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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.

The molecular weights of these elements are unknown.

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General formulae and chemical characters of compounds. (M = Be, Ca, Sr, or Ba). MO, MO,H,,MO, (no BeO, known), MS, MSH, (no BeS H, known), MX,(X=F, Cl, Br, I), MSO, M2NO, MCO,, &c. The only compounds which have been gasified are BeCI, and BeBr

The oxides MO may be prepared by direct combination of metal with oxygen, or by decomposing the hydroxides (MOH) by heat (BaOH, is not decomposed by heat alone). The hydroxides MOH, where M-Ca, Sr, or Ba, are obtained by combining water with the oxides MO, or by precipitating solutions of salts of M by potash or soda. Beryllium hydroxide, BeOH,, 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. HO 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.

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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.

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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,O) at 300°-400°; SrO,H, at a higher temperature; BaOH 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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MO2H,.8H2O. Beryllium hydroxide, BeO,H,, is easily changed by heat to BeO+ H2O; it is insoluble in water and has not an alkaline reaction towards litmus. When freshly precipitated this hydroxide dissolves in KOHAq or NaOHAq, but is reprecipitated on heating. The freshly precipitated hydroxide also dissolves in (NH),CO,Aq and K,CO2Aq; by boiling the solution in (NH),COAq a basic carbonate of beryllium is precipitated. BeOH, forms a number of hydrates the compositions of which vary with small variations in the conditions under which they are prepared; they are all readily decomposed by heat.

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The peroxides MO, (M = Ca, Sr, Ba) shew no alkaline reaction towards litmus; they are insoluble in water, but all form compounds (hydrates) with water. They are all decomposed by heat to MO+O; BaO, is the most stable towards heat. No peroxide of beryllium has been obtained.

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The oxides and hydroxides are all white solids; BeOH, is much more gelatinous than the other hydroxides. The specific gravities of the oxides MO are, approximately, 3.08 for BeO, 3·15 for CaO, 4·5 for SrO, and 5.4 for BaO; of the hydroxides MO,H,, 2.08 for CaO,H,, 3.62 for SrO,H,, and 4.49 for BaO H The heats of formation of these oxides and hydroxides, in aqueous solutions, from calcium to barium, increase as the atomic weights of the metals increase.

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The sulphides CaS, SrS, and BaS are prepared (1) by 399 heating the oxides MO in a stream of carbon disulphide mixed with carbon dioxide, (2) by heating a mixture of the sulphates MSO, with charcoal; MSO+ 4C = MS + 4CO.

The hydrosulphides MSH, are usually obtained by reactions between the hydroxides, generally in aqueous solution, and sulphuretted hydrogen; thus

MOH ̧ + 2H ̧S = MSH ̧ + 2H ̧O.

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These compounds are also formed when the sulphides MS interact with a little water;

2MS + 2H2O = MS ̧H ̧+ MO2H ̧.

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The sulphides and hydrosulphides are white, or yellowish white, solids; they are more easily decomposed by heat, and by interaction with water, than the corresponding oxygen compounds. Besides the compounds MS and MS,H the following sulphides are known :-CaS, CaS,, SrS, BaS,, BaS. H2O.