571 
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 proportion, 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 alight verdigris green, contained, in 200 
grains, silica 130, oxide copper 20, lead 15, iron 7, lime 
13, alumina 11. 
** A specimen of blue glass contained, in 200 grains, silica 
163, oxide iron 19, oxide copper |, alumina 3, lime 4.” 
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 
