AMMONIACAL COMPOUNDS OF COBALT. 557 red heat it loses ammonia and hydrochlorate of ammonia, leaving chloride of cobalt. The latter may be reduced to the metallic state by passing a current of hydrogen gas over it in a tube heated to redness. When digested with water upon oxide of silver, the chlorine is withdrawn from the new compound, whilst the oxygen of the oxide takes its place; a red strongly alkaline liquid, oxide of purpureocobaltia, is thus produced, which unites with acids, and forms a peculiar class of salts: this alkaline solution emits no smell of ammonia. Fremy, in an elaborate series of researches on the ammoniacal compounds of cobalt, has shown (Ann. de Chimie, III. xxxv. 257) that, independently of the ammoniacal compounds obtained with the ordinary salts of the metal, and of the above compounds described by Claudet, three other sets of salts may be procured, which he regards as compounds of different oxides of cobalt with various proportions of ammonia: the first of these bases he names oxycobaltia. Its salts crystallize readily; they have for the most part an olive colour, and may be dissolved in a solution of ammonia without change, but when placed in cold water they are decomposed with evolution of oxygen and deposition of a green basic salt: the salts of this base appear to contain a binoxide of cobalt, which, however, cannot be isolated. The second base, from the yellow colour of its salts, he terms luteocobaltia; this base has been isolated; it has a strongly alkaline reaction, and its salts crystallize easily. The third base is termed fuscobaltia; it forms brown uncrystallizable salts. The base of Claudet's salts, which Fremy termed, from the red colour of its compounds, roseocobaltia, is, according to Gibbs and Genth, a mixture of two isomeric bases, one of which, roseocobaltia, neutralizes 3 atoms of a monobasic acid; the other, purpureocobaltia, neutralizes only 2 atoms of acid. Further details regarding the preparation of these different compounds are also contained in a paper by Gibbs and Genth (Chem. Gaz. 1857, p. 181), who have described an additional series, to which they give the name of salts of xanthocobalt, from the brilliant yellow colour of these compounds. The chloride of xanthocobaltia (Є0,→Cl, 10 H ̧N 2 NO. H2→, or Co2OCl2, 5 H,N,NO,.HO) may be obtained in crystals by decomposing the sulphate of this base with a solution of chloride of barium; and the sulphate (Єo,,, 10 H2N, 2 NO, 2 Se ̧. H2e, or Co2O,, 5 H,N,NO,, 2 SO,. HO) is easily procured by transmitting a rapid current of nitrous acid through an ammoniacal solution of sulphate of cobalt, taking care to preserve the alkalinity of the liquid by the occasional addition of ammonia. The solution gradually assumes a dark yellowish 4 558 AMMONIACAL COMPOUNDS OF COBALT. brown colour, and if left to evaporate, spontaneously deposits the sulphate of the new base in the form of thin plates derived from the right rhombic prism. All the compounds of each of these bases, when boiled with a solution of caustic potash or of soda, are decomposed, and hydrated sesquioxide of cobalt is precipitated, whilst ammonia is expelled. The following table will afford a general comparative view of these different classes of salts, including the double salts which ammonia forms with the protoxide of the metal; they are probably compounds, of very complex constitution, formed on the ammonium type:~ 1. Double Salts of Ammonia and Protoxide of Cobalt. Nitrate Єo 2 NO3, 6 H ̧N, 2 H ̧Ð 2 Chloride EoCl2, 6 H2N, 3 H2O. Nitrate. Sulphate 2 [(€oᎾ, ᎦᎾ) 5 H3N], 3 H Ꮎ. 4. Salts of Fuscobaltia. Nitrate. €o,€g, 2 N,Đ, 8 HạN, 3 H,Đ Chloride Nitrate. Chloride 2 ស Єo,cle, 8 H2N, 3 H2O. 5. Salts of Xanthocobaltia. 6. Salts of Roseocobaltia (Gibbs and Genth). Nitrate. Єo, 6 NO3, 10 H ̧N, 2 H‚Ð 2 7. Salts of Purpureocobaltia. Acidsulphate Co23, 4 Se ̧, 10 H2N. 5 H2O (722) SULPHIDES OF COBALT.-Three sulphides of this metal may be procured,—a protosulphide, Єo; a sesquisulphide, Єo,,; and a bisulphide, CoS. The latter may be obtained by heating CHLORIDE, SULPHATE AND NITRATE OF COBALT. 