MODIFIED ly COMPRESSION. 127 
weight, and the compound retaining its fufibility in low 
heats *. 
In the early part of 1804, fome experiments were made 
with barrels, which I wifhed to try, with a view to another 
feries of experiments. The refults were too interefting to be 
pafled over; for, though the carbonic acid in them was far 
from being completely conftrained, they afforded fome of the 
fineft examples I had obtained, of the fufion of the carbonate, 
and of its union with filex. 
On the 13th of February, an experiment was made with 
pounded oyfter-fhell, in a heat of 33°, without any water be- 
ing introduced to aflift compreflion. The lofs was apparently 
of 12 per cent. The fubftance of the fhell had evidently been 
in vifcid fufion : it was porous, femitranfparent, fhining in fur- 
face and fracture; in moft parts with the glofs of fufion, in 
many others with facettes of cryftallization. The little tube 
had been fet with its muzzle upwards ; over it, as ufual, lay a 
fragment of porcelain, and on that a round mafs. of chalk. 
At the contact of the porcelain and the chalk, they had run 
together, and the’ chalk had been evidently in a very foft ftate ; 
for, refting with its weight on the porcelain, this laft had been 
prefled mto the fubftance of the chalk, deeper than its own 
breadth, a rim of chalk beimg vifible without the furface of 
the porcelain ; juft as when the round end of a knife is preffed 
upon 
* The retentive power here afcribed to the procelain tubes, feems not to accord 
with what was formerly mentioned, of the carbonic acid having been driven 
through the fubftance of the tube. But the lofs by this means has probably been 
fo fmall, that the native properties of the carbonate have not been fenfibly 
changed. ' Or, perhaps, this penetrability may not be fo univerfal as I have 
been induced to think, by having met with it in all the cafes which I tried. 
In this doubt, I ftrenuoufly recommend a further examination of this fubjec& to 
gentlemen who have eafy accefs to fuch procelains as that of Drefden or of 
Seve. i 
