the usual price of copper; the cost of labour is nearly the same. The durability of copper may be taken to be three or four times that of zinc. It requires to be laid by skilled workmen. 1789a. 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 oz. to the foot superficial. Exposed to the air its lustre is soon gone; it assumes a tarnish of a dull brown colour, gradually de pening 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, when its cost, which is about six or eight times that of iron fastenings, can be afforded. Copper nails for fastening slates in roofing are recommended in lieu of even zine nails. 17896. 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, as on the surface is formed a film of verdigris, which is poisonous. Brass. 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; it is then 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 beaten into very thin leaves and drawn into very fine wire. The extremes of the proportions of zinc used in it are from 12 to 25 per cent. of the whole. Even with the last, if well manufactured, it is quite malleable, although zinc 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. Cast brass weighs 525 lbs. per cubic foot. 1790a. Delta metal is an alloy, an improved brass, hard, durable, and strong as mild steel, possessing a beautiful fine colour. When melted it produces sound castings of fine grain; it can be forged and rolled hot and cold, and takes a very high polish. It is being used for all kinds of machinery, house, door, and harness fittings, stair plates, &c. To test the action of acids on wrought iron, steel, and delta metal, rolled bars of each were immersed for six and a half months in acid water; the weights when put in were 1·1805 lbs., 1-2125 lbs., and 1.2787 lbs. respectively. After that period they were found to be 06393 lbs., 0·6614 lbs., and 1.2633 lbs. respectively; showing a loss of 46-3, 45-45, and 1.2 per cent. respectively. This Delta metal is said to be now extensively used for underground machinery in mines. Bronze or Bell-metal. 1791. Copper with tin (which last melts at 426° Fahr. and resists oxidation better than any of the more common metals) in the proportion of one-tenth to onefifth 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. Bronze weighs 513 lbs. per cubic foot. 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 sulpur. When purified from these, it is of a light blue colour, between lead and tin, inclining to blue. The ore, after being hand-dressed to free it from foreign matter, 16 first calcined, 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, being ground in a mill, is mixed with one e ghth of its weight of charcoal, or with ; one third of its bulk of powdered coal. This mixture is placed in 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. By the intense heat of a furnace the ore is reduced, the zinc is volatilized, escaping 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. At the Vieille Montagne Zine Company's Works, the pots are placed in the furnaces at six o'clock every morning; at six o'clock in the evening the smelting is complete; the metal is then drawn out and run into metal moulds, after which it passes into the rolling house, and is again melted and recast in a metal mould to produce ingots of the proper size and weight for the required gauge of the sheets to be rolled; this second melting is also desirable to obtain proper purity. 1793. Under rollers at a high temperature, zine may be extended into plates of great 'enuity and elasticity, or drawn into wire. These rollers are from 2 feet 8 inches to 6 feet n 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 70, 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 then not 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. 1791. Zine, 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. Dr. von Petenkoffer, however, has stated that zine is oxidized to the extent of 130 grains per square foot in twenty-seven years, about two-fifths of the oxide being removed by the moisture of the atmosphere. Its expansion and contraction are greater than those of any other metal: thus, supposing 10030 to represent the expansion, 10019 is that of copper, and 1.0028 that of lead; but the thicker the zinc, the less its contraction and expansion. The tenacity of zinc is from 7,000 to 8,000. The weight of a cubic foot varies from 424 lbs. to 449 lbs. The tenacity of zine 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 threefourths of copr. 1795. 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. The Vieille Montagne Zine Mining Company, about the year 1861, took steps to improve the quality of the zinc for use in this country, the mode of laying zine roofs, and for the prevention of the us of thin gauges of sheets which are unfit for the purpose. Their zinc possesses a reputation for its purity and excellence. The result and the better understanding of the merits of the material, has caused it to be now extensively used for purposes which are noticed in the following chapter. of this care, 1795a. A sheet of pure zinc, as stated by J. Edmeston in his Report on Zine, will be of an even colour, without black spots or blotches; it will be very ductile, bending readily backwards and forwards in the hand; and it will not easily break. If impure, it will be the opposite of all this. If there be any iron in it, it will be worthless; if it contain any lead, it will still, though to a less extent, contain the germs of destruction within itself. 