Evening star. [volume] (Washington, D.C.) 1854-1972, 1902-12-17
INCANDEsCENT LAMPS.
Details of Process, Long Regarded as
Trade Secret.
From the Electrical World.


The manufacture of an incandescent cleo
trio lamp is of special interest because
many of the operations have heretofore
been regarded trade secrets and care
fully kept from the public. The delicate
filaments which produce the light are
formed by squirting paste made from eel
lulose (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 charred. and The
filament now practically consists of char
coal. 1t is then suspended in an atmos-
phere of hydrocarbon vapor, in a vessel In
which a partial vacuum has been made, and
a current of electricity sufficient to bring
1t to incandescence is sent through 1t. This
decomposes the hydrocarbon, and a carbon
SCOT somewhat resembling a graphite Is
deposited the f1lament. This is tech
nically known flashing" After this
treatment the f1lament has metallic luSter
resembling polished steel.
The glass bulbs are blown in molds to
secure absolute uniformity, and as they
come from the glass house they are per-
fectly smooth at the rounded end, and have
a long open neck. To the rounded end is
fused a short length Of glass tubing open
ing into the interior OF the bulb. This is
subsequently used for connecting the bu'b
to the exhaust pump.
For making the connection through the
glass between the carbon f1lament and the
wire the most satisfactory material is plati-
num- because it adhereS firmly to fused
glass and because it expands and contracts
at the same rates. If this were not the
case, when it got hot through the passage
of the current it would either expand more
or less than the surrounding glass, and
either break it or make space through
which air would break. So through the
little glass stopper which will eventually
project down into the neck of the bulb are
fused two platinum wires. This stopper.
which has flange at one end, is now call
ed the mount or step.
Next the f1lament Is fastened to the ends
of the platinum which projects from the
stem. This is accomplished by means of n
special cement which will stand red hea-.
Over this paste is deposited layer of car
bon. The paste is then dried in oven
and the stem, with it's attached filament, Is
fastened onto the bulb by fusing the flange
on it's upper end about the neck of the
bulb.
After this Joint is carefully tested to oe
sure there are no leaks, the exhaustion of
the air is accomplished by means of me-
chanical air pump. the last traces of gas or
air being removed from the bulb by chem
ical means. When the vacuum is suffi-
ciently high the tube through which the
air has been exhausted is sealed off by
means of a small lamp. leaving the small
round tip seen on the spherical end of the
finished lamp.
The lamp is now practically completed,
and is sent to the testing department. Here
it. is subjected to a series of severe tests
before It is considered ready for the market
If it passes these successfully the base 0he
portion by means of which 1t Is screwed
into a brackeD is cemented on, and the
completed lamp goes to the shipping de-
partment.