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a. Telluriates, when heated on charcoal before the blowpipe in the reducing flame, impart to it a green colour, often detonating slightly and yielding tellurium and a white sublimate of tellurious anhydride (Te0.).
B. By the action of boiling hydrochloric acid, telluriates are reduced to tellurites.
y. With carbonate of sodium on charcoal, telluriates (like tellurites) give a mass containing telluride of sodium.
8. Sulphurous acid gas (SO2), passed into a hot hydrochloric solution of a telluriate, precipitates the tellurium.
Telluriates may be recognized by the formation of several insoluble compounds, such as that of barium, and by the tests a, and ß.
Of the acid-radicals containing tellurium combined with sulphur, only two are known. Their salts are termed sulphotellurites and sulphotelluriates. The sulphotellurites containing the metals of the first and second subdivisions are yellow crystalline salts, soluble in water: the insoluble salts of the third subdivision are white or yellow; of the fourth, brown or black. The sulphotelluriates have scarcely been examined.
SECTION III.—The aluminates, chromites, chromates, perchromates,
ferrites, ferrates, manganates, permanganates, bismuthates, stannates, metastannates, platinates, rhodiates, rutheniates, iridiates, osmites, osmiates, aurates, tungstites, tungstates, molybdates, vanadites and vanadiates ; the sulphostannates, sulphoplatinates, sulphorhodiates, sulphorutheniates, sulphiridiates, sulphosmiates, sulphaurates, sulphomolybdates, and
sulphovanadiates. SALTS OF THE COMPOUND ACID-RADICALS WHICH CONTAIN
OXYGEN AND SULPHUR COMBINED WITH METALS. A very large class of compound acid-radicals, some of which are extremely powerful, are produced by the union of monatomic and biatomic molecules of certain basic radicals with a preponderating proportion of an acid element. Many of these bodies form salts of great stability_witness the chromates, stannates, tungstates, and molybdates; but their hydrogen compounds, or acids, are usually unstable. Some of these compound acid-radicals are monobasic, some bibasic, and others tribasic; the latter are known, in many instances, to yield acid salts containing 1 or 2 eqs. of basic hydrogen unreplaced by a metal.
Most of these acid-radicals are very easy of detection. They form numerous insoluble compounds, some of which are of extremely brilliant colours; in addition to this, the comparative readiness with which they may be caused to decompose, greatly facilitates their recognition.
One compound acid-radical containing aluminium and oxygen is known; or at least the compound called hydrate of aluminium is considered to be an acid (aluminic acid); and when this body is acted upon by hydrate of potassium, the potassium salt is formed. Viewed in this light, the formula H, A1,0, may be assigned to the acid, and KH,A1,0, to the potassium salt. Other modes of representing these compounds may be seen on referring to pp. 109, 110. Several aluminates have been obtained.
Of the acid-radicals containing chromium and oxygen, one only is of any analytical importance that, namely, which is contained in chromic acid (HCro,); the salts of the other acid-radicals, which are known as chromites and perchromates, are of rare occurrence. The chromites have the general formula MCr, 0,; the potassium, magnesium, and iron salts are tolerably well known.
SALTS OF THE CHROMIC RADICAL, OR CHROMATES. These salts are usually made from the potassium salt, which is easily prepared by fusing chromic oxide ([Cr,],0z) with nitrate of potassium in a crucible. The chromates are often of a red or yellow colour.
Many chromates, when strongly heated, yield chromic oxide and oxygen, while others (e.g. chromate of magnesium) yield chromites; other blowpipe reactions of the compounds of chromium will be found on p. 111.
THE HYDROGEN SALT (HCro,), or chromic acid, has not yet been isolated; when its aqueous solution is concentrated, fine crimson acicular crystals separate, which consist of the compound Cr,0.g, i. e. chromic anhydride*. This body possesses the property of uniting with 2 eqs. of certain neutral chromates to form new salts, which require no additional equivalent of basic radical. These salts have been called bichromates; terchromates are also known, and some compounds even which may be termed quadri
* Just as chlorochromic acid may be viewed as chloride of chromyle (CrO,Cl), so anhydrous chromic acid may be considered as the oxide of that radical ([Cro],0); there is, however, some ground for doubling the formulæ here assigned to chromyle and the neutral chromates.
chromates. All such salts are usually of a darker colour than the simple chromates, which are generally yellow. The bichromates, &c. are thus formed:2KCro,+Cr,0,=K,Cr,Oc.
of potassium. The chromates of the first and second divisions of the basic elements are soluble, the barium salt excepted; most of the other chromates are insoluble in water, but easily soluble in acids.
The chromates may be recognized, not only by the formation of insoluble salts, but by several processes of decomposition.
The most remarkable insoluble salts of this series are those of barium, silver, mercury, and lead.
THE POTASSIUM and SODIUM Salts are soluble.
The Barium Salt is produced by the action of a soluble barium salt on solutions of neutral chromates or of bichromates.
Its formula is BaCroc.
