Lead nitrate, Pb(NO3)2, is obtained by dissolving the metal or oxide in aqueous nitric acid; it forms white crystals, not easily soluble in cold water, readily in hot water and almost insoluble in strong nitric acid. It was mentioned by Libavius, who named it calx plumb dulcis. It is decomposed by heat into oxide, nitrogen peroxide and oxygen ; and is used for the manufacture of fusees and other deflagrating compounds, and also for preparing mor dants in the dyeing and calico-printing industries. Basic nitrates, e.g., etc., have been described.
Lead Phosphates.—The normal orthophosphate, is a white precipitate obtained by adding sodium phosphate to lead acetate ; the acid phosphate, is produced by precipitating a boiling solution of lead nitrate with phosphoric acid ; the pyro phosphate and meta-phosphate are similar white precipitates.
Lead Borates.—By fusing litharge with boron trioxide, glasses of a composition varying with the proportions of the mixture are obtained, e.g., Pb2B6011,4H20 ; , PbB407,41120; some of these are used in the manufacture of glass.
Lead silicates are obtained as glasses by fusing litharge with silica; they play a considerable part in the manufacture of the lead glasses (see GLASS).
Lead chromate, is prepared industrially as a yellow pigment, chrome yellow, by precipitating sugar of lead solution with potassium bichromate. The beautiful yellow precipitate is little soluble in dilute nitric acid, but soluble in caustic potash. The vermilion-like pigment which occurs in commerce as "chrome red" is a basic chromate, prepared by treating recently precipitated normal chromate with a properly adjusted propor tion of caustic soda, or by boiling it with potassium chromate. Several other basic chromates of varying shades are known.
Lead acetate, (called "sugar" of lead, on account of its sweetish taste), is manufactured by dissolving massicot in aqueous acetic acid. It forms colourless transparent crystals, soluble in one and a half parts of cold water and in eight parts of alcohol. On exposure to ordinary air they become opaque through absorption of carbonic acid, and form a crust of basic carbonate. An aqueous solution readily dissolves lead oxide, with formation of a strongly alkaline solution containing basic acetates (Acetum Plumbi or Saturni). When carbon dioxide is passed into
this solution the whole of the added oxide, and even part of the oxide of the normal salt, is precipitated as a basic carbonate chemically similar, but not quite equivalent as a pigment, to white lead.
Analysis.—When mixed with sodium carbonate and heated on charcoal in the reducing flame lead salts yield malleable globules of metal and a yellow oxide-ring. Solutions of lead salts (colour less in the absence of coloured acids) are characterized by their behaviour to hydrochloric acid, sulphuric acid and potassium chromate. But the most delicate precipitant for lead is sul phuretted hydrogen, which produces a black preiipitate of lead sulphide, insoluble in cold dilute nitric acid, less so in cold hydro chloric, and easily decomposed by hot hydrochloric acid with formation of the characteristic chloride.