dipped in sand. He presses it down, so that it may fill the whole of the cavity, striking off the superfluous clay with a flat wooden rule. The newly-formed brick is then turned out of the mould on to a thin board, somewhat larger than a brick, and it is removed by a boy to a latticed wheelbarrow, and conveyed, covered with fine dry sand, to the hack. A handy moulder, working fifteen hours, will mould 5000 bricks. In the hacks, which are eight courses in height, the bricks are arranged diagonally above each other, with a passage between each for the circulation of air round them. The time required for drying in the hacks will, of course, depend on the fineness of the weather; it is but a few days if the season be propitious; and they are then turned and reset wider apart, after which, in about six or eight days, they are ready for the clamp or kiln. If the weather be rainy, the bricks in the hack must be covered with wheat or rye straw; and as they ought to be thoroughly dry before removing to the clamp or kiln, a few are generally selected from different parts, and broken, to ascertain if the operation of drying has been well performed. The moisture arising from bricks when burning is very injurious to their soundness.

-1816. In the brickfields about London, bricks are mostly burnt in what are called clamps. These are generally oblong in form, and their foundations are made with the driest of the bricks from the hacks, or with common worthless bricks, called place bricks. The bricks for burning are then arranged, tier over tier, to the height assigned to the clamp, according to the quantity to be burnt, and a layer of breeze or cinders, two or three inches deep, is placed between each course of bricks, and the whole, when built up, covered with a thick stratum of breeze. On the western face of the clamp a vertical fireplace is formed, about 3 feet in height, from which flues are driven out by arching the bricks over, so as to leave a space about one brick wide. The flues run in a straight direction through the clamp, and are filled with a mixture of coals, breeze, and wood, closely pressed together. If the bricks are required to be burnt quickly, the flues should not be more than 6 feet apart; but if time do not press, the flues need not be nearer than 9 feet to each other, and the clamp is allowed to burn slowly. It is possible, if required, to burn a clamp in a period of from 20 to 30 days, according to the dryness of the weather.

1817. The kilns which are used for burning bricks are usually 13 feet long, by 10 feet 6 inches in width, and 12 feet in height... The walls are one brick and a half thick, and incline inwards as they rise. A kiln is generally built to contain 20,000 bricks at each burning. The fireplace consists of three arches, which have holes at top for distributing heat to the bricks. These are placed on a lattice-like floor, and first undergo a gentle action of the fire for two or three days, in order to dry them thoroughly. As soon as they thus become ready for burning, the mouth of the fireplace is dammed up with what is called a shinlog (which consists of pieces of brick piled against each other, and closed with wet brick earth), leaving above it sufficient room to introduce a faggot. The kiln is then supplied with brushwood, furze, heath, faggots, &c., and the fire is kindled and kept up until the arches assume a white appearance, and flames appear through the top of the kiln. The fire is then slackened, and the kiln gradually cooled. This process of alternately raising and slacking the heat of the kiln is repeated till the bricks are thoroughly burnt, which is usually accomplished in about eight and forty hours.

1818. The practice of steeping bricks in water after they have been burnt, and then again burning them, has been found to have the effect of considerably improving their quality. 1819. There are several sorts of bricks, which may be classed as follows: malms or marl stocks, stocks, place bricks, fire bricks, paving bricks, compass bricks, concave or hollow bricks, and Dutch or Flemish bricks. There are still other varieties; but from their being now but little used, we shall pass them over.

1820. The marl for the marl stock, which is of a bright yellowish uniform colour and texture, is not always to be had, especially in the London districts; in consequence of which, several years ago, it was discovered that chalk mixed in certain portions with loam, and treated in the usual manner, proved an excellent substitute for it. It not only was found to improve the colour, but to impart soundness to the brick; and the practice is now generally adopted about London. At Emsworth, in Hampshire, and also at Southampton, ooze, or sludge, from the sea-shore, containing much saline matter, is used for a similar purpose these bricks, however, have not the rich brimstone colour of the London malm stock, nor the regular stone-coloured hue of the Ipswich bricks.

