FERRICYANIDES-NITRO-PRUSSIDES. 757 to prevent the action of the acid from proceeding too far, otherwise the compound acquires a green colour, owing to the formation of Pelouze's magnetic cyanide of iron. When this blue compound is treated with a solution of potassic ferrocyanide, it is reconverted into the original white compound, and pure potassic ferricyanide is obtained in the liquid, one atom of the yellow salt losing an atom of potassium, which is transferred to the blue compound : K‚Fe"(FeCy ̧)'''+K1(FeCy ̧)" = K„Fe”(FeCy)" + K ̧(FeCy)'''. From the foregoing statements it will be seen that several different blue compounds containing iron and cyanogen may be procured. The composition of these bodies may be thus represented :Ordinary Prussian blue Basic ditto Turnbull's blue, or ferrous ferricyanide. = Fe,,Fcy3, 18 H2O Fe,Cy18, 18 H2O = Fe,,Fdcy2, H2е Fe,KCY, HO = FeK,Fdcy, x H20 Williamson's blue, or ferropotassic ferricyanide Hydroferricyanic Acid (H,Fdcy).-This compound may be obtained in reddish-brown deliquescent crystals, by evaporation of the liquid in which ferricyanide of lead has been decomposed by means of diluted sulphuric acid.* According to Schafarik, it may also be obtained by mixing a cold saturated aqueous solution of potassic ferricyanide with 2 or 3 times its bulk of fuming hydrochloric acid: ferricyanic acid is gradually deposited in brown-green, thin, brilliant needles, which may be dried on a porous tile. (1585) 3. NITRO-PRUSSIDES.-When the vapour, not of nitric oxide (NO), but of nitrous anhydride (NO), is transmitted through a solution of hydroferricyanic acid, it is absorbed, hydrocyanic acid and a new acid, the hydronitro-prussic, are formed :Hydroferricyanic acid. Hydronitro-prussic acid. 2 H,FeCy+N,, = HFе,Cy12 ̧ + 2 HCy. 3 10 2 3 This acid may be obtained in crystals with 2 H2O. Gerhardt represented the compound as containing 1 atom of oxygen less than is given in the foregoing formula; but its composition appears to have been settled by Hadow (Journ. Chem. Soc., 1866, P. 341). The nitro-prussides were originally procured by the following *The relations of the ferrocyanides and ferricyanides may be further illustrated by the following formula, which represent one as a ferrous, the other as a ferric, compound: Ferrocyanide of potassium Fe"Cy 2, 4 KCy process, recommended by Playfair, by whom these salts were discovered (Phil. Trans., 1849, p. 481): 2 Common nitric acid is to be diluted with an equal bulk of water, and when cold, powdered potassic ferrocyanide is to be added in the proportion of 270 parts of the anhydride, N→ (5 atoms) to 422 parts (2 atoms) of the ferrocyanide. The mixture gradually assumes a brown colour, cyanogen and hydrocyanic acid are liberated, whilst a brisk effervescence occurs, owing to the escape of carbonic anhydride and nitrogen, and the salt is dissolved, forming a mixture of potassic ferricyanide and nitro-prusside with potassic nitrate; heat must be applied gradually to the solution by means of a water-bath, until gas ceases to be evolved, and the liquid, instead of giving a blue precipitate with a ferrous salt, produces a dark green or slate-coloured precipitate. It must then be allowed to cool, by which means a large quantity of potassic nitrate, mixed with a small proportion of oxamide, will be separated. The strongly-coloured mother-liquor must next be neutralized with potassic or sodic carbonate, by which a greenishbrown precipitate is caused; and the liquid, after filtration, must be evaporated and allowed to crystallize. The sodic salt crystallizes more readily than the potassic nitro-prusside, which, although anhydrous, is somewhat deliquescent. A much more productive method is the one given by Hadow, which consists in mixing a solution of potassic ferricyanide with one of corrosive sublimate, acidulated with acetic acid, and then adding a definite quantity of sodic nitrite. The reaction which occurs may be thus represented : Ferricyanide. Sodic nitrite. Acetic acid. 2 K,FeCy+HgCl2 + 2 NaNO, + 2 H¤2H ̧Ð ̧ Nitro-prusside. 2 3 Potassic acetate. = Na,K,,Fe,Cу10N, ̧ + HgCy2 + 2 K¤H ̧Ð ̧ + 2 KCl + H ̧Ð. A mixture of potassic and sodic nitro-prusside is formed, whilst the soluble potassic acetate remains in the liquid. If properly performed, a large portion of mercuric cyanide separates from the solution without difficulty, but the purification of the salt requires care; for the necessary details the reader is referred to Hadow's paper. 2 Sodic Nitro-prusside (Na,Fe,Cy10N ̧Ð ̧, 4 H2→).—This salt crystallizes in fine prisms of a ruby-red colour, which require about 2 parts of cold water for solution. Its solution is decomposed by exposure to the sun's rays, Prussian blue being deposited, whilst nitric oxide escapes. Baric nitro-prusside 2 NITRO-PRUSSIDES-NITROSULPHIDES. 