Salt obtained in this manner is very pure. But it has been estimated that a single salt plant should contain at least 5,000 acres of land to make the solar system practical. Salt is found beneath the ground in almost every part of the world. Sometimes the salt lies near the surface or even above it. Rocks of salt that appear above the ground are called salt licks. However, most salt veins lie far beneath the earth's surface and the salt must be mined in much the same way that coal is mined. Shafts are sunk and elevators are installed in them. The miners descend, and by means of compressed air drills and electric crushing and shoveling machines, break loose the halite. Elevators take the salt to the top of a tippler, a building that may be eight stories high. On its way down through the building, it goes through crushers, passes over screens that separate it into crystals of various sizes, and is put in sacks or bulk carloads. These are shipped to consumers. But, Much of the salt produced in the United States comes from salt wells. This salt is dissolved by water and pumped to the surface. A salt well is drilled in much the same way that a water or oil well is drilled. The salt well gas a double pipe, or casing, sunk into it. One pipe is inside the other, leaving space between the two. Pure, fresh water is pumped down through this space to the salt vein below. It forms a solution of salt and water, which is heavier than pure water. The brine sinks to the bottom of the well. The solution is then forced up the inner pipe by the pressure of the fresh water that continues to come down. When a vein of salt lies very deep, air pressure forces the brine to the surface. The brine that comes from the well contains only the impurities that disso!.
lve in water. Solid impurities are left at the bottom of the well. The brine is refined in about the same manner as sea salt. More than 12 percent is taken from the sea, over 29 percent from mines, and about 57 percent for wells.
