The chemistry of the materials of engineering by Sexton A

Author:Sexton, A[lexander] Humboldt. [from old catalog]
Language: eng
Format: epub
Tags: Building materials, Chemistry, Technical
Publisher: Manchester, Technical publishing company, limited; [etc., etc.]
Published: 1900-03-25T05:00:00+00:00

often contains small quantities of antimony, copper, zinc, and other metals, which interfere with its ductility or make it hard, and when it has been desilvered by the zinc process there is a considerable amount of zinc left. To remove these impurities the lead is softened. From 10 to 50 tons is melted in a large reverberatory furnace, and kept melted and exposed to the air for many hours, with frequent stirring. The metals present are mostly more oxidisable than the lead. They therefore oxidise more rapidly, and pass into the scam with a considerable quantity of oxide of lead. This is skimmed off from time to time, and the process is continued till the lead is quite soft.

Commercial Lead, —Commercial lead is cast in " pigs," each weighing about 1 cwt. It is usually very pure, and rarely contains any constituents which injure its quality. Impurities are easily removed, and most, if left, would interfere more with the manufacture than the use of the metal. The presence of a minute trace of zinc renders the metal less powerfully resisting to the action of the acid. Chemical lead— i.e,j lead for making sulphuric acid chambers—is always desilverised by the Pattinson process.

Uses of Lead. —Lead is largely used in the form of sheet for roofing and other purposes, its power of resisting atmospheric corrosion rendering it valuable. It is also largely used for acid chambers and other appliances in chemical works, on account of its power of resisting acids, and for gas and water pipes. A lead sheet lin. in thickness weighs about 6 lb. per square foot.

Litharge (PbO) has mauy uses in the arts. Ked lead (Pb304) is used as a pigment, and white lead (PbCOsPbO, OH2) is used for the same purpose, and as a base for paints.

Tin.

Tin is not much used by the engineer. Physical Properties. —Tin is nearly silver white in colour, and has a bright metallic lustre. It is malleable, and can be

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