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also very similar; boron at one end of the

and thallium at the other, are separated from the other members of the group; although differing widely in most of their properties, boron and thallium approach each other in some respects.

group,

CHAPTER XXV.

467

THE ELEMENTS OF GROUP IV.

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•463 (?)

of gases.

2

6
8
10

12 Even series. C=11.97 Ti=48 Zr= 90 Ce=139.9

Th=231.8 Group IV.

3
5
7

9

11
lodd series. Si=28:3 Ge=72:3 Sn=117.8

Pb=2064
Even-series CARBON.
TITANIUM. ZIRCONIUM.

CERIUM.

THORIUM. elements Atomic weights

11.97
48

90
139.9

231.8
The molecular weights of these elements are unknown.
Sp. grs. (approx.) 3.3 (diamond)

?
4.15

607 Atom. weights

36

?
21.7
20-9

39.4
spec. graus.
Sp. heats

148

0666
*0448

·0276 The melting points of these elements have not been determined ; cerium is said to fuse considerably above 500° but under 900°, and zirconium at a higher temperature than cerium. Carbon, titanium, and thorium, have not been melted. Appearance, and Colourless, Iron-grey, lus- Black powder, Grey, lustrous, Dark-grey, lusgeneral physical transparent, trous, powder. resembling a- solid; very duc- trous, metalproperties. highly refrac

morphous car- tile; fairly mal- like, powder. tive, crystals

bon; also hard, leable. (diamond); also

brittle, very lusblack, amor

trous, grey, phous, powder;

crystals. also black, lus

Very porous, trous, crystal

and absorbs
line, solid (gra-

large volumes
phite). S. G. of
graphite 2-25;
of amorphous
carbon abt. 1.9.
Graphite is
fair conductor
of electricity.
Amorphous
carbon is very
porous and ab-

freely. Occurrence and Diamond and Titanium oxide, Zirconium Occurs as sili- Thorium oxide, preparation. graphite occur silicate, and á oxide, ZrO2, cate in the rare Th02, is found

native; enor- few other com- occurs in a few mineral cerite; in a few rare mous quantities pounds, occur rare minerals.

also in very

minerals. of CO2 occur in in certain rare Prepared by re- small quantities Prepared by rethe

air; carbon- minerals. Many ducing K ŽrF6 in various mine- ducing Thci, by ates of Ca, Mg, iron-ores vapour by rals, and in Na or K. Fe, &c. are com- tain small Kor Na; or by some clays. mon minerals. quantities of Ti aluminium, Prepared by CO2 found in all compounds. when the Zr electrolysing waters. Carbon Prepared by re- crystallises out Ce,Cle mixed compounds ducing vapour on cooling. with NaCl. form chief parts of K TiF6 by of all living or- K or Na. ganisms. Dianjond has not been prepared artificially. Amorphous carbon prepared by heating oil, fat, &c. in absence of air.

a

sorbs gases

con

Group IV. continued.
Even-series CARBON.
TITANIUM ZIRCONIUM. CERIUM.

THORIUM elements General chemical Heated in air or Burns brilliant- Amorphous Zr Burns to Ce0, Burns when properties. oxygen, burns ly when heated burns when when heated in heated in air to

to CO and C02; in air or oxygen, heated in air or air or oxygen. Thoz diamond burns forming Ti02. oxygen; crystal. Combines di- Soluble in only at very

Combines di- line is superfici- rectly with C, HICIAą, but higi tempera- red with Cl. ally oxidised. Br, and I; also very slowly in tures in oxygen. No hydride Insoluble in with S, and P. HNO3.49. Prue" Combines di- known. most acids, but Decomposes

perties have rectly with H Combines di- easily dissolved warm water been little exawhen electric rectly with N by HFAq. slowly with for- mined. sparks are at high temper- Oxidised by mation of Ce,03 Atom is tetrapassed from atures. molten KOH, and H.

valent in gascarbon poles in Decomposes KNO3, or

eous

molecule atmosphere water at 100°, KCIO3.

ThCl of H.

giving Ti02 Atom is tetra-
Combines di- and H.

valent in gas-
rectly with S at Atom is tetra- eous molecule
high tempera- valent in gas- ZrCl4.
tures.

eous molecule
Combines with TiClt.
many metals to
form bodies re-
sembling alloys.
Graphite is oxi-
dised by heating
with KCIO, and
HNO3Aq to
graphitic acid
Cu11405; no
other form of ,
carbon gives
this acid.
Exhibits allo-
tropy very
markedly.
Atom is tetra-
valent in gas-
eous molecules.

General formulae and characters of compounds. Carbon is 468 characterised by the enormous number of compounds which it forms by combining with some or all of the elements hydrogen, oxygen, and nitrogen.

The chlorides MCI, except CeCl, and the fluorides MF, have been gasified and their vapour-densities determined ; the oxides CO and CO2, and the sulphide CS,, have also been gasified; the formulae of these compounds are therefore molecular; the formulae of the other compounds are the simplest that express their compositions.

None of the elements of the family except carbon forms any compound with hydrogen : the hydrides of carbon are exceedingly numerous.

Oxides: CO, (? TiO); (? C,O), Ti,O, Ce,O, ; MO, M = any element of the family.

Sulphides: CS, CS,, (? C,S3), TiS,, Ce,S3, ThS..

