What is salt?
Sodium chloride or common salt is the chemical compound NaCl. Salt occurs naturally in many parts of the world as the mineral halite and as mixed evaporates in salt lakes. Seawater has lots of salt and contains an average of 2.6% (by weight) sodium chloride. Underground salt deposits are found in bedded sedimentary layers and in dome deposits. Salt deposits can also be found on the surface, the dried-up residue of ancient seas like the famed Bonneville Salt Flats in Utah.
Sodium chloride crystals are cubic in form. Table salt consists of tiny cubes tightly bound together through ionic bonding of the sodium and chloride ions. It can be modified by temperature. Salt varies in color from colorless, when pure, to white, gray or brownish, typical of rock salt (halite). Chemically, it is 60.663% elemental chlorine (Cl) and 39.337% sodium (Na).
Properties of Pure Sodium Chloride:
Molecular weight - NaCl |
58.4428 |
Atomic weight - Na |
22.989768 (39.337%) |
Atomic weight - Cl |
35.4527 (60.663%) |
Eutectic composition |
23.31% NaCl |
Freezing point of eutectic mixture |
-21.12° C (-6.016°F) |
Crystal form |
Isometric, Cubic |
Color |
Clear to White |
Index of refraction |
1.5442 |
Density or specific gravity |
2.165 (135 lb/ft3) |
Bulk density, approximate (dry, ASTM D 632 gradation) |
1.154 (72 lb/ft3) |
Angle of repose (dry, ASTM D 632 gradation) |
32° |
Melting point |
800.8° C (1,473.4° F) |
Boiling point |
1,465°C (2,669° F) |
Hardness (Moh's Scale) |
2.5 |
Critical humidity at 20 °C, (68° F) |
75.3% |
pH of aqueous solution |
neutral |
Sodium chloride is sold in several different particle sizes (gradation) and forms, depending on the intended end use. Discrete crystals can be seen in rock salt used for deicing. Fine granules are typical of table salt and even finer popcorn salt. Kosher salt, pickling salt and ice cream salt are slightly coarser. Small compressed pellets are used in water softeners and large salt blocks are used as salt licks for livestock. When viewed under strong magnification, all sodium chloride is crystalline. Very large cubic crystals, of two, three or more inches in size, can be seen in some salt mines. They are transparent and cleave into perfect cubes when struck with a hard object.
The purity of salt produced in North America varies depending on the type of salt (evaporated, rock, and solar) and the source. Rock salt typically ranges between 95% and 99% NaCl, and mechanically evaporated salt and solar salt normally exceed 99% NaCl. Evaporated salt made with purified brine has the highest purity, in some cases 99.99% NaCl.
Common salt or sodium chloride is considered by the U.S. Food and Drug Administration as safe for its intended use as a food additive. This GRAS (generally recognized as safe) classification, and the universal use of sodium chloride since antiquity, affirms its safety.
Much of the above information come from The Salt Institute. This industry trade association is the world's foremost source of information on salt. Anyone interested in salt should visit their website at www.saltinstitute.org.
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