762

CHROMICYANIDES-PLATINO-CYANIDES.

salts. Cobalticyanide of zinc is white; that of nickel is gelatinous, and of a pale blue; that of cobalt is .of a pale red; that of copper, of a pale blue; the ferrous, manganous, and stannous, as well as mercurous and argentic cobalticyanides, are white: salts of lead give no precipitate with the soluble cobalticyanides.

(1587) 5. CHROMICYANIDES.-Chromic salts yield with potassic cyanide a pale bluish-grey precipitate (ErCy), which is not soluble in excess of the potassic cyanide; but if a mixture of hydrated chromic oxide with a solution of potash and an excess of hydrocyanic acid, be exposed to the air, the liquid acquires a reddishbrown colour, and a potassic chromicyanide is formed (Beckmann), corresponding to the ferricyanides and cobalticyanides. These salts are of small importance, and have been but little examined. Potassic chromicyanide (K ̧¤rCy) forms brownish-red anhydrous prisms; its solution precipitates nitrate of silver, white; salts of cobalt, blue; and ferrous salts of a brick-red: but it gives no precipitate with ferric salts, or with nitrate of lead.

6 and 7. OSMIO-CYANIDES and RUTHENIO-CYANIDES may, according to Claus, be obtained, corresponding in composition to the ferrocyanides, which they greatly resemble in the colour of the precipitates they form when mixed with salts of copper, iron, zinc, and lead.

(1588) 8. PLATINO-CYANIDES.-Gmelin ascertained that platinum is capable of entering into combination with cyanogen, and forming a series of double cyanides, which are amongst the most beautiful substances that are known: these compounds are analogous to the foregoing, but their composition differs from that of any of the preceding series: for example, the following formulæ represent a few of the platino-cyanides :

Potassic platino-cyanide is best formed by dissolving platinous chloride in a solution of potassic cyanide; but it may also be obtained by fusing potassic ferrocyanide with spongy platinum; or by heating a concentrated solution of platinic chloride with an excess of potassic cyanide. This beautiful salt forms long transparent rhombic prisms, which are yellow by transmitted, and blue by reflected light: it is very soluble in water, and more sparingly so in alcohol and in ether. Magnesic platino-cyanide is a beautiful salt which crystallizes in rosettes from its solution in a mixture

of alcohol and ether: these crystals form square prisms, which are of a rich crimson by transmitted light, and green or blue by reflected light; they are very soluble in water, and the solution is colourless.* The most characteristic tests of the platinocyanides are the formation of a beautiful smalt-blue precipitate when a platino-cyanide is added to a solution of mercurous nitrate in excess, and a flocculent blue precipitate with cupric salts.

12

(1589) There is another very beautiful series of salts, commonly termed the platini-cyanides, which crystallize in prisms of a coppery lustre when viewed by reflected light, but they appear to be green by transmitted light, and polarize light powerfully; their solutions, however, are colourless. These salts, when dissolved in water, produce a white precipitate with argentic and mercuric salts, a blue with the mercurous salts, and a greenish blue with the cupric salts. These salts have been carefully examined by Hadow, who has shown that the usually received formula (M,PtCy) is erroneous, and that they are more complicated in construction. The salt commonly known as potassic platini-cyanide is really a chloroplatino-cyanide 2 (KPtCy12Cl), 21 H2O=[5 K,PtCу,,K,PtCy,Cl2. 3 H2O, 18 H2O]; but salts exist which correspond in appearance with this, containing, in place of the 2 atoms of chlorine, either 2 atoms of bromine, or of NO, or 1 atom of SO. In order to prepare these compounds in a state of purity, Hadow converts the potassic platino-cyanide into the colourless perchloroplatino-cyanide (K,PtCy,Cl), or into the perbromoplatino-cyanide (K,PtCy,Br.), by the use of an excess of chlorine or bromine, and crystallizing out the salt. He then mixes the compound so obtained, with the platino-cyanide, in the ratio of 5 atoms of the latter with 1 atom of the former; and, on crystallizing, the copper-coloured compound is obtained in a state of purity. The platini-cyanides, so called, appear to be double salts of the platino-cyanides with the perchloroplatino-cyanides.

2

2

*The changes of colour which this salt experiences by change in its condition of hydration are very remarkable (Hadow). The ordinary red salt (Mg,PtCy1, 7 H20) when gently warmed, even under water, becomes yellow, and if crystallized at 160°, yellow crystals with 6 H2 are deposited. At 212° the salt still retains 2 H, when it is white, and between 300° and 400° it becomes anhydrous, and is then yellow. These singular changes of colour may be strikingly displayed by allowing a strong solution of the salt to evaporate on a sheet of white paper. When dry, a crimson surface is obtained, but a drop of water upon any point destroys the colour at that spot instantly; on drying, it again re-appears. When heated, the red salt first becomes yellow; as the temperature rises it is rendered white; and by a somewhat stronger heat it again becomes yellow. By breathing on the paper, the salt resumes the water that it had lost, the yellow spot becoming successively white, yellow, and eventually crimson.

764

RHODI-CYANIDES AND IRIDI-CYANIDES.

2

The platino-cyanides are, indeed, remarkable for their strong tendency to form double salts. Amongst others a very beautiful double salt of potassium and magnesium (MgPtCy,,K,PtCy,, 7 H2O) may be obtained. For further details respecting the platino-cyanides, see Knop, Liebig's Annal. xliii. 111; Quadrat, ib. lxiii. 164, and lxx. 300; and Hadow, Q. J. Chem. Soc. xiii. 106.

