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Boron is said to exist both as an amorphous powder and as metal-like, hard, lustrous, crystals; but recent investigation shews that the so-called crystalline boron is a compound of boron and aluminium.

General formulae and chemical characters of compounds. 454 The compounds BCI,, BBry, and BF,, have been gasified ; these formulae are molecular. No compounds of the other even-series elements have yet been gasified; the formulae given are the simplest that express the compositions of these compounds. Gaseous aluminium and indium chlorides have the molecular composition MCI,, and gallium chloride appears to exist in the gaseous state both as GaCl, and Ga,cl,. There are indications of the existence of a hydride of boron, probably BH,; but the compound has not been isolated. The compounds of the elements of this family, with the exception of those of boron, have not been very fully investigated : there are many points in the chemical history of boron which require elucidation.

Oxides: MO
Haloid compounds: MX,
Sulphides: M.Sz.

Acids: H,BO, H,B,O., H.B.0,; no acids of other elements are known.

Salts: M 3X; X = SO,, 2NO3, PO,, &c.; M = Sc, Y, La, Yb, not B.

The oxides M,0, with the exception of B,0,, are obtained 455 by adding an alkali to the solution of a salt, and heating the hydrated oxide which is pptd. B,0, is found in waters in various volcanic districts; it is formed by heating boron in oxygen.

Boric oxide, B,0,, is acidic; it dissolves in water, and from this solution crystals of ortho-boric acid, H,BO,, separate on evaporation. By heating ortho-boric acid to 1000 metaboric acid, H,B,C,, is obtained ; and at 160° tetra- or pyro-boric acid, H,B,C,, is formed. Salts are known derived from each of these acids; borax, one of the most important salts, is sodium tetra-borate Na,B,0,; the ortho-borates are very unstable salts, it is doubtful whether they exist in solution in water. A solution of boric oxide in water reacts as if it contained dibasic metaboric acid, H.BO, Boric acid is an extremely weak acid. Dilute aqueous solutions of alkali borates precipitate metallic oxides, not borates, from solutions of many metallic salts; that is to say, these dilute solutions behave as if they contained boric acid and free alkali, pro

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duced by the action of the water on the borate. Borates are ill-defined salts; many basic salts seem to exist. Boric oxide combines with a few anhydrides of strong acids to form compounds in which the boric oxide acts as a base; thus B,0,.P,0(? BPO,) is a stable compound; B,0,. «SO, also exists but is decomposed by heat, or by water.

The other oxides M,Oz (M=Sc, Y, La, Yb) are basic; they dissolve in acids and form salts; they are insoluble in solutions of alkalis. Hydrates of Y,03(Y,02.6H,0) and La Oz (La 03. 3H,0) have been obtained, but not by the direct reaction of water with the oxides. Lanthanic hydrate is said to turn red litmus blue.

The sulphides M,Sz, where M=B or La, are formed by passing carbon disulphide vapour over heated B,0, or Lag; they are easily decomposed by cold water to MO, and H.S.

Haloid compounds of boron, yttrium, and lanthanum, have been prepared. Boron chloride and bromide, BCl, and BBrz, are obtained by heating boron in chlorine and bromine, respectively, or by passing chlorine, or bromine, over a strongly heated mixture of boric oxide and carbon.

Boron fluoride, BF,, is formed by heating boric oxide with calcium fluoride to a full white heat.

Boron chloride and bromide are liquids, boiling without decomposition at 17° and 90° respectively; boron fluoride is a gas. These haloid compounds are all decomposed by water; BCl, and BBr, to solutions of boric oxide and hydrochloric, or hydrobronic, acid ; BF, is partly decomposed to boric oxide and hydrofluoric acid, but the latter combines with some unchanged BF, to form fluoboric acid HBF, (=HF.BF). Boron chloride, BCl,, combines with many other compounds to form stable double compounds; e.g. 2BC1,.3NH,; BCI, POCI,; BCI.NOCI; BCI .HCN. Yttrium and lanthanum chlorides

. are obtained as YCI, 6H2O, and 2 LaCl .15H,O, respec

, tively, by dissolving the oxides in HClAq and evaporating. The anhydrous chlorides have also been obtained. These chlorides form several double compounds chiefly with other chlorides; e.g. YС1.3HgC1.9H,0; 2LaCl,. 3PtCl,.24H,0; 2 LaCl .3Auc.21H O. The haloid compounds YBrı, YI, 2YF, H,O, La Br,. 77,0, and 2La F, H, O, have been isolated.

