The Union and journal. [volume] (Biddeford, Me.) 1858-1882, 1870-06-24
How Glass is Made.

The formation of window glass Is Of.
fected by blowing the melted matter, on
metal, rs It Is called. into hollow spheres,
which are Afterwards made To expand In
to circular sheets. The workman Ii pro-
vided with q long iron tube, one end OF
which he thrusts Into the melted glass,
turning Il round until . certain quantity.
sufficient for the purpose Is gathered or
adhercs to tho extremity. Tho tube Is
then drawn from the furnace; tho lump OF
glass whichadheres Is rolled upon smooth
iron table. and the workman blows strong
" with his mouth through the tube. The
glass In consequence Of It's ductility, Is
gradually inflated like bladder, and 10
prevented from falling of by rotary mo-
ton constantly communicated 10 tho tube.
The imitation II assisted by the heat, which
causes the air and moisture Of the breath
to expand with great power. Whenever
the glass becomes 30 stiff by cooling. rs to
render tho imitation difficult, II Is again
held over the fire to soften It and blowing
Is repeated, until the globe Is expanded to
the requisite thinness. Il is then received
by another workman. upon an iron rod.
while the blowing iron Is detached. It Is
now open at It's extremity and by the means
Of tho centrifugal force acquired from It's
rapid whirling, It spreads into smooth.
uniform sheet, OF equal thickness through
out, excepting n prominence at tho center
where the iron rod Is attached.
Alter the glass has received tho shape
which 1t Is to retain, It Is transferred to
q hot chamber, or annealing furnace, In
which It's temperature Is gradually reduc-
ell, until Il becomes cold. This process Is
Indispensable to tho durability of glass |;
for, II It Is cooled 1t becomes extremely
brittle, and flies In pieces ut the slightest
touch of any hard substance. This effect
Is shown in the substances called Rupert's
drops which IRE made by suddenly cool
Ing drops of green glass by letting them
drop into cold water. These drops fly TO
pieces with IN explosion whenever their
small extremity Is broken of The Bolog-
ma phials, and some other vessels of un-
anncaled glass, break into thousand
pieces II flint or other hard and angular
substance Is dropped into them. This
phenomenon seems to depend upon tho
same permanent and strong In equality Of
pressure for when these drops are heated
so red rs to be soft, and left to cool grad
ually, the property of bursting Is lost and
the specific gravity Of tho drop is increas-
ed.
Flint glass. so called from It's having
been originally made of pulverized flints,
differs from window glass In containing q
larger quantity of the rel oxide of lead.
The proportion of Its materials differ; but
In round NUMBERS, It consists Of about
three parts of fine sand. two of rcd lead
and ode of pearl-ash, with small quanti-
ties of nitre arsenic, and manganese. II
fuses mt lower temperature than crown
glass, ha, q beautiful transparency, great
reflective power. and comparative solt-
ness which enables II to be cut and polish
cd with ease. On this account 1t Is much
used for glass vessels of every description.
especially those which are intended 20 be
ornamented by cutting. It is also en-
ployod for lenses and other optical glasses.
Flint glass Is worked by blowing, mold.
ing. pressing and grinding. Articles Of
complete form, such rs lamps and wine
glasses, are formed In pieces, which are
afterwards joined by simple contact while
tho glass Is hot. 1t appears that tho red
lead used in the manufacture Of flint glass
gives up u part Of tho oxygen and passes
rs protoxide. .r. sa.
The name of cut-glass Is given In COM
mercc. to glass which Is ground and pol
ished In figures with smooth surface, APP
pcaring rs II cut by incisions of a sharp
instrument. This operation Is chiefly
confined to flint glass which being more
tough, soft and brilliant, than the other
kinds, Is more easily wrought, and pro-
duces specimens OF greater lustro. An
establishment for cutting glass contains a
great number of wheels Of stone, metal
and wood. which arc made to revolve
very rapidly, by steam engine or other
power. The cutting of the glass consists
In grinding away successive portions, by
holding them upon the surface Of these
wheels. Tho first or rough cutting, Is
sometimes given by wheels OF stones re-
sembling grindstones. Aiterward, wheels
of iron arc used having their edges cover
cd with sharp sand, or with emery, In
different states of finencss. The last pol.
ish Is given by brushing wheels, covered
with putty. which Is AN oxide Of tin and
lead. To prevent the friction from ex-
citing so much heat rs to endanger tho
glass, small stream Of water continually
drops upon the surface Of the wheel.
Among the ancient specimens of paint
ed glass, some pieces have been found In
which the colors penetrate through the
glass so that the figure appears In any
section made parallel to the surface. II
Is supposed that such pieces can only have
been made In the manner Of mosaic, by
accumulating traverse filaments of glass
of different colors, and uniting them by
heat. the process being one Of great labor:
They are described by Winchelnianu and
Cayins, from some specimens brough.
from Romo.-CScientific American.