“8 EFFECTS of HEAT 
are fufible, others refra€tory ; the carbonate, when conftrained 
by preflure 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 whinftone ; and we fup- 
pofe, according to the Huttonian Theory, that the whin and the 
{par 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 fufibilities ; 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 ftill 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 cryftals, 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 affumed their peculiar forms 
with perfect regularity. From this I concluded, that when the 
whin congealed, which muft have happened about 28° or 30° 
of Wepcwoop, the {par was ftill liquid. I therefore expeted, 
if I could compel the carbonate to bear a heat of 28° without 
decompofition, that it would enter inte fufion. The fequel will 
fhew, that this conjecture was not without foundation. 
I sHALL now enter upon the defcription of thofe experiments, 
the refult of which I had the honour to lay before this Society 
on the 30th of Auguft laft (1804) 3 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 
