Patterns (for Gold and Silver Works) as I have sometimes taken great Pleasure to Look upon. Sometimes the Bodies mingled by the Fire are Differing enough as to Fixidity and Volatility, and yet are so combin'd by the first Operation of the Fire, that it self does scarce afterwards Separate them, but only Pulverize them; whereof an Instance is afforded us by the Common Preparation of _Mercurius Dulcis_, where the Saline Particles of the Vitriol, Sea Salt, and sometimes Nitre, Employ'd to make the Sublimate, do so unite themselves with the Mercurial Particles made use of, first to Make Sublimate, and then to Dulcifie it, that the Saline and Metalline Parts arise together in many successive Sublimations, as if they all made but one Body. And sometimes too the Fire does not only not Sever the Differing Elements of a Body, but Combine them so firmly, that Nature her self does very seldom, if ever, make Unions less Dissoluble. For the Fire meeting with some Bodies exceedingly and almost equally Fixt, instead of making a Separation, makes an Union so strict, that it self, alone, is unable to Dissolve it; As we see, when an Alcalizate Salt and the Terrestrial Residue of the Ashes are Incorporated with pure Sand, and by Vitrification made one permanent Body, (I mean the course or greenish sort of Glass) that mocks the greatest Violence of the Fire, which though able to Marry the Ingredients of it, yet is not able to Divorce them. I can shew you some pieces of Glass which I saw flow down from an Earthen Crucible purposely Expos'd for a good while, with Silver in it, to a very vehement Fire. And some that deal much in the Fusion of Metals Informe me, that the melting of a great part of a Crucible into Glass is no great Wonder in their Furnaces. I remember, I have Observ'd too in the Melting of great Quantities of Iron out of the Oar, by the Help of store of Charcoal (for they Affirm that Sea-Coal will not yield a Flame strong enough) that by the prodigious Vehemence of the Fire, Excited by vast Bellows (made to play by great Wheels turn'd about by Water) part of the Materials Expos'd to it was, instead of being Analyz'd, Colliquated, and turn'd into a Dark, Solid and very Ponderous Glass, and that in such Quantity, that in some places I have seen the very High-wayes, neer such Iron-works, mended with Heaps of such Lumps of Glasse, instead of Stones and Gravel. And I have also Observ'd, that some kind of Fire-stone it Self, having been employ'd in Furnaces wherein it was expos'd to very strong and lasting Fires, has had all its Fixt Parts so Wrought on by the Fire, as to be Perfectly Vitrifi'd, which I have try'd by Forcing from it Pretty large Pieces of Perfect and Transparent Glass. And lest You might think, _Eleutherius_, that the Question'd Definition of Heat may be Demonstrated, by the Definition which is wont to be given and Acquiesc'd in, of its contrary Quality, Cold, whose property is taught