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COBALT.

Section 1.
IRON.

NICKEL.
Appearance, and Greyish-white; lus- White; lustrous; mal-
general physical trous; crystalline; mal- leable; ductile; tena-
characters. leable; ductile; fair cious; hard; slightly

conductor of electricity; magnetic.
hard; magnetic.
Iron obtained by elec-
trolysis of FeCl,Aq is
said to be silver-white

and very soft.
Occurrence, and Found native but not in Metal is found in me-
preparation. large quantities; oxides, teorites.

sulphides, carbonates, Chief ore contains ar-
&c. occur in enormous senide of Ni; sulphides,
quantities, and very silicates, &c. also occur,
widely distributed. not widely distributed,
Prepared by reducing but in considerable
Fe2O3 by Cat very high quantities.
temperatures; or by re- Prepared by reducing
ducing Fe203 or FeCl2 Nio by C or H.
by H; or by electrolysis

of FeCl2Aq.
General chemical Oxidised, chiefly to Slowly oxidised in
properties. Fe3O4, by strongly heat- moist air; oxidised by
ing in oxygen.

strongly heating in
Slowly oxidised by oxygen.
exposure to ordinary Dissolved by most
moist air.

acids.
Combines directly with Decomposes steam at
Cl, Br, and I, also with S. red-heat.
Dissolved by most
acids.
Forms compounds re-
sembling alloys with C
and Si.
Decomposes steam at
red-heat.

Closely resembles

nickel.

485

General formulae and characters of compounds. Nickel and cobalt very closely resemble each other in their chemical properties. The salts of cobalt are generally pink when hydrated and blue when anhydrous; the hydrated salts of nickel are usually green, and the anhydrous salts, yellow. Cobaltic chloride Cocl, form a large series of compounds with ammonia, e.g.

Co,C1..10NH,.2H,0; Co,C1.10NH,; Co,C1.12NH, These compounds resemble the chromium-ammonia compounds; corresponding nickel compounds are not known.

The cyanides of iron and cobalt form compounds with potassium cyanide of the forms K M(CN), and K,M(CN)., (M = Fe or Co); the acids of which these compounds are salts, viz. H. M(CN), and H M(CN), have been obtained. Nickel cyanide does not form a corresponding salt; the compound K, Ni(CN), is known.

The only compound of the three metals the vapour density of which has been determined is Fe Clo; the valency of the atom of iron cannot be decisively determined from the composition of this molecule; the atom is probably tetravalent.

The formulae for the compounds of the three metals, with
the exception of the haloid compounds, are the simplest by
which their compositions can be expressed.

Oxides. MO, MRO4, M,0,: hydrates of all are known.
Sulphides. MS, MS,
Haloid compounds. MX4, M,X..
Salts. Mx, M,3X; X =so, 2NO, PO,, &c.

Oxides. Ferrous oxide Feo is difficult to prepare free 486 from ferric oxide, as it combines very rapidly with oxygen. The hydrated oxide FeO.H,0 is obtained by pptg. ferrous sulphate dissolved in air-free water with potash in absence of oxygen.

Nickelous oxide Nio, and cobaltous oxide Coo, are obtained by ppg. solutions of the corresponding salts by alkalis and heating the ppts. out of contact with air. These oxides combine with oxygen when carefully heated in air, forming the oxides M,0, which at a higher temperature are decomposed to MO and oxygen,

The protoxides, MO, dissolve in acids forming salts MX.

The oxides M,0, are formed by heating the oxides MO in air; Fe, O, is also obtained by adding an alkali to a hot mixture of ferrous and ferric sulphates (or other salts) in the ratio Feso, : Fe (SO)g. Ferroso-ferric oxide, Fe, O., interacts with acids to form both ferrous and ferric salts; e.g.

FeO, + 4H SO, Aq = FeSO Aq + Fe (SO2),Aq + 4H,O. The corresponding oxides of nickel and cobalt form nickelous salts only, and evolve oxygen, or chlorine if hydrochloric acid is used.

Ferric oxide Fe,O., is obtained by adding an alkali to a solution of a ferric salt, e.g. to Fe (SO2), Aq, and drying and heating the hydrated oxide, Fe,0,.3H,O, so obtained. This oxide interacts with acids to form ferric salts.

