20 C.M. Wetherill on the Crystalline Nature of Glass. 
ine mass which contained cavities with small transparent 
oats. These had a composition similar to that of a transpa- 
rent bottle glass pena from the same materials in the same 
proportions, Thus 
Glass crystals. Bottle glass. 
Silica, 55°85 56°84 
ime, 24-14 21°15 
Magnesia, 7°63 6°37 
umina, 2°22 3°64 
Peroxyd iron, 1:06 2°59 
a, 8:47 8°69 
Potassa, ~ 0°63 
Manganese, traces traces 
100-00 99°68 
Spec. gravity, 2°824 2°724 
For the composition of a partially devitrefied glass which was 
formed in the same furnace, under different circumstances, he 
‘ound : 
Vitreous part. Devitrefied part. 
Silica, 62°40 
ime, 18°14 18°65 
Magnesia, 4°47 6°12 
Alumina, 2h 4:98 
Peroxyd iron, 2°66 0°71 
Alkalies, 5°12 5°87 
anese, traces traces 
100-00 100°00 
Spec. gravity, 2°610 2°857 
‘Leydolt (Wien. Acad. Bericht, viii, 261) introduces his experi- 
ments upon glass pray by observations of himself and others 
upon ns of glass and slag in which crystals are visible 
Sim hee aid of Sides : acid. : 
Thus Prechtl melted a souacianibte quantity of feldspar with 
one and a half ewt. of glass and cooled the mass in water. In 
the inside of the lump, where the refrigeration had been more 
ual, were found numerous crystals of feldspar, with well 
angles and edges, one of the crystals having the volume 
of shea be 
the specim ens of glass with rceptible crystals illus- 
Roun ae Leydolt are the following Sateen: a 
1. Green flint glass, perfectly peaaaparen containing opaque 
grains, | aber are resolved by the microscope into well defined 
ge a sa a line in diameter. 
glass flux, of emerald color, containing man u wes 
four-sided prisms, of white tinge and pearly luster us aa eee 
