Ordinarybricks are moulded in this country 0 inches long, 5 inches wide, and three inches hick, and are reduced by drying and burning o about 9 inches long, 41 inches wide, and a )roportionate thickness.
Kiln-burnt bricks, are, as their name ins flies, burnt in a kiln or oven instead of a damp, and have no ashes mixed with the day. Marl or maim stocks, which are either burnt, take their name from the marl originally used in them, which has now riven place to chalk. Dutch clinkers are a kind of small, hard, yellow bricks. Fire bricks, also called Windsor bricks, are 11 inch thick, and of a quality to resist the action of are. Paving bricks, draining bricks, capping or coping bricks, Coggin bricks, compass bricks for wells and circular works, feather-edged or thin bricks for the external parts of wooden buildings, and many other varieties of form, size, and quality, are also made. In some cases, a smooth or glazed surface is produced in the burning.
Much ingenuity has been directed, and of late years with great success, to the substitu tion of machinery for hand-labour in many of the processes of brick-making. The contri vances for this purpose are necessarily too complicated for description within our limits ; but as a general remark it may be observed, that the increased solidity and closeness of texture obtained in bricks so made recom mend them for use in the brick-work of rail way arches and tunnels, which has been found in some cases subject to decay from the alter nations of temperature and moisture. The comparative costliness of machine-made bricks has hitherto impeded their general use ; but machinery is already very extensively employed in the manufacture of draining and other tiles and other superior articles of the brick character.
It is known that the ancients were in pos session of a method of making bricks which, though having considerable strength, and a remarkable power of resisting heat, were yet of such small specific gravity that they floated on the surface of water. About the year 170C M. Fabbroni, an Italian, suggested that these bricks were probably made of a kind of earth found in Sicily, called mountain meal, con taining 55 per cent. of silica, 15 of
12 of clay, 3 of lime, 1 of iron, and 14 of water. Bricks formed of this material were found to be very slow conductors of and to be so light as to float in water. They • are not quite .so strong as common bricks, but can be made so by the addition of a little more pure clay. They unite well with and resist the action of mortar. These vari ous qualities render such a material very ser viceable for the construction of various parts of ships liable to be exposed to great heat; such as stoves; cooking arrangements, steam engine furnaces, 8.7c.; where lightness and in combustibility are wanted. Such bricks also might be used for constructing floating-houses on ornamental waters.
The recent repeal of the brick duty has already begun to produce beneficial effects, by allowing scope for the exercise of inventive talent. The duty, which was 5s. 10d. per thousand on ordinary bricks, increased largely if the bricks were either larger in size or of superior quality- ; so that the maker was de terred from any departure from ordinary size and quality. The number of bricks charged with duty- during the last few years, has varied from 1,200 to 1,000 millions. Since the repeal of the duty, measures have been taken to in troduce brick ornaments in architecture. Messrs. Bowers of Tunstall have patented a method of making brick ornaments by which the substance assumes a much more vitrified appearance than ordinary brick. A hydraulic press is used to force the prepared clay into moulds ; and the ornament is produced with a degree of sharpness equal to fine carving. It is intended to apply such liricks to the for mation of cornices, mouldings, skirting ;boards, finger-plates for doors, pilaster facings, orna mental archivolts, picture frames, upholsterers' fittings, Cc. The surface is so hard and smooth, that it is capable of being painted, grained, or gilt.
Mr. Robert's hollow bricks, introduced in 1849, are valuable for many purposes where dry, warm, and light brickwork is required.