will crush it; and that it will bear 15,300 upon a square inch without permanent alteration. The weight of cast and bar iron is as follows: 1781. Lead, the heaviest of the metals except gold and quicksilver, is found in most parts of the world. It is of a bluish white when first broken, is less ductile, elastic, and sonorous than any of the other metals, its specific gravity being from 11300 to 11479, and a cubic foot, therefore, weighing about 710 lbs. It is soluble in all acids and alkaline solutions, fusible before ignition, and easily calcined. The ore, which is easily reduced to the metallic state by fusion with charcoal, is found mineralised with sulphur, with a slight mixture of silver and antimony, in diaphanous prismatical crystals, generally hexagonal, white, yellowish, or greenish, in Somersetshire, about the Mendip Hills. About Bristol, and in Cumberland, it takes the form of a white, grey, or yellowish spar, without the least metallic appearance; in some places it is in a state of white powder or native ceruse; and in Monmouthshire it has been found native, or in a metallic state. 1782. Exposure to air and water does not produce much alteration in lead, though it quickly tarnishes and acquires a white rust, by which the internal parts are defended from corrosion. Pure water, however, does not alter it; hence the white crust on the inside of lead pipes through which water flows must probably be owing to some saline particles in the water. Lead will form an union with most other metals: one exception, however, is iron. Next to tin, it is the most fusible of metals. It is run from the furnace into moulds which form what are called pigs, from which it is run into sheets, pipes, &c. 1783. Sheet lead is of two sorts, cast and milled. The thicker sort of the former, or the common cast sheet lead, is manufactured by casting it on a long table (with a rising edge all round it) from 18 to 20 feet in length, which is covered with fine pressed sand beaten and smoothed down with a strike and smoother's plane. The pig lead is melted in a large vessel, near this table, and is ladled into a pan of the shape of a common triangular prism, whose length is equal to the width of a sheet, from which pan it is poured on to the table or mould. Between the surface of the sand and the strike, which rides upon the edges of the table, a space is left which determines the thickness of the sheet. The strike bears away the superfluous liquid lead before it has time to cool, as it moves by hand along the edges of the table before mentioned. When lead is required to be cast thin, a linen cloth is stretched on an appropriate table over a woollen one; in which case the heat of the lead, before spreading it on the cloth, must be less than will fire paper, or the cloth would be burnt. The strike must for the purpose be passed over it with considerable rapidity. 1784. In manufacturing milled lead, it is usual first to cast it into sheets from 8 to 10 feet long according to circumstances, but the width is regulated by the length of the rollers through which it is to be passed in milling; the thickness varies from 2 to 5 inches. By a mechanical action it is made to pass through rollers whose distance from each other is gradually lessened until the sheet is reduced to the required thickness. For a long time a great prejudice prevailed against milled sheet lead; but it is now generally considered that, for the prevention of leakage, milled is far superior to cast lead, wherein pin holes, which have naturally formed themselves in the casting, often induce the most serious con sequences. 1785. The thickness of sheet lead varies from 5 to 12 pounds in weight to the superficial foot, and is used in covering large buildings, in flats or slopes, for gutters, the hips, ridges, and valleys of roofs, the lining of cisterns, &c. The subjoined table shows the weight of lead per superficial foot from one sixteenth of an inch to one inch and a half thick: Leaden pipes are either cast bent, or soldered. To cast them, a mould is made of brass, wherein down the middle a core of iron is loosely supported at such a distance from the mould all round, as is equal to the contemplated thickness of the pipe. When pipes are made by soldering, a core of wood is provided round which the sheet lead is rolled, and the edges are brought together and joined with solder, which is a mixture of two parts lead and one part tin. 1786. In cottages and inferior buildings the glazing is executed in lead prepared in the glazier's mill from what are called cames. These are slender rods 12 or 14 inches long, and in passing through the mill receive grooves on their upper and under edges. Into the grooves the panes or quarries of glass are inserted in common lead lights. SECT. VII. COPPER. 