History of salt
, also referred to as table salt or by its chemical formula NaCl, is an ionic compound made of sodium and chloride ions. All life has evolved to depend on its chemical properties to survive. It has been used by humans for thousands of years, from food preservation to seasoning. Salt's ability to preserve food was a founding contributor to the development of civilization. It helped to eliminate dependence on seasonal availability of food, and made it possible to transport food over large distances. However, salt was often difficult to obtain, so it was a highly valued trade item, and was considered a form of currency by certain peoples. Many salt roads, such as the via Salaria in Italy, had been established by the Bronze Age.
All through history, availability of salt has been pivotal to civilization. In Britain, the suffix "-wich" in a placename means it was once a source of salt, as in Sandwich and Norwich. The Natron Valley was a key region that supported the Egyptian Empire to its north, because it supplied it with a kind of salt that came to be called by its name, natron. Today, salt is almost universally accessible, relatively cheap, and often iodized.
History
Ancient world
, the earliest known town in Europe, was built around a salt production facility. Located in present-day Bulgaria, the town is thought by archaeologists to have accumulated wealth by supplying salt throughout the Balkans.Salt was of high value to the Jews, Greeks, Tamils, Chinese, Hittites and other peoples of antiquity. Aside from being a contributing factor in the development of civilization, salt was also used in the military practice of salting the earth by various peoples, beginning with the Assyrians.
In the early years of the Roman Republic, with the growth of the city of Rome, roads were built to make transportation of salt to the capital city easier. An example was the Via Salaria, leading from Rome to the Adriatic Sea. The Adriatic, having a higher salinity due to its shallow depth, had more productive solar ponds compared with those of the Tyrrhenian Sea, much closer to Rome. The word "salary" comes from the Latin word for salt. A persistent modern claim that the Roman Legions were sometimes paid in salt is baseless; the word salary ultimately derives from an allowance—salārium—paid to Roman soldiers for the purchase of salt.
s and drilling rig from Qing dynasty Zigong, China extracting brine from deep underground wells.
During the late Roman Empire and throughout the Middle Ages salt was a precious commodity carried along the salt roads into the heartland of the Germanic tribes. Caravans consisting of as many as forty thousand camels traversed four hundred miles of the Sahara bearing salt to inland markets in the Sahel, sometimes trading salt for slaves: Timbuktu was a noted salt and slave market.
Salt in Chinese history was both a driver of technological development and a stable source of revenue for the imperial government.
Cities and wars
Salt has played a prominent role in determining the power and location of the world's great cities. Liverpool rose from just a small English port to become the prime exporting port for the salt dug in the great Cheshire salt mines and thus became the entrepôt for much of the world's salt in the 19th century.Salt created and destroyed empires. The salt mines of Poland led to a vast kingdom in the 16th century, only to be demolished when Germans brought in sea salt. Venice fought and won a war with Genoa over spices. However, Genoese Christopher Columbus and Giovanni Caboto would later destroy the Mediterranean trade by introducing the New World to the market.
Cities, states and duchies along the salt roads exacted heavy duties and taxes for the salt passing through their territories. This practice even caused the formation of cities, such as the city of Munich in 1158, when the then Duke of Bavaria, Henry the Lion, decided that the bishops of Freising no longer needed their salt revenue.
The gabelle—a hated French salt tax—was enacted in 1286 and maintained until 1790. Because of the gabelles, common salt was of such a high value that it caused mass population shifts and exodus, attracted invaders and caused wars.
In American history, salt has been a major factor in outcomes of wars. In the Revolutionary War, the British used Loyalists to intercept Revolutionaries' salt shipments and interfere with their ability to preserve food. During the War of 1812, salt brine was used to pay soldiers in the field, as the government was too poor to pay them with money. Before Lewis and Clark set out for the Louisiana Territory, President Jefferson in his address to Congress mentioned a mountain of salt, 180 miles long and 45 wide, supposed to lie near the Missouri River, which would have been of inconceivable value, as a reason for their expedition.
During India's independence movement, Mohandas Gandhi organized the Salt Satyagraha protest to demonstrate against the British salt tax.
English "-wich towns"
Wich and wych are names associated with brine springs or wells in England. Originally derived from the Latin vicus, meaning "place", by the 11th century use of the 'wich' suffix in placenames was associated with places with a specialised function including that of salt production. Several English places carry the suffix and are historically related to salt, including the four Cheshire 'wiches' of Middlewich, Nantwich, Northwich and Leftwich, and Droitwich in Worcestershire. Middlewich, Nantwich, Northwich and Droitwich are known as the "Domesday Wiches" due to their mention in the Domesday Book, "an indication of the significance of the salt-working towns in the economy of the region, and indeed of the country". Salt was very important to Europe because it was hard to trade with Africa and they needed to produce it themselves.Salt trade
were essential aspects of government revenue in imperial China and retained its significance until 20th century.During modern times, it became more profitable to sell salted food than pure salt. Thus sources of food to salt went hand in hand with salt making. The British controlled saltworks in the Bahamas as well as North American cod fisheries. The search for oil in the late 19th and early 20th centuries used the technology and methods pioneered by salt miners, even to the degree that they looked for oil where salt domes were located.
Salt production
On an industrial scale, salt is produced in one of two principal ways: the evaporation of salt water or by mining. Evaporation can either be solar evaporation or using some heating device.Solar evaporation of seawater
In the correct climate it is possible to use solar evaporation of sea water to produce salt. Brine is evaporated in a linked set of ponds until the solution is sufficiently concentrated by the final pond so that the salt crystallizes on the pond's floor.Open pan production from brine
One of the traditional methods of salt production in more temperate climates is using open pans. In open-pan production, salt brine is heated in large, shallow open pans. The earliest examples of this date back to prehistoric times and the pans were made of either a type of ceramic called briquetage, or lead. Later examples were made from iron. This change coincided with a change from wood to coal for the purpose of heating the brine. Brine would be pumped into the pans and concentrated by the heat of the fire burning underneath. As crystals of salt formed, these would be raked out and more brine added.Closed pan production under vacuum
The open pan salt works has effectively been replaced with a closed pan system where the brine solution is evaporated under a partial vacuum.Salt mines
In the second half of the 19th century, industrial mining and new drilling techniques made the discovery of more and deeper deposits possible, increasing mine salt's share of the market. Although mining salt was generally more expensive than extracting it from brine via solar evaporation of seawater, the introduction of this new source reduced the price of salt due to a reduction of monopolization. Extraction of salt from brine is still heavily used; for example, vacuum salt produced by British Salt in Middlewich has 57% of the UK marketfor salt used in cooking.