78 EFFECT'S of HEAT 



are fufible, others refractory ; the carbonate, when conftrained 

 by preffure to endure a proper heat, may be as fufible as the 

 muriate. 



One circumftance, derived from the Huttonian Theory, 

 induced me to hope, that the carbonate was eafily fufible, 

 and indicated a precife point, under which that fufion ought 

 to be expected. Nothing is more common than to meet with 

 nodules of calcareous fpar inclofed in whinflone ; and we fup- 

 pofe, according to the Huttonian Theory, that the whin and the 

 fpar had been liquid together \ the two fluids keeping fepa- 

 rate, like oil and water. It is natural, at the junction of thefe 

 two, to look for indications of their relative mobilities \ and we 

 find, accordingly, that the termination of the fpar is generally 

 globular and fmooth; which feems to prove, that, when the 

 whin became folid, the fpar was flill in a liquid ftate ; for had 

 the fpar congealed firft, the tendency which it fhews, on all oc- 

 cafions of freedom, to fhoot out into prominent cryflals, would 

 have made it dart into the liquid whin, according to the pecu- 

 liar forms of its cryftallization ; as has happened with the various 

 fubftances contained in whin, much more refractory than it- 

 felf, namely, augite, felfpar, &c. ', all of which having con- 

 gealed in the liquid whin, have afliimed their peculiar forms 

 with perfect regularity. From this I concluded, that when the 

 whin congealed, which mull have happened about 28 ° or 30* 

 of Wedgwood, the fpar was flill liquid. I therefore expected, 

 if I could compel the carbonate to bear a heat of 28 ° without 

 decompofition, that it would enter into fufion. The fequel will 

 mew, that this conjecture was not without foundation. 



I shall now enter upon the defer iption of thofe experiments, 

 the refult of wjiich I had the honour to lay before this Society 

 on the 30th of Augufl laft (1804) ; fully aware how difficult it is, 

 in giving an account of above five hundred experiments, all tend- 

 ing to one point, but differing much from each other in vari- 

 ous 



