Improvements in Electrodes for Electric Arc Lamps.
Year: 1899

page_text: Date of Application, 17th July, 1899
Complete Specification Left, 17th Apr., 1900-Accepted, 19th May, 1900
Improvements in Electrodes for Electric Arc Lamps.
I, HUGO BREMER, Manufacturer, of the Neheimer Metall waaren- and Werkzeug-
Fabrik, of Neheim-on-the-Ruhr, in the Kingdom of Prussia, do hereby declare the
nature of this invention to be as follows:-
Numerous attempts have been made to increase the luminosity of arc lamp carbons
by incorporating with the carbon a suitable quantity of metallic salts, but without
the expected success, chiefly because the colour of the light was thereby effected
prejudicially,or because the slag gradually separated from the carbon,acted injuriously
to such an extent,as to render the increase in the production of light of comparatively
sinall value.
I have found, after many experiments, that the elements fluorine, iodine and
bromine, in the shape of their compounds with calcium, magnesium or similar metals,
with or without the addition of pulverized metals or oxides, yield a light of agreeable
slightly yellow colour and great intensity, provided that in the case of fluorine
compounds the fluorine constitutes at least 5 per cent of the entire carbon mixture.
The best results have been obtained with a inixture containing 30 to 50 per cent
of calcium fluoride, and as a rule the intensity of the light increases with the contents
of metallic salts, until it reaches 70 or 80 per cent, but such a large percentage of
metallic salts is not desirable on account of the secondary effects produced by the
slag, and the reduction in the strength of the carbons.
Hitherto it has not been found practicable to add more than 25 per cent of metallic
salts, in consequence of which the increase of luminosity was so small, that such an
addition did not seem to be advantageous, because already with an addition of 20 to
25 per cent, the heat caused the formation of ashes and the internal decomposition of
the carbon, already after a short time, which was in inverse ratio to the percentage
of metallic salts.
A remedy for this evil was provided by forming on the carbon a glassy or metallic
coating or film according to my invention described in a concurrent application for
patent, which invention also provided a means for applying to the surface of the
carbon simultaneously with this coating certain chemicals adapted to act beneficially
on the slag, which is always produced from the metallic salts and collects on the edge
or surface of the carbon.
As the formation of slags or excretions on carbons containing metallic salts cannot
be altogether avoided, care should be taken, that they drop off either as hard
particles or in the shape of liquid drops, For example, carbons containing calcium
Huoride give an easily fusible yellow slag, which cools slowly and produces the
following evil, viz. after a sufficient quantity of liquid slag has collected at the edge
Pi871

page_text: of the carbon, a drop will fall off, which before cooling adheres immediately to the
edge of the lower carbon, where the consecutive drops will gradually form a ring on
the edge of the carbon and interfere very injuriously with the burning of the carbon,
as well as with the emission of light.
The coating, which may be of borax, silica, metals, or other materials has the
effect, that the drops of slag will congeal immediately after they have separated and
will slide or roll down along the lower carbon without producing any injurious effect
or that fewer drops will be formed.
The fusibility of the slag is increased, if the coating adds to its several chemical
elements already contained in the slag, such as salts of lime or soda, for instance if
the coating consists of water glass applied by a brush or other means.
I have found that carbon electrodes containing fluoride of calcium or inagnesium or
other metallic salts are apt to flicker unless this tendency is counteracted by
incorporating with the carbon mixture a sufficient quantity of potassium, boron or
sodium salts. The best effect is produced by adding the said salts in a calcined con-
dition, because ordinary borax which has been proposed for this purpose, and also
other chemicals, give off their water of crystallisation in the process of baking,
and the vapours thus produced have an injurious effect on the density of the
carbon.
A good carbon electrode made according to the present invention may
contain 5-40 per cent of bromine or fluorine, 1-30 per cent of a metallic salt,
and 1 to 10 per cent of a salt of boron, potassium or sodium, or it may contain 5-40
per cent of fluorine or bromine and 10-30 per cent of calcium, or it may
contain 20-70 per cent of calcium fluoride.
Dated this 12th day of July 1899
FAIRFAX & WETTER,
Agents for the Applicant.
Improvements in Electrodes for Electric Arc Lamps.
I, HUGO BREMER, Manufacturer, 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 he
particularly described and ascertained in and by the following statement :-
Numerous attempts has been made, to increase the luminosity of arc lamp
electrodes, by mixing with the carbon salts of calcium, magnesium, strontium, and
other suitable :netals, but without the expected result, partly because the quantity
of these admixtures was so small, that the least inequality of distribution caused
considerable fluctuation of the arc, and partly because the slag produced by the
mineral admixtures (unless they are used in very small quantity) was of such a nature,
that it formed at the extremity of the electrode a solid ring, gradually obscuring the
flame and finally extinguishing the arc.
This evil grew in direct ratio with the percentage of the luminiferous metallic
base salts mixed with the carbon and rendered a high percentage impracticable.
Moreover, it is not generally known that the salts to be mixed with the carbon
should be calcined or relieved of any water of crystallisation, in order to avoid porosity
of the electrode.
I have found, that the slag can be rendered harmless when the quantity of
luminiferous metallic salt is largely increased by adding to the carbon a suitable
quantity of a flux, such as a fluoride, -iodide-or-bromide, which has the property of

