The Savannah morning news., 1902-10-27
INCANDEsCENT LAMPS.
Details of the Process, Long Re-
garded as n Trade Secret.
From the electrical World

From the Electxical World.
The manufacture of an incandescent
electric lamp is of special interest be-
cause many of the operations have
heretofore been regarded as trade Sc
crets and carefully kept from the pub
lie.
The delicate filaments which produce
the light are formed by squirting a
paste made from cellulose (wood pulp
through dies, from which it energies
in the form of fine threads, which
when dried are tough and flexible
These threads before they are dry are
formed into the desired shape.
They are then packed in carbon dust
and subjected to intense heat for many
hours. The cellulose is completely char
red, and the fiament now practically
consists of charcoal. 1t is then sus-
pended in an atmosphere of hydrocar-
bon vapor, in a vessel in which a par
tial vacuum has been made, and a
current of electricity sufficient to bring
1t to incandescence is sent through it.
This decomposes the hydrocarbon, and
a carbon SCOT somewhat resembling
graphite is deposited on the filament.
This is technically known as clash
ing" After this treatment the fila
ment has metallic luster resembling
polished steel.
The glass bulbs are blown in moIds
to secure absolute uniformity and as
they come from the glass house they
are perfectly smooth at the rounded
end, and have long open neck. TO
the rounded end is fused a. short length
OF glass tubing opening into the inte-
rlor or the bulb. This is subsequently
used for connecting the bulb to the
exhaust pump.
For making the connection through
the glass between the carbon filament
and the wire the most satisfactory ma
terial Is platinum, because it adheres
firmly to fused glass and because it
expands and contracts at the same
rates. If this were not the case when
1t got hot through the passage of the
current 1t would either expand more
or less than the surrounding glass, and
either break it or make a space
through which air would leak. So
through the little glass stopper which
will eventually project down into the
neck of the bulb are fused two plati-
flange at one end, is now called the
mount or stem.
Next the filament is fastened to the
ends of the platinum which projects
from the stem. This is accomplished
by means of a special cement with
will stand a red heat. Over this paste
is deposited a layer of carbon. The
paste is then dried in an oven, and the
stem, with it's attached filament, is
fastened onto the bulb by fusing the
fiange on its upper end about the neck
of the bulb.
After this joint is carefully tested to
be sure there are no leaks, the exhaus-
ton of the air is accomplished by
means of a mechanical air pump, the
last traces of gas or air being removed
from the bulb by chemical means.
When the vacuum is sufficiently high
the tube through which the air has
been exhausted is sealed off by means
of small lamp, leaving the small
round tip seen on the spherical end Of
the finished lamp.
The lamp is now practically COM
pleted and is sent to the testing depart
ment. Here 1t is subjected to a Sc
ries of severe tests before it is consid-
cred ready for the market II 1t
passes these successfully the base (the
portion by means of which 1t is screw
ed into a bracket) Is cemented on, and
the completed lamp goes to the ship
ping department,