1787. Copper, among the first of the metals employed by the early nations of the world, is neither scarce nor difficult to work and extract from its ore. When pure it is of a pale red colour, its specific gravity 8600, and a cubic foot will weigh 537 lbs. ; the weight of a bar 1 foot long and 1 inch square is 3.81 lbs. These, however, vary as it is more or less hammered. Its elasticity and hardness are very considerable, and it is so malleable that it may be hammered into fine leaves. It is also very tenacious, a wire of a tenth of an inch in diameter being capable of sustaining 360 lbs. 1788. Though the ore is found in Cornwall and other parts of England, the finest in this country is the Parys mine in Anglesea, which yields principally the yellow sulphuretted ore of copper, to an annual amount of from 40,000 to 80,000 tons. This ore usually contains from one and a half to twenty-five per cent. of copper, and is partly dug in what are called packages, and partly blasted by gunpowder, and then broken into small pieces previous to its being roasted. This operation is performed in kilns, whose shape has a resemblance to lime-kilns, in which expedients are used for removing the ore as it is roasted, and adding fresh ore. The kilns are arched level with the upper surface of the ore, and adjoining and communicating with the kiln is the floor of a condensing chamber to receive the sulphureous vapours generated in the kiln, which fall down in the form of the finest flowers of sulphur. Several hundred tons at one time are put into the kiln, and for completing the operation six months are required. The ore is reduced to one fourth of its previous quantity by roasting, and is then washed and pressed to remove the impurities. The richer ores are then dried, and removed for smelting and refining in reverberatory furnaces, from which it is at length produced in short bars or pigs. The water which filters through the fissures is often highly impregnated with sulphate of copper, and this water is pumped up into rectangular pits about thirty feet long, twelve broad, and two deep, to mix with that in which the roasted ore has been washed; and in it are immersed pieces of iron, which, combining with the sulphuric acid, precipitate the copper in the form of a red-coloured powder slightly oxidated. The precipitate thus obtained very frequently gives above 50 per cent. of pure copper, and is even more profitable to the worker than the metal produced from the crude ore. 1789. Sheet copper was formerly much used for its lightness to cover roofs and flats; but it is almost superseded now by the use of zine, which is much cheaper, and nearly if not quite as durable; and which, moreover, is not so liable to be corrugated by the action of the sun. Copper is reduced to sheet by being passed through large rollers, by which it can be rendered very thin. The thickness generally used is from 12 to 18 ounces to the foot superficial. Exposed to the air its lustre is soon gone; it assumes a tarnish of a dull brown colour, gradually deepening by time into one of bronze; and, lastly, it takes a green rust or calx, called patina by the antiquaries, which, unlike the rust of iron, does not injure and corrode the internal parts, confining itself to the surface, and rather preserving than destroying the metal. Hence, one of the most important applications of copper is in cramps for stone work, especially when they are exposed to the air. It may be here well to observe, that if water is collected from roofs for culinary purposes, copper must not be used about them, neither should any reservoirs for collecting and holding it be made of that metal. 1790. Alloyed with zinc, it forms brass for the handles of doors, shutters, locks, drawers, and the furniture generally of joinery. The usual proportion is one part of zinc to three of copper; than which it is more fusible, and is of a fine yellow colour, less liable to tarnish from the action of the air, and so malleable and ductile that it can be beat into thin leaves and drawn into very fine wire. Its specific gravity is 8370, and the weight of a cubic foot is 523 lbs. The weight of a bar 1 foot long and 1 inch square is 3.63 lbs. The extremes of the highest and lowest proportions of zinc used in it are from 12 to 25 per cent. of the brass. Even with the last, if well manufactured, it is quite malleable, although zine by itself scarcely yields to the hammer. The appearance of brass is frequently given to other metals by washing them over with a yellow lacquer or varnish. 