BRICK

BRICK, a kind of artificial stone made of baked clay. 1. The art of making bricks is so simple that it must have been practised in the earliest ages of the world; probably before mankind had discovered the method of fashioning stones to suit the purposes of building. The book of Genesis informs us, that burnt bricks were employed in the construction of Babel. Now, as this structure appears to have been raised about four hundred years after the period of the Flood, we may say, without much exaggeration, that the method of making bricks existed from the very origin of society. Bricks seem to have been in common use in Egypt while the Israelites were in subjection to that nation; for the task assigned them was the making of brick; and we are informed in Exodus that the Israelites built two Egyptian cities. No particulars are given in Scripture of the method of making bricks; but as straw was one of the ingredients, and as it very seldom rains in Egypt, it is probable that their bricks were not burnt, but merely baked by the heat of the sun. The same mode of making bricks seems still to be practised in the East; for the ruins of the tower near Bagdad are formed of unburnt bricks. We have seen specimens from that place; they are large, but thin, and have a brown colour. It is not at all likely that structures of unburnt brick should have been able to resist the weather since the time of Nebuchadnezzar; and hence it is probable that the tower in question was raised by the Arabs in comparatively modern times.

The art of brick-making was carried to considerable perfection by the Greeks. Pliny informs us that they made use of bricks of three different sizes, distinguished by the following names: didoron, or six inches long; tetradoron, or twelve inches long; and pentadoron, or fifteen inches long (lib. xxxv. c. 14). That the Romans excelled in the art of making bricks we have the amplest evidence, since brick structures raised at Rome 1700 years ago still remain as entire as when first built. Brick-making has been carried to great perfection by the Dutch, who have long been in the

habit of forming their floors, and even in some cases of paving their streets with bricks. And it is remarkable how long their bricks will continue uninjured in such situations. Though brick-making has long been carried on in England, and especially in the neighbourhood of London, upon a very great scale, and though the process upon the whole is conducted in this country with very considerable skill, yet it must be acknowledged that English bricks are by no means so durable as Dutch bricks. We are disposed to ascribe this inferiority not so much to the nature of the materials employed in the manufacture of English bricks, as to the mode most frequently employed in London in building houses. Few of the London houses, comparatively speaking, are freeholds. Most of them are built upon ground let for a lease of a certain number of years, which seldom exceeds ninety-nine years. After the expiration of this period, the house becomes the property of the landlord who let the ground. Thus it becomes the interest of the builder to construct the house so that it shall last only as long as the lease. Hence the goodness of the bricks becomes only a secondary object. Their cheapness is the principal point. The object, therefore, of the brickmakers is not to furnish durable bricks, but to make them at as cheap a rate as possible. Accordingly, the saving of manual labour, and of fuel, has been carried by the makers of London bricks to very great lengths. We cannot but consider this mode of proceeding as very objectionable, and as entailing a much heavier expense upon London than would have been incurred had twice the original price been laid out upon the bricks when they were first used, and had the houses been constructed to last a thousand instead of a hundred years. No doubt, certain advantages attend these ephemeral structures. The inhabitants are enabled, once every century, to suit their houses to the prevailing taste of the day; and thus, there are no antiquated houses in London. But as the increase of the price of all the materials of building has more than kept pace with the increase of the wealth of individuals, it is to be questioned whether the houses are always improved when they are pulled down and rebuilt.

2. The best material for making brick is what in the English language is called loam, a term usually applied to a natural mixture of sand and clay. Such a mixture may be converted into brick without any addition whatever. Marl likewise answers the purpose of common bricks very well, indeed better than most other mixtures. Marl is a natural mixture of limestone and clay in variable proportions. Now, the more lime it contains, the better does it answer for a manure; and the less lime it contains, the more suitable it is to the brick-maker.

It would be in vain to attempt a particular detail of the constituents of clay, because they vary too much from each other to admit of any correct generalization. We believe, however, that clays very frequently consist of decomposed felspar, in which case we may conceive them as composed of about three parts of silica in the state of a very fine powder, and one part of alumina. This is the case with porcelain clay. Indeed, the porcelain clay of Cornwall appears incontrovertibly to be nothing else than decomposed felspar, or perhaps felspar which never had assumed any other form than that of clay. The rock from which it is taken is an agglutinated mixture of quartz and this clay. The quartz is separated by washing. Such a rock might probably be converted into most beautiful brick, merely by cutting it out in the proper shape, and subjecting it to the requisite heat; or rather, by kneading the whole into a paste with the requisite quantity of water, moulding it into bricks, and then drying and burning them.

