Penny le Couteur & Jay Burreson

by Napoleon's Buttons: How 17 Molecules Changed History

  Today olive oil is generally recognized for its positive effects on cardiac health and for the delicious flavor it imparts to food. Its role in keeping alive the tradition of soap making and thus combating dirt and disease during medieval times is less well known. But the wealth that olive oil brought to ancient Greece ultimately allowed the development of many of the ideals of that culture that we still value today. The roots of present-day Western civilization are found in ideas fostered in the political culture of classical Greece: concepts of democracy and self-government, philosophy, logic and the beginning of rational inquiry, scientific and mathematical investigations, education, and the arts.

  The affluence of Greek society permitted the participation of thousands of citizens in the process of inquiry, in rigorous debate, and in political choices. More than any other ancient society, men (women and slaves were not citizens) were involved in decisions that affected their lives. Trade in olive oil provided much of the society’s prosperity; education and civic involvement followed. The glories that were Greece—now considered to be the foundation of today’s democratic societies—would not have been possible without the triglyceride of oleic acid.

  15. SALT

  THE HISTORY OF common salt—sodium chloride, with a chemical formula of NaCl—parallels the history of human civilization. So valued is salt, so needed and so important, that it has been a major player not only in global trade but in economic sanctions and monopolies, wars, the growth of cities, systems of social and political control, industrial advances, and the migration of populations. Today salt is something of an enigma. It is absolutely essential to life—we die without it—but we are told to watch our salt intake as salt can kill. Salt is cheap; we produce and use enormous quantities of it. Yet for almost all of recorded history and probably for centuries before any history was recorded, salt was a precious commodity and often very expensive. The average person at the beginning of the nineteenth century would have had great difficulty in believing that we now routinely throw mounds of salt on roads to eliminate ice.

  The price of many other molecules has dropped through the efforts of chemists, either because we can now synthesize the compound in laboratories and factories (ascorbic acid, rubber, indigo, penicillin) or because we can make artificial substitutes, compounds whose properties are so similar that the natural product is less important (textiles, plastics, aniline dyes). Today we rely on newer chemicals (refrigerants) for the preservation of food, so spice molecules no longer command the price they once did. Other chemicals—pesticides and fertilizers—have increased crop yields and hence the supply of such molecules as glucose, cellulose, nicotine, caffeine, and oleic acid. But of all compounds, salt has probably had the largest increase in production coupled with the most precipitous drop in price.

  GETTING SALT

  Throughout history humans have collected or produced salt. Three main methods of salt production—evaporating seawater, boiling down salt solutions from brine springs, and mining rock salt—were all used in ancient times and are still in use today. Solar evaporation of seawater was (and still is) the most common method of salt production in tropical coastal regions. The process is slow but cheap. Originally seawater was thrown onto burning coals, and the salts were scraped off when the fire was extinguished. Larger quantities could be harvested from the sides of coastal rock pools. It would not have taken much imagination to realize that artificial shallow lakes or “pans,” constructed in areas where tidal flow could be used to fill the pans as needed, could provide much greater quantities of salt.

  Raw sea salt is of much lower quality than either brine salt or rock salt. Although seawater is about 3.5 percent dissolved salts, only about two-thirds of this is sodium chloride; the rest is a mixture of magnesium chloride (MgCl2 ) and calcium chloride (CaCl2 ). As these latter two chlorides are both more soluble and less abundant than sodium chloride, NaCl crystallizes out of solution first, so it is possible to remove most of the MgCl2 and CaCl2 by draining them away in the residual brine. But enough remains to give sea salt a sharper taste, which is attributable to these impurities. Both magnesium and calcium chloride are deliquescent, meaning they absorb water from the air, and when this happens, salt containing these additional chlorides clumps and is difficult to pour.

  The evaporation of seawater was most effective in hot, dry climates, but brine springs, underground sources of highly concentrated solutions of salt—sometimes ten times more concentrated than seawater—were also an excellent source of salt in any climate, if there was wood for the fires necessary to boil off the water in the brine solutions. Wood demand for salt production helped deforest parts of Europe. Brine salt, uncontaminated by magnesium and calcium chloride, which lessened the effectiveness of food preservation, was more desirable than sea salt but also more expensive.

  Deposits of rock salt or halite—the mineral name of the NaCl found in the ground—are found in many parts of the world. Halite is the dried remains of old oceans or seas and has been mined for centuries, particularly where such deposits occur near the earth’s surface. But salt was so valuable that as early as the Iron Age people in Europe turned to underground mining, creating deep shafts, miles of tunnels, and large caverns hollowed out by the removal of salt. Settlements grew up around these mines, and the continued extraction of salt led to the establishment of towns and cities, which grew wealthy from the salt economy.

  Salt making or mining was important in many places in Europe throughout the Middle Ages; so valued was salt that it was known as “white gold.” Venice, center of the spice trade for centuries, started as a community that obtained a living by extracting salt from the brines of the marshy lagoons in the area. Names of rivers, towns and cities in Europe—Salzburg, Halle, Hallstatt, Hallein, La Salle, Moselle—commemorate their links with salt mining or salt production, as the Greek word for salt is hals and the Latin is sal. Tuz, the Turkish name for salt, shows up in Tuzla, a town in a salt-producing region of Bosnia-Herzegovina, as well as in coastal communities in Turkey with the same or similar names.