1791. Copper with zinc in the proportion of one tenth to one fifth of the whole forms a composition called bronze or bell-metal, used in the foundery of statues, bells, cannons, &c. When tin forms nearly one third of the alloy, a beautiful white close-grained brittle metal is formed, susceptible of a very high polish, which is used for the specula of reflecting telescopes. SECT. VIII. ZINC. 1792. Zinc is found in all quarters of the globe. In Great Britain it is abundant, though therein never found in a native state. It usually contains an admixture of lead and sulphur. When purified from these, it is of a blue light colour, between lead and tin, inclining to blue. The ore, after being hand-dressed to free it from foreign matter, is roasted, by which the sulphur of the calamine and the acid of the blende are expelled. The product is then washed to separate the lighter matter, and the heavy part which remains is mixed with one eighth of its weight of charcoal. The mixture, being reduced in a mill to a powder, is placed in the pots, resembling oil jars, to be smelted. A tube passes through the bottom of each, the upper end being terminated by an open mouth near the top of the pot, and the lower end going through the floor of the furnace into water. The pots being filled with the mixture of ore and charcoal, an intense heat is applied to them by means of a furnace, by which, as the ore is reduced, the zinc is volatilized, and escapes through the tube into the water, wherein it falls in globules, which are afterwards melted and cast into moulds. Thus procured, however, it is not pure, as it almost invariably contains iron, manganese, arsenic, and copper. In order to free it from these, it is again melted and stirred up with sulphur and fat, the former whereof combines with the heterogeneous metals, leaving the zinc nearly pure, and the latter preventing the metal from being oxidated. 1793. Under rollers at a high temperature, zine may be extended into plates of great tenuity and elasticity, or drawn into wire. These rollers are from 2 feet 8 inches to 6 feet in length, and the original thickness of the plate subjected to them is about 1 inch. A wire, one tenth of an inch diameter, will support 26 pounds. If zinc be hammered at a temperature of 300, its malleability is much increased, and it becomes capable of much bending. Its fracture is thin, fibrous, and of a grain similar to steel. It can be drawn into wire th of an inch in diameter, which is nearly as tenacious as that of silver. The specific gravity is somewhat below 7·0, but hammering increases it to 7.2. When heated, it enters into fusion at a heat of about 680° or 700°: at a higher temperature it evaporates; and if access of air be not permitted, it may be distilled over, by which process it is rendered purer than before, although not then perfectly pure. When heated red hot, with access of air, it takes fire, burns with an exceedingly beautiful greenish or bluish flame, and is at the same time converted into the only oxide of zinc with which we are acquainted, consisting of 23:53 parts of oxygen combined with 100 of metal. 1794. On the first introduction of zinc into this country as a material, the trades with which it was likely to interfere used every exertion to prevent its employment; and, indeed, the workmen who were engaged in laying it, being chiefly tinmen, were incompetent to the task of so covering roofs as to secure them from the effects of the weather. Hence, for a considerable period after its first employment, great reluctance was manifested by architects in its introduction. A demand for it has, however, gradually increased of late, and the comparatively high prices of lead and copper will not entirely account for the disparity of consumption. In France, in the year 1836, the quantity consumed exceeded 12,000 tons, whilst, in the same year, in England the consumption amounted only to between 2000 and 3000 tons. 1795. Zinc, though subject to oxidize, has this peculiarity, that the oxide does not scale off as that of iron, but forms a permanent coating on the metal, impervious to the action of the atmosphere, and rendering the use of paint wholly unnecessary. Its expansion and contraction is greater than those of any other metal: thus, supposing 10030 to represent the expansion of it, 10019 is that of copper, and 1·0028 that of lead; hence, in use, proper attention must be paid to the circumstance, or a substantial and durable covering of zinc will not be obtained. The method of accomplishing this is, of course, by always allowing plenty of play in the laps. 1796. The tenacity of zinc to lead is as 16 616 to 3.328, and to copper as 16.616 to 22.570; hence a given substance of zinc is equal to five times the same substance in lead, and about three fourths of copper. The sheets in general use are 12, 14, 16, 18, and 20 ounces to the foot superficial; and as 18 thicknesses of 16 ounces to the foot are half an inch thick, the following show the thicknesses of the different weights: Plates or sheets of 10 ounces to the foot are 0.0611 inch thick. The comparative weights of the different materials used in covering buildings may be roughly stated as follows: A square of pantiling will weigh about 7 cwt. plain tiling 14 cwt. 6 cwt. 5 cwt. zinc (15 oz.) 1 cwt. And as the timbers employed, of course, are less in dimension as the weight diminishes, it follows that a less quantity of timber is requisite when zinc can be employed. 1797. It is a good material for water-cisterns and baths, rain-water pipes, - in short, for almost all purposes where lead has been hitherto employed; and latterly a method has been invented, by which it is formed into sash-bar for skylights and ornamental sashes; for which purposes, strength excepted, it is superior to iron, as not being liable to rust, and loosen the putty and glass. It is, in every respect, equal to copper, and not more than one third the cost of it. SECT. IX. SLATES. Its 1798. Slate is a species of argillaceous stone, and is an abundant and most useful mineral. The slate district in England is of considerable extent. This material is so soft, that the human nail will slightly scratch it, and is of a bright lamellated texture. constituent parts are argyll, earth, silex, magnesia, lime, and iron; of the two first and the last in considerable proportion. The building slate is the schistus tegularis. 1799. The slates used about London are brought chiefly from Bangor, in Caernarvonshire; but the most esteemed is a pale blue-green slate, brought from Kendal, in Westmorland, and called Westmorland slates. Those from Scotland are not in much repute. Slate quarries usually lie near the surface; and, independent of the splitting grain, along which they can be cleft exceedingly thin, they are mostly divided into stacks, by breakings, cracks, and fissures. Slate is separated from its bed, like other stones, by means of gunpowder, and the mass is then divided into scantlings by wedges, and, if necessary, sawn to its respective sizes by machinery. The blue, green, purple, and darker kinds are most susceptible of thin cleavage, the lighter-coloured slates being coarser. The instruments used in quarrying and splitting slates are slate-knives, axes, bars, and wedges. In fixing them on roofs the zar is used. This is an instrument made of tempered iron, about 16 in. long and 2 in. wide, like a large knife bent a little at one end, with a wooden handle at the other, and having a projecting piece of iron on its back, drawn to a sharp point, to make holes in the slates for the nails, the other side being used to chip and cut the slates to their required size, as when brought from the quarry they are not sufficiently square and cleaned for the slater's use. 1800. A fine sound texture is the most desirable among the properties of a slate; for the expense of slating being greatly increased by the boarding whereon it is placed, if the slate absorbs and retains much moisture, the boarding will soon become rotten. But a good slate is very durable. Its goodness may be judged of by striking it as you would a piece of pottery, wherefrom a sonorous, clear, bell-like sound is a sign of excellence; but many pieces of the slate should be tried before a conclusion can be arrived at. It is thought to be a good sign, if, in hewing, it shatters before the edge of the zax. The colour, also, is some guide, the light blue sort imbibing and retaining moisture in a far less degree than the deep black-blue sort. The feel of a slate is some indication of its goodness: a good one has a hard and rough feel, whilst an open absorbent slate feels smooth and greasy. The best method, however, of testing the quality of slates is by the use of water, in two ways. The first is, to set the pieces to be judged of edgewise in a tub of water, the water reaching above half way up the height of the pieces: if they draw water, and become wet to the top in six or eight hours' time, they are spongy and bad; and as the water reaches less up them, so are the pieces better. The other method is, to weigh the pieces of slate, and note their weights. Let them then remain for twelve hours in water, and take them out, wiping them dry. Those that on re-weighing are much heavier then they were previous to their immersion should be rejected. Where the character of a slate quarry is not previously known, experiments of these sorts should never be omitted. 