7. ..Ifitriats of lead. Born-lead, or murio-earbonate.—This ore has a pale yellow color, is reducible to metallic lead by the agency of soda, and is not altered by the hydrosnlphurets. At the blow pipe it melts first into a pale yellow trans parent globule, with salt of phosphorus and oxide of copper; and it manifests the presence of muriatic acid by a bluish flame. It is fragile, tender, softer than carbonate of lead, and is sometimes almost colorless, with an adamantine lustre. Spec. gray., 606. Its constituents, ac cording to Berzelius, are lead, 25.84; oxide of lead, 57.07 ; carbonate of lead, 6.25; chlorine, 8'84. silica, 1.46; water, 0.54; in 100 parts. The carbonate is an accidental ingredient, not being in equiv alent proportion. Klaproth found chlo rine, 13-67; lead, 39.98 ; oxide of lead, 22•57 ; carbonate of lead, 23.78.
8. Arseniate of lead.—lts color of a pretty pure yellow, bordering slightly on the greenish, and its property of exhaling by the joint action of fire and charcoal a very distinct arsenical odor, are the only characters which distinguish this ore from the phosphate of lead. The form of the arsemate of lead, when it is crystal lized, is a prism with six faces, of the same dimensions as that of phosphate of lead. When pure, it is reducible upon charcoal, before the blowpipe, into metallic lead, with the copious exhala tion of arsenical fumes. Its spec. gray. is 5.05. It consists of oxide of lead, 77.5; arsenic acid, 12.5 ; phosphoric acid, 7.5; hydrochloric acid, 1.5.
9. liolybate of lead, or yellow lead, is found at Southampton, Mass. It occurs in obtuse octohedrons and tabular crys tals. Spec. gray. 5-05. It consists of oxide of lead, 38 molybdie acid, and 2.08 oxide of iron.
The foregoing are the most common ores of lead, all of which, except the chro mate and molybdate, are used to procure metallic lead. It is, however, from the sulphuret (galena) that the great bulk of the lead of commerce is obtained. Under the article ifetallurgy the treatment of lead ores is noticed, and it may therefore be here merely stated that the chief object to attain, after having procured a clean ore, is to get rid of the sulphur—which may be accomplished either by roasting in the open air or in reverberating furna ces. In this way the sulphur is volatiliz ed, and the lead, either as oxide or re duced to the state of metal, runs into the basin or crucible of the furnace when it is deoxidized by being kept in contact with ignited charcoal. In Germany and
France another mode is adopted, which consists in throwing into the reverberat ing furnace 28 per cent. of old iron. In a short time the sulphur leaves the lead and passes over to the iron, and the lead is in the state of pure metal in the bot tom of the furnace. This plan saves time and labor, but the iron is lost. Its value, however, is trifling.
The uses of lead and its oxides arc very numerous : the latter as paints, chiefly, and the former in roofing, and as gutters, cisterns, and pipes. For these this me tal has many advantages ; it is soft and malleable, so that two edges may be fold ed over and hammered water-tight with out soldering • this prevents rupture from expansion, which often occurs in solder ed vessels. As a means of carrying wa ter it is in constant use, though liable to many objections. The metal, when pure, is perfectly insoluble in water, hut the oxide and carbonate of lead are soluble in water containing an excess of carbonic acid. When water runs through a lead pipe it oxidizes it in a very short time, forming a white or yellow crust on the inside. This dissolves to a small extent in the water, and this latter, when drank, produces all the symptoms of poisoning by lead. On this account, lead pipes have been superseded by iron, zinc, gutta per cha, and glass pipes. Dr. Christison has shown, that the purer the water, that is the more pure it is from saline matters, the greater is the corrosion of the pipe and the amount of lead dissolved : but that if the water contain much saline mat ter, especially sulphates, the lead is pre cipitated out of the water and no injury can arise. He recommended that new leaden pipes should be plugged up for a few days with a solution of sulphate of soda or phosphate of soda until the whole inside of the pipe was coated with a crust of sulphate or phosphate of lead, which effectually protects the pipe from any further action. If this cannot be conve niently done, a zinc cistern may be used to receive the water which has flowed through the pipe : after having lain a few hours, the lead present iu the water will be thrown down as a dark powder on the surface of the zinc. Should this plan not be adopted, the water should be allowed to run freely through the pipes for two days before it be applied to any domet.tie purpose. Vessels of lead should never be used for culinary or dairy purposes. Lead is used for making shot and solder. It forms an imperfect alloy with copper.