incorporated, and maintained at a red heat, in an earthen crucible, till no more carbonic oxide escapes :

BaO.SO+C=4CO+BaS.

The sulphate of baryta is sometimes mixed with lampblack, resin, and starch, made up into balls with a little water, and these carbonized in a coal fire.1

The black mass is powdered, boiled with a small quantity of water, and filtered while hot; on cooling, the sulphide of barium crystallizes out in thin, nearly colorless plates. If the sulphide be required for the preparation of some other salt of barium, the crude mass obtained as above may be boiled with a larger quantity of water, so that the solution shall not crystallize on cooling." Properties. The crystals appear to contain 6 eqs. of water. When exposed to the air, sulphide of barium is decomposed by the atmospheric water and carbonic acid, evolving sulphuretted hydrogen:

BaS+HO+CO,=BaO.CO,+HS.

Sulphide of barium is oxidized by steam, at a red heat, hydrogen being evolved, and sulphate of baryta produced.

When sulphide of barium is dissolved in water, it appears to undergo partial decomposition, hydrate of baryta and hydrosulphate of sulphide of barium being formed; double compounds of baryta with sulphide of barium (crystallizing with water) are also produced under these circumstances.

The aqueous solution of sulphide of barium, when exposed to the air, absorbs oxygen, first becoming yellow from the production of a higher sulphide, and afterwards depositing crystals of hyposulphite of baryta (BaO.S,O,).

Sulphide of barium is a sulphur-base. Hydrosulphate of sulphide of barium (BaS.HS) may be prepared like the corresponding compound of potassium. Barium forms also a tersulphide (BaS,), and a pentasulphide (BaS,). Silicofluoride of Barium, 3BaF.2SiF, is thrown down as a crystalline precipitate, when hydrofluosilicic acid is added to chloride of barium; this compound is very sparingly soluble in water and acids, and is decomposed by heat into fluoride of barium and terfluoride of silicon, which escapes.

STRONTIUM.

Sym. Sr. Eq. 43.8.

§ 193. This metal was first obtained by Sir H. Davy, in 1808. It is named from Strontian, in Argyleshire, where it was first discovered.

Strontium is by no means so abundant in nature as barium; it occurs chiefly in the forms of sulphate and carbonate, and is found in small quantity in certain mineral waters. It may be prepared by the same methods as barium, which it

1 When sulphate of baryta, free from iron, is ignited with a small quantity of carbonaceous matter, a mass possessed of phosphorescent properties is obtained, which is termed Bologna phosphorus.

2 When the sulphide of barium is prepared below a bright red heat, the aqueous solution obtained from the ignited mass contains much hydrate of baryta and a higher sulphide of barium.

3 When the mass obtained in the preparation of sulphide of barium is treated with successive small portions of water, the first two solutions are yellow, and contain considerable quantities of hydrosulphate of sulphide of barium and the higher sulphides of barium; the third is a solution of nearly pure sulphide of barium, while the succeeding solutions contain gradually increasing quantities of baryta, the last being nearly pure baryta-water.

much resembles in its appearance, properties, and combinations. It is heavier than oil of vitriol, and less fusible than barium.

The oxide of strontium is prepared from the native carbonate or sulphate, in exactly the same way as baryta. It is similar to that oxide in its properties, and combines with water very energetically, to form hydrate of strontia.

Crystallized hydrate of strontia has the formula SrÓ.HO+9Aq, and is easily converted into carbonate by exposure to air. At 212° F. (100° C.) it loses the whole of its water of crystallization, becoming converted into SrO. HO, which is not decomposed at a red heat.

NITRATE OF STRONTIA, SrO.NO,.

This salt is prepared in the same manner as nitrate of baryta.

The ordinary crystals are anhydrous, colorless octohedra, which decrepitate when heated, and are ultimately decomposed, leaving anhydrous strontia. They are soluble in five parts of cold, and in considerably less of boiling water, and insoluble in absolute alcohol. At a low temperature, the solution deposits prismatic crystals, of the formula SrO.NO,+Aq, which effloresce in air.

Nitrate of strontia is employed in the preparation of the red fires used upon the stage, and in fireworks; a common mixture for these purposes consists of 40 parts of nitrate or strontia, 13 of flowers of sulphur, 10 of chlorate of potassa, and 4 of tersulphide of antimony.

SULPHATE OF STRONTIA (SrO.SO,) is found in nature in the form of celestine, crystallized in rhomboidal prisms, and in considerable quantity, associated with sulphur, in the neighborhood of volcanoes; it is the commonest mineral of

strontia.

The sulphate may be prepared artificially by precipitating a solution of nitrate of strontia with sulphuric acid. Its properties exactly resemble those of sulphate of baryta; it is somewhat more soluble in water and acids. It may be completely dissolved by a solution of common salt.

Carbonate of strontia (SrO.CO,) constitutes the mineral known as strontionite ;1 its crystals belong to the right prismatic system; it may be prepared in the same manner as carbonate of baryta. Its properties resemble those of the latter, but its carbonic acid is more easily expelled.

