LEAD. This is one of the metals most anciently known, being mentioned in the books of Moses. It has a gray-blue color, with a bright metallic lustre when newly cut, but it becomes soon tarnished and earthy-looking in the air. Its texture is close, without perceptible cleavage or ap pearance of structure ; the specific gravity of common lead is 11352 ; but of the pure metal, from 1138 to 1144. It is very malleable and ductile, but soft and desti tute of elasticity ; fusible at 612° Fahr., by Crighton, at 634° by Kupfer, and crys tallizable on cooling, into octahedrons im planted into each other so as to form ar assemblage of four-sided pyramids. There are four oxides of lead. 1 The suboxide, of a grayish-blue cola!, which forms.a kind of crust upon a plate of lead long exposed to the air. It is procured in a perfect state by calcining oxalate of lead in a retort ; the dark gray powder which remains, is the pure sub oxide. 2. The protoxide is obtained by exposing melted lead to the atmosphere, or, more readily, by expelling the acid from the nitrate of lead by heat in a plati num crucible. It is yellow, and was at one time prepared as a pigment by cal cining lead, but is now superseded by the chromate of this metal. Litharge is mere ly this oxide in the form of small spangles, from having undergone fusion ; it is more or less contaminated with iron, copper, and sometimes a little silver. It contains likewise some carbonic acid. The above oxide consists of 104 of metal, and 8 of oxygen—its prime equivalent being 112, upon the hydrogen scale • and it is the base of all the salts of lead. 3. The plum beous suroxide of Berzelius, the sesqui oxide of some British chemists, is the well-known pigment called RED LEAD or minium. It consists of 100 parts of metal and 10 of oxygen. 4. The plumbic sur oxide of Berzelius, or the peroxide of the British chemists, is obtained by putting i red lead in chlorine water, or in dilute nitric acid. It is of a dark brown, almost black color, which gives out oxygen when heated, and becomes yellow oxide. It kindles sulphur when triturated with it.
This oxide is used by the analytical che mist to separate, by condensation, the sulphurous acid existing in a gaseous mixture.
Among the ores of lead some have a metallic aspect; are black in substance, as well as when pulverized; others have a stony appearance, and are variously colored, with usually a vitreous or greasy lustre. The specific gravity of the latter ores is always less than 5. The whole of them, excepting the chloride, become more or less speedily black, with sul phureted hydrogen or with hydrosul phurets ; and are easily reduced to the metallic state upon charcoal, with a flux of carbonate of soda. after they have been properly roasted. They diffuse a whitish or yellowish powder over the charcoal, which, according to the manner in which the flame of the blowpipe is directed upon it, becomes yellow or red ; thus in dicating the two characteristic colors of the oxides of lead.
The lead ores most interesting to the arts are 1. Galena, snlphuret of lead (See GA LENA.) This ore has the metallic lustre of lead with a crystalline structure deriv able from the cube. When heated cau tiously at the blowpipe it is decomposed, the sulphur flies off, and the lead is left alone in fusion ; but if the heat be con tinued, the colored surface of the char coal indicates the conversion of the lead into its oxides. Galena is a compound of lead and sulphur, in equivalent propor tions, and therefore consists, in 100 parts, of 861 of metal, and 131 of sulphur, with which numbers the analysis of the galena of Clausthal by Westrumb exactly agrees. Its specific gravity, when pure, is 7.56. Its color is blackish gray, without any shade of red, and its powder is black, characters which distinguish it from blend,e or sulphuret of zinc. Its structure in mass is lamellar, passing sometimes into the fibrous or granular', and even compact. It is brittle. The specular galena, so called from its brightly polish ed aspect, is remarkable for brightly the slickensides of Derbyshire—thin seams, which explode with a loud noise when accidentally scratched in the mine.