Experiment XLVI
We have often taken notice, as of a remarkable thing, that Metalls as they appear to the Eye, before they come to be farther alter’d by other Bodyes, do exhibit Colours very different from thoſe which the Fire and the Menſtruum, either apart, or both together, do produce in them; eſpecially conſidering that theſe Metalline Bodyes are after all theſe diſguiſes reducible not only to their former Metalline Conſiſtence and other more radical properties, but to their Colour too, as if Nature had given divers Metalls to each of them a double Colour, an External, and an Internal; But though upon a more attentive Conſideration of this difference of Colours, it ſeem’d probable to me, that divers (for I ſay not all) of thoſe Colours which we have juſt now call’d Internal, are rather produc’d by the Coalition of Metalline Particles with thoſe of the Salts, or other Bodyes employ’d to work on them, than by the bare alteration of the parts of the Metalls themſelves: and though therefore we may call the obvious Colours, Natural or Common, & the others Adventitious, yet becauſe ſuch changes of Colours, from whatſoever cauſe they be reſolv’d to proceed may be properly enough taken in to illuſtrate our preſent Subject, we ſhall not ſcruple to take notice of ſome of them, eſpecially becauſe there are among them ſuch as are produc’d without the intervention of Saline Menſtruums. Of the Adventitious Colours of Metalline Bodies the Chief ſorts ſeem to be theſe three. The firſt, ſuch Colours as are produc’d without other Additaments by the Action of the fire upon Metalls. The next ſuch as emerge from the Coalition of Metalline Particles with thoſe of ſome Menstruum imploy’d to Corrode a Metall or Precipitate it; And the laſt, The Colours afforded by Metalline Bodyes either Colliquated with, or otherwiſe Penetrating into, other Bodies, eſpecially fuſible ones. But theſe (Pyrophilus,) are only as I told you, the Chief ſorts of the adventitious Colours of Metalls, for there may others belong to them, of which I ſhall hereafter have occaſion to take notice of ſome, and of which alſo there poſſibly may be others that I never took notice of.
And to begin with the firſt ſort of Colours, ’tis well enough known to Chymiſts, that Tin being Calcin’d by fire alone is wont to afford a White Calx, and Lead Calcin’d by fire alone affords that moſt Common Red-Powder we call Minium: Copper alſo Calcin’d per ſe, by a long or violent fire, is wont to yield (as far as I have had occaſion to take notice of it) a very Dark or Blackiſh Powder; That Iron likewiſe may by the Action of Reverberated flames be turn’d into a Colour almoſt like that of Saffron, may be eaſily deduc’d from the Preparation of that Powder, which by reaſon of its Colour and of the Metall ’tis made of is by Chymiſts call’d, Crocus Martis per ſe. And that Mercury made by the ſtreſs of Fire, may be turn’d into a Red Powder, which Chymiſts call Precipitate per ſe, I elſewhere more particularly declare.
Annotation I.
It is not unworthy the Admoniſhing you, (Pyrophilus,) and it agrees very well with our Conjectures about the dependence of the change of a Body’s Colour upon that of its Texture, that the ſame Metall may by the ſucceſſive operation of the fire receive divers Adventitious Colours, as is evident in Lead, which before it come to ſo deep a Colour as that of Minium, may paſs through divers others.
Annotation II.
Not only the Calces, but the Glaſſes of Metalls, Vitrify’d per ſe, may be of Colours differing from the Natural or Obvious Colour of the Metall; as I have obſerv’d in the Glaſs of Lead, made by long expoſing Crude Lead to a violent fire, and what I have obſerv’d about the Glaſs or Slagg of Copper, (of which I can ſhow you ſome of an odd kind of Texture,) may be elſewhere more conveniently related. I have likewiſe ſeen a piece of very Dark Glaſs, which an Ingenious Artificer that ſhow’d it me profeſs’d himſelf to have made of Silver alone by an extreme Violence (which ſeems to be no more than is needfull) of the fire.
Annotation III.
Minerals alſo by the Action of the Fire may be brought to afford Colours very differing from their own, as I not long ſince noted to you about the variouſly Colour’d Flowers of Antimony, to which we may add the Whitiſh Grey-Colour of its Calx, and the Yellow or Reddiſh Colour of the Glaſs, where into that Calx may be flux’d.
And I remember, that I elſewhere told you, that Vitriol Calcin’d with a very gentle heat, and afterwards with higher and higher degrees of it, may be made to paſs through ſeveral Colours before it deſcends to a Dark Purpliſh Colour, whereto a ſtrong fire is wont at length to reduce it. But to inſiſt on the Colours produc’d by the Operation of fire upon ſeveral Minerals would take up farr more time than I have now to ſpare.