Over the centuries, salt was valued for gold weight. Because of her began and ended the war, Bunty broke out, the whole cities were bought for it, and the influence of a person was determined by the number of available stocks of salts.
Basically, the value of salt was due to its wonderful property - the ability to save food products. People knew about it from ancient times, and perhaps it was thanks to the use of salt, humanity managed to avoid many epidemics and pass through the "bottle of neck" evolution.
For prevention of products, salt can be used in two states: in a dry form or as a salt solution. The first method was mainly used by our ancestors, but the storage of products in the brine is also practiced today.
Salt has a property that allows you to kill microorganisms: it literally pumps all the liquid from the bacteria, as a result of which it dies. This occurs due to the phenomenon, which is called osmosis - "The process of one-sided diffusion through a semi-permeable membrane of a solvent molecules in the direction of a larger concentration of the dissolved substance from an amount with a smaller concentration of the dissolved substance" [source].
The bacterium devoid of fluids ceases to multiply and dies, so the food, clumsy in the brine or sprinkled with salt, does not deteriorate.