Salt concentration in a healthy person varies within a very narrow range. Lost salt must be replaced; excess salt must be excreted. Salt deprivation causes loss of weight and appetite, cramps, nausea, and inertia and can, in extreme cases of depletion of body salt—such as in marathon runners—lead to vascular collapse and death. Excess sodium ion intake, however, is known to contribute to high blood pressure, a significant factor for cardiovascular disease, and to kidney and liver disorders.
The average human body contains about four ounces of salt; we are continuously losing salt, mainly through perspiration and excretion in urine, and so we have to replace it on a daily basis. Prehistoric man filled his dietary need for salt from the meat of the largely herbivorous animals he hunted, as raw meat is an excellent source of salt. As agriculture developed and grains and vegetables became a larger part of the diet, supplementary salt was needed. While carnivorous animals do not seek out salt licks, herbivorous animals need to do so. Humans in parts of the world where little meat is eaten and vegetarians require additional salt. Supplemental salt, a necessity as soon as humans adopted a settled agrarian way of life, must be obtained locally or through trade.
TAXING SALT
The human need for salt, together with its specific methods of production, have historically made this mineral peculiarly fitted for political control, monopoly, and taxation. For a government, a tax on salt would produce a reliable income. There was no substitute for salt, and everyone needed it, so everyone would have to pay. Salt sources were known; the production of salt is difficult to hide, salt itself is bulky and hard to conceal, and its transportation can be easily regulated and taxed. From 2000 B.C. in China, where the Emperor Hsia Yu ordered that the imperial court would be supplied by salt from Shantung Province, down through the ages, salt has been profitable for governments through taxes, tolls, and tariffs. In biblical times salt, considered a spice and taxed as such, was subject to customs duty at the many stopping places along caravan routes. After the death of Alexander the Great in 323 B.C., officials in Syria and Egypt continued to collect a salt tax that had originally been imposed by the Greek administration.
Throughout all these centuries the process of gathering taxes required tax collectors, many of whom became wealthy by increasing tax rates, adding extra duties, and selling exemptions. Rome was no exception. Originally the Ostia saltworks on the Tiber delta were taken over by the Roman state, so that salt could be supplied at reasonable rates to everyone. Such largesse did not last. The revenues from taxing salt offered too great a temptation, and a salt tariff was imposed. As the Roman Empire expanded, so did salt monopolies and salt taxes. Tax gatherers, independent agents supervised by the governor of each Roman province, levied taxes wherever they could. For those who lived far from salt-producing areas, the high cost of salt not only reflected transportation costs but tariffs, taxes, and duties at every step of the way.
Throughout the Middle Ages in Europe the taxation of salt continued, often in the form of tolls imposed on barges or carts carrying salt from salt mines or coastal production plants. It reached its height in France with the infamous, oppressive, and much-hated salt tax known as the gabelle. Reports on the origin of the gabelle vary. Some accounts say Charles of Anjou in Provence imposed it in 1259, others that it started as a general tax applied to commodities like wheat, wine, and salt in the late thirteenth century to help maintain a permanent army. Whatever its true origin, by the fifteenth century the gabelle had become one of France’s main national levies, and the name referred only to the tax on salt.
But the gabelle was not just a tax on salt. It also carried the requirement that every man, woman, and child over the age of eight purchase a weekly amount of salt, at a price set by the king. Not only could the salt tax itself be raised, but the obligatory ration could also be increased at the monarch’s whim. What was once intended as a uniform tax on the population soon extracted higher penalties on some regions of France than others. In general, those provinces that obtained their salt from Atlantic salt works were subject to the grande gabelle, more than twice what was paid in regions—known as Les Provinces des Petites Gabelles—where salt was supplied from Mediterranean saltworks. Through political influence or treaty arrangements some areas were exempt from the gabelle or paid only a fraction; at times there was no gabelle in Brittany and a special low rate in Normandy. At its height the gabelle increased the price of salt more than twenty times its real cost for those citizens in Les Provinces des Grandes Gabelles.
