Salt (45 page)

In 1678, Dr. Thomas Rastel of Droitwich wrote:

Besides the white salt above spoken of we have another sort called clod salt, which adheres to the bottom of the vats and which after the white salt is laded out, is digged up with a steel picker. This is the strongest salt I have seen and is most used for salting bacon, and neat’s [ox] toungues: it makes the bacon redder than other salt, and makes the fat meat firm.

T
HE WORD CHEMISTRY
was first used in the early 1600s, although the science was not considered an independent field of research until the end of the century. One of the accomplishments of early chemists had been to identify some of the salts that precipitated out of brine. But despite this work, it seems that very few people in the seventeenth century had any idea what a salt was.

A 1636 book by Bernard Palissy, with the dreamy title
How to Become Rich and the True Way in Which Every Man in France Could Grow and Multiply Their Treasury and Possessions,
states that “sugar is a salt.” In listing all the “various salts,” Palissy includes “grape salt, which gives taste and flavor to wine.” It is not surprising that he concluded that it was impossible to list all the salts. In John Evelyn’s 1699 discourse on salads, he states that sugar is sometimes referred to as “Indian salt.”

Apparently, there was little definition of salt other than as something made of white crystals. This began to change in the early seventeenth century, when Johann Rudolf Glauber, a German chemist, took a cure in a spring near Vienna and extracted from the water a salt that he called
sal mirabile.
The salt was hydrated sodium sulphate, though Glauber could not have put it that way, because Davy had not yet discovered sodium. Glauber sold his discovery as a secret cure, a mineral bath of allegedly wondrous health benefits. It became so famous that today, though it is more used in metallurgy, textiles, and other industries than as a bath salt, it is still commonly known as Glauber’s salt. Enough of an entrepreneur to keep his formula secret, Glauber was also enough of a scientist to reveal, after his fortune was made, that when sulphuric acid was applied to common salt, producing hydrochloric acid, a process that had already been well known for centuries, the residue, that had always been thrown out, was Glauber’s salt.

Later in the same century, Nehemiah Grew, a British plant physiologist who is credited with being the first human ever to witness and document plants having sex, studied the celebrated health spring water of Epsom in Surrey, England. He isolated a salt, magnesium sulphate, ever after known as Epsom salt. Epsom salt is now used not only medicinally but in the textile industry, for explosives, in match heads, and in fireproofing.

But Nehemiah Grew was even less forthcoming than Glauber about his discovery. Only after years of speculation was it discovered by chemist Caspar Neuman in 1715 that Epsom salt could be made by applying sulphuric acid to the mother liquor.

Mother liquor is the dark blood-red water that remains after common salt precipitates out of brine. An eighteenth-century London chemist named John Brown discovered that Epsom salt could be boiled out of the mother liquor without sulphuric acid. Brown also found another salt in the liquid. The study of this third salt, now known to be magnesium chloride, unleashed a chain of discoveries, including Davy’s 1808 announcement that he had found a new element, magnesium. In 1828, Antoine Bussy isolated workable quantities of the metal, and an industry was born. Magnesium is used to prevent corrosion of steel and in explosives, lightbulbs, and lightweight metal alloys.

At the time of Neuman’s early-eighteenth-century experiments with mother liquor, the liquid was called bittern, and salt makers usually threw it away or fed it to animals or even poor people as a cheap source of salt. The Dutch found that it worked well for washing windows. Despite pleas from scientists, most saltworks continued to throw out their leftover bittern.

Then, in 1792, sodium carbonate, soda, was made from mother liquor. Soda found in nature had been used since ancient times in early industries such as glassmaking. Natron is a form of soda. In fact, Davy named sodium after soda because it was one of the element’s best known compounds. The manufacture of artificial soda started numerous industries. Sodium hydrogen carbonate, bicarbonate of soda, is used in food as well as for glassmaking and textiles. Sodium carbonate is used in making paper, plastics, detergents, and the artificial fabric rayon.

By the time of the Civil War, commercially made soda was common, and soda fountains had already become widespread in America. A popular American women’s magazine gave a recipe for making carbonated drinks.

Put into a tumbler lemon, raspberry, strawberry, pineapple or any other acid syrup, sufficient in quantity to flavor the beverage very highly. Then pour in very
cold ice-water
till the glass is half full. Add half a teaspoonful of bicarbonate of soda (to be obtained at the druggist’s) and stir it well in with a teaspoon. It will foam up immediately, and must be drank during the effervescence.

