562

SEPARATION OF COBALT FROM OTHER METALS.

consists of Єo,,, and corresponds to 73'44 of metallic cobalt. Some chemists, however, prefer to reduce this oxide in a current of dry and pure hydrogen in the manner shown in fig. 344. The tube, e, is weighed when empty; then a certain proportion of the oxide of cobalt is introduced into the bulb, and the tube is again weighed; hydrogen is generated in the bottle, a, and allowed to traverse the vessels, b, c, and d: b contains a solution of potash, and c one of nitrate of silver, which are designed to arrest any traces of arseniuretted hydrogen; oil of vitriol is placed in d for the purpose of drying the gas: a dull red heat is next applied to

the lamp may then be removed from the bulb, but the current of hydrogen must be maintained till the tube is quite cold. The tube and its contents are finally weighed a third time, and the proportion of metallic cobalt, which a given weight of the oxide under trial contained, is thus ascertained; but the process is not to be recommended, as, if the tube be weighed full of hydrogen, the weight is too little, and if the hydrogen be displaced by atmospheric air, the finely divided reduced metal is apt to become partially oxidized.

(728) Separation of Cobalt from the Metals of the Alkalies and Alkaline Earths, and from Aluminum.-This is readily effected by converting the cobalt into acetate, and transmitting sulphuretted hydrogen, as has been already mentioned in the preceding paragraph. Another plan consists in the addition of sulphide of ammonium to the solution previously neutralized by ammonia. If alumina be present, it will accompany the cobalt, but if this precipitate be redissolved in acid, and again thrown down by means of caustic potash in excess, the alumina will be retained; the oxide of cobalt is, however, apt to carry down traces of alumina; these may be removed by treating the precipitated oxide by means of a mixture of ammonia and chloride of ammonium,

EXTRACTION AND PURIFICATION OF NICKEL.

563

which dissolves the cobalt, but leaves any traces of alumina which may have accompanied it. The cobalt is again precipitated by sulphide of ammonium.

The separation of cobalt from zinc is not easy. One of the best methods consists in precipitating the two metals together in the form of sulphides, dissolving this precipitate in nitric acid, and then adding an excess of carbonate of potassium, and evaporating to dryness. After the mixed carbonates of zinc and cobalt have been well washed, they are heated in a bulb-tube in a current of dried hydrochloric acid: in this process the carbonic acid is expelled, and the metals are converted into chlorides, whilst water is formed. The open end of the tube is in this case bent downwards at a right angle, and the aperture is made to dip into a small quantity of water contained in a flask the chloride of zinc, which is volatile, is carried forward in the current of gas; a portion of it is condensed in the bend of the tube, and the remainder is dissolved in the water placed for its reception. Chloride of cobalt alone remains in the bulb. The portion of the tube in which the chloride of zinc has been condensed is cut off when the operation is complete, and is allowed to fall into the flask. The zinc and the cobalt are then easily determined separately by the usual methods.

§ II. NICKEL: Ni"=59, or Ni=29'5. Sp. Gr. 8·82.

(729) NICKEL is a metal the peculiar characters of which were first recognized in 1751 by Cronstedt: it has a remarkable analogy with cobalt, and always occurs associated with it in nature, both as a constituent of meteoric iron, and in its ores, which present a composition similar to those of cobalt. It is most abundant in the form of kupfernickel (arsenide of nickel), and is extracted either from this ore or from speiss, which is an impure arseniosulphide of nickel, formed during the manufacture of smalt (720).

Preparation. As the metal itself is now extensively used in alloys, of which German silver is one of the most important, great pains have been taken to procure it in a state of comparative purity, and several processes have been proposed.

1.-According to Louyet, the method by which nickel is extracted from speiss at Birmingham on the large scale is as follows:-The speiss is first fused with chalk and fluor-spar, the metalliferous mass so obtained is reduced to powder, and roasted for twelve hours to expel the arsenic; the residue is next dissolved

564

:

NICKEL-PROPERTIES.

in hydrochloric acid; the solution is diluted, and the iron converted into a ferric salt by the cautious addition of bleaching powder. Milk of lime is then carefully added so long as peroxide of iron falls, which carries down with it the last portions of arsenic this precipitate is well washed, and the liquid, which contains all the cobalt and nickel, is treated with a current of sulphuretted hydrogen; the sulphides of copper, bismuth, and lead, are thus precipitated, and are thoroughly washed. All the nickel and cobalt still remains in the liquid; this liquid is boiled to expel sulphuretted hydrogen, neutralized with lime, and is again treated with chloride of lime the whole of the cobalt is thus thrown down as peroxide; after which the whole of the nickel is separated from the solution in the form of hydrated oxide by adding milk of lime so long as any precipitate is pro

duced.

2.-Nickel may be obtained pure upon a small scale, by dissolving the roasted ore in aqua regia, evaporating to expel the excess of acid, redissolving in water, and transmitting a current of sulphuretted hydrogen. The filtered liquid is boiled with nitric acid, to convert the iron into a ferric salt; the solution is precipitated by an excess of caustic ammonia, filtered from the oxide of iron, and to the blue liquid caustic potash is added until the blue tint nearly disappears; a pale green precipitate, consisting of hydrated oxide of nickel and potash is thus obtained, which must be well washed with hot water to remove the potash, and then reduced by ignition in a current of hydrogen gas: when obtained in this manner it is generally pyrophoric. If heated for an hour by means of a blacksmith's forge, in a crucible lined with charcoal, a well-fused button of carbide of nickel is produced. button of the pure metal may however be procured by heating the oxalate of nickel intensely in a crucible with a luted cover, without any other reducing agent than the carbonic oxide furnished by its own decomposition.

