222 yARMERs' AND MECHANICS' JOURKAL. 



bricks, fire bricks, and floatiiig'bricks. The first of these arc of a 

 fine yellow color, hard and well burnt ; they are made in the neigh- 

 borhood of London, and are used in the outside of buildings. The 

 cutting bricks are made of the finest kind of marie ; and, as we 

 have already observed, are employed in the construction of arches 

 over windows and doors. Fire bricks, sometimes called Windsor 

 bricks, because an excellent kind of them are made at Hedgesley, 

 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 purpose in Eng- 

 land. 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 Marseilles, at Colento in Spain, and at Pitane in Asia. This in- 

 vention, however, was completely lost, until M. Fabbroni publish- 

 ed a discovery of a method to imitate the floating bricks of the an- 

 cients. 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, M. Fabbroni tried seveial experiments with mineral agaric, 

 guhr, lac-lun(P, 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 Casteldclpiano, in the territories of 

 Sienna. According 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 I 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 

 i(s v.eiglit, its bulk is scarcely diminished. Bricks composed of 

 Ibis sul)statire, 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 wa- 

 ter, unite perfectly with lime, are subject to no alteration from heat 

 or cold, and the baked differ from the unbaked only in the sono- 

 rous qualily which they have acquired from the fire. Their 

 strength is little inferior to that of common bricks, but much great- 

 er in proportion to their weight ; for M. Fabbroni found, that a 

 floating brick, measuring 7 inches in length, 4 1-2 iti breadth, and 

 one inch eight lines in thickness, weighed only 14 1-2 ounces; 

 whereas, a common brick weighed 3 pounds 6 3-4 ounces. The 

 use of these bricks may be very important in the construction of 

 powder magazines and reverberating furnaces ; as they are 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 build- 

 ings 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 M. Falihroni, were perhaps formed of these bricks ; 

 and perhaps they wvre employed in (he celebrated ship, sciit by 