1821. The finest marl stocks, which are technically called firsts, or cutters, are principally used for arches of doorways and windows, quoins, &c., for which purposes they are rubbed and cut to their proper dimensions and form. There is also a red cutting brick, whose

texture is similar to the malm cutter, which must not be confounded with the red stock. The next best, which are chiefly used for principal fronts, are called seconds: they are not quite so uniform in colour, nor so bright as the last, but are, nevertheless, a handsome and durable brick.

1822. Stocks are red and grey, both sorts being equal in texture. The red sort are burnt

in kilns. The grey stocks are less uniform in their colour than seconds, and are of rather an inferior quality. They are used for common fronts, and walls.

1823. Place bricks, or peckings, sometimes also called sandel, or samel bricks, are those which, having been outermost or furthest from the fire in the clamp, or kiln, have not received sufficient heat to burn them thoroughly. They are, consequently, soft, uneven in texture, and of a red colour. These should never be used in a building where durability is required.

1824. Burrs and clinkers are such bricks as have been violently burnt, or masses of several bricks run together in the clamp or kiln.

1825. The red bricks derive their colour from the nature of the soil whereof they are composed, which is generally very pure. The best of them are used for cutting-bricks, and are called red rubbers. In old buildings they are frequently found set in putty, and often carved into ornaments over arches, windows, doorways, &c.

1826. Fire bricks, so called from their capability of resisting the most violent action of the fire, are of a dark red colour, and of very close texture; they are made about 9 inches long, 4 inches broad, and 14 inches thick. The loam of which they are made is yellow, harsh to the touch, and contains a considerable portion of sand. Their quality renders them highly serviceable in furnaces and ovens. The greatest part of those used about London were formerly brought from Hedgerly, a village near Windsor, whence they obtained the name of Windsor bricks. This sort of brick is made also in various parts of Wales, whence they are called Welsh lumps.

1827. Paving bricks are for the purpose which their name implies, and their dimensions are the same as those of the foregoing sort.

1828. Compass bricks are circular on the plan, and are chiefly employed for steyning, or walling round wells.

1829. Concave or hollow bricks are made like common bricks, but hollowed on one side in the direction of their length, and are adapted to the construction of drains and water

courses.

1830. Dutch clinkers and Flemish bricks vary little in quality; they are exceedingly hard, and are used for the paving of stables, yards, &c., though they are by some objected to, as being too hot for the horses' feet. The former are 6 inches long, 3 inches broad, and 1 inch thick, and are often laid on edge in various fanciful forms, as the herring-bone, &c.

1831. By the 17th Geo. III. cap. 42. all bricks made for sale shall, when burnt, be not less than 84 inches long, 24 inches thick, and 4 inches wide. The very limitation is enough to prove the total disregard of the ministers of this country, at all times, to the advancement of the arts. It is scarcely possible to be believed that the statute still continues in force.

1832. Bricks laid in the summer season should be well saturated with water previous to laying; and if the work be left for a day only, the walls should be as carefully covered up as in the winter, for in hot weather the mortar sets too rapidly, and hence the necessary cohesion is destroyed; an evil much aggravated by the dust constantly hanging about the bricks, more especially at that season of the year.

1833. Three hundred and thirty well-burnt bricks may be generally taken as weighing 20 cwt.. so that a cubic foot weighs about 125 lbs; and it is found by experiment, that to crush a mass of solid brickwork whose section is 1 foot square, a weight of 300,000 lbs. averdupois must be applied.

1834. TILES, which in their constituent parts partake much of the nature of bricks, are plates of clay baked in a kiln, and used instead of slates, or other covering of the roofs of houses. The clay whereof tiles are formed will always make good bricks, though the converse does not hold, from the toughness required on account of their being so much thinner than bricks. The common kinds are made of a blue clay, found in many parts about London, though mostly deeper seated than brick earth. The best season for digging it is in September and October, and it should then lie exposed during the winter. It may, however, be turned up in January, and worked in February; and, as in brick, so in tilemaking, the more care bestowed on beating and tempering the clay, the better will be the tiles. Tiles are burnt in a kiln constructed on the same principles as the brick-kiln, but with the addition of a cone, having an opening at top round the chamber of the kiln. They require much care in burning. If the fire be too slack, they will not burn sufficiently hard; and if too violent, they glaze, and suffer in form.

