LEAD. This very useful metal has a blueish gray colour, and considerable brilliancy when fresh surfaces are formed by cutting. if it has not been cooled too rapidly, it is so soft that, even when in pieces of considerable thickness, it may be easily bent. It soils slightly, and leaves on paper or cloth a mark after friction resembling that of plumbago. Its specific gravity is 11.4. Lead may be reduced to thin laminae; but its tenacity is extremely slight, so that a wire about -hth of an inch in diameter breaks with a weight of 30 pounds. It fuses at about 612°, and crys tallises when slowly cooled. It is not a volatile metal, for in close vessels it may be heated to whiteness without subliming. When exposed to the air, it absorbs oxygen and carbonic acid slowly, and acquires a superficial coating of carbonate of lead. If it be exposed to air and water, it is oxidised and converted into carbo nate of lead with considerable rapidity ; this carbonate has the appearance of minute shining brilliant scales. Though at common tempe ratures lead is slowly acted upon by the oxy gen of the air, it is readily oxidised when the beat is raised.
The ores of lead, strictly speaking, are few in number. Indeed the only one which can properly be considered as a working ore is the Sulphuret, or Galena. This almost uni
versally diffused ore occurs in attached crystals and massive. The crystals are opaque and leaden gray. The massive varieties have a granular structure. By the blowpipe on charcoal the sulphur is first dissipated, and then metallic lead is obtained. In Cornwall and Scotland the veins of this ore traverse primary rocks ; in Derbyshire it occurs in veins or beds in transition rocks. It very commonly contains a considerable portion of silver. There are many minerals in which lead forms a component ingredient, but most of the lead of commerce is procured from the sulphuret.
Lead forms many useful substances in com bination with other bodies. Protoxide of lead is massicot, and the dentoxide is Minium, both used as colours. Oxychloride of lead forms patent yellow. Carbonate of lead forms White Lead. Acetate of lead is Sugar of Lead. Di-acetate of lead forms Goulard's Extract. Chromate of lead is a beautiful yellow pig ment. The manufacture of RED LEAD and WHITE LEAD will be noticed in separate articles.
Of the alloys of lead, three are of some importance. Alloyed with antimony, lead forms Type.metal. Pewter consists of about 80 parts tin and 20 lead. Equal parts of tin and lead form Plumber's Solder.