472

NITRATE AND CARBONATE OF BARIUM.

or with a solution of the acid carbonate of sodium, microscopic crystals of the same form as those of the native sulphate of barium are deposited upon the sides of the tube. At a bright red heat the sulphate fuses into a white enamel and by boiling the powdered sulphate of barium with the carbonate either of potassium or of sodium, or, more rapidly by fusing it with either of these salts, the artificial sulphate is partially converted into the carbonate. It may be easily formed by precipitating a salt of barium with any soluble sulphate, when it falls as a heavy white powder. If nitric acid or any nitrate be present in the solution, the precipitate carries down with it a portion of the nitrate, and this can only be removed by long washing with boiling water. Sulphate of barium is used as a permanent white by artists in water colours. It is also employed for adulterating white lead; when ground with oil, however, it becomes partially transparent, and impairs the opacity of the lead pigment.

(633) NITRATE OF BARIUM (Ba 2 NO, = 261, or BaO,NO;= 130'5; Sp. Gr. 3·284: Composition in 100 parts, BaÐ, 58·62; N ̧Ð1⁄2, 2 5 4138) crystallizes in anhydrous octohedra, when a solution of the carbonate of barium in nitric acid is evaporated. It is insoluble in alcohol, and requires eight or ten times its weight of cold water, and 3 of boiling water, for solution. Nitric acid precipitates it in crystals from its solution, unless very dilute: when heated, it first decrepitates strongly, and afterwards fuses; on ignition, the whole of the acid is expelled, with an appearance of ebullition owing to the escape of oxygen and nitrogen, whilst pure baryta remains.

:

(634) CARBONATE OF BARIUM (Ba¤Ð ̧ = 197, or BaO,CO, = 985); Sp. Gr. 44: Composition in 100 parts, BaÐ, 77·69; ЄO„, 22 31. This compound forms the mineral called witherite it occurs, both massive and crystallized, usually in six-sided prisms terminated by six-sided pyramids. It is abundant in the leadveins in the north of England, and is also found in Styria and in Siberia. It is easily prepared artificially by precipitating a salt of barium by the carbonate of one of the alkali-metals; it then forms a white powder, which is very sparingly soluble in pure water, and is insoluble in water charged with saline matter: an aqueous solution of carbonic acid dissolves it rather freely. If suspended in a solution of sulphate of potassium, or of sulphate of sodium, in the cold, and frequently agitated, freshly precipitated carbonate of barium is converted into sulphate; but if sulphate of barium be boiled with a carbonate of one of the alkali-metals, carbonate of barium and sulphate of the alkaline metal are pro

CHARACTERS OF THE SALTS OF BARIUM.

473

duced. Ignition of the carbonate does not expel the carbonic acid, but if it be mixed with charcoal and intensely ignited, it is partially decomposed; pure baryta is obtained, and may be dissolved out with water. If mixed with an equal weight of carbonate of calcium, carbonate of barium is decomposed without much difficulty when ignited in a current of steam: the hydrate of baryta may be dissolved out of the mixture by water.

Carbonate of barium is now manufactured to some extent as a substitute for a portion of the alkali and oxide of lead in the making of plate and flint glass: the silicate of barium fuses and becomes incorporated with the other silicates. This carbonate is prepared from the sulphate, which is reduced to the form of sulphide by ignition with carbonaceous matter: the sulphide is then dissolved in water, and decomposed by a current of carbonic acid: the carbonate is thus precipitated as a fine white powder.

(635) CHARACTERS OF THE SALTS OF BARIUM.-The salts of barium with colourless acids are colourless. The carbonate and all the soluble salts act as powerful poisons, and have an acrid, disagreeable taste. The best antidote when they have been taken internally is the sulphate of sodium or of magnesium.

Salts of barium when in solution are easily recognized by giving with sulphuric acid a white precipitate of sulphate of barium, which is insoluble in the acids. Barium is, for the purposes of analysis, usually estimated in the form of sulphate; 100 parts correspond to 65.66 of Ba and 34'34 of SO. The presence of citrate either of sodium or ammonium prevents the precipitation of sulphate of barium in neutral and alkaline solutions; but these salts do not redissolve the sulphate of barium after it has once been deposited. On acidulating with hydrochloric acid the solution containing the citrates, the sulphate of barium is precipitated in the usual manner (Spiller).

