The Adventitious Colours produc'd upon Metalls, or rather with them, by Saline Liquors, are many of them so well known to Chymists, that I would not here mention them, but that besides a not un-needed Testimony, I can add something of my own, to what I shall repeat about them, and divers Experiments which are familiar to Chymists, are as yet unknown to the greatest part of Ingenious Men. That Gold dissolv'd in _Aqua Regia_ ennobles the _Menstruum_ with its own Colour, is a thing that you cannot (_Pyrophilus_,) but have often seen. The Solutions of Mercury in _Aqua-fortis_ are not generally taken notice of, to give any notable Tincture to the _Menstruum_; but sometimes when the Liquor first falls upon the Quick Silver, I have observ'd a very remarkable, though not durable, Greenness, or Blewness to be produc'd, which is a _Phænomenon_ not unfit for you to consider, though I have not now the leisure to discourse upon it. Tin Corroded by _Aqua-fortis_ till the _Menstruum_ will work no farther on it, becomes exceeding White, but as we elsewhere note, does very easily of it self acquire the consistence, not of a Metalline _Calx_, but of a Coagulated matter, which we have observ'd with pleasure to look so like, either to curdled Milk, or curdled Whites of Eggs, that a person unacquainted with such Solutions may easily be mistaken in it. But when I purposely prepar'd a _Menstruum_ that would dissolve it as _Aqua-fortis_ dissolves Silver, and not barely Corrode it, and quickly let it fall again, I remember not that I took notice of any particular Colour in the Solution, as if the more Whitish Metalls did not much Tinge their _Menstruums_, though the conspicuously Colour'd Metalls as Gold, and Copper, do. For Lead dissolv'd in Spirit of Vinegar or _Aqua-fortis_ gives a Solution cleer enough, and if the _Menstruum_ be abstracted appears either Diaphanous or White. Of the Colour of Iron we have elsewhere said something: And 'tis worth noting, that though if that Metall be dissolv'd in oyl of Vitriol diluted with water, it affords a Salt or Magistery so like in colour, as well as some other Qualities, to other green Vitriol, that Chymists do not improperly call it _Vitriolum Martis_; yet I have purposely try'd, that, by changing the _Menstruum_, and pouring upon the filings of Steel, instead of oyl of Vitriol, _Aqua Fortis_, (whereof as I remember, I us'd 4 parts to one of the Metall) I obtain'd not a Green, but a Saffron Colour Solution; or rather a thick Liquor of a deep but yellowish Red. Common Silver, such as is to be met with in Coines, being dissolv'd in _Aqua fortis_, yields a Solution tincted like that of Copper, which is not to be wondred at, because in the coining of Silver, they are wont (as we elsewhere particularly inform you) to give it an Allay of Copper, and that which is sold in shops for refined silver, is not (so far as we have tryed) so perfectly free from that ignobler Metall, but that a Solution of It in