The Scranton tribune. [volume] (Scranton, Pa.) 1891-1910, 1902-12-11
INCANDESCENT LAMPS.
Details of the Process, Long Regard
ed as a Trade Secret.
From the Electrical World.

From the Electrical 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 1ilaments which produce
the light are formed by squirting a
paste made from cellulose (wood pulp
through dies, from which it emerges 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.
Whey are then packed in carbon dust
and subjected to intense heat for many
hours. The cellulose is completely
charred, and the tilament now practic-
ally consists of charcoal. 1t is then
suspended in an atmosphere of hydro
carbon vapor, in a vessel in which a
partial vacuum has been made, and a
current of electricity sufficient to bring
it 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 "hash-
ing" After this treatment the filament
has a metallic lustre resembling pol
ished steel.
The glass bulbs are blown in moulds
to secure absolute uniformity, and as
they come from the giass-houSe they
are perfectly smooth at the rounded
ends and have a long open neck. To
the rounded end is fused a short length
of glass tubing opening into the in-
terror of the bulb. This is subsequent
ly used for connecting the bulb to the
exhaust Dump.
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 eX-
pands and contracts at the same rates.
II this We're 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 leak. So through the
little glass stopper which will eventu-
ally project down into the neck of the
bulb are fused two platinum wires.
This stopper which has a fange 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 which
will stand a red heat. Over this paste
is deposited 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 fusng the
flange on it's upper end about the neck
of the bulb.
After this Joint is carefully tested to
be sure there are no leaks, the en-
haustion OF the air is accomplished by
means of 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 de-
partment. Here it is subjected to a
series of severe tests before it is con-
sdered ready for the market If il
passes these successfully the base Che
portion by means of which it is
screwed into n brackeD is cemented on,
and the completed lamp goes to the
shipping department.