In addition to the many familiar domestic uses of salt, more dominant applications of the approximately 250 million tonnes per year production (2008 data) include chemicals and de-icing.
Chemical functions Salt is used, directly or indirectly, in the production of many chemicals, which consumes most of the world's production. It is used to
flocculate and increase the
density of the drilling fluid to overcome high downwell gas pressures. Whenever a drill hits a salt formation, salt is added to the drilling fluid to saturate the solution in order to minimize the dissolution within the salt stratum. to promote "salting out" of dyestuff precipitates, and to blend with concentrated dyes to increase yield in dyebaths and make the colors look sharper. One of its main roles is to provide the positive ion charge to promote the absorption of negatively charged ions of dyes. The omnipresence of salt in coastal areas poses a problem in any
coating application, because trapped salts cause great problems in adhesion. Naval authorities and ship builders monitor the salt concentrations on surfaces during construction. Maximal salt concentrations on surfaces are dependent on the authority and application. The
IMO regulation is mostly used and sets salt levels to a maximum of 50 mg/m2 soluble salts measured as sodium chloride. These measurements are done by means of a
Bresle test. Salinization (increasing salinity, aka
freshwater salinization syndrome) and subsequent increased metal leaching is an ongoing problem throughout North America and European fresh waterways. In highway de-icing, salt has been associated with
corrosion of bridge decks, motor vehicles, reinforcement bar and wire, and unprotected steel structures used in road construction.
Surface runoff, vehicle spraying, and windblown salt also affect soil, roadside vegetation, and local surface water and groundwater supplies. Although evidence of environmental loading of salt has been found during peak usage, the spring rains and thaws usually dilute the concentrations of sodium in the area where salt was applied.
Substitution Some agencies are substituting
beer,
molasses, and
beet juice instead of road salt. Airlines utilize more
glycol and
sugar rather than salt-based solutions for deicing.
Food industry and agriculture Salt is added to food, either by the food producer or by the consumer, as a flavor enhancer, preservative, binder,
fermentation-control additive, texture-control agent, and color developer. The salt consumption in the food industry is subdivided, in descending order of consumption, into other food processing, meat packers,
canning, baking, dairy, and grain mill products. Salt is added to promote color development in bacon, ham and other processed meat products. As a preservative, salt inhibits the growth of bacteria. Salt acts as a binder in
sausages to form a binding gel made up of meat, fat, and moisture. Salt also acts as a flavor enhancer and as a
tenderizer.
Medicine Sodium chloride is used together with water as one of the primary solutions for
intravenous therapy.
Nasal spray often contains a
saline solution. Sodium chloride is also available as an oral tablet and is taken to treat low sodium levels.
Firefighting Sodium chloride is the principal extinguishing agent in dry-powder
fire extinguishers that are used on combustible metal fires, for metals such as magnesium, zirconium, titanium, and lithium (Class D extinguishers). The salt forms an oxygen-excluding crust that smothers the fire.
Cleanser Since at least
medieval times, people have used salt as a cleansing agent rubbed on household surfaces. It is also used in many brands of
shampoo and toothpaste and is commonly used to deice driveways, parking lots, and walkways.
Infrared optics Sodium chloride crystals have a
transmittance of at least 90% (through 1 mm) for
infrared light having wavelengths in the range 0.2–18
μm. They were used in optical components such as windows and lenses, where few non-absorbing alternatives existed in that spectral range. While inexpensive, NaCl crystals are soft and
hygroscopic – when exposed to the water in ambient air, they gradually cover with "frost". This limits application of NaCl to dry environments, vacuum-sealed areas, or short-term uses such as prototyping. Materials that are mechanically stronger and less sensitive to moisture, such as
zinc selenide and
chalcogenide glasses, are more widely used than NaCl. ==Chemistry==