Improvements in Electrodes for Arc Lamps.
Year: 1899

page_text: VISIONAL SPECIFICATION.
Improvements in Electrodes for Arc Lamps.
I, HUGO BREMER, Manufacturer, of the Neheimer Metallwaaren -u. Werk-
zeugfabrik, of Neheim-on-the-Ruhr, Prussia, do hereby declare the nature of this
invention to be as follows:-
Carbon electrodes for arc lamps are usually made in the shape of cylindrical
rods or pencils. Attempts have been made to lengthen the life of arc lamp elec-
trodes by giving them the shape of plates, but without success, because if the
plates are made of the ordinary carbon mixture, the arc will be very short, and
the carbons are liable to form knife edges, in consequence of which little or no
light is emitted to one side of the electrodes. Moreover, the light was so unsteady,
that wicks could not be used, the current passing through the lamp was subject
to rapid variations, and a hissing noise occurred, whenever the current was pass-
ing over from one spot of the electrode to another.
These defects can be avoided by using, instead of the ordinary carbon mixture,
a mixture containing at least 5 per cent. of metallic or metalloid salts, as here-
after described. Such electrodes form a longer arc, so that the distance between
the upper and the lower electrode is at least 8 to 10 millimetres, and ample light
will be emitted to both sides (front and back of the lamp). The changing of the
are from one spot of the electrode to another situated right or left of the same,
takes place more slowly and gradually, and is not attended with violent fluctua-
tions of current.
Plate-shaped electrodes offer to the current a much larger area in flowing to
the point of combustion, and are consequently heated less, than is the case with
ordinary pencil-shaped electrodes.
If it is desired, on the contrary, to have a greater density of current near the
point of combustion, the plate may be provided with parallel and preferably ver-
tical slots, so as to form bars or prongs, or several bars or pencils may be placed
vertically side by side, so as to form a row, with narrow slots between, and in
case the bars are round, they may touch each other.
I prefer to produce electrodes in the shape of flat plates, and to press the same
in suitable moulds, so as to form vertical ribs or veins which may be round or
angular and extend from a point below the top to the lower edge of the plate, so
s to occupy only a part of its height.
Pencil-shaped electrodes may be placed side by side and perforated axially to
eceive a wick.
Electrodes made as described above, may burn 100 hours, without requiring
he arc to be enclosed, and more light can be produced by a given number of Watts,
han by the electrodes hitherto known.
The various forms of electrodes have the common feature, that the outline of a
ross section at right angles to the line of feed is approximately a rectangle, the
ong side of which has at least twice the length of the short side, or the said out-
ne may form a pair of angles or of parallel or concentric curves.
The metallic or metalloid salts contained in the carbon mixture, as mentioned
D

page_text: above, consist preferably of fluoride or bromide of calcium or magnesium, to
which may be added some salts of potassium, boron, or sodium in a calcined con-
dition, in order to prevent flickering. The carbon electrode may be provided
with a suitable coating, preferably by heating the electrode to red heat, and then
dipping it into a liquid mass consisting of a salt of boron, so that when taken out
of the bath and allowed to cool, the carbon will have a glassy coating. The fused
salt employed for this purpose should be of such a nature, that it will have a
reducing effect on the slags produced during the burning of the calcareous car-
bon and will absorb the same.
Dated this 9th day of September 1899
ATC Daps.
I, HUGO BREMER, Manufacturer, of the Neheimer Metallwaaren -u. Werk-
zeugfabrik, of Neheim-on-the-Ruhr, Prussia, 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:-
Carbon electrodes for are lamps are usually made in the shape of cylindrical
rods or pencils. Attempts have been made to lengthen the life of arc lamp elec-
trodes by giving them the shape of plates, but owing to the close proximity of the
two electrodes, which with currents at ordinary pressures are only from two to
three millimetres apart, the radiation of light is very unsatisfactory. As the
starting point of the arc, which yields by far the greatest portion of the light, is
alternately situated on one side of the carbon and then on the other, one side of
the electrode (viz., that which happens to be on the side opposite to the starting
point) is always in the shadow. Moreover, the are burns at one time only on a
small part of the edge formed by a plate-shaped electrode, and thereby makes a
recess in the same, until the are becomes too long and the regulating apparatus
begins to act. This brings the entire electrodes nearer to each other, and the are
is struck at a new spot situated some distance from the recess mentioned above;
generally at the point where the electrodes have come most closely together.
In the case of carbons having the usual composition, this new ignition is atten-
ded with a certain diminution of light and a hissing or humming sound, which
defects reduce or destroy the practical value of flat electrodes.
car-
These defects are not removed by making electrodes of two or more round ca
bon rods joined together by narrow ribs or strips.
On the other hand, it is well known, that the addition of calcium or magnesium
salts to the carbon serving as raw material for the manufacture of ordinary arc-
lamp electrodes has the effect of increasing the light emitted by the arc.
I have found, however, that in the case of flat or elongated carbon electrodes,
or electrodes composed of a series of round carbon rods, or generally in electrodes
where, owing to their large sectional area (for a given current) the are will fre-
quently jump from one part to another, the presence of a considerable quantity
of luminiferous mineral matter in the carbon mixture will render the change of
the arc from one spot to another more gradual and easy, and will avoid the hiss-
ing noise which otherwise occurs with each re-ignition; in other words, it will
produce a smooth and comparatively noiseless re-ignition.
It is evident, that any lengthening of the arc tends to increase the radiation of
light, as will be seen from the accompanying diagram, in which Fig. 1 illustrates

page_text: a pair of carbons placed close together, so as to produce a short arc b, and Fig. 2
a pair of carbons placed further apart, so as to produce a long are 6. My inven-
tion therefore consists in an improved composition of carbon electrodes with large
sectional area, which cause the arc to change frequently from one point of the elec-
trode surface to another, in other words, it consists in mixing with the carbon from
which the said electrodes are made, luminiferous metallic salts or other materials,
which are known to have the property of lengthening the arc.
- Such electrodes may have the shape of flat plates, or of round pencils placed
side Dy side in a row or group forming a straight line or a circle or other suitable
figure, and the metallic salts should constitute at least 5 per cent. of the carbon
mixture.
The metallic salts contained in the carbon mixture, as mentioned above, con-
sist preferably of fluoride or bromide of calcium or magnesium, to which may be
added some salts of potassium, boron or sodium in a calcined condition, in order
to prevent flickering. The carbon electrode may be provided with a suitable
coating, preferably by heating the electrode to red heat, and then dipping it into
a liquid mass consisting of a salt of boron, so that when taken out of the bath
and allowed to cool the carbon will have a glassy coating.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that what
I claim is
1. The improvement in the composition of plate-shaped or other arc-lamp elec-
trodes having a comparatively large sectional area which causes the are to jump
frequently from one spot of the electrode to another, which consists in mixing
with the carbon serving as raw material for the said electrodes, a luminiferous
metallic salt or other substance adapted to lengthen the arc, for the purpose of
reducing the noise caused by the re-ignition of the arc, substantially as described.
2. Arc lamp electrodes having the composition and properties described.
Dated this 1st day of Juno 1900.
FAIRFAX & WETTER,
Agents,
37 and 39, Essex Street, Strand, London.