them, and their own weight on the boarding. The countesses and all other description of slates, when intended to be laid in a good manner, are also laid on boards.

When the slater has finished the eaves, he strains a line on the face of the upper slates, parallel to its outer edge, and as far from it as he deems sufficient for the lap of those he intends shall form the next course, which is laid and nailed even with the line, crossing the joints of the upper slates of the eaves. This lining and laying is continued close to the ridge of the roof, observing throughout to cross the different joints, by laying the slates one above another. The same system is uniformly followed in laying all the different sorts of slates, with the exception of those calied patent slates, as are hereafter explained.

The largest kinds of slate, are found to lay firm on battens, which are, consequently, much employed, and produce a very considerable saving of expense in large buildings. A batten is a narrow portion of deal, about two inches and a half, or three inches wide; four of them being commonly procured from an eleven inch board.

For countess slates, battens three-quarters of an inch thick, will be of adequate substance; but for the larger and heavier kinds, inch battens will be necessary. In baitening a roof for slates, the battens are not placed at an uniform distance from each other, but so as to suit the length of the slates; and as these vary as they approach the apex, or ridge of the roof, it follows that the slater himself is the best judge where to fix them, so as best to support the slates.

A roof, to be covered with patent slates, requires that the common rafters be left loose upon their purlines, as they must be so arranged that a rafter shall lie under every one of the meeting-joints. Neither battening nor boarding is required for these slates. The number of rafters will depend on the width of the slates; hence if they be of a large size, very few will suffice. This kind of slating is likewise commenced at the eaves; but no crossing or bonding is required, as the slates are laid uniformly, with each end reaching to the centre of the rafter, and butted up to each other throughout the length of the roof. When the eaves-course is laid, the slates which compose it are screwed down to the rafters by two or three strong inch and half screws at each of their ends. A line is then strained about two inches below the upper edge, in order to guide the laying of the next course, which is laid with its lower edge touch ing the line. This lining, laying with a lap, and screwed

down, is continued till the roof is completely covered. The joints are then secured by filletting, which consists in covering all the meeting-joints with fillets of slate, bedded in glazier's putty, and screwed down through the whole into the rafters. The fillets are usually about three inches wide, and of a length proportionate to that of the slates, whose joints they have to cover. These fillets are solidly bedded in the putty, and their intersecting joints are lapped similar to those of the slates. The fillets being so laid, and secured by one in the middle of the fillet and one in each lap, are next neatly pointed all round their edges with more putty, and then painted over with the colour of the slate. The hips and ridges of such slating are frequently covered by fillets, which produces a very neat effect; but lead, which is not much dearer, is by far the best kind of covering for all hips and ridges. The patent slating may be laid so as to be perfectly water-tight, with an elevation of the rafters considerably less than for any other slate or tile covering. The rise in each foot of length in the rafter is not required to be more than two inches, which, in a rafter of fifteen feet, will amount to only two feet six inches: a rise scarcely perceptible from the ground.

Slating is performed in several other ways, but the principles already explained, embrace the most of them. Some workmen shape and lay their slates in a lozenge form. This kind of work consists in getting all the slates to an uniform size, of the shape of a geometrical square. When laid on the roof, which must be boarded, they are bonded and lapped as in common slating, observing only to let the elbow, or half of the square, appear above each slate that is next beneath it, and be regular in the courses all over the roof. One nail or screw only can be used for such slating; hence it soon becomes dilapitated. It is commonly employed in places near to the eye, or where particular neatness is required.

It has been ascertained, that a slate one inch thick will, in an horizontal position, support as much, in weight, as five inches of Portland stone similarly suspended. Hence slates are now wrought and used in galleries, and other purposes, where it is essential to have strength and lightness combined.

Slates are also fashioned into chimney-pieces; but are incapable of receiving a polish like marble. It makes excellent skirtings of all descriptions, as well as casings to walls, where dilapidations, or great wear and tear are to be ex

pected. For these purposes, it is capable of being fixed with joints, equally as neat as wood: and may, if required, be painted over so as to appear like it. Stair-cases may also be executed in slate, which will produce a resemblance of marble.

MENSURATION OF PLASTERERS' AND SLATERS' WORK.

'Plasterers' work is executed by the yard square; and the dimensions are taken in feet and inches.

If a room consists of more than four quoins, the additional corners must be allowed at per foot run.

In measuring ceilings with ribs, the superficies must be taken for plain work; then an allowance must be made for each mitre, and the ribs must be valued at so much per foot run, according to the girth; or by the foot superficial, al=lowing moulding work.

