and Observations on Shell and Bone. 
3i 7 
Experiments on Porcellaneous Shells. 
Shells of this description, when exposed to a red heat in a 
crucible, during about a quarter of an hour, crackled and lost 
the colours of their enamelled surface ; they did not emit any 
apparent smoke, nor any smell like that of burned horn or car- 
tilage. Their figure remained unchanged, excepting a few 
flaws; and they became of an opaque white, tinged partially 
with pale gray, but retained part of their original gloss. 
The shells which had not been exposed to fire, (whether en- 
tire or in powder,) dissolved with great effervescence in the 
various acids ; and the solution afterwards remained colourless 
and transparent. 
But the shells which had been burned, upon being dissolved, 
deposited a very small quantity of animal coal; and thereby the 
presence of some gluten was denoted, although the proportion 
was too small to be discovered in the solution of the shells 
which had not been burned. 
The various solutions were filtrated, and were examined by 
pure ammoniac and acetite of lead ; but I never obtained any 
trace of phosphate of lime, nor of any other combination of phos- 
phoric acid. 
The carbonate of lime was afterwards precipitated by carbo- 
nate of ammoniac ; and, from many experiments it appeared, 
that porcellaneous shells consist of carbonate of lime, cemented 
by a very small portion of animal gluten. 
Previous to the experiments on shells composed of nacre or 
mother of pearl, I examined some Patellae from Madeira. 
When these were exposed to a red heat in a crucible, there 
was a perceptible smell, like that of horn, hair, or feathers. 
Tt 
MDCCXCIX. 