It is a pale yellow precipitate, nearly as insoluble in water as the sulphate, but soluble in hydrochloric, nitric, or chromic acid, and in solutions of bichromates.
THE STRONTIUM, CALCIUM, and MAGNESIUM SALTs are soluble.
THE FERRIC, MANGANOUS, and MANY OTHER Salts of the third subdivision are brown or yellow precipitates, nearly insoluble in water.
THE CUPROUS Salt is unknown. The CUPRIC Salt is produced by adding a cupric salt to a soluble chromate. 'With bichromates no precipitate is produced. It is a yellowish brown precipitate. It is soluble in nitric acid, and in hydrate of ammonium.
The Silver Salt is produced by the action of a soluble silver salt on a chromate. It is a crimson crystalline precipitate.
Its formula is AgCroz.
It is soluble in alkaline chromates, in hydrate of ammonium, and in acids. When formed in acid solutions, this precipitate is the bichromate (Ag, Cr,0,), and has a more brilliant colour,
THE MERCUROUS Salt is produced by a soluble mercurous salt when added to a solution of a chromate: it is a red precipitate., Its formula is Hg, Cr0,; but frequently the salt 3Hg, Cr0,,(Hg.), is precipitated. It is slightly soluble in solutions of ammonium salts, in water, and in nitric acid.
THE MERCURIC Salt resembles the mercurous salt very closely. It is soluble in excess of many soluble mercuric salts.
The Lead Salt is produced by the action of a soluble lead salt on chromate or bichromate of potassium. It is a yellow precipitate.
Its formula is PbᏟrO.
It is slightly soluble in excess of the chromate or bichromate of potassium, and in hydrate of potassium ; it is insoluble in chloride of ammonium and in water, but soluble in nitric acid.
This acid-radical may also be recognized by the following experiments :
a. Chromates, when heated before the blowpipe with a borax bead, give evidence of chromium in the green tint produced ; care must, however, be taken that other interfering bases are absent.
B. When boiled for some time with hydrochloric acid, chromates are reduced, yielding the sesquichloride (Cr C1), with evolution of chlorine. If sulphuric acid be employed instead, oxygen is set free.
y. The passage of hydrosulphuric acid through the aqueous solution of a chromate also effects its reduction,-a chromic salt with separation of sulphur being the results : : 4KCr0, +5H,S=2Cr, H,02+2K_S+24,0+38.
green ppt. Sulphurous anhydride (802) produces a similar effect, sulphuric and hyposulphuric acids being formed. Nascent hydrogen and many other reducing agents also give the same results.
Numerous organic bodies are capable of rapidly reducing the chromates—such substances as alcohol, sugar, oxalic and tartaric acids. When warmed with alcohol and hydrochloric acid, a chromate decomposes thus :
4KCrO, +10HCl +3C,1,0=2Cr, C1, +4KC1+8H,0+3C,1,0. alcohol. green
chloride. The hydrochloric acid acts partly as a solvent for the chromic hydrate, which we may suppose to be formed at first.
8. Fused with carbonate of sodium many insoluble chromates yield the soluble chromate of sodium (see p. 112).
The chromic radical is generally recognized by the formation of the insoluble silver and lead salts, and by the tests a. and ß.
SALTS OF THE PERCHROMIC RADICAL, OR PERCHROMATES. The hydrogen compound of this radical is known, but only as dissolved in ether: it is obtained by the action of a hydrochloric solution of peroxide of barium on bichromate of potassium; the perchromic acid thus liberated is taken up by ether, which becomes of a beautiful blue colour. It is immediately decomposed by hydrate of potassium, but may be made to unite with ammonium and certain organic bases, forming comparatively stable salts, from which acids separate the blue perchromic acid, which then speedily decomposes into chromic acid and oxygen.
Of compound acid-radicals containing iron and oxygen, two are known, but they are of very slight importance. When carbonate of sodium and ferric oxide are strongly ignited, a compound termed ferrite of sodium is said to be obtained in very small proportion. Similar salts are believed to be formed when a solution containing ferric chloride and the chloride of an alkaline earth is precipitated (under certain conditions) by a hydrate of the first subdivision. But the only definite acid-radical of iron and oxygen is that contained in the ferrates (MFeO,). The ferrate of potassium is obtained by igniting iron or ferric oxide with hydrate or nitrate of potassium, by the action of chlorine on ferric oxide suspended in hydrate of potassium solution, or by the electrolytic evolution of oxygen gas from an iron plate immersed in a concentrated solution of hydrate of potassium. By all these methods the potassium salt is obtained, sometimes in the crystalline form; it dissolves in water, forming a red-violet solution, which is instantly decomposed and decolourized by ammoniacal salts and the weakest reducing agents, and even by a heat of less than 100°: the products of this decomposition are ferric oxide and oxygen. The hydrogen compound, or ferric acid, cannot be obtained, as any attempt at its liberation results in its instant decomposition.
Of the acid-radicals containing manganese and oxygen, two are well known and easily produced. These are the manganic (Mn0,) and permanganic (Mn,C.) radicals. They are both monobasic. The potassium salt of the former is obtained by igniting man