Improvements in the Manufacture of Filaments for Incandescing Electric Lamps.
Year: 1898

page_text: Date of Application, 10th Mar., 1898-Accepted, 14th May, 1898
Improvements in the Manufacture of Filaments for Incandescing
Electric Lamps.
I, WILLIAM LAWRENCE VOELKER, of 38, Bernard Street, Russell Square, in the
County of London, Electrician, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and.
ascertained in and by the following statement:―
This invention relates to the use of the carbides of the following metals for manu-
facturing filaments for use in incandescent electric lighting. and in-another-applica
tion:-I-have-fully-described-the-processes of making these-carbides-with the electric
furnace, und will only describe the process for-making-the-carbides and-filaments
for this special purpose: First--and-foremost-are-the-chemicals used-for-these
carbides. This is of the highest-importance, the The oxides of the metals used
should have a low specific heat as this will determine the efficiency of the finished
lamp, and I will enumerate a few starting with the elements having the highest
molecular weight :-uranium, thorium, ytterbium, erbium, cerium, calcium and
magnesium. and-taking Taking one-or--more--of the cheaper-oxides-of-the-alkaline
earth-metals-such as lime and magnesium, or uranium or thorium or start-with
the-chemically-pure-nitrates-and-in the thorium cerium combination (such as is used
for impregnating incandescent ing gas mantles) I use a saturated solution of same,
the chemically pure nitrate or nitrates, and add to this a hot saturated solution of cane
sugar, and of in such a proportion that the carbon of the sugar shall be somewhat in
excess of that the quantity necessary for the formation of the carbide. This solution
is now evaporated and then gradually heated to a bright red heat without access
to the of atmospheric air; and the resultant mass will be an intimate mixture of
carbon, thorium and cerium oxides. The mass is now transferred to the carbon
crucible of an electric furnace and melted. The product is now a true carbide, or
the a union of the metals thorium and cerium with carbon, and in this condition it
must be kept, as any free-uneombined-oxide will unfit it for oxidation will render
it unfit for use in the manufacture of incandescing filaments. These carbides are is
How ground to an impalpable powder in a mill that is kept free from moisture, The
pulverized carbides-are-now and is then ground together with a viscous mixture
composed of one part gun-cotton and three parts of oil of cassia or crude india rubber
dissolved in benzol. The mass when well ground together is then transferred to a
strong steel cylinder with a piston plunger and a small hard die made from a diamond
or sapphire set in the bottom. With hydraulic pressure, the mass is forced through
this small die in the shape of a fine filament, of fifteen to twenty thousandths of an
inch in diameter as required. The filament or expressed thread is kept from sticking
together by dusting same with carbon powder if expressed while warm, or if expressed

page_text: cold, it can be allowed to fall and circle over a cone with apex pointing towards
the die. The thread should not be allowed to be in contact with the air but be
permitted to fall in a case or box connected with the press, and the air in the box
should be kept keep free from moisture by chemical or other means. This thread can
be spooled and then cut into lengths suitable for the filaments and allow for
(allowance being made for shrinkage) and baked at a gradually increasing temperature
in black lead or graphite boxes. When After these boxes are have been maintained
at a white heat, say for five minutes, they are allowed to cool either in the blast
furnace; or are removed from the furnace and covered with hot sand and allowed to
cool slowly to the normal temperature. Then-the The filaments are then removed to
a chemically dried atmosphere or kept in vessels containing some fluid hydrocarbon
such as benzol or naphtha. If taken from the latter, the filaments are treated at
once to an electroplating process in this the following manner :-The filaments are
mounted on temporary mounts attached to a ground glass stopper through which
electrical connections run; which-terminate same terminating at one end in spring
clips which hold and electrically connect to-hold the filaments. and-connect-same; this
This stopper also has a tube at the other end, which connects with an air pump.
When a filament is mounted the usual glass bulb is placed over it and fits the stopper
accurately. The bulb is then emptied exhausted of air and the electric current
turned on, and as the hydrocarbon is yielded repelled and volatalized in the bulb, the
filament will, he when sufficiently heated, become coated with a thin veneer of steel
coloured carbon. when-heated-sufficiently high-by-the currents-passing through. In
this condition the filaments are not affected by moisture although it is best always to
keep them in dried dry air. The filaments are now formed into cone-shaped or other
bodies, or are mounted on their proper holders and this-is sealed to the glass bulb.
and the The finished lamp is then exhausted; with-a-mercury pump by mechanical;
chemical-or-electrical-means, and but before complete exhaustion, the electric current
is again passed through the filaments, and this being heated to high incandescense to
expel all remaining air, from-the-filament, and also to oxidize the thin veneer of
carbon, thus leaving from sume and leave the pure carbide filament to give light.
The efficiency of such a lamp us-above-mentioned will depend largely up-on the
oxides used to form the carbide filament. The lower the specific heat of the element
metal used, the more efficient the lamp, and these specific heats are well known to
the chemist and electrician. I do not limit myself to the use of any particular
carbide. nor-the-method-described of handling the carbides-in-the various processes
of treating-the-filament.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
1. An electrode-cone, body or filament For use in a lamp for producing light by
incandescing ence in a vacuum, such a carbide filament being formed of a metal or of
metals combined with carbon in the proportion of their chemically combined weights,
and prepared substantially as herein described.
1
S. S. BROMHEAD,
Agent for Applicant, 171, Queen Victoria Street, London, E.C.