Common salt is a mineral substance composed primarily of
sodium chloride (NaCl), a chemical compound belonging to the larger class of
ionic salts; salt in its natural form as a crystalline mineral is known as rock salt or
halite. Salt is present in vast quantities in the
sea where it is the main mineral constituent, with the open ocean having about 35 grams (1.2 oz) of solids per litre, a
salinity of 3.5%. Salt is essential for
animal life, and saltiness is one of the
basic human tastes. The tissues of animals contain larger quantities of salt than do plant tissues; therefore the typical diets of nomads who subsist on their flocks and herds require little or no added salt, whereas cereal-based diets require supplementation. Salt is one of the oldest and most ubiquitous of food seasonings, and
salting is an important method of
food preservation.
Some of the earliest evidence of salt processing dates back to around 6,000 years ago, when people living in
Romania were boiling spring water to extract the salts; a
saltworks in China has been found which dates to approximately the same period. Salt was prized by the ancient Hebrews, the Greeks, the Romans, the Byzantines, the Hittites and the Egyptians. Salt became an important article of trade and was transported by boat across the Mediterranean Sea, along specially built salt roads, and across the Sahara in camel caravans. The scarcity and universal need for salt has led nations to go to war over salt and use it to raise tax revenues. Salt is also used in religious ceremonies and has other cultural significance.
Salt is produced from salt mines or by the
evaporation of seawater or mineral-rich spring water in shallow pools. Its major industrial products are
caustic soda and
chlorine, and it is used in many industrial processes and in the manufacture of
polyvinyl chloride,
plastics,
paper pulp and many other products. Of the annual production of around two hundred million
tonnes of salt, only about 6% is used for human consumption; other uses include water conditioning processes, de-icing highways and agricultural use. Edible salt is sold in forms such as
sea salt and table salt which usually contains an
anti-caking agent and may be
iodised to prevent
iodine deficiency. As well as its use in cooking and at the table, salt is present in many processed foods. Too much sodium in the diet raises
blood pressure and may increase the risk of
heart attacks and
strokes. The
World Health Organization recommends that adults should consume less than 2,000 mg of sodium which is equivalent to 5 grams of salt per day.
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