1801. The following comparison of the advantages of slates over tiles is given by the late Bishop of Llandaff. That sort of slate, other circumstances being the same, is esteemed the best which imbibes the least water; for the water imbibed not only increases the weight of the covering, but in frosty weather, being converted into ice, swells and shivers the slate. This effect of frost is very sensible in tiled houses, but is scarcely felt in those which are slated, for good slates imbibe but little water; though tiles, when well glazed, are rendered in some measure similar to slate in this respect. The bishop took a piece of Westmorland slate and a piece of common tile, and weighed each of them carefully. The surface of each was about thirty square inches. Both the pieces were immersed in water about ten minutes, then taken out, and weighed as soon as they had ceased to drip. The tile had imbibed about a seventh part of its weight of water, and the slate had not imbibed a two-hundredth part of its weight; indeed, the wetting of the slate was merely superficial. He placed both the wet pieces before the fire; in a quarter of an hour the slate was perfectly dry, and of the same weight as before it was put in the water; but the tile had lost only about twelve grains it had imbibed, which was, as near as could be expected, the very same quantity that had been spread over its surface; for it was the quantity which had been imbibed by the slate, the surface of which was equal to that of the tile. The tile was left to dry in a room heated to sixty degrees, and it did not lose all the water it had imbibed in less than six days. We here subjoin a succinct account of the different sorts of slates brought to the London market, and enumerate them in the order of their goodness and value. 1802. Westmorland slates. These are from 3 ft. 6 in. to 1 ft. in length, and from 2 ft. 6 in. to 1 ft. in breadth. They should be nailed with not less than sixpenny and eightpenny copper or zinc nails (iron nails should never be used); and a ton in weight of them will cover about two squares and a quarter. We may here observe, that the weight of the coarsest Westmorland slates is to that of common tiling as 36 to 54. 1803. Welsh rags are next in goodness, and are nearly of the same sizes as those last mentioned; but a ton of these will cover only one square and three quarters. 1804. Imperials are from 2 ft. 6 in. to 1 ft. in length, and about 2 ft. wide. 1805. Duchesses run about 2 ft. long and 1 ft. wide, and are nailed usually so as to show a ten and a half inch gauge. 1806. Countesses, of which a ton will cover about three squares, run about 1 ft. 8 in. in length by about 10 in. in width. 1807. Ladies are generally about 15 in. long, and about 8 in. wide. These are sold by the thousand of twelve hundred, which quantity will cover about four squares. 1808. There are still other sorts of slates which have been used in and about London, as the Dennybole, &c. The Tavistock slates were at one period in considerable demand. They are sold by the thousand of ten hundred, which quantity covers about three squares and forty feet. The smallest slates in use are called Doubles: they run about 13 in. in length by 6 in. in width. The bond or lap of a slate is the distance between the nail of the under slate and the lower end of the upper slate, and, as in tiling, the gauge in slating is the visible depth of the slate. 1809. Several years ago, a patent was obtained for slating roofs without hoarding or battens. In this the slates were all reduced to widths equal to the distance between centre and centre of the rafters. On the backs of these last they are screwed by two or three strong inch and half screws at each of their ends. Over the junctions of the slates, on the backs of the rafters, fillets of slates about two and a half or three inches wide, bedded in putty, are screwed down, to prevent the entrance of rain. The handsome regular appearance of this sort of slating gained it at first much celebrity; but it was soon abandoned, on account of the disorder it is liable to sustain from the slightest partial settlement of the building, not less than from the constant dislodgement of the putty, upon which greatly depended its being impervious to rain. 1810. Slating is sometimes laid lozengewise; but it is much less durable than when laid in the common method. SECT. X. BRICKS AND TILES. 1811. A brick is a factitious sort of stone, manufactured from argillaceous or clayey earth, well tempered and squeezed into a mould. When so formed, bricks are stacked to dry in the sun, and finally burnt to a proper degree of hardness in a clamp or kiln. use of bricks is of the highest antiquity. They are frequently mentioned in the historical The |