By keeping the syrup and the carbonate of soda in the house, and mixing them as above with ice-water you can at any time have a glass of this very pleasant drink; precisely similar to that which you get at the shops. The cost will be infinitely less.—Godey’s Lady’s Book,
1860

For many centuries there had been a great confusion between potash and soda. The name potash is derived from the process used for making potassium carbonate, cooking down water and wood ash in earthen pots. Like soda, potash had many industrial applications long before it was chemically understood. Among other things, it was used in making glass and soap.

Before sodium carbonate in the form of baking soda was manufactured, potash was used in baking. Amelia Simmon’s cookbook, originally published in Hartford and then Albany in 1796, is considered the first American cookbook not only because it was published after the Revolution, but because it was written by an American, for Americans. Simmons used enormous quantities for apparently huge cakes. One recipe, for “Independence cake,” called for twenty pounds of flour, fifteen pounds of sugar, ten pounds of butter, and twenty-four eggs. Many of her baking recipes called for “pearl-ash,” which was potash, as a rising agent.

HONEY CAKE

Six pound flour, 2 pound honey, 1 pound sugar, 2 ounces cinnamon, 1 ounce ginger, a little orange peel, 2 tea spoons pearl-ash, 6 eggs; dissolve the pearl-ash in milk, put the whole together, moisten with milk if necessary, bake 20 minutes.—
Amelia Simmons,
American Cookery,
1796

In 1807, when the potash industry was already many centuries old, Davy connected a piece of potash to the poles of a battery and caused the release of a metal at the negative pole. According to his cousin Edmund, Davy began dancing around the room in ecstasy, realizing that he had isolated another element. He named his newly discovered metal potassium after potash.

U
NTIL THE LATE
eighteenth century, bleaching was accomplished by soaking fabric in buttermilk and then laying it out on the ground to be whitened in sunlight for weeks. These areas, known as bleach fields, took up enormous spreads of land. The nineteenth-century Industrial Revolution created a far greater demand for both soap and bleach. Industry was blackening entire cities, and as skies—and clothes—became covered with soot, it was becoming difficult to find enough space for bleach fields in urban areas.

Another self-taught chemist, a Swede named Carl Wilhelm Scheele, in 1774, twelve years before his celebrated discovery of oxygen, first described a substance called chlorine and noted that it had the ability to bleach. Scheele was also one of the first to study the fermenting attributes of lactic acid.

But it was not until 1786, ten years after Scheele’s observations on chlorine, that a practical application was pursued by the great French chemist Claude-Louis Berthollet, who showed that chlorine, when absorbed in potash, created a liquid bleach. Yet another salt-based industry was founded. In little more than a year, industrial bleaching became a major activity in the British textile industry.

In 1810, Davy isolated chlorine and proved that it too was an element, a greenish gas which he named for the Greek word for greenish yellow.

Chlorine has become an important industry. Not only used for bleach, water treatment, and sewage treatment, it is also an ingredient in plastics and artificial rubber. And, as with so many scientific discoveries, a military application was found. Chlorine was the basis for gas warfare. In 1914, at the outbreak of World War I, chlorine gas was exploded in canisters, but later in the war, artillery shells filled with carbonyl chloride proved to be more effective. Known as mustard gas, the compound is credited with 800,000 casualties.

C
HEMISTS AND ENTREPRENEURS
were beginning to understand that “salt” was one of a very specific group of substances that were often found together and that what we now call “common salt” was in many ways the least valuable of the group. In 1744, Guillaume François Rouelle, a member of the French Royal Academy of Sciences, wrote a definition of a salt that has endured. He said that a salt was any substance caused by the reaction of an acid and a base. For a long time, the existence of acids and bases had been known but little understood. Acids were sour tasting and had the ability to dissolve metal. Bases felt soapy. But Rouelle understood that an acid and a base have a natural affinity for each other because nature seeks completion and, as with all good couples, acids and bases make each other more complete. Acids search for an electron that they lack, and bases try to shed an extra one. Together they make a well-balanced compound, a salt. In common salt the base, or electron donor, is sodium, and the acid, or electron recipient, is chloride.