759 (Bа,,Fе¿CÓ1N ̧Ð ̧, 6 H2O) crystallizes in fine octohedra of a dark red colour. The nitro-prussides give a pale green precipitate with salts of copper, and a flesh-coloured precipitate with those of silver. With salts of zinc a salmon-coloured precipitate is produced; with salts of nickel, a dirty white; with salts of cobalt, a flesh-coloured precipitate; and with ferrous salts, a salmon-coloured precipitate is formed. The ferric salts, and the salts of lead, of mercury, and of tin, give no precipitates with the nitro-prussides. Chlorine is without effect upon solutions of the nitro-prussides; but they are decomposed when boiled with the alkalies, part of the iron being separated as a crystalline hydrated ferric oxide, whilst the solution becomes orange-coloured, owing to the formation of a new compound containing both cyanogen and iron. They are also decomposed by boiling oil of vitriol. If their solutions be boiled with mercuric oxide, nitric oxide is evolved, and cyanide of mercury is formed. Sulphuretted hydrogen also decomposes them. The most delicate and characteristic test for the nitroprussides is the production of a magnificent purple colour when mixed with solutions of the alkaline monosulphides, such as K,S or KHS. This coloration is extremely intense, and may be employed to indicate very minute traces either of a soluble sulphide or of a nitro-prusside. The colour, however, speedily disappears if any of the polysulphides are present. It appears to be due to the formation of a double salt of the nitro-prusside with the sulphide of the alkaline metal. By boiling the liquid, nitrosulphide of iron and of the alkaline metal is obtained.* * Nitrosulphides of Iron.-A remarkable class of compounds may be obtained by the reaction of potassic nitrite and hydrosulphide of ammonium upon the salts of iron (Roussin, Ann. de Chimie, III. lii. 285). If to a mixture of a solution of hydrosulphide of ammonium and potassic nitrite a solution of ferrous sulphate or chloride be added drop by drop, keeping the mixture constantly agitated, it is found that on raising the liquid to the boiling point, the blackish precipitate which is at first formed is almost entirely redissolved. If the solution be boiled for a few minutes and then filtered, an extremely dark liquid runs through; this, on cooling, deposits hard, sandy, or needle-shaped crystals; the supernatant liquid presents only a slightly yellow tint. If a ferric salt be substituted for a ferrous salt, a similar result is obtained, but a considerable quantity of sulphur is left upon the filter. The crystals thus formed are well-defined oblique prisms with a rhombic base. They are black and opaque, very heavy, sparingly soluble in cold water, but soluble in twice their weight of boiling water. Alcohol, wood-spirit, fousel oil, and concentrated acetic acid also dissolve them freely, but they are absolutely insoluble either in chloroform or in carbonic disulphide. The effect of ether upon them is remarkable; they instantly become liquid if exposed to the vapour of ether, and are soluble in ether in almost unlimited quantity. Traces of ether or of alcohol in chloroform can be detected with certainty by agitating the specimen under trial with a few of the crystals. If pure the liquid will remain abso 760 COBALTICYANIDES NITROSULPHIDES. (1586) 4. COBALTICYANIDES.-When potassic cyanide is added to a salt of cobalt, it gives a reddish-brown precipitate (EoCy), which is soluble in excess of potassic cyanide. The double cyanide of cobalt and potassium (4 KCy,ЄoCy,) thus obtained is decomposed on the addition of hydrochloric acid, and the cyanide of cobalt is precipitated; but if, previously to the addition of hydrochloric acid, it be exposed to the air, it absorbs oxygen, potash is liberated, and potassic cobalticyanide is produced :— 2 0, 2 4 (ЄoCy9, 4 KCy) + 2 H2O + →2 = 4 K2oCy+ 4 KHO. After this change has occurred, the addition of hydrochloric acid causes no precipitate. Potassic cobalticyanide corresponds in composition to the ferricyanide of the same metal. A hydrocobalticyanic acid (H,EoCy) may be obtained by decomposing cupric cobalticyanide with sulphuretted hydrogen. lutely colourless, but the presence of one part of alcohol or of ether in 1000 will yield a coloured solution. These crystals have a brilliant metallic lustre: their taste is at first inky, followed by a persistent bitterness. The new salt is permanent in air containing a trace of ammonia; but, if the substance be in the least acid, gradual decomposition ensues, and ruddy fumes are seen in the bottle. It is not decomposed by a temperature of 212°, but if the heat be gradually increased, it is resolved at a little below 280° into sulphur, ammonium sulphite, nitric acid, and ammonium nitrate, leaving a residue of sulphide of iron. When heated sharply it deflagrates, emitting white fumes, which have an odour like that of burning gunpowder. The concentrated mineral acids immediately decompose the nitrosulphide; but acetic, hydrochloric, and oxalic acids have no effect upon it. Solutions of caustic potash and ammonia, when added to its aqueous solutions, cause a deposition of the crystals, unaltered in composition, scarcely