Page:Theophrastus - History of Stones - Hill (1774).djvu/343

 Recoure to Fire to give them their Colour; and that therefore it is not probable, the ame Power hould be able to take it away; for the Truth of this, is only, that the Colour of the native Turquoies of ome Countries is not equally pread through the whole Mas, but lodged in different Parts of it in Form of Veins and Striæ: It is to dilodge the Colour from thee Veins, and diffue it equally thro' the whole Mas, that they have Recoure to Heat: A very gentle Fire is all they dare trut on this Occaion, and is always found ufficient. What I would oberve from the Whole of this is, that this Effect of Fire on the rough Turguoies, is a Proof that their Colour is owing to the fame Particles with that of the Sapphire; and that this dilodging and diffuing it through the whole Mas, is the firt Step toward the diipating and entirely driving it off; for a little too long Continuance in the ame Heat, will, as the Workmen too often find to their Sorrow, wholly drive off the Blue, and leave the Matter colourles, as the Sapphire when taken from the Fire,