SALT Winery • though usually so denominated, is chemically, the muriate of soda, and, according to recent discoveries, a chloride of sodium, being a compound of chlorine, with the metallic base of soda. This salt is obtained by a variety sf methods. It is either dug out of the earth in a solid form, and dissolved, purified, and evaporated for use ; or sea-water is eve either by natural or artificial means, and salt is obtained from the ' residuum. The most abundant supply of rock-salt in this country is obtained from the mines in Cheshire, where the brine is pumped up from the brine-pits, saturated with rock-salt, and then boiled. One hundred tons of the saturated solution of rock salt in sea-water will be found to yield about twenty-three tans of salt.
The celebrated mines of Poland, whence the rock-salt has been continually abstracted in immense quantities for a period of upwards of five hundred years, where, at times, they have 20,000 tons ready for sale, is, however, not so pro ductive as those in Cheshire. At Cordova, in Spain, there is a mountain of pure rock-salt, from 400 to 500 feet high, and a league in circuit; the depth below the surface of the ground is unknown. In Louisiana, near the river Missouri, there is said to be a mountain of pure rock-salt of the best quality, which is 80 miles long, 45 miles wide, and of an immense height.
The waters of the ocean every where abound with common salt, though in different proportions : the average has been calculated to be about one-thirtieth of its weight. In the cold climates, the quantity of salt in the sea-water does not appear to be nearly so great as between the tropics. In Russia, and other northern countries, the salt is usually obtained from the sea-water, by freesing the latter; the ice, which is nearly fresh, being then removed, the remaining brine is very strong, and is subsequently evaporated by boiling. In the southern of Europe, and other warm countries, the usual mode of obtaining the salt by spontaneous evaporation. A fiat piece of ground near the sea is chosen, and banked round, to prevent its being overflowed at high water. The space within the banks is divided by low walls into several compartments, which successively communicate with each other. At flood tide, the first of
these is filled with sea-water; which, by remaining a certain time, deposits its impurities, and loses part of its aqueous fluid. The residue is then sufferedto run into the next compartment, and the former is filled again as before. From the second compartment, after a due time, the water is transferred into a third, which is lined with day, well rammed and levelled. At this period, the empor ration is usually brought to that degree, that a crust of salt is formed on the surface of the water, which the workmen break, and it immediately fills to the bottom. They continue to do this until the quantity is sufficient to be raked out and dried in heaps : this is called b In several parts d France, and t of China, the sands of the sea shore are washed. and the brine thus obtained is subsequently evaporated in boilers. In various places of Germany and France, the salt waters are pumped up to the top of very extensive sheds, filled with brushwood, over which it is duly distributed by means of gutters, whence, falling in drops from sprig to sprig, a rapid evaporation takes place over an immense surface ; the same water is pumped up many times before it is sufficiently concentrated to be drawn off into boilers, which complete the operation. In Mr. Bakewell's Travels in the Tarentaise, is riven an interesting description of a great work of this kind, at Montiers ; which the author says, is perhaps the best conducted of any in Europe, with respect to economy. Although the waters of Montiers have only half the strength of sea-water, yet the process of evaporation is so conducted as to afford a good profit ; the arrangements are necessarily very simple and inge nious, and might probably be introduced with great advantage in many parts of our own coast. We have not space for the details. The graduation houses, described at page 669 in Dr. Ure's Chemical Dictionary, (second edition,) are works of a similar kind, and are there explained by engravings.