Evening star. [volume] (Washington, D.C.) 1854-1972, 1902-10-18
INCANDESCENT LAMPS.
Details of the Process, Long Regarded
as a Trade Secret.

FROM the Electrical WORTH.
The manufacture Of an incandescent cleo
trio lamp is of special interest because
many of the operations have heretofore
been regarded as trade secrets and care
fully kept from the public
The delicate filaments which produce the
light are formed by squirting paste made
from cellulose (wood pulp through dies
from which it energies in the form of fine
threads, which when dried are tough anu
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 celluiose is completely charred, ana
the filament now practically consists OIL
charcoal 1t Is then suspended in an at
moSphere of hydrocarbon Napor. IN a NeSsei
in which a partial vacuum has been made
and current of electricity Sufi1clent TO
bring il to incandescenCe Is sent through
it. This decomposes the hydrocarbon. ana
a carbon SCOT somewhat resembling graph
lite is deposited on the tilament ms Is
technically known Flashing. After
this treatment the flament has a metallic
ulster resembling polished steel.
The glass bulbs are blown in molds to Sc
cure absolute uniformity. and as they come
from the glasshouse they are perfectly
smooth at the rounded end and nave 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 pulD
to the exhaust pump.
For making the connection through the
glass between the carbon filament and the
wire the most satisfactory material Is
platinum, because Il adhereS firmly TO
fused glass and because it expands and
contracts at the same rates. If this were
not the case when il got hot through the
passage Of the current it would either cx-
pand 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 eFehtuai-
" project down into the neck OF the OuID
are fused two platinum wires. This stop
per. which has a fiange at one end, is now
called the mount or stem.
Next the filament is fastened 10 the tildS
of the platinum which projects from the
stem. This is accomplished by means OK
special cement which will stand a red neat.
over this paste is deposited a layer of car
bon. The paste is then dried in an oven.
and the stem with its attached hlament, Is
fastened onto the bulb by fusing the ftange
on it's upper end about the neck of the bulb.
After this joint IS carefully tested % be
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 chelni-
cal means. When the vacuum Is sufficient
ly 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 completed
and is sent to the testing department. Here
it is subjected to a series of severe tests be-
fore 1t Is considered ready for the market
If 1t passes these successfully the base tthe
portion by means of which ii is screwed
into a braCkeD Is cemented on. and the
completed lamp goes to the shipping depart
ment.