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In chemistry, a salt is a chemical compound composed of cations (positively charged ions) bound to anions (negatively charged ions). They are typically the product of a chemical reaction between a base and an acid, the base contributing the cation and the acid contributing the anion.
A familiar example is table salt, in common usage simply called salt. It is the specific salt sodium chloride, and is described thoroughly in that article. Its formula is NaCl and it is the product of the base sodium hydroxide, NaOH and hydrochloric acid, HCl. Table salt is derived by purification from sea salt, by mining directly from pockets of salt trapped in impervious rock (see Salt mine) or by the boiling of fossile saline solutions.
In general, salts are ionic compounds which form crystals. They are usually soluble in water, where the two ions separate. Salts typically have a high melting point, low hardness, and low compressibility. If molten or dissolved in water, they conduct electricity.
Salts are named according to their constituent ions. The cationic components, often metal ions or ammonium, are given first, followed by the anionic components. Cations are often named according to the their conjugate acid:
- acetates are the salts of acetic acid
- carbonates are the salts of carbonic acid
- chlorides are the salts of hydrochloric acid
- cyanates are the salts of cyanic acid
- nitrates are the salts of nitric acid
- nitrites are the salts of nitrous acid
- phosphates are the salts of phosphoric acid
- sulfates are the salts of sulfuric acid
SaltSalt is an essential element to human existence since our bodies require salt in order to function properly. The concentration of sodium ions in the blood is directly related to the regulation of safe body fluid levels.
And while we're all familiar with the many uses of salt in cooking, we may not be aware that salt is used in a plethora of applications. From manufacturing pulp and paper to setting dyes in textiles and fabric, and producing soaps and detergents, just to name a few.
The first written reference to salt is found in the Book of Job, recorded about 2,250 BC. There are 31 other 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 was one of the most valuable commodities known to man. 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, lowering it to be sure that the poorest citizens could easily afford this important part of the diet.
Salt's preservative ability was also a foundation of civilization. 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 40,000 camels traversed 400 miles of the Sahara bearing salt, sometimes trading it for slaves.
- Rome's soldiers were sometimes paid in salt, salarium argentum, from which we take our English word, “salary”.
- The Latin word for salt, "sal," the French word "solde" (meaning pay) and "soldier", are similarly related.
- “He is not worth his salt”, is a common expression. It originated in ancient Greece where salt was traded for slaves.
- 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, immortalized in Leonardo Da Vinci’s famous painting.
- The salting of greens, preferred by the Romans, led to the Latin "sal" (salt) as an integral part of "salad."
- Magnesium carbonate was first added to salt in 1911 to make it flow more freely.
- Iodine was first added in 1924, creating iodized salt for the table in order to reduce the incidence of simple goiter.