The process by which the salt is extracted from the brines, is divided into two operations; the schlotage, or evaporation, and the soccage, or crystallization. The brine is rapidly heated to violent ebullition, and fresh liquid continually added to replace the evaporated water. A considerable deposit is then formed, which consists chiefly of a double sulphate of soda and lime, and is removed from time to time. After about twenty-four hours, when a scum of crystallized salt begins to form on the surface, the temperature is allowed to fall considerably below the boiling point of water, and maintained at that point for several days, while the crystallization is proceeding. The higher the temperature at which the crystals are deposited, the finer the grain of the salt. It is found that when chloride of magnesium is present in considerable quantity, a film of crystals of salt is continually formed upon the surface of the brine, and much retards the evaporation; this evil has been obviated by the addition of sulphate of soda, which converts the chloride of magnesium into sulphate of magnesia.1

The crystals of salt are afterwards drained, dried by exposure to air, and packed.

The mother-liquors of the salt-works are employed for the preparation of sulphates of soda and magnesia, bromine and iodine.

2

Properties.-The ordinary rock-salt is usually contaminated with sesquioxide of iron, to which its peculiar rusty color is due. Perfectly pure rock-salt is transparent and colorless. Its cleavage always exhibits the form of the cube. Common crystallized salt contains various impurities, consisting chiefly of sulphate of soda, chloride of calcium, sulphate of lime, chloride of magnesium, and sulphate of magnesia; the chlorides of calcium and magnesium confer upon it the property of becoming moist when exposed to air, which is not exhibited by pure salt.

Chloride of sodium crystallizes in cubes which are sometimes aggregated together in the form of hollow, four-sided pyramids; occasionally, it is deposited from urine in octohedra; the crystals contain no water of crystallization, and are generally transparent; they are unalterable in moderately dry air.

When heated, the crystals decrepitate, from the expansion of a little water mechanically inclosed: if heated to redness, they fuse to a clear liquid, which becomes crystalline on cooling; at a bright red heat, the salt volatilizes, unchanged, in thick white fumes. 1 part of chloride of sodium dissolves in about 2.7 parts of water; its solubility is very slightly increased by elevation of temperature. A saturated solution has a specific gravity of 1.205, and boils, according to Gay-Lussac, at 2290.5 F. (110° C.); if such a solution be exposed to a temperature of 14° F. (-10° C.), large transparent prisms are formed, of the composition NaCl+4Aq. These crystals effloresce in the air at low temperatures, and are easily converted into the anhydrous cubical crystals. When a saturated solution of chloride of sodium is boiled in an open vessel, the ordinary cubical crystals are deposited. Chloride of sodium is almost insoluble in alcohol.

Uses of Chloride of Sodium.-Its use as a condiment suggests itself at once; again, its great antiseptic properties render it peculiarly applicable to the preservation of meat and other articles of food. The enormous consumption of chloride of sodium for the manufacture of carbonate of soda has already been mentioned. posed chiefly of earthy carbonates, deposited in consequence of the escape of carbonic acid; this fills up the interstices in the heap, which is therefore changed every five or six years.

1 Berthier has recommended hydrate of lime for the decomposition of the chloride of magnesium, when hydrate of magnesia is precipitated, and chloride of calcium remains in solution; on continuing the evaporation, the latter salt decomposes the sulphate of soda, yielding chloride of sodium, and sulphate of lime, which is deposited.

2 Rose found, in the crystals of rock-salt from Wieliczka, a peculiar hydrocarbon (C2Hg), which is confined in cavities in the salt, and escapes with a crackling noise on dissolving the crystals in water.

Chloride of sodium is also employed in glazing the coarser kinds of earthenware; for this purpose, it is thrown into the kiln in which such ware is baked, at a full red heat, when it is converted into vapor, which acts upon the surface of the clay in such a manner as to produce a silicate of soda, forming a true glass. Since the clay from which earthenware is fabricated almost invariably contains sesquioxide of iron, the decomposition may be represented by the following equation, where the clay is regarded as neutral silicate of alumina, containing sesquioxide of iron :

Al,0,.3SiO,+Fe,0,+3NaCl=A1,0,+3(NaO SiO,)+ FeCl ̧.

The sesquichloride of iron is expelled in the state of vapor. If no sesquioxide of iron be present, nevertheless silicate of soda is formed, the aqueous vapor which is found amongst the products of combustion in the kiln taking part in the reaction, thus:

A1,0,.3SIO,+3HO+3NaCl=Al ̧0 ̧+3(NaO.SiO,)+3HCl.

The bromide and iodide of sodium crystallize in cubes which are very soluble in water; they are prepared in the same manner as the corresponding compounds of potassium, which they very much resemble. The iodide of sodium occurs, it will be remembered, in the mother-liquors of salt-works, &c.

The fluoride of sodium crystallizes in anhydrous cubes, which require 25 parts of water for solution.

Sulphides of SODIUM.

§ 176. The sulphides of sodium are probably as numerous as those of potassium, but only the first of the series, NaS, appears to be well-known. This sulphide is obtained by methods exactly similar to those employed for the preparation of the sulphide of potassium, and crystallizes in large prismatic crystals, containing 9 eqs. of water. This compound resembles sulphide of potassium in all its properties; it is oxidized in the same manner when exposed to air, and also combines with the sulphur-acids.