Salt tax collectors—referred to as gabelle farmers, as they harvested the taxes from the people—would monitor the per capita use of salt to ensure consumption obligations were met. Attempts to smuggle salt were rife despite severe penalties for being discovered with contraband salt; a common punishment in such cases was a sentence to the galleys. Peasant farmers and poor city dwellers were the most severely affected by the harsh and unfairly applied gabelle. Appeals to the king for relief from this onerous tax fell on deaf ears, and it has been suggested that the gabelle was one of the main grievances responsible for the French Revolution. It was abolished at the height of the revolution in 1790, and more than thirty gabelle collectors were executed. But the abolition did not last. In 1805 Napoleon reintroduced the gabelle, a measure he claimed was necessary to pay for his war against Italy. It was not finally eliminated until after World War II.
France was not the only country where such taxes on a necessity of life were burdensome. In coastal Scotland, particularly around the Firth of Forth, salt had been produced for centuries before it was ever taxed. Solar evaporation was not feasible in the cool, damp climate; seawater was boiled in large vessels, which were originally wood-fired and later coal-fired. By the 1700s there were more than 150 such saltworks in Scotland, plus numerous others that were peat-fired. The salt industry was so important to the Scots that the Eighth Article of the 1707 Treaty of Union between Scotland and England guaranteed Scotland a seven-year exemption from English salt taxes and after that a reduced rate forever. England’s salt industry was based on the extraction of salt from brine as well as the mining of rock salt. Both methods were a great deal more efficient and profitable than the coal-fired seawater method of Scottish production. The industry in Scotland needed relief from English salt taxes in order to survive.
In 1825 the United Kingdom became the first country to abolish its salt tax, not so much because of the resentment this tax had generated among the working class throughout the centuries as because of the recognition of the changing role of salt. The Industrial Revolution is usually thought of as a mechanical revolution—the development of the flying shuttle, the spinning jenny, the water frame, the steam engine, the power loom—but it was also a chemical revolution. Large-scale production of chemicals was required for the textile industry, for bleaching, soap making, glassmaking, potteries, the steel industry, tanneries, paper manufacturing, and the brewing and distilling industries. Manufacturers and factory owners pushed for the repeal of the salt tax because salt was becoming vastly more important as a starting material in manufacturing processes than as a preservative and food culinary supplement. Removal of the salt tax, sought by generations of the poor, became a reality only when salt was recognized as a key raw material for industrial prosperity in Britain.
Britain’s enlightened stance on salt taxes did not extend to her colonies. In India a British-imposed salt tax became a symbol of colonial oppression seized upon by Mahatma Gandhi as he led the struggle for Indian independence. The salt tax in India was more than a tax. As many conquerors had found over the centuries, control of salt supplies meant political and economic control. Government regulations in British India made the nongovernmental sale or production of salt a criminal offense. Even collecting salt formed through natural evaporation around rock pools at the seacoast was outlawed. Salt, sometimes imported from England, had to be purchased from government agents at prices established by the British. In India, where the diet is mainly vegetarian and the oft
en intensely hot climate promotes salt loss through sweating, it was especially important that salt be added to food. Under colonial rule the population was forced to pay for a mineral that millions had traditionally been able to gather or produce themselves at little or no cost.
In 1923, almost a century after Britain had eliminated the salt tax on its own citizens, the salt tax in India was doubled. In March 1930, Gandhi and a handful of supporters started a 240-mile march to the small village of Dandi, on the northwest coast of India. Thousands joined his pilgrimage, and once they reached the shoreline, they began to collect salt incrustations from the beach, to boil seawater, and to sell the salt they produced. Thousands more joined in breaking the salt laws; illegal salt was sold in villages and cities all over India and was frequently confiscated by the police. Gandhi’s supporters were often brutalized by the police, and thousands were imprisoned. Thousands more took their places making salt. Strikes, boycotts, and demonstrations followed. By the following March the draconian salt laws of India had been modified: local people were permitted to collect salt or make it from local sources and sell it to others in their villages. Although a commercial tax still applied, the British government’s salt monopoly was broken. Gandhi’s ideals of nonviolent civil disobedience had proven effective, and the days of the British Raj were numbered.
