3 1 6 4n Attempt to male a Thermometer 
obvious to need being mentioned. But in a naked fire 
where the heat is neceffarily mo:e fluttering, and une- 
qua!_ m different parts of the fuel, feme precaution will be 
required. 
The thermometer-piece may generally be put into the cru- 
cible, along with the fubjea-matter of the experiment. But 
Where the matter is of fuel, a End as to melt and ftick to it 
the piece may be previoufly inclofed in a little cafe made of 
emu e c ay. The imallnefs of the pieces will admit of this 
eing done without inconvenience, at ieaft in any but the 
imal eft crucibles, as the pieces themfelves may be diminifhed 
to any fee that may be found proper, provided only that one 
of the dimensions, five-tenths of an inch, be preferved, as 
. For the v ^y imalleft fort of crucibles, the cafe may be put 
in clofe to the crucible, fo as to form as it were an addition to 
IS bulk on the outfide. If ,t be afked, why the cafe is. not always 
thus put in by the fide of the crucible ? it is anfwered, that in 
ju gmg of the heat of large crucibles from a thermometer- 
piece placed on the outfide of them, we may fometimes be 
eceived, as the piece m its little cafe has been found to heat 
iooner than the matter in the larger veffel ; but in /mail ones, 
' he crucible and cafe are nearly alike in bulk, there is little 
danger of error from this caufe. 
X. Thefe thermometer-pieces poffefs fome fingular proper- 
ties which we could not have expetted to find united in any 
fubftance whatever, and which peculiarly fi t them for J 
purpofes they are here applied to. 
1. When baked by only moderate degrees of fire, though 
they are, like other clays, of a porous texture, and incite 
7 
water ; 
