Improvements relating to Carbon Electrodes for Arc Lamps.
Year: 1899

page_text: Date of Application, 17th July, 1899
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PROVISIONAL SPECIFICATION.
Improvements relating to Carbon Electrodes for Arc Lamps.
I, HUGO BREMER, Manufacturer, of the Neheimer Metallwaaren-and Werk-
zeug-Fabrik, of Neheim-on-the-Ruhr, in the Kingdom of Prussia, do hereby
declare the nature of this invention to be as follows:
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It is well-known fact, that the addition of calcium compounds to carbon elec-
trodes for arc lamps will materially increase their luminosity, but at the same
time cause the formation of slag, which after a short time reduces the lumi-
nosity, or completely extinguishes the lamp. Another defect of such electrodes
is, that they burn off rapidly, owing to the ashy decay of the outer layer
at the incandescent extremities of the carbons, this decay being most marked
at the extreme end and diminishing towards the clamping screw. Consequently
one half or two thirds of the carbonacious material will burn, while the
remainder or mantle is amorphous, does not conduct electricity and only serves
to increase the formation of slags.
According to my present invention the finished carbon electrode containing
metallic salts is heated to red heat, and dipped into a liquid mass consisting
of a salt of boron or similar material, 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 must be of such a nature, that it will have a reducing effect on
the slags produced during the burning of the calcareous carbon, and will
absorb the same.
During the burning of such electrodes in an are lamp, the lower end of the
positive carbon will become highly incandescent, after a sufficient part of the
coating has been removed to establish contact and close the electric circuit. The
glassy coating will melt for a height of about 15 millimetres and will be caused
to boil, but without dropping off, because its coherent nature or viscosity will
prevent this. Instead of this, it flows around the lower parts of the electrode
and evaporates only at the very hottest part, about 1 to 2 millimetres from the
lower edge of the electrode.
On the whole extent of the remaining surface the electrode will remain closed
air-tight, so as to completely avoid the incineration mentioned above, in con-
sequence of which the consumption of carbons is much slower than with other
calcareous carbons.
The slag produced by the lime occasionally forms short hard leaflets at the
edge of the electrode, but it may be seen, that from time to time the molten
borax reaches the said leaflets or scales, dissolves them and draws them up into
the boiling mass, if it has not previously dropped in small and innocuous
particles.
The boiling mass surrounding the electrode is much heavier by the absorp-
tion of the lime and occasionally gives off drops.
Instead of calcareous compounds other metallic salts may be mixed with the
carbon forming the electrode, and instead of a glassy coating, a metallic coat-
ing produced by electro-deposition or other means may be used for excluding
1

page_text: the air. This has the advantage, that the metal will melt together with the
slag and increase the specific gravity of the same.
Dated this 12th day of July 1899
FAIRFAX & WETTER,
Agents for the Applicant.
Improvements relating to Carbon Electrodes for Arc Lamps.
I, HUGO BREMER, of the Neheimer Metallwaaren-and Werkzeug-Fabrik, of
Neheim-on-the-Ruhr, in the Kingdom of Prussia, do hereby declare the nature
of this invention and in what manner the same is to be performed to be parti-
cularly described and ascertained in and by the following statement:-
Among the many attempts which have been made for prolonging the
duration of carbon electrodes is the coating with a metal or salt, such as borax
or an alkali silicate, in order to prevent the disintegration of the heated carbon
by contact with the atmosphere.
On the other hand the fuminosity of the carbon electrodes has been increased
by mixing them with salts of calcium, magnesium, strontium, or other suit-
able metals, but such clectrodes generally suffer from the defect, that they pro-
duce slag which accumulating near the crater gradually obscures the same, and
finally chokes the arc, unless special precautions are taken to select salts or
mixtures of salts which produce slag adapted to drop off in the shape of scales
or liquids.
This invention relates to that kind of carbon electrodes for electric arc, lamps,
in which the carbon is uniformly mixed with luminiferous mineral matter,
preferably alkaline earths, and which are coated with a thin layer of fusible
salt or metal adapted to protect the electrode from contact with air, excepting
at the extreme illuminating end, where the coating melts under the tempera-
ture of the voltaic arc.
The following calcium salts may be contained in the carbon mixture serving
as raw material for the manufacture of electrodes, viz., calcium carbonate,
fluoride or silicate.
I select the material for the coating in such a manner, that it serves a
double purpose, viz., firstly, to protect the surface of the carbon from atmo-
spheric disintegration, and secondly, to combine with the slag produced by the
burning of the carbon, so as to form a liquid which falls off easily in drops.
This is the case, if the coating consists of boracic acid or of an acid borate, for
instance borax, which salts, when fused by the heat of the voltaic arc, will com-
bine with the basic slag, such as lime, magnesia, or strontia, thereby forming
a borate of lime or other alkaline earths, which falls off easily in drops.
I wish, however, to include neutral borates, which are known to act as a
flux, capable of absorbing, when in a fused condition, alkaline earths and other
bases.
If the glassy coating consists of an alkali-silicate, it will, when fused by the
heat of the arc and brought in contact with the slag form a double silicate
of lime, magnesia or other base, which falls off in drops.
The coating is preferably applied to the carbon electrode by heating the other-
wise finished electrode to red heat and then dipping it into a liquid consisting
of fused boric acid, or a borate or silicate, so that, when taken out of the bath,
the carbon will have a glassy coating.
.
During the burning of such electrodes in an arc-lamp, the lower end of the

page_text: positive carbon will become highly incandescent, after a sufficient part of the
coating has been removed to establish contact and to close the electric circuit.
The glassy coating will melt for a height of about 15 millimetres and will be
caused to boil, but on account of its coherent nature or viscosity will not drop
off. It flows around the lower parts of the electrode and evaporates only at the
very hottest part, about 1 to 2 millimetres from the lower edge of the electrode.
On the whole extent of the remaining surface the electrode will remain closed
airtight, so as to completely avoid the incineration of the carbon.
The slag produced by the lime or other metallic base contained in the elec-
trode occasionally forms short hard leaflets at the edge of the electrode, but it
may be seen, that from time to time the molten coating reaches the said leaflets
or scales, dissolves them and draws them up into the boiling mass, if it has not
previously dropped off in small and innocuous particles.
The boiling mass surrounding the electrodes is rendered heavier by the absorp-
tion of the lime or other base, and occasionally gives off drops.
Electrodes may be provided with a thin metallic coating produced by electro-
deposition or other means, instead of using a glassy coating, in which case the
slag will be rendered heavier by the absorption of the fused metal and will
thereby be caused to drop off more easily. I do not, however, claim the use
of a metallic coating, except for carbons containing at least five per cent. of
luminiferous mineral matter.
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. A carbon electrode for arc lamps containing luminiferous mineral matter
uniformly mixed with the carbon, and provided with an airtight coating consist-
ing of a boron compound or similar material adapted to melt at the extremity
of the electrode and then to absorb or dissolve the slag produced by the burning
of the electrode, substantially as and for the purpose described.
2. A carbon electrode for arc lamps containing luminiferous mineral matter
mixed with the carbon, and provided with an airtight coating composed of sub-
stances adapted to melt together with the slag produced by the burning of the
electrode and thereby to render the same more liquid or to cause it to drop
off by altering the specific gravity of the slag, substantially as described.
3. A carbon electrode for arc lamps having mineral admixtures and a pro-
tective coating composed and combined as described and for the purpose specified.
Dated this 17th day of April 1900.
FAIRFAX & WETTER,
Agents, 37 and 39, Essex Street, Strand, London.
FAIRFAX & WETTER,
Agents, 37 and 39, Essex Street, Strand, London.