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CHARACTERS OF THE SALTS OF NICKEL.

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be freed from all impurities except traces of iron and cobalt: it was at one time used as a means of purifying nickel for commercial purposes. Other double sulphates of nickel may be formed. Sulphate of nickel in the solid form absorbs 6 atoms of ammoniacal gas. An insoluble basic sulphate is obtained by adding to a solution of the normal sulphate a quantity of hydrate of potash insufficient for its complete decomposition.

(734) CARBONATES OF NICKEL.-There are several basic carbonates of nickel, of a green colour. The normal carbonate is precipitated as a crystalline powder, when a solution of nitrate of nickel is poured into a large excess of a solution of the acid carbonate of sodium.

(735) CHARACTERS OF THE SALTS OF NICKEL.-The salts of this metal are of a delicate green colour, both when in the solid state and when in solution; they redden blue litmus feebly. They have a sweetish astringent metallic taste, and when taken internally excite vomiting.

Before the blowpipe, salts of nickel give in the oxidating flame with borax a reddish-yellow glass, which becomes much paler as it cools. The addition of a salt of potassium colours the bead In the reducing flame, greyish particles of reduced nickel are disseminated through the bead.

blue.

In solution, sulphuretted hydrogen gives no precipitate if the liquid be acidulated with sulphuric acid; but it precipitates a diluted solution of acetate of nickel, if nearly neutral, very perfectly when aided by a gentle heat. Sulphide of ammonium gives a black sulphide slightly soluble in excess of the precipitant, forming a dark-brown solution. Ammonia gives a pale green precipitate, soluble in excess of ammonia, forming a bright blue solution, from which an excess of potash precipitates a green compound of oxide of nickel and potash. Hydrates of potash and soda throw down a pale-green bulky hydrated oxide of nickel, insoluble in excess of the alkali. The carbonates of the alkaline metals give a pale apple-green precipitate of basic carbonate of nickel, which is readily soluble in carbonate of ammonium. Ferrocyanide of potassium gives a greenish white, and ferricyanide of potassium a yellowish-green precipitate, both of which are soluble in hydrochloric acid. Acid oxalate of potassium in a neutral solution, if not too dilute, causes the deposition of a greenishwhite sparingly soluble double oxalate of nickel and potassium, soluble in excess of ammonia.

(736) Estimation of Nickel.-Nickel is best estimated in the

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NICKEL-SEPARATION FROM COBALT.

form of protoxide which, when precipitated by means of caustic potash, requires patient washing with hot water to remove the adhering alkali: 100 parts of protoxide of nickel contain 78.67 of the metal.

Separation of Nickel from the Alkalies and Earths, and from Zinc.-For this purpose the same processes as those adopted for the separation of cobalt (728) may be employed.

(737) Separation from Cobalt.-The following method, advised by Liebig and slightly modified by Hadow, is the best for this purpose. The nitric solution of the cobalt and nickel having been freed from all other metals except potassium or sodium, after being nearly neutralized with carbonate of potassium, is mixed with an excess of hydrocyanic acid, and then with pure caustic potash, after which the mixture is left exposed to the air in a shallow open dish for a few hours. During this time oxygen is absorbed, and the liquid acquires a pale yellow colour. A cobalticyanide of potassium (K,ЄoCy) is formed, and a double cyanide of nickel and potassium (2 KCy,NiCy,) is produced at the same time. The formation of the cobalticyanide may be traced as follows: cyanide of cobalt is first formed; 2 HCy+Єo→=ЄoCy2+H2, and this cyanide of cobalt, by exposure to air with an excess of cyanide of potassium and hydrocyanic acid, yields cobalticyanide of potassium, whilst oxygen is absorbed and water is separated; 4ЄoCy, + 12 KCy +4 HCy+0,4 K,ЄoCy, +2 H2O. The double cyanide of nickel and potassium is very simply formed; for with nickel no compound corresponding to the cobalticyanide is obtained; 4 KCy+NiO+ H,O=2 KCy,NiCy,+2 KHO. If the strongly alkaline solution be now boiled and a solution of mercuric nitrate be added in slight excess, so as to produce a precipitate which, from its yellowish colour, shows that the oxide of mercury is in excess, the nickel salt is decomposed, hydrated oxide of nickel is precipitated, and cyanide of mercury is produced; 2 KCy, NiCy2+HgO+H2O= 2 KCy,HgCy,+NiO,H2O.