9 and 10. RHоDI-CYANIDES and IRIDI-CYANIDES.-Both rhodium and iridium yield double cyanides analogous to the ferricyanides, but potassic rhodi-cyanide is decomposed by acetic acid, with separation of the insoluble rhodic cyanide. This reaction may be employed in the separation of rhodium from iridium, since acetic acid does not decompose the iridium salt.

(1590) Potassic iridi-cyanide (K,frCy) forms colourless crystals, and is characterized by giving a deep indigo precipitate with the ferric salts.

It appears from the foregoing statements, that cyanogen has a strong tendency to produce, with several of the metals, electronegative compounds, which form with hydrogen a series of wellmarked acids. The number of atoms of metal which are united with the cyanogen to constitute the radicles of these acids, varies with the nature of the metal; three different classes of these hydro-acids are known, the first class being dibasic, the second tribasic, and the third tetrabasic; the composition of their salts with potassium is exhibited as follows:

:

3. Tetrabasic Ruthenio-cyanide

(1591) SULPHOCYANIDES.-When potassic cyanide is fused with sulphur, or even when a solution of the cyanide is boiled with flowers of sulphur, the two bodies enter into combination, and a new compound (KCyS) is formed: this compound is also readily prepared by calcining in a covered crucible at a dull red heat an intimate mixture of 3 parts of anhydrous potassic ferrocyanide, 2 of flowers of sulphur, and I part of potassic carbonate. The melted mass when cold must be treated with boiling water, and the filtered liquid evaporated; on cooling, striated prismatic

crystals of potassic sulphocyanide will be deposited: the salt may be obtained pure by recrystallization from alcohol. In this operation potassic cyanide is first formed, whilst metallic iron is separated; the latter is converted partially into ferrous sulphide, and potassic cyanide into sulphocyanide, which is separated from the iron by solution in water.

Potassic Sulphocyanide (KCyS=97) is anhydrous, but very deliquescent. It resembles nitre in appearance and in taste; it is not poisonous. Boiling alcohol dissolves it abundantly: it fuses on the application of heat. This salt is commonly supposed to contain a particular monobasic radicle to which the name of sulpho-cyanogen (CyS=Scy) has been given. The radicle is, however, not known in a separate condition, but it forms an acid compound with hydrogen, and yields numerous well-marked salts. Some chemists prefer to regard the sulphocyanides as representa. tives of the cyanates, in which the oxygen of the latter salts has had its place supplied by sulphur; and the decomposition of hydrosulphocyanic acid by the aid of heat and acids resembles that of cyanic acid under similar circumstances :

2 HЄNO + 2 H,→ = €0, + €0, + 2 H2N.

Ꮋ Ꮎ

2

Ammonium sulphocyanide would then correspond to a sulphuretted urea, as ammonium cyanate does to ordinary urea.

following table represents both views:

The

The view which admits the existence of sulphocyanogen as the salt-radicle of these compounds, renders a simple and satisfactory account of the metamorphoses to which the sulphocyanides are subject, and it will be made use of here.

The sulphocyanides of sodium and ammonium are anhydrous and deliquescent. Small quantities of one of these salts

766

HYDROSULPHOCYANIC ACID.

exist in the saliva of man and of the sheep. A considerable quantity of ammonium sulphocyanide is formed during the distillation of coal gas, and is arrested by the hydrated ferric oxide employed for absorbing sulphuretted hydrogen. It may be extracted from the mixture by simple washing, and by digestion with lime may be converted into calcic ferrocyanide. The majority of the sulphocyanides are soluble both in water and in alcohol; their most characteristic property is the production of an intense blood-red colour when their solutions are mixed with one of the ferric salts: if the red liquid thus formed be acidulated with hydrochloric acid, and fragments of zinc be added, sulphuretted hydrogen is disengaged, and the colour disappears. Ferric sulphocyanide does not form crystals. Sulphocyanide of lead is sparingly soluble; it is slowly deposited in brilliant anhydrous crystals when solutions of acetate of lead and potassic sulphocyanide are mixed. Basic acetate of lead gives a white precipitate with the soluble sulphocyanides. The sulphocyanides also give a white precipitate (EuCyS) when added to a mixture of a ferrous salt with a salt of copper: with mercurous salts and with the salts of silver and of gold, they produce white precipitates.

(1592) Hydrosulphocyanic Acid (HCyS); Fusing pt. 10° (-12°C.); Boiling pt. 216° (102° C.).—When dry mercurous sulphocyanide (HgCyS) is decomposed by exposure to a current of sulphuretted hydrogen, mercurous sulphide is produced, and a colourless oily liquid is formed; it consists of hydrosulphocyanic acid. This acid crystallizes into a radiated mass at 10°. It boils and may be distilled at 216° (Vogel). Its odour is pungent, and resembles that of acetic acid. It is a dangerous poison, and has a strongly acid taste. In its concentrated form it soon undergoes decomposition into hydrocyanic acid and hydropersulphocyanic acid (H,Cy,S), since 3 HCyS-HCy+H2Cy ̧ ̧.

Hydrosulphocyanic acid may be obtained in solution by suspending the sulphocyanide of copper, of mercury, or of silver in water, and decomposing it by means of a current of sulphuretted hydrogen. When its diluted solutions are boiled, it gradually undergoes decomposition, ammonia, carbonic disulphide, and carbonic anhydride being formed. If it be in a more concentrated state it is resolved into hydrocyanic and hydropersulphocyanic acid; and these changes occur more quickly in the presence of other acids.

Solutions of hydrosulphocyanic acid, and of the sulphocyanides are decomposed by the action of nitric acid, and of chlorine, a bright yellow precipitate being occasioned, which was formerly supposed to be sulphocyanogen (CyS); the composition of this precipitate,