Salt Research Paper

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Salt is an essential nutrient but harmful when consumed to excess. The abundance or lack of salt in various locations made it a valuable, traded commodity throughout history. After 1800, salt became a part of manufacturing—for alkali, analine dyes, and rayon, for instance— and more recently for melting snow and ice. More than half of the total amount of salt produced annually is now destined for industrial use.

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Salt (chemical compound NaCl) is essential for human life. The cells of our bodies exist in a bath of salty fluids, and since we excrete salt by sweating, urinating, and spitting it is necessary to take in appropriate amounts of salt to maintain a steady concentration in our bloodstreams. Since other animals share our salty bodies, a diet rich in meat supplies enough salt to replace losses, but diets that consist almost wholly of grain and other vegetable foods lack enough salt to maintain the salt balance. Resulting shortage manifests itself in a persistent craving for mineral salt, wherever it can be found.

But salt is also an addiction. People who get used to adding salt to their food soon find unsalted food flat and tasteless. This is not usually harmful since kidneys excrete excessive salt into the urine, but a lifetime of eating lots of salt can sometimes bring on dangerously high blood pressure. In practice, consuming some salt is a necessity for vegetable eaters but most of the table salt people use today and have consumed for centuries is over and above what our bodies actually require.

Salt in Early History

As long as humans lived as hunters and gatherers, the meat in their diet meant that salt intake was adequate to their bodily needs. But when settled farming villages arose in different parts of the world, beginning about 11,000 years ago, much enlarged human populations soon killed off most wild game animals within reach, so communities came to depend mainly on vegetable foods and had to find ways to supplement them with small but essential quantities of mineral salt.

Fortunately, salt is common. The oceans constitute the Earth’s most obvious salt reservoir; but salt lakes, salty earth and salt springs exist in desert and some other inland locations. But from the point of view of farmers, geography played a nasty trick on them, since where rain fell regularly and crops grew best, salt was thoroughly leached from surface soils, and carried off to the sea in streams. So in well-watered landscapes local salt supplies were hard or impossible to find.

Just how local populations coped with this problem in Neolithic times is completely unknown, and written records surviving from early civilizations have nothing to say about salt either. But we do know that durable precious objects like gems, shells, flint and obsidian traveled across hundreds of miles in Neolithic times and when the domestication of donkeys permitted caravan trade to get organized, beginning perhaps about 5000 BCE, the radius and regularity of overland trade exchanges increased. So there is every reason to believe that salt and other consumables, like mood-altering drugs, were also exchanged across long distances from the time farming populations first began to feel the craving for supplies of mineral salt.

In Southwest Asia, where wheat and barley farming originated, the closest and richest source of mineral salt was the Dead Sea shore, and it is probably not an accident that Jericho, situated on the Jordan River, and controlling the best route to the Dead Sea, is the earliest fortified site archaeologists have discovered. Dues in kind collected from travelers passing through on their way to gather salt from the shore of the Dead Sea may well have enriched Jericho’s rulers and done much to sustain the stronghold they built about 8000 BCE.

Nothing comparably suggestive about long-distance salt trade is known about other early centers of agriculture. But millet farmers in China and Africa, root and rice farmers in Southeast Asia, corn, squash and bean farmers in Mexico, potato and quinoa farmers in Peru all needed mineral salt to supplement their diets as much or more than the wheat and barley farmers of Southwest Asia did. That is because the Southwest Asian cereal farmers acquired a more diversified array of domesticated animals than others, and so had more meat as well as better transport at their disposal.

When what we call civilization brought states and cities and radical differentiation among occupational specialists into being, beginning about 3500 BCE, the salt trade surely grew, if only because larger human populations continued to depend on the crops village farmers produced. But for a long time there is little or no written or archaeological evidence of salt transport and trade that anyone can point to.

Yet we can surmise that where concentrations of mineral salt were not available on land surfaces, people soon learned how to tap the vast stores of salt dissolved in seas and oceans. That required artificial arrangements to construct shallow ponds of seawater, and then allow the sun’s heat to evaporate the water until the salt became too concentrated to remain dissolved. It was not hard to discover this technique, since salt is deposited naturally on the seashore wherever natural pools evaporate in summer time. Artificial pond building and tending was therefore probably invented many times over along suitably warm and dry coastlines. Mediterranean and Indian Ocean coasts were especially well suited to salt production, and we can assume that as the technique became familiar, adequate sources of salt for needy farmers were in fact created by deliberate action. After all, it only needed patience to produce mineral salt dependably once picks and shovels had shaped a suitably shallow pond and closed off its inlet.

Salt as a Trading Commodity

Around the shores of the Mediterranean, the practice of evaporating sea salt probably established itself with the spread of agriculture itself. Later, when farming also established itself further north in Europe, where climate was wetter and evaporation slower, it was too cool and it rained too much to allow reliable salt production through evaporation. Instead, first peddlers then ships began to carry Mediterranean salt to the northlands. Records of the salt trade begin to appear in medieval times. By then northerners depended for most of their salt on imports from Mediterranean saltpans.

