Salt
Common salt, or the chloride of sodium, is found in many parts of the world in solid beds. Sea-water contains about 4 ounces of salt in every gallon. The springs of New York State furnish an enormous annual supply. Rock-salt is seldom pure enough for use, and where no natural brine-springs exist, an artificial one is formed by sinking a shaft into the rock-salt and introducing water, if necessary. This, when saturated, is pumped up and evaporated more or less rapidly in large iron pans. Besides its use for preserving meats, by absorbing water from the flesh, it is used as a source of sodium in the manufacture of caustic soda, and as a source of chlorine in the production of chlorohydric acid. It fuses at a red heat, and is hence used for glazing stoneware, earthenware, etc. This property renders sea-water unfit for foundry purposes. See SEA-WATER.
Salt-cake is the sulphate of soda as prepared for the manufacture of soap and glass. This compound is of great value as a flux for smelting valuable metals. By using a little on the surface of the metal in the crucible, the scum and dirt readily unite with the salt-cake, and the appearance of the metal is much improved. See FLUX.