When the clay proceeds from the decomposition of hornblende, as is likewise often the case, it contains about three parts and a half of silica, one of alumina, one of lime, and about one and a half of oxide of iron. Sometimes the grains of sand which exist in clay consist of fragments of felspar. In such cases the clay may be fused by heat.

No mixture of alumina and silica, in any proportions whatever, can be fused by the strongest heat which can be raised in our furnaces. Hence such mixtures are best adapted for making fire-bricks, crucibles, and glass-house pots. Stourbridge clay is such a mixture, blackened by coaly matter. It answers these purposes better than any other clay in England. It is a slate clay belonging to the coal formation, and contains interspersed coaly matter. There is a similar bed of clay upon the banks of the Calder, about ten miles east from Glasgow. Mr Buttrey uses it to make the crucibles in which he fuses steel, a process requiring the most intense heat that can be raised in furnaces. Its quality seems fully equal to that of Stourbridge clay. Neither can a mixture of lime and alumina be fused, in whatever proportions the ingredients be mixed. But a mixture of silica, lime, and alumina, is very fusible, and the fusion is most readily effected when we employ two parts of silica to one of lime. The presence of oxide of iron also renders clay fusible, but not unless its proportion be much greater than ever is likely to occur in any clay used for the manufacture of bricks.

For making common bricks, the most durable mixture ought to be common clay and limestone or chalk. Perhaps the best proportions would be three parts of clay, and one part of limestone or chalk in powder. When such a mixture is exposed to heat, it would experience an incipient fusion, and would thereby be rendered much harder and denser than common bricks. The consequence would be, that it would imbibe much less water, and would therefore be much less liable to crack and fall to pieces in winter, than common bricks. For when water has insinuated itself into the pores of a common brick, and is converted into ice, it undergoes an expansion which dislocates the parts of the brick and reduces it to fragments. This is often conspicuously the case with tiles, which, from their exposed situation, are more liable to be soaked with water than common bricks. Hence also covering the surface of the brick with a coating of paint has a great tendency to preserve them from cracking and breaking. This practice is frequently followed in England.

It would be foreign to the object of this article to enter into any long details respecting the chemical investigations and the opinions entertained at different periods respecting the nature of clay. At first it was supposed to be a peculiar species of earth, but Hellot demonstrated that it consisted at least of two constituents; for sulphuric acid had the property of destroying its plastic nature, and of rendering it scarcely more adhesive than sand. The portion that remained behind did not effervesce with acids. It was not therefore of a calcareous nature. Mr Pott went a step farther; he showed, in the continuation of his Lithogéognosia, that sulphuric acid formed, with the por-

tion of clay which it dissolved, a salt possessing the properties of alum. In the year 1769 Baumé published his Dissertation on Clays, which he had drawn up in consequence of a premium offered by the Academy of Sciences at Bordeaux, for the best solution of the following question:—What are the principles and constituents of clay, and the natural changes which it experiences, and what are the methods of rendering it fertile? The academy did not consider Baumé's solutions as satisfactory. He published his Memoir, in consequence, as a kind of defiance. He had been employed along with Macquer in making numerous experiments on clay, with a view to the improvement of the porcelain manufacture in France. Guided by these experiments, he drew as a conclusion that clay is a mixture of two different substances: 1. Silica in a state of purity; 2. Silica combined with an under-dose of sulphuric acid. It was the second of these constituents that gave to clay its fattish and plastic nature. Margraaf had long before (in 1756) demonstrated that the ingredient of clay which Baumé took for a salt, and which he affirmed was soluble in water, was a peculiar species of earth, different from every other, which constitutes the basis of alum, which dissolves in sulphuric acid, but which does not form alum unless a portion of potash be added to the solution. Thus, by the labours of Hellot, Pott, Baumé, and Margraaf, the nature of clay was completely developed. It was ascertained to be a mixture of alumina and silica, in variable proportions. It was shown, also, that it sometimes contained sulphuric acid, and not unfrequently potash. Hence the reason why, in some cases, it could be converted into alum by digestion in sulphuric acid, without the necessity of adding any potash to the solution. Modern chemists have added considerably to these facts. They have shown that chalk, felspar, mica, hornblende, oxide of iron, coal, bitumen, &c. are not unfrequently mixed with it; and that these additions alter its qualities considerably, and render it fit or unfit for the different purposes to which clay is usually applied.