We know far less about salt production along the coasts of the Indian and Pacific oceans. Still it is very likely that the practice of sea water evaporation spread very widely there within climatic limits, and supplied inland farmers with the salt they needed either through peddling, or by moving it cross-country through systems of reciprocal gift-giving among neighboring farmers. In the Americas an organized salt trade existed among Mayans and Aztecs and salt was also used in religious rituals. But nothing is known of how ordinary farmers got salt. Both Mexico and Peru had dry areas where salt existed on the surface for the taking and evaporating seawater was perhaps unnecessary. In Africa, too, inland salt abounded, and Roman records show that distributing salt mined from surface deposits in the Sahara desert became an important source of wealth for West African rulers when camel caravans began to carry it both north and south of the Sahara after about 300 CE.

In general, then, early farmers were able to get hold of the small amounts of mineral salt they needed to maintain the necessary saltiness of their bodily fluids. The salt they consumed came from multiple, sometimes local, sometimes distant sources, and left next to no trace in archaeological or written records. Distributing the small quantities of salt everyone needed required no special effort or organization; and large-scale transport of salt by ship or caravan remained exceptional.

This began to change in China under the Han dynasty when Emperor Wudi, in 119 CE, sought to repair his imperial finances by monopolizing salt and iron, in order to sell these essential commodities to his subjects at artificially high prices. This appears to be the first time a powerful government embraced the idea of taxing salt, and it was not in fact very successful, since the Chinese bureaucracy was not actually able to control salt distribution from the multiple sources along the coast and inlands well. Yet the idea of taxing salt was too enticing to give up since it was something everyone needed and, if government officials could successfully monopolize supplies, both rich and poor were ready to pay a lot for it.

When the technology of salt production in China shifted toward underground mining, effectual monopolization became more nearly practicable. A critical breakthrough occurred under the Tang dynasty when, about 780 CE, new taxes on salt were dedicated to maintaining the canal and transport system that linked the Yangzi (Chang) with the Huang (Yellow) River, thus supplying the imperial capital with food and other resources from the south in far greater quantity than before.

Increasingly efficient and productive underground mining of salt in the inland province of Szechwan was what made it possible to tax salt so heavily as to make it a major source of imperial finance. Techniques were complex and expensive to install. Consequently producing salt from underground became easy to monopolize. What happened was this: Chinese engineers learnt how to exploit underground salt beds in Szechwan by drilling wells, pouring water into them to dissolve the salt and then pumping saturated brine back to the surface. They then passed the brine through a succession of evaporation vats, precipitating mineral salt of varying qualities quicker and in larger quantities than sea water (with only about 3 percent of its weight consisting of salt) could possibly supply. The salt administration under the Tang and later dynasties became extraordinarily sophisticated, controlling the manufacture, distribution, and sale of salt throughout China, and lowering prices in regions close to the coast so as to compete with illegally manufactured sea salt, which the government was never able to eliminate completely.

Salt manufacture and distribution thus became a major source of tax income for the Chinese government and helped to sustain China’s political cohesion across subsequent centuries. The scale and technical efficiency of salt mining in Szechwan was unmatched elsewhere. Indeed it should be recognized as the largest industrial complex on Earth before steam engines permitted the rise of Manchester and Birmingham in England after 1780.

Indian and European governments imitated the Chinese in trying to tax salt, but wherever numerous, small-scale salt evaporation sites existed along the seacoast, government monopolies were hard to enforce, and salt taxes remained both unpopular and marginal. But in central Europe, in and around Salzburg, Austria, underground salt beds existed near the surface, and the Hapsburg monarchy (1273–1918) grew great very largely on the strength of income from taxes on salt, produced, as in China, from underground. The French monarchy tried to do likewise, but since the French coastline abounded in privately managed salt pans, efforts to impose monopoly prices met with indifferent success since even in inland provinces, where the salt tax was most vigorously enforced, smuggling untaxed salt could not be prevented. Everywhere the salt tax remained unpopular, and when the French revolution broke out in 1789 the National Assembly abolished the tax.

Further east, near Cracow in Poland, beds of unusually pure underground salt also existed, and the soil on top of it was so dry that salt could be mined by using picks and shovels, leaving extensive underground caverns behind. Today these caverns run for miles a few yards beneath the surface. Salt merchants from Venice discovered (or perhaps enlarged and reorganized) these mines in the fourteenth century. The salt trade had been important for Venetians from the time of the city’s foundation in the sixth century, since the climate along the adjacent coast of the Adriatic was especially dry and well suited to the Mediterranean style of salt-making by evaporation. Venetians (in competition with other Mediterranean seafarers) had supplied salt to northern Europe for centuries; and the expansion of salt production in Poland did not disrupt Mediterranean salt-making and export to the north.

