rally White, as Bones and Eggshels,
will grow Black upon the being Burnt, and White again when they are
perfectly Calcin'd.

_EXPERIMENT IV._

But yet I much Question whether that Rule delivered by divers, as well
Philosophers as Chymists, _adusta nigra, sed perusta alba_, will hold as
Universally as is presum'd, since I have several Examples to allege against
it: For I have found that by burning Alablaster, so as both to make it
appear to boyl almost like Milk, and to reduce it to a very fine Powder, it
would not at all grow Black, but retain its Pure and Native Whiteness, and
though by keeping it longer than is usual in the fire, I produced but a
faint Yellow, even in that part of the Powder that lay nearest the top of
the Crucible, yet having purposely enquired of an Experienced Stone-cutter,
who is Curious enough in tryng Conclusions in his own Trade, he told me he
had found that if Alabaster or Plaster of Paris be very long kept in a
Strong fire, the whole heap of burnt Powder would exchange its Whiteness
for a much deeper Colour than the Yellow I observ'd. Lead being Calcin'd
with a Strong fire turns (after having purhaps run thorough divers other
Colour) into _Minium_, whose Colour we know is a deep red; and if you urge
this _Minium_, as I have purposely done with a Strong fire, you may much
easier find a Glassie and Brittle Body darker than _Minium_, than any white
_Calx_ or Glass. 'Tis known among Chymists, that the white _Calx_ of
Antimony, by the further and more vehement operation of the fire, may be
melted into Glass, which we have obtain'd of a Red Colour, which is far
deeper than that of the _Calx_ of Burnt Antimony, and though common Glafs
of Antimony being usually Adulterated with _Borax_, have its Colour thereby
diluted, oftentimes to a very pale Yellow; yet not onely ours made more
sincerily, was, as we said, of a Colour less remote from Black, than was
the _Calx_; but we observ'd, that by Melting it once or twice more, and so
exposing it to the further operation of the Fire, we had, as we expected,
the Colour heightned. To which we shall add but this one Instance, (which
is worth the taking notice of in Reference to Colours:) That, if you take
Blew, but Unsophisticated, Vitriol, and burn it very slowly, and with a
Gentle degree of Heat, you may observe, that when it has Burnt but a
Little, and yet so far as that you may rub it to Powder betwixt your
fingers, it will be of a White or Whitish Colour; B