A term commonly used in chemistry to denote a compound in definite proportions, formed by the union of an acid with an alkaline, earthy, or metallic base. We have already given a brief enumeration of some of the most remarkable, under the article Chemistry. In consequence, however, of the progressive discoveries which for the last half century have been continually made, and are still making, in chemistry, many deductions, which, at the time they were made, were considered as conclusive facts, have since been either wholly abandoned, or subjected to considerable modifications. A salt has usually been denominated by chemists a neutral salt, when the proportions of the constituents are so adjusted, that the resulting substance does not affect the colour of infusion of litmus or red cabbage. When the predominancy of acid is evinced by the reddening of these infusions, the salt is said to be acidulous, and the prefix super, or bi, is used to indicate the excess of acid: thus we call one particular salt super-tartrate of potash, and another, bi-sulphate of lime, where the acid exists in excess.

But when, on the contrary, the acid matter is in too small a quantity to completely neutralize the alkalinity of the base, the salt is said to be with an excess of base, and the prefix sub is attached to its name: thus we have the sub-phosphate of bismuth, etc.

The commercial name of a salt differs from that by which it is known to chemists: it may therefore be proper to show what kinds of salt are to be understood by the popular names which they bear in the shops.

Ammoniacal Mixed Salt, muriate of lime.

Ammoniacal Secret Salt of Glauber, sulphate of ammonia.

Arsenical Neutral Salt of Macquer, super-arseniate of potash.

Bitter Cathartic Salt, sulphate of magnesia.

Common Table Salt, muriate of soda.

Digestive Salt of Sylvius, or Diuretic Salt, acetate of potash.

Epsom Salt, sulphate of magnesia.

Febrifuge Salt of Sylvius, muriate of potash.

Fusible Salt, phosphate of ammonia.

Fusible Salt of Urine, triple-phosphate of soda and ammonia.

Glauber's Salt, sulphate of soda.

Marine Salt, muriate of soda.

Marine Argillaceous Salt, muriate of alumina.

Microcosmic Salt, triple-phosphate of soda and ammonia.

Nitrous Ammoniacal Salt, nitrate of ammonia.

Salt of Amber, succinic acid.

Salt of Benzoin, benzoic acid.

Salt of Canal, sulphate of magnesia.

Salt of Colcothar, sulphate of iron.

Salt of Egra, sulphate of magnesia.

Essential Salt of Lemons, super-oxalate of potash.

Salt of Saturn, acetate of lead.

Salt of Seidlitz, sulphate of magnesia.

Salt of Seignette, triple-tartrate of potash and soda.

Salt of Soda, sub-carbonate of soda.

Salt of Sorrel, super-oxalate of potash.

Salt of Tartar, sub-carbonate of potash.

Salt of Vitriol, purified sulphate of zinc.

Salt of Wisdom, a compound-muriate of mercury and ammonia.

Perlate Salt, phosphate of soda.

Polychrest Salt of Glauber, sulphate of potash.

Sedative Salt, boracic acid.

Spirit of Salt, muriatic acid.

Sulphureous Salt of Stahl, sulphate of potash.

Wonderful Salt, sulphate of soda.

Wonderful Perlate Salt, phosphate of soda.

Salt, Culinary; is in chemical language the muriate of soda: but 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 of methods. It is either dug out of the earth in a solid form, and dissolved, purified, and evaporated for use; or sea-water is evaporated, either by natural or artificial means, and salt is obtained from the purified 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 f&und to yield about twenty-three tons 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 productive 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 freezing 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 parts of Europe, and other warm countries, the usual mode of obtaining the salt is by spontaneous evaporation. A flat 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 suffered to 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 clay, well rammed and levelled.