100 EFFECTS of HEAT 
by which the laft could be counteracted ; but I faw no remedy 
for the firft. I began, therefore, to defpair of ultimate fuccefs 
with tubes of porcelain *. 
ANOTHER circumftance confirmed me in this opinion. I 
found it impracticable to apply a heat above 27° to thefe tubes, 
when chargedas above with carbonate, without deftroying them, 
either by explofion, by the formation of a minute rent, or by 
the actual fwelling of the tube. Sometimes this fwelling took 
place to the amount of doubling the internal diameter, and 
yet the porcelain held tight, the carbonate fuftaining but a 
very fmall lofs. This ductility of the porcelain in a low 
heat is a curious fact, and fhews what a range of temperature 
is embraced by the gradual tranfition of fome fubftances from 
a folid to a liquid ftate: For the fame porcelain, which is 
thus fufceptible of being ftretched out without breaking in a 
heat of 27°, ftands the heat of 152°, without injury, when ex- 
pofed to no violence, the angles of its fracture remaining fharp 
and entire. 
IV. 
* IT am neverthelefs of opinion, that, in fome fituations, experiments with com- 
preflion may be carried on with great eafe and advantage in fuch tubes. I allude 
to the fituation of the geologifts of France and Germany, who may eafily procure, 
from their own manufaétories, tubes of a quality far fuperior to any thing made 
for fale in this country. 