SALT AS A STARTING MATERIAL
The removal of the salt tax in Britain was important not only to those industries that used salt as part of their manufacturing processes but also to companies that made inorganic chemicals, where salt was a major starting material. It was particularly significant for another sodium compound, sodium carbonate (Na2CO3 ), known as soda ash or washing soda. Soda ash, used in soap making and needed in large quantities as the demand for soap increased, came mainly from naturally occurring deposits, often incrustations around drying alkaline lakes or from residues from burning kelp and other seaweeds. Soda ash from these sources was impure and supplies were limited, so the possibility of producing sodium carbonate from the plentiful supplies of sodium chloride attracted attention. In the 1790s Archibald Cochrane, the ninth earl of Dundonald—now considered one of the leaders of Britain’s chemical revolution and a founder of the chemical alkali industry—whose modest family estate on Scotland’s Firth of Forth bordered on numerous coal-fired saltpans, took out a patent for converting salt to “artificial alkali,” but his process was never a commercial success. In France in 1791, Nicolas Leblanc developed a method of making sodium carbonate from salt, sulfuric acid, coal, and limestone. The onset of the French Revolution delayed establishment of Leblanc’s process, and it was in England where the profitable manufacture of soda ash began.
In Belgium in the early 1860s, the brothers Ernest and Alfred Solvay developed an improved method of converting sodium chloride to sodium carbonate using limestone (CaCO3) and ammonia gas (NH3). The key steps were the formation of a precipitate of sodium bicarbonate (NaHCO3) from a concentrated solution of brine, infused with ammonia gas and carbon dioxide (from limestone):
and then production of sodium carbonate by heating the sodium bicarbonate:
Today the Solvay process remains the main method of preparing synthetic soda ash, but discoveries of massive deposits of natural soda ash—the Green River basin of Wyoming, for example, has soda ash resources estimated at over ten billion tons—have decreased the demand for its preparation from salt.
Another sodium compound, caustic soda (NaOH), has also long been in demand. Industrially, caustic soda or sodium hydroxide is made by passing an electric current through a solution of sodium chloride—a process known as electrolysis. Caustic soda, one of the ten most produced chemicals in the United States, is essential in extracting aluminum metal from its ore and in the manufacture of rayon, cellophane, soaps, detergents, petroleum products, paper, and pulp. Chlorine gas, also produced in the electrolysis of brine, was originally considered a by-product of the process, but it was soon discovered that chlorine was an excellent bleaching agent and a potent disinfectant. Today the production of chlorine is as much a reason for commercial electrolysis of NaCl solutions as the production of NaOH. Chlorine is now used in the manufacture of many organic products, such as pesticides, polymers, and pharmaceuticals.
From fairy tales to biblical parables, from Swedish folk myths to North American Indian legends, different societies around the world tell stories of salt. Salt is used in ceremonies and rites, it symbolizes hospitality and good fortune, and it protects against evil spirits and ill luck. The important role of salt in shaping human culture is also seen in language. We earn a salary—the derivation of the word comes from the fact that Roman soldiers were often paid in salt. Our words for salad (originally dressed only with salt), sauce and salsa, sausage and salami all come from the same Latin root. As in other languages, our everday speech is “salted” with metaphors: “salt of the earth,” “old salt,” “worth his salt,” “below the salt,” “with a grain of salt,” “back to the salt mine.”
The ultimate irony in the story of salt is that despite all the wars fought over it, despite the battles and protests over taxation and tolls imposed on it, despite migrations in search of it and the despair of hundreds of thousands imprisoned for smuggling it, by the time the discovery of new underground salt deposits and modern technology had vastly decreased its price, the need for salt in food preservation was already greatly diminished—refrigeration had become the standard method of preventing decomposition of food. This compound that throughout history has been honored and revered, desired and fought over, and sometimes been valued more highly than gold, is nowadays not only cheap and readily available but is considered commonplace.
16. CHLOROCARBON COMPOUNDS
IN 1877 THE ship Frigorifique sailed from Buenos Aires to the French port of Rouen with a cargo of Argentinian beef in its hold. While today this passage would be seen as routine, it was in fact a historic voyage. The ship carried a cooled cargo that signaled the beginning of the era of refrigeration and the end of food preservation by molecules of spice and salt.