Two oxychlorides of boron, BOCl and BOC1,, are known.

The salts of the elements we are considering, so far as they have been examined, belong to the form M .3X where X = SO, 2N03, PO,, &c. No definite salts have been obtained by replacing the hydrogen of acids by boron, although

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boric oxide conibines with a few strongly acidic oxides (s. par. 455). Several salts of yttrium, scandium, lanthanum, and ytterbium have been prepared ; few basic salts are known. The sulphates seem all to combine with sulphate of potassium to form double salts; these are not alums; they generally have the composition M, (SO),.3K SO,

So far as the odd-series elements of Group ÍII.' have been ex- 459 amined, it appears that the four elements scandium, yttrium, lanthanum, and ytterbium, are closely related, and that boron is distinctly separated from the other members of the family.

203-64 460

5.9

Odd-series ALUMINIUM

GALLIUM.

INDIUM

TIALLIUM. elements Alomic weights 27.02

69

1134 The molecular weights of these elements are unknown. Sp. grs. (approx.) 2-6

7.5

11.8 Atom. weights

30°

290°

10-5
11.8
15.2

173
spec. graus.
Sp. heats

.225
.08
-057

*031 Melting points 700°-800°

175° (approx.) Appearance, and White; very malle. Silver-white; crys- White; lustrous; Grey-white; very general physical able and ductile; talline; hard, melts soft.

lustrous; soft; fairly properties. hard; tough; very very easily; rather

malleable and ducsonorous; good con- brittle.

tile; crystalline; ductor of electricity.

may be distilled in

hydrogen. Occurrence and Oxide of aluminium Compounds occur in Compounds occur in Compounds of thalpreparation. occurs as corundum, small quantities in a small quantities in lium occur in small

sapphire, &c. Sili- few zinc blendes. certain zinc blendes. quantities in various
cates occur in clay, Prepared by electro- Prepared by precipi- widely distributed
felspar, &c. in enor- lysing an alkaline tation by means of minerals.
mous quantities. solution of a basic pure zinc from a Prepared by electro-
Prepared by reduc- sulphate.

solution of the sul- lysis of aqueous soluing Al.Cle.2NaCl by

phate.

tion of TINO3, &c. ; sodium or potas

by reduction of same sium, or by electro

solution by zinc; or lysis of the fused

by fusing TIC with salt.

KCN. General chemical Unchanged in air; Oxidised superfici. Oxidised at mode- Oxidises in air at orproperties. thin pieces heated in ally by heating in rately high tempera- dinary temperaair are burnt to oxygen to full red- ture in air.

tures.
Al2O3.
ness.

Soluble in most di- Combines directly
Superficially oxi- Combines directly lute acids.

with Cl, Br, I, P, dised by melting in with Cl, Br, and I. Does not decompose and S. oxygen. Dissolves in acids, water at 100°.

Dissolves in Combines at high also in KOHAq, Atom of indium is H.S04Aq or temperatures with S, with evolution of H. trivalent in the gas- HNO3Aq with evoP, and As, also Atom of gallium is eous molecule InCiz. lution of H. with N. trivalent in the gase

Decomposes water Decomposes water ous molecule GaClzi

at red-heat with evoat 100°, evolving H. existence of gaseous

lution of H. Dissolves in hot Ga2Cle is doubtful,

Atom is monovalent HCIAq or

in the only known H2804Aq.

gaseous molecule Unchanged by mol

TICI.
ten KOH or KNO3 ;
but dissolves in boil-
ing KOHAq giving
an aluminate and H.
Atom of aluminium
fs trivalent in the
gaseous molecule
AlCl3,

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General formulae and characters of compounds. The compounds AICI,, (? Ga, Cl), GaC1, InCl, and TICI, have been gasified; these formulae are molecular. Al,Br, and Al I. also appear to exist as gases; but from the results of recent work it is probable that at higher temperatures the molecules AlBr, and All, are formed. The formulae given to the other compounds are generally the simplest formulae which express the compositions of the different bodies; they are not necessarily molecular.

