The daily morning journal and courier. [volume] (New Haven, Conn.) 1894-1907, 1902-12-22
INCANDESCENT LAMPS.
Details Of the Process, Long Regarded
as a Trade Secret.

Details Of the Process, Long Regarded
as a Trade Secret.
The manufacture of an incendescent
electric lamp is of special interest be-
cause many Of the operations have
heretofore been regarded as trade Sc
I crets and carefully kept from the pub
lie.
The delicate flaments 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 complete
~ charred, and the filament now practi-
cally 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 incandescency 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 flash
ing" After this treatment the fila
ment has a metallic luster resembling
polished steel.
The glass bulbs are blown in moulds
to secure absolute uniformity, and as
they come from the glasshouse they are
perfectly smooth at the rounded end
and have a long open neck. To the
rounded end is fused a short length of
glass tubing opening into the interior
of 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 1t adheres
firmly to fused glass and because it ex-
pands 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 it or make a 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 fiange at one
end is now called the mount or stem.
Next the fllament Is fastened to the
ends of the platinum which project
from the stem This Is accomplished
by means of a special cement which
will stand 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 fas-
tened on to 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 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 compile
ted, and is sent to the testing depart
ment Here it is subjected to- heries
of severe tests before 1t Is considered
ready for the market. If 1t passes
these successfully the base (the portion
by means of which it Is screwed into
brecket) is cemented on, and the COM
pleted lamp goes to the shipping de-
ment-Electrical World