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acid; but by nitric acid it is converted into vanadic sulphate, which is a soluble salt.

THE CARBONATE and THE OXALATE seem to be soluble.

The Ferrocyanide is produced by the action of ferrocyanide of potassium: it is a bulky, lemon-yellow precipitate, which becomes green by exposure to the air.

THE FERRICYANIDE is produced by ferricyanide of potassium, as a gelatinous yellow-green precipitate.

THE PHOSPHATE is soluble.

In most instances the other special reagents of the present and three preceding subdivisions have been found to give no characteristic reactions with vanadic salts; the action of others has not been ascertained.

The insoluble hydrate, sulphide, and ferrocyanide are the most characteristic vanadic salts.

TER-SALTS OF VANADIUM.

2

The oxide of this series (V2O,) plays the same part as the corresponding oxide of molybdenum; and this metal occurs in nature in the form of a vanadiate, just as molybdenum occurs as a molybdate. Several salts, however, containing other salt-radicals than oxygen, belong to the ter- or pervanadic series. The vanadiates are colourless, yellow, or occasionally red,— while the ter-salts are also generally red or yellow, and give solutions of the same colour: by the action of reducing agents (e.g. H2S or H2O) they

become blue.

THE CHLORIDE (VCl ̧) is a liquid which dissolves in large excess of water, forming a pale yellow solution, which decomposes in a few days, becoming green or blue, and evolving chlorine, and forming the bichloride VC12.

THE IODIDE and THE CHROMATE are unknown.

THE OXIDE is produced by the action of nitric acid on the lower oxides, or directly from the ores; it may also be obtained by the action of the hydrates of potassium or ammonium on vanadic salts. It is a reddish yellow or brickred precipitate. Its formula is V2O. It dissolves in the hydrates of potassium and ammonium, forming vanadiates, the solutions of which are yellow or brown (most metallic vanadiates are soluble). 1 part of ter-oxide requires 1000 parts of boiling water for solution. It dissolves readily in acids.

The Sulphide is not produced by hydrosulphuric acid gas; but by the addition of sulphydrate of ammonium a brown precipitate falls. Its formula is V, S. It dissolves in the hydrates, sulphides, and carbonates of the first subdivision, forming sulphovanadiates. It is not decomposed by sulphuric acid.

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THE SULPHATE is soluble.

THE CARBONATE does not exist.

THE OXALATE is soluble.

THE FERROCYANIDE is produced by ferrocyanide of potassium, as a beautiful green precipitate, which is insoluble in acids.

THE FERRICYANIDE is unknown.

THE PHOSPHATE is yellow, and comparatively soluble in water.

The other special reagents of the present and three preceding subdivisions have generally been found to give no characteristic reactions with ter-salts of vanadium.

Ter-salts of vanadium may be recognized best by the formation and reactions of the oxide, and also of the sulphide.

SALTS OF SELENIUM AND TELLURIUM.

These two bodies, which will be fully treated of in the next Chapter, are mentioned here because they are precipitated as sulphides from their acid solutions, in conjunction with the members of the fourth subdivision, by the passage of hydrosulphuric acid gas.

The Sulphide of selenium is yellow. Its formula is SeS2. It dissolves in excess of sulphydrate of ammonium.

If the sulphide be dissolved in nitrohydrochloric acid and evaporated to dryness, selenious anhydride (SeO2) will be obtained, which may be recognized by the following reactions:

a. If a portion be dissolved in water, with which it combines to form selenious acid (H, SeO), and some hydrochloric acid and a strip of zinc be then introduced into the solution, the zinc will become coated with a coppercoloured film, and subsequently red or red-brown flocks of selenium are deposited.

3. If another portion of the selenious anhydride, or some of the precipitated selenium of experiment a. be dried at a gentle heat, and then volatilized before the blowpipe flame, a peculiar odour, resembling that of horse-radish, is perceived.

The Sulphide of tellurium is a dark brown precipitate. Its formula is TeS. It is soluble in excess of sulphydrate of ammonium, and in boiling solutions of the hydrates of potassium and sodium, yielding salts known as sulphotellurites.

We now subjoin a method for the analysis of the 2nd Section of this subdivision, supposing that we have one only of its important members present. The Table for the 1st Section has been already given (p. 190).

On pp. 246 and 247, the synopsis of reactions will be found.

Analysis of Subdivision IV.

SECTION II.-Salts of metals which form Sulphides soluble in Sulphide of Ammonium.

The salt may be one of TIN, ANTIMONY, ARSENIC, PLATINUM, or GOLD.

If, as is probable, it is a sulphide, wash thoroughly; add hydrochloric acid; boil, and add, while boiling, a few drops of nitric acid, drop by drop, until the precipitate is dissolved. Pour the solution down the funneltube of a hydrogen apparatus fitted with an "arsenic-tube" (see p. 213). Apply the heat of a spirit-lamp, urged by a blowpipe, to the arsenic-tube. The formation of a mirror after the lapse of a few minutes indicates

the presence of Arsenic or Antimony. Dissolve the mirror out of the tube by a drop of hot nitric acid; evaporate in a porcelain dish to dryness at 100° C.; redissolve in a drop of water, and add

nitrate of silver. A yellow or

If no mirror is obtained when the action in the hydrogen apparatus has ceased, brush the black powder which is found, carefully from the surface of the zinc; it may contain Tin, Antimony, Platinum, or Gold. Wash it by decantation, boil it with hydrochloric acid, and filter.

Any residue indicates the
presence of
Platinum or Gold.
Boil in hydrochloric acid,
and add a drop or two of
nitric acid, just to dissolve;
boil to decompose any nitric

acid remaining, then add
some concentrated solution
of oxalic acid, and keep
warm for some time.

A brown

red precipitate precipitate,

indicates

Arsenic ;

no change

indicates

Antimony.

or yellow
metallic

spangles, in-
dicates the
presence of
Gold.

If no precipitate occurs, the solution should be neutralized with ammonia; a yellow precipitate will indicate the presence of Platinum.

Perfect solution indicates the presence of

Tin or Antimony. Boil the hydrochloric solution, add a drop or two of nitric acid, or a crystal of chlorate of potassium; cool, and add excess of solution of sesquicarbonate of ammonium: the formation of a precipitate insoluble in excess indicates

the presence of

Tin.
This should be
verified by re-
ducing this
precipitate by
fusion with
cyanide of
potassium,
dissolving the
washed metal
in hydrochloric
acid, and test-
ing it with pro-
tochloride of

mercury: a
white or grey
precipitate
indicates

Tin.

The solution may contain

Antimony. Pass hydrosulphuric acid gas into it,

and then acidify with hydrochloric acid: a reddish-orange precipitate indicates the presence of Antimony.

[blocks in formation]

(see page 192) (see page 196)|(see page 204) (see page 207)

[blocks in formation]

* Signifies that a precipitation occurs, but not

+ Signifies that the precipitate which is formed consists of

[blocks in formation]

of the salt indicated in the horizontal column.

the salt indicated in the horizontal column next below.

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