A Salt Box

Common salt is art of man's philosophical and religious history. Homer called it divine; Plato declared it a substance dear to gods. The Bible exclaims, "Ye are the salt of the earth." It is the symbol of purity in the Catholic church, it seals Jewish covenants, and it is considered unlucky to spill. (Judas has an overturned salt cellar in front of him in Leonardo Da Vinci's, The Last Supper.) In Roman times those worth their salt were given a salarium, the origin of the word salary. And Rome's major highway was the Via Salaria or Salt Road. Marco Polo even noted salt coins bearing the seal of the Great Khan of Cathay.

The human body contains about eight ounces of salt, which is essential to life. Prior to refrigeration, salt was used a preservative and helped to end the "kill-a-meal-a-day" syndrome. Not surprisingly, salt is the product of the oldest continuously operating mine in the world - the Hallstatt Mine near Salzburg ("Salt Town"), Austria - dating back to the Iron Age, 1000 BC.

Salt is most visible at meal times, but an extremely small proportion is used for direct human consumption. From one-half to two-thirds of the salt output is used in the chemical industry to produce numerous sodium and chlorine chemicals. The most important of these are the chloralkalies - chlorine and caustic soda (sodium hydroxide) - that are extracted from the brine using electrolysis. Salt is used with limestone in the Solvay process to produce soda ash and with sulfuric acid to yield hydrochloric acid and salt cake. In cold winter climates, such as northeastern United States and eastern Canada, salt is spread on the roads as a deicing agent. It is used as a food preservative as well as in a variety of other applications, from the processing of textiles to the manufacture of dyestuffs.

From: Industrial Minerals: Geology and World Deposits, by Peter W. Harben and Robert L. Bates.