to the hydrate of potassium (KHO), and although for convenience and analogy sake we speak of this hydrate, yet it is more correct to regard the substance so called as a solution of the gas ammonia (NH ̧) in water (H2O); for it will be seen that NH, HO=NH,+H2O.

Sulphydrate of ammonium (NH, HS).

This salt is prepared by passing hydrosulphuric acid (HS) into a solution of hydrate of ammonium until the liquid is fully saturated and the gas escapes unabsorbed. The sulphide of ammonium ([NH], S) is obtained by dividing a solution of hydrate of ammonium into two equal parts, and after having saturated one part with hydrosulphuric acid, adding the reserved part to it.

Carbonate of ammonium ([NH]2CO3).

The commercial carbonate is a sesquicarbonate, but when dissolved in hot water the solution is said to contain the neutral carbonate. The common preparations of this salt are of sufficient purity for almost every analytical purpose.

Oxalate of ammonium ([NH1], C2 O̟1+aq or [NH]2Ō+aq).

This salt may be prepared by exactly neutralizing a solution of oxalic acid by carbonate or hydrate of ammonium: 1 part of crystals should be dissolved in 24 parts of water for use as a solution for testing.

Phosphate of ammonium ([NH]1⁄2 HPO1).

This salt may be prepared by decomposing the acid phosphate of calcium by carbonate of ammonium.

SALTS OF BARIUM.

Chloride of barium (BaCl+aq).

This salt is generally found in commerce of sufficient purity for ordinary analytical purposes. It sometimes contains lead: it may be purified by crystallization. To prepare the solution for testing, 1 part should be dissolved in 10 of water. This salt may also be readily made by dissolving the carbonate of barium (a commonly occurring mineral) in hydrochloric acid, and crystallizing the product.

Fluoride of barium (BaF).

This salt may be prepared by adding hydrofluoric acid (HF) to a solution of chloride of barium containing hydrate of ammonium as long as a precipitate is formed. The precipitate must then be quickly washed with water on a filter and dried.

Oxide of barium or baryta (Ba, 0).

This compound is best prepared from nitrate of barium purified by recrystallization. The nitrate, finely powdered, is introduced little by little into a crucible maintained at a bright red heat. After cooling, the crucible is broken, and the fused mass is separated from foreign matters and preserved from the air. The decomposition is as follows::

This salt may be prepared by dissolving the oxide in boiling water, filtering the solution into a bottle or flask, and closing the latter by a cork to exclude

the air, which, from the carbonic acid gas which it contains, would soon convert the hydrate into the carbonate of barium. The above solution on cooling deposits the hydrate in large crystals, which may always, by a second or sometimes a third crystallization, be obtained perfectly pure. This substance may also be prepared by heating to redness in a crucible a mixture of 6 parts of finely powdered sulphate of barium (Ba, SO) with 1 part of powdered charcoal and 14 of flour, and boiling the resulting mass with water for a long time in a loosely-corked flask: the solution is to be filtered whilst hot with the same precaution as in the first process. The decompositions which occur are these:-

(a) Ba2 SO1+2C=Ba, S+2CO2

(B) Ba, S +2(H2O)=H, S +2(BaHO).

As it is important that this reagent should be quite free from the salts of the alkalies, the second process is a very convenient method, since, from the great insolubility of the sulphate of barium, it may be easily washed free from all soluble impurities, among which the alkaline salts are the most usual and most deleterious. For testing, a cold saturated solution of the crystallized hydrate may be employed.

Carbonate of barium (Ba, CO).

This salt occurs in a state of comparative purity as a mineral: for analytical purposes, however, it should always be precipitated by carbonate of sodium or ammonium from the pure chloride of barium (BaCl); the precipitate is to be thoroughly washed, and then stirred with distilled water so as to form a pasty mass; in this condition it should be preserved for use in a stoppered bottle. This salt, like the preceding, should be absolutely free from soluble salts.

SALTS OF CALCIUM.

Chloride of calcium (CaCl).

This may be preparad in the purest form by dissolving the finest white marble (Ca., CO) or precipitated carbonate of calcium, or, better still, small crystals of Iceland spar, in hydrochloric acid (HCl), the hydrochloric acid not being in sufficient quantity to dissolve the whole of the carbonate.

Oxide of calcium (Ca, O).

Freshly burnt quicklime just from the kiln should be taken, the white pieces selected and preserved in a well-stoppered bottle.

Sulphate of calcium (Ca, SO4+2 aq).

This salt may be prepared by precipitating pure chloride of calcium with sulphuric acid (H, SO,), washing the precipitate thoroughly, and then digesting the sulphate of calcium formed, with repeated agitation, in cold water. It is almost insoluble, and therefore the saturated solution may be used.

SALT OF MAGNESIUM.

Sulphate of magnesium (Mg, SO1+7 aq).

The commercial salt (Epsom salts) is of sufficient purity for all ordinary analytical purposes. 1 part should be dissolved in 10 parts of water.

SALTS OF IRON.

Protosulphate of iron or ferrous sulphate (Fe, SO+7 aq).

The commercial salt is of sufficient purity for employment in analysis. The solution is made by agitating the crystals with cold water, out of contact with the air.

Sesqui- or perchloride of iron, or ferric chloride (Fe, Cl2).

This salt may be easily prepared by dissolving pianoforte wire (the purest form in which iron occurs commercially) in hydrochloric acid, boiling the solution, and adding nitric acid (HNO,) drop by drop until the original greenish-brown colour of the solution has changed to a bright yellow, or until a drop of the solution taken out on a glass rod is no longer precipitated blue on the addition of ferricyanide of potassium (K, Cfdy). Excess of ammonia solution is then added, and the precipitate produced thoroughly washed with hot water; it is then dissolved in hydrochloric acid, care being taken that enough acid is not added to dissolve the whole.

