Page:Theophrastus - History of Stones - Hill (1774).djvu/215

 is the Effect of the extreme Force of Fire; and that the bet ort of Glas is that in the making of which Flints have been ued, is a Truth as much known now, as it was in the Days of Theophratus.

The Things of which our Glas is made, are, Pot-ahes, ome tony, arenaceous, or crytalline Matter, as Sand, Flints, or Crytal; and Manganeze, a ferrugincous Subtance: To which ome add a mall Quantity of pure Salt of Tartar: Thee Ingredients are calcined into what the Workmen call Fritt; and afterwards run, by Violence of Fire, into Glas of different Colours and Degrees of Purity, according to the different Ingredients.

The Glas of the Antients was, in the different Ages of the World, in different Degrees of Purity and Excellence, according to the Ingredients of which they made it; which were Sand, Natrum, and Flints. Sand was the firt Ingredient ever ued or thought of for the making Glas; and for many Ages, there was even no other Sand ued among the Greeks than that found clean wahed on the Banks and in the Beds of Rivers, and this, from its Ue, might very probably acquire the Name of Uëlitis, or Glas-and.

In the beginning of this Sentence, the other Copies of this Author have. I have ventured to follow Salmaius in his mot rational Opinion, that it was in the Original, and a little afterwards to give , for what has hitherto tood , according to De Laet; who very jutly upects, that Flints were much more likely to be made an Ingredient in Glas than Bras. And, indeed, when we conider the many Chams and greater as ome affirm, of the Uelitis, a vitrifiable Sand, it owes its Production to the extreme Force of Fire: The bet is that, in the making of which Flints have alo been ued; for beides that they melt and mix with the running Mas, they have a peculiar Excellence in the making the Glas, inomuch that they give the Differences in the Clearnes of the Colour.