Improvements in Electrodes for Aro Lamps.
Year: 1898

page_text: Date of Application, 29th July, 1898-Accepted, 25th Mar., 1899
Improvements in Electrodes for Aro Lamps.
I, HrGO BREMER, of Neheim on the Ruhr, in the Empire of Germany, Manu-
facturer, 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 improvements in arc lamps and it has for its object
the increase of the luminous intensity of such lamps. For this purpose there are
introduced into the electrodes, small quantities of chalk, lime, magnesia, or other
similar substances which are rendered incandescent by the intense heat of the
voltaic are and thus as is well known considerably increase the luminous
intensity.
In the manufacture of carbon pencils the above mentioned substances may be
mixed with the carbon paste and be baked with the latter. The result is that
although the resistance of the carbons is thus increased, the said carbons will
still retain a sufficient conductivity for the purpose in view. The special
arrangement of the carbons, according to their composition, is the object of this
patent.
One of the electrodes may also be composed of carbide of calcium, because this
substance contains in intimate combination with the carbon the necessary lime,
whilst having a sufficient electrical conductivity. In most cases it will be suffi-
cient to form one of the electrodes (the negative one), in this manner because it
will communicate to the other electrode the necessary quantity of lime in the
form of powder. It is to be remarked that by the use of this substance, the
voltaic arc is considerably enlarged and a sufficient arc will be obtained with a
compartively small intensity of current.
The addition of the material to be rendered incandescent, by mixing it with
the original carbon paste which is baked in the well known way as is done in the
case of carbons for arc lamps which are at present in use, has for its object and
result that, on one hand an extremely small intensity of current will be suffi-
cient to form the arc, whilst on the other hand the large voltaic arc is capable
of sending more light to the outside, whereas in ordinary arc lamps it is retained
in part inside the crater which is formed and is prevented from passing out by
electrodes. Moreover, the light produced by carbons with which the said sub-
stance has been mixed, has a colour which is much more agreeable to the eye
and is much more favourable for the purpose of distinguishing colours. A favour-
able result will already be perceived in the case of carbons containing 2 to 40
per cent. of lime.
The carbide of calcium which may, if desired, be employed as an electrode,
contains as is well known greater proportions of lime, so that whether it is added
mechanically or only combined with the carbon it produces the same results.
Besides the above mentioned combinations, it is of particular advantage to form the
main body or mass of the electrodes of a mixture of carbon and lime, etc., whilst
the core of the said electrodes is also formed of a mixture of carbon and lime or of

page_text: one of the aforesaid mixtures. In any case the carbon should be in greater pro-
portions than any of the admixed substances, with the object of producing a
more steady light, because the greatest percentage of carbon considerably
increases the power of the electrodes. This last fact is realised principally when,
by reason of the elongated are which is produced, the positive carbon is arranged
below and the negative carbon is arranged above in are lamps of which one of
the electrodes or both electrodes are formed of one of the above mentioned
mixtures.
Since the particles of carbon which are carried from the positive carbon to the
negative carbon follow the same path as the hot air which ascends along the car-
bons, the result is that the are will burn much more steadily, because, if it
burnt from the top down towards the bottom it would have to work against the
ascending air, and would, therefore, have much less length; but it is just upon
the length of the arc that the intensity of the light depends. The electroles
composed of carbon and lime, or of one of the above mentioned mixtures, may also
be made by means of "briquettes," that is to say, of wood charcoal composed of
waste or wood sawdust compressed in the form of briquettes which are then sub-
jected to a very high temperature, care being taken that only a very small
quantity of air shall come in contact therewith. This wood charcoal, as com-
pared with all other kinds of wood charcoal, has the advantage that it is more
suitable for the manufacture of electrodes composed of carbon and lime for the
reasons that it is more pure, its specific gravity is higher and it enters more
readily into combination with the fime to form carbide of calcium, which com-
bination takes place whilst the electrodes are burning. Further, the light which
is emitted by electrodes manufactured with this briquette charcoal is much more
steady, and this fact is in case of an electrode mixed with lime of the very
greatest importance, because the arc is considerably enlarged and is consequently
very sensitive to the slightest influences in the presence of impurities.
Finally, in are lamps having electrodes consisting of a mixture of carbon and
lime, it is also possible to employ an ordinary homogeneous carbon as the positive
carbon, and a carbon admixed with lime as the negative carbon.
In fact, it has been ascertained that a very steady light such as is necessary for
indoor lighting can only be produced by the use of an ordinary carbon without
admixture or with only a very slight admixture, together with a carbon with an
admixture of lime, because every percentage of lime contained in the positive
carbon causes the light to flicker, whilst the lime coming from the negative
carbon is sufficient to bring out the advantages of this light, that is to say its
greater intensity, its more pleasant colour and its larger are.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is
(1) An arc lamp having electrodes composed of a mechanical mixture of carbon
with the substances hereinbefore mentioned, which are baked together, or in
which the electrodes are formed chiefly of carbon or of a mixture of carbon with
the above mentioned substances, and having one or more cores composed of the
above mentioned non-conducting substances alone, or mixed with carbon in such
proportions that the central portion of electrodes will have a greater proportion
than the outer portion or envelope.
(2) An are lamp in which the electrodes or one of the electrodes are or is
formed of carbide of calcium or of a baked mixture of the latter with carbon.
(3) An arc lamp in which the electrodes are formed of one of the above men-
tioned mixtures and in which the positive carbon is arranged underneath with
the object of obtaining an arc of greater steadiness of burning.
(4) An arc lamp in which the electrodes are formed of wood charcoal briquettes
with or without an addition of lime in one or in the two electrodes.
(5) In an arc lamp, the arrangement of an ordinary homogeneous carbon or a

page_text: carbon having a very slight admixture, as a positive carbon, and of a carbon
admixed with lime (said carbon containing at least three per cent. more lime or
similar substance than the positive carbon) or of a similar substance, as the
negative carbon, substantially as hereinbefore described.
Dated this 20th day of July 1898.
ROBERT E. PHILLIPS, Assoc.M.Inst.C.E., M.I.Mech. E.,
Chartered Patent Agent,
70, Chancery Lane, London, W.C., Associate Agent.