Salt

Salt is a mineral composed primarily of sodium chloride (NaCl). It is one of the five basic tastes experienced by humans. Salt is essential for life because it provides two vital dietary minerals: sodium and chlorine. In its natural crystalline form, it is known as halite or rock salt. When it is processed into a fine, granulated form for food, it is called table salt.

The physical properties of salt are quite unique. Salt crystals are typically translucent and cubic in shape. While they usually appear white, impurities can give them a blue or purple tinge.

When sodium chloride dissolves in water, it separates into Na+ and Cl− ions. This process makes the salt highly soluble, at a rate of 359 grams per litre. Salt also changes the physical properties of water. A salt solution has a lower freezing point than pure water. For example, a solution with 23.31 wt% salt freezes at −21.12 °C. It also has a higher boiling point, reaching approximately 108.7 °C when saturated.

There are several ways to harvest and process salt. One method involves extracting salt from deep underground mines.

Another method is the evaporation of seawater or mineral-rich spring water in shallow pools.

This is often seen in salt pans where the sun dries the water to leave salt behind.

Once collected, salt is often refined for specific uses. Table salt is typically refined to contain 97 to 99 percent sodium chloride. To keep the salt free-flowing, manufacturers often add anti-caking agents like magnesium carbonate or sodium aluminosilicate.

Humans have relied on salt for thousands of years. Some of the earliest evidence of salt processing dates back to around 6050 BC in Romania. Neolithic people there used a process called briquetage to boil spring water and extract salt.

In China, salt was harvested from Xiechi Lake near Yuncheng as early as 6000 BC. Because salt was so important for preserving meat, it became a major trading commodity. Ancient civilizations like the Greeks, Romans, and Egyptians prized it highly. It was used in trade for luxury goods, such as Egyptian salt fish being traded for Lebanese cedar.

Salt has also played a massive role in politics and economics. Because it was scarce and necessary, nations often fought wars over it. In Africa, slabs of rock salt were used as a form of currency in Abyssinia.

Governments throughout history have also used salt taxes to raise revenue. In France, an oppressive salt tax was a cause of the French Revolution. In 1930, Mahatma Gandhi led the Dandi March to protest colonial salt taxes in India. He demonstrated how to make salt from the sea to inspire the independence movement. Even the word "salary" comes from the Latin word for salt.

While we use salt for flavor, its largest global use is actually industrial. The world produces about three hundred million tonnes of salt annually. Only a small percentage of this is used for human consumption. The majority of salt serves as a feedstock for chemical production. It is used to create chlorine and caustic soda. These chemicals are necessary to make plastics, paper pulp, and polyvinyl chloride. Salt is also used for de-icing highways, water conditioning, and in agriculture.

In terms of human health, salt is both necessary and potentially dangerous. Sodium acts as an electrolyte and an osmotic solute in the body. This makes it essential for many biological functions. However, eating too much salt can increase the risk of cardiovascular diseases like hypertension. To prevent health issues, many countries add iodine to table salt. Iodine is a micronutrient that prevents conditions like goitre or intellectual disabilities. The World Health Organization recommends that adults consume less than 2,000 mg of sodium, or about 5 grams of salt, per day.