22 



ILLUSTRATIONS OF THE 



iiduLim obtained after combuflion under a pref- 

 fure no greater than the weight of the atmo- 

 fphere. It is in like manner reafonable to be- 

 lieve, that, on the application of heat to calca- 

 reous bodies under great compreffion, the car- 



bonic gas would be forced to remain 



the ge- 



neration of quicklime would be prevented, and 

 the whole might be foftened, or even complete- 

 melted ; which laft efFe6l, though not di- 

 redlj dedacible from any experiment yet made, 

 is rendered very probable, from the analogy of 

 certain chemical phenomena. 



1 6. An analogy of this kind, derived from a 

 property of the barytic earth, was fuggefted by 

 that excellent chemift and philofopher, the late 

 Dr Black. The barytic earth, as is well known, 

 has a ftronger attradion for fixed air than com- 

 mon calcareous earth has, fo that the carbonate 

 of barytes is able to endure a great degree of 

 heat before its fixed air is expelled. Accord- 

 ingly, when expofed to an increafing heat, at a 

 certain temperature, it is brought into fufion, 

 the fixed air fl:ill remaining united to it : if the 

 heat be further increafed, the air is driven olf, 



th 



earth lofes its fluidity 



d 



appears m a 



cauilic Hi 

 earth, wh 



Here, it is pi 



that the baryt 



fufible, or very refradlory, per 



fef as well as the calcareou 

 to the prefence of the fixed 



owes its fufibility 



d it is th 



fore 