17956. Common zinc is destroyed by the sulphuric acid in the atmosphere where much coal is burned; and by muriatic acid in the neighbourhood of the sea. Cement does not injure zinc; but lime, and calcareous waters destroy it; and zinc pipes to flues over wood fires are destroyed by them. 1796 GALVANIZED IRON is a designation misapplied to that iron which may have received a coating of zine; it should be called zinked iron. The metal is first cleaned perfectly by the joint action of dilute acid and friction, and then plunged into a bath of melted zinc, covered with sal ammoniac, and stirred until the iron is sufficiently coated with zinc. No galvanic action whatever occurs between the metals; it is simply a coating. This process, it is stated, was invented in France by Maloin, in 1742, but not patented antil 1836 by Sorel. The efficacy of the process depends upon the skill employed in removing every trace of the scales of the hydrous oxide of iron, and in its further treatment. The coating must not become loosened, or any hole be made through it, as moisture obtaining access to the iron will rapidly extend, and the scales of the oxide of iron will force up the slight zinc covering, when the iron will be gradually destroyed, unless it be at once painted. When well executed it may perhaps be durable for a lengthened period, but when badly prepared it is not so valuable as iron well painted (par. 1779b.). At the Houses of Parliament, where the iron roofing plates were galvanized, it was found necessary from 1960 to commence coating them with paint or some other material. 1796a. The other process, which might be properly called zinked-tinned iron, is thus performed:-The sheets of iron are pickled, scoured, and cleaned, as for ordinary tinning. A wooden bath is half filled with a solution-the proportion of 2 quarts of muriate of tin with 100 quarts of water. Over the bottom of the bath is spread a thin layer of finely granulated zine, then a cleaned plate, and so on alternately; the zinc and iron and the fluid constitute a weak galvanic battery, and the tin is deposited from the solution so as to coat the iron, in about two hours, with a dull uniform layer of metal. The iron in this state is then passed through a bath containing fluid zinc covered with sal ammoniac mixed with an earthy matter, to lessen the volatilization of the sal ammoniac, which becomes as fluid as treacle. Two iron rollers are driven by machinery to carry the plates through the fluid at any velocity previously determined; the plates thus take up a very regular and smooth layer of zinc, which owing to the presence of the tin beneath, assumes its natural crystalline character. This is said to be the process adopted by Messrs. Morewood and Rogers, whose patents date in 1846 and 1850. It is asserted that iron thus prepared does not warp or buckle; that the plate is not affected by the heat of the zinc, whereas thin sheet iron, kept in molten zinc for a few minutes, becomes so brittle that it will not bear folding or grooving; that the plate is equally covered with zinc, whereas by the dipping process the lower half receives more than the upper: and that zine is not contaminated by iron as when dipped, the contamination increasing with each dipping until the zinc in the bath becomes so injured as to be worthless, it being well known that the alloy of zinc and iron is more oxidizable than zinc alone, or than zinc and tin. Professor Brande has stated that in common tinned plate, the combination is such that the oxidization of the iron is accelerated by the tin, so that the iron is the protecting, and the tin the protected, metal, but in this case the reverse effect ensues, the iron is the protected metal, and the zine the protector. 17966. Time has proved that galvanized iron has corroded after seren years in a roofgutter; and the state of most of the roofs to railway sheds and stations and such like places, proves that at least some sorts of galvanized iron will decay; the difficulty always is to ascertain what description of coating the iron has undergone. Galvanized iron bolts do not act upon oak either in sea or in fresh water, when care has been taken not to remove the zinc in driving them. 1796c. Galvanized iron is said to be nearly the same cost as zinc, and to be less than one quarter as liable to expansion or contraction: to be equally as durable as lead; less in first cost, and not to require boarding; to be not quite one-third the price of copper, and to be equally as durable; and as compared with plain iron, the cost is increased about two-thirds, but that it increases the strength and durability of the iron. 1797. The soldering used is composed of spirits of salts killed by putting about three ounces of zinc to a pint of spirit; care must be taken that this solder soaks well between the laps, SECT. IX. SLATE. 1798. Slate is a species of argillaceous stone, and is an abundant and most useful mineral. This material is so soft, that the human nail will slightly eratch it, and is of a bright lamellated texture. Its constituent parts are argill, earth, silex, magnesia, lime, and iron; of the two first and the last in considerable proportion. The building slate is the schistus tegularis 1799. Mica slate is a species of gneiss, distinguishable by containing little or no felspar, so that it consists chiefly of quartz and mica. It has a laminated or slaty structure. with the silky lustre of mica; it is a tough material in directions parallel to its layers, but is more perishable than gneiss. In thin layers it may be used for roofing purposes. Chlorite slate is also laminated soft, and easily cut, but more opaque than tale, and is sometimes used for roofing purposes. It has a green or greenish grey colour and silky lustre. Hornblende slate is hard, tough, durable, and impervious to water, and is used for flagstones. Grauwacke slate is a laminated claystone, containing sand and sometimes fragments of mica and other minerals. It is used for roofing and flag stones. All these descriptions of slate are inferior to the ordinary clay slate. 1800. 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 sticks, 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-col ured slates being coarser. The instruments used in quarrying and splitting slates, are slate knives, axes, bars, and wedges. 