A new invention in the formation of bricks, by M. Le gressicr, has lately been announced in the ?rehives den Decouvertcs et des Inventions Xauvelles, pendant Pan nee 1809. The principle, however, is merely that of Mr Cartwright's, followed out to a greater extent than has perhaps ever been done in this country. NE. Le gressier proposes, that the bricks should be formed in seven different moulds, according as they are to be pla ced in the middle or on the exterior of the walls ; in the bottom or on the top; in the arches or in the corners; and by the proper disposition of these bricks in the building, every pressure, either longitudinally or late rally, is resisted, in proportion to the strength of the in dentures by which they are locked together. But as our limits will not admit of a detailed account of this supposed new invention, we shall present the reader with the original article.* Besides the place bricks, and grey and red stocks, which are used in common building, there are marls facing bricks, cutting bricks, fire bricks, and floating bricks. The first of these are of a fine yellow colour, hard and well burnt ; they are made in the neighbour hood of London, and are used in the outside of build ings. The cutting bricks are made of the finest kind of marls; and, as we have already observed, are em ployed in the construction of arches over windows and doors. Fire bricks, sometimes called Windsor bricks, because an excellent kind of them are made at Hedge sley, a village near Windsor. They contain a large proportion of sand, and will stand the utmost fury of fire, and are consequently used for coating furnaces, and lining the ovens of glass-houses. Clay for fire bricks is got at most great collieries, but particularly at Stourbridge, which produces the best clay for this pur pose in England. Floating bricks are a very ancient invention: they are so light as to swim in water ; and Pliny tells us, that they were made at :1Iarseilles, at Co lento in Spain, and at Phalle in Asia t This invention, however, was completely lost, until M. Fabbroni pub lished a discovery of a method to imitate the floating bricks of the ancients.I According to Posidonius, these bricks were made of a kind of argillaceous earth, which was employed to clean silver plate. But as it
could not be our tripoli, which is too heavy to float in water, NI. Fabbroni tried several experiments with mi neral agaric, Buhr, lac-Iun2c, and fossil meal, which last was found to be the very substance of which he was in search. This earth is abundant in Tuscany, and is found near Casteldelpiano, in the territories of Sienna. Ac cording to the analysis of M. Fabbroni, it consists of 55 parts of siliceous earth, 15 of magnesia, 14 of water, 12 of argil, 3 of lime, and one of iron. It exhales an argillaceous odour, and when sprinkled with water, throws out a light whitish smoke. It is infusible in the fire, and though it loses about an eighth part of its weight, its bulk is scarcely diminished. Bricks com posed of this substance, either baked or unbaked, float in water ; and a twentieth part of argil may be added to their composition without taking away their property of swimming. These bricks resist water, unite per fectly with lime, are subject to no alteration from heat or cold, and the baked differ from the unbaked only in the sonorous quality which they have acquired from the fire. Their strength is little inferior to that of com mon bricks, but much greater in proportion to their weight; for NI. Fabbroni found, that a floating brick, measuring 7 inches in length, 4 in breadth, and one in ch eight lines in thickness, weighed only 14? ounces ; whereas, a common brick weighed 5 pounds 6? ounces. The use of these bricks may be very important in the construction of powder magazines and reverberating furnaces ; as they arc such bad conductors of heat, that one end may be made red hot, while the other is held in the hand. They may also be employed for buildings that require to be light ; such as cooking places in ships, and floating batteries, the parapets of which would be proof against red hot bullets. The turrets which were raised on the ships of the ancients, says NI Fabbroni, were perhaps formed of these bricks ; and perhaps they were employed in the celebrated ship, sent by Hiero to Ptolemy, which carried so many buildings, consisting of porticoes, baths, halls, &c. arranged in mosaic, and ornamented with agates and jasper.
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