a. When a sulphocyanide (that of potassium, for instance) is boiled with nitric acid, or when chlorine gas is passed into the aqueous solution of a sulphocyanide, a yellow precipitate is produced, to which the name "pseudosulphocyanogen" has been given: the probable constitution of this body is HC, N, S..

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B. Most sulphocyanides, when heated in a closed tube, yield a sublimate of sulphur, together with many other products. The ammonium suffers very remarkable changes, and yields, among other volatile bodies, bisulphide of carbon, sulphide of ammonium, hydrosulphuric acid, and sulphur.

This acid-radical may be recognized by its insoluble silver and lead salts, and by the decomposition described under a.

Of acid-radicals formed by the union of cyanogen with metals, there are three which more especially demand notice: they are known respectively as ferrocyanogen, ferricyanogen, and cobalticyanogen. The number of these compounds of carbon, nitrogen, and metals, or rather of cyanogen and metals, is, however, very great. They are generally formed by the direct union of two metallic cyanides, which, instead of combining to form a double salt, appear to undergo a total change in the arrangement of their constituent molecules :

2KCy+FeCy=K2(FeCy ̧).

Some few of these compounds do, however, appear to partake far more of the characters of double salts than of simple salts which contain compound acid-radicals: such compounds are those formed by the cyanides of zinc and copper-KCy, ZnCy, and KCy, Cu,Cy; while in other compounds, such as those of iron, manganese, cobalt, and platinum, so complete a metamorphosis has been effected, that no hesitation can be felt in ascribing to them a constitution differing from that of the others. The two compounds containing cyanogen and iron-ferrocyanogen (FeCy) and ferricyanogen (Fe,Cy)-are well known in combination with basic radicals, forming very stable salts: the former of these radicals is bibasic, the latter tribasic. Chromium and manganese yield several radicals; but their salts are not stable. The best known of these last mentioned compound radicals are chromicyanogen (Cr,Cy,) and manganicyanogen (Mn, Cy), which are each tribasic. Cobalt forms a radical of the formula Co2Cy, the

salts of which (cobalticyanides) are very stable. The metals allied to platinum yield several radicals by union with cyanogen.

SALTS OF FERROCYANOGEN, OR FERROCYANIDES.

A ferrocyanide is produced when an alkaline cyanide meets with iron, or an iron salt, under appropriate conditions.

Ferrocyanides are decomposed by heat in most cases nitrogen gas is evolved, and a residue of iron and carbon left.

THE HYDROGEN SALT (H,Cfy), or hydroferrocyanic acid, is produced when hydrochloric acid is added to a concentrated solution of ferrocyanide of potassium. It separates on the addition of ether, in the form of minute white, yellowish, or bluish crystals floating in the ether. It is soluble in water.

This radical is best recognized by the formation of certain characteristic salts; but it may also be identified by the products of its decomposition.

The chief insoluble ferrocyanides are the calcium, ferrous, ferric, cupric, argentic, and lead salts.

THE POTASSIUM and SODIUM SALTS are soluble.

THE BARIUM SALT dissolves in about 36 parts of cold water.

THE STRONTIUM SALT is soluble.

The Calcium Salt is a white precipitate.

Its formula is KCaCfy+14aq.

It requires about 800 parts of cold water for its solution, and is even less soluble in water containing ammonium salts.

The Magnesium Salt is a white precipitate.

Its formula is Mg,Cfy+6aq; but when an ammonium is present in the solutions employed, the precipitate appears to be MgNH Cfy.

It is insoluble in chloride of ammonium, readily soluble in hydrochloric acid.

The Ferrous Salt is a white, or more usually a pale blue precipitate, which is rapidly converted by the air or oxidizing agents into the ferric salt, becoming a deep blue in consequence. Its formula is KFe,Cfy,, or KFeCfy, Fe,Cfy.

It is nearly insoluble in water.

The Ferric Salt is produced by the action of ferric salts on a solution of ferrocyanide of potassium. It is a deep blue precipitate, known as Prussian blue.

Its formula is (Fe2)¿Cfy ̧•

It is insoluble in water, and in dilute hydrochloric acid (see p. 126).

THE CUPROUS SALT is a white precipitate. Its formula is (Cu),Cfy. It is soluble in the hydrate, but insoluble in the other salts of ammonium.

The Cupric Salt is a brownish red precipitate.

Its formula is CuCfy.

It is insoluble in water, ammonium salts, and acids.

THE SILVER SALT is white. Its formula is Ag,Cfy. It is soluble in cyanide of potassium, in the hydrate but not in the other salts of ammonium. Hydrochloric acid does not act upon it; but nitric acid dissolves out one-fourth of its silver, converting it into ferricyanide. Sulphuric acid dissolves it. It is insoluble in water.

THE MERCUROUS SALT is not known; ferrocyanide of potassium precipitates yellowish white flakes (which contain no mercury) from solutions of mercurous salts.

THE MERCURIC SALT is white.

THE LEAD SALT is white. Its formula is Pb, Cfy. It is sparingly soluble in hot hydrate of ammonium, and entirely in chloride of ammonium, but not in the other common ammonium salts. It is insoluble in water, but partially soluble in sulphuric acid.

