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Boyle, in his treatise on the porosity of bodies, andin the appendix to his sceptical chymist published in1680, mentions an experiment, in which a like colourwas introduced into glass without fusion. A mixture ofgold and mercury having been kept in digestion for somemonths, the fire was at last immoderately increased, inso-much that the glass burst with a violent explosion : thelower part of the glass was found tinged throughout of atransparent red colour, which seemed, he says, to emulatethat of a not common ruby.

About the fame time Casiius discovered the precipita-tion of gold by tin, and that glass might be tinged of aruby colour by melting it with this precipitate. I cangive no further account of his experiments, having neverhad the good fortune to meet with his treatise.

The process was soon after brought to perfection byKunckel, who fays he prepared the ruby glass in largequantity, and sold it for about forty shillings an ounce;and that he made a chalice of it for the elector ofCologn, weighing no less than twenty four pounds, afull inch thick, and of an uniform fine colour through-out. He has no where communicated the process hefollowed, but some useful observations relating to it aredispersed through his writings : he fays, that one partof the precipitate by tin is sufficient to give a rubycolour to twelve hundred and eighty parts of glass, and asensible redness to upwards of nineteen hundred parts :that the success is by no means constant, and that afterlong practice, he still frequently failed: that oftentimesthe glass comes out of the fire colourless as crystal, andreceives its ruby colour on being afterwards exposed to asmoky flame, insomuch that he imagines the discoveryof the ruby glass did not arise from simply melting thegold precipitate with glass* but from the subsequent soft-ening