The method above described is only used in casting large sheets of lead; in casting sheets of smaller dimensions, the table or mould, which is placed in an inclined position, is, in lieu of sand, covered with a piece of woollen stuff, nailed down at both ends, and over that is placed a very fine linen cloth.

In this process great attention must be paid to the heat of the liquid metal, and a piece of paper is used as a test; if the paper take fire, the lead is too hot, and would destroy the linen; if it be not shrunk and scorched, it is not hot enough.

When the sheets are required to be very thin, it is necessary to make the peel and strike of one piece. It is a kind of wooden box without a bottom, being closed only on three sides; the back of it is about seven or eight inches high, and the two sides, like two acute angles, diminish to the top; the width of the middle makes that of the strike, which again makes that of the sheet to be cast.

The strike is so placed, that the highest part is towards the lower, and the two sloping sides towards the upper end of the table. The top part of the table, where the metal is poured in, is covered with a pasteboard, which serves as a bottom to the case, and prevents the linen from being burnt while the metal is pouring in.

The strike or peel being filled with lead, according to the intended size of the sheet, two men, one at each side, seize hold of it, and with greater or less velocity, as the sheet is to be more or less thick, force it down the inclined table; for the thickness of the sheet always depends upon the velocity with which the strike slides down the table. The sheet-lead, after casting, is frequently reduced by rollers.

As this particular department is so intimately connected with the business of a plumber, we shall not be considered as departing from the subject by inserting the following tables, from Hutton's Mensuration.

Plumber's work is commonly estimated by the pound or hundred weight; but the weight may be discovered by the measure of it, in the manner below stated. Sheet-lead used in roofing, guttering, &c. is commonly between seven and twelve pounds weight to the square foot; but the following table shows by inspection the particular weight of a square foot for each of several thicknesses.

In this table the thickness is set down in tenths and hundredths, &c. of an inch; and the annexed corresponding numbers are the weights in avoirdupois pounds and thousandth parts of a pound. So the weight of a square foot of

or of an inch thick is 5 pounds and %% of a pound; and the weight of a square foot to one-ninth of an inch thickness is 6 pounds and of a pound. Lead pipe of an inch bore is commonly 13 or 14 pounds to the yard in length.

EXAMPLES:

1. How much weighs the lead which is 39 feet 6 inches long, and 3 feet 3 inches broad, at 84 lbs. to the square foot?

2. What cost the covering and guttering of a roof with lead, at 188. per cwt.; the length of the roof being 43 feet, and the breadth or girth over it 32 feet, the guttering 57 feet long, and 2 feet wide; the former 9,831 lbs. and the latter 7,373 lbs. to the square foot ?-Answer, 1157. 9s. 14d

It is now time to direct our attention to the manufacture of lead pipes, which are universally employed for small water-pipes, from the facility of bending them in any direction, and soldering their joints.

Lead pipes are sometimes cast in an iron mould, made in two halves, forming, when put together, a hollow cylidner, of the size of the intended pipe; in this cylinder, or mould, is put an iron rod or core, 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 by 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 the cog-wheels and pinions, is drawn so far out, that about two inches of it only remain in the end of the pipe; 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 again poured into the mould, which, uniting with the end of the first piece, forms the pipe of considerable length; and the operation is repeated till it be of the length required.

Another and a much better method is, to cast the lead in an iron mould upon a cylindrical iron pipe, of a size proportioned to the bore of the pipe to be made, and leaving a space between the core and the mould three or four times the thickness of the intended pipe, and in short lengths, which are afterwards drawn through holes in pieces of steel, similar to the process of wire-drawing, till the pipe is reduced to the required thickness.

Another method is that for which the celebrated ironmanufacturer, Mr. John Wilkinson, of Brosely, took out a patent in 1790, and which, since the expiration of his patent, has been successfully practised by many other manufacturers. This method consists in casting a circular piece of lead, about eighteen inches long, with a core or hole longitudinally through its centre. This piece is of considerably larger diameter than that of the pipe intended to be made. The core or hole at one extremity suddenly decreases, so as to form on the internal surface of the piece of lead a stop or shoulder, against which a polished iron triblet or mandrel, which has been passed thus far along the core, rests. This triblet or mandrel is of somewhat greater length than the length required of the pipe to be manufactured, which, generally speaking, is from seven to nine feet. An iron screw, having a loop at the opposite end, is then passed down the other end of the core, and is screwed into that part of the mandrel which rests against the shoulder. In this state

the mandrel, with the circular piece of lead fixed fast on it, is taken to the drawing-table.

