medieval times, people have used salt as a cleansing agent rubbed on household surfaces.
Biological functions
In humans, a high-salt intake has long been known to generally raise blood pressure, especially in certain individuals. More recently, it was demonstrated to attenuate Nitric Oxide production. Nitric oxide (NO) contributes to vessel homeostasis by inhibiting vascular smooth muscle contraction and growth, platelet aggregation, and leukocyte adhesion to the endothelium [[1]]
Dietary sodium and cardiovascular and renal disease risk factors: dark horse or phantom entry? http://ndt.oxfordjournals.org/cgi/reprint/23/7/2133
Crystal structure
The crystal structure of sodium chloride. Each atom has six nearest neighbors, with octahedral geometry.Sodium chloride forms crystals with cubic symmetry. In these, the larger chloride ions, shown to the right as green spheres, are arranged in a cubic close-packing, while the smaller sodium ions, shown to the right as silver spheres, fill the octahedral gaps between them.
Each ion is surrounded by six ions of the other kind. This same basic structure is found in many other minerals, and is known as the halite structure. This arrangement is known as cubic close packed (ccp). It can be represented as two interpenetrating face-centered cubic (fcc) lattices, or one fcc lattice with a two atom basis. It is most commonly known as the rocksalt crystal structure.
It is held together with an ionic bond and electrostatic forces.
Road salt
While salt was once a scarce commodity in history, industrialized production has now made salt plentiful. About 51% of world output is now used by cold countries to de-ice roads in winter, both in grit bins and spread by winter service vehicles. This works because salt and water form a eutectic mixture. Adding salt to water will lower the freezing temperature of the water, depending on the concentration. The salinity (S) of water is measured as grams salt per kilogram (1000g) water, and the freezing temperatures are as follows.
