Page:Theophrastus - History of Stones - Hill (1774).djvu/344



N a Letter of the 19th of lat Month, which you did me the Honour to read before the I endeavoured, principally by means of ome Experiments I had been lately making, to ettle the Quetion o much diputed among the preent Naturalits, Of, what the blue Gems in general are coloured from. What engaged me in the Dipute, was an Objection raied againt the Opinion I had declared myelf of in this Cae, in my Notes on Theophratus: And I am very happy to find, that even the Gentlemen who made that Objection are now convinced, that it is to Copper alone that the Sapphire and Turquoie owe their beautiful Blue.

For myelf, I mut acknowledge, that tho' I have long been convinced of the Fact, the Manner in which it was effected, was long a great Difficulty to me: The Mentruum in which my Tincture of Copper, (which proved to