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The cobalticyanide of potassium is not decomposed by the oxide of mercury, but remains in solution, and may be filtered from the oxide of nickel, which requires to be carefully ignited in a platinum crucible till it ceases to lose weight. After cautiously neutralizing the filtrate with nitric acid, the cobalt may then, by the addition of a solution of mercurous nitrate, be precipitated as a white mercurous cobalticyanide: the precipitate is collected, dried, and ignited, when pure oxide of cobalt is left.

If, instead of precipitating the mixed cyanides by means of mercury, a solution of chloride of soda be added in excess to the

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boiling alkaline liquid, in quantity sufficient to destroy the free cyanide of potassium, the nickel is precipitated of an intense black as sesquioxide; in this form it may be readily washed, and by ignition it may be converted into the protoxide, in which state it may be weighed. Traces of nickel which escape discovery by other methods may thus often be detected in cobalt. Care must be taken to ascertain the absence of manganese, as it would go down with the nickel, accompanied by traces of iron, if the latter metal were present.

§ III. URANIUM:

120, or U=60. Sp. Gr. 18'4.

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(738) URANIUM is a metal the compounds of which are but sparingly distributed over the surface of the earth. It was originally discovered by Klaproth, in pitchblende, which contains nearly 80 per cent. of the black oxide of uranium (2 UO,U2O); the remainder of the mass consists of variable quantities of copper, lead, iron, arsenic, and frequently of cobalt and nickel. Uranite, which is a mineral of micaceous structure, of rarer occurrence, consists of a hydrated double phosphate of calcium and uranium (Ea′′ 2 (U ̧Ð1⁄2)" 2 PO, 8 H2O, or CaO, 2 U2O, PO, 8 HO). Chalcolite (Eu′′ 2 (U ̧Ð1⁄2)" 2 PO, 8 H2O) is a similar mineral, in which copper takes the place of calcium.

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In order to extract uranium from pitchblende, the mineral is heated to redness, and thrown whilst red-hot into water, after which it admits of being readily pulverized: Ebelmen then treats the ore in the following manner :-The fine powder is washed with diluted hydrochloric acid, heated with charcoal, and digested in strong hydrochloric acid, by which the earthy matters and most of the iron, arsenic, and sulphur are removed: the washed residue is roasted and then treated with nitric acid; the solution thus obtained is evaporated nearly to dryness, to expel the excess of acid, and is diluted, by which means most of the arseniate of iron is precipitated. Sulphuretted hydrogen is then transmitted through the filtered solution, and the liquid is filtered from the sulphides of copper, lead, and arsenic thus thrown down; after which it is again evaporated until crystals of uranic nitrate begin to be formed. This salt is decomposed by heating it to redness, and the oxide of uranium which is left is mingled with charcoal and heated in a glass tube through which a current of dry chlorine is passing; carbonic anhydride and carbonic oxide are thus formed, and a volatile green chloride of uranium (UCl2) sublimes. This chloride, when heated with potassium in a platinum crucible,

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OXIDES OF URANIUM.

yields chloride of potassium and metallic uranium: intense heat is evolved during the reaction of the potassium on the chloride of uranium, and the resulting metal is partially fused. The isolation of metallic uranium is due to Péligot (Ann. de Chimie, III. v. 5), the substance originally supposed to be the metal having been proved by him to be its protoxide.

Uranium as thus obtained is of a steel-white colour: it appears to be slightly malleable; it is not oxidized by exposure to air or to water at ordinary temperatures: but if heated in the air it burns brilliantly sulphuric and hydrochloric acids dissolve it with extrication of hydrogen gas. In its chemical relations it is somewhat analogous to iron and manganese.

