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of its elements, or by adding sulphuretted hydrogen, or ammonium sulphide, to a neutral solution of a thallous salt. A compound TI,S. As S, analogous to K,S. As, S, is known.

Salts of the form M,3X (X = SO,, 2N03, CO3, {PO,, &c.) are obtained by dissolving the different hydrated oxides, M,Oz. «H,O, in acids and evaporating. The salts are generally soluble in water; the thallic salts are easily decomposed, sometimes even by solution in water, and are readily reduced to thallous salts, TX. The sulphates, with the exception of thallic sulphate, combine with sulphates of the alkali metals to form alums, M.380,.X,80,.246,0 (X = alkali metal except Li.) Thallous sulphate (T1,SO,) forms an alum with aluminium sulphate, Al,.380,. TI SO.. 247,0.

Several basic salts of aluminium, and a few of the other elements, are known.

The thallous salts, T1, X, are generally stable bodies; they are similar to, and usually isomorphous with, salts of potassium.

Of the four odd-series elements of Group III., three, viz. aluminium, gallium, and indium, are evidently very closely related; the fourth, thallium, is to a great extent separated from the others.

Thallium shews marked similarities with the alkali metals which belong to Group I.; at the same time the properties of some of its compounds-e.g. the acidic character of Ti,Sz, and the probable existence of an unstable potassium thallatesuggest relations with the most negative element of Group III., viz. boron.

Boron, which is the first member of the group, to some extent summarises the properties of the other members. Oxide of boron is acidic ; aluminium oxide is acidic towards strong alkalis; the solubility of Ga,0,. H,0 and In,Og.<H,0 in concentrated potash solution shews that these oxides have feebly inarked acidic functions; an acidic oxide of thallium probably exists. Oxide of boron also shews basic functions towards some acidic oxides, e.g. So, and P,03; all the other oxides of

are basic towards most acids. The positive character of boron is shewn in its interaction with steam at high temperatures.

Neither the group-character nor the family-character distinctly preponderates in Group III. The even-series elements from scandium to ytterbium form a closely related class; the odd-series elements from aluminium to indium are

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the group

also very similar; boron at one end of the group,

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

CHAPTER XXV.

467

THE ELEMENTS OF GROUP IV.

.463 (?)

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=206.4
Even-series CARBON.
TITANIUM ZIRCONIUM.

CERIUM

THORITM. 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
6.7

7.7 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, powden 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

of gases.
graphite 2-25;
of amorphous
carbon abt. 1.9.
Graphite is a
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 a 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 con- 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. Diamond has not been prepared artificially. Amorphous carbon prepared by heating oil, fat, &c. in absence of air.

sorbs gases

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

THORIUM, elements General chemical Heated in air or Burns brilliant- Amorphous Zr Burns to CeO2 Burns when properties. oxygen, burns ly when heated burns when when heated in heated in air to to CO and CO2; in air or oxygen, heated in air or air or oxygen.

Thoạt diamond burns forming Ti02. oxygen; crystal. Combines di- Soluble in only at very

Combines di- line is superfici- rectly with ci, HCIAą, but high tempera- rectly with Cl. ally oxidised. Br, and l; also very slowly in tures in oxygen. No hydride Insoluble in with S, and P. HNO3 Aq. ProCombines di- known. most acids, but Decomposes

perties have rectly with II 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°, KC103.

ThClt. of H.

giving Ti02 Atom is tetraCombines di- and H.

valent in gasrectly with S at Atom is tetra

eous

molecule
high tempera- valent in gas- ZrCl4.
tures.

eous molecule
Combines with TiCl4.
many metals to
form bodies re-
sembling alloys.
Graphite is oxi-
dised by heating
with KC103 and
HNO3Aq to
graphitic acid
C11405; no
other form of
carbon gives
this acid.
Exhibits allo-
tropy very
markedly.
Atom is tetra-
valent in gas-
eous molecules.

4

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 CS2, 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,OX; MO, M = any element of the family.

Sulphides: CS, CS,, (1 C,S.), Tis,, Ce,$s, Ths.

Haloid compounds: MX, M= any element of the family; C,C1, &c., Ti,Cl, Ce,Clo; Tici,

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Acids: H,CO,Aq; salts of the form M,Ti0, and M,ZrO; are known (M = an alkali metal); the hydrates Tio ..H,0 and Zr0,. 1,0 are acidic.

Salts: carbon does not form salts by replacing the hydrogen of acids; M.2X (X=SO4, 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, + H2O + CaCl, Aq. The dioxides,

CaCO3 ,, 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.z: from these alkali carbonates, carbonates of most metals can be obtained. An aqueous solution of carbon dioxide probably contains carbonic acid, H,CO3; 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, Tio.H,0, Tio,24,0; ZrO2.H,O, ZrO2.2H,0; ThO2.2H,0; 2Ce0,.3H,0. These hydrated dioxides are soluble in acids, and from these solutions salts of the form M. 2X (X=SO4, 2NO3, &c.) are obtained. The solution of CeO2.XH,0 in acids seems to contain cerous salts Ce,.3X, as well as ceric salts Ce2X.

Most of the dioxides MO,. xH,O exhibit acidic properties. None of them dissolves in solutions of alkalis to form salts. When however titanium dioxide, TiO2, 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 NaHTi0g. Zirconium dioxide, ZrO,, fused with Na,Co, behaves similarly to Tio,; the zirconates Na Zr0, and Na Zro, are said to have been

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