KEEPING COOL
Since at least 2000 B.C., people have used ice to keep things cool, relying on the principle that solid ice absorbs heat from its surroundings as it melts. The liquid water produced drains away, and a new supply of ice is added. Refrigeration, on the other hand, involves not solid and liquid phases but liquid and vapor phases. As liquid evaporates, it absorbs heat from its surroundings. The vapor produced by evaporation is then returned to the liquid state by compression. This compression stage is what puts the re in refrigeration—vapor is returned to a liquid, then re-evaporates causing cooling, and the whole cycle repeats. A key component of the cycle is an energy source to drive the mechanical compressor. The old fashioned icebox, where ice had to be added continually, was technically not a refrigerator. Today we often use the word refrigerate to mean “to make or keep cool” without considering how it is done.
A true refrigerator needs a refrigerant—a compound that undergoes the evaporation-compression cycle. As early as 1748 ether was used to demonstrate the cooling effect of a refrigerant, but it was more than a hundred years before a compressed ether machine was employed as a refrigerator. Around 1851, James Harrison, a Scotsman who had immigrated to Australia in 1837, built an ether-based vapor-compression refrigerator for an Australian brewery. He and an American, Alexander Twining, who had made a similar vapor-compression refrigeration system at about the same time, are considered to be among the first developers of commercial refrigeration.
Ammonia was used as a refrigerant in 1859, by Ferdinand Carré of France—another claimant to the title of first commercial developer of refrigeration. Methyl chloride and sulfur dioxide were also used in these early days; sulfur dioxide was the cooling agent for the world’s first artificial skating rink. These small molecules effectively ended the reliance on salt and spices for food preservation.
In 1873, after successfully establishing land-based refrigeration for the Australian meat
-packing industry as well as the breweries, James Harrison decided to transport meat on a refrigerated ship from Australia to Britain. But his ether-based evaporation-compression mechanical system failed at sea. Then in early December 1879 the S.S. Strathleven, equipped by Harrison, left Melbourne and arrived in London two months later with forty tons of still-frozen beef and mutton. Harrison’s refrigeration process was proven. In 1882 a similar system was installed on the S.S. Dunedin, and the first cargo of New Zealand lamb was shipped to Britain. Though the Frigorifique is often referred to as the world’s first refrigerated ship, technically the claim better fits Harrison’s 1873 attempt. It was not, however, the first successful voyage of a refrigerated ship. This latter title more rightly belongs to the S.S. Paraguay, which arrived in Le Havre, France, in 1877 with a cargo of frozen beef from Argentina. The Paraguay’s refrigeration system was designed by Ferdinand Carré and used ammonia as a refrigerant.
On the Frigorifique the “refrigeration” was maintained by water that was cooled by ice (stored in a well-insulated room) and then pumped around the ship in pipes. The ship’s pump broke down on the journey from Buenos Aires, and the meat was spoiled before it arrived in France. So although the Frigorifique predated the S.S. Paraguay by a number of months, it was not a true refrigerated ship; it was only an insulated ship, keeping food chilled or frozen with stored ice. What the Frigorifique can claim to be is a pioneer in transporting chilled meat across the ocean, even if it was not a successful pioneer.
Irrespective of whose claim to the first refrigerated ship is most valid, by the 1880s the mechanical compression-evaporation process was set to solve the problem of transporting meat from the producing areas of the world to the larger markets of Europe and the eastern United States. Ships from Argentina and the even more distant cattle and sheep pastures of Australia and New Zealand faced a two- or three-month journey through the warm temperatures of the tropics. The simple ice system of the Frigorifique would not have been effective. Mechanical refrigeration began to increase in reliability, giving ranchers and farmers a new means of getting their products to world markets. Refrigeration thus played a major role in the economic development of Australia, New Zealand, Argentina, South Africa, and other countries, where great distances from markets reduced their natural advantages of abundant agricultural production.
Penny le Couteur & Jay Burreson Page 27