Lond. Murias Sodae, Edin. Dub. Chloride of Sodium. Muriate of Soda. Common Salt.

Syru Muriate de Soude (F.), Salzaures Natrum (G.), Zout (Belg.), Salt (Dan., Swed.), Sal commune (I.), Sal (S.), Melh (Arab.), Poppoo (Tarn.), Loon(H.), Nemuck (Pers.), Locnoo (Cyng.), Lavana (Sans.), Garam (Malay), Uyah (Jay.), Tarreeke (Esquimaux.)

This salt is one of the most abundant productions of nature, being found in almost every country of every quarter of the globe; either existing in mineral springs2 or lakes3; spread in strata under the surface of the ground4, or rising from it into mountains1; and to its presence also the ocean owes its saltness.2 In all these situations, however, it is generally mixed with earths and other matters; and, therefore, must undergo several processes to bring it to the degree of purity in which it occurs as an article of commerce.

1 Duncan's New Edinburgh Dispensatory, 216.

2 The salt spring of Luneberg yields 75,600 gallons of brine in twenty-four hours, of which 1/4th is saline matter, making the annual produce 55,000,000 lbs. of salt. - Kirwans Geo. Essays, p. 392.

3 These lakes are generally dry in the summer, being formed by the small streams from the hills settling in the valleys, and dissolving the salt of the soil. There is a lake or valley of this description eighteen miles from Aleppo, called in Arabic Subkhet al Jibool, or Valley of Salt; in which the salt is found, in the summer, crystallised from half an inch to two inches thick. - Russell's Aleppo, 2d edit. -i. 55.

4 The stratum of rock salt in Cheshire is 50 feet thick. The salt mine of Wiliska, near Cracow in Poland, is 6691 feet long, 1115 feet broad, and 743 feet deep. - Core's Travels, i. 197.

In Cheshire, where the greater part of the salt used in this country is made, the brine is pumped up from very deep wells, and evaporated in wrought-iron pans, which are generally about twenty or thirty feet long and broad, and nine or twelve inches deep; strongly set upon masonry over a large furnace, from which flues proceed under every part of the pan. They are protected from the weather by light pyramidal roofs of boards, sufficiently open, however, to admit of the escape of the steam from the boiling brine. When the brine attains the temperature of 100° Fahrenheit, it grows turbid, and carbonate of lime and of iron are separated. These are partly taken off by skimming, but much of the mass falls to the bottom, and cannot be removed until the first deposition of crystallised salt gives it a sufficient body to enable the workmen to rake it out. After this is carefully done, the evaporation is continued at a boiling heat, when the salt gradually forms, and falls to the bottom of the pan in beautifully white, delicate crystals, which are fished out, as they collect, with wooden vessels, and poured into large wpoden, hollow cones, having a hole at the apex, which is undermost.

When the salt is sufficiently drained, the cones filled with it are taken to a large room heated by stoves, where they remain until thoroughly dry.3 In warm climates, the sea-water is evaporated in shallow ponds by the heat of the sun; and in this mode what is denominated bay-salt is made; but in colder countries the evaporation is carried on by artificial heat, in a way similar to the Cheshire process. The crystals of the salt procured by these means are more perfect and pure, the more slowly the evaporation is conducted. Many improved processes have been invented for making culinary salt.4

The following table, drawn up by Dr. Henry, shows the components in the different varieties of salt used in this country: -

1 Near Cordova, in Spain, is a mountain of common salt 500 feet high, and nearly three miles in circumference.

2 The average quantity of salt contained in sea-water varies in different latitudes. Between 10° and 20° south, it amounts to rather more than one twenty-fourth; between 18° and 34° north, it is rather less than one twenty-fourth; and at the equator it is nearly one twenty-fifth. - Thomson's Chymistry, 4th edit, vol. iv. p. 441.

3 Aikin's Dictionary of Chymistry.

4 See Hobart's Engineer and Mechanics' Encyclopaedia, art. Salts.

The common salt of commerce, however, still contains small portions of chloride of magnesium, chloride of calcium, and sulphate of lime. To separate these, dissolve the salt in four times its weight of pure water, and drop into the filtered solutions, first, chloride of barium, and then carbonate of soda, as long as any precipitate falls. Filter and evaporate the clear fluid slowly till the salt crystallizes, which is pure chloride of sodium.2

Qualities.- Pure chloride of sodium3 is inodorous : its taste is agreeable, and strictly salt; and, when pure, it is perfectly devoid of any degree of bitterness. It is in regular cubes, which contain no water of crystallisation, and are not affected by exposure to the atmosphere. When it deliquesces, it contains chloride of magnesium. Its crystals decrepitate4 when heated, and melt in a red heat, losing about two per cent. of their weight; and, in a still greater heat, the salt is volatilised undecomposed in white fumes. Its specific

1 M. Berthier's analysis differs from that of Dr. Henry. From two specimens he obtained the following results:-Chloride of sodium 884; sulphate of magnesia .076; sulphate of lime .010; water and oil .030; with a minute portion of sulphate of soda, in 1000 parts.- Annates des Mines, xiii. p. 225.

2 Thomson s Chyndstry, 4th edit. ii. 377.

3 The term muriate, or hydrochlorate, of soda' is not chymically correct when applied to the dry salt; for in this state it is a compound of chlorine and soda, or a chloride, and becomes a hydrochlorate only when water is added; which, being decomposed, forms hydrochloric acid by giving up its hydrogen to the i chlorine, and soda by transferring its oxygen to the sodium or metallic base of that alkali. Dry, pure sea-salt, therefore, is a chloride .of sodium, the chlorine being in the proportion of 59.305 to 40.695 of the sodium, according to the analysis of Berzelius.

4 D ecrepitation is produced in two ways : 1. By expansion of the surfaces of crystals that are bad conductors of caloric-namely those of Chloride of Sodium, Sulphate of Potassa, Iodide of Potassium : 2. By giving out aeriform products - such as occur in Bicyanide of Mercury, Tartar Emetic, Bitartrate of Potassa, Acetate of Copper, Nitrate of Baryta.

. gravity is 2.126. It is nearly equally soluble in cold and in hot water; rather more than two and a half parts of either being required to dissolve one of salt.1 It is insoluble in pure alcohol. It consists of 1 eq. of sodium = 23.3, 1 of chlorine =35.42, equivalent = 58.72; being truly a chloride of sodium. It is decomposed by sulphuric acid and nitric acid. Medical properties and uses - This salt is tonic and anthelmintic in moderate doses; emetic and purgative in larger, and externally stimulant. In the ordinary mode of using it, the tonic power of salt operates in assisting the process of digestion; and, consequently, taken more freely, it proves useful in dyspepsia, and in correcting the weakened state of the intestines, which favours the propagation of worms. In large doses it is said to check vomiting of blood, and may be used as a purgative, although it is seldom employed.2 As a local stimulant, its solution in tepid water, in the proportion of ss. or j; to Oj. of water, forms the common domestic enema. It is used also as a fomentation to sprained and bruised parts; and, dissolved in a large proportion of water, it forms the best stimulant general bath, whether used cold, or in a tepid, or in a hot state. To act as a tonic, the dose of chloride of sodium may be from grs. x. to 3j but to operate by stool from ss. to j. is necessary. It should be largely diluted. Officinal preparation. -Murias Sodae siccatum, E. D.