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 parallelopipeds 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 founderies to cast the scoria 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 founderies 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 scoria of iron and copper founderies 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, but the 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 by the ancients, which were so light as to swim in water. "Pitane in Asia, et in ulterioris Hispaniae civitatibus Maxilum et Calento, fluit latares, qui cicatiz non merguntur in aqua." (Plini Natur. Histor. lib. xxxv. c. 14.) Pliny does not mention the part of the world in which the earth employed in the manufacture 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 is known in Italy by the name of Lotte di Lucca. In more recent mineralogical books it is distinguished by the name of ferrina fossilit (bergmuth). Hauy 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:

| Substance | Percentage | |---------------|------------| | Silica | 55 | | Magnesia | 15 | | Alumina | 12 | | Lime | 3 | | Iron | 1 | | Water | 14 |

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

| Substance | Percentage | |---------------|------------| | Silica | 79 | | Alumina | 5 | | Oxide of iron | 3 | | Water | 12 | | Loss | 1 |

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.

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 outsides. 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 toothing, 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.