It has been estimated through scientific analysis that the water of the seas contains about four and a half million solid cubic miles of salt. All these salts have reached into the seas from the earth. The rain water and melted snow water dissolve minerals from rocks and flow down through the rivers into the oceans and seas. These are main sources of salt deposits in ocean and sea water. It has been found that on the whole sea water contains about three to three-and-half percent of common salt. But millions of years ago evaporation took place from the water of bays, which were cut off from the sea and became salt lakes.
Now the question arises, how do we get common salt?
Common salt in fact is a compound of sodium and chlorine. It also contains several minerals such as iodine. One atom of sodium combines with one atom of chlorine and forms one molecule of sodium chloride.
Since sea has an abundant quantity of salt, it remains the main source of its supply. To obtain it through artificial means, water is led into wide, shallow basins about 3 feet deep. In the first one the solid impurities like sand, mud and tiny living creatures get settled. Calcium sulphate is also separated from the water in this basin. The water then flows into a succession of basins and evaporates there. In the process, sodium chloride is deposited there. This is collected, dried, refined and purified.
In cold countries, a different method is used for the extraction of salt. In this, sea water is allowed to freeze, since the ice from frozen sea water does not incorporate the molecules of salt. These accumulate in the unfrozen water under the ice and make it more salty. The floating ice is gradually removed and further frozen, until only a little highly saline water remains. This is collected and evaporated by means of artificial heat, and salt is collected.
There are many salt deposits in the world. The salt formations of Kansas, Oklahoma, Texas and New Mexico in the U.S.A. cover an area of about 100,000 square miles and are the largest in the world.
Common salt is basically used for flavouring and preserving food.