With carbonate of potassium or of sodium a white precipitate of carbonate of barium is produced in solutions which contain barium. Hydrosulphate of ammonium gives no precipitate in such solutions. Phosphate of sodium gives a white precipitate which is soluble in diluted nitric or hydrochloric acid. Salts of barium, when mingled with alcohol, tinge its flame of a yellowish-green colour. In the spectroscope the spectrum of the barium salts is distinguished by a remarkable series of bright bands in the green, with fainter bands in the red. (Part I., fig. 82, Ba, page 172.) Barium salts are distinguished from those of strontium by forming an insoluble silicofluoride of barium when mixed with silicofluoric acid;

474

CHLORIDE AND SULPHATE OF STRONTIUM.

and by yielding no immediate precipitate with oxalic acid, but the mixture on standing deposits tufts of acicular crystals of acid oxalate of barium. A solution of hyposulphite of sodium occasions a crystalline precipitate of the sparingly soluble hyposulphite of barium.

§ II. STRONTIUM: Sr"=875, or Sr=438. Sp. Gr. 2:54.

(636) STRONTIUM is an element much less abundantly diffused than barium, which it closely resembles in properties. It is found both as carbonate and as sulphate, and is procured in the metallic state in the same way as barium, to which it bears a relation similar to that existing between potassium and sodium. Strontium is a malleable metal of a pale yellow colour. When heated in the air, it burns with a crimson flame, emitting sparks. Water is decomposed by it with evolution of hydrogen: diluted nitric acid dissolves it, but the concentrated acid is almost without action even when boiled upon it.

2

(637) STRONTIA (Sr0=103'5, or SrO = 51.8: Sp. Gr. 4611) may be obtained from its nitrate by ignition. When mixed with water it slakes, and forms a crystalline hydrate (Sr, H2O. 8 H2O; Bloxam): these crystals require 50 times their weight of cold and 24 of boiling water for solution; 8 H2 are expelled by heat, the remaining atom being fixed at all temperatures; at a full red heat the latter hydrate fuses, furnishing a mass of sp. gr. 3625 both the hydrate and its solution absorb carbonic acid rapidly from the air. No peroxide of strontium can be formed. (638) CHLORIDE OF STRONTIUM (SrCl2. 6 H2O 158.5 + 108, or SrCl, 6 HO=79'3+54; Sp. Gr. anhydrous, 2'96, cryst. 1603) crystallizes in slightly deliquescent needles, which require less than their weight of cold water for solution; alcohol dissolves it, and the solution burns with a crimson flame. tium is rendered anhydrous by a moderate heat; if heated strongly it fuses.

=

Chloride of stron

Silicofluoride of strontium (SrF,SiF, 229'5) is prepared by adding hydrofluosilicic acid to a salt of strontium: it is tolerably soluble in water, thus furnishing a character which distinguishes the compounds of strontium from those of barium.

(639) SULPHATE OF STRONTIUM (SrSO

=

183.5, or SrO,SO ̧ = 918; Sp. Gr. 3'9): Compòsition in 100 parts, Sre, 56.52; SO3, 43'48.-This substance is found crystallized in rhombic prisms isomorphous with those of sulphate of barium; it is, however, easily distinguished from it by its lower density. Many

NITRATE AND CARBONATE OF STRONTIUM.

475

specimens of this mineral have a delicate blue tint, whence it derives its mineralogical name of celestine: it often contains crystals of native sulphur. Sulphate of strontium is very sparingly soluble in water, but is taken up by boiling sulphuric acid, and is soluble to some extent in a solution of chloride of sodium. It may be formed by mixing a solution of any sulphate with a solution of a salt of strontium.