3. Clay intended to be made into bricks ought to be dug out of the earth and exposed to the air and weather for a considerable time before it is employed. The longer this exposure is continued, so much the better will it be fitted for making bricks. This exposure answers a variety of purposes. If the stones, by the decomposition of which the clay has been formed, are not entirely decomposed, this exposure serves to complete the process, by promoting the disintegrating action of the air and rain. The exposure serves likewise to pulverize the clay, which is essential to the making of good bricks. We have little doubt that the same amelioration in the clay would be produced by simply drying it in the open air, and then grinding it to powder in a mill. By such a process the quality of the bricks would be prodigiously improved. Nor do we conceive that such an addition would greatly enhance the expenses of the brickmaker, at least in those districts where the mill could be driven by water.

When the clay has been reduced to powder, the next step is to make it into a stiff paste with water. Too much water should not be employed, because it is injurious to the strength of the bricks; and the utmost care should be taken to mix the whole of the clay as equally as possible with the water. If some parts of the paste be moister than others, it will occasion an inequality in the texture of the bricks formed of it, will render them apt to crack, and will greatly injure both their strength and their beauty. Hence the great importance of working the clay for a considerable length of time before moulding it into bricks. It is in this part of the process that we believe British brickmakers in general are most defective. As far as we have had an opportunity of witnessing the pro-

cess of kneading the clay, as conducted either in the neighbourhood of London or Edinburgh, we have always found a great sparing of labour. Hence we believe the reason why so many of the English bricks appear full of cracks, even when sold to the builder. Such bricks ought never to be purchased, as it is perfectly obvious that they cannot make a durable building.

The kneading of the clay is performed in some places by men's feet, in others by the feet of horses, and in others by machinery. The last method is undoubtedly the best; and we conceive likewise that it might be rendered the cheapest. It would be easy to devise machinery for kneading the clay, upon principles similar to those employed in mashing by the London porter brewers. And, if such a machine were driven by water, we conceive that it would not be nearly so expensive as either men or horses.

When the clay is sufficiently kneaded, it is moulded into the form of a brick, by being put into a very simple wooden mould; and the upper part of the brick is made smooth and even by cutting off the superfluous part with a wooden knife. The process is very simple, and is conducted by the workmen with great rapidity. A good brickmaker would mould about 5000 bricks in a day. He disengages the bricks from the mould by a gentle stroke on the back of the mould; and the wet bricks are at first arranged in rows upon long boards. When sufficiently dry to be handled, they are turned, and at last piled up in loose walls, which are thatched with straw to keep off the rain. In this position they are allowed to remain till they have become as dry as they can become in the open air.

In many cases the clay used for brick-making is destitute of the requisite quantity of sand. If such clay were made into bricks, it would shrink so much in their burning, that the bricks would lose their shape, and would probably crack in every direction. To prevent this, it is necessary to add a certain quantity of sand. This sand should not be very fine. It answers best when the particles are of such a size as to be readily distinguished by the naked eye. Even when as large as coriander seeds, it has been found to answer better than very fine sand. The brickmakers in the neighbourhood of London bring their sand from the bottom of the Thames near Woolwich, where it is raised by boats employed for that purpose, and brought up the river for the use of the brick-makers.

4. No general directions can be given respecting the quantity of sand to be mixed with the clay, because that depends upon the nature of the clay and upon the uses for which the bricks are intended. The more sand is added, the more accurately do the bricks retain their shape, and the less apt are they to crack during the burning, but at the same time their strength is diminished. Chemical lutes are often composed of four parts of sand and one part of clay. Such mixtures do not contract much in burning, and, therefore, are not apt to crack and drop off, which is the reason why chemists employ them. But they have not the adhesiveness of brick after being burned, and would not therefore answer the purposes of the brick-maker. In stone-ware the mixture consists of about four parts of clay and one of fine sand. It burns to a hard cohesive substance, capable of striking fire with steel. Such a proportion, then, in many cases would answer the purposes of the brick-maker.

The London brick-makers make another addition to the clay, which we believe is peculiar to them. They add to every three parts of the clay about one part of the ashes from the fire-places of the city of London. These ashes contain some earthy matter; but they consist in a great measure of small coal unburnt and little altered, which has fallen through the interstices of the grate. The conse-

Brick. quence is, that such a mixture, when sufficiently heated, takes fire and burns of itself, though very slowly; so that the London bricks are burned in a great measure by means of the fuel mixed with the clay of which they are composed.

It is essential to dry the bricks thoroughly in the open air before burning them; for when heat is applied to wet clay, the water which it contains being prevented from escaping by the adhesiveness of the mixture, is converted into steam, and cracks, and breaks the mass of clay to pieces. Indeed, after the bricks are rendered as dry as they can become in the open air, they ought to be exposed at first to a gentle heat, which ought to be raised to redness very slowly, and in proportion as the moisture of the brick is dissipated. Water adheres with such obstinacy to clay, that it is never all driven off by the heat at which bricks are burnt. But the portion which remains is so intimately combined with the clay, as to constitute one solid mass, which has no great tendency to absorb an additional quantity of water.

