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proceeds from gold, and that gold dissolved and broughtto redness might be made to communicate a like colour tofactitious gems or glass. Neri, in his art of glass dated1611, gives a process on this principle, which he fays wasfound to succeed : he directs the gold to be dissolved inaqua regia, the menstruum to be evaporated or drawn offby distillation, more aqua regia added, and the abstractionrepeated five or fix times : the remaining matter is to becalcined till it becomes purple, and then mixed with aproper quantity of the finest white or crystal glass. Butthough this process may be supposed to have sometimesproved successful, it doubtless very often miscarried ; inso-much that the introduction of this desirable colour intoglass was very little known for many years after.

Glauber, in the second part of his philosophical fur-naces published in 1648, gives another method of pro-ducing a red colour by gold in a matter which is of thevitreous kind, though not perfect glass. When powderedflint or sand is well ground with four times its weight offixt alkaline salt, the mixture melts in a moderately strongfire, and when cold looks like glass, but on account ofits over-proportion of alkaline salt it runs into a liquidstate on being exposed to the air : on adding this liquorto solution of gold in aqua regia, the acid, which heldthe gold dissolved, unites with the alkali which held theflint dissolved, and the gold and flint precipitate together,in form of a yellow powder, which by calcination be-comes purple : this powder being mixed with three orfour times its weight of the alkaline solution of flint,the mixture dried, and kept melted in a strong fire foran hour, a mass is obtained, of a transparent ruby colour,and of a vitreous appearance, though still soluble inwater or by the moisture of the air, on account of the^redundance of salt.

Z 2

Boyle,