337 
on the Newry pitch-stone , &c. 
I ignited 400 grains of green-stone, wliich lost 5 grains ; 
and charged it into an iron retort as usual. The receiver 
increased 0,2 in weight, and there was no smell. On ex- 
amining the contents of the retort after the distillation, I 
found that the powdered stone had been converted at the 
bottom into a vesicular glass, and at the top into a pumice, 
but that a hole had opened in the upper part of the neck of the 
retort. It seemed therefore that, in the first place, most of 
the volatile matter must have escaped, whatever that volatile 
substance may have been, through the hole, but that the tem- 
perature having been lowered in its vicinity by the admission 
of air, the formation of glass was checked as far as that in- 
fluence extended, and the result was pumice. Why the glass 
was vesicular and not compact, I shall leave to conjecture. It 
is probable that farther experiments may elucidate that point. 
NOTE. 
To assist in forming a judgment whether manganese really 
existed or not in the Meissen pitch-stone, to 100 grains of 
the pulverised stone was added 0,1 of oxide of manganese, 
and fused. The colour was whitish, as before, but as the 
great heat necessary to fuse the substance might have dis- 
coloured the manganese, the following experiments were 
made. To 99,9 grains of pure white glass, 0,1 of black 
oxide of manganese was added. It fused into a violet-co- 
loured glass ; but when the heat was increased the colour 
was removed. To try, therefore, whether a violet glass 
might be produced from a fusion at a lower temperature of 
X x 
MDCCCXXII. 
