LEAD MANUFACTURE. Lead was known to and used by the Greeks and Romans for various purposes. Among others it was employed for pipes to convey water, just as it is now. The lead-mines of this island were worked by the Romans. The chief of them are in Cornwall, Devonshire, Somersetshire, Derbyshire, Durham, Lancashire, Cumberland, Westmoreland, Shropshire, Flintshire, Den bighshire, Merionethshire, and Montgomery shire ; in Scotland, in Dumfriesshire, Lanark shire, Ayrshire, and Argyleshire. Lead is also found in Ireland, in the counties of Armagh, Wexford, Wicklow, Waterford, Clare, and Down.
The ore of lead, when extracted from the mine, is called Galena, and is combined with various earthy matters. The first processes subsequent to its extraction are those of crushing or pounding and washing the ore. The ore is then smelted, sometimes in a com mon smelting furnace and sometimes in a reverberatory furnace; and the melted metal is allowed to run into a large iron pan, from which it is ladled into cast-iron moulds. It then constitutes what is called Pig-Lead. In this state lead always contains more or less of silver. The proportion is sometimes ex ceedingly minute, varying from 1 to 30 ounces in a ton of lead. The extraction of the silver is always performed when it exists in a proportion sufficient to pay the expense of the process, which varies in different localities according to the cost of fuel. The process of extraction, which is called refining, depends upon the well known circumstance, that lead, when heated to redness, absorbs a large por tion of oxygen from the air, and is converted into an oxide ; while silver does not undergo any such change, but retains its metallic form at almost any temperature. Mr. Pattinson, of Newcastle, has introduced an improved process, in which the crystallising properties of melted lead are brought into requisition.
The most extensive use of lead is in the forms of sheets and pipes. To make sheet lead, the pigs are brought to a state of fusion in a large pot or cistern, near which is placed the table on which the sheet is to be cast. This table, which is usually from 18 to 20 feet long and 6 feet wide, is made either of wood or cast iron. The wooden table has its
surface protected by a layer of fine sand, which is wetted and spread evenly and firmly, over it before the melted lead is poured on. To prevent the lead from running over the sides, a ledge is provided, two or three inches thick, and two inches high, which forms the margin of the table. An instrument called a strike is also provided to regulate the thick ness of the sheet, and to spread tho melted metal evenly over the table. In casting the sheet the fused metal is taken from the cistern with an iron ladle, and put into a triangidar shaped iron shovel or peel, placed at the head of the table, which peel being raised so as to pour out the lead upon the table, the strike is brought into use to spread it evenly over the whole surface : the surplus, if any, falling into a vessel placed for its reception at the foot of the table. A sheet of lead weighs 9 cwts., so that its length and breadth will be greater in proportion to the diminution of its thickness. The thickness of sheets of lead is frequently reduced by means of heavy rollers worked by steam power. Rolled sheet-lead is made by the repeated compression, between steel rollers, of a block of lead several inches in thick ness.
Lead pipes are sometimes made, when great exactness of shape is not required, by bend ing a length of sheet lead of the necessary width over a mandril, and soldering the edges together ; but the more usual method of ma nufacture is by casting and drawing. The casting-box employed is an iron cylinder made in two parts, and put together longitudinally with flanges ; inside of this cylinder is placed an iron rod or core, which is so fixed as to be concentric to the cylinder, without touching it ; a space is thus left, into which the melted lead is poured. When this is set, the core is removed, and the cylinder opened, so as to withdraw the pipe, which is much thicker than is needed, and must be lengthened, while its substance is reduced, by drawing it through a succession of holes in steel plates, dimi nishing gradually in diameter. The making of lead shot is described elsewhere [Suor Kum