CHAPTER III.
SIMPLE COMPOUNDS.UNDER the designation simple compounds are included all compounds con-
taining but two elements, with the exception, however, of the persulphides,
peroxides, polyhalides, etc., which are considered to have complex cations
(Chap. IV). The metal hydroxides and cyanides, in which the radicals OH
and CN behave as single elements, are also classed as simple compounds.
METHODS OF PREPARATION. Simple compounds are prepared:
(1) Synthetically from the elements:
Br 2 + H 2 = 2 HBr (No. 35a).
Cf. also Cerium Hydride (No. 32); Fel 2 (No. 39); FeCl 3 (No. 42); CrCl 3 (No. 44);
S 2 C1 2 (No. 45); PC1 3 (No. 46); Bil 3 (No. 48); BiBr 3 (No. 49); SnCl 4 (No. 50);
SiCl 4 (No. 51); PjS, (No. 54); HgS (No. 55); Mg 3 N 2 (No. 61); Mg 3 P 2 (No. 63).
Frequently the synthetic preparation of compounds between two elements
takes place in stages:
P + 3 Cl = PCI,,
PC1 3 + 2 Cl = PC1 5. (No. 46)
Cf. also SO 3 (No. 28); SbCl 5 (No. 47); SnS 2 (No. 56).
(2) By the interaction of two substances, each containing one of the ele-
ments which are to be combined:
(a) By the action of an element upon a compound:
Fe + 2 HC1 = FeCl 2 + H 2. (No. 43)
Cf. also A1C1, (No. 43).
(6) By the chemical reaction between two compounds (double decomposi-
tion or metathesis), as, for example, in the precipitation of a sulphide from the
solution of a metallic salt by means of hydrogen sulphide:
CuCl 2 + H^ = CuS + 2 HC1.
Cf. MnS (No. 57); TiS 2 (No. 58); CrN (No. 62); and BrH (No. 35b).
(3) By the breaking down of more complicated compounds:
2 HNO 3 = H 2 O + N 2 O 4 + O (No. 29)
Cf. also Cr 2 O 3 (No. 30); Cu 2 O (No. 31); copper hydride (No. 33); cyanogen
(No. 59); BaS (No. 87).
Certain simple compounds which were formerly prepared by double decom-
position, or by the breaking down of more complicated compounds, are now
most advantageously obtained directly from the elements, even industrially;
both because the requisite conditions for their formation are now better
understood and because some elements are far more accessible than formerly.
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