The Binoxide of Strontium (SrO,) is deposited as a hydrate, in crystalline scales, when a solution of binoxide of hydrogen is added to a solution of strontia. This substance cannot be formed, like the binoxide of barium, by passing oxygen over heated baryta.

Chloride of Strontium (SrCl) is obtained by decomposing the carbonate or sulphide with hydrochloric acid; it forms deliquescent needles of the formula SrCl+6Aq, which lose all their water when gently ignited; they are very soluble in water, and moderately so in alcohol. This salt is almost insoluble in concentrated hydrochloric acid.

The Sulphide of Strontium exactly resemble those of barium in preparation and properties.

1 Carbonate of strontia is also found in some mineral waters.

CALCIUM.

Sym. Ca. Eq. 20.

§ 194. We are indebted for the discovery of calcium to Sir H. Davy, who first obtained it, in 1808.

The natural sources of this metal are very numerous; it occurs chiefly in the forms of carbonate of lime, which constitute the different varieties of limestone, chalk, and marble, found in all parts of the world. Gypsum, the sulphate of lime, is another form in which this metal occurs. Phosphate of lime is also found in the mineral kingdom. Fluoride of calcium constitutes the mineral known as fluor-spar.

This metal is obtained in the same way as barium, and is very similar to it. It combines with oxygen to form an oxide, CaO, and a binoxide, CaO,.

Preparation. This very useful substance is prepared by the decomposition of carbonate of lime by heat. The operation is carried out on a very large scale in kilns or furnaces, so constructed that the products of combustion of the fuel (wood, turf, or, sometimes, coal), shall pass through the carbonate; for it is found that the carbonic acid is much more easily expelled when the carbonate is heated in a stream of another gas, than in a crucible.

The various forms of carbonate of lime do not give up their carbonic acid with the same facility, in consequence of the difference in their texture; chalk or limestone is much more easily decomposed than marble, and, being much more abundant, is always employed on the large scale. Moist limestone is much more easily caustified than that which is perfectly dry.

The lime-kilns are of two kinds, in one of which the process is interrupted after every operation, whilst in the other it is continuous.

The simplest form of lime-kiln is a tall conical furnace, over the hearth of which the lime-burner constructs an arch with large lumps of the limestone to be burnt; upon this arch the rest of the limestone is heaped, so as to fill up the furnace; the fire is then kindled, and the operation allowed to continue (for about three days and nights), until the whole of the lime is thoroughly burnt. The heat is raised gradually, so that the stones forming the arch may not crack. The continuous lime-kiln is an inverted cone of brick-work, with an aperture at the lower part, through which the burnt lime is withdrawn. A layer of brushwood is placed at the bottom, upon this a layer of coal, then a layer of limestone, the coal and limestone being arranged in alternate layers, until the kiln is filled. The fire is then lighted, and as soon as the upper layers have sunk in the mouth of the kiln, fresh charges of coal and limestone are introduced. The lime is raked out from the bottom at intervals of about half an hour.

The lime thus obtained is by no means pure; it usually contains silica, alumina, and sesquioxide of iron, derived from the limestone, together with alkaline sulphates and chlorides from the ashes of the fuel. For many purposes the

presence of the three former impurities is of no consequence, and the lime may be freed from the two latter by slaking it, throwing the hydrate upon a filter, washing with water till the washings are no longer rendered turbid by nitrate of silver (after acidulating with nitric acid), and igniting the purified hydrate in an earthen crucible.

Very nearly pure lime may also be obtained by heating oyster-shells, or fragments of Carrara marble, to bright redness, either in an open fire, or in an earthen crucible with a hole in the bottom.

Lime of absolute purity may be prepared by saturating dilute nitric acid with powdered marble, evaporating to dryness, and igniting the residual nitrate.

Properties of Lime.-Anhydrous lime, or quicklime, is a soft, white, amorphous solid, of specific gravity varying between 2.5 and 3. It preserves the external appearance which the carbonate presented before ignition. Ordinary quicklime has usually a gray color, probably due to a trace of carbon. Lime is one of the most infusible bodies which we possess; it resists the highest heat of our furnaces. A mass of lime heated in the flame of the oxyhydrogen blowpipe emits a most dazzling white light, and fuses at the edges.

When exposed to air, quicklime very soon absorbs water, the lumps crumbling to a bulky powder, which is hydrate of lime, or slaked lime; when a mass of lime is moistened with water, very energetic combination takes place, and occasionally a slight explosion, due to the sudden evolution of steam; the mass splits in all directions, and finally crumbles to a dry powder of hydrate; the slaking takes place more rapidly, and a more finely-divided hydrate is obtained when hot water is employed. Ordinary quicklime frequently contains fragments which will not slake, but are left as cinder-like masses in the midst of the hydrate; these masses appear to consist of semi-fused silicate of lime, and are most frequently found in lime which has been over-burnt, i. e. calcined at too high a temperature."

