reach ducker than is needed, must be lengthened, while its sub stance is reduced, b' drawing It through a succession of holes in steel plate., diminishing gradually in diameter, similarly to the method Lead Apt is made by pouring the melted metal from a great height Into water. This process was invented in 178•2 by a workman named Watts, residing at Bristol; who is said to have conceived the idea in a dream, and to have proved its practicability by pouring some melted lead from the tower of the church of St. Mary lledcliffe at Bristol. ' Having secured the invention by a patent, he sold, it to parties possessed of adequate capital ; and the patent having long since expired, the process is now in COMM use. In order to give to the lead the quality of assuming • more perfectly globular form in cooling, the metal is previously alloyed with 2 per cent of arsenic, or with a small quantity of mercury, which latter is used in order to Obviate an objection caused by the poisonous quality of arsenic. Shot formed by granulation are made in a high tower, in the top of which the melting-room is built. Clime to the furnace placed a large colander or perforated plate, into which a portion (determined by experiment) of the scoria produced in melting the metal is placed ; after which the metal is ladled into it. Being somewhat deta:ncd by the scoria, the lead is partially cooled and divided into separate portions, which pass through the colander in the form of globules ; these globules follow in such rapid succession as to have the • ce, to a cursory observer, of a continued stream. The globules fall into • vessel of water placed on the lower floor of the tower. Near Newcastle, deserted coal-pits are used instead of lofty towers. At New York, lead abet are made in a building of moderate height, with a blast of air constantly rushing upwards; this quickens the cooling, and the shot are said to comprise a smaller number of defective globules. Under any system of manufacture, however, the shot are of various sizes, and a small proportion are Imperfect as regards sphericity. Having been per fectly dried by artificial heat, they are sorted according to their sizes by means of a series of sieves, the meshes of which have different degree. of fineness. A sieve having the smallest mesh is first used, that the smallest sized shot may pass through and be collected. What remain are transferred to the sieve next In fineness, to separate shot of of the second size, and so on in succession. The process of separating the imperfect shot is very simple. A shallow wooden tray is suspended by conic from the ceiling of the room, and into this a certain quantity of shot is put.. By raising one end of the tray, and giving it a motion from side to side, the shot roll about : such as are perfectly spherical finding their way off the tray into a reservoir placed at its lowest aide; while thou which are of imperfect form run against and are detained by the sides of the tray, so that they can be collected in a separate vessel after the perfect shot have all con off. A very delicately constructed machine is now used in some shot-works instead of this tray. The shot thus sorted ere then polished by putting about half • ton together into an iron barrel which that quantity will nearly fill. By menu of a rotary movement given to the barrel, the abet are made to rub against each other, and thus acquire a black colour and a lustrous appearance. The finished shot, varying from ith to of an inch in diameter, are finally tied up in bags.
Litkarge, Red-feud, and White-lead are compounds, the chemical nature of which hasbeen noticed in connection with the chemistry of load ; we treat here simply of • few manufacturing details. Litharge is produced in the act of cupellation for extracting the silver, already described. It is used in the making of flint-glass; and in preparing
certain malts of had which are employed In dyeing and calico-printing; or, when mixed with coal and heated in a furnace, it may be made to yield up Its metallic element, which is then called refined lead. Red lead, or minium, is made by the medium of a reverberatory furnace. The pigs of lead are melted in these furnaces,and while in a fluid state, the metal is raked and stirred 17 means of an apparatus suspended from • chain, and held by a workman. The stirring continues several hours, by which time the metal, through Imbibing oxygen, bas lost its fluidity, Its whitish colour, and its metallic, lustre, and has become a grayish-yellow powder. A birther proems separates a small portion of unchanged lead from the powder, which then becomes a yellow pigartait called messiest ; and this maasiout, by a Rearm] exposure to th reverberatory furnace, becomes converted into the still more useful pigment red lead. Waitslead forms the hula of nearly all the pigments used by the bowie-14%10er. It is very unwholesome, giving rise to a disease called the sezintcr's ea:e (l'amlues Colic], and attempts have frequently been made to aupeisecle it by other substances, but it still remains the staple article of the trade. It is a carbonate of lead, and is produced in various ways ; but the usual process in the Newcastle district is the,following. In a large square room ashes are laid on the floor; then a thick layer of tanners spent bark ; then a series of earthen lots, each containing about a pint of vinegar ; then a series of email plates of sheet-lead, covering the open mouths of the vinegar-pots ; then a layer of boards ; then a second layer of tan • then a second of vinegar-pots, covered by a second series of leaden plates—and so on : until a pile 20 or 30 feet high is built up. The room thus filled often contains 10,000 or 12,000 pots of vinegar, covered by three or four tons of lead ; and iu a Large factory there may ho ten or a dozen of auch rooms. The room is then closed, and is kept closed fur many weeks. The tan gives forth heat enough to induce chemical action, and an intricate series of decompositions and re-compositions follow. The result ie, that the lead combines with oxygen and carbonic acid to form a flaky white substance, which, after a few more processes, becomes white-lead—sold either as a dry earthy substance, or as a kind of thick paste ground up with linseed oil. The late Mr. I'attineon was among those who introduced substitutes for white-lead. One was an oxychloride, made from a solution of chloride of lead with a solution of lime, soda, or other alkali.
In the lead trade, the imports, which are only small, are almost wholly from Spain, the produce of exceedingly rich mines situated at Adra in Granada. The quantity furnished by these mines varies much ; their greater or less produce has a great influence upon the price of lead in every market of the world ; and at times has acted injuriously upon the mine-owners in this country. The home produce was about 78,000 tous of ore iu 1848, yielding 55,000 tone of lead; and 97,000 tons of ore in 1857, yielding 09,000 tons of lead—the ratio being about 70 per cent. of lead in the ore. England produces three fourthe of all the lead ore raised in the United Kingdom. At the prices of 1857, the lead was worth about 1,500,0001., besides the silver extracted from it. The Alston district, on the confine, of Northum berland and Durham, yielded'the largest return in 1S57 (17,000 tons); but Cornwall gave the richest per-centage of silver, averaging 37 ounces to the ton. The imports of lead (pig and sheet) in 1858, were about 14,000 tons. The exports in the same year were about 20,000 tons; besides 6000 tons of white lead, red lead, and litharge.