Page:The American Cyclopædia (1879) Volume XIV.djvu/602

578 and the Kanawha region it has gradually decreased since 1862, when the business appears to have been most flourishing. In Massachusetts, Pennsylvania, Kentucky, Indiana, and Illinois the business is rapidly becoming unproductive, while Missouri and Tennessee no longer report any saline in actual operation. But the total production for 1870 was greater than that for 1860 by about 5,000,000 bushels, nn increase of 40 per cent. The salt industry is now very much depressed, especially in the Kanawha valley and at Syracuse, from the fact that the great strength of the Michigan and Goderich brines and the abundance of fuel in those localities enable these brands of salt to be successfully sold where Onondaga salt made from brines only half as strong, and Ohio and Kanawha salt made from brines still weaker, formerly commanded the market. In addition to these disadvantages, the Onondaga and Kanawha salt is driven from eastern markets by Liverpool salt, which is brought to our eastern seaports at a merely nominal charge by ships that load in return tobacco, cotton, and breadstuffs. Throughout the region lying on both flanks of the Rocky mountains the demand is rapidly increasing, and is mainly supplied from local sources, chiefly brine springs. In 1870 Utah produced 1,950 bushels, Idaho 13,400, Colorado 7,500, and Kansas 10,000. The production is rapidly increasing with the settlement of the country, and is almost without competition. On the Pacific coast salt has long been produced near Los Angeles and further north, and the production increased from 44,000 bushels in 1860 to 174,835 in 1870. The salt is obtained entirely by evaporation of sea water. Salt was formerly produced in Oregon, but is not now manufactured there.—Manufacture of Salt. The separation of salt from brines and sea water is conducted in three distinct ways: 1, by evaporation by the heat of the sun in shallow reservoirs, principally practised with sea water in the southern temperate or tropical regions; 2, by artificial heat, in very long shallow pans, as in Cheshire, or in kettles, as at the Onondaga salines; 3, by exposing sea water to intense cold, when the ice formed is nearly pure, and a concentrated brine remains, which is afterward subjected to one of the first two processes. Weak brines are frequently brought to a certain strength by solar evaporation, and then finished by boiling; or more frequently they are pumped up into elevated reservoirs, and suffered to trickle over the surface of bundles of brush or thorns built up into walls, sometimes 30 to 50 ft. high and 5,000 ft. long, fully exposed to the sun and wind; the great amount of surface thus obtained causes the evaporation to go on very rapidly, and a few repetitions of the process bring very weak brines to suitable strength for boiling. This process is known as “graduation;” and the same effect is sometimes obtained by allowing the water to trickle over ranges of cords suspended perpendicularly.

The third process is practised in northern Europe. In nearly every locality certain details are employed in the evaporation due to peculiarities in the brines, in the fuel employed, proximity to the sea, &c. As an illustration of the general methods employed when treating sea water, the operations at Berre near Marseilles are thus described by Dr. T. Sterry Hunt, in a paper published in the “Geological Survey of Canada” for the years 1853-'6. The waters of the Atlantic contain from 2.5 to 2.7 per cent. of common salt, and those of the Mediterranean about 3 per cent. While the latter therefore afford a stronger brine, the dry and hot summers of the southern shores are also more favorable for the evaporation (which is conducted without artificial heat) than the cooler and more rainy coasts of Brittany and La Vendée. The Mediterranean waters, moreover, contain about 0.8 per cent. of sulphates and chlorides of calcium, magnesium, and potassium; and from the residue, or mother liquors, after most of the common salt has been separated, it is found that salts of magnesia and potash and sulphate of soda may be obtained of almost equal value with the salt which is the primary object of the manufacture. The salines of Berre, however, where these operations are very successfully conducted upon a grand scale, do not use the strong sea water, but are supplied from a lake which, though connected with the tide, is freshened fully one half by streams from the interior. Other advantages afforded by the situation compensate for this weakness of the brine. The broad receiving basins of these salines must be so situated that they can be flooded at very high tides, and be protected by dikes against their incursions when supplies of salt water are not wanted. A clayey soil is important to prevent infiltration, and give strength to the dikes. The water being let into the great shallow basins, it is allowed to remain till it deposits its sediments and begins to evaporate by the warmth of the sun. It is thence conducted successively through other basins of 10 to 16 in. depth, in which the evaporation goes on, and the lime it contained is deposited as a sulphate. As its bulk decreases smaller shallow basins suffice for holding it after it is separated from the sediments and lime, and in these it is concentrated by continued evaporation to a saturated brine. When this marks 25° Baumé, it is transferred to the salting tables, upon which the crystalline crusts soon collect. Pure salt to the extent of 25 per cent. of the whole product separates between 25° and 26°, and may be kept by itself, the brine in this case being removed to another table. Upon this salt of second quality is deposited to the extent of 60 per cent. of the whole, between 26° and 28.5°; and upon other tables the remainder is collected between the last degree named and 32°. The last product, though somewhat impure and deliquescent from the magnesian salt it contains, is preferred