SALT, a name which, though generally applied to all crystallized substances that are easily soluble in water, and even to those which are not soluble, is em ployed in common life to designate the muriate of soda in whatever way it is obtained. As the various che mical and mineral salts have been already fully de scribed in our articles CHEMISTRY and MINERALOGY, we propose at present to give an account of the ma nufacture of muriate of soda, for the purposes of do mestic economy, and of the various brine springs and mines, Sze. of rock salt, from which it is often ob tained.
Salt is obtained from three different sources.
1. From sea water, by evaporation, either by means of the heat of the sun, or by boiling.
2. From natural brine springs, salt lakes and rivers, by evaporation or boiling.
3. From native rock salt or muriate of soda.
1. Manufacture of Salt from Sca [Vizier.
1. By the heat of the sun.—In warm countries where the rays of the sun possess sufficient heat to produce a rapid evaporation, salt of the very best kind is ma nufactured without the aid of any artificial heat. This manufacture is carried on to a great extent in France, Spain, and Portugal.
In the south of France, the land chosen as the place of manufacture is generally clayey, and not liable to be inundated. It is then surrounded by a bank or wall having inlets next the sea, which may be opened or shut by proper sluices. The land thus en closed is divided into compartments of from 50 to 100 acres. When the water has evaporated to such a degree that the deposition of the salt has commenced, the brine is pumped out of the compartments on a platform divided into compartments conducted by a common gutter, and elevated so as to have a free ex posure to the air. As the evaporation advances more brine is pumped up till a crust of salt about three inches thick has been deposited. When the crust has become hard, it is broken into pieces and laid up in heaps in a place protected from rain. A fluid called the bittern, from its containing a number of the earthy bitter salts, drains from these heaps for a long time, and it requires three years exposure to drain them till the salt is esteemed perfectly good. If this drain
ing has not been completely effected, the salt will deliquesce and have a disagreeable bitter taste. The bittern is in some places collected for the purpose of procuring from it sulphate of magnesia, and other substances containing magnesia. The salt procured by this process has been called Bay Salt, and has al ways been in great request for preserving animal fond. For farther information on the subject, see our articles FRANCE, and INDIA.
2. By artificial heat.—The preparation of salt by heat is adopted only in countries where fuel can be bad at a very moderate price, or where the sun's heat is too weak to effect the evaporation with sufficient ra pidity.
In salt works of this kind, a long and low building called a saltern, is erected near the shore. It is divid ed into two parts, one called the fore-house for receiv ing the fuel and covering the workmen; the other the pan or boiling house, for receiving the furnace and boiler. There are two openings from the back of the furnaces into the fore-house, and from them is raised a wall to prevent the ashes from flying into the salt pans, and in that wall is a door forming a communica tion between the two houses. The pans, which are of an oblong form, are commonly 15 feet long, 12 feet broad, and 15 inches deep. They consist generally of plates of wrought iron united with nails, with a strong cement in the joints. The bottom of the pan is sus tained by strong iron bars placed across it. The sides of the pan are sometimes made with lead, as iron is apt to oxidate. Round the sides of the pan is a walk five or six feet broad, from which the workmen draw out the salt. The roofs of the salterns are fastened with pegs of wood, as iron nails would moulder away in a few months.