The Indianapolis journal. [volume] (Indianapolis [Ind.]) 1867-1904, 1902-10-04
INCANDEsCENT LAMPS.
Details of Their Making Long Held as
Trade Secret.
Electrical World.

Electrical World.
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 careful
ly kept from the public.
The delicate flaments which produce the
light are formed by squirting paste made
from cellulose (wood pulp through dies.
from which 1t 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 i'm 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 II
to incandescence is sent through IT. This
decomposes the hydrocarbon, and a carbon
SCOT somewhat resembling graphite is de-
posted on the filament: This is technically
known as flashing" After this treatment
the flament has metallic luster re-
sembline polished steel
The glass bulbs blown in moIds To
secure absolute uniformity, and as they
come from the glasshouse they are per-
a long open neck. To the rounded end is
fused a short length Of glass tubing OMEN
ing 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 bringing current the most satisfactory
material Is platinum, because il adheres
firmly to fused glass and because il ex-
pands and contracts at the same rate. IL
this were not the case when II got hot
through the passage of the current 1T would
either expand more or less than the sur
rounding glass, and either break ii 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 platinum wires
This stopper, which has 1ange at one
end, is now called the mount stem.
Next the filament Is fastened 10 the ends
the stem. This is accomplished by means
OF special cement W. ich will stand a 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 fila
ment. is fastened 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 no leaks. the exhaustion of
mechanical air pump. the last traces of gas
or air being removed from the bulb by
chemical means. When the vacuum is suf-
ficently 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 enc Of the finished
lamp.
The lamp is now practically completed
and Is sent 10 the testing department Here
IL is subjected 10 a series of severe tests be-
fore IL is considered ready for the market
If IL passes these successfully the base fthe
portion by means OF which IL Is screwed
into brackeD is cemenfed on, and the
completed lamp goes to the shipping de-
paTtmeut.