Bricks are most commonly burnt in a kiln. This is a very simple structure, usually about thirteen feet long, ten and a half wide, and twelve feet high. The walls are one foot two inches thick, and incline a little to each other as they ascend. The bricks are placed on flat arches, having holes left in them like lattice-work. After the bricks are arranged on the kiln, to the number of about 20,000, they are covered with old bricks or tiles. Some brush-wood is then kindled in the kiln, and a moderate fire kept up till the bricks are rendered as dry as possible. The time required for this is two or three days; and the bricks are known to be dry when the smoke (which is at first black) becomes transparent. The mouth of the kiln is then filled up with pieces of brick and clay, leaving only room to introduce a faggot at a time. This structure at the mouth of the kiln is called a shinlog. The kiln is then supplied with faggots of furze, heath, fern, or whatever vegetable substance can be procured at the cheapest rate, till the arches look white, and the fire appears at the top. The fire is then diminished, and at length allowed to go out, and the kiln is permitted to cool. This burning process usually lasts about forty-eight hours.

The method of burning bricks in the neighbourhood of London is very different from this; and we do not know whether it be practised anywhere else. It obviously originated from the difficulty of procuring a sufficient quantity of vegetable matter to burn the enormous number of bricks consumed every year in London. If we consider the immense extension of houses which has taken place in London within the last fifty years, and if we consider that this vast city, containing nearly 1,500,000 inhabitants, is almost renewed every century, we may be able to form some notion of the prodigious quantity of bricks which it must consume. In the country round London there is a particular kind of clay, well known by the name of London clay. This clay is almost everywhere covered with a bed of gravel, which varies in thickness according to the elevation of the surface. Hence the whole of the country round London is fit for making bricks. Nothing more is necessary than to dig through the surface of gravel, and get to the clay.

We have already mentioned, that about a fourth part of the London bricks consists of small coal kneaded up along with the clay. When the bricks are sufficiently dry, they are piled up on each other in parallelopipedons to the intended height. Between each two rows of brick there is strewed a quantity of cinders, amounting to about three inches in thickness. At the distance of about nine feet from each other, perpendicular spaces are left, about a brick wide, which serve the purpose of flues. These

are made by arching the bricks over so as to leave a space between each about a brick in width. Over the whole is strewed a pretty thick covering of cinders. The flues are filled likewise with cinders, or, if they cannot be had, with coal. The fire-place is usually at the west end, and is generally three feet high. The fire, when once kindled in the fire-place, propagates itself very slowly through the whole clamp, as bricks piled in this manner are called. So very slow is the progress, that bricks in the neighbourhood of London take about three months in the burning. The heat is very intense, and, as the fuel is mixed up with the clay itself, every part of the brick is sure to be sufficiently burnt.

We conceive that the mixture of about one fourth of chalk with the clay of which the London bricks are made, would greatly improve their quality. The consequence would be an incipient fusion, which would render their surface much more compact and solid. The only difficulty would be to proportion the quantity of chalk so as to prevent complete fusion, which would run the bricks into each other, and destroy them entirely. Bricks made of materials which have undergone complete fusion would be greatly superior to common bricks. They would perfectly resist the action of the weather, and would, therefore, last much longer than common bricks. In Sweden it is customary at some of the iron foundries to cast the scoriae into bricks, which they employ in constructing their furnaces. Such furnaces the writer of this article has seen; and he was assured by the gentleman who had the charge of the works, that they answered fully better than common bricks. It would be easy to make any quantity of such bricks in some of the large iron foundries of Great Britain. We are persuaded that such bricks might be brought into use for a variety of purposes with great advantage, and might even constitute a lucrative article of manufacture. Bricks made from the scoriae of iron and copper foundries would vie in beauty with marble and porphyry, and would possess a lustre of surface to which few marbles could reach.

Few parts of Great Britain are so well adapted for the making of bricks, according to the London plan, as the neighbourhood of Newcastle-upon-Tyne. There the enormous heaps of small coal, which are of no use whatever, would furnish abundance of fuel at a much cheaper rate than even the London ashes; while the magnesian limestone that occurs in such plenty in the neighbourhood of Sunderland would enable the brickmaker to give the clay the requisite degree of fusibility.

As bricks form an article of taxation, and furnish a considerable revenue to government, their size has been regulated by act of parliament. They must not be less than eight and a half inches long, two and a half thick, and four inches wide. But, for various purposes, they are nevertheless made of very different and very considerable sizes.