1835. Plain or crown tiles are such as have a rectangular form and plane surface. They should be 10 inches long, 6 inches broad, and g of an inch thick, according to the statute, and they will weigh each from 2 to 25 lbs. They are manufactured with two holes in them, through which, by means of oak pins, they hang upon the laths. In using all coverings of this species, one tile laps over another, or is placed over the upper part of the one immediately below; that part of the tile which then appears uncovered is called the gauge of the tiling. If, in plain tiling, the gauge be 6 inches, about 740 tiles will cover one square, or 100 feet superficial.

1836. Ridge roof and hip tiles are formed cylindrically, to cover the ridges of houses. They should be 13 inches long, and girt about 16 inches on the outside. Weight about

5 lbs.

1837. Gutter tiles are about the same weight and dimensions as ridge tiles, but are for the valleys of a roof. They are now rarely used, their place having been long since sup

plied by lead.

1838. Pan or Flemish tiles have a rectangular outline, with a surface both convex and concave, thus, They have no holes for pins, as plain tiles have, but are hung on to the laths by a knot of their own earth on their underside, nearest the ridge, formed when making. They are often glazed, should be 14 inches long and 10 inches broad, and weigh from 5 to 5 lbs. They are usually laid at a 10 inch gauge, and a square at that gauge will take 170 pan tiles.

1839. The largest sort of paving tiles are 1 foot square and 1 inch thick. size, called 10 inch tiles, are, in fact, only 9 inches square and 1inch thick.

The next

SECT. XI.

LIME, SAND, WATER, AND CEMENT.

1840. Lime has not been found in a native state; it is always united to an acid, as to the carbonic in chalk. By subjecting chalk or limestone to a red heat it is freed from the acid, and the lime is left in a state of purity, and is then called caustic or quicklime, which dissolves in 680 times its weight of water. It is not our intention here to enter into any account of either of the theories relative to the formation of lime, facts being of more importance to the architect in its employment than the refined fancies of the scientific chemist. The calcareous minerals are mostly distinguished by their effervescing with and dissolving in an acid, as also by their being easily scratched or cut with a knife. respect of the lime obtained from chalk, Dr. Higgins (in his work on calcareous cements, Lond. 1780) says, "It should be observed, that the difference between chalk lime and the lime obtained from the various limestones, chiefly consists in the greater retention or expulsion of the carbonic acid gas contained in them."

In

1841. An account of the stone from which lime may be obtained in the different counties of England would unnecessarily extend this article; we shall, therefore, after observing that the use of marble for burning to lime would be too expensive, state the varieties of limestone as, 1. the compact; 2. the foliated; 3. the fibrous; and, 4. the peastone. The compact limestones are of various colours, in hues inclining to grey, yellow, blue, red, and green, and to a smoky sort of colour besides. It is usually found massive, often compounded with extraneous fossils, particularly shells. Its internal appearance is dull, the texture is compact, the fracture small, fine, and splintery; fragments indeterminately angular, more or less sharp-edged; semihard, sometimes soft, brittle, and easily frangible. Specific gravity varies from 2500 to 2700, and it is composed of lime, carbonic acid, and water, mostly with a portion of argyll and oxide of iron, and sometimes of inflammable matter.

1842. The foliated limestones are such as calcareous spar, statuary marble, &c.; the fibrous limestones, such as satin spar; and the pea stone, another species of spar. It may be remarked, that the various sorts of marble, chalk, and limestone may be divided into those which are nearly pure carbonate of lime, and those containing in addition from one twentieth to one twelfth of clay and oxide of iron. Though the best limestones are not such as contain the greatest quantity of clay, yet," observes Mr. Smeaton, “none have proved good for water building, but what, on examination of the stone, contained clay; and though, he continues, "I am very far from laying down this as an absolute criterion, yet I have never found any limestone containing clay in any considerable quantity, but what was good for water works, the proportion of clayey matter, being burnt, acting strongly as a cement; and limes of this kind all agree in one more property, that of being of a dead frosted surface on breaking, without much appearance of shining particles.