Haloid compounds: MX, M= any element of the family; C,Cl., &c., Ti,Cl, Ce,Clo; Tici,.

469

Acids: H,CO, Aq; salts of the form MTi0, and M.ZrO, are known (M = an alkali metal) ; the hydrates Ti0g.xH,O and ZrO . 1,0 are acidic.

Salts: carbon does not form salts by replacing the hydrogen of acids; M.2X (X = SO,, 2NO,, &c.) M=Ti, Zr, Ce, Th; Ce,3X, and Ti,3X.

Oxides. The dioxides M0, are produced by heating the elements in oxygen; the dioxides of titanium, zirconium, cerium, and thorium, are also obtained by precipitating solutions of salts of these elements by ammonia, and drying and heating the hydrated oxides so obtained. Carbon dioxide is most easily obtained by decomposing a metallic carbonate by an acid, e.g. Caco, + 2HCIĀq=CO, +1,0 + CaCl Aq. The dioxides, with the exception of CO,, are solids, insoluble in water, some of them insoluble also in most acids; carbon dioxide is a colourless, odourless, gas which can be condensed to a liquid, and, at a very low temperature, to a snow-like solid.

Carbon dioxide dissolves freely in water; the solution reddens blue litmus and interacts with alkalis to form salts M,CO,: from these alkali carbonates, carbonates of most metals can be obtained. An aqueous solution of carbon dioxide probably contains carbonic acid, H,CO; ; but this compound has not been isolated; the sulphur compound thiocarbonic acid, H,CS,, is known as a solid.

By precipitating solutions of salts (M2X) of titanium, zirconium, cerium, and thorium, hydrated dioxides MO,. «H,0 are obtained. Many of these hydrated oxides seem to exist; the following, obtained by drying under different conditions, are among the more important, Ti0g. H,O, Ti0,.21,0; ZrO2. H,O, ZrO,.2H,0; ThO2.2H,0; 2Ce0,.31,0. These hydrated dioxides are soluble in acids, and from these solutions salts of the form M. 2X (X = SO,, 2NO3, &c.) are obtained. The solution of Ce02.XH,0 in acids seems to contain cerous salts Ce,. 3X, as well as ceric salts Ce2X.

Most of the dioxides MO2.2H,0 exhibit acidic properties. None of them dissolves in solutions of alkalis to form salts. When however titanium dioxide, Ti02, is fused with sodium carbonate, a quantity of carbon dioxide is evolved corresponding with that calculated on the assumption that sodium titanate Na,Ti0, is produced ; the fused mass is separated by water into NaOHAq and NaHT10g. Zirconium dioxide, Zro,, fused with Na, Co, behaves similarly to Tio,; the zirconates Na,Zro, and Na Zro, are said to have been obtained. Thorium dioxide, ThO,, does not decompose Na,CO, when heated with this salt, nor does it form salts by fusion with solid potash or soda. The fact that when hydrated cerium dioxide, Ce0g.xH,0, is precipitated by adding potash to a solution of ceric sulphate, Ce(SO), the whole of the potash cannot be removed from the precipitate by washing with water indicates the possible formation of an unstable potassium cerate.

Carbon monoxide, CO, is obtained by heating the dioxide with carbon (CO, +C=2CO), or by the interaction of (1) formic acid, or (2) oxalic acid, with concentrated hot sulphuric acid ;

(1) H,CO, + H2SO4 = CO + H,0.H,SO,,

(2) H,C,04 + H2SO, = CO + CO, + H,0. H2SO4. This oxide is a poisonous gas; salts of formic acid H.CO, can be obtained from it, and as the oxide is produced from the acid, the oxide is sometimes called formic anhydride.

The sesquioxides Ti,0; and Ce,0, are obtained by reducing the higher oxides MO,; in the case of titanium this is done by heating Tio, to redness in dry hydrogen, in the case of cerium it is better to heat cerous oxalate, Ce,(C,0z)z, in hydrogen. Ti,0, is oxidised to Tio, by continued heating in air ; Če,O, is very easily oxidised by mere exposure to air. Both oxides dissolve in acids forming salts; a large series of cerous salts Ce. 3X is known; only titanous sulphate, Ti,(SO2),. 8H,0, seems to have been obtained as a definite solid.

The sulphides, with the exception of CS,, have not 470 been much examined. Titanium disulphide, Tisz, is a dark coloured stable solid, obtained by the interaction of titanium tetrachloride and sulphuretted hydrogen at high temperatures. Thorium disulphide, ThS,, resembles TiS,; it is obtained by passing hydrogen mixed with hydrogen sulphide over heated Th02. Cerium sesquisulphide, Ce,Sz, is a golden coloured solid formed by passing sulphuretted hydrogen over hot Ce0g. None of these sulphides exhibits any tendency to form thiosalts by interacting with alkali sulphides, or by fusion with alkalis.

Carbon disulphide is a mobile, very refractive, liquid, boiling at 47°; its vapour is very inflammable. It is obtained by the direct union of its elements at high temperatures. This sulphide is the anhydride of thio-carbonic acid H,CS, ; when CS, interacts with concentrated Na SAq sodium thio-carbonate Na,CS, is formed; the acid H,CS, is obtained as a dark M. E. C.

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