371 



moreover, when the chemical affinity is satisfied, of dissolving 

 the oxides, and probably the metals themselves when in a 

 state of fusion ; the latter, on the cooling of the glass, 

 being deposited in globules throughout its interstices, (at 

 least the appearance presented by the glass seems to favour 

 such an opinion.) 



" The colours produced by the fusion of metals with glass, 

 being different in many cases from those obtained when their 

 oxides were employed, and presenting the dull untransparent 

 appearance which is so remarkable in ancient glass, led me 

 to suppose that the ancients did not employ any colouring mat- 

 ter unknown at the present day, but that, being unacquainted 

 with the mineral acids, they employed the metals either in 

 the metallic state, in filings, or else in an imperfect state of 

 oxidation. To determine the probability of this conjecture, 

 I selected three specimens of mosaic glass, analyzed by 

 Klaproth ; and substituting for the oxides, in the same rela- 

 tive pi*oportion, the metals in a minute state of division, I 

 obtained coloured glasses of nearly the same colour as 

 the mosaics, while the colours produced when the oxides 

 were employed were not only perfectly different, but the 

 glasses were clear and transparent. 



" One of a lively copper red, opaque and very bright, 

 contained, in 200 grains, silica 142, oxide lead 28, copper 

 15, iron 2, alumina 5, lime 3. 



" Another, of a light verdigris green, contained, in 200 

 grains, silica 130, oxide copper 20, lead 15, iron 7, lime 

 13, alumina 1 1. 



"A specimen of blue glass contained, in 200 grains, silica 

 163, oxide iron 19, oxide copper 1, alumina 3, lime J." 



The Secretary read a note by George J. Knox, Esq., 

 " on a gaseous Compound of Fluorine and Cyanogen." 



When recently ignited fluoride of silver is mixed with 

 several times its weight of dry solid cyanogen, and heated 



