The lead that lines the Chinese tea-boxes, is reduced to a degree of thinness, to which European plumbers cannot, it is said, approach. The following account of the process by which these plates are formed, was communicated to a writer in the Gentleman's by an intelligent mate of an East-Indiaman : The caster sits by a pot, containing the melted metal, and has two large stones, the lower one fixed, and the upper moveable, having their surfaces of contact ground to each other, directly before him. Ile raises the upper stone by pressing his foot upon its side, and with an iron ladle pours into the opening a proper quantity of the fluid metal. He then lets fall the upper stone, and thus forms the lead into an extremely thin irregular plate, which is afterwards cut into a proper shape.
Cast sheet lead, used for architectural purposes, is techni cally divided into lead of 51b. 541b• 61h. 62,1b. 71b. Sib. and Sp). by which is understood that every superficial foot is to contain those respective weights, according to the price agreed upon.
The milled lead used by plumbers is very thin, seldom containing more than 41b. to the foot. It is by no means adapted to gutters or terraces, nor indeed to any part of a building that is much exposed either to great wear, or to the effects of the sun's rays : in the former case it soon wears away ; in the latter it expands and cracks. It is laminated in sheets of about the same size as those of cast lead, by means of a roller, or flatting-mill.
To cast pipes without soldering, a kind of mill, furnished with arms, or levers, to turn it by, is used. The moulds, which are of brass, consist of two pieces, which open and shut by hooks and hinges; their inward calibre, or diameter, being according to the size of the intended pipe, and usually about two feet and a half in length. In the middle is a core, or round piece of brass, or iron, rather longer than the mould, and of the thickness of the proposed inward diameter of the pipe. This core passes through two copper rundles, one at each end of the mould, which they serve to close ; and to this is joined a small copper tube, about two inches long. of the intended thickness of the leaden pipe. These small tubes retain the core in the centre of the cavity of the mould. The core being in the mould, with the rundles at its two ends, and the lead melted in the furnace, the metal is taken up in a ladle and poured into the mould through a small aperture, in the shape of a funnel, at one end. When the mould is full, a hook is passed into the end of the core, which, by turning the mill, is drawn out ; the mould is then opened, and the pipe itself is taken away. if it be desired to have the pipe lengthened, one end of it is put in the lower part of the mould, with the extremity of the core passed into it : the mould is then shut, and the upper rundle and tube applied as before ; the pipe serving for rundle and tube at the other end. Fresh metal is then poured in, which unites itself with the former length of pipe ; and the operation being repeated, a pipe of any required length may be obtained.
Pipes are made of sheet-lead, by beating it round wooden cylinders of the length and thickness required ; and then soldering up the edges.
Both these methods are now superseded, by the use of a machine, worked by steam, which produces a much neater article, of almost any length, and at considerably less expense.
Solder is used by plumbers to secure the joints of lead work, where other means would be improper, or impossible.
It is a rule, that solder should be easier of fusion than the metal intended to be soldered ; and that it should be as nearly as possible of the same colour. The plumber, therefore, uses what is technically called soft solder, which is a compound of equal parts of tin and lead, fused together, and run into moulds, not much unlike, in shape, to a gridiron : in which state it is sold to the manufacturer by the pound. In the operation of soldering, the surfaces, or edges, intended to be united are scraped very clean, and brought close up to each other, in which state they are secured by an assistant, while the plumber lays a little resin, or borax, upon the joint, to prevent an oxidation of the metal. The heated solder is then brought in a ladle and poured on the joint, after which it is smoothed and finished, by rubbing it about with a red-hot grozing iron ; and, when completed, it is made smooth by tiling.
For the method of laying embossed figures upon a leaden ground, see the article LEAD.
In covering terraces, or flats, with sheet-lead, a bottom, as level as possible, should be first laid of plaster, or of boards; if the latter, they should be of sufficient substance to prevent their warping, or flying upwards ; for if this be not attended to, the lead w ill soon become unsightly, and be liable to crack. As the sheets of lead never exceed in their breadth above six feet, it becomes necessary, in covering large surfaces, to have joints, are managed several ways; but, in all, the main object is to have them Nv te r- t ig t . The preferable mode is by forming laps or roll-joints, which is done by having a roll, or strip of wood, about two inches square, but rounded on its upper side, nailed under the joint of the sheets, where the edges lap over each other ; one of these edges is to be dressed up over the roll on the inside, and the other is to be dressed over them both on the outside, by which means the water is prevented from penetrating. No other thstening is required than what is acquired from the ham mering of the sheets together down upon t he flat; nor should any other be resorted to, where sheet-lead is exposed to the vicissitudes of the weather, because they occasion it to expand and shrink, which, if prevented by too much tiistening, would cause it to crack, and be quickly good for nothing but the melting-pot. Circumstances sometimes occur, that pre clude the use of rolls, and then the method by seams is resorted to : this consists in simply bending the approximate edges of the lead, up and again over each other, and then dressing them down close to the flat, throughout their length. But this is not equal to the roll, either for neatness or security. Soldering is also sometimes had recourse to, for securing the joints; but this is not to be recommended, as lead so fixed will be sure to leak after an exposure to the sunshine of a single summer. Leaden flats and gutters should be always laid with a current, to keep them dry. A fidl from back to front, or in the direction of the length of the sheet, is the general rule. A quarter of an inch to the foot run is a sufficient inclination : but the fall, or current, as it is called, is generally agreed upon between the carpenter and plumber, while the former is preparing the ground, or platform, on which the lead it to be laid.