page_text: fusing at the temperature of the arc and absorbing the basic slag formed by the
luminiferous mineral matter, which then falls off in drops or small particles.
Instead of adding a metallic base salt and a flux to the carbon separately; they
may be chemically combined, before, they are mixed with the carbon. -
The most suitable salts I have found for my purpose are fluorides, especially
calcium fluoride and cryolite, partly because they produce a light of greater intensity
and more agreeable colour, than that obtained with calcium chloride or other calcium
salts, and partly because the slag produced by calcium fluoride is more or less liquid,
instead of being hard and solid, like the slag produced by other calcium salts.
The quantity of luminiferous mineral matter to be mixed with the carbon may be
from 15 to 60 per cent. of the carbon mixture, preferably from 25 to 30 per cent; the
quantity of the flux depends partly on the nature and quantity of the luminiferous
base and partly on the nature of the flux.
In the case of fluorine compounds, the fluorine contained in the same should
constitute at least 5 per cent of the entire carbon mixture. The-same-rule-may-be
observed-if-the-admixtures-consist-of-bromine-and-iodine-compounds.
The total quantity of mineral matter contained in the carbon, that is to say, the
luminiferous salts and the flux, should be at least 15 per cent, and not more than 80 per
cent of the carbon mixture. A higher percentage would be too detrimental to the
strength of the electrode, and to the temperature of the arc.
I have found, that carbon electrodes containing fluoride of calcium or magnesium,
are apt to flicker, unless this tendency is counteracted by incorporating with the
carbon mixture a sufficient quantity of salts of boron or potassium, or sodium, such
as boric acid, borax, potassium carbonate or silicate, sodium carbonate or silicate.
A good carbon electrode made according to the present invention may
contain 10-60 per cent of calcium fluoride, and one to ten per cent of a suitable
salt of boron, potassium, or sodium.
If the slag produced by the burning of the upper carbon forms a viscous liquid
which falls off in drops and if the lower carbon is uncoated, the drops which fall upon
the edge of the lower carbon will adhere to the same, and the consecutive drops will
gradually form on the edge of the lower carbon a ring which interferes with the
burning of the carbon, as well as with the emission of light.
If, however, the lower electrode has a glassy coating of borax, a silicate or other
suitable material, the drops of slag from the upper electrode will congeal imme-
diately after they have separated and will slide down along the lower carbon, without
producing any injurious effect. The lower carbon should therefore be provided with
a glassy coating, and it is advantageous to coat also the upper carbon with a glassy
substance, or by electro-deposition, in order to avoid the rapid incineration or asby
decay of the same through contact with the atmosphere.
Having now particularly described and ascertained the nature of the said inven-
tion 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 in addition to 15 to 60 per cent of a
luminiferous metal-or metallic base sult such as a compound of calcium or nag-
nesium, at least five per cent of fluorine in the shape of a suitable compound such as
calcium fluoride, substantially as described, and for the purpose specified.
2A-earbon-electrode-for-are-lamps-containing-in-addition-10-8-luminiferous base;
at-least-five-per-eent-of-iodine-or-bromine;-in-the-shape--of-a--suitable--compound;
substantially-as-described-and-for-the-purpose-spee:fied:
23. A carbon electrode for arc lamps containing in addition to a luminiferous metal
Ar-base salt, at least five per cent of fluorine, one-or-bromine in the shape of a
suitable compound, and a compound of boron, potassium or sodium, which have been
added to the carbon mixture in a calcined condition, or free from water of crystallisa-
tion, substantially as described and for the purpose specified.
34 A carbon electrode for arc lamps containing from 10 to 60 per cent of calcium

page_text: fluoride uniforinly mixed with the carbon, substantially as described and for the
purpose specified.
In-mineralised-carbon-electrodes-for-are-lamps;-the-combination-of-an--upper
electrode-with-a-lower-electrode-having-a-glassy-eeating,-
described.
as-and-for--the--
--purpose
DL A 1 1000
FAIRFAX & WETTER,
Agents, 37 and 39, Essex Street, Strand, London
FAIRFAX & WETTER,
Agents, 37 and 39, Essex Street, Strand, London