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; But if you Prosecute the Calcination, this Body which by a light Adustion was made White, will pass through other Colours, as Gray, Yellowish, and Red; and if you further burn it with a Long and Vehement fire, by that time it comes to be Perustum, it will be of a dark purple, nearer to Black, not only than the first Calx, but than the Vitriol before it at all felt the fire.  I might add that Crocus Martis (per se as they call it) made by the Lasting violence of the Reverberated flames is not so near a Kin to White, as the Iron or Steel that afforded it was before its Calcinations; but that