180 "On the Floating Bricks 
half an inch above the point, and holding ‘them there: till 
the tallow. begins to fmoke. -This method, known to. alt 
watchmakers, may be-of.ufe to other artifts, and therefore 
not unworthy of the notice I have taken of it. dis 
——__-___ 
XIII. Account of M. Faxpront’s Difcovery of a Method 
to wmitate the Floating Bricks of the Ancients * 
Pauw Y mentions two cities in Spain, Maffilua and 
€alento, in which a kind of bricks.were made that would 
float in water. It is certain that Pliny docs not here fpeak 
6f hollow bricks; for thefe would have had too little ftrength 
for building.. He mu then mean folid bricks, but com- 
pofed of a fubftance fufficiently porous and light to float in 
water. ‘Thefe bricks, accordmg to Pofidonius, were made 
of a kind of argillaceous earth, which was employed to clean 
filver plate. As this earth could not be our tripoli, which is 
nich’ too heavy to float in water, M. Fabbroni thought 
that it might be that earth called commonly /ac luna, foftil 
meal, mineral agarie, and cuhr: this earth is abundant in 
Tufeany, and is there actually employed for cleaning plate.” 
Guhr is hquid, and the /ac lune approaches near to the 
mineral and calearcous agaric. The foffil meal, aecording 
to M. Fabbroni, is a mixt earth which exhales an argilla- 
ceous odour, and throws out a light whitifh fmoke when 
fprinkled with water. It does not effervefee with acids’ “is 
infufible in the fire, in which it lofes an eighth part of its 
weight, though it becomes fearcely diminifhed in bulk; and 
aécording to the analyfis made by M. Fabbroni, confifts of 
the following component parts: filiceous earth 55, mag- 
* Extracted from a fall work of 24 pages odtavo, publithed at Venice, 
laft year, under the following title: Dy wia_fingolariffima /pecie dé.mattoni 
Offa ritrovamento degli antichi mattoni gallegianti, différtaxione leita nella 
publica adunanza det Georgofili di Fireaxe, l'anno 1791, dal Signor 
FABBRONI. 29 igs 
nefia 
ee 
(fo a. 