By fusing together equal weights of carbonate of soda and sulphur, a liver of sulphur may be prepared, exactly similar to that obtained with carbonate of potassa, and sometimes used in medicine.

A hydrosulphate of sulphide of sodium, NaS.HS, is prepared by the same methods as the corresponding compound of potassium.

A sulphide of sodium appears to be an essential constituent of the color known as ultramarine. The natural ultramarine is extracted from the mineral known as lapis lazuli; it consists chiefly of silica, sulphuric acid, sulphur, alumina, soda, lime, and oxide of iron.1

This pigment was first artificially prepared by Guimet, in 1827. The process by which it is obtained requires very great precaution to insure success, since the conditions necessary for the production of a perfect color are not thoroughly understood; every manufacturer has his own prescription for its preparation, but

1 The following are the results of an analysis of lapis lazuli :Silica

45.40

the essential part of the process appears to be the fusion, at a high temperature, of a mixture of soda, or carbonate of soda, sulphur, silica, and clay containing a little iron, and the subsequent roasting of the mass thus obtained. The product is washed with water, and dried. It is yet doubtful whether the presence of iron is essential (as is generally asserted) to the production of a blue color.

Ultramarine is very stable in the air; it resists the action of alkalies, and of a high temperature; acids, however, bleach it immediately, with evolution of sulphuretted hydrogen, showing that the sulphide which is present is essential to the color. If carbonate of potassa be substituted for carbonate of soda in the preparation of artificial ultramarine, a white compound is obtained, so that sodium would appear to be a necessary constituent.

Green ultramarine is said to consist of blue ultramarine which has not been roasted.

LITHIUM.

Sym. Li. Eq. 6.5.

§ 177. This somewhat rare metal was discovered in 1818, by Arfwedson. Its name is derived from 2005, stony, because it was first obtained from a mineral.1

Davy prepared lithium from the oxide, lithia, by means of the galvanic, battery. Hitherto this metal has been obtained only in small quantity, but it is probable that larger quantities of it might be prepared by methods similar to those in use for extracting potassium and sodium from their oxides.

Lithium is very similar to potassium and sodium, and, like these metals, decomposes water at the ordinary temperature.

The OXIDE OF LITHIUM, LITHIA (LiO), occurs in certain minerals, particularly in spodumene, petalite, and lepidolite. The last is generally employed for the preparation of lithia; the powdered mineral is mixed with two parts of quicklime, and strongly heated; the mass is reduced to powder, and boiled with milk of lime, when alumina, sesquioxide of iron, and silica, are left undissolved, whilst the filtered solution contains potassa, soda, lithia, and a little lime; this solution is acidulated with hydrochloric acid, and concentrated, in order that most of the chloride of potassium may crystallize out; the lime is precipitated from the solution by carbonate of ammonia, the filtered liquid evaporated to dryness, and the residue ignited, to expel ammoniacal salts; this residue, consisting of the chlorides of potassium, sodium, and lithium, is digested with alcohol, which dissolves the chloride of lithium; this latter, after the evaporation of the alcohol, is decomposed by sulphuric acid, and the sulphate of lithia thus obtained subsequently converted into acetate by double decomposition with acetate of baryta; the solution of acetate of lithia, filtered from the sulphate of baryta, is evaporated to dryness, and the residue ignited, when it is converted into carbonate of lithia, from which hydrate of lithia may be obtained by decomposition with hydrate

of lime.

Properties.-Hydrate of Lithia (LIO.HO) resembles in its properties the hydrates of potassa and soda, but is less soluble in water, and does not deliquesce in air.

Its solution has a strongly alkaline reaction, and its basic properties are very

The chief minerals from which lithium is obtained are lithion-spodumene (3(LiO.SiO3), 4 (Al2O3.8SiO) ); petalite (silicate of soda, lithia, and alumina), and lepidolite or lithia-mica (containing silicates of alumina and lithia and silicofluoride of potassium).

powerful. Hydrate of lithia possesses the peculiar property of readily attacking platinum at a high temperature.

The Salts of Lithia are colorless, and much resemble those of potassa and soda; the nitrate is very soluble and deliquescent; the sulphate is soluble, and may be obtained in fine crystals; the carbonate is rather sparingly soluble; its solution has an alkaline reaction.

Phosphate of Lithia is sparingly soluble in water, and the double phosphate of lithia and soda is almost insoluble, so that we may test for lithia by mixing its solution with phosphate of soda, evaporating to dryness, and extracting with water, when the double phosphate of lithia and soda remains undissolved.

Chloride of Lithium crystallizes in cubes of the formula LiCl+4Aq; it is deliquescent, and very soluble in water; it also dissolves readily in alcohol, therein differing from the chlorides of potassium and sodium.

The salts of lithia, when exposed on platinum wire to the inner blowpipe-flame impart a red color to the outer flame.

From the foregoing brief description of the characters of the salts of lithia, it will be seen that this oxide forms a sort of conuecting link between the alkalies and alkaline earths.

