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SECTION I.-SALTS OF BARIUM, STRONTIUM, AND CALCIUM. Precipitated by carbonate of ammonium ([NH,], CO,), and not redissolved by the addition of chloride of ammonium (NH ̧Cl).

SECTION II.-SALTS OF MAGNESIUM.

Precipitated by carbonate of ammonium ([NH,], CO,), and redissolved by the addition of chloride of ammonium (NHCl). Since so many insoluble salts occur in this group, there is less difficulty in recognizing its different members than in the case of the preceding subdivision.

The group-test is carbonate of ammonium ([NH,],CO,).

SECTION I.-Precipitated by Carbonate of ammonium ([NH ̧], CO2), and not redissolved by Chloride of ammonium (NH ̧C1).

SALTS OF BARIUM, STRONTIUM, AND CALCIUM.

SALTS OF BARIUM.

Solution for the reactions:-chloride of barium (BaCl) in water.

Barium forms two combinations with oxygen, a protoxide (Ba2O) and a peroxide (Ba,O2). The protoxide is the type of a large number of barium salts; these are white unless the acidradical in them introduces colour into the compound; those which are soluble are extremely poisonous.

When heated before the blowpipe, especially in the presence of a reducing agent such as charcoal, they are frequently converted into oxide; in these cases the oxide remains infusible, and becomes somewhat incandescent; but if the salt resists decomposition, as do the chloride, bromide, and iodide, it remains as a fused mass upon the charcoal. A platinum wire moistened with a solution of a barium salt imparts a yellowish-green tinge to the blowpipe flame; this may also be observed with insoluble salts if they are previously moistened with an acid,-hydrochloric acid for instance. Barium salts impart no colour to the borax-bead.

The principal insoluble salts by means of which barium may

be recognized are these:-the chromate, hydrate, sulphate, carbonate, phosphate, and silicofluoride.

The Chromate is produced by the action of chromate of potassium (KCrO2) on solutions of barium salts; in very dilute solutions it appears only after standing. It is a pale yellow precipitate. Its formula is BaCrO2. It is almost absolutely insoluble in water, but is dissolved by most acids.

THE HYDRATE is produced by the action of the hydrates of potassium (KHO) or of sodium (NaHO) in moderately concentrated solutions of barium salts. The hydrate of ammonium (NH, HO) produces no precipitate. It is to be observed that the salts of potassium and sodium may generally be employed indifferently as reagents, as they almost invariably act in the same manner; the salts of ammonium can only in certain instances be substituted for those of potassium or sodium, as in most cases they exercise an action peculiar to themselves. Many substances in fact are soluble in ammonium salts, but not in the salts of the fixed alkalies. The hydrate of barium is a white amorphous precipitate.

The formula of the hydrate is BaHO+41aq. Whenever H2O is written as aq, it is always to be understood to signify "water of crystallization," or water loosely combined with the substance: this water need never be taken into account in writing the equation which represents the reaction; in the present case, for instance, the change which takes place is simply a mutual transference of acid and basic radical between the acting substances, and may be represented thus:

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The hydrate of barium is comparatively soluble in water, 1 part dissolving in 35 parts of water at 13° C., and in 2 parts at 100° C. It is immediately dissolved by those acids whose barium salts are soluble, and it is decomposed by most others.

The Sulphate is produced by the action of sulphuric acid (H2SO), or of soluble sulphates on solutions of barium salts: in very dilute solutions it becomes evident only after standing

for a few seconds. It is a white pulverulent precipitate, which glistens somewhat in the light.

Its formula is Ba, SO..

It is one of the most insoluble substances known, 1 part dissolving in 43,000 parts of water: its solubility is not perceptibly increased by the presence of chloride of ammonium or chloride of sodium, nor by acids, although there are circumstances in which certain salts of citric acid prevent the formation of the precipitate of sulphate of barium.

The Carbonate is produced by the action of the neutral carbonate of potassium or ammonium (K,CO, or [NH ̧],CO1) on solutions of barium salts. It is a white precipitate.

The formula is Ba, CO,.

This salt is slightly soluble in solutions of ammonium salts (especially in chloride of ammonium); it is almost perfectly insoluble in water, 1 part dissolving in 15,420 parts of water at the boiling temperature: it is readily decomposed by most acids; but dissolves in solution of carbonic acid (H,CO,), forming the soluble acid carbonate of barium (BaHCO2), thus:—

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The Oxalate is produced by the action of the oxalate of potassium or ammonium (K,C,O, or [NH,1,C,O,) on solutions of barium salts. It is a white pulverulent precipitate.