(640) NITRATE OF STRONTIUM (Sr 2 NO,=211*5, or SrO,NO, =1058; Sp. Gr. anhydr. 2.857, cryst. 2.113) crystallizes from hot concentrated solutions in anhydrous octohedra, which are soluble in 5 parts of cold water and half their weight of boiling water; by crystallizing it at a low temperature it may be obtained in efflorescent crystals with 5 H2O. If strongly heated, it decrepitates, and then is decomposed with loss of oxygen and nitrogen, leaving pure strontia. It is used by the makers of fireworks to give a splendid crimson colour to their flames, and is prepared for them by reducing the native sulphate to sulphide by heating it with charcoal, dissolving the sulphide in water, and decomposing it with diluted nitric acid. It crystallizes best from an acid solution. A mixture of 40 parts of nitrate of strontium with from 5 to 10 of chlorate of potassium, 13 of sulphur, and 4 of sulphide of antimony, deflagrates with a magnificent red colour; the mixture is dangerous both to prepare and to preserve, having more than once been the occasion of frightful accidents to the manufacturers from its becoming ignited spontaneously. Nitrate of strontium is insoluble in alcohol.

(641) CARBONATE OF STRONTIUM (Sr€Ð ̧=147'5, or SrO,CO2 =738); Sp. Gr. 365: Composition in 100 parts, Sr0, 70'2; ЄO2, 298. This compound forms the strontianite of mineralogists; it occurs both massive and crystallized, near Strontian in Argyleshire, and hence the name 'strontia' given to the earth which it contains. Mere ignition is insufficient to decompose this salt. It is scarcely soluble in water, but is dissolved by a solution of carbonic acid. The process of preparing it consists in precipitating a salt of strontium by the carbonate of one of the alkaline metals.

(642) CHARACTERS OF THE SALTS OF STRONTIUM.-The salts of strontium with colourless acids are all colourless: they have a bitter acrid taste, but are not poisonous. They are distinguished before the blowpipe by the red colour which they communicate to the flame. By the spectroscope they are seen to furnish several bright bands in the red and orange part of the spectrum, and a brilliant band in the blue. (Fig. 82, Sr, Part I. p. 172.) The flame

of strontium to the eye seems to have the same colour as that of lithium, but the spectra of the two cannot be confounded. Reagents produce upon strontium salts the same effects as upon salts of barium, excepting that neither silicofluoric acid nor the hyposulphite of sodium yields any precipitate in the solutions of the salts of strontium. Oxalic acid gives an immediate turbidity in them. The compounds of strontium are distinguished from those of calcium by the gradual formation of a white precipitate on agitation after the addition of a solution of sulphate of calcium. The sulphate of strontium is used for determining the amount of strontia in analysis; 100 parts of it correspond to 56.52 of strontia.

§ III. CALCIUM: Єa"=40, or Ca=20. Sp. Gr. 1'578.

(643) CALCIUM forms one of the most abundant and important constituents of the crust of the globe. It is the metallic basis of lime, and derives its name from cala, lime. Calcium occurs in nature in combination with fluorine, forming the different varieties of fluor-spar; it is still more abundant in the various forms of carbonate of calcium; and it is also met with in large quantities as gypsum, which is a hydrated sulphate of calcium.

Calcium was obtained by Matthiessen (Q. J. Chem. Soc. viii. 27) by the electrolytic decomposition of a mixture consisting of 2 equivalents of chloride of calcium and 1 equivalent of chloride of strontium. The mass may be fused in a Hessian crucible, in the centre of which is placed a porous tube filled with the same mixture, and into this an iron wire passed through the stem of a tobacco-pipe is inserted: this wire is connected with the platinode of the battery, the zincode of which consists of a plate of sheetiron bent into a cylindrical form, and immersed in the melted mass exterior to the porous tube: the calcium is reduced, and preserved from oxidation by so regulating the heat that a film of solidified salt shall form upon the surface of the mixture in the porous cell. Lies Bodart obtains it still more easily by fusing iodide of calcium with an equivalent quantity of sodium.

Calcium is a light, yellowish metal, of the colour of gold alloyed with silver; in hardness it is intermediate between lead and gold; it is very malleable, and can readily be hammered into leaves thinner than writing paper. It melts at a red heat. At ordinary temperatures it tarnishes within a day or two, even in dry air, and in the presence of moisture it is slowly oxidized. When heated to redness on platinum foil, it burns with a brilliant scintillating white light. It readily amalgamates with mercury: