Page images
PDF
EPUB

ganese, or one of its oxides, with hydrate of potassium in contact with air, or with hydrate of potassium mixed with nitrate or chlorate of potassium. The manganates of the first and second subdivisions are known; they are dark bluish green compounds, those of the alkaline metals dissolving in water to form green solutions. The hydrogen compound is not known.

Permanganic acid (HMn, 0) is produced by the action of dilute nitric acid on the aqueous solution of a manganate. Its colour is a beautiful violet; the solutions of the alkaline permanganates have the same tint. The permanganates, as far as known, are all soluble, no precipitates being formed with saline solutions except in cases where the latter act as reducing agents, and precipitate the peroxide of manganese (Mn, 0,).

Of acid-radicals containing bismuth and oxygen, one only is known. When bismuthic oxide (Bi, 03) is fused with hydrate of potassium, or when it is suspended in a concentrated solution of hydrate of potassium through which a current of chlorine is passing, a double salt of bismuthate of potassium and bismuth is formed, which contains the radical Biog. One or two salts are known, and the hydrogen compound (HBi03).

Of acid-radicals containing tin and oxygen, two are known. Their hydrogen compounds are stannic acid (H, Sn, 03) and metastannic acid (H, H, Sn, 0,5). The acids themselves being very insoluble bodies, no characteristic reactions can be obtained from them, except such as, by destroying the radical, prove the presence of its metallic constituent.

Of the acid-radicals containing the rare metals of the fourth subdivision combined with oxygen, none are of analytical importance. The higher oxides of platinum, rhodium, ruthenium, iridium, osmium, and gold have the property of uniting with the elements of water to form acid compounds, and with the oxides of some few basic radicals, as those of the first subdivision, to form salts. These salts, with the exception of the gold compounds, have not been thoroughly examined. The existence of a definite auric acid (HAUO,) is doubtful; but the anhydride (Au, 0,) is known: the aurate of potassium too has been obtained, crystallized, in small needles of a yellow colour, and having the formula KAu0, +3aq; a solution of this salt in water produces preci. pitates in many metallic solutions, proving that there are many insoluble aurates ;-insoluble, that is, in water, for they frequently dissolve in excess of of their precipitants to form double salts. It will be at once seen that these acid-radicals correspond closely to those mentioned under Section III. of the first subdivision of the acid-radicals (p. 276).

Of the acid-radicals which contain tungsten combined with oxygen, one only is of any analytical importance, although another is known to exist in a few compounds. The tungstic radical (W0,) is a very powerful one, and forms stable salts termed tungstates, which impart to water a bitter metallic taste.

SALTS OF THE TUNGSTIC RADICAL, OR TUNGSTATES. These salts are not decomposed by heat alone, unless their basic constituent is volatile or compound, and when heated on charcoal sometimes yield the brown oxide, although they are reduced or decomposed in different ways according to the base present. The other blowpipe reactions of tungstic acid and tungstates will be found among the processes of decomposition employed for detecting the tungstic radical (see p. 236).

The HYDROGEN SALT (HWO) does not appear to be known; for when the acid is liberated by the action of other acids upon solutions of tungstates in the cold, the white precipitate which occurs, though thought by some to be the acid, rapidly becomes yellow when the solutions are heated, or when the precipitate is allowed to stand. This yellow body has the formula W,02, and so bears the same relation to the acid (HWO,) as auric anhydride (Au, 0,) does to auric acid (HA_0,), or hypochlorous anhydride (C1, O) to to the acid (HC10). Tungstic anhydride is lemon-yellow and crystalline. Recent researches have shown that there are many modifications of tungstates, in which varying quantities of oxygen and tungsten are united to form acid-radicals ; yet they will all group in a singular manner around the anhydride (W,03), which may be produced by the decomposition of all. The union of the anhydride with normal tungstates gives, on the other hand, compound salts resembling the bichromates, &c.

Tungstates may be recognized by the formation of some of the most characteristic insoluble salts, but are more usually identified by processes of decomposition.

The tungstates of the first subdivision are soluble; all the other salts, excepting that of magnesium, are insoluble in water.

The Barium Salt is produced by the action of soluble barium salts on the neutral tungstate of potassium: it is a white precipitate. Its formula is BaW0,. It is insoluble in water and in phosphoric acid, but is decomposed by stronger acids ; it is dissolved by a boiling solution of oxalic acid.

THE STRONTIUM and Calcium Salts are white precipitatos, sparingly soluble in water.

THE MAGNESIUM SALT is soluble.

THE FERROUS and MANY OTHER SALTS containing metals of the third and fourth subdivisions are insoluble, or nearly so, in water.

THE CUPRIC Salt is obtained by the action of a soluble cupric salt on tungstate of sodium: it is a grass-green precipitate. Its formula is CuWO. It is insoluble in water and oxalic acid, soluble in acetic and phosphoric acids.

THE SILVER SALT is a white insoluble powder, produced when a silver salt is added to a solution of bitungstate of sodium. Its formula is Ag, W.0..

The Mercurous Salt is produced by the action of a soluble mercurous salt upon tungstate of potassium: it is a yellow precipitate, so insoluble in water as to be used for the quantitative estimation of tungstic acid.

THE MERCURIC Salt is white if the mercury solution be in excess ; otherwise it is yellow, red, or brown. It is insoluble in water.

THE LEAD SALT is a white precipitate, insoluble in cold water or cold nitric acid, soluble in hydrate of potassium.

Tungstates are, however, most readily recognized by the decomposition of their acid constituent; the following tests may be employed :

a. Tungstic anhydride (W203) does not volatilize when heated on charcoal, but yields a brown oxide of tungsten ; before the blowpipe, with microcosmic salt, this body ([W,0,] which, as we have seen, may be easily produced from tungstates) gives in the reducing flame a fine blue colour, which disappears in the oxidizing flame; if iron be present, a blood-red colour will be produced.

B. Solutions of the tungstates containing the alkaline metals are precipitated by hydrochloric, nitric, acetic, sulphuric, and phosphoric acids ; and the precipitate is insoluble in all the above acids, excepting the last-named, which dissolves it readily. Oxalic, tartaric, and citric acids do not separate the anhydride (W,0%).

7. When the body, W,03, is precipitated from a soluble tungstate by the addition of a mineral acid, a small quantity of tungstic acid remains in solution; and if then a strip of zinc be introduced into the acid solution, the liquid will be coloured blue from the formation of the blue oxide of tungsten.

This radical is usually recognized by the formation of the insoluble barium and mercurous salts; but more especially by the tests a. and y. (See also p. 237.)

SALTS OF THE MOLYBDIC RADICAL, OR MOLYBDATES. The radical Moo, bears considerable resemblance to the radical Wo, : the soluble molybdates have a faint metallic taste; several of the insoluble salts have a yellow colour.

Heated alone, they are fixed, unless their base is volatile or decomposable; on charcoal, before the blowpipe, several molybdates are partially reduced, particularly in the presence of carbonate of sodium.

THE HYDROGEN SALT (HM002) is not known; when an attempt is made to liberate it by the action of acids on molybdates, the anhydride (Mo, 0,) separates as a white curdy precipitate. This body unites with molybdates to form bimolybdates, &c., analogous to the bichromates, bitungstates, &c.

Molybdates are recognized by the formation of certain insoluble salts, and also by several processes of decomposition.

The molybdates of the first subdivision are soluble in water; the others insoluble, or sparingly soluble.

THE POTASSIUM and SODIUM Salts are soluble.

The Barium Salt is produced by the action of soluble barium salts on molybdate of potassium : it is a white precipitate, probably having the

formula BaM00g. It is insoluble in water, but soluble in dilute nitric or hydrochloric acid.

THE STRONTIUM and CALCIUM Salts are white, insoluble in water.
THE MAGNESIUM Salt is comparatively soluble, particularly in hot water.

THE FERROUS and MANY OTHER SALTS of the third and fourth subdivisions are yellow or brown precipitates, insoluble in water, soluble in hydrochloric or nitric acid.

The CUPRIC Salt is yellowish green, insoluble (or nearly so) in water, decomposed by acids and alkalies.

THE SILVER Salt is greenish white, slightly soluble in water and in dilute nitric acid.

THE MERCUROUS SALT is white, soluble in 500 or 600 parts of water, decomposed by nitric acid.

The Lead Salt is produced by precipitating plumbic nitrate with normal molybdate of ammonium: it is a white insoluble precipitate. The native variety is the chief ore of molybdenum. Molybdates may also be detected by several processes of decomposition :

a. Molybdic anhydride, when heated in the reducing flame on platinum wire, imparts a yellowish green tinge to the light; it also gives with microcosmic salt a fine green colour, and with borax a brown bead, when heated in the inner blowpipe flame.

B. When to a neutral concentrated solution of a soluble molybdate, a few drops of hydrochloric or nitric acid are added, the anhydride (Mo, 0,) separates ; it dissolves, however, on the addition of more acid, or even upon dilution with much water. Oxalic and phosphoric acids do not produce this effect,

7. By immersing a strip of zinc in a hydrochloric solution of a molybdate, a blue colour is produced, from separation of the blue oxide of molybdenum; the colour gradually changes to green, and then becomes nearly black.

d. By evaporating nearly to dryness a nitric solution of an alkaline phosphate or of phosphoric acid, and adding a drop of molybdate of ammonium, a yellow precipitate is obtained, which is insoluble in hot nitric acid.

6. A trace of hydrosulphuric acid produces in solutions of molybdates a blue colouration ; larger quantities of the gas give a brown precipitate of molybdous sulphide (Mo, S.).

Molybdenum is usually recognized, when existing as the molybdic radidical, by the precipitation of the barium and lead salts, and by the tests ß. and d. (See also p. 241.)

Of acid-radicals containing vanadium and oxygen, two are known; of these the vanadic only is of any importance; the vanadites are derived from the binoxide (V,0,).

SALTS OF THE VANADIC RADICAL, OR VANADIATES. The acid-radical VO, resembles the tungstic and molybdic radicals in many points : many of its salts are yellow or orange; they have no characteristic taste. Generally speaking, they are comparatively soluble in water.

A red heat produces no change in the vanadiates, unless the basic constituent is volatile or decomposable. Vanadic anhydride (V203) heated on charcoal is partially reduced to a lower oxide, and partly to vanadium itself; vanadiates of the heavy metals yield alloys of vanadium.

THE HYDROGEN SALT (HVO,) is unknown, the addition of an acid to a soluble vanadiate precipitating the anhydride (V, 03) in an impure state, as a yellow substance, soluble in acids, yielding yellow solutions. From the anhydride, vanadiates and bivanadiates are prepared.

This radical may be recognized both by the formation of insoluble salts and by certain processes of decomposition.

Many vanadiates are soluble in water.
THE POTASSIUM and Sodium Salts are soluble.

The Ammonium Salt (NH, VO,) is remarkable for being quite insoluble in a saturated solution of chloride of ammonium.

The Barium Salt is produced by the action of a soluble barium salt on an aqueous solution of vanadiate of ammonium: it is a yellow gelatinous precipitate, which becomes white and dense after standing. Its formula is BaVO, It is slightly soluble in water, and dissolves with a red colour in suphuric acid.

THE STRONTIUM Salt is a white crystalline granular precipitate, more soluble than the barium salt.

THE CALCIUM SALT is soluble, and THE MAGNESIUM SALT exceedingly soluble in water.

THE FERRIC, NICKEL, and many Salts containing metals of the third and fourth subdivisions are yellow and soluble in water.

THE CUPRIC Salt is soluble.

The Silver Salt is obtained by the action of nitrate of silver on vanadiate of ammonium, and is a pale yellow or white precipitate, soluble in nitric acid and in hydrate of ammonium.

THE MERCUROUS, MERCURIC, and LEAD SALTs are yellow and more or less soluble in water.

The vanadic radical may also be recognized by processes of decomposition, &c. :-

a. Vanadiates generally fuse when heated; the anhydride (V,03) does not volatilize. With borax or microcosmic salt, the anhydride gives a green glass in the reducing, and a yellow in the oxidizing flame.

B. Vanadic anhydride dissolves in the stronger acids, forming yellow or red solutions, which often become colourless on ebullition, and yield red or yellow crystallized compounds or salts of vanadic acid. The sulphate of vanadic acid is said to have the formula V, (SO2).

7. Hydrosulphuric acid precipitates a mixture of binoxide of vanadium and sulphur from an acid solution of vanadic oxide.

d. Ferrocyanide of potassium produces a beautiful green precipitate with soluble vanadiates.

« PreviousContinue »