SALT of COBALT.

Nitrate of cobalt (CoNO3+3 aq).

This salt may be purchased in a state fit for use: it is troublesome to prepare from cobalt ore. 1 part is to be dissolved in about 10 of water.

SALT OF COPPER.

Protosulphate of copper or cupric sulphate (Cu, SO1+5 aq).

The commercial salt is always contaminated with ferric sulphate; for analytical purposes the metallic copper obtained by electrolysis may be dissolved in hot sulphuric acid (H2SO1); or the pure hydrate, oxide, or carbonate may be taken, and heated with diluted sulphuric acid. The salt should be crystallized from its solution. 1 part should be dissolved in 10 parts of water.

SALT OF SILVER.

Nitrate of silver (AgNO1).

Fig. 5.

This is best obtained by dissolving pure silver in nitric acid (HNO,) which has been diluted with about its own bulk of water, evaporating the solution to dryness, and gently fusing the residue. The fused mass may be dissolved in water when cold, and then crystallized. It is thus obtained quite free from acid. If silver coin (i. e. silver alloyed with copper) be employed, it is necessary, after dissolving it in nitric acid, to precipitate the silver as chloride by the addition of hydrochloric acid, to filter it, and then to wash it till it no longer contains a trace of the soluble copper salt. The pure chloride of silver is now to be placed in a small dish of porous earth

enware, placed in a larger dish or basin; both vessels are then to be so far

filled with water, to which a few drops of hydrochloric acid have been added, that their contents do not mix. A piece of zinc is to be laid under the inner vessel, and connected with the chloride of silver by means of a bent platinum wire, when the desired action will at once commence, and after the lapse of a short time the whole of the chloride of silver will have been "reduced" to the metallic state: the change may be represented by the two equations-(1) HCl +Zn=ZnCl+H

(2) AgCl+H = HCl +Ag.

The small dish is now to be removed, and the finely divided silver which it contains to be repeatedly washed with dilute hydrochloric acid, and, finally, with pure water. When quite free from hydrochloric acid, the silver is to dissolved in nitric acid, crystallized and fused as mentioned above*. For 1 part of the fused salt is dissolved in 20 parts of water.

use,

This salt is met with in commerce of sufficient purity: 1 part should be dissolved in 6 parts of water.

SALTS OF MERCURY.

Protonitrate of mercury or mercurous nitrate (Hg, NO3).

This salt is obtained by leaving metallic mercury in contact with nitric acid (HNO3) without applying heat. In order to preserve it in the state of mercurous nitrate, some metallic mercury must always be kept in its solution.

Perchloride of mercury or mercuric chloride (HgCl). The commercial salt is sufficiently pure. 1 part is to be dissolved in 16 parts of water.

Peroxide of mercury or mercuric oxide (Hg, O).

This salt may be purchased tolerably pure. It should volatilize when heated without leaving a residue.

SALT OF BISMUTH.

Oxyhydrate of bismuth or mixed oxide and hydrate of bismuth
(BiH, O3, Bi2 03).

The commercial basic nitrate of bismuth may be used instead of the basic hydrate (for the conversion of metallic sulphides soluble in alkalies into oxides by boiling it with such alkaline solutions): it must be free from arsenic (As).

The metal bismuth may be purified from arsenic by fusing it with nitrate of potassium (KNO,); it may then be dissolved in dilute nitric acid, and the

* By this fusion a portion of nitrite is said to be formed;--this may be separated by dissolving the fused mass in cold water, evaporating and crystallizing afresh.

solution diluted with water till a precipitate begins to form; from this precipitate the solution is filtered, and the filtrate evaporated until it is of sufficient concentration to crystallize. The crystals are then digested with water containing a little nitric acid, excess of ammonia solution added, and the precipitate of basic hydrate washed thoroughly and dried.

SALT OF PALLADIUM.

Protochloride of palladium or palladious chloride (PdC1).

The metal palladium is dissolved in nitro-hydrochloric acid, the solution evaporated to dryness on the water-bath, by which means palladic chloride is first formed, but this salt (Pd, Cl ̧) is converted into palladious chloride (PdCl) with evolution of chlorine at the temperature employed: after the first evaporation, hydrochloric acid should be added, and the liquid again evaporated; water is then to be poured on the salt, and the whole carried to dryness once more on the water-bath.

SALT OF TIN.

Protochloride of tin (SnCl).

This salt is obtained by dissolving the granulated metal in hydrochloric acid (the concentrated acid diluted with its own bulk of water); the mixture is to be heated, care being taken to stop the action before all the tin and hydrochloric acid have been consumed: the solution of the chloride is then to be decanted clear from the residual metal, and poured into a bottle containing a few fragments of pure tin: a little dilute hydrochloric acid should also be added.

SALT OF PLATINUM.

Per- or bichloride of platinum or platinic chloride (PtCl2). This salt is prepared in precisely the same manner as the palladious chloride.

SALT OF GOLD.

Terchloride of gold or auric chloride (AuCl,).

This salt may be prepared as the palladious chloride if the metallic gold is pure. If, however, the gold contains copper (Cu) or silver (Ag), the nitrohydrochloric solution is at once evaporated to dryness on the water-bath, and redissolved in water, by which means the whole of the silver remains as chloride. The aqueous solution is then slightly acidified with hydrochloric acid and boiled with a solution of oxalic acid; the gold is thus precipitated in the metallic form, while the copper remains in solution; if, however, any copper still contaminates the gold in the form of oxalate of copper, it may be removed by treating the metal with ammonia solution.

SALTS OF ETHYLE.

Oxide of ethyle or ether ([C2 H,]2O).

This is obtained of sufficient purity in commerce for the ordinary analytical operations. If, however, ether free from water is required, it is