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Series 7, (Ag,0, C2,0,, In,,, Sn, 0,), but that it is succeeded in the series by elements whose highest typical oxides (Te0 1,0) are composed of a greater number of atoms of oxygen relatively to the atoms of the other element than Sb,oz.

Finally, we ought to examine the relations of Group V. and Series 7 to other groups and series. It is impossible to do this at present except in the merest outline. Looking at this subject broadly, it may be said that the members of Group I. shew greater differences among themselves, and the members of Group VII. are more closely related among themselves, than the members of the intermediate groups; and that the variation of properties from the first to the last member of a series is very marked in Series 2, but becomes, on the whole, less marked as we pass through Series 3, 4, 5, to Series 11. If we may apply so vague a generalisation as this, we should conclude that antimony ought to exhibit very well marked analogies with the other members of the group in which it occurs; and that although it must widely differ from the other elements in its series, yet it will probably not differ to so very marked an extent as, say, nitrogen differs from the other members of Series 2, or phosphorus from the other members of Series 3. These tentative and somewhat vaguely worded conclusions, are fairly borne out by the actual relations between antimony, the members of Group V. on the one hand, and the members of Series 7 on the other hand.

In the sketch which has now been given of the periodic law, each group of elements has been treated as a whole. But the more detailed study of these groups will shew us that each, except Group VIII., is more or less sharply divided into two sub-groups; one sub-group contains the elements belonging to even series, the other sub-group contains the elements which are placed in odd series,

This division of the groups into sub-groups is sometimes marked, e.g. in Group VI.; sometimes it is almost hidden by the distinct way in which all the members of the group are stamped with the characteristics of the groups, e.g. in Group V. Some groups, for instance Group II., exhibit very clearly both the general characteristics of the group, and the division into two sub-groups the members of either of which are more like each other than they are like the members of the other subgroup.

This division into sub-groups is rendered very clear in the annexed table.

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The name family is often applied to a sub-group; thus it may be said that in Group V. the group-character preponderates over the family-character, but that the family-character is more marked than the group-character in Group VI.

Those groups in which neither character is much in the ascendancy are best suited for exhibiting the general applications of the periodic law. For this reason we shall begin our detailed study of this law by considering Group II.

The position of an element in the scheme of classification arising out of the periodic law is indicated by the use of Roman numerals to express the group, and Arabic numbers to express the series ; thus the positions of antimony, nitrogen, and iodine, respectively, are defined by the notation V. - 7, V.-2, and VII. – 7.

395

[blocks in formation]

Melting points

(approx.) Atom. weights

54

365

spec. gravs. Colour, appear

ance, &c.

25-3

34.9

Occurrence and preparation

General chemical

properties

White, lustrous, Whitish-yellow;abt. Clear whitish-yel- Gold-yellow; fairly
hard.

as hard as lead, very low; harder than ductile.
ductile, but becomes lead, ductile and
brittle when ham- malleable.

mered.
Not widely distri- Carbonate, phos- Carbonate and sul- Carbonate,sulphate,
buted. Oxide occurs phate, sulphate, sili- phate occur in some and silicate, occur
in a few rocks. cate, &c. very widely rocks and water, but in some rocks, water,
Prepared by reduc- diffused in rocks, not very widely and plants, but not
ing fused BeCl2 by water, plants, and diffused. Prepared very widely diffused.
Na, not by electro- animals. Prepared by electrolysis of Prepared by elec-
lysis of BeCig by electrolysis of fused SrCly, or by trolysis of BaCl

mixture of CaCl2 reducing SrCl2 by mixed with NH CI, with SrCl, and Zn -Na amalgam. or by reducing NH4C, or by re

BaCl2 by vapour ducing CaCl, by

of K.
Zn-Na amalgam.
Not oxidised in ord. Quickly oxidises in Closely resembles Closely resembles
air; even when heat- moist air; decom. Ca; decomposes cold Ca.
ed in 0 is only super- poses cold H20 ra- H20 more rapidly, Oxide (Bao) very
ficially oxidised. pidly; burns in air Oxide (Sro) strongly strongly basic and
Does not decompose at red heat.

basic and alkaline. alkaline.
H20 even at red Combines with Ci,
heat.

Br, I, P, and S, at
Combines with CI, high temperatures.
Br, and I, at high Oxide (Cao)strongly
temps.; does not basic and alkaline.
combine directly Strongly positive
with S.

metal.
Dissolves in
KOHAg forming
Beo and H.
Oxide (BeO) basic
but not alkaline.
Distinctly metallic.

397

398

General formulae and chemical characters of compounds. (M = Be, Ca, Sr, or Ba). MO, MO,H,,MO, (no Beo, known), MS, MS, H, (no Bes H, known), MX, (X= F, CI, Br, I), MSO, M2NO,, MCO, &c. The only compounds which have been gasified are Beci, and BeBrz.

The oxides MO may be prepared by direct combination of metal with oxygen, or by decomposing the hydroxides (MO,H) by heat (BaO,H, is not decomposed by heat alone). The hydroxides MO,, where M=Ca, Sr, or Ba, are obtained by combining water with the oxides Mo, or by precipitating solutions of salts of Mby potash or soda. Beryllium hydroxide, Beo H., is prepared by precipitating an aqueous solution of a salt of Be by NH Aq, and drying at about. 100°. The peroxides MO, (M =Ca, Sr, or Ba) are produced by interactions between HO Aq and solutions of salts of M; the compounds MO,. «H,0 thus obtained lose water when dried, when M = Ba the drying is conducted over sulphuric acid in vacuo, when M = Sr the hydrated peroxide is dried at 100°, and when M = Ca the temperature is raised to 130°. Bao, is also obtained by heating BaO in oxygen at about 200°; the other oxides MO do not directly combine with oxygen.

The oxides CaO, Sro, and BaO are somewhat soluble in water; the solubility increases from Cao to Bao. The solutions are alkaline towards litmus paper; they interact with acids to produce salts and water; they precipitate hydrates of iron, copper, manganese, and many other heavy metals, from solutions of salts of these metals; they absorb and combine with carbon dioxide. These oxides combine with water forming hydroxides which are very stable compounds. Beryllium oxide, Beo, is insoluble in water; it does not directly combine with water. This oxide has no alkaline properties; it interacts with acids to form salts and water. None of these oxides, except Beo, is easily reduced, e.g. by heating with C, or in H or CO.

The hydroxides MO H, where M = Ca, Sr, or Ba, are fairly soluble in water; the solubility increases as the atomic weight of M increases; CaO, H, is decomposed by heat (to CaO +H,0) at 300°—400°; Sro,H, at a higher temperature; BaO,H, is not decomposed even at a full red heat. These hydroxides do not interact with solutions of the alkalis (potash, soda, ammonia). They form compounds with water (hydrates); the most marked of these hydrates have the composition

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