96 EPPECTS of HEAT 
to fhrink three times more than the pyrometer-pieces in the 
fame temperature. It loft, too, almoft entirely, its power of im- 
bibing water, and acquired a great additional {pecific gravity. 
‘On feveral occafions, I obferved, that mafles of chalk, which, 
before the experiment, had fhewn one uniform character of 
whitenefs, aflumed a ftratified appearance, indicated by a feries 
of parallel layers of a brown colour. This circumftance may 
hereafter throw light on the geological hiftory of this extraor- 
dinary fubftance. 
I wave faid, that, by mechanical conftraint, almoft the 
whole of the carbonic acid was retained. And, in truth, at 
this period, fome lofs of weight had been experienced in all 
the experiments, both with iron and porcelain. But even this 
circumftance is valuable, by exhibiting the infinenee of the 
carbonic acid, as varied by its quantity. 
Wuen the lofs exceeded 10 or 15 fer cent *. of the weight 
of the carbonate, the refult was always of a friable texture, 
and without any ftony character; when lefs than 2 or 3 per 
cent. it was confidered as good, and pofleffed the properties 
of a natural carbonate. In the intermediate cafes, when 
the lofs amounted, for inftance, to 6 or 8 per cent., the re- 
fult was fometimes excellent at firft, the fubftance bearing 
every appearance of foundnefs, and often poflefling a high cha- 
racter of cryftallization ; but it was unable to refift the ac- 
tion of the air; and, by attracting carbonic acid or moifture, 
or both, crumbled to duft more or lefs rapidly, according to 
circumftances. This feems to prove, that the carbonate of 
lime, though not fully faturated with carbonic acid, may pof- 
fefs the properties of limeftone ; and perhaps a difference of 
this 
* T have found, that, in open fire, the entire lofs fuftained by the carbonate va- 
ries in different kinds from 42 to 45.5 per cent. 