1843. Among the strongest limes, and such as will set under water, those most in use in the metropolis and its neighbourhood are procured from Dorking, Merstham, and the vicinity of Guilford. The most celebrated in the West of England is the blue lias of Somersetshire, and in the north that about the county of Sunderland, whereof very large quantities are exported to Scotland. The Dorking and other limes of that part are burnt from a chalk formation so extremely hard that it is quarried even for the purposes of masonry. Those of Merstham particularly are obtained from an indurated chalk marle (clay and chalk) which is so hard that it partakes of the nature of stone. The known property of the lias formation for setting under water renders it an invaluable material in the hands of the architect. In the neighbourhood of Bath it is called Bath brown lime,

and when prepared for cementing with metallic cement, is said to be wind slacked; that is, after burning, it is placed in roofed sheds open at the sides, and the atmosphere is thus introduced to act upon it. The colour of the lias, previous to burning, is blue; after it has passed the kiln, it is of a rich brown colour. No accurate analysis of this has come to our knowledge; but we have understood that specimens have been analysed, containing as much as 90 per cent. of carbonate of lime, the residuum probably consisting of alumen and iron. The magnesian limestone of Sunderland lies north-west of the red sandstone. In the vicinity of South Shields, in the county of Durham, the formation becomes extensive, and is to be traced to the Tees below Winston Bridge. The Whitby quarry near Callercoats has been described in the 4th volume of the Geological Transactions. The Sunderland limestone is of a bronze colour, and from containing inflammable matter, does not require so much fuel to convert it into lime.

1844. Before limestone is burnt it seems to possess no external character by which a distinction can be made between the simple and the argillo-ferruginous limestones; whatever the colour of the former, they become white when burnt, whilst the latter partake more or less of a slight ochrey tint. Brown lime is the most esteemed for all sorts of cements, whilst for common purposes, the white sorts, which are more abundant, are sufficiently useful. In England, the limestones in colour generally incline to a red or blue, and those which are found firm, weighty, and uniform in texture are to be preferred. Masses broken from large rocks and beds on the sides of hills, and those when newest taken and deepest dug, are most to be valued.

1845. The process of analysing limestones is so eminently useful to all concerned in building, that we cannot refrain from transcribing the method used by Smeaton in his own words. "I took about the quantity of five pennyweights (or a guinea's weight) of the limestone to be tried, bruised to a coarse powder, upon which I poured common aquafortis, but not so much at a time as to occasion the effervescence to overtop the glass vessel in which the limestone was put, and added fresh aquafortis after the effervescence of the former quantity had ceased, till no further ebullition appeared by any addition of the acid. This done, and the whole being left to settle, the liquor will generally acquire a tinge of some transparent colour; and if from the solution little or no sediment drops, it may be accounted a pure limestone (which is generally the case with white chalk and several others), as containing no uncalcareous matter in its composition. When this is well settled, pour off the water, and repeatedly add water in the same way, stirring it, and letting it settle till it becomes tasteless. After this, let the mud be well stirred into the water, and without giving it time to settle, pour off the muddy water into another vessel, and if there is any sand or gritty matter left behind (as will frequently be the case), this collected by itself will ascertain the quantity and species of sabulous matter that entered into the texture of the limestone. Letting, now, the muddy liquor settle, and pouring off the water till no more can be got without an admixture of mud, leave the rest to dry, which, when of the consistence of clay, or paste, is to be made into a ball, and dried for further examination."

1846. The loss of limestone by burning is about four ninths of its weight, shrinking, however, but little. When completely burnt, it falls freely, in slaking, into powder, and then occupies about double its previous bulk.

