The Democratic advocate. [volume] (Westminster, Md.) 1865-1972, 1886-07-24
Tempered Glassware.
From Tie Glassicare Reporter.


about the properties of this
glass Some claimed it was malleable;
others that it could not be broken. In
fact, tempered glass was called upon to SUI
persede all other materials, The excite
went being over, tempered glass may now
take its rank among valuable inventions,
subject, however, to many defects in its
present state.
The process of tempering glass, as is
well known, consists in heating piece of
glass, say window pane, to such degree
as to approach malleability, but not enough
to lose its shape; the glass in this state is
instantly plunged into bath composed of
fatty and resiDous matter, which is heated
and maintained liquid at temperature
ranging from 300 deg. to 600 deg, ac-
cording to the quality of the glass. The
difference of temperature between the NAL
leable state, about l 400 deg, and that of
the bath constitutes the temper.
Glass in the plastic state, when plunged
into cold water, will fly to pieces when
dropped indiscriminately, but if piece of
very fluid glass is allowed to fall into water
in the shape of a tear or drop, it will be
perceived that the outside of the glass
cools at once, while the inside remains part
ly fluid for some time, as can be distin-
guished by the red color showing through
the water. This cooling will continue until
the mass is perfectly solid. This indicates
that the outside layer becomes at once con-
densed by cooling, while the inside remains
fluid and consequently more distended.
This cooling process goes on, the outside
layer COMPRISING the next adjoining, until
the whole mass is thoroughly cooled This
peculiar form and state of glass is known
as Prince Rupert's drops. Though hard
blow may be struck upon the thick part of
these drops, it has no perceptible effect,
but if the thin tail end is ruptureds the
whole mass instantly flies to pieces. The
glass appears to be under great state of
tension, and the least rupture of the equi-
librium, such as the breaking of the slender
thread terminating the drop, is sufficient
to destroy the mass.
Until the discovery Of tempered glass
by NJ De la Bastie, it had always been
considered that unless lamp chimney or
any other piece of glass was perfectly an
nealed, difference of temperature brought
on suddenly would invariably cause
breakage. The Bastie glass would seem
to prove this view to be erroneous, as the
tempered glass can sustain sudden and ex-
treme changes Of temperature without
breaking. Molten lead has been poured
into glass bowl or tumbler without pro-
ducing fracture. A piece of plate glass
tempered by the Bastie process, having been
heated among Goals, was suddenly plunged
into cold water without producing any eff
feet This experiment, repeated five times
in succession, did not seem to impair the
qualities of the glass, for on dropping from
fifth story window it did not break. 1t
may be said, however, that if in the heat
ing the temperature should reach the point
at which it would be annealed, the temper
would be destroyed. This action does not
seem to take place when the period of re-
heating it is not continued too long. A
plate of glass 6lx43 inches and three
sixteenths inch thick could only be broken
under the shock of weight of ounces
falling 13 feet, while an ordinary piece of
glass of the same dimensions would break
under half of that weight falling about
sixteen inches.
NJ. Siemens, of Dresden, says that the
strength of glass is increased fifty times
by being tempered A bent plate of glass
laid upon the floor with the convex side
upward is capable of resisting the weight
of an ordinary man without breaking.
The glass while subjected to the weight
will hatten out but as soon as the pres
sure is removed it will spring back at once
to its original shape. Hardened glass
seems to be lest dense than ordinary glass;
it is harder, however, and is more difficult
to cut by the diamond and tempered tools;
it also possesses a much superior elasticity
over the ordinary glass.
Since tempered glass, however, cannot
be cut with the diamond without flying to
pieces, its use must necessarily be limited
to definite sizes not requiring to be modi-
fed; this is quite drawback to its use.
1t would seem, however, ti1t some of the
defects have already been overcome, for at
the Paris Exposition quite display of
tempered goods was made by the Societe
Anonyme da FerTe Trenpe, at Paris
Among other things was quite display Of
druggists and chemical glassware, mortar,
pestles, beakers, covered bowls, tunnels;
also variety of plain and cut glass tumb-
lers, goblets, decanters, globes, and Chin
neys; opal plates; depohshed bowl with
cut facets; colored glass, engraved, cut, etc
1t is said that the making of articles vary
ing in thickness is hazardous, as many of
them are apt to fly to pieces either in the
making or cutting.
A MINISTER'S S WARM REcEPTIoN.-A
well-known minister was sent south from
New Jersey few years ago to labor among
the colored people. They received him
with many demonstrations of joy, and at
the first meeting which he held one old
colored preacher prayed for him with great
earnestness, thus 30 Lord bress dis yer
brudder what's come down from de nori