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the sulphate Ti,(SO4)3 which is obtained by dissolving the corresponding oxide Ti,o, in concentrated sulphuric acid and evaporating; and titanic salts obtained by dissolving the dioxide, TiO2, in acids. Most of the titanic salts are basic salts, e.g. TiO.SO,; 5Ti02. N,05. «H,0; 2T10, P,0z. «H,0; &c.; a few normal salts are known, e.g. Ti(SO2)2.3H,0.

Zirconium forms one series of salts, the zirconic salts, represented by the sulphate Zr(80.), and one or two others. Most of the zirconium salts are basic salts, e.g. 3Zr0,. SO,; 3Zr0,.21,05; 5Zr0.4P,0g, &c.

The salts of thorium are all thoric salts, e.g. Th(SO2)2; Th(NO2)...CH,0; Th,(PO.), «H,0, &c. The thoric salts are usually normal; a few basic salts are known, e.g.

2Th0,. 7Se0, 2H,O.
Cerium resembles titanium in that it forms two classes of
salts. The cerous salts Ceg. 3X are numerous; e.g.

Ce (803); «H,0; Ce(NO3)3. «H,0; CePO, &c.
The chief representatives of the ceric salts are

Ce(80,),. «H,0, and Ce(NO),
The salts of all the metals of the family form many double
salts generally by combination with salts of the alkali, and
alkaline earth, metals.

Carbon is evidently separated from the other even series 473 members of Group IV. by its distinctly non-metallic character. The other elements are all metals in their physical properties; their oxides are basic, but most of them shew acidic functions. As the atomic weight increases the elements become more distinctly metallic in their chemical properties. In a few respects, e.g. existence of M,0, and corresponding salts, cerium is more closely related to titanium than to any

other member of the family.

The three elements titanium, zirconium, and thorium exhibit very marked similarities; the existence of the com

; pounds K,MF, is characteristic,

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474
Odd-series

SILICON.
GERMANIUM.

TIN.

LEAD.
elements
Atomic weights

28.3
72.3
117.8

206.4
The molecular weights of these elements are unknown.
Sp. grs. (approx.)

2-5
5.5
7:3

11.4 Atom. weights

11.2
13:1
16-1

18:1
spec. gravs.
Melting points abt. 1000°

900°
230°

330°
(approx.)
Sp. heats
.203
*077
*055

*031 Appearance, and Brown, amorphous Grey-white; lus- White; crystalline; White with greyish general physical powder; also as trous; crystalline; lustrous; not hard; tinge; soft; crystalproperties. greyish-black,

very brittle.

rather brittle, but line; very malleable; needle-shaped, very

ductile and malle- ductile, but not tehard, metal-like, lus

able at certain tem- nacious. trous, crystals ; also

peratures. Also as as crystalline plates

a grey powder, S. G. resembling graphite

5.8, produced by in appearance. Gra

keeping ordinary tin phitic Si conducts.

at very low temperaelectricity.

tures for some time. Occurrence and Enormous quanti- The sulphide is Found native; but Found native in preparation. ties of silicates occur found in argyrodite chiefly as oxide small quantities;

as clays, felspars, &c. a rare mineral (chief- SnO2; very widely chief ore is Pbs, Prepared by reduc- ly Ag2S) from Frei- distributed, but not widely distributed ing vapour of SiCl4 berg.

in very large quan- in fairly large by K or Na; or by Prepared by reduc- tities.

quantities. reducing K,SiF6 by ing Ge0, in hydro- Prepared by reduc- Prepared by reducK or Al.

gen, or by strongly ing SnO2 by carbon, ing Pbo by carbon heating the

same or .by electrolysing or potassium craoxide with carbon. aqueous solutions of nide; also by elecsalts.

trolysis of solutions

of salts. General chemical Amorphous Si burns Oxidised to GeO2 by Burns to SnO2 when Oxidised superproperties. to Sio, when heated nitric acid ; insoluble strongly heated in ficially in moist air: in air; crystalline Si in IICIAq; dissolves air.

heated in air burns does not oxidise even in H2SO4A.

