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 I ſuppoſe, theſe Inſtances may Suffice to ſatisfie you, that Minerals are to be excepted out of the forementioned Rule, which perhaps, though it ſeldome fail in ſubſtances belonging to the Vegetable or Animal Kingdome, may yet be Queſtion’d even in ſome of theſe, if that be true, which the Judicious Traveller Bellonius affirms, that Charcoales made out of the Wood of Oxycæder are White; And I could not find that though in Retorts Hartſhorn and other White Bodies will be Denigrated by Heat, yet Camphire would not at all loſe its Whiteneſs, though I have purpoſely kept it in ſuch a heat, as made it melt and boyl.