The drawing-table in the principle of its operation resembles the block described in the Wire Manufacture in every respect, though it is far more powerful. The table generally used is about thirty feet long, by two feet wide; having at one end a powerful cylinder with a chain attached to it. This cylinder receives motion from a steam-engine, or other first mover, and can be thrown in and out of geer by an adaptation of any one of the appropriate modes described under the article" Mill-geering.' About two-thirds the length of the bench from the cylinder, or roller, are two pins or stops to hold a steel plate, which has a gradation of conical holes. Through the largest of these holes, which is somewhat less than the diameter of the circular piece of lead, the loop that is screwed on to the end of the mandrel is passed, and attached to a hook at the extremity of the chain, which chain is affixed to the cylinder or roller. The cylinder being now thrown into geer, the piece of lead is drawn through the hole in the steel plate, which diminishes it in diameter, and increases it in length; and this operation is carried successively through the series of gradually decreasing holes in the draw-plate, until the pipe is reduced to the required diameter. The cylinder is now struck out of geer, and the mandrel liberated from the chain, which is immediately attached to the other end of it. The steel draw-plate being now removed, the stops against which it rested allow the mandrel to pass between them, but detain the lead pipe, which, consequently, by striking the cylinder into geer, allows the mandrel to be extricated from it. A small portion of pipe being cut off at both ends, the pipe is considered finished. Through the whole of the operation, great care is taken to keep the mandrel and steel plate well oiled.

As no acid can pass through lead pipe without becoming more or less affected by its deleterious qualities, it is necessary in cases where acids are used, to have pipes made of iron, or of lead lined with tin. To line lead pipe with tin, the lead pipe must be cast in a vertical mould, which has a core of somewhat larger diameter than the intended bore of the pipe passing down its centre. When the pipe is cast, and the metal is set, this mandrel is drawn out of the mould, and another of smaller diameter is substituted. About as much coarse resin as will lay on a shilling is now thrown into the space between the pipe and the core or mandrel just passed down the mould. This resin by the heat of the lead

is melted, and runs to the bottom of the mould. The melted tin being now poured in, the resin will float on its surface, and, consequently, as the tin rises, anoint the tin in every part, and act as a flux, and unite the two vessels. As soon as the tin is set, the last-mentioned mandrel is drawn out, and the external mould being removed, the lead now lined with tin is, when quite cold, ready to be submitted to the process of drawing. Various other equally simple processes are adapted to this purpose.

PAPER MANUFACTURE.

PAPER, that highly valuable substance, which enables us to communicate our thoughts to persons situate at the most distant quarters of the civilized globe, is manufactured from rags, by the aid of machinery.

It was formerly necessary to assort with great care the rags which were intended to be manufactured into paper; and none but the whitest and best, and which, consequently, were the most expensive, could be made into paper of the finest quality; but since the introduction of chlorine (which was discovered by Scheele) into our bleaching establishments, the necessity of this assortment has been greatly obviated; which as it was soon conceived that that chemical agency, was capable of bleaching linen, was also applicable to the whitening of the rag during the process of paper-making.

At that period of the process, when the rag is coming into a state of pulp, chlorate of lime, which was first manufactured by Mr. Tennant, of Glasgow, is introduced into the vat; and, by its chemical action on the fibre, whitens or bleaches the whole mass; thus enabling the manufacturer to produce a whiter and much finer quality of paper from rags of a secondary quality, than he had heretofore done from rags of the most expensive description. It must, however, be admitted that, as in all bleaching processes where the fibre is more or less deteriorated by the action of chlorine, the paper manufactured and whitened by this agent is not so strong as that formerly produced; as may be observed in some thick and beautifully white papers frequently offered to the public