Minium, or Red Lead, 2PbO, PbO2; specific gravity, 9·08, is a compound of protoxide of lead with the dioxide. It is of a brilliant red colour, much used in the arts, and especially in the preparation of flint-glass.
§ 773. Sulphide of Lead, PbS = 239; Pb, 86·61 per cent., S, 13·39 per cent., occurring in the usual way, is a black precipitate insoluble in water, dilute acids, alkalies, and alkaline sulphides. It dissolves in strong nitric acid with separation of sulphur, and in strong hydrochloric acid, with evolution of SH2. Fuming nitric acid does not separate sulphur, but converts the sulphide into sulphate.
§ 774. Sulphate of Lead, PbSO4 = 303; specific gravity, 6·3; PbO, 73·61 per cent., SO3, 26·39 per cent., when produced artificially is a heavy white powder, of great insolubility in water, 22,800 parts of cold water dissolving only one of lead sulphate; and if the water contains sulphuric acid, no less than 36,500 parts of water are required. The salts of ammonia (especially the acetate and tartrate) dissolve the sulphate, and it is also soluble in hyposulphite of soda. The sulphate can be readily changed into the carbonate of lead, by boiling it with solutions of the alkaline carbonates. The sulphate of lead, fused with cyanide of potassium, yields metallic lead; it may be also reduced on charcoal, and alone it may be fused without decomposition, provided reducing gases are excluded.
§ 775. Acetate of Lead, Sugar of Lead, Pb(C2H3O2)23OH2 = 379, is found in commerce in white, spongy masses composed of acicular crystals. It may, however, be obtained in flat four-sided prisms. It has a sweet metallic taste, is soluble in water, and responds to the usual tests for lead. The P.B. directs that 38 grains dissolved in water require, for complete precipitation, 200 grain measures of the volumetric solution of oxalic acid, corresponding to 22·3 grains of oxide of lead.
§ 776. Chloride of Lead, PbCl2 = 278; specific gravity, 5·8; Pb, 74·48 per cent., Cl, 25·52 per cent., is in the form of brilliant crystalline needles. It is very insoluble in cold water containing hydrochloric or nitric acids. According to Bischof, 1635 parts of water containing nitric acid dissolve one part only of chloride of lead. It is insoluble in absolute alcohol, and sparingly in alcohol of 70 to 80 per cent. It fuses below red heat without losing weight; at higher temperatures it may be decomposed.
Carbonate of Lead.—The commercial carbonate of lead (according to the exhaustive researches of Wigner and Harland[821]) is composed of a mixture of neutral carbonate of lead and hydrate of lead, the best mixture being 25 per cent. of hydrate, corresponding to an actual percentage of 12·3 per cent. carbonic acid. The nearer the mixture approximates to this composition the better the paint; whilst samples containing as much as 16·33 per cent., or as little as 10·39 per cent., of CO2 are practically useless.
[821] “On the Composition of Commercial Samples of White Lead,” by G. W. Wigner and R. H. Harland.—Analyst, 1877, p. 208.