any of the compound being retained in the liquid. Chlorine and iodine decompose it, causing a separation of nitric oxide and of sulphur. It is also immediately decomposed by mercuric oxide with evolution of nitric oxide; with the peroxide of lead it yields nitrate of lead and sulphur; it is also decomposed by potassic permanganate; solutions of nitrate of silver, corrosive sublimate, cupric sulphate, and ferric chloride decompose the solution of this compound, with evolution of nitric oxide and precipitation of black sulphides. Ferrous sulphate is without effect upon it. With nitrate of lead it gradually deposits oblique rhomboidal prisms, which are sparingly soluble in water, soluble in ether, and deliquescent in ether vapour. Roussin attributes to the black crystals a composition represented by the following formula, Fe,S,H2(NO),: By calculation. 168 or 37 33 By expt. 160 The formula suggested for the compound by Roussin is (Fe,S,N,0,.FeS,N ̧ ̧. HS). One remarkable point in the composition of this substance, which has been called dinitrosulphide of iron, is that the iron is not indicated by any of the usual tests of the metal, such as ammonia, potassic ferrocyanide, or hydrosulphide of ammonium. If it be boiled with a concentrated solution of caustic soda, ammonia is disengaged in abundance, and crystallized ferric oxide is depo POTASSIC COBALTICYANIDE. 761 Potassic Cobalticyanide (K,ЄoCy).-This salt was discovered by Gmelin. It crystallizes in yellowish flattened prisms, which are anhydrous, and isomorphous with those of potassic ferricyanide. It is sparingly soluble in water. This salt may be obtained either by dissolving cyanide of cobalt in an excess of potassic cyanide, and exposing it to the air; or by dissolving hydrated oxide of cobalt by the aid of a gentle heat in a solution of potash, supersaturated with hydrocyanic acid; in both cases oxygen is absorbed :— 4 ЄoCy2 + 12 KCy + 4 HCy + →2 = The corresponding salt of sodium (Na ̧¤oCy, 2 H2O) crystallizes in long, transparent, colourless needles; that of barium in efflorescent prisms (Bag, 2 EoCy, 22 H2O). Solutions of these cobalticyanides occasion precipitates in a large number of metallic sited. The solution contains a new salt, which, on evaporation, is deposited in black, well-defined crystals, aggregated in inverted hollow square pyramids. This salt, sulphuretted nitrosulphide of iron and sodium (3 Na,S,Fe,SN20) is soluble in a solution of soda, but insoluble in caustic potash or ammonia. It is decomposed by metallic solutions, and by iodine, with evolution of nitric oxide, in a manner very similar to that in which the same compounds behave to the dinitrosulphide of iron. Acids decompose the salt with facility at ordinary temperatures, and occasion the deposition of a red flocculent substance (Fe,,,NO2, 4 H2S?) which readily subsides, and should be washed with a weak solution of sulphuretted hydrogen. By prolonged washing it loses a portion of its sulphuretted hydrogen. This substance is soluble in alcohol and in ether; when dry it becomes slowly decomposed, emitting fumes of nitric oxide and ammonia, and leaving a residue of sulphide of iron. It is soluble in solutions of the alkalies as well as in those of their carbonates and sulphides, producing salts analogous to the compound with sodium already described. Nitrosulphide of iron (Fe,S,N,,). This compound is obtained by decomposing the foregoing sodium compound (3 Na,S,Fe,S,N,, ), by adding gradually dilute sulphuric acid to a boiling solution of the salt. Sulphuretted hydrogen is evolved in abundance, and the nitrosulphide of iron is precipitated in the form of a black heavy powder. It is insoluble in water, in alcohol, and in ether. It is permanent while moist, but if dried is gradually decomposed, with evolution of nitric oxide. When dry and freshly prepared it burns like tinder if touched with an ignited body. It is soluble in the alkalies, and in the sulphides of the alkaline metals, forming a new class of salts. The sodium compound (Fe,S,N,,, Na,S,H,O) is easily obtained as an intensely dark red crystalline substance of metallic lustre, by dissolving nitrosulphide of iron in disodic sulphide, and allowing the solution to crystallize over sulphuric acid. An interesting relation has been observed between the nitrosulphides and the nitroprussides. The crystals of both classes belong to the oblique prismatic system. If a solution of the nitrosulphide of iron and sodium be mixed with one of mercuric cyanide, mercuric sulphide is precipitated, and sodic nitroprusside is obtained in solution. On the other hand, if sodic nitroprusside in solution be mixed with an excess of an alkaline sulphide a magnificent purple colour is produced, which passes on boiling into a reddish green, and nitrosulphide of iron and sodium is formed, whilst sulphocyanide of the alkaline metal remains in solution. Probably the formula of the nitrosulphides will require a modification similar to that proposed by Hadow for the nitroprussides. |