Year: 1879

The artificial mineral substance
called glass is made by melting to-
gether sand or flint, and in alkali.
either potash or soda. For many cen
turies previous to the Christian era
the invention was known, although
both the date and the manner Of its
discovery are uncertain. Some sup
pose that it was found out by accident;
the potash contained in the ashes of
the wood used by party of sailors,
who had made large fire on the sea
beach, having been united by the heat
with the sand of the beach and melted
into glass. This lucky accident is
alleged to have happened on the coast
of Syria, where the earliest manufac-
ture of glass unquestionably began.


All visitors to the Centennial Ex-
hibition, at Philadelphia, Will recall
the process for Observation-Disclosures
They must have learned there, from the
exquisite variety of specimens dis
played, that the manufacture of glass
has now been carried to very high
degree Of perfection. The materials
used for flint or white glass are sand,
potash, the preparations oflead, termed
red lead, and litharge, with small
quantity Of some other mineral sub
stance. After being well purified, these
are mixed, and then melted together,
being exposed to an intense heat in
large melting pots made of clay, and
| built into an immense furnace The
sand and potash are the essential arti-
cles in the making of glass. But the
| 1oo oI Ao1 Io.
is found to make the glass melt much
more readily, also to give it greater
| brilliancy and to render it less liable to
crack. When these ingredients are
thoroughly melted and united (which
process usually takes two or three days
the mouth Of the melting pot is opened,
and the liquid glass within is ready to
be formed by the workmen into any
shape desired.


The mode adopted is to take On the
end of an iron tube some of this sub
stance, which is then in a moist, te-
nacious and plaster state, and to blow
through the tube and roll the soft mass
on fiat iron plates, pressing it with
various shaped tools. The workman
at last fashions it to the shape desired,
| WHICH IL retains Wn0n cOlu.


Perhaps no other substance known
could be moulded into such variety
of forms; for melted glass seems to ex-
ceed all things in its ductility and te-
nacity. Its consistence is something be-
tween that OF soft putty and treacle,
neither solid nor liquid, but capable OF
being bent, blown out, pulled, pre-
pared, twisted or cut, so as to assume,
at the wish of the workman, the yari-
GUS forms required.


When the glass articles are made
they have to be annealed, that is, cooled
slowly in an oven for that purpose. II
they did not undergo this process, they
would crack on the slightest blow, and
would not warm liquids. The quail
ties that render glass so valuable when
manufactured, are its hardness, and
the polish of its surface, which makes
it so readily to be cleansed, when soiled;
its beautiful transparency, enabling it
to preserve its contents when it is used
to form vessels for liquids; and its be-
ing so incorrosive, that it is not acted
upon by any ordinary substances, not
even by the strongest acids, with one
exception. Its value, again, as sub
stance for glazing windows depends on
its transparency and its insolubility
so that while it admits the light and
even the warmth of the sun, it perfect
| ly excludes the wind and the wet, and
even to great extent, the cold. In
fact, it is nothing but the circumstance
of its being so common, so constantly
before our eyes, that renders us for the
most part, insensible to its exceeding
value and its great beauty.


Although glass readily allows the
light to pass through it, yet when it is
made into certain shapes it has great
effect upon the light, sometimes, for in
stance, bringing it into one point
Such pieces Of glass are termed lenses,
and are used for making telescopes,
microscopes, etc., and singly for spec
tacles. The dark green glass, of which
wine bottles are made, is merely
glass Of the coarsest kind, it being made
of the common dark colored sand, and
the coarsest alkah.