158 
JBricks. 
or laterally, is resisted, in proportion to the strength of the inden- 
tures by which they are locked together. 
Besides the place bricks and grey and red stocks, which are 
used in common building, there are marie 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 
neighbourhood 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 pro* 
portion of sand, and will stand the utmost fury of fire, and are con- 
sequently used for coating furnaces, and lining the ovens of glass- 
houses. Clay for fire bricks is got at most great collieries, but par- 
ticularly 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 Marseilles, at Colento in Spain, and at Pitane in Asia. 
This invention, however, was completely lost, until M. Fabbroni 
published a discovery of a method to imitate the floating bricks of 
the ancients. 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 several experiments with mineral 
agaric, guhr, lac-lunse, and fossil meal, which last was found to be 
the very substance of which he was in search. This earth is abun- 
dant in Tuscany, and is found near Casteldelpiano, 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 one of iron. It exhales an argillaceous odour,, 
and when sprinkled with water throws out a light whitish smoke. 
It is infusible in the Are, and though it loses about an eighth part 
of its weight, its bulk is scarcely diminished. Bricks composed 
of this substance, either baked or unbaked, float in water ; and a 
twentieth part of argil may be added to their composition with- 
out taking away their property of swimming. These bricks re- 
sist water, unite perfectly 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 common bricks, but much 
greater in proportion to their weight; for M. Fabbroni found, that 
