Page:Theophrastus - History of Stones - Hill (1774).djvu/342

 about one fiftieth Part. The Lead gives, in this Cae, an additional Denity to the Glas, which adds greatly to the Lutre of the counterfeit Gem; as the more dene the tranparent Matter is, the more bright and vivid the metalline Tinge appears through it; but while Lead thus increaes the Denity, it debaes the Glas in another repect of equal Conequence, in that it makes it ofter. Whichever of thee Subtances, however, is made the Subject of this Experiment, the Effect will be the ame; for if we bring to the Trial of only a clear Charcoal Fire, a genuine Sapphire, and either of thee factitious Subtances, and throw them together into it, we hall oon ee that they owe their Colours to Particles of a very different Kind; for the Genuine will be een to emit a fine clear blue Flame, the Counterfeit not o much as the leat Vapour; and when, after this, they are taken out together, the true Sapphire hall be found wholly colourles and tranparent as a Piece of Crytal, and the Counterfeit or Glas, unaltered.

Fire, which is thus able to divet the Sapphire of its Colour, has alo the fame Effect on the Turguoie; as the Workers on it well know: And this is eaily accounted for, if they are coloured, as I am convinced they are, by a fine metalline Sulphur. But I will venture to affirm, that it could not be the Cae, if thoe Gems were coloured by a Zaffer.

Let it not be here objected, that the Workers on the native Turquoies are obliged to have Recoure