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of sulphuric acid with calcium fluoride CaF.;

,

thus CaF, + H SO, Aq = Caso, + 2HFAQ (compare preparation of HCI, HBr, and HI, Chap. xi. par. 153). Hydrogen fluoride is a colourless strongly smelling and irritating gas at temps. above 20°, and a light mobile liquid at temps. under 20°. The vapour-density points to the existence of the gaseous molecule HF only at fairly high temperatures, and to the existence of the gaseous molecule H, F, at temps. not very far above 20°. Liquid hydrogen fluoride chars organic matter rapidly, and dissolves many bodies which are insoluble in all other acids, e.g. strongly heated silica, titanium oxide, boron, silicon, &c. An aqueous solution of this compound interacts with metals and basic oxides similarly to aqueous solutions of hydrochloric, hydrobromic, and hydriodic, acids; fluorides,

Ba Bi salts of the form MF (M=K, Na, &c.), are produced.

2 3' The metallic fluorides shew great readiness to combine with hydrogen fluoride and produce double compounds; e.g. KF.HF, BiFg.3HF, &c. Some of the fluorides of non-metallic elements also combine with hydrogen fluoride; the products in some cases react as acids; thus SiF .2HF is a dibasic acid (H SiF6, flrosilicic acid), and BF, HF is a monobasic acid (HBF, fuoboric acid). A few similar compounds of hydrogen chloride and bromide are known, e.g. HAUCI, and HAuBr,, both of which react as monobasic acids (s. par. 441.)

Hydrofluoric acid, HFAq, is an extremely weak acid; its affinity for bases is less than 5 when that of hydrochloric acid

is taken as 100 (8. Chap. x111. pars. 251, 255). 450

Whether fluorine does or does not interact with water and solutions of alkalis similarly to chlorine, bromine, and iodine, cannot be determined until the properties of fluorine have been more fully investigated.

The chemical properties of fuorine, so far as they have been investigated, shew that this element is very similar to the elements chlorine, bromine, and iodine; but, at the same time, there are fairly marked differences between fluorine and these three elements. No one of the four elements shews any

tendencies to react as a metal. 451 MANGANESE is the second member of the even-series of

Group VII. The sketch of the chemical properties of manganese given in pars. 195–199 of Chap. XI. shews that manganese is at once metallic and non-metallic in its chemical functions. The oxides MnO, Mn, 0, and Mn , are basic; Mno,

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is feebly acidic. A series of manganous salts MnX (X =SO, 2NO,, {PO, &c.) exists; a few manganic salts Mn, 3X are also known. Permanganic acid, H, Mn,Og, has been isolated and a number of permanganates have been obtained as definite stable salts, generally isomorphous with perchlorates MCI,O, (M = K,, Ba, &c.). Many manganates, MMnO,, are also known; these salts do not correspond in composition with any salts derived from acids of chlorine, bromine, iodine, or fluorine; they are similar to the sulphates, selenates, and tellurates MXO, (M=K,, Ba, &c.; X = S, Se, Te).

Manganese, then, shews very feeble analogies with the other elements which are placed in the same group with it.

If the three generalisations stated in par. 446 are applied 452 to Group VII., they would lead us to expect that the unknown members of the even series of this group should resemble manganese, but

should on the whole be more distinctly metallic than this element; and that the unknown members of the odd series of the group should resemble the halogen elements, but should be less decisively non-metallic than these elements; the unknown members of series 9 and 11, Group VII., might fairly be expected to form a few salts by the interactions of their oxides with acids.

CHAPTER XXIV.

453

THE ELEMENTS OF GROUP III.

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12 Even series. B=10.9 Sc=44 Y*= 89-6 La=138.5 Yb*=173 Group III.

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11
load series. Al=27-02 Ga=69 In=1134

TI=20364 Even-series BORON.

SCANDIUM. YTTRIUM.

LANTHANUM.

YTTERBICN. elements Atomic weights 10.9

8966
138.5

173 The molecular weights of these elements are unknown, Sp. grs. (approx.) 2:5

62 Atom. weights 4:3

22:3 seu. gruvs. Sp. heats •5 (?) not determined. not determined.

*0449 not determined. Appearance, and Dark greenish- Not isolated. Grey powder, Steel-grey pow- Not isolated general physical brown powder.

der ; or, when properties. Non-conductor

compressed, of electricity.

lustrous, greyHas not been

white, hard,par-
melted.

ticles.
Fairly malle-
able and ductile.
Melts at full

red-heat.
Occurrence and
Chief com-

Small quanti- Occurs as sili- Silicate occurs, Small quantipreparation pounds occur- ties of silicate cate in small with silicates of ties of silicate

ring in rocks occur in a rare quantities with Ce, Di, Fe, and occur in a rare
and waters are Swedish mine- silicate of scan- Ca, in a few rare Swedish mine-
boric oxide ral.
dium and ytter- minerals.

ral.
B20, and borax Element has bium.

Prepared by re- Element has not Na2B407; not not been iso- Prepared by ducing LaClg been isolated. widely distri- lated.

electrolysing by potassium. buted, nor in

fused largequantities.

Y C13.X

NaCI,
Prepared by

or by de-
strongly heating

chlorinating the B203 with SO

same salt by sodium.

dium. General chemical Burns in air or

Burns when Oxidises in ordiproperties. oxygen to B20%.

heated in air, nary air to Decomposes

giving Y203. La203. steam at red

Decomposes Decomposes heat forming

water, rapidly cold water B203 and H.

when warmed. slowly, hot waOxidised by

Dissolves in di- ter rapidly, with heating with

lute acids, also evolution of hyHNO3, H,804

in hot KOHAq, drogen. molten Kon,

with evolution
or molten

of hydrogen.
KNO,
Combines di-
rectly with CI,
Br, I, S, and
also with N.
Atom of boron
is tri-valent in
gaseous mole-

cules. * There are still some doubts whether these elements are or are not mixtures of two or more distinct kinds of matter.

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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, BBrz, and BF,, have been gasified ; these ulae 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 MC1,, 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: MOL
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, z 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 ocide, 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,0,, 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,B,0, 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.O.P,0, (? BPO2) is a stable compound; B,03.&SO, also exists but is decomposed by heat, or by water.

The other oxides M,0g (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,03.6H,0) and La,, (La 0.3HO) 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.O, or La,,; 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 BBrg, 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, BFg, 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; BCI, 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 fuoboric acid HBF, (=HF.BF). Boron chloride, BC1,, combines with many other compounds to form stable double compounds; e.g. 2BC1,. 3NH,; BC1,. POCI,; BCI. NOCI; BCI.HCN. Yttrium and lanthanum chlorides are obtained as YCl.6H,O, and 2LaCl,.151,0, 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. YCI,.3HgCl.9H,0; 2LaCl,.3ětCI. 24H,0; 2 LaCl,.3AuCl,.21H0. The haloid compounds YBr, YI, 2YFH,0, LåBr. 781,0, and 2La F, H,0, 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,, 2N03, PO,, &c. No definite salts have been obtained by replacing the hydrogen of acids by boron, although

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