Sources Of Salt
( Originally Published Early 1900's )
At one time nearly the whole of the salt used as food and for industrial purposes was obtained from sea-water, and in many countries where the climate is dry and warm and there is a convenient sea-board, large quantities are still so obtained. In Portugal more than 250,000 tons are annually produced, and about the same quantity is obtained on the Atlantic and Mediterranean coasts of France. Spain has salt-works in the Balearic Islands, the Bay of Cadiz, and elsewhere, which turn out annually 300,000 tons; and even the small Adriatic seaboard of Austria produces every year from 70,000 to 100,000 tons. The peninsula and islands of Italy yield about 165,000 tons, and there are still a few establishments in England and Scotland; but in these latter countries the industry has been almost entirely driven out by the rock-salt works. The salt obtained from this source is called sea " or " bay " salt. The works are generally called salt gardens —saline (Spanish) — salz garten, in Austria. They consist of a series of large, shallow evaporating reservoirs. The sea water is admitted, and flows slowly from one to another, all the while evaporating under the heat of the sun, until finally the dry salt remains in crystalline crusts on the salting-tables in the final basins. These reservoirs vary from ten to sixteen inches in depth, the sediment and many of the impurities being deposited in the earlier and deeper basins in the first stages of evaporation. Between the temperatures of 25 and 26 degrees (Baume) pure salt is deposited, equal to about twenty-five per cent. of the whole. This is kept pure by conducting the brine to separate salting-tables at this temperature, and, after it reaches 26 degrees, carrying it on to other basins, where a second quality, equal to about sixty per cent of the whole, is formed. After the brine reaches 28.3 degrees it is led into still other basins, where the remainder of the salt is deposited. The salt is raked up and sold just as it is formed, with the slight purification resulting from a few months' exposure to the weather, which is customary. The evaporating surface of these shallow basins covers, in many establishments, hundreds of acres. Those at Berre, on the Mediterranean, have an area of 815 acres. Sea-salt has been obtained in this way in many of the seaboard States of the United States, but not to any extent. The other great source of common salt is the vast mineral deposits. Salt also occurs as a mineral in an almost pure state, and associated with the rocks of almost every geologic period. Many of the deposits are of vast extent, and are another great commercial source of this substance. This mineral deposit is called rock-salt, and is evidently the result of the evaporation of great shallow bodies of salt-water in remote ages, as is proved by its generally stratified nature, with beds of clay intervening, and the occurrence of marine shells and fossils in the surrounding rock formation. Large mines are worked in England and all the European countries, and in many places throughout the world. The most famous of all is the mine at Williczka, nine miles from Cracow, in Galicia, which has been worked continuously for upward of six hundred years. It is stopped-out in longitudinal and transverse galleries, with frequent large vaulted chambers supported by massive pillars. These extend on four different levels, and have a total length of 30 miles, the mine being 1 mile 1,279 yards long by 830 yards wide and 284 yards deep. The lower levels contain streets and houses, constituting a complete village ; and many of the miners, of whom there are 800 to 1,000, rarely come above ground. The salt is sold just as it is dug out of the mine, and 55,067 tons are annually extracted. The total extent of this deposit is 500 by 200 miles, with an average depth of 1,200 feet. Salt is also obtained in many localities from mineral deposits by means of salt-wells. In some cases the water occurs naturally in the salt strata, and the saturated brine is reached by deep borings (sometimes 1,500 feet); in other cases water is introduced into the borings and then pumped out again, two concentric tubes being employed. After the brine is secured it is evaporated by artificial heat in large iron vats. The salt-wells in Onondaga County, New York, near Syracuse and Salina, are a large and important industry. Michigan has the largest output next to New York, and many other States produce it to some extent ; but the home supply is not equal to the demand, and there is a large annual importation into the United States.