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CXVIII. That its fiery Power is very great, is evident from this remarkable Inſtance: That a certain Ship which was laden with Cloaths, by ſome Accident letting in Water; the Cloaths being wetted by that Means, the Gypſum that was put among them took fire, and burnt both the Cloaths and the Ship.
CXIX. In Syria and Phœnicia they prepare a Gypſum by Fire; putting into proper Furnaces Stones, principally of the Marble, and other Kinds, which are of the moſt ſimple Texture, and heating them to a certain Degree; the harder Kinds they lay upon thoſe which burn more readily; and when burnt,
leſs elegant than the Rhomboidal or plated Kinds. Thoſe reſemble the foliaceous Talcs; and theſe the ſofter of the Alabaſters. We may always by Glaſſes diſtinguiſh the flaky Texture of the Selenite in the Gypſum; and thoſe unerring Teſts by Weight and Firmneſs, give convincing Proofs of the Truth. Gypſum is lighter as well as ſofter than Spar; but differs very little in either of theſe Qualities from the pure Selenite: To which we may add the Effect of Fire; for the fineſt Plaiſter in the World is made of an abſolute pure plated Selenite, found in the Fiſſures of the Strata of the common Gypſum at Montmartoe.
We have, in England, five diſtinct Kinds of Gypſum: 1. A pure white tender Kind; 2. A grey, firm, and compact one: 3. A yellowiſh; this alſo is tender: 4. A reddiſh Kind; all theſe are of a dull coarſe Aſpect; but we have a 5th, which is bright, clear, and gloſſy, and is moſt excellent of all; and, beſide theſe, Saxony affords a native Plaiſter Duſt, white, and