1801. The tenacity of slate is from 9,600 to 12,800. The modulus of elasticity varies from 13,000,000 to 16,000,000. The resistance to rupture is 5000. The weight of a cubic foot is from 175 lbs. to 181 lbs. The transverse strength of Welsh slate is greater than any other mineral product of the stone kind. For such qualities as strength, space, and cleanliness, no other material is so cheap as slate. 1802. The slates used about London are brought chiefly from Bangor in Carnarvonshire The slate quarries of North Wales are the most important in this country. The chief works are situated as follows, and belong respectively to the geological formations named :— Penrhyn, Bangor Llanberis, Dinorwic } Cambrian. Llangollen, Llangollen: Upper Silurian. Ffestiniog, Port Madoc: Lower Silurian. The large quarries at Penrhyn near Bangor, belonging to Colonel Pennant, and from which the best Bangor slates are obtained, are worked in successive terraces; the slate is obtained in immense masses by blasting, therefore the waste is enormous, but being got rid of without difficulty, the price is kept moderate. These quarries have been variously estimated as yielding from 30,000l. to 40,000l. worth of slates per annum. Many smaller ones have lately been opened near Bangor, all supplying "best Bangor" slates, without affecting the produce of the well-established works at that place. The Llangollen quarries are remarkable for the size of the slates they can obtain. 1803. The Delabole quarries in Cornwall have been worked for a considerable period; these slates are shipped from Tintagel and Boscastle. This grey-blue slate, confined till lately to the western counties, is now obtained in London; the Wellington College at Sandhurst, Berkshire, is roofed with them. The Tavistock slates from Devonshire were at one period in considerable demand. One of the most esteemed slates is of a pale bluegreen, brought from Kendal in Westmoreland, and called Westmoreland slate. There are quarries in the neighbourhood of Ulverstone, in Lancashire; and the Cumberland seagreen slate works are at Maryport. 1804. The extended use of this material for paving, shelving, cisterns, &c., has caused numerous companies to be formed for the working of old, and of many new, quarries, chiefly in North and South Wales. Amongst the companies putting forth peculiarities of slate, are the Dorothea West, Green, Blue, and Red, Slate Company, situate in Carnarvonshire, which supplied the pale green slates for the Charing Cross Railway Hotel, the London Bridge Hotel, and the Star and Garter Hotel at Richmond. The Llanfair Green and Blue Slate Company is also to be noticed. 1805. The slates of Scotland are not in much repute. The Balahulish quarries in the north of Scotland are very extensive, as between five and seven millions of roofing slates are quarried annually. The weight of this number would be about 10,000 tons, and the quantity of rubbish being generally five or six times as much as the slates, some 50,000 or 60,000 tons of refuse have to be disposed of, which in this case are thrown directly into the sea, securing an immense saving of expense. 1806. The more important slate quarries in Ireland are in the southern division of the country, viz., Killaloe, county Tipperary; Valentia, county Kerry; Benduff, near Glandore Harbour, county Cork; and near Ashford Bridge, county Wicklow. The chief one is at Curraghbally, situate about six miles from Killaloe. The colour of the slates is a dull bluish grey, preferred by many to the decided blue of the Bangor quarries; they are greatly used in the west of Ireland, where they have superseded the Welsh slates. The colour of the Valentia slates is rather greener than those above mentioned. They are generally thicker and more uneven on the surface, and so are better suited for the exposed aspects of buildings in the western counties. This quarry has more capabilities for sawn flags and slabs, of which a large amount is now exported to England for cisterns, baths, urinals, &c. The Banduff quarry is nearly given up. The slates from Ashford Bridge both in colour and quality closely resemble the Bangor slates. (Wilkinson, Geology, &c. of Ireland, 1845.) 1807. 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 readily be judged by striking it as a piece of pottery is struck; 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 zar. 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 tried 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 than 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. 1808. The following comparison of the advantages of slates over tiles is given by R. Watson, former Bishop of Llandaff. That sort of slate, other circumstances being the same, is esteemed the best which imbibes the least water; for water 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 Westmoreland 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 into 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. 1809. Professor Ansted states that the best slates are those which are most crystalline, and which, when breathed upon, give out a faint argillaceous odour; when this was given out strongly, then the slates would readily decompose. 1810. The largest slab of slate, perhaps, ever as yet obtained, was the one sent by the Llangollen Slate Company to the International Exhibition of 1862. It was 20 feet long, 10 feet wide, and weighed 4 tons; the thickness, however, was not named. The Welsh Slate Company, whose quarries are at Festiniog, in Merionethshire, sent several slabs averaging 14 feet by 7 or 8 feet. All the slate from this neighbourhood possesses the remarkable quality of splitting with great facility, and with wonderful accuracy of surface, into thin laminæ or sheets. Some of these thinly divided sheets are obtained 5 to 10 feet long from 6 to 12 inches wide, and not more than the sixteenth of an inch in thickness. They are so clastic as to bend like a veneer of wood. (Hunt, Handbook, 1862 ) SECT. X. BRICK AND TILE. 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. The se of bricks is of the highest antiquity. They are frequently mentioned in the historical |