Besides silicic acid, quicklime often contains magnesia, alumina, &c. When it contains large quantities of these impurities it slakes very feebly, and is called poor lime, but if it be pretty pure and slakes easily, it is termed fat lime.

Uses.-Quicklime is used chiefly for the preparation of mortar, and for agricultural purposes. It is very useful in the laboratory for drying certain gases, for abstracting the water from alcohol, and for decomposing various organie substances.

HYDRATE OF LIME, SLAKED LIME, CaO.HO.

The hydrate is always prepared by slaking quicklime.

Properties. It forms a fine white powder, which loses its water at a red heat, but does not fuse. When exposed to air, it absorbs carbonic acid, and is converted into a mixture of carbonate of lime and hydrate of lime; after long exposure it ceases to absorb carbonic acid, and is then found to contain single equivalents of hydrate and carbonate.

Hydrate of lime is very sparingly soluble in water, 1 part requiring about 1000 parts of water; it is less soluble in hot water than in cold, so that a cold saturated solution becomes turbid when heated to the boiling point.3 Lime-water should therefore always be prepared with cold water; the best plan is to place a considerable quantity of freshly-slaked lime, previously washed with water to remove alkaline salts, in a large bottle, which is then filled up with cold distilled

The hydrate is also more finely divided when a larger quantity of water has been used than the lime is capable of absorbing.

2 Imperfectly burnt limestone will not slake, but, when immersed in water, forms a hard mass which is a compound of hydrate and carbonate of lime.

3 The hydrate of lime deposited upon boiling lime-water is not redissolved to any perceptible extent when the water is allowed to cool.

water, and shaken from time to time; it is then allowed to stand, in order that the excess of lime may subside; the bottle should always be kept filled with water. If a saturated solution of hydrate of lime be evaporated in vacuo over oil of vitriol, it deposits the crystallized hydrate in six-sided tables.

Lime-water has a distinct alkaline reaction, and a feebly alkaline taste. When lime-water is exposed to air, a pellicle of carbonate forms upon its surface, and if this be broken, a fresh pellicle forms until all the lime is precipitated; hence, lime-water must be kept in well-closed bottles.

A mixture of finely divided hydrate of lime with water, is termed milk or cream of lime, according to its consistence. Hydrate of lime is much more soluble in solution of sugar than in pure water; the solution is usually known as sugar-lime, and is useful in the laboratory.

$195. USES OF HYDRATE OF LIME.-This substance is applied to numerous purposes in the arts and manufactures. It is chiefly employed in the preparation of mortar for building purposes; this is usually composed of 1 part of freshly-slaked lime, and 2 or 3 parts (or even more, according to the quality of the lime) of sand, mixed with water to a paste, which is spread in a thin layer between the stones to be cemented.

The hardening of mortar is explained partly on mechanical, partly on chemical principles. The chief chemical alteration which mortar undergoes, consists in the conversion of a part of the lime into carbonate, which is capable of combining with unaltered hydrate of lime, to form a solid mass. It also appears that the deposition of minute crystals of carbonate of lime helps materially to bind the particles together. These reasons may afford a satisfactory explanation of the rapid setting of the mortar; but direct experiments and analyses of very old mortars have shown that its ultimate conversion into a hard stone-like mass, must be attributed in great measure to the formation of a silicate of lime, by the action of lime upon the sand, in the presence of moisture. The sand has, moreover, a most important mechanical effect in preventing the mass from shrinking too much when dried, and in forming a number of nuclei around which the lime adheres.

The nature of the sand is not without influence upon the quality of the mortar; rough irregular grains are preferable to those which are quite smooth; the sand should also be as pure as possible. Mortar does not set firmly when dried too quickly; hence it sets better in temperate seasons than in hot summers.

Water containing much alkaline chloride should not be employed for the preparation of mortar, since its action upon lime would give rise to the production of chloride of calcium, which would prevent the drying of the mortar.

Hydraulic mortars and cements are such as set under water, and are not disintegrated by its action. These are usually prepared either from natural or artificial mixtures of carbonate of lime with silica, or silicate of alumina or of magnesia.

They are prepared from limestones containing certain proportions of the three latter ingredients. When a limestone of this description is calcined, a double silicate of alumina (or magnesia) and lime is formed, which is capable of combining with water to produce a compact hydrate which resists the action of that solvent.

Even dolomite (carbonate of lime and magnesia) calcined at a moderate heat, exhibits the property of a hydraulic lime; and half-burnt lime (containing still a certain quantity of carbonate) will also set under water.

In order that a limestone containing silica may be employed for the production of hydraulic lime, it is necessary that this ingredient be present in a state in which it is capable of entering readily into combination with the lime, which is the case with the silica contained in clay. If carbonate of lime be mixed with gelatinous silica, a good cement is obtained on calcination, but if sand or rock