This acid-radical may also be detected by the following processes of decomposition:

a. If ferrocyanide of potassium or sodium be made by boiling any other ferrocyanide* with the hydrates or carbonates of potas

* Insoluble ferrocyanides may be thus decomposed, an alkaline salt of the radical, and an insoluble carbonate of the base being formed. Thus, to take two examples

(Fe)Cfy,+6KHO=3K,Cfy+2Fe,H,O; or
Ba,Cfy+Na,CO ̧=Na¿Cfy+Ba ̧CO ̧.

sium or sodium and filtering, and the resulting solution then evaporated to dryness and ignited in a small covered crucible, a fused mass will be obtained, and, in that part of it soluble in water, an alkaline cyanide will be found, which may be identified by any of the usual tests, while the residue, insoluble in water, may, after due washing, be dissolved in hot hydrochloric or nitric acid and tested for iron.

B. When an alkaline ferrocyanide is heated with dilute sulphuric acid, the characteristic odour of hydrocyanic acid is perceptible.

γ.

y. But when powdered ferrocyanide of potassium (or of sodium) is heated with concentrated sulphuric acid, scarcely a trace of hydrocyanic acid is evolved, but only carbonic oxide gas (CO), according to the following equation :—

Ferrocyanogen is usually recognized by the formation of the ferrous and ferric salts; occasionally also the cupric and uranium compounds are employed for this purpose, as well as the process given under a.

SALTS OF FERRICYANOGEN, OR FERRICYANIDES.

The potassium salt is obtained by passing chlorine into a solution of ferrocyanide of potassium, until a drop of the solution no longer produces a blue precipitate with a ferric salt.

When heated, ferricyanides undergo decompositions very similar to those of the ferrocyanides.

THE HYDROGEN SALT (H, Fe, Cy, or H, Cfdy), or hydroferricyanic acid, is obtained by the action of hydrofluosilicic acid upon ferricyanide of po

tassium.

This radical may be recognized by the formation of the ferrous, ferric, zinc, and silver salts.

THE POTASSIUM, SODIUM, BARIUM, STRONTIUM, CALCIUM, and MAGNESIUM SALTS are soluble.

The Ferrous Salt is produced by the action of ferricyanide of potassium: it is a blue precipitate. Its formula is Fe, Cfdy. It is insoluble in water and in hydrochloric acid.

The Ferric Salt is thought to be produced by the action of ferricyanide of potassium. It is a very soluble salt, and only appears in the form of a brownish green solution.

THE ZINC SALT is produced by the action of ferricyanide of potassium: it is an orange brown precipitate. Its formula is Zn, Cfdy. It dissolves in ammonium salts.

THE CUPROUS SALT is reddish brown. Its formula is (Cu), Cfdy. It is soluble in the hydrate, but not in other salts of ammonium; it is insoluble in hydrochloric acid.

THE CUPRIC SALT is brownish or greenish yellow. Its formula is Cu, Cfdy. It is soluble in the hydrate and carbonate of ammonium, but not in other ammonium salts, unless with the aid of heat.

THE SILVER SALT is orange yellow. Its formula is Ag, Cfdy. It dissolves in the hydrate, and in a hot solution of the carbonate of ammonium, but is insoluble in other ammonium salts.

THE MERCUROUS and MERCURIC SALTS are yellow.

THE LEAD SALT is deposited gradually in dark brownish red crystals. Its formula is Pb, Cfdy. It is somewhat soluble in water. It is decomposed by dilute sulphuric acid into sulphate of lead and hydroferricyanic acid. The constituents of this radical may be detected by its decomposition, in the manner described under ferrocyanogen; but the formation of the characteristic ferricyanides above mentioned must be relied on for its distinction.

SALTS OF COBALTICYANOGEN, OR COBALTICYANIDES.

These salts are produced by the direct action of an alkaline cyanide upon cyanide of cobalt. 4 eqs. of cyanide of potassium with 2 eqs. of cyanide of cobalt only differ from 1 eq. of cobalticyanide of potassium by 1 eq. of potassium, which in the reaction decomposes 1 eq. of water, producing 1 eq. of hydrogen and 1 eq. of hydrate of potassium :

4KCy+2CoCy+H2O=K, (Co2 Cy1)+KHO+H. Cobalticyanogen, it will be observed, is analogous to ferricyanogen; the cobalt compound corresponding to ferrocyanogen is unknown, or at least its existence is very doubtful.

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THE HYDROGEN SALT (H, Co2 Cy。 or H, Cocy), or hydrocobalticyanic acid, crystallizes in deliquescent needles. Heated above 100°, it is decomposed. It is soluble in water and in alcohol, but does not dissolve in ether.

This acid-radical may be recognized both by the formation of insoluble salts, and by its decomposition.

THE POTASSIUM, SODIUM, BARIUM, STRONTIUM, CALCIUM, and MAGNESIUM SALTS are soluble.

THE FERROUS SALT is a white precipitate. Its formula is Fe, Cocy.

THE FERRIC SALT is soluble.

THE ZINC SALT is a white precipitate.

THE CUPROUS SALT is unknown.

THE CUPRIC SALT is produced by the action of soluble cupric salts on cobalticyanic acid: it is a sky-blue precipitate. Its formula is Cu, Cocy+ 3aq. It is soluble in hydrate of ammonium, insoluble in water and acids.