  Today, through tourism, salt is still the source of wealth for some of these old salt towns. In Salzburg, Austria, salt mines are a major tourist attraction, as they are at Wieliczka, near Cracow in Poland, where, in the great caverns hollowed out by salt removal, a dance hall, a chapel with an altar, religious statues carved from salt, and an underground lake now enchant thousands of visitors. The largest salar, or saltpan, in the world is the Salar de Uyuni in Bolivia, where tourists can stay at a nearby hotel made entirely from salt.

  The salt hotel near Salar de Uyuni in Bolivia. (Photo by Peter Le Couteur)

  TRADING SALT

  That salt has been a trade commodity from earliest times is shown in records from ancient civilizations. The ancient Egyptians traded for salt, an essential ingredient in the mummification process. The Greek historian Herodotus reported visiting a salt mine in the Libyan desert in 425 B.C. Salt from the great salt plain at Danakil in Ethiopia was traded to the Romans and Arabs and exported as far as India. The Romans established a large coastal saltworks at Ostia, which was then at the mouth of the River Tiber, and around 600 B.C. built a road, the Via Salaria, to transport salt from the coast to Rome. One of the main thoroughfares in present-day Rome is still known as Via Salaria—the salt road. Forests were felled to provide fuel for the saltworks at Ostia, and subsequent soil erosion washed increasing amounts of sediment into the Tiber. Extra sediment hastened the expansion of the delta at the river mouth. Centuries later Ostia was no longer on the coast, and the saltworks had to be moved out to the shoreline again. This has been cited as one of the first examples of the impact of human industrial activity on the environment.

  Salt was the basis for one of the world’s great trade triangles and coincidently for the spread of Islam to the west coast of Africa. The extremely arid and inhospitable Sahara Desert was for centuries a barrier between the northern African countries bordering the Mediterranean and the rest of the continent to the sou
th. Though there were enormous deposits of salt in the desert, south of the Sahara salt was in great demand. In the eighth century Berber merchants from North Africa began to trade grains and dried fruit, textiles and utensils, for slabs of halite mined from the great salt deposits of the Sahara (in present-day Mali and Mauritania). So abundant was salt at these sites that entire cities such as Teghaza (city of salt), built from blocks of salt, grew up around the mines. The Berber caravans, often comprising thousands of camels at a time, now laden with slabs of salt, would continue across the desert to Timbuktu, originally a small camp on the southern edge of the Sahara on a tributary of the Niger River.

  By the fourteenth century, Timbuktu had become a major trading post, exchanging gold from West Africa for salt from the Sahara. It also became a center for the expansion of Islam, which was brought to the region by the Berber traders. At the height of its power—most of the sixteenth century—Timbuktu boasted an influential Koranic university, great mosques and towers, and impressive royal palaces. Caravans leaving Timbuktu carried gold, and sometimes slaves and ivory, back to the Mediterranean coast of Morocco and thence to Europe. Over the centuries many tons of gold were shipped to Europe through the Saharan gold/salt trade route.

  Saharan salt was also shipped to Europe as the demand there for salt increased. Freshly caught fish must be preserved quickly, and while smoking and drying were rarely possible at sea, salting was. The Baltic and North Seas teemed with herring, cod, and haddock, and from the fourteenth century onward millions of tons of these fish, salted at sea or in nearby ports, were sold throughout Europe. In the fourteenth and fifteenth centuries the Hanseatic League, an organization of north German towns, controlled the trade in salt fish (and almost everything else) in the countries bordering the Baltic Sea.

  The North Sea trade was centered in Holland and the east coast of England. But with salt available to preserve the catch, it became possible to fish even farther afield. By the end of the fifteenth century fishing boats from England, France, Holland, the Basque region of Spain, Portugal, and other European countries were regularly sailing to fish the Grand Banks off Newfoundland. For four centuries fishing fleets plundered the vast schools of cod in this region of the North Atlantic, cleaning and salting the fish as they were caught and returning to port with millions of tons of what seemed an inexhaustible supply. Sadly this was not the case; Grand Banks cod were brought to the brink of extinction in the 1990s. Today a moratorium on cod fishing, introduced by Canada in 1992, is being observed by many, but not all, of the traditional fishing nations.

  With salt in such demand, it is hardly surprising that it was often considered a prize of war rather than a commodity of trade. In ancient times settlements around the Dead Sea were conquered specifically for their precious supplies of salt. In the Middle Ages the Venetians waged war against neighboring coastal communities who threatened their all-important salt monopoly. Capturing an enemy’s supply of salt was long considered a sound wartime tactic. During the American Revolution salt shortages resulted from a British embargo of imports from Europe and the West Indies into the former colony. The British destroyed salt works along the New Jersey coast to maintain the hardship affecting the colonists as a result of the high prices for imported salt. The 1864 capture of Saltville, Virginia, by Union forces during the American Civil War was seen as a vital step in reducing civilian morale and defeating the Confederate army.