Fire-bricks are made in the same way as common bricks. Fire-brick materials are different. The best clay for their bricks, composition is Stourbridge clay; and, instead of sand, it is usual to mix the clay with a quantity of old fire-bricks, or crucibles, or glass pots, reduced previously to powder. This mixture answers the same purposes as sand, while it does not communicate the tendency to fusion when it comes in contact with various fluxes that are communicated by siliceous sand.

There is a kind of bricks mentioned by Pliny as used Swimming by the ancients, which were so light as to swim in water, bricks. "Pitane in Asia, et in ulterioris Hispaniae civitatibus Maxilum et Calento, sunt lateres, qui ciccati non merguntur in aqua." (Plinii Natur. Histor. lib. xxxv. c. 14.) Pliny does not mention the part of the world in which the earth employed in the manufactures of these bricks was

found, though in all probability it could not be far from the cities where the bricks are said by Pliny to have been made. He says that the material employed was a kind of pumice stone. But it was quite unknown to the moderns, till, in the year 1791, Fabroni found a substance at Castel del Piano, not far from Santa Fiora, situated between Tuscany and the Papal dominions, which formed bricks capable of swimming in water. This is a white earthy matter, which constitutes a bed in that place, and was known in Italy by the name of Latte di Luna. In more recent mineralogical books it is distinguished by the name of farina fossilis (bergmehl). Haily considers it as a variety of talc, and Brochant as a variety of meerschaum. According to the analysis of Fabbroni this substance is composed of

But it has been recently analysed by Klaproth, who found its constituents,

We see from this analysis that this mineral is neither a variety of talc nor of meerschaum. One would be disposed to consider it as a hydrate of silica; for both the alumina and oxide of iron are present in so small proportions, that we can scarcely consider them as in chemical combination.

Considering the composition of this earth, it is rather singular that it is capable of being agglutinated by a red heat. We rather suspect that the bricks of Fabbroni, which swim in water, have but very little strength. This, if it be the case, must greatly circumscribe their utility.

The colour of the London bricks is not red, as is the case with common bricks and tiles, but a light brownish yellow. This colour is more pleasing to the eye than common brick red, and on that account the London bricks are preferred for building houses. The brick-makers assign a curious enough reason for this colour. According to them, their bricks are kept as much as possible from contact with the air during their burning. The consequence of this is, that the iron contained in them is not oxidized to so great a degree as in common bricks. But this mode of reasoning is far from being exact. If air were excluded entirely, the bricks would not be burnt at all, because the fire would be extinguished. But if enough of air be admitted to burn the coal mixed with the clay, which must be the case, that air must also act upon the iron, and reduce it to the state of peroxide. Indeed, there can be no doubt that the iron in the London yellow bricks is in the state of peroxide as well as in the red bricks, for the peroxide of iron gives various colours to bodies, according to circumstances. We find bodies tinged with it red, yellow, and brown, according to the substances with which the oxide is combined. We ascribe the yellow colour of the London bricks to the ashes of the coals, which, by uniting with the peroxides of iron, form a kind of yellow ochre. (L.)

Brick-layer, an artificer, whose business is to build with bricks, or make brick-work. The London brick-layers form a regular company, which was incorporated in 1568,

and consists of a master, two wardens, twenty assistants, and seventy-eight on the livery.

Brick-laying, the art of framing edifices of bricks. Moxon has written a treatise expressly on the art of brick-laying, in which he describes the materials, tools, and methods of working, used by brick-layers.

Great care is to be taken that bricks be laid joint on joint in the middle of the walls as seldom as may be; and that good bond be made there as well as on the outside. Some brick-layers, in working a brick and half wall, lay the header on one side of the wall perpendicular to the header on the other side, and so all along the whole course; whereas, if the header on one side of the wall were toothed as much as the stretcher on the other side, it would be a stronger toothed, and the joints of the headers of one side would be in the middle of the headers of the course they lie upon of the other side. If bricks be laid in winter, they ought to be kept as dry as possible; if in summer, it will save cost to employ boys to wet them, for they will then unite better with the mortar than if dry, and make the work stronger. In large buildings, or where it is thought too much trouble to dip all the bricks separately, water may be thrown on each course after they are laid. If bricks be laid in summer they must be covered; for if the mortar dries too hastily, it will not bind so firmly to the bricks as when left to dry more gradually. If bricks be laid in winter they should also be well covered, to protect them from rain, snow, and frost; which last is a mortal enemy to mortar, especially where it has been wetted just before the frost assaults it. See BUILDING.