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(739) OXIDES OF URANIUM.-Uranium forms two principal oxides, a protoxide, or uranous oxide, UO, and a sesquioxide, or uranic oxide, 2O: two intermediate oxides may also be obtained, the black oxide, 2 UO,,,, and the green oxide, НO‚¤‚Ð ̧

2 3

2

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3*

The protoxide, or uranous oxide (UO=136, or UO=68), may be obtained in several ways: one of the easiest consists in igniting uranic oxalate in closed vessels, or in a current of hydrogen. In its anhydrous state the dilute acids are without action upon it, but its hydrate, which may be obtained in reddish-brown flocculi, by adding ammonia to a solution of the chloride, UCl,, is readily soluble in the acids; it forms green crystallizable salts, which have a strong tendency to absorb oxygen.

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The black oxide (2 UO,U, ̧) may be procured by heating the protoxide to bright redness, and suddenly cooling it, or by igniting uranic nitrate. It furnishes a pure and intense black, highly prized for colouring porcelain.

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The green oxide (UЂ܂Р̧; sp. gr. 7:31), which corresponds in composition to the magnetic oxide of iron, is procured by heating the black oxide moderately in a current of oxygen or in the open air; by more intense ignition it becomes re-converted into the black oxide, and is again partially re-oxidized as it cools. It is soluble in hot concentrated sulphuric acid, but does not form distinct salts.

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The sesquioxide, or uranic oxide, (1⁄2Ð ̧) partakes of the character both of an acid and of a base. It is with difficulty obtained in a pure state. By exposing uranic oxalate to the sun's rays, a brownish-violet powder, which is a hydrate of the green oxide, (U ̧Ð 3 H2O) is deposited, while carbonic anhydride makes its escape: this precipitate absorbs oxygen on exposure to the air, and becomes converted into a greenish-yellow mass, which, according to Ebelmen, is a hydrate of the sesquioxide (U ̧, 2 H2O). The sesquioxide

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OXIDES AND CHLORIDES OF URANIUM.

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may be obtained in the anhydrous state as a brick-red powder, by heating this hydrate to a temperature not exceeding 572°. Uranic oxide reacts readily with acids, and forms salts of a bright yellow colour. Péligot found that the oxide (UO) evinced a strong tendency to unite with elementary bodies like a metal, and hence he proposed to call it uranyl, and he explained the fact that the normal uranic salts are all formed by the action of this oxide upon two atoms of monobasic acid instead of on six atoms. Uranic nitrate, for instance, which furnishes long striated prisms, consists, even when crystallized from a strongly acid solution, of (U ̧Ð1⁄2)′′ 2 NO3, 6 H2O. Numerous uranic double salts have also been formed; uranic sulphate of potassium consists of (K2(U2O2)" 2 SO4, 2 H2O). If an attempt be made to procure uranic oxide by decomposing the solutions of these salts by the addition of an alkali, an insoluble yellow precipitate, consisting of a compound of the sesquioxide with the alkali, frequently called a uranate of the base, falls; uranate of potassium has the formula K ̧‡, 2 U‚Ð ̧ and the other similar compounds have a corresponding composition; this compound cannot be decomposed even by boiling water: the commercial yellow oxide is a hydrate retaining about 2 per cent. of ammonia, from which heat expels the water and ammonia, and also converts the sesquioxide into the black or the green oxide. The compounds of uranic oxide with the earths, however, stand a strong heat without decomposition, and are employed to communicate a beautiful and peculiar yellow to glass.

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(740) CHLORIDES OF URANIUM.-The bichloride (UCl,), uranous chloride (Péligot's protochloride, UCl) is a green, volatile, deliquescent compound, which is decomposed by water; the method of preparing it has already been described (738). If dry hydrogen gas be transmitted over the uranous chloride, while it is being heated to redness in a glass tube, a chloride (Cl) is produced, which crystallizes in slender dark-brown needles, which are but slightly volatile: they are very soluble in water, and form a deep purple solution, from which ammonia throws down a brown suboxide; this oxide absorbs oxygen from the air rapidly. An oxychloride (OCI), or (U2O,,UCl), somewhat analogous to chlorochromic acid (789), is formed by passing chlorine over the protoxide of the metal, constituting Péligot's chloride of uranyl: it is deliquescent, and forms a yellow solution with water; with the chlorides of the alkaline metals it forms remarkable double salts; the double salt with chloride of potassium consists of (KCl,UOC1. H2O), and crystallizes in rhombic tables of a greenish-yellow colour.

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