Modern chemistry sense is from 1790. Meaning "experienced sailor" is first attested 1840, in reference to the salinity of the sea. Salt was long regarded as having power to repel spiritual and magical evil. Many metaphoric uses reflect that this was once a rare and important resource, such as worth one's salt (1830), salt of the earth (Old English, after Matthew v.13). Belief that spilling salt brings bad luck is attested from 16c. To be above (or below) the salt (1590s) refers to customs of seating at a long table according to rank or honor, and placing a large salt-cellar in the middle of the dining table.
Some cultures, especially in Africa and Brazil, prefer a wide variety of different rock salts for different dishes. Pure salt is avoided as particular colors of salt indicates the presence of different impurities. Many recipes call for particular kinds of rock salt, and imported pure salt often has impurities added to adapt to local tastes.[12] Historically, salt was used as a form of currency in barter systems and was exclusively controlled by authorities and their appointees. In some ancient civilizations the practice of salting the earth was done to make conquered land of an enemy infertile and inhospitable as an act of domination. One biblical reference to this practice is in Judges 9:45: "he killed the people in it, pulled the wall down and sowed the site with salt."[13]
Hope no one gets turned into a pillar of salt today.