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XXI. For ſome burſt[1] and fly in Pieces in the Fire: as, though not fuſible, yet not of Power wholly to reſiſt the Force of the Heat; which is alſo
- ↑ Some few Species of Flints are Subſtances of this Kind, and above all others that found in whole Strata (not in detached Maſſes or Nodules, as our common Flints are) and called Chert or Whern in ſome Parts of England; a Lump of this, put into a moderate Fire, will, as the Heat penetrates it, fly to Pieces in Scales or thin Flakes, which fall off, fromTime to Time, till the whole is reduced to a Maſs of coarſe Powder: but it is an Error to infer from this, that theſe Stones are not fu-
reous Matter, either in detached Pieces of different Figures and Textures; or in whole Veins. The various Kinds of them contain different Quantities of different Metals, but generally too ſmall to be worth the Charge and Trouble of working. Gold, Silver, Copper, and Iron are frequently found thus in them, But the principal Subſtances of which they are formed are Salts, Sulphurs, and Earths. The common Coppers of our Shops is made from different Kinds of them, in different Quantities; and no Species yields it in ſuch Plenty as the echinated Kind of the Chalk Pits of Kent and Surrey. The Marchaſites, as thoſe are particularly called which are not in detached Pieces, but run in Veins, or fill the perpendicular Fiſſures of Strata, often abound with Copper, and with a mineral, arſenical Juice, ſeldom found in the others; ſome of theſe alſo contain Antimony; others Biſmuth, and ſome Iron and Tin. When they are very rich in theſe Metals, they loſe the Name of Marchaſites, andare called Ores. The Mineral, called in ſome Parts of England Mundick, is of this Kind, containing Copper and ſometimes other Metals; but the Sulphur is ſo abundant in theſe kinds of Ores, that they are not to be fluxed without great Trouble; the Addition of Lime, or ſome ſimilar Subſtance, is often neceſſary to bring them to fuſe at all, and at beſt they are the moſt troubleſome, and leaſt profitable; unleſs where very rich indeed, of any Ores in the World.
This Author however was not ſingle, though erroneous, in his Opinion of the Pyritæ and Molares melting in the Fire; his Maſter Ariſtotle had probably led him into it, who has, Met. L. 4. c. 6. τήκεται δὲ κὰι ὁ λίθος ὁ πυρίμαχος, ὥστε στάζειν κὰι ῥεῖν, τὸ δὲ ηγνύμενον ὅταν ῥυῇ πάλιν γίγνεται σκληρὸν, κὰι αἱ μύλιαι τήκονται ὥστε ῥεῖν.