The compounds of gallium and indium have not been very fully investigated.

Oxides: M,0,; also InO and probably Gal; also TI,O.
Sulphides: MS,; also TI S.

Haloid compounds: Mci,, in one case M.Clo; also
GaCl,; also TICI.
Salts: M 3X; also TI X (X=SO,, 2NO,, {PO,, &c.).

. The oxides M,0, are obtained by adding ammonia to solutions of salts of the several metals, and drying and heating the hydrated oxides so formed. The hydrated oxides obtained are A1,0,.3H,0, (? Ga 3.3H,0), In,O, 3H,0, and T1,0,H,O. The oxides, and the hydrated oxides, are insoluble in water; but it is possible, by dialysing a solution of A1,02H 0 in AICI Aq, to obtain an aqueous solution of hydrated aluminium oxide. The hydrates M,0,.2H,O, except T1,0,. H,0, are soluble in solutions of caustic potash; potassium aluminate, K, A1,0, is obtained by evaporating the solution of aluminium hydrate; the solution of indium hydrate gives a precipitate of the oxide when boiled ; and the solution of gallium hydrate is decomposed by carbon dioxide with precipitation of gallic oxide.

The oxides M,O, all dissolve in acids forming salts M 3X ; the thallic salts are very unstable and are easily reduced to thallous salts, TI X.

When thallic hydrate T1 O..H,O is suspended in concentrated potash solution and chlorine is passed into the liquid, the hydrate partially dissolves, forming a violet coloured liquid, which possibly contains the potassium salt of a thallium acid ; no salts of this hypothetical acid have however been isolated.

Thallous oxide, TI,O, is strongly basic and alkaline. When a solution of thallous sulphate, Ti,SO,, is mixed with a solution of baryta in the proportion T1,80, : Ba(), H,, the liquid is filtered from precipitated barium sulphate, evaporated

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and allowed to crystallise, the hydrated oxide T1,0.2H,0 is obtained. When this hydrate is heated to 100° in absence of air T1,0 is formed. Thallous oxide is very soluble in water and the solution closely resembles KOHAq or NaOHAq in its properties; it has a corrosive action on the skin, a hot and burning taste, turns red litmus blue, absorbs and combines with carbon dioxide, and neutralises acids forming thallous salts, Tl,X. There can be little doubt that the solution contains the hydroxide TIOH, and that the composition of hydrated thallous oxide is better expressed by the formula 2TIOH. H,O than by the formula T1,0. 21.0. The haloid compounds, MCI, are obtained ; (1) by 463

,

; heating the elements in chlorine, M = Ga and In; (2) by heating an intimate mixture of the oxides M,0, and carbon in chlorine, M = Al and In; or (3) by adding HClAq to the hydrated oxides M,03, M=Tl. The other haloid compounds are obtained by similar methods.

The vapour density of aluminium chloride agrees with the formula Alci,; that of gallico chloride shews that at moderate temperatures the gaseous compound probably consists of molecules of Ga,cl, but at higher temperatures it consists of molecules of GaCl; gaseous indium chloride has the molecular composition Incl, ; thallic chloride has not been gasified, at 100 it separates into thallous chloride, Tici, and chlorine. The chlorides, MCI,, are all deliquescent solids; they are all, except probably TICI,, partially decomposed by hot water with formation of various oxychlorides of more or less complex compositions. These chlorides all combine with many other chlorides to form double compounds; e.g. AICI. PCI, ; AICI. POCI,; AICI.KCI; InCI.3KCI; TICI, 3KCI.

Thallous chloride, Ticí, is formed as a white precipitate when HClAq is added to a solution of thallous oxide. This chloride is only slightly soluble in water; it has been gasified without decomposition; it combines with various chlorides to form double compounds; the compound 2TICI. PtCl, resembles, and is isomorphous with, 2KCI. Ptci.

The sulphides M,S, are obtained by the direct union 464 of their elements at high temperatures. A compound K,S. TI,S, (possibly a thio-thallate of potassium) is produced by heating thallous sulphide (T1,) with sulphur and potassium carbonate. A similar compound of potassium and aluminium sulphides seems to exist.

Thallous sulphide, Tl,S, is obtained by the direct union

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