1847. There are many sorts of kilns for burning limestone, varying in form with the fuel employed, and the combination of the process itself with some other, such, for instance, as making coke, and sometimes bricks. The limestone, however, is generally burnt in kilns whose plans are circular and section resembling an inverted truncated cone; of late more frequently made spheroidal. The heat is in either case obtained from a fireplace under the limestone, which rests on bars, that can, when the kiln is a perpetual one, egg-formed, or a draw kiln, be removed, to let out the lime as it is burnt, whose deficiency, on extraction, is supplied by fresh stone at the top of the kiln. Sod kilns are sometimes used for lime burning. These are formed by excavating the earth in a conical form, and then building up the sides as the earth may require. In using these, the limestone is laid in with alternate layers of fuel to the top of the kiln, and the top being covered with sods, so as to prevent the heat from escaping, the fire is lighted, and the process effected. The lime is not removed till it is thoroughly cool. This mode is a tedious operation, and, because of the quantity of fuel consumed, far from economical. In the common lime-kiln, the fire is never suffered to go down, but as the well-burnt lime is removed, fresh lime is supplied. There is a species of kiln called a flame-kiln, in which the calcination is effected with peat. In this kiln the process of burning bricks is carried on at the same time.

1848. Lime burners have made the important observation, that the quantity of stone calcined and the quantity of fuel expended depend on the quality of the fuel. Hence the kiln is constructed with reference to the fuel, rather than to the nature of the stone to be calcined. Limestone, taking an average time, requires burning about sixty hours to reduce it to lime, when the heat is strong and well regulated: but of course no general rule can be laid down, as different species will require different periods of time. The principal object

to be accomplished, is the expulsion of the carbonic acid gas which enters into its composition.

1849. That lime is generally most esteemed which heats most in slaking, and slakes the quickest, falling into a fine powder. If there be among it coarse unslakeable lumps called core, that will not pass through the screen, either the stone has not been sufficiently burnt, or it originally contained extraneous matter; which not only indicates defect in quality, but that it will be, as they more or less abound, more costly in use.

1850. From the experiments of Mr. Smeaton and of Dr. Higgins, it is sufficiently proved that, when chalk or stone lime is equally fresh when used, the cementitious properties of both are nearly, if not quite, equal; but from the circumstance of quicklime absorbing carbonic acid more or less in proportion as its texture is solid or spongy, so it gradually parts with its cementing nature, becoming at length altogether unfit for the purposes of mortar. Thus, though each of the sorts may be equally good, if properly burnt and quite fresh from the kiln, yet from the chalk lime so much more easily and rapidly taking in the carbonic acid than stone lime does, it is not so fit for general use; and, indeed, now the metropolis is so well supplied with the harder chalk and stone limes, there is no excuse for its use, and it should in sound building be altogether banished.

1851. The following table, from Smeaton, contains a list of the limestones he examined on the occasion of building the Eddystone Lighthouse.

1852. In forming mortar from the lime, it must, when slaked, be passed through a sieve leaving only a fine powder, an operation usually performed with a quarter inch wire screen set at a considerable inclination to the horizon, against which the lime is thrown with a shovel after slaking. That which passes through is fit for use; the core falling on that side of the screen against which the lime is thrown, being entirely rejected for the purpose in question, though it is an excellent material for filling in the sides of foundations under wood floors where they would otherwise be next the earth, and the like. The sifted or screened lime is next to be added to the sand, whose quantity will vary as the quality of the lime, of which we shall presently speak. In making mortar, there is no point so important as respects the manufacture itself, as the well tempering and beating up the lime with the sand after the water is added to them. In proportion, too, as this is effectually done, will a small proportion of lime suffice to make a good mortar. The best mode of tempering mortar is by means of a pug-mill with a horse-track similar to the clay-mills used for making bricks. But if such cannot be had, the mortar should be turned over repeatedly, and beaten with wooden beaters, until it be thoroughly mixed. That this process should be carefully performed, will appear of the more importance when it is considered that it thereby admits a greater proportion of sand, which is not only a cheaper material, but the presence of it renders a less quantity of water necessary, and the mortar will consequently set sooner the work, too, will settle less; for as lime will shrink in drying, while the sand mixed with it continues to occupy the same bulk, it follows that the thickness of the mortar beds will be less variable. It may be taken, indeed, as an axiom, that no more lime is necessary than will surround the particles of sand.

1853. In most of the public works executed in Great Britain of late years, the proportion of lime to sand is as 1 to 3; and when the former is made from good limestone, the sand is by no means too much in proportion. Dr. Higgins, in his experiments, has gone so far as to recommend 7 parts of sand to 1 of lime, which, for mortar, perhaps carrying the point to the extreme.

1854. Various additions are made to mortar, in order to increase its hardness and