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It is slightly soluble in a solution of chloride of ammonium, and dissolves in 200 parts of water (either cold or boiling). It is readily dissolved by most acids, but not by acetic acid (HÃ or HC, H2O2).

The acid oxalate is produced by the action of oxalic acid (HC2O1) on solutions of barium salts; it appears, after standing for a few minutes, as a white crystalline precipitate: the crystals are very acute rhombohedrons. Its formula is BaHCO1. 1 part of this salt dissolves in 336 parts of water at 15°.5 C.; it is more soluble in hot water, but less so in alcohol. It is dissolved readily by most strong acids.

THE FERROCYANIDE is produced by the action of ferrocyanide of

potassium (K,Cfy) on concentrated solutions of barium salts. It is a dense pale yellow and crystalline precipitate. Its formula (disregarding its water of crystallization) is KBaCfy; thus being in reality a ferrocyanide of potassium and barium. It is soluble in 36-38 parts of water at 14° C., and in 11.85 parts of boiling water.

THE PHOSPHATE is produced by the action of phosphate of sodium (Na, HPO1) on solutions of barium salts. It is a white pulverulent precipitate. Its formula is Ba, HPO,. It dissolves easily in solutions of many ammonium salts, from which it is reprecipitated by the hydrate of ammonium (NH, HO). 1 part dissolves in 20,570 parts of water at 20° C.; it is readily dissolved by most acids, even by acetic acid.

The Silicofluoride is produced by the action of hydrofluosilicic acid (H, Si, F.) on solutions of barium salts. It is a white, transparent and gelatinous precipitate, the separation of which is promoted by shaking and stirring the liquid, and by the addition of alcohol to it.

Its formula is Ba, Si, F..

1 part of this salt is soluble in 3802 parts of water at the ordinary temperature, or in 733 parts of water acidulated with hydrochloric acid: it is more soluble in hot water; nearly insoluble in alcohol.

The special tests employed for the detection of the various members of the preceding subdivision produce no precipitates with solutions of barium salts.

The special tests for barium which the student should particularly remember are these:-the yellowish-green blowpipe flame, the insolubility of the chromate and of the sulphate, and the production of the nearly insoluble silicofluoride.

SALTS OF STRONTIUM.

Solution for the reactions:-nitrate of strontium (SrNO,) in

water.

Strontium, like barium, forms two combinations with oxygen, a protoxide (Sr,O) and a peroxide (Sr, O2). The protoxide may

be regarded as the type of the large number of salts which this metal forms. Salts of strontium resemble barium salts in most of their chemical characters, but differ from them in being destitute of poisonous properties.

When heated before the blowpipe, strontium salts are for the most part converted into the oxide, which remains infusible, and becomes somewhat incandescent when the blowpipe flame is directed upon it. The chloride, bromide and iodide resist decomposition under these circumstances, and remain fused, and not decomposed even on charcoal. A wire moistened with a solution of any strontium salt imparts a fine crimson colour to the flame, which, unlike the similar colour imparted by lithium, does not disappear after long heating. The borax-bead is colourless and transparent.

The principal insoluble salts by which strontium is recognized are the hydrate, the sulphate, the carbonate, the oxalate, and the phosphate.

THE CHROMATE is soluble.

THE HYDRATE is produced by the action of hydrate of potassium (KHO) on rather concentrated solutions of strontium salts: the hydrate of ammonium (NH, HO) produces no precipitate. It is white and flocculent.

Its formula is SrHO+4}aq.

It is less soluble in water than the corresponding barium salt; 1 part requiring 50 parts of cold water, or 2-4 parts of boiling water for its solution. It is dissolved by those acids whose strontium salts are soluble, and decomposed by most others.

The Sulphate is produced by the action of sulphuric acid (H, SO,) or of soluble sulphates on solutions of strontium salts, unless they are extremely dilute. It is a white pulverulent precipitate.

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It is somewhat more soluble than the corresponding barium salt. A solution of chloride of ammonium does not dissolve it; but in a solution of chloride of sodium it is gradually but completely taken up, although it is reprecipitated by the addition

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