100 EFFECTS OP HEAt. 



th« carbonate (brinks upon itfelf and agglutinates into a firtfl 

 mafs, which in point of hardneis and fperific gravity ap-^ 

 preaches very near to common lime-flone, an.I foraetimes equals 

 it, and whicii has frequently acquired the fj)arkling frafture, 

 the femi-tranfparency, the flifceptibility of polifli, and tiio 

 general afped of marble. The fame refult is obtained when 

 a folid piece of chalk is treated in a fimilar manner, and the 

 Oi-Mt eontrac- chalk being previonfly meafured in Wedgwood's gage, is 

 *hjdk ^ ^ found to contra6t during the action of heat three times more 

 than the pyrometer pieces do in the fame temperature. During 

 the action of heat, the carbonate is found to have loft very lit- 

 tle of its weight; that lofs amounting in many cafes to lefs 

 than one per cent, and in fome experiments it has urtdefgone 

 no fenfible lofs at all, or fo very fmall a one, that it may be 

 negledled without fear of error. When thrown into an acid, 

 this artificial limeftone effervefces violently as it ditTolvcs, the 

 difcharge of gas continuing whilft the fmalleft atom of carbo' 

 jiate remains viiible. 

 Irnperfcft fufion I have been in poiTeffion of this fadt fince the year 1801, and 

 of the chalk. I long attempted in vain to carry the experiment farther, fo as 

 to accomplifl^ the fufion of the carbonate. In one folitary and 

 accidental inftance, I had fucceeded in obtaining it in a ftale 

 of real froth, which could not have been produced without 

 previous liqiiefadion; but being unable to repeat this refult, I 

 was unwilling to publith it or any of the fads already ftaled, 

 till I could do fo in a more fatisfaclory manner. In thecourfe 

 of laft winter, with the help of many improvements in my 

 mode of operation, and of ftronger apparatus, I at lafl ac- 

 quired the power of performing repeatedly and even with 

 tolerable certainty, what at firft had been the effed of chance. 

 Aftual fufion* In thefe experiments carbonate of lime has not only been ag- 



Tliis obfervatian relates to the pyrometer pieces fold by the late 

 Mr. Wedgwood, which were formed of a mixture of aluminc 

 with Cornifli porcelain clay. This let having been the only o»e 

 ever diftrlbuted amongft cheniifts, muft certainly be looked upon as 

 the ftandard. Other fcts had previoufly been made by him of 

 Cornifh clay alone, which had never been fent abroad, or at leaft 

 only given to fbme friends. It is poflible that the difcordance ah 

 laded to in this note, may have been occafioned by experiments 

 made with thdfe firft Pets, which may have pofTefled different pro-" 

 perties from thole afterwards fold. 



glutinatedj 



