Edgefield advertiser. [volume] (Edgefield, S.C.) 1836-current, 1902-12-24
INcANDEScENT LAMPS.
Details of the Process, Long Regarded
as a Trade Secret.

The manufacture of an incandescent
electric lamp is Of special interest be-
cause many of the operations have
heretofore been regarded as trade sec
rets and carefully kept from the pub
lie.
The delicate filaments which pro-
duce the light are formed by squirting
paste made from cellulose (wood
pulp) through dies, from which it
emerges in the form Of fine threads,
which when dry are tough and fiexi-
BILE. These tarea> 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 COM
pletely charred, and the filament now
practically consists of charcoal. 1t is
then suspended in an atmosphere OF
hydrocarbon vapor, in a vessel In
which q partial vacuum has been made
and a current of electricity sufficient
to bring 1t to incandescence is sent
through it. This decomposes the fv-
drocarbon, and carbon SCOT some
what resembling graphite is deposited
On the filament. This is technically
known as flashing" After this
treatment the filament has a metallic
lustre resembling polished steel.
The glass bulbs are blown in molds
to secure absolute uniformity, and as
they come from the glasshouse they
are perfectly smooth at the rounded
end, and have long open neck. To
the rounded end Is fused q short
length Of glass tubing opening into the
interior of the bulb. This Is subse-
quently used for connecting the bulb
to the exhaust pump.
For making the connection th 'ough
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 1t
expands and contracts at the same
rates. If this were not the case when
1t got hot through the passage of the
current it would either expand more or
less than the surrounding glass, and
either break 1t or make 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,
mum wires. This stopper, which has a
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 which
will stand q red heat. Over this paste
Is deposited a layer of carbon. The
paste Is then dried in an oven, and
the stem, with its attached filament
Is fastened onto the bulb by fusine
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 ex
haustion 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 a 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 g
series of severe tests before 1t Is con
sidered ready for the market. If II
passes these successfully the base
(the portion by means of which it Is
screwed into a bracket) Is cementet
on, and the completed lamp goes to the
shipping department.-The Electrical
World.