All the same it is likely, though not sure, that Polish salt mines lowered prices and increased the quantity of salt available along the Baltic coast and in Holland. Only careful study of salt prices could tell for sure what happened; but there is reason to believe that more and cheaper salt began to flow across the Baltic in the fourteenth century since that was when European fishermen began to sail further and further into the Atlantic, preserving their catch by covering the fish with salt and storing them in barrels for days or weeks until they returned home and took their catch ashore. Very likely the Polish government, unlike their Hapsburg neighbor, was too weak to monopolize mined salt, so market prices prevailed. If so, that meant lower prices, since mining Polish salt was comparatively simple, quantities were easy to increase, and shipping down the Vistula was inexpensive. All we know for sure is that after about the mid-fourteenth century, salt, cheap enough for fishermen to buy and use in large quantities, became available along the Baltic, North Sea, and Atlantic coasts as never before. Some came from Poland, some from old-fashioned Mediterranean salt pans, which could expand production almost as easily as the Polish miners by building more evaporation ponds. Dutch (and other) ships, carrying salt to and fro, kept market prices low for them both.

Historical Implications

This was important for world history, and goes far to explain why European instead of Japanese seamen discovered America. For, even though fishermen do not usually tell where fishing is best, there is good reason to believe that exploration of the breadth of the Atlantic carried European fishermen to the Grand Banks and the shores of Newfoundland some decades before Columbus made his famous voyage. And it is certain that their voyaging, together with what the Portuguese did to explore the coast of Africa, accumulated knowledge of winds and currents and other skills needed for the trans-oceanic voyaging that European navigators achieved so spectacularly between 1492 and 1522.

Nothing similar happened in the North Pacific where Japanese fishermen had boats just as good as what Europeans had, but lacked large amounts of cheap salt, so stayed close to shore where they could get their catch to market within a day or two. Once out of water, fish rot quickly, so catching them across an ocean from where they were sold, as Europeans began to do after about 1450, made no sense without cheap and abundant salt to preserve the catch. Japanese fishermen therefore lost the chance of harvesting salmon and other fish in American coastal waters, and, of course, did not discover America either.

One may therefore argue that Europe’s expanding salt supply, by permitting deep sea fishing to flourish as never before, tipped world history toward transoceanic navigation and settlement—an achievement that dominated human history for the next five hundred years by profoundly reshaping global demography, economics and politics. If so, this surely counts as the biggest impact salt ever had on human affairs.

After about 1800, official salt monopolies and systems of taxation built upon them weakened or disappeared, not just in revolutionary France, but in other European countries and in Asia as well. In India, for example, British efforts to maintain salt taxes were never very successful and by the 1930s protest against the salt tax became one of Mohandas Gandhi’s ways of mobilizing popular opinion against the Raj, when he went to jail for personally making untaxed sea salt. Even in China the salt administration suffered serious disruption when a long series of rebellions broke out, beginning in 1774 and climaxing with the Taiping convulsion of 1850–1964.

Wherever cheaper and more abundant salt became available, whether from breakdown of tax monopolies or through improved methods of production and distribution, it could be used to preserve meat and other foods as well as fish. This added a good deal to human food supplies in many parts of the world. In the Polish and German part of Europe this was particularly evident, beginning as early as the fourteenth century, for, in addition to salted ham and sausages, sauerkraut, made by salting cabbages, provided a very valuable source of vitamins otherwise seriously lacking from their winter diets.

Eventually, beginning about 1800, all the age-old uses of salt for human consumption and food preservation were eclipsed, at least in scale, when chemists learned how to use salt in various industrial processes. It became an ingredient for manufacturing such diverse items as alkali, analine dyes, rayon and innumerable other new chemicals. A still more recent use for salt is for melting snow and ice from roads in winter. As a result, more than half of the total amount of salt produced annually at the close of the second millennium—something like 225 million tons—was destined for industrial uses. And, strange to say, taxing cheap and abundant salt no longer attracts much attention from the world’s governments.


  1. Adshead, S. A. M. (1992). Salt and civilization. New York: St. Martin’s Press.
  2. Bergier, J. (1982). Une histoire du sel [A history of salt]. Fribourg, France: Presses Universitaires de France.
  3. Ewald, U. (1985). The Mexican salt industry 1560–1980. Stuttgart, Germany: Gustav Fischer.
  4. Hocquet, J. (1978–1979). Le sel et la fortune de Venise. Lille, France: Universite de Lille.
  5. Multhauf, R. P. (1978). Neptune’s gift: A History of common salt. Baltimore: Johns Hopkins University Press.
  6. Litchfield, C. D., Palme, R., & Piasecki, P. (2000–2001). Lu monde du sel: Melanges offerts a Jean-Claude Hocquet. Innsbruck, Austria: Berenkampf.
  7. Vogel, H. (1993). Salt production techniques in ancient China: The Aobo Tu. Leiden, Brill.
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