E

In measuring common work the principal things to be observed are as follow:-first, to make deductions for chimneys, windows, and doors; secondly, to make deductions for rendering upon brick work, for doors and windows; #thirdly, if the workman find materials for rendering between quarters, one-fifth must be added for quarters; but if workmanship only is found, the whole must be measured as whole work, because the workman could have performed the whole much sooner if there had been no quarters; fourthly, all mouldings in plaster work are measured by the foot superficial, the same as joiners, by girting over the mouldings with a line.

Slaters' work is measured and reduced into squares, containing 100 feet superficial. If in measuring the slating on a roof, it be hipped on all sides with a flat at top, and the plan of the building be rectangular, add the length and breadth of two adjoining sides of the eaves, and the length and breadth of two adjoining sides at the flat together, multiply the sum by the breadth of the slope, and the product will give the area of the space that is covered. Add the number of square feet produced, by multiplying the girts of the roof by the length of the slates at the eaves; to the area also, for the trouble of putting on the double row of slates, add the number of square feet produced by multiplying the length of the hips by one foot in breadth, and the sum will be the whole contents, and yield a compensation for the trouble and waste of materials. If there be no flats, add the two adjoining sides and twice the length of the ridge for the length; multiply the sum by the breadth of the slips, for

the arca of the space covered, and add the allowances as before.

Another plan is to allow in addition to the nett dimensions of the work, six inches for all the eaves, and four inches for the hips.

All faced work in slate skirting, stair-cases, galleries, &c. is charged by the foot superficial, without any addition.

PLUMBING,

Is the art of casting and working in lead, and using the same in the covering and for other purposes in building.

To the plumber is also confided the pump-work, as well as the making and forming of cisterns and reservoirs, large or small closets, &c. for the purposes of domestic œconomy. The plumber does not use a great variety of tools, because the ductility of the metal upon which he operates does not require it.

The tools used, consist of an iron hammer, rather heavier than a carpenter's, with a short thick handle; two or three wooden mallets of different sizes; and a dressing and flatting tool.

This last is of beech, about eighteen inches long, and two inches square, planed smooth and flat on the under surface, rounded on the upper, and one of its ends tapered off round as a handle. With this tool he stretches out and flattens the sheet-lead, or dresses it to the shape required, using first the flat side, then the round one, as occasion may require.

The plumber has also occasion for a jack and trying plane, similar to that of the carpenter.

With this he reduces the edges of sheet-lead to a straight line, when the purposes to which it is to be applied require it.

Also a chalk line, wound upon a roller, for marking out the lead into such breadths as he may want.

His cutting tools consist of a variety of chisels and gouges as well as knives.

The latter of these are used for cutting the sheet lead into slips and pieces after it has been marked out by the chalk line.

Files of different sizes; ladles of three or four sizes, for melting the solder; and an iron instrument called grozingirons.

These grozing-irons are of several sizes, generally about twelve inches in length, tapered at both ends, the handle end being turned quite round, to allow of its being firmly held while in use: the other end is a bulb of a spindle, or spherical shape, of a size proportioned to the soldering intended to be executed. They are, when required for use, heated to redness.

The plumber's measuring rule is two feet in length, di · vided into three equal parts of eight inches each; two of its legs are of box-wood, duodecimally divided; and the third consists of a piece of slow tempered steel, attached to one of the box legs by a pivot on which it turns, and falls, when not in use, into a groove cut in such leg for its reception. This steel leg can be passed into places where the others cannot enter; and it is also useful for occasionally removing the oxide or any other extraneous matters from the surface of the heated metal.

Scales and weights are also necessary; and he must be supplied with centre-bits of all sizes; and a stock to work them, for the purpose of making perforations in lead or wood, through which he may want to insert pipes, &c. Compasses, to strike circular pieces, to line or cover figures of that shape, are occasionally required.

Lead is obtained from ore, and, from its being generally combined with sulphur, it has been denominated "sulphuret." After the ore has been taken from its bed it is smelted, first being picked, in order to separate the unctuous and rich, or genuine ore from the stony matrix, and other impurities; the picked ore is then pounded under stampers worked by machinery, and afterwards washed to carry off the remainder of the matrix, which could not be separated in picking. It is next put into a reverberatory furnace, to be roasted; during which operation, it is repeatedly stirred, to facilitate the evaporation of the sulphur. When the surface begins to assume the appearance of a paste, it is covered with charcoal, and well shaken together: the fire is then increased, and the purified lead flows down on all sides into the basin of the furnace, whence it runs off into moulds prepared for its reception. The moulds are capable of receiving 154lbs. of lead each, and their contents, when cool, are, in the commercial world, called pigs.

Lead is of a bluish-white colour, and when newly melted, or cut, is quite bright; but it soon becomes tarnished on exposure to the atmosphere; assuming first a dirty grey colour, and afterwards becomes white. It is capable of