Nickelic oxide Ni,O3, and cobaltic oxide Co, O., are obtained by oxidising solutions of nickel or cobalt salts in

presence

of an alkali; e.g. by passing chlorine into potash containing Ni0.xH 6 or Co.Ho in suspension. These oxides dissolve in acids to form salts MX and evolve oxygen, or chlorine if hydrochloric acid is used; they are decomposed to MO and oxygen when heated in air.

When ferric oxide is heated with potash and a little bromine, or when very finely divided iron is heated with potassium nitrate, and the product is poured into water, a reddish

solution is obtained which is decomposed by addition of a little nitric acid giving a pp. of ferric hydrate and evolving oxygen. From the quantities of ferric hydrate and oxygen thus obtained, the existence, in the red solution, of a salt K, FeO, potassium ferrate, is inferred. The corresponding barium salt, BaFeO,, is said to have been obtained as a solid. Corresponding

nickelates or cobaltates are unknown. 487 Sulphides. The sulphides MS are obtained by adding

hydrogen sulphide or ammonium sulphide to aqueous solutions of salts of the three metals. None of these sulphides shews any acidic functions. When ferrous sulphide, Fes, is

heated with sulphur, iron disulphide, Fes,, is obtained. 488 Haloid compounds. The metals" dissolve in hydro

chloric acid to form solutions of the chlorides MCI,; crystals of the hydrated chlorides MCI,. «H,0 are formed on evaporation.

Ferrous chloride is easily oxidised to a basic ferric chloride by evaporating its solutions in air; nickelous and cobaltous chlorides are stable in air. Ferrous chloride has been gasified but the vapour density has not been finally determined ; the numbers obtained seem to point to the existence of gaseous molecules having the composition Fe, Cl, at moderate temperatures, and the composition FeCl, at ħigher temperatures.

Ferric chloride, Fe,cl, is obtained by heating iron in a stream of chlorine; crystals of the hydrate Fe, Cl.12H 0 are obtained by dissolving iron in aqua regia, or by passing chlorine into a solution of ferrous chloride, and evaporating. Vickelic and cobaltic chlorides, M,Cl., are very unstable and

are easily decomposed to the chlorides MCI, and chlorine. 489 Salts. Iron forms two series of salts; the ferrous salts Fex,

and the ferric salts Fe,.3X. Nickel and cobalt form only one series of definite stable salts MX. Ferrous salts are very numerous; they are more or less easily oxidised to basic ferric salts. Several normal ferric salts exist, but the greater number are basic salts. Both series of salts form numerous double salts. Ferric sulphate forms alums, Fe,350,.M SO,.24H,O,

where M =K, Na, or NH,. 490 Iron is distinctly related to manganese, the last element of

Series 4. The relation is shewn in the composition of the oxides MO, M,Ox, and M,0z, of the salts MX and M2.3X, and in the existence of ferrates analogous to the manganates, K,MO,

Iron is distinctly metallic, but the formation of ferrates shews that it has negative tendencies.

491

Nickel and cobalt are less like manganese than iron is; they are decidedly metallic in their chemical characters.

The three elements of Section 1 of Group VIII. form a
link connecting the negative metals chromium and manganese,
which are the highest members of Series 4, with the positive
metal
copper

which forms the first member of Series 5.
Section 2.
RHODIUM
RUTHENIUM.

PALLADIUM.
Atomic weights
104
104:4

106.2 The molecular weights of these elements are unknown. Sp. grs. (approx.)

118
12-1

11:3 Atom. weights

8.8
86

9.4
spec. graus.
Sp. heats
*058
-061

06 Melting points

abt. 2000

above m. p. of rhodium. abt. 1500°-1600° Occurrence, and These metals occur in small quantities in many platinum ores. They are preparation. usually separated in the form of ammonio-chlorides, 2NH4CI. MC14;

when these are strongly heated the metals are obtained. · Appearance, and Greyish-white; very White; lustrous; less White; hard; lustrous; general physical hard; much less ductile ductile and malleable ductile, and malleable; properties. than Pd; scarcely than Pd.

most fusible of the softened in oxyhydro

metals of this section gen flame.

or of Section 3 of Group

VIII. General chemical Oxidises at a red-heat, Oxidised by heating Oxidised superficially properties. when in powder; also powdered metal in air. in ordinary air.

combines with CI at Oxidised by heating Slowly dissolved by hot red-heat.

with KOH, or KNO3, HCAQ or H2SO4A9, Unacted on by any acid forming K RuO4 which readily by HNO3Aq. when pure; when alloy- is soluble in water. ed with Pt, Pb, Cu, &c. Combines directly with dissolves in aqua regia. Cl when heated. Oxidised by fusion with Slowly dissolved by KNO3 or Ba02.

aqua regia.

