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Borates are
Boric oxide

duced by the action of the water on the borate.
ill-defined salts; many basic salts seem to exist.
combines with a few anhydrides of strong acids to form
compounds in which the boric oxide acts as a base; thus
BO. PO (BPO) is a stable compound; B,O,.SO, also

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2

exists but is decomposed by heat, or by water.

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The other oxides M ̧O, (M=Sc, Y, La, Yb) are basic; they dissolve in acids and form salts; they are insoluble in solutions of alkalis. Hydrates of YO,(Y,O,.6H,O) and La2O, (La,0,. 3H,O) have been obtained, but not by the direct reaction of water with the oxides. Lanthanic hydrate is said to turn red litmus blue.

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456

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2 3

The sulphides M,S,, where M = B or La, are formed by passing carbon disulphide vapour over heated BO, or La ̧O̟ ̧; they are easily decomposed by cold water to M,O, and H,S. 457 Haloid compounds of boron, yttrium, and lanthanum, have been prepared. Boron chloride and bromide, BCI, and BBr,, 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.

458

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

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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; BCI, and BBr, to solutions of boric oxide and hydrochloric, or hydrobromic, 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, BCI,, combines with many other compounds to form stable double compounds; e.g. 2BC1. 3NH; BC. POCI,; BC. NOCI; BCI,.HCN. Yttrium and lanthanum chlorides are obtained as YC1.6H2O, and 2LaCl,.15H,0, respectively, by dissolving the oxides in HCIAq and evaporating. The anhydrous chlorides have also been obtained. These chlorides form several double compounds chiefly with other chlorides; e.g. YC,.3HgCl,.9H2O; 2LaCl,. 3PtCl. 24H ̧O; 2 LaCl. 3AuCI. 21HO. The haloid compounds YBг,, YI, 2YF. HO, LaBr,.7H ̧0, and 2LaF. H2O, have been isolated. Two oxychlorides of boron, BOCl and BOCI,, 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, 2NO, PO, &c. No definite salts have been obtained by replacing the hydrogen of acids by boron, although

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boric oxide combines with a few strongly acidic oxides
(8. 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). 3K2SO.

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So far as the odd-series elements of Group III. 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.

GALLIUM.

Odd-series elements

Atomic weights

Sp. grs. (approx.)

Atom. weights

spec. gravs. Sp. heats

Melting points (approx.) Appearance, and general physical properties.

Occurrence and preparation.

General chemical properties.

ALUMINIUM.

27.02

2.6

10.5

69

113.4

The molecular weights of these elements are unknown.

5.9

7.5 15.2

11.8

[blocks in formation]

INDIUM.

Silver-white; crys- White; lustrous;
talline; hard, melts soft.
very easily; rather
brittle.

Oxidised superfici-
ally by heating in
oxygen to full red-

ness.

Combines directly
with Cl, Br, and I.
Dissolves in acids,
also in KOHAq,
with evolution of H.
Atom of gallium is
trivalent in the gase-
ous molecule GaClg;
existence of gaseous
GagCle is doubtful.

*057 175°

Compounds occur in
small quantities in
certain zinc blendes.
Prepared by precipi-
tation by means of
pure zinc from a
solution of the sul-
phate.

Oxidised at mode-
rately high tempera-
ture in air.
Soluble in most di-
lute acids.
Does not decompose
water at 100°.
Atom of indium is
trivalent in the gas-
eous molecule InClg.

THALLIUM.

203-64 460

11.8

17.3

031 290°

Grey-white; very lustrous; soft; fairly malleable and ductile; crystalline; may be distilled in hydrogen.

Compounds of thal-
lium occur in small
quantities in various
widely distributed
minerals.
Prepared by electro-
lysis of aqueous solu-
tion of TINO, &c.;
by reduction of same
solution by zinc; or
by fusing TiCl with
KCN.

Oxidises in air at or-
dinary tempera-

tures.
Combines directly
with Cl, Br, I, P,
and S.
Dissolves in
H2SO4Aq or
HNO3Aq with evo-
lution of H.
Decomposes water
at red-heat with evo-
lution of H.
Atom is monovalent
in the only known
gaseous molecule
TICI.

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462

General formulae and characters of compounds. The compounds AICI,, (GaCl), GaCl, InCl,, and TICI, have been gasified; these formulae are molecular. Al,Br, and AlI also appear to exist as gases; but from the results of recent work it is probable that at higher temperatures the molecules AlBr, and AlI, 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.

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Oxides: M,O,; also InO and probably GaO; also TIO.
Sulphides: M,S,; also TIS.
Haloid compounds: MCI,, in one case M.Cl; also
GaCl,; also TICI.

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Salts: M3X; also Tl,X (X = SO, 2NO, PO1, &c.).

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The oxides MO, 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,.3H0, (? Ga,0,.3H,O), In 0.3H0, and TIO. H2O. The oxides, and the hydrated oxides, are insoluble in water; but it is possible, by dialysing a solution of AlO.H2O in AlCl Aq, to obtain an aqueous solution of hydrated aluminium oxide. The hydrates M,O,.H2O, except TIO. HO, are soluble in solutions of caustic potash; potassium aluminate, K,Al,O,, 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.

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

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When thallic hydrate Tl,O,. H2O 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, TO, is strongly basic and alkaline. When a solution of thallous sulphate, Tl,SO,, is mixed with a solution of baryta in the proportion Tl,SO, : Ba(H2, the liquid is filtered from precipitated barium sulphate, evaporated

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and allowed to crystallise, the hydrated oxide Tl,O. 2H,O is obtained. When this hydrate is heated to 100° in absence of air TIO 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, TX. There can be little doubt that the solution contains the hydroxide TlOH, and that the composition of hydrated thallous oxide is better expressed by the formula 2TIOH. H2O than by the formula TO. 2H,O.

The haloid compounds, MC, are obtained; (1) by 463 heating the elements in chlorine, M Ga and In; (2) by heating an intimate mixture of the oxides M,O, and carbon in chlorine, M = Al and In; or (3) by adding HCIAq to the hydrated oxides M2O,, M=Tl. The other haloid compounds are obtained by similar methods.

The vapour density of aluminium chloride agrees with the formula AICI,; that of gallic 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, TICl, 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. KCl; InCl ̧.3KCI; TICI. 3KCl.

Thallous chloride, TICI, is formed as a white precipitate when HCIAq 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, 2KCl. PtCl.

The sulphides M,S, are obtained by the direct union 464 of their elements at high temperatures. A compound K,S. Tl,S (possibly a thio-thallate of potassium) is produced by heating thallous sulphide (Tl,S) 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

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

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466

Salts of the form M,3X (X=SO,, 2NO,, CO, PO,, &c.) are obtained by dissolving the different hydrated oxides, MO.жH2O, 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,. 3SO,. X,SO,. 24H,O (X = alkali metal except Li.) Thallous sulphate (Tl,SO,) forms an alum with aluminium sulphate, Al,. 3SO. TI,SO,. 24H,O.

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

The thallous salts, Tl,X, are generally stable bodies; they are similar to, and usually isomorphous with, salts of potas

sium.

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 TS,, and the probable existence of an unstable potassium thallate— suggest 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,O,. xH2O and In,O,.H2O in concentrated potash solution shews that these oxides have feebly marked acidic functions; an acidic oxide of thallium probably exists. Oxide of boron also shews basic functions towards some acidic oxides, e.g. SO, and PO; all the other oxides of the group 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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