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,], CO,) 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 (BaHCO,), thus :—

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

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 (HA or HC, H2O2).

The acid oxalate is produced by the action of oxalic acid (H,C,O) 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 BaHCO̟ ̧. 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, HPO) 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,O,). 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 SrH0+4ļaq.

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, SO1) or of soluble sulphates on solutions of strontium salts, unless they are extremely dilute. It is a white pulverulent precipitate.

Its formula is Sr, SO..

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

of sulphuric acid (H, SO1). 1 part dissolves in 6895 parts of water at 14° C., and in 9638 parts of boiling water.

The Carbonate is produced by the action of the neutral carbonates of potassium or ammonium (K,CO, or [NH1],CO,) on solutions of strontium salts: it is a white precipitate.

Its formula is Sr, CO,.

This salt is more soluble in solutions of ammonium salts, especially chloride of ammonium, than is the corresponding barium compound. It dissolves in 18,045 parts of water at the ordinary temperature, but in a much less quantity of boiling water; it is readily decomposed by most acids; but in solutions of carbonic acid gas (CO) it dissolves without decomposition, in the same manner as the carbonate of barium, forming the analogous compound, namely, the acid carbonate of strontium (SrHCO2).

The Oxalate is produced by the action of oxalic acid (H,C,O), or of soluble oxalates, even in dilute solutions of strontium salts. It is a white precipitate.

Its formula is Sr.C2O..

This salt is very soluble in hot aqueous solutions of chloride or nitrate of ammonium; it is very sparingly soluble in cold water, but dissolves in 19-2 parts of boiling water; it is dissolved readily by most strong acids, but not by acetic acid (HC,H,O,, or HA). THE FERROCYANIDE is soluble.

THE PHOSPHATE is produced by the action of phosphate of sodium (Na,HPO1) on solutions of strontium salts. Its formula is Sr,HPO,. It dissolves readily in most ammonium salts, but is reprecipitated by the addition of hydrate of ammonium (NH,HO). It is insoluble in water, but dissolves in most acids.

THE SILICOFLUORIDE is soluble, especially in the presence of acids.

The special tests of the first subdivision are without welldefined action on salts of strontium.

The special tests for strontium which the student should particularly remember are these:-the blowpipe flame, the action of sulphates on soluble strontium salts, and the absence of the reaction with chromates and silicofluorides; by means of this last

test this metal is usually distinguished from barium, the reactions of which in most other respects are so similar to its own.

SALTS OF CALCIUM.

Solution for the reactions:-chloride of calcium (CaCl) in water.

Calcium, like the two preceding metals, forms two combinations with oxygen, a protoxide (CaO), and a peroxide (CaO): it combines with almost every acid-radical to produce salts; which, like those of barium and strontium, are all proto-salts. They are colourless, except in cases where the acid-radical introduces colour. They are devoid of poisonous properties.

These salts resemble those of the two preceding metals in their behaviour when heated before the blowpipe on charcoal, being for the most part decomposed into the oxide (lime). This oxide. remains infusible, and is remarkably incandescent, the light which it emits increasing with the intensity of the heat, and reaching its maximum only when the lime is subjected to the highest temperature at our disposal-such, for instance, as that produced by the oxyhydrogen blowpipe. The light thus obtained has been utilized, and is known as the "lime light." The chloride, bromide, and iodide of calcium resemble the corresponding salts of barium and strontium in remaining undecomposed before the blowpipe flame on charcoal. A platinum wire, moistened with a solution of a calcium salt, tinges the flame of an orange-red colour; the colour, however, imparted by a pure salt of calcium is a very pure red, the orange tint which it generally has being in fact owing to the presence of a trace of sodium; the red of pure calcium salts may even be mistaken for the crimson of strontium compounds; actual comparison, nevertheless, shows the difference. The red colour may be observed even with the insoluble salts of calcium, by heating them before the blowpipe after they have been moistened with a strong acid, such as hydrochloric acid. The borax-bead is colourless.

The principal insoluble salts of calcium are the hydrate, the sulphate, the carbonate, the ferrocyanide, and the phosphate.