AMMONIUM.

NH, Am. Eq. 18.

§ 178. This metal has never yet been obtained in the separate state; it is strictly hypothetical, and the grounds upon which its existence is assumed have been stated in the description of the compounds of nitrogen and hydrogen. The method by which the so-called amalgam of ammonium is prepared, together with the properties of this amalgam, have been detailed in the same place (§91). Since the compounds produced by the combination of ammonium with the electro-negative elements, and of oxide of ammonium with the oxygen-acids, are very analogous to those formed by potassium and sodium, we have deferred the history of these compounds till the present occasion.

OXIDE OF AMMONIUM, NH,O=AmO. Eq. 26.

A very good reason for supposing this compound to exist, although it has not been isolated, is found in the complete analogy between the salts, which are formed when ammonia (NH) is brought into contact with hydrated acids, and the corresponding salts of potassa and soda. When liberated from its compounds, oxide of ammonium is decomposed into ammonia and water.

NITRITE OF OXIDE OF AMMONIUM, NITRITE OF AMMONIA.

NH,O.NO,=AmO.NO.

§ 179. This salt is prepared by decomposing nitrite of silver with chloride of ammonium, filtering from the precipitated chloride of silver, and evaporating the filtrate in vacuo; it may likewise be obtained by passing nitrous acid into excess of ammonia, and evaporating over lime. It forms a mass of confused crystals, which are easily decomposed by heat; they are very soluble in water, and the solution, like the solid, evolves nitrogen when heated, according to the equation:

NH2O.NO,=4HO+N ̧.

According to Millon, if the solution be rendered slightly alkaline by ammonia, this decomposition will be gradual, but if a slight excess of a mineral acid bet

added, it will take place very rapidly. Concentrated sulphuric acid effects the same decomposition.

This salt is sometimes employed for the preparation of nitrogen (§ 80).

NITRATE OF OXIDE OF AMMONIUM, NITRATE OF AMMONIA.
NH,O.NO,=Am0.NO,.

The nitrate is prepared by dissolving ordinary sesquicarbonate of ammonia in moderately dilute nitric acid, perfectly free from hydrochloric acid, till the carbonate is slightly in excess; the solution is then evaporated down, till a drop placed upon a watch-glass solidifies on cooling, when the whole is poured out upon a clean stone slab, broken up, and preserved in a stoppered bottle.

If the evaporation be arrested at an earlier period, distinct crystals may be obtained on cooling, which are six-sided prisms, of the formula NH,O.NO,+Aq. Properties.-Nitrate of ammonia deliquesces on exposure to air, and is very soluble in water, with great reduction of temperature. When heated, it fuses at about 226° F. (108° C.), and at 482° F. (250° C.) is rapidly decomposed into water and oxide of nitrogen :

NH,O.NO,=4HO+2NO.

If the temperature be raised so high that the vessel becomes filled with white fumes, there are produced, beside the oxides of nitrogen, a quantity of nitric oxide, free ammonia, and nitrite of ammonia. In the presence of spongy platinum, the salt is decomposed at 320° F. (160° C.), yielding water, nitric acid, and nitrogen

5(NH,O.NO,)=2(HO.NO,)+18HO+N ̧. This salt deflagrates violently with carbon, and other combustible bodies, at a high temperature. When thrown into a redhot crucible, it deflagrates, emitting a pale yellow light, probably due to a combustion of the ammonia at the expense of the nitric acid. When heated with an excess of concentrated sulphuric acid, nitrate of ammonia is decomposed in the same manner as when heated alone. Nitrate of ammonia is employed as a source of nitrous oxide, and is also occasionally used to facilitate the incineration of organic substances, and in the preparation of refrigerating mixtures.

§ 180. SULPHITE OF OXIDE OF AMMONIUM, SULPHITE OF AMMONIA, NH,O. SO, AmO.SO,.-When sulphurous acid is passed through an aqueous solution of ammonia, combination takes place, with disengagement of heat. The sulphite may be crystallized from this solution. It is very soluble in water; the solution evolves ammonia when boiled; the crystals, when beated, evolve ammonia and water, whilst a bisulphite sublimes. The solution of sulphite of ammonia, prepared by passing sulphurous acid into solution of ammonia, is sometimes employed in analysis.

SULPHATE OF OXIDE OF AMMONIUM, SULPHATE OF AMMONIA.

NH,O.SO.=Am0.SOg

Sulphate of ammonia occurs native as mascagnine, which is an efflorescence upon recent lavas.

1 A class of substances exists, composed of ammonia (NH3) in combination with certain anhydrous acids. Thus with sulphurous acid, the compound NH,.SO, (sulphite of ammon); with sulphuric acid NH ̧.SO, (sulphate of ammon), sometimes improperly termed sulphamide). These compounds are converted into the corresponding ammoniacal salts, when boiled with water. The amides, properly so called, are compounds of amidogen (NH2) with an acid, minus 1 equivalent of its oxygen, and may often be produced by the elimination of 2 equivalents of water from the ammoniacal salt. They are converted into salts of oxide of ammonium by boiling with water. Sulphamide (NH2.SO2) is a white deliques