The very thin sheet-lead, with which the tea-chests from China are lined, is made, accordin to common report, in the following manner :—A man sits upon a floor with ae flat stone him, and another movable one at his side on a stand ; his fellow-workman stands beside him with a vessel full of melted lead, and having poured out a certain quantity on the large flat atone upon the floor, the other immediately lifts the movable stone, and dashing it on the fluid lead, presses it out into a fiat and very thin plate ; the stone and lead are then quickly removed, and the operation renewed, which is in quick succession. The rough edges are afterwards cut oft soldered together for use.
The Tinning of Sheet-Lead may be effected in two ways. lira, place the sheet of lead upon a hot stove, until it acquires sufficient heat to keep melted tin poured upon it in a fluid state; then throw a little powdered resin over the sheet, and when it has melted, with a greasy rag rub the tin and resin over the sheet of lead until it is completely covered with the tin ; after which, wipe off the superfluous matter.. Secondly, the tin in the cold state, and in small quantities at a time, may be laid on the plate of lead, carefully to fuse the tin, (but not more so,) and by the help of resin and similar manipulation to the first-mentioned plan, the lead may be perfectly coated.
Lead Pipe.---The next article of importance in the lead manufacture is pipe or tubing. There have been various modes of producing it : the original mode, from some specimens of very old pipe that we have seen, appears to have been the wrapping of a strip of sheet lead, with parallel aides, round a cylinder, so as to make their edges meet, and then unite them with solder. The speci mens alluded to present phenomena worthy of notice in this place : the lead was full of holes, and was corroded more or less in every part, except at the seam, which the solder had entirely protected; and the solder itself was as sound and perfect as when it first left the plumber's hands.
Another mode of making lead-pipe, which probably succeeded the foregoing, and is still practised by some plumbers, is the following :—An iron mould is provided, which is divided into halves, and forms, when put together, a hollow cylinder of the external diameter of the extended pipe ; in this cylinder is put an iron rod or cord, extending from the top to the bottom, and leaving all round a space between it and the cylinder of the intended thickness of the pipe. The lead is poured in at a spout, formed by two corresponding notches cut in each half of the mould, and a similar hole is made at another place for the escape of air. The mould is fastened down upon a bench, upon which, at one end, and in a line with its centre, is a rack moved with toothed wheels and pinions. When the pipe is cast, a hook at the end of the rack is put into an eye at the end of the iron core, which, by the action of cog-wheels and pinions, is drawn so far out that about two inches of it only remain in the end of the the two halves of the mould, which fasten together by wedges or screws, are now separated from the pipes, and are fastened upon the iron core, and the two inches of lead-pipe attached to it. Melted lead is now again poured into the mould, when the fluid lead unites with the end of the first piece of pipe ; and this process being continued, pipe of any required length may be made.
A third method, which was patented in 1790 by the great iron master, John Wilkinson, consists in casting a very thick pipe in a mould, having a cylindrical Fore of the same diameter as the intended pipe, and then inserting a polished iron mandril up the bore of the pipe, in which it is to be successively passed tkugh a series of round grooves, precisely in the same manner as has been described under our article how, for making round bars. Every time that the pipe is passed through, the lead is compressed upon the mandril, consequently in its thickness, but extended in length, while the internal bore remains unaltered, except the improvement it derives from condensation of the metal against the polished mandril.
A fourth method is mentioned in Mr.Wilkinson's specification, which, since the expiration of the patent, has been, and is still practised with unimportant varia tions by all the considerable manufacturers of lead pipe : it consists as follows:— Very thick short pieces of pipe are cast, similar to those described in the pre ceding method ; the external diameter may be two or three times that of the intended pipes, but the internal the same. The central hole for the mandril or triblet does not extend the entire length of the pipe, but terminates with a much smaller hole at the extremity ; a stop to the triblet is thus formed, which is employed in the succeeding operation, which is that of drawing the lead pipe through a hole precisely in the same manner as wire is drawn. The triblet or polished mandril is of somewhat greater length than the pipe intended to be manufactured by it, which is comnionly from nine to twelve feet. Through the small hole of the cast-lead pipe is then passed a screw, which is screwed into the end of the triblet, that abuts against the shoulder; and it is by this con nexion with the triblet that the lead pipe is drawn successively through a series of separate steel plates, each having a different sized hole, and which are suc deposited in solid recesses made in very firm bearings, and are ex for smaller after the pipe has passed through the larger one. The table or draw bench on which the operation is conducted is usually about 30 feet in length ; it is provided with a strong endless hitch-chain passing around chain wheels at the ends of the bench, to one of which the power is communi cated. The screw fastened to the end of the triblet passes through the draw hole, and is then secured by a hook and eye, or other fastening, to the endless chain ; the machinery being then thrown into gear by the ordinary means, the chain drags the lead through the steel hole, by which its dimensions are reduced, and its length increased. The motion of the chain is now reversed, either by machinery connected with the power, or the chain is thrown out of gear with the power, when the chain can usually be drawn back by hand, and the draw plate changed ; when, by throwing into gear again, the work is renewed, and so continued until reduced to the required dimensions ; a small piece of each end of the pipe being cut off it is finished.