Huntsville gazette., 1884-10-18
Tempered Glass.


It is not very long since the discovery
of M. Alfred de la Bastie filled all our
newspapers with paragraphs, more or
less ridiculous, about the properties OF
this glass. Some claimed it was MALE
able; others that it could not be bro
ken. In fact, tempered glass was to
supersede all other materials. The ex-
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 a window pane, to such a
degree as to approach malleabilty, but
not hot enough to lose its shape; the
glass in this state is instantly plunged
into bath composed of fatty and res
inous matter, which is heated and main
tanned liquid at a temperature ranging
from three hundred to six hundred de-
grees, according to the quality of the
glass. The difference of temperature
between the malleable state, about
l,4O0 degrees, and that of the bath con-
stitutes the temper.
Glass in the plastic state, when
plunged into cold water, will fly to
pieces if dropped indiscriminately, but
if piece of fluid glass is allowed to fall
into water in the shape of tear or drop,
it will be perceived that the outside of
the glass cools at once, while the inside
remains partly fluid for some time, IS
can be distinguished by the red color
showing through the water. This cool
ing will continue until the mass is per-
fectly solid. This indicates that the
outside layer becomes at once con-
densed BY cooling, while the in
side remains fluid and consequently
more distended. This cooling process
goes on, the outside layer COMPRISING
the mex: 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 ef-
feet, but If the thin tail end is ruptured
the whole mass instantly flies to pieces.
The glass appears to be under a great
state of tension, and the least rupture OF
the equilibrium, such as the breaking OF
the slender thread terminating the drop,
is sufficient to destroy the mass.
Until the discovery of tempered glas.
by M. de la Bastie, it had always been
considered that unless lamp chimney
or any other piece of glass was perfectly
annealed, differences of temperature
brought on suddenly would invariably
cause breakage. The Bastie glass
would seem to prove this view to be er-
roneous. as the tempered glass can sus-
tain sudden and extreme changes OF
temperature without breaking. Molten
lead has been poured into a glass bowl
or tumbler without producing a frac-
ture. A piece of plate glass tempered
by the Bastie process, having been
heated among Goals, was suddenly
plunged into cold water without pro-
ducing any effect. This experiment,
repeated five times in succession, did
not seem to impair the qualities of the
glass, for on dropping it from a
fifth story window it did not break. 1t
may be said, however, that if in the
heating the temperature should reach
the point at which it would be an
nealed, the temper would be destroyed.
This action does not seem to take place
when the period of reheating is not con-
tinued too long. A plate of glass ST
by A inches and three-sixteenths
inch thick could only be broken under
the shock of weight of seven ounces
falling thirteen feet, while an ordinary
piece of glass of the same dimensions
would break under half of that weight
falling about sixteen inches.
M SinvpnnJ of nraCHan fboA
the strength of glass is increased fifty
times by being tempered. A bent plate
of glass laid upon the floor, the convex
side upward, is capable of resisting the
weight of an ordinary sized man with
cut breaking. The glass while subjected
to the weight will tlatten out, but as
soon as the pressure is removed it will
spring back to its original shape
Hardened glass seems to be less dense
than ordinary glass; it is harder, how
ever, 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, can
not be cut with the diamond without
flying to pieces, its use must necessarily
Dc uIullcu W ueHHlte Sizes NOT IT.
quiring to be modified; this is quite
drawback to its use. 1t would seem,
however, that some of the defects have
already been overcome, for at the Paris
Exposition quite display of tenn
pered goods was made by the Societe
Anonyme du Verre Trempe, of Paris.
Among other things was quite display
of druggists and chemical glassware,
mortars. pestles, beakers, covered
bowls, tunnels; also variety of plain
and cut glass tumblers, goblets, de-
canters, globes and chimneys; opal
plates; depolished bowl with cut
facets, colored glass, engraved, cut,
etc. 1t is said that the making of ar.
ticles varying in thickness is hazardous,
as many of them are ant To fly to nieces