96 EFFECT'S of HEA<t 



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 fpecific gravity. 

 On feveral occalions, I obferved, that mafles of chalk, which, 

 before the experiment, had fhewn one uniform character of 

 whitenefs, afliimed a ftratined 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 have 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 influence of the 

 carbonic acid, as varied by its quantity. 



When the lofs exceeded 10 or 15 per 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 conlidered as good, and pollened 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 pofTefling a high cha- 

 racter of cryftallization j but it was unable to refift the ac- 

 tion of the air ; and, by attracting carbonic acid or moifture, 

 or both, crumbled to dull 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 



* I have found, that, in open fire, the entire lofs fuftained by the carbonate va- 

 ries in different kinds from 42 to $$•$ per cent. 



