IMPROVEMENTS IN ELECTRIC INCANDESCENT LAMPS
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by Gustav Pfannkuche and Alfred
Albert Dixon at the Office of the Commissioners of Patents on the 12th
August 1882.
GUSTAV PFANNKUCHE of Charlotte Street, Fitzroy Square in the County of
Middlesex, Electrical Engineer and ALFRED ALBERT DIXON of Gateshead-on-Tyne,
in the County of Durham "IMPROVEMENTS IN ELECTRIC INCANDESCENT LAMPS
"
This invention relates to the construction of electric incandescent lamps as set
forth below. The carbon burners enclosed in an exhausted bulb or globe or tube
have heretofore been made of a filament for instance of a piece of bamboo or rattan
or French whisk and such like material, which after undergoing a cleansing
process is carbonized in different ways and then used as a burner, or made of paper
or thread similarly treated.
Now, experience has shown that those materials in which the natural state of the
fibre is best preserved during their treatment for carbon burners, and which
contain the greatest number of original fibres, are best capable of withstanding the
deteriorating influence of the electric current. The conclusions drawn from these
facts therefore seem to show that the material used for the production of a carbon
burner should consist of fibres in their natural state and of the largest number of
such fibres in a given cross-section of the burner. These conclusions lead to the
idea of first producing a compound raw material which will fulfil the conditions
mentioned above and from which compound raw material the carbon burner is to
be formed.
According to our invention we take strong fibres, such as hemp or flax, after it
has been dried, and the outer hard skin removed and has thus acquired hair-like
condition, as if ready for spinning; we then by preference clean it by exposure to
an alkaline solution or acidulated water and after arranging the fibres parallel with
each other, we bind them together by soaking in a heavy hydrocarbon oil or in a
mixture of saturated solution of sugar and la up black and gum, or similar binding
solutions. After this process we compress by means of presses or otherwise into a
Off this raw
plate or rod or board or any other shape convenient for the purpose.
inaterial while still in a flexible state, we take pieces without cutting across the
fibres constituting the material, gauge them by drawing through a round edged

page_text: -
hole in a draw-plate or otherwise, then carbonize by baking in a crucible filled with
graphite, or in a strong vessel containing hydrocarbon gas and exposed to heat and
after having done this we bring the carbonized material down to the required
resistance by depositing carbon on the surface by means of carbonaceous vapours or
other well known means.
Having thus succeeded in producing a carbon burner we connect each end to a
thin strip of platinum in the following manner: We punch a hole a little larger in
size than the carbon burner, through the platinum strip, about ½ inch or so from
the end, then we temporarily put a piece of metal through the hole and bend the
end of the platinum strip back across the hole and on to itself so that it encloses
the piece of wire temporarily put into the hole and now projecting from it in a
direction which is the same as the length direction of the platinum strip. We then
nip the bent parts on each side of the wire. The wire is then taken out of the hole
or socket, the hole filled up with a soft carbonaceous conducting cement and the
end of the carbon burner pushed into it; we are thus enabled to establish good
electrical connection between the platinum strips and the carbon burner. We may
also make such connections by bending a platinum strip into the shape shown
3
and put the carbon burners through holes punched through the two upper-
most parts a and b of the platinum strip so that the carbon rests on the third
one whilst the space between them is filled up with a carbonaceous cement.
Instead of the platinum or other metal strips wire can be used but has then to be
flattened out at one end. Connection between carbon and platinum or other metal
being thus made the platinum or other metal strips are sealed into a glass socket.
A glass bulb with the outer diameter of its neck smaller than the inner diameter of
the open glass socket is then fitted into the socket and the space between the two
is filled up by several layers of cement, vacuum cement, and plaster of Paris, or
similar substances; after this has dried the bulb is exhausted.
Another mode of closing the open end of the bulb consists in shaping the lower
part of the glass bulb conically inside so that a closing plug made of cement or
burnt clay or other suitable material can be ground in into it or cemented in.
A shoulder is moulded on to the glass outside and a brass cap with a thread cut on
its outer surface fitted on to it. A cover made of some strong material is then
screwed on to this brass cap and having also a shoulder projecting inward, it will,
when screwed down sufficiently, drive the clay or cement plug firmly into the
conical opening of the glass bulb. The conducting wires with the burner connected
to them pass of course through the air-tight plug.
In case the carbon burners should want to be brought to uniform cross-section
they may be drawn through a metal ring made hot by the passage of an electric
current or otherwise.
The aforesaid construction of burner or bridge is also applicable to other
constructions of incandescent lamp bulbs.