Dissolved by dilute to PbO and higher when heated in oxy- Atom is tetravalent HNO3Aq; oxidised oxides. gen.

in gaseous molecules to Snog, by conc. Dissolved by sulSoluble in HFA; GeCl4 and Geld. nitric acid.

phuric and nitric not in HCIAq or

Soluble in KOHAq acids.
HNO,Ag.

with evolution of H, Combines directly Amorphous Si, but

and formation of with Cl and S. not crystalline Si,

K2Sn03.

Atom is divalent and dissolves in

Combines directly tetravalent in gasKOHAq forming

with Cl, and with s. eous molecules. K,SiO2 and H.

Atom is divalent and
Oxidised by molten

tetravalent in gas-
KOH.

eous molecules.
Combines directly
at high temperatures
with Cl, also with S,
and N.
Combines with seve-
ral metals to form
bodies resembling
alloys.
Exhibits allotropy.
Atom is tetravalent
in gaseous mole-
cules.

475 General formulae and chemical characters of compounds.

Silicon is the only member of the family which forms a
compound with hydrogen. Numerous compounds of silicon
with carbon, hydrogen, and oxygen, the silico-organic com-

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pounds, are known. The compounds Sici, SiBr, Sil.; GeCl, GeId, GeS; SnCl2, SnCl,; PbCl2, Pb(CH), have been gasified and their vapour densities have been determined.

Oxides: MO,, M=any element of the family; MO, M = Ge, Sn, Pb; also Sn,0,, Pb,0,, and Pb,0,. Hydrates of most of these oxides are known : some of them are acidic.

Sulphides: MS,, M=any element of the family except Pb; Ges, SnS, PbS.

Haloid compounds: MX, M = any element of the family except Pb; MCI, M = any element of the family except Si; Si,X.

Salts: salts of Si are unknown; MX, X = SO4, 2NO3, PO4, &c.; a few stannic salts Sn. 2X are known.

Salts derived from acidic hydroxides; M,XO3, X = Si, Sn, Pb; also many complex silicates, some complex stannates, and probably one or two plumbites M.Ph0,; (M=K, Na, &c.).

Silicon hydride, SiH,, is obtained mixed with hydrogen 476 by decomposing any alloy of magnesium and silicon by hydrochloric acid. The hydride is obtained pure by the interaction between sodium and the compound SiH(OC,H), Silicon hydride is a colourless gas, condensing under great pressures to a colourless liquid; it is decomposed by heating to about 400°; it is very inflammable when mixed with air; the gas interacts with an aqueous solution of potash to form potassium silicate and hydrogen; SiH, + 2KOHAq+H,O=K_SiO, Aq + 4H,

Oxides. The dioxides Sioe Geon, and Sno, are obtained 477 by strongly heating the elements in air; Geo, and Sno, are more readily obtained by oxidising the elements by concentrated nitric acid. Silica, Sio,, is usually prepared by decomposing an alkali silicate by an acid, evaporating to dryness, heating, and removing the alkali salt of the acid by solution in water. Lead dioxide, Pb0, is obtained by evolving oxygen in contact with a lower oxide of lead in presence of an alkali; the usual method is to suspend PbO in concentrated KOHAq and pass in chlorine, or to boil PbO with KOHAq and KCIOA. The oxides Geo, SnO, and P60, are obtained by adding an alkali to solutions of the corresponding chlorides, MCI,, and drying the hydrated oxides so produced.

The oxides are all white, or nearly white, solids, insoluble in water. Silicon dioxide, SiO,, when strongly heated is insoluble in ordinary acids except hydrofluoric; Geo, probably forms salts by interacting with acids, but these salts have not

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yet been isolated; hydrated stannic oxide, SnOz.«H,O, dis-
solves in most acids to form salts, but few have been isolated,
and most of these are basic salts; plumbic oxide, PbO,, dis-
solves in HCIAq, HNO,Aq, &c. to form plumbous salts, PbCl,,
Pb.2NO3, &c. but it appears to dissolve without change in
acetic and phosphoric acids, and these solutions possibly contain
plumbic salts, Pb.2X. All the dioxides, MO,, are more or
less distinctly acidic. Hydrated silicon dioxide, SiOz.«H,O,
dissolves in solutions of caustic alkalis, and silicates are
obtained from these solutions; of the vast number of silicates
which are known, many occur in minerals; those which may
be called normal silicates belong to the forms M Sio, and

Ba Mg
M. SiO,, M=K, Na, ,

&c. The other hydrated di

2 2 oxides MO.«H,O, where M = Sn or Pb, dissolve in concentrated aqueous potash, or in molten potash containing a very little water, and salts are obtained on evaporating in vacuo; these salts belong to the form X MO, where X = K or Na.

