Experiment IX
When we Diſſolve in Aqua Fortis a mixture of Gold and Silver melted into one Lump, it uſually happens that the Powder of Gold that falls to the bottom, as not being Diſſoluble by that Menſtruum, will not have its own Yellow, but appear of a Black Colour, though neither the Gold, nor the Silver, nor the Aqua Fortis did before manifeſt any Blackneſs. And divers Alchymiſts, when they make Solutions of Minerals they would Examine, are very Glad, if they ſee a Black Powder Præcipitated to the Bottom, taking it for a Hopefull Sign, that thoſe Particles are of a Golden Nature, which appear in a Colour ſo ordinary to Gold parted from other Metalls by Aqua Fortis, that it is a trouble to the Refiner to Reduce the Præcipitated Calx to its Native Colour. For though, (as we have try’d,) that may be Quickly enough done by Fire, which will make this Gold look very Gloriouſly (as indeed ’tis at leaſt one of the Beſt wayes that is Practis’d for the Refining of Gold,) yet it requires both Watchfulneſs and Skill, to give it ſuch a Degree of Fire as will ſerve to Reſtore it to its Luſtre, without giving it ſuch a One, as may bring it to Fuſion, to which the Minuteneſs of the Corpuſeles it conſiſts of makes the Powder very apt. And this brings into my Mind, that having taken a Flat and Bright piece of Gold, that was Refin’d by a Curious and Skilfull Perſon on purpoſe to Trye to what height of Purity Gold could be brought by Art, I found that this very piece, as Glorious as it look’d, being rubb’d a little upon a piece of fine clean Linnen, did ſully it with a kind of Black; and the like I have obſerv’d in Refin’d Silver, which I therefore mention, becauſe I formerly ſuſpected that the Impurity of the Metall might have been the only Cauſe of what I have divers times obferv’d in wearing Silver-hilted Swords, Namely, that where they rubb’d upon my Clothes, if they were of a Light-Colour’d Cloath, the Affriction would quickly Black them; and Congruouſly hereunto I have found Pens Blackt almoſt all over, when I had a while carri’d them about me in a Silver Ink-caſe. To which I ſhall only add, that whereas in theſe ſeveral Inſtances of Denigration, the Metalls are worn off, or otherwiſe Reduc’d into very Minute Parts, that Circumſtance may prove not Unworthy your Notice.