SALT. See Soimmr. Common salt is either procured in the solid crystalline state called rock-salt (q.v.), as a natural brine from wells or springs, or by the evaporation of sea-water. In the first ease, it is obtained by mining, often at great depths, as at North wich in Cheshire; at Salzburg, Madgeburg. Berchtesgaden, and Wimpfen in Germany; Cracow in Poland; in the Punjab and other parts of the world.
Rock-salt almost always contains impurities, and therefore is dissolved in water, can the insoluble matters mixed with it are deposited at the bottom. The brine is then drawn off and evaporated by artificial heat in large iron pans.
Natural brine is obtained at Droitwich and Stoke in 'Worcestershire, and Nantwich to Cheshire. At Droitwich the shaft is only sunk 175 ft., and the brine rises to the sur face and overflows if not pumped. There are, however, reservoirs made for it, into which it is puniped, and from which it is distributed to the various works, lchich are little more than large sheds, with numerous openings in their roofs to allow the steam free egress. Flues run from end to end of the floors, and on these rest the iron evaporating-pans, which are about 65 ft. long by 25 broad, and about 18 in. in depth In other olaces very deep shafts have been sunk, and the brine requires to be pumped from a great depth. The flues heat the brine nearly to boiling-point, and as a large surface is exposed, the evaporation is very rapid. and the crystals are small, as in the fine table-salt. If, however, the heat is more gentle, the salt is coarser, and is fit for curing meat, fish, etc. ; and when very slow, a much coarser kind, called bay-salt, is pro duced. Salt is obtained from sea-water in many parts of the world, and this is effected by simply evaporating it in brine-pits or shallow square pools, dug on the shore for the purpose. When the evaporation has proceeded to a certain extent, the liquid assumes a reddish color; a pellicle of salt forms on its surface. which soon breaks and sinks down, to be followed by another; and the crystallization then proceeds rapidly. When com plete, the salt is removed to sheds open at the sides, and then piled in heaps, in order that the chloride of magnesium may be removed. This is very easy, for as it is extremely deliquescent, it liquefies by exposure to the atmosphere, and runs out. The salt is then redissolved and crystallized, if great fineness is required.
SALT (ante), sodium chloride—chemical symbol, NaCi—an essential constituent of food, the use of which dates from the earliest ages. The Romans are thought to have b'ien the first to manufacture it. Many ancient philosophers treat of it scientific ally, but the correct view or is composition as the chloride of sodium is of quite recent origin, sir Humphrey Davy having first experimentally demonstrated it in 1810. Salt
is presentIn every part of the human frame, organized in the solids and dissolved in the fluids. Besides its use as an article of food, immense quantities are consumed in the yeservation of meats, etc., and for other industrial purposes. The annual rate of con in different countries, being estimated at 50 lbs. for each person in the [jited States, while in Great Britain it is 22 lbs., and in France only 15 lbs. The salt of commerce may be roughly classed under two general heads, that which is found in its crystalline state in deposits of rock-salt, and that which is produced by the evaporation and purification of salt brines. Deposits of rock-salt are not confined to any one series of strata. but appear at various depths in the crust of the earth and in nearly every geologi cal horizon. Thus the great English deposits in Cheshire and Worcestershire, as well as the deposits in France and Germany, occur in different members of the triassi• group; the mines of Wieliztka in Austrian Galicia. those at the base of the Carpathian moun tains, thOse in Tuscany and Sicily, belong in the tertiary; in the Austrian Alps deposits exist in the oolitic limestone; and in other places they occur in the carboniferous and even in the Silurian strata. The deposits in Petit Anse island, Vermilion bay, La., are only from 16 to 18 ft. below the surface, while those in Ontario, Canada, lie at a depth of fully 800 feet. Very Hale rock-salt, as such, is used either in England or in the United the large quantities mined in the former country being mostly exported. But the deposits of rock-salt are usually turned into artificial brines by dissolution in water while still iu the mines, and the product of these brines furnishes much of the salt that is used in England. The natural brines must, of course, include the sea-water which is largely depended upon in South and Central America, in the West Indies, and in southern Europe. Very little salt is made from sea-water in the United States—not more than 400,000 hush. annually. The natural brines proper are the salt springs and wells which result from the accidental dissolution of rock-salt deposits by passing cur rents of water. These are found with more or less•frequency in almost every country; they abound in England, in northern Italy, in Prussia, and especially in Russia. Salt hikes also are frequent in the latter country, hut in the Great Salt lake the United States possesses the largest known inland body of salt water.