So much do these two Colours depend upon the Disposition of the
little parts, that the Bodies wherein they are to be met with do consist
of. And we find, that if Whitewine Tartar, or even the white Crystalls of
such Tartar be burnt without being truly Calcin'd, the _Cap. Mortuum_ (as
the Chymists call the more Fixt part) will be Black. But if you further
continue the Calcination till you have perfectly Incinerated the Tartar, &
kept it long enough in a Strong fire, the remaining _Calx_ will be White.
And so we see that not only other Vegetable substances, but even White
woods, as the Hazel, will yield a Black Charcoal, and afterwards Whitish
ashes; And so Animal substances naturally 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.
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