559 carbonate of cobalt with sulphur, not allowing the temperature to rise too high. The most important of these is the protosulphide, which may be procured in a hydrated condition by precipitating a solution of acetate of cobalt by sulphuretted hydrogen, or by mixing any neutral solution of a salt of cobalt with sulphide of ammonium. In this form it speedily absorbs oxygen from the air, and becomes converted into sulphate of cobalt. If a mixture of oxide of cobalt with persulphide of potassium (the liver of sulphur) be fused in a covered crucible, fused sulphide of cobalt is obtained at the bottom of the crucible. The sesquisulphide, which is occasionally met with in octohedra of a grey colour, may be obtained by heating sesquioxide of cobalt to about 500° in a current of sulphuretted hydrogen. 2 (723) CHLORIDE of Cobalt (EoCl2=130, or CoCl=65; Sp. Gr. 2.937) is obtained as a lilac-coloured anhydrous mass, by passing chlorine over metallic cobalt; it is volatile at a high temperature. By dissolving the oxide or the carbonate of cobalt in hydrochloric acid, the hydrated chloride may be obtained in ruby-red octohedral crystals with 6 H,, of sp. gr. 1.84, which are readily soluble in water and in alcohol; its aqueous solution when concentrated, or when mixed with an excess of strong hydrochloric acid, is of a deep blue colour, but on dilution it becomes pink. This dilute solution may be used as a sympathetic ink; characters traced with it on paper, though invisible when cold, become blue by heat, and again fade as the hygroscopic moisture of the paper is restored from the air: the colours of this ink may be varied at pleasure; the addition of a small proportion of a ferric salt renders it green; zinc produces a red, and copper a yellow tint. Anhydrous chloride of cobalt absorbs 4 atoms of ammonia, and if its solution be mixed with an excess of ammonia it deposits crystals, consisting of EoCl2, 3 [(HN),→.] (724) SULPHATE OF COBALT (CoSe, 7 H2O=155+126, or CoO,SO. 7 HO=77'5+ 63; Sp. Gr. anhydrous, 3'531) is isomorphous with sulphate of magnesium. The anhydrous salt contains 38.06 of metallic cobalt or 48 38 of the protoxide. = NITRATE OF COBALT (Go 2 NO ̧ . 6 H2O 183 + 108, or CoO, NO. 6 HO=91'5+54; Sp. Gr. 1.83) is prepared by dissolving the oxide in nitric acid. It is a deliquescent salt, which is sometimes employed as a reagent for the blowpipe: a fragment of the compound under examination is supported either upon charcoal, or upon a bent platinum wire, and moistened with a minute quantity of a strong solution of the nitrate of cobalt. When treated in this way, many of the compounds of magnesium 560 CARBONATES OF COBALT-TESTS FOR COBALT. yield a pale pink-coloured mass after ignition; those of zinc give a green residue, and those of aluminum a blue. If a concentrated solution of nitrite of potassium be gradually added to a solution of nitrate of cobalt acidulated with nitric or with acetic acid, a beautiful orange-yellow compound is precipitated in microscopic four-sided prisms with pyramidal summits; it is sparingly soluble. According to A. Stromeyer, it consists of [Єo ̧Ð ̧, 2 N ̧Ð ̧,6 (KNÐ ̧) . 2 H2O], or [Co2O„,2 NO„, 3 (KO,NO¿) . 2 HO], and contains 13.6 of metallic cobalt. A hydrated arseniate of cobalt (Єo, 2 As→.8 H2Ð, or 3 CoO,AsO, 8 HO) is found native, in minute crystals, and is known as cobalt bloom. (725) CARBONATES OF COBALT.-Cobalt resembles magnesium, zinc, nickel, and copper, in the circumstance that when solutions of its normal salts are mixed with a solution of carbonate of sodium or potassium, the precipitate which falls is not a normal carbonate, but a mixture of normal carbonate with hydrated oxide of cobalt. If the two solutions be mixed when hot, the red precipitate is said to have the formula (5 Єo✪, 2 CO2. 