Section 3.
IRIDIUM.
OSMIUM.

PLATINUM.
Atomic weigh

192-5
193* (?)

1943 The molecular weights of these elements are unknown. Sp. grs. (approx.)

21.1
214

21.2 Atom, weights

9.1
9.0

9.1
spec. graus.
Sp. heats
0326
0311

0324 Melting points

abt. 2500° infusible at full white-heat. abt. 2000 Occurrence, and These metals occur in small quantities associated (? alloyed) with each preparation. other and frequently with rhodium, ruthenium, and palladium. They

are usually separated as 2NH4Cl.MC14, and are obtained by strongly

heating these compounds. Appearance, and White; lustrous ; White with tinge of Silver-white; very lusgeneral physical brittle, but fairly mal- blue; hard; crystalline; trous; fairly hard; very properties. leable at red-heat. also a black,

malleable and ductile; phous, powder.

expands by heat less

than any other metal. General chemical When finely divided Oxidises readily to Not oxidised by heating properties. oxidises slowly when Os04, when heated in in air or oxygen.

heated in air, and dis- air in state of finely Oxidised by heating
solves in aqua regia; divided powder : in this with solid potash.
in compact form is in- state is also oxidised to combines directly with
soluble in all acids. Os04 by nitric acid. Cl.
Oxidised by fusion with Combines directly with Dissolved by aqua
potash and potassium Cl.

regia.
nitrate.
Combines directly with

Ci. * Exact value of atomic weight of osmium is doubtful; numbers vary from 193 to 199.

amor

492

493

General formulae and chemical characters of compounds of metals of Sections 2 and 3. The platinum metals—i.e. rhodium, ruthenium, palladium, iridium, osmium, and platinum--are characterised by their insolubility in most acids : the three metals placed in Section 3 are also characterised by their high specific gravities. Gold resembles the platinum metals both in being insoluble in most acids and in being very heavy. Gold and the platinum metals are often named the noble metals.

The double chlorides 2KCI. MCI, are characteristic of the platinum metals. The chlorides of these metals combine with ammonia and form several series of more or less complex ammonia-compounds. The higher oxides of these metals are acidic in their reactions with alkalis. Osmium is characterised by the easily gasified oxide OsO,; this is the only compound of the platinum metals the vapour density of which has been determined. The compounds of the platinum metals have not been fully investigated.

Oxides. All the metals form protoxides MO, and dioxides MO, The protoxides are usually unstable. The dioxides usually dissolve in acids, but few definite salts have been isolated. The hydrated dioxides, which are not obtained by direct interactions between the oxides and water, generally dissolve in alkali solutions; in some cases salts of the form K MOą, or basic salts «K,0.YMO,, have been separated. I'rioxides, MOz, are known where M = Rh, Ir, or Os : these oxides dissolve in alkali solutions. Tetroxides of ruthenium and osmium are known, MO,: they are solids with low melting points and boiling about 100°; they form salts by interacting with alkalis.

Chlorides. All the metals form dichlorides MCI,, and tetrachlorides MCI, Trichlorides MCI,, are known where M = Ru, Rh, or Ir. The di- and tetra-chlorides combine with alkali chlorides forming compounds of which 2KCI.MCI, and 2KCI. MCI, are representatives ; these double compounds are usually known as chloro-platinites (rhodites, ruthenites, &c.), and chloro-platinates (rhodates, &c.), respectively.

Salts. Very few salts of the platinum metals have been isolated. They all seem to be unstable and ill-defined compounds. Most of the salts are either basic, e.g. Rh,0.31 0.4H.0; or double salts, e.g. Pt2NO,. 2 AgNO,

The platinum metals are evidently possessed of most of the physical properties which we are accustomed to associate with

494

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496

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