  It has even been suggested that a lack of dietary salt might have prevented wartime wounds from healing and was thus responsible for the death of thousands of Napoleon’s soldiers during the 1812 retreat from Moscow. Lack of ascorbic acid (and the subsequent onset of scurvy) seems as likely a culprit as lack of salt under these circumstances, so both these compounds could join tin and lysergic acid derivatives as chemicals that thwarted Napoleon’s dreams.

  THE STRUCTURE OF SALT

  Halite, with a solubility of about 36 grams in every 100 grams of cold water, is far more soluble in water than are other minerals. As life is thought to have developed in the oceans and as salt is essential for life, without this solubility of salt life as we know it would not exist.

  The Swedish chemist Svante August Arrhenius first proposed the idea of oppositely charged ions as an explanation for the structure and properties of salts and their solutions in 1887. For over a century scientists had been mystified by a particular property of salt solutions—their ability to conduct electrical currents. Rainwater shows no electrical conductivity, yet saline solutions and solutions of other salts are excellent conductors. Arrhenius’s theory accounted for this conductivity; his experiments showed that the more salt dissolves into solution, the greater the concentration of the charged species—the ions—needed to carry the electrical current.

  The concept of ions, as proposed by Arrhenius, also explained why acids, despite seemingly different structures, have similar properties. In water all acids produce hydrogen ions (H+) which are responsible for the sour taste and chemical reactivity of acid solutions. Although Arrhenius’s ideas were not accepted by many conservative chemists of the time, he displayed a commendable degree of perseverance and diplomacy in campaigning determinedly for the soundness of the ionic model. His critics were eventually convinced, and Arrhenius received the 1903 Nobel Prize in chemistry for his electrolytic dissociation theory.

  By this time there was both a theory and practical evidence for how ions form. British physicist Joseph John Thomson in 1897 had demonstrated that all atoms contain electrons, the negatively charged fundamental particle of electricity that had been first proposed in 1833 by Michael Faraday. Thus if one atom lost an electron or electrons, it became a positively charged ion; if another atom gained an electron or electrons, a negatively charged ion was formed.

  Solid sodium chloride is composed of a regular array of two different ions—positively charged sodium ions and negatively charged chloride ions—held together by strong attractive forces between the negative and positive charges.

  The three-dimensional structure of solid sodium chloride. The lines joining the ions are nonexistent—they are included here to show the cubic arrangement of the ions.

  Water molecules, although not consisting of ions, are partially charged. One side of a water molecule (the hydrogen side) is slightly positive, and the other side (the oxygen side) is slightly negative. This is what allows sodium chloride to dissolve in water. Although the attraction between a positive sodium ion and the negative end of water molecules (and the attraction between negative chloride ions and the positive end of water molecules) are similar to the attractive force between Na+ ions and Cl- ions, what ultimately accounts for the solubility of salt is the tendency for these ions to disperse randomly. If ionic salts do not dissolve to any extent in water, it is because the attractive forces between the ions are greater than the water-to-ion attractions.

  Representing the water molecule as:

  with δ- indicating the partial negative end of the molecule and δ+ the partial positive end of the molecule, we can show the negative chloride ions in aqueous solution as surrounded by the slightly positive end of water molecules:

  and the positive sodium ion in aqueous solution as surrounded by the slightly negative end of water molecules:

  It is this solubility of sodium chloride that makes salt—by attracting water molecules—such a good preservative. Salt preserves meat and fish by removing water from the tissues; in conditions of much-reduced water levels and a high salt content, the bacteria that cause decay are unable to survive. A lot more salt was used in this manner to keep food from decaying than was deliberately added to enhance flavors. In regions where dietary salt came mainly from meat, additional salt for food preservation was an essential factor in maintaining life. The other traditional methods of food preservation, smoking and drying, very often required the use of salt as part of the process. Food would be soaked in a brine solution prior to the actual smoking or drying. Communities without a local source of salt were dependent on s
upplies obtained by trade.

  THE BODY’S NEED FOR SALT

  From earliest times, even if it was not needed for food preservation, humans recognized the necessity to obtain salt for their diet. Ions from salt play an essential role in the human body, maintaining the electrolyte balance between cells and the fluid surrounding the cells. Part of the process that generates the electrical impulses transmitted along neurons in the nervous system involves what is called the sodium-potassium pump. More Na+ (sodium) ions are forced out of a cell than K+ (potassium) ions are pumped into it, resulting in a net negative charge of the cytoplasm inside the cell compared with the outside of the cell membrane. Thus a difference in charge—known as a membrane potential—is generated, which powers electrical impulses. Salt is therefore vital for the functioning of nerves and ultimately muscle movement.

  Cardiac glycoside molecules, such as the digoxin and digitoxin found in foxglove, inhibit the sodium-potassium pump, giving a higher level of Na+ ions inside the cell. This ultimately increases the contractive force of the heart muscles and accounts for the activity of these molecules as heart stimulants. The chloride ion from salt is also needed in the body to produce hydrochloric acid, an essential component of the digestive juices in the stomach.