4 H2O). If the salts be mixed at the ordinary temperature, the precipitate is of a brighter red, and has a composition (4 ¤0✪, 2 ¤Ð ̧.7 H‚Ð). If either of these precipitates be boiled with an excess of carbonate of sodium, it assumes an indigo-blue colour, and is converted into the compound 4 ¤¤Ð, ¤Ð ̧ . 4 H2O, which absorbs oxygen and becomes green during washing. 3 2 A true normal carbonate [3 Єo¤Ð ̧ . 2 H2Ð, or 3 (CoO,CO2) . 2 HO] is formed by digesting either of the basic carbonates of cobalt with the acid-carbonate of sodium or ammonium. (726) CHARACTERS OF THE SALTS OF COBALT.-The crystallized salts of cobalt are red; when anhydrous they are usually lilac-coloured. Their solutions when in a very concentrated form are blue; at a particular stage of dilution they are red when cold, but become blue on heating them, the red colour returning as the liquid cools: when mixed with a larger proportion of water they exhibit a delicate rose colour, and this tint is perceptible even when the solution is very much diluted. They have an astringent metallic taste. Before the blowpipe the compounds of cobalt are easily recognized by the intense blue colour which they communicate to a bead of borax in the oxidating flame. In solution the salts which this metal forms with the mineral acids give no precipitate with sulphuretted hydrogen, if the liquid ESTIMATION OF COBALT. 561 be slightly acidulated with sulphuric or hydrochloric acid; but the cobalt is completely precipitated by it from a dilute neutral solution of the acetate. With sulphide of ammonium they yield a black sulphide. Carbonate of potassium gives a rose-coloured basic carbonate, which is soluble in carbonate of ammonium. Hydrate of potash gives a blue basic salt, which by excess of the alkali becomes rose-coloured. Ammonia produces a similar effect, but readily dissolves the precipitate, forming a brownish solution which rapidly absorbs oxygen from the air, and becomes red. The soluble oxalates give a sparingly soluble pink oxalate of cobalt, which is soluble in nitric acid and in ammonia. Ferrocyanide of potassium gives a dirty green, and ferricyanide of potassium a bulky reddish-brown precipitate; the latter reaction occurring even in ammoniacal solutions. (727) Estimation of Cobalt.-Cobalt may be estimated with accuracy in the metallic form. Supposing that no compound of any other metal susceptible of precipitation by sulphuretted hydrogen be present, the solution is to be neutralized by means of carbonate of potassium, mixed with a solution of acetate of potassium, and the cobalt precipitated as sulphide by a current of sulphuretted hydrogen, the precipitate allowed to settle in a beaker closed by a glass plate, then collected on a filter and washed. The alkalies are prevented from effecting the complete precipitation of cobalt, as well as of iron, of nickel, of copper, and of many other metals, by the presence of certain kinds of organic matter, such as that derived from the paper of the filter; special precautions are therefore required to avoid this accident. For this purpose the neck of the funnel with the filter and its contents is introduced into a small flask, a hole is made with a glass rod in the bottom of the filter, and the precipitate is washed into the flask; the filter after being moistened with concentrated nitric acid, is again washed; it is then dried, burnt, and the ash added to the contents of the flask, which are now boiled with nitric acid until the sulphide of cobalt is dissolved. The liquid so obtained is diluted and poured off from any particles of undissolved sulphur, and the solution of cobalt may be evaporated to dryness, then mixed with sulphuric acid to convert it into sulphate, and the excess of acid expelled by a moderate heat. 100 parts of sulphate of cobalt indicate 38.06 of the metal. After the sulphide has been brought into solution by the nitric acid, the cobalt may also be precipitated in the form of hydrated oxide by an excess of pure potash; the oxide is then thoroughly washed with boiling water, dried, ignited, and weighed: the black oxide thus procured |