,*{8S ACTION OF HEAT MODIFIED 



Upon (he whole, were falisfadory, fincfe Ihey feemed t» 

 eftabli{h forae of the eiTenlia! points of this Inquiry. 



Thefe experiments prove, that, by mechanical conftraint, 

 the carbonate of lime can be made to undergo flrong heat, 

 without calcination, and to retain almoll the whole of its car- 

 bonic acid, which, in an open fire, at the fame temperature, 

 would have been entirely driven off: and that, in thefe cir- 

 cumftances, heat produces fome of the identical effefls afcrib- 

 ed to it in the Hattonian Theory. 

 Pounded car- By this joint aftion of heat and preflure, the carbonate of 



^n>Tff\T J'ine which had been introduced in the flate of the finefl 



in ICS ICVcl at 



varieties became powder, is agglutinated into a firm mafs, pofTeffing a degree 

 ftoil^^raaSS' '"^° "^ hardnefs, coinpa(5lnefs, and fpecific gravity * nearly ap- 

 proaching to thefe qualities in a found limeftone; and forae 

 of the refults, by their faline fra6lure, by their femitranf- 

 parency, and their fufceptibility of poliQi, deferve the name 

 of marble. 



The fame trials have been made with all calcareous fub- 

 fiances ; with chalk, common limeftone, marble, fpar, and 

 ;, the fhells of fifli. All have Ihevvn the fame general property, 



with fome varieties as ia temperature. Thus, I found, that, 

 in tbe fame circumftances, chalk was more fufceptible of ag- 

 glutination than fpar ; the latter requiring a heat two degrees 

 higher than the former, to bring it to the fame pitch of ag- 

 glutination. 



The chalk ufed in my firft experiments, always afTumed the 

 character of a yellow marble, owing probably to fome flight 

 contamination of iron. When a folid piece of chalk, whofe 

 bulk had been previoufiy meafured in the gauge of Wedgwood's 

 pyrometer was fiibmitted to heat under compreffion^ its con- 

 tra61ion was remarkable, proving the approach of the particles 

 during their confolidation ; on thefe occafions, it was found 

 to ft^rink three times more than the pyrometer-pieces in the 

 fame temperature. It loft, too, almoft entirely, its power of 

 imbibing water, and acquired a great additional fpecific 

 jrravitv. On feveral occafions, I obferved, (hat mafTes of 

 clialk, which, before the experiment, had fliewn one uniform 

 character of whitenefs, afTumed a ftratified appearance, in- 

 dicated by a feries of parallel layers of a brown colour. This 



* See Appendix. 



6 circumftanca 



