The basics

Salt is the common name for the chemical compound sodium chloride (NaCl). Sodium chloride is made of sodium ions and chloride ions. Each sodium ion carries a single positive electric charge. Each chloride ion carries a single negative charge. Unlike charges attract each other. The larger chloride ions, shown here as green spheres, arrange themselves in a cubic close-packing, while the smaller sodium ions, shown here as silver spheres, fill all the cubic gaps between them. This structure is known as the halite structure and this arrangement is known as cubic close packed. This is most commonly known as the rocksalt crystal structure.
Salt is an important ingredient of life. A large section of the "Peng-Tzao-Kan-Mu", a treatise on pharmacology written in 2700BC, devotes details to more than forty kinds of salt. Roman soldiers received salt as part of their wages. "Salarium argentum" means "salt money" in Latin came to be called "salary" in English. In a treatise on the "Dignity and Utility of Salt" by Jean de Marcounille Percheron, Paris 1584, salt is likened in value to the four elements of earth, air, fire and water. Salt has been termed the "fifth element".


Healing Salt

Salt has its reputation as an incorruptible cleansing substance. It is universally regarded as potent against the  machinations of demons that bring much harm to humankind. Real harm is the failure of humankind to achieve life's aim, evil presents itself as obstacles preventing humankind to live life the way nature designed it to be.
Rock salt is worn on the neck as an amulet by the Neopolitan. Moroccans use salt as a talisman against evil. Laotian and Thai women bathe with salt after childbirth to immunise themselves from demonic assault. The Germans, the Balkans and the Todas of southern India, newborns are salted immediately. We see this preactised earlier by the Jews in Ezekiel 16:4. In England's northern counties, there is a custom of tucking a small bag of salt into a baby's clothing on his first outing. In Bohemia, mothers place a little bread and salt in the pocket of their daughters to protect her from evil glances. When a girl goes out for a walk the mother sprinkles salt on the ground behind her, so that she won't lose her way.
The peasants of Hartz mountain region in Germany place three grains of salt in a milk pot to keep witches away from the milk. In Normandy, peasants throw a little salt into the milk pot to protect the cow (who gave the milk) from influences of witchcraft. In the Aberdeen county of Scotland, salt is placed on the lid of a churn to preserve butter from uncanny influences. In Egypt, salt is thrown on burning coals and set down on the loads prior the journey of the caravan with the prayer, "May you be blessed in going and coming." In England, the Saxons use salt salve is used to disenchant from "nocturnal goblin visitors". The salve is applied at the patient's forehead, palms of his hands and soles of his feet. The patient should then taste the salt, a portion of it to be thrown to the fire, and pray for protection.
Before performing a spell, it is thus important to lay down a pinch of salt in each corner of the room. In the book Jewish Magic and Superstition: A Study in Folk Religion, Joshua Trachtenberg (on page 160) said, "Very often salt and bread were jointly prescribed to defeat the strategems of spirits and magicians. When a witch assaults a man, he can bring about her death by forcing her to give him some of her bread and salt. Murderers ate bread and salt immediately after their crime to prevent the return of their victim's spirits to wreak vengeance upon them... The common practice of bringing salt and bread into a new home before moving in, usually explained as symbolic of the hope that food may never be lacking there, was probably also in orign a means of securing the house against the spirits."

The Jews would set salt on a table before beginning a meal "because it protects one against Satan's denunciations".
In the time of Elisha, the men of Jericho complain to the prophet that, despite the pleasing location of the city, its waters are contaminated and it grounds barren. Elisha draws on the cleansing powers of salt to purify and heal the contaminated springs of Jericho so there shall be no more deaths or miscarriage.

 

2 Kings 2:20-22 (The Holy Bible, King James Version)
And he said, Bring me a new cruse, and put salt therein. And they brought it to him.
And he went forth unto the spring of waters, and cast the salt in there, and said, Thus said the Lord, I have healed these waters; there shall not be from thence any more death or barren land.
So the waters were healed unto this day, according to the saying of Elisha which he spake.

The Holy Water of the Roman Catholic church is prepared by exorcising and blessing salt and water separately, after which the salt is dissolved in the water and a benediction pronounced upon the mixture. The official prayer from the ritual reads as follows:

 

"Almighty God, we ask you to bless this salt, as once you blessed the salt scattered over the water by the prophet Elisha. Wherever this salt (and water) is sprinkled, drive away the power of evil, and protect us always by the presence of your Holy Spirit. Grant this through Christ our Lord. Amen"

The Jewish tradition forbids leaven and ferments on the altar. Salt is not only decreed meat sacrifices, it presents itself as a pure and holistic food preservative. It is easy to understand this law as salt functions to remove whatever remaining blood after a slaughter.

 

Leviticus 2:11-13 (The Holy Bible, King James Version)
No meat offering, which ye shall bring unto the Lord, shall be made with leave: for ye shall burn no leave, nor any honey, in any offering of the Lord made by fire.
As for the oblation of the firstfruits, ye shall offer them unto the Lord, but they shall not be burnt on the altar for a sweet savour.
And every oblation of thy meat offering shall thou season with salt, neither shalt thous suffer the salt of the covenant of thy God to be lacking from thy meat offering: with all thine offerings thou shalt offer salt.

A "salt covenant" suggests an unbreakable covenant. This is probably the origin for the word "salvation".

 

Numbers 18:19 (The Holy Bible, King James Version)
All the heave offerings of the holy things, which the children of Israel offer unto the Lord, have I given thee, and thy sons and thy daughters with thee, by a statute for ever: it is a covenant of salt for ever before the Lord unto thee and to thy seed with thee.

2 Chronicles 13:5 (The Holy Bible, King James Version)
Ought ye not to know that the Lord God of Israel gave the kingdom over Israel to David for ever, even to him and to his sons by a covenant of salt?

Salt and bread also became a guarantee for hospitality and friendliness. Cicero, in his treatise for friendship, cited the proverb "Many pecks of salt must be eaten together to bring friendship to perfection". In the Spanish province of Andalusia, it is regarded as flattery to call a wife or sweetheart "the salt box of my love". There is also a phrase "There is salt between us" as having no salt brings disloyalty and barrenness.