Experiment XII
The way, Pyrophilus, of producing Whiteneſs by Chymical Præcipitations is very well worth our obſerving, for thereby Bodyes of very Differing Colours as well as Natures, though diſſolv’d in Several Liquors, are all brought into Calces or Powders that are White. Thus we find that not only Crabs-eyes, that are of themſelves White, and Pearls that are almoſt ſo, but Coral and Minium that are Red, being diſſolv’d in Spirit of Vinegar, may be uniformly Præcipitated by Oyl of Tartar into White Powders. Thus Silver and Tin ſeparately diſſolv’d in Aqua Fortis, will the one Præcipitate it ſelf, and the other be Præcipitated by common Salt-water into a White Calx, and ſo will Crude Lead and Quickſilver firſt diſſolv’d likewiſe in Aqua Fortis. The like Calx will be afforded as I have try’d by a Solution of that ſhining Mineral Tinglaſs diſſolv’d in Aqua Fortis, and Præcipitated out of it; and divers of theſe Calces may be made at leaſt as Fair and White, if not better Colour’d, if inſtead of Oyl of Tartar they were Præcipitated with Oyl of Vitriol, or with another Liquor I could Name. Nay, that Black Mineral Antimony it ſelf, being reduc’d by and with the Salts that concurr to the Compoſition of common Sublimate, into that Cleer though Unctuous Liquor that Chymiſts commonly call Rectifi’d Butter of Antimony, will by the bare affuſion of ſtore of Fair Water be ſtruck down into that Snow-white Powder, which when the adhering Saltneſs is well waſh’d off, Chymiſts are pleas’d to call Mercurius Vitæ, though the like Powder may be made of Antimony, without the addition of any Mercury at all. And this Lacteſcence if I may ſo call it, does alſo commonly enſue when Spirit of Wine, being Impregnated with thoſe parts of Gums or other Vegetable Concretions, that are ſuppos’d to abound with Sulphureous Corpuſcles, fair Water is ſuddenly pour’d upon the Tincture or Solution. And I remember that very lately I did, for Tryal ſake, on a Tincture of Benjamin drawn with Spirit of Wine, and brought to be as Red as Blood, pour ſome fair Water, which preſently mingling with the Liquor, immediately turn’d the whole Mixture White. But if ſuch Seeming Milks be ſuffer’d to ſtand unſtirr’d for a convenient while, they are wont to let fall to the bottome a Reſinous Subſtance, which the Spirit of Wine Diluted and Weakned by the Water pour’d into it, was unable to ſupport any longer. And ſomething of Kin to this change of Colour in Vegetables is that, which Chymiſts are wont to obſerve upon the pouring of Acid Spirits upon the Red Solution of Sulphur, diſſolv’d in an Infuſion of Pot-aſhes, or in ſome other ſharp Lixivium, the Præcipitated Sulphur before it ſubſides, immediately turning the Red Liquor into a White one. And other Examples might be added of this way of producing Whiteneſs in Bodyes by Præcipitating them out of the Liquors wherein they have been Diſſolv’d; but I think it may be more uſefull to admoniſh you, Pyrophilus, that this obſervation admits of Reſtrictions, and is not ſo Univerſal, as by this time perhaps you have begun to think it; For though moſt Præcipitated Bodyes are White, yet I know ſome that are not; For Gold Diſſolv’d in Aqua Regis, whether you Præcipitate it with Oyl of Tartar, or with Spirit of Sal Armoniack, will not afford a White but a Yellow Calx. Mercury alſo though reduc’d into Sublimate, and Præcipitated with Liquors abounding with Volatile Salts, as the Spirits drawn from Urine, Harts-horn, and other Animal ſubſtances, yet will afford, as we Noted in our firſt Experiment about Whiteneſs and Blackneſs, a White Præcipitate, yet with ſome Solutions hereafter to be mentioned, it will let fall an Orange-Tawny Powder. And ſo will Crude Antimony, if, being diſſolv’d in a ſtrong Lye, you pour (as farr as I remember) any Acid Liquor upon the Solution newly Filtrated, whilſt it is yet Warm. And if upon the Filtrated Solution of Vitriol, you pour a Solution of one of theſe fix’d Salts, there will ſubſide a Copious ſubſtance, very farr from having any Whiteneſs, which the Chymiſts are pleas’d to call, how properly I have elſewhere examin’d, the Sulphur of Vitriol. So that moſt part of Diſſolv’d Bodyes being by Præcipitation brought to White Powders, and yet ſome affording Præcipitates of other Colours, the reaſon of both the Phænomena may deſerve to be enquir’d into.