The monoxides Sno and Pbo dissolve in acids to form salts; GeO also dissolves in acids, but no salts have yet been isolated ; a few stannous salts and a considerable number of plumbous salts, MX, have been isolated. Plumbous oxide, PbO, dissolves in conc. potash or soda solution; a few salts of the form M.PbO, have been obtained, M=K, Na, or Ag.

The sesquioxides Sn,0, and P6,0, are obtained by the action of weak oxidisers on solutions of stannous or plumbous salts, MX, in presence of an alkali ; Sn,0, easily oxidises in air to SnO,; Pb,0, interacts with dilute acids as if it were PbO.PbO,, a plumbous salt (PbX) is formed and PbO, remains.

Sulphides. The only sulphide of silicon is sis,; it is prepared by passing carbon disulphide vapour over a heated mixture of silica and carbon. The sulphides Ges, and Sns are obtained by passing sulphuretted hydrogen into acidified solutions of germanic and stannic chlorides, respectively. GeS is obtained by heating Ges, in hydrogen; and SnS by passing sulphuretted hydrogen into an acidified solution of stannous chloride. When sulphuretted hydrogen is passed into an acidified solution of a lead salt, PbS is pptd. There are indications of the existence of a higher sulphide of lead than PbS, but none has been isolated. Both stannous and stannic sulphide, SnS and SnSg, dissolve in solutions of alkali sulphides to form alkali thio-stannates, M SnSg; PbS fused with an alkali carbonate probably forms an alkali thio-plumbate;

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478

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SnCl

GeS dissolves in potash solution, probably forming a thio-germanate.

Haloid compounds. The tetrachlorides MCI, M = Si, 479 Ge, Sn, are obtained by heating the elements in a rapid stream of chlorine ; Sici, is better prepared by heating a mixture of silica and carbon in chlorine; Geci, by heating a mixture of germanium and mercuric chloride (HgCl,); Snci, by passing chlorine into stannous chloride, Snci,. When chlorine is passed into a solution of PbCl, in HClAq, the gas is absorbed ; on heating this solution, chlorine is evolved ; addition of water to the solution ppts. lead dioxide Pb0,; the solution probably contains PbCl, but this compound has not yet been certainly isolated.

The tetrachlorides, SiCl,, GeCl,, and SnCl,, are liquids boiling at moderate temps.; Sici, boils at 57°, GeCl, at 86°, SnCI, at 115o. Sicl, is decomposed by water to silica (SiO) and hydrochloric acid; SnCl, dissolves in water, and on evaporation various hydrates, SnCl.«H,, are obtained. combines with many chlorides and other compounds to form double compounds; e.g.

SnCl. 2SeoCle; SnCI.PCI,; SnCl,.2PH,; SnCl.N,Oz.

The tetrafluorides MF, M=Si, Ge, Sn, are obtained by the interaction of hydrofluoric acid with the oxides MO,. Sif is gaseous, the others are solids. They all combine with potassium fluoride to form characteristic salts K MF. When SiF, is passed into water, silicic acid and fluosilicic acid H SiF are formed (3SiF4 +3H,0 + Aq=2H SiF Aq+ H SiO2). Potassium fuosilicate, K Sif,, is obtained by neutralising this acid by potash. Acids of the form H, MF, when M = Ge or Sn are not known.

Silicon trichloride, Si, Cig, is obtained by heating the tetrachloride with silicon : no corresponding haloid compounds of the other members of the family are known.

The dichlorides Mcle, where M = Ge, Sn, or Pb are formed when the metals are heated in hydrochloric acid gas; PbCl, is usually obtained by adding HCIAq to the solution of a lead salt, and crystallising from hot water. GeCl, is a liquid ; the others are solids. SnCl, is decomposed by much water giving oxychlorides, «Sn0.ySncl. H,0. Pbci, dissolves in hot

,.zH PbCl water without change; oxychlorides of lead are obtained by heating this solution with lead oxide, Pbo. No fluoride of lead has yet been isolated.

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