Used in alchemy for a fundamental principle of nature, a member of the triad mercury, sulphur, and salt, corresponding to spirit, soul, and body; or to fire (or air), water, and earth. Paracelsus regarded these as the mystical elements of all compound bodies. All forms of matter were reducible to one or other of them -- everything was either a sulphur, a mercury, a salt, or a compound. The philosopher's stone was said to be a compound of all three. Thus salt is the physical rudiment, as illustrated by the cubical crystals of common salt. Ancient thought regarded such elements as fundamental principles which manifest on various planes, nor did it make hard and fast distinctions between physical and nonphysical; but modern thought has given a fictitious reality to physical objects, and regards the ancient use of the terms as metaphorical. The veneration shown for salt was not a mere deification of its physical virtues, but a recognition of the salt-principle in nature, of which ordinary salt is merely a physical emblem. The well-known stimulant, flavoring, and preservative qualities of salt prove it to be a physical manifestation of an important principle; such phrases as bread and salt, and salt of the earth are therefore theosophy, as concerns not merely figures of speech but a use of salt in its more radical sense. For the same reason it played an important part, along with other substances, in sacrificial ceremonies.

The word was also used to include other bodies besides sodium chloride or common salt, and is still used in chemistry in this generic sense. With some alchemists we find arsenic taking the place of salt in the fundamental triad, and this would be one of the salts of arsenic.

The Roman Catholic ritual of the exorcism of salt, promulgated in 1851 and 1852 under the sanction of Cardinal Engelbert, Archbishop of Malines, and of the Archbishop of Paris, runs: "The Priest blesses the salt and says: 'Creature of Salt, I exorcise thee in the name of the living God . . . become the health of the soul and of the body. Everywhere where thou art thrown may the unclean spirit be put to flight' " (IU 2:85). A Qabbalistic version is similar.

Smith's Bible Dictionary
Indispensable as salt is to ourselves, it was even more so to the Hebrews, being to them not only an appetizing condiment in the food both of man, (Job 11:6) and beset, (Isaiah 30:24) see margin, and a valuable antidote to the effects of the heat of the climate on animal food, but also entering largely into the religious services of the Jews as an accompaniment to the various offerings presented on the altar. (Leviticus 2:13) They possessed an inexhaustible and ready supply of it on the southern shores of the Dead Sea. See: Sea, The Salt, THE SALT There is one mountain here called Jebel Usdum, seven miles long and several hundred feet high, which is composed almost entirely of salt. The Jews appear to have distinguished between rock-salt and that which was gained by evaporation as the Talmudists particularize one species (probably the latter) as the "salt of Sodom." The salt-pits formed an important source of revenue to the rulers of the country, and Antiochus conferred a valuable boon on Jerusalem by presenting the city with 375 bushels of salt for the temple service. As one of the most essential articles of diet, salt symbolized hospitality; as an antiseptic, durability, fidelity and purity. Hence the expression "covenant of salt," (Leviticus 2:13; Numbers 18:19; 2 Chronicles 13:5) as betokening an indissoluble alliance between friends; and again the expression "salted with the salt of the palace." (Ezra 4:14) not necessarily meaning that they had "maintenance from the palace," as Authorized Version has it, but that they were bound by sacred obligations fidelity to the king. So in the present day, "to eat bread and salt together" is an expression for a league of mutual amity. It was probably with a view to keep this idea prominently before the minds of the Jews that the use of salt was enjoined on the Israelites in their offerings to God.

Easton's Bible Dictionary
used to season food (Job 6:6), and mixed with the fodder of cattle (Isa. 30:24, "clean;" in marg. of R.V. "salted"). All meat-offerings were seasoned with salt (Lev. 2:13). To eat salt with one is to partake of his hospitality, to derive subsistence from him; and hence he who did so was bound to look after his host's interests (Ezra 4:14, "We have maintenance from the king's palace;" A.V. marg., "We are salted with the salt of the palace;" R.V., "We eat the salt of the palace"). A "covenant of salt" (Num. 18:19; 2 Chr. 13:5) was a covenant of perpetual obligation. New-born children were rubbed with salt (Ezek. 16:4). Disciples are likened unto salt, with reference to its cleansing and preserving uses (Matt. 5:13). When Abimelech took the city of Shechem, he sowed the place with salt, that it might always remain a barren soil (Judg. 9:45). Sir Lyon Playfair argues, on scientific grounds, that under the generic name of "salt," in certain passages, we are to understand petroleum or its residue asphalt. Thus in Gen. 19:26 he would read "pillar of asphalt;" and in Matt. 5:13, instead of "salt," "petroleum," which loses its essence by exposure, as salt does not, and becomes asphalt, with which pavements were made. The Jebel Usdum, to the south of the Dead Sea, is a mountain of rock salt about 7 miles long and from 2 to 3 miles wide and some hundreds of feet high.
one of the cities of Judah (Josh. 15:62), probably in the Valley of Salt, at the southern end of the Dead Sea.

meditation in real salt mine