3.—It may also be obtained in laminæ by the electrolysis of a solution of the double sulphate of nickel and ammonium.

Properties.-Pure nickel is a brilliant, silver-white, hard, but ductile metal, little more fusible than iron, which, according to Deville, it even surpasses in tenacity. At ordinary temperatures it is susceptible of magnetism, but it loses this property almost entirely if heated to a point exceeding 630°, though it recovers its magnetic power on cooling. Nickel becomes oxidized by exposure to a current of air at a high temperature. The metal is easily attacked at ordinary temperatures by chlorine or bromine

ALLOYS AND OXIDES OF NICKEL.

565

if suspended in water. It is also readily dissolved by nitric acid and by aqua regia, and is dissolved slowly with evolution of hydrogen by diluted sulphuric or by hydrochloric acid. Owing to the remarkable whitening power which nickel exerts on brass, it is now much used in the manufacture of packfong, or German silver, a compound of zinc, nickel, and copper, in which the proportions of the metals may vary considerably. A good alloy consists of 5 equivalents of copper, 3 of zinc, and 2 of nickel, or, in 100 parts, of 51 of copper, 306 of zinc, and 184 of nickel. Packfong is of a yellowish-white colour, and when freshly polished closely resembles silver in appearance. Tutenag is the name given by the Chinese to a similar alloy, consisting of 8 parts of copper, 6 of zinc, and 3 of nickel.

The native arsenides of nickel are important, as they form the principal ores of the metal. Kupfernickel (NiAs) is arsenide of nickel; it contains 44 parts of nickel to 56 of arsenic; part of the arsenic in this ore is sometimes displaced by an equivalent amount of antimony. It has a reddish colour, and a metallic lustre. It is not attacked by hydrochloric acid, but is soluble in nitric acid, and is decomposed when heated in air or in a current of chlorine. Arsenical nickel (NiAs) is another native compound of the two metals: by ignition in closed vessels it loses half its arsenic, and becomes converted into kupfernickel. A compound of nickel with arsenic and sulphur, corresponding to mispickel, and known as nickel glance (NiSAs, or NiS,,NiAs), is also found native.

(730) OXIDES OF NICKEL.-Nickel forms two oxides; a protoxide, NiO, and sesquioxide, Ni ̧ ̧.

3

Protoxide of Nickel (NiO=75, or NiO=375); Sp. Gr. 5'74; Composition in 100 parts, Ni, 78.67; 0, 21.33.-This oxide may be obtained in the anhydrous form by igniting the nitrate or the carbonate of the metal in a covered crucible, when it is left of an olive-green colour. It may be precipitated from its salts by hydrate of potash, as a bulky light-green hydrate (NiÐ,H,O?), and may be obtained crystallized by decomposing the solution of carbonate of nickel in ammonia by ebullition. Oxide of nickel is readily soluble in acids, forming salts which have a pale green colour. It yields insoluble compounds with potash and with soda, which, however, may be decomposed by frequent washings with boiling water. Baryta, strontia, and several other bases also form with it insoluble compounds; ammonia dissolves it, forming a deep blue solution. A solution of chloride of ammonium also dissolves it slowly.

2

The sesquioxide (Ni2=166, or Ni2O,=83), is a black powder which may be procured as a hydrate with 3 H2O, by treating the hydrated protoxide with a solution of chloride of soda. It does not combine with acids, and gives off a portion of its oxygen by ignition, or by heating it with nitric or sulphuric acids, which form with it salts of the protoxide.

(731) SULPHIDES OF NICKEL.-Three of these compounds are known; a subsulphide, a protosulphide, and a bisulphide. The protosulphide (NiS=91) occurs native as millerite in greyish or yellowish capillary crystals, which are insoluble in hydrochloric, but soluble in nitric acid: it may be formed artificially by fusion of sulphur with nickel. It may also be procured by fusing a persulphide of one of the alkaline metals with biarsenide of nickel, and is left in yellow crystalline scales. A black hydrate of this sulphide is produced when a salt of nickel is precipitated by sulphide of ammonium; in this form it absorbs oxygen from the air, and is gradually converted into sulphate of nickel. The subsulphide (Ni,S) may be formed by reduction of the sulphate of nickel by means either of charcoal or of hydrogen gas. The bisulphide (NiS) is left as a steel-grey powder on treating with water the mass obtained by heating to redness an intimate mixture of carbonate of nickel, carbonate of potassium, and sulphur.

=

2

(732) CHLORIDE OF NICKEL (NiCl, 130, or NiCl=65) is formed by dissolving the oxide in hydrochloric acid. Its solution, on evaporation, yields green hydrated crystals with 9 H2; by heat it may be obtained as a yellowish-brown anhydrous mass, which at a high temperature is volatile, and condenses in yellow crystalline scales, which are dissolved slowly by boiling water. If heated in a current of air, a portion of the chlorine is expelled, and a corresponding quantity of oxide of nickel is formed.

3

It

(733) SULPHATE OF NICKEL (NISO1,7 H2O=155+126, or NiO, SO ̧ . 7 HO=77'5+63).—This salt may be obtained by dissolving metallic nickel, or its oxide or carbonate, in sulphuric acid. crystallizes in green rhombic prisms, which require 3 parts of cold water for solution: the prismatic crystals, when exposed to light, are converted into small regular octohedra, aggregated together in the form of the original crystal, which becomes opaque. It may be obtained in octohedra at once with 6 H, (sp. gr. 2037), by crystallizing at a temperature between 60° and 80°. A double sulphate of potassium and nickel (NiSOK,SO4.6 H2O; Sp. Gr. anhydrous, 2.897, cryst. 2190) may be formed by adding caustic potash to the impure solution of speiss, and by repeated crystallizations may

2

2