Improvements in Carbons for Electric Arc Lamps.
Year: 1899

page_text: Improvements in Carbons for Electric Arc Lamps.
I, JOHN AMBROSE FLEMING, Professor of Electrical Engineering in University
College, Gower Street, London, W.C., in the County of Middlesex, do hereby
declare the nature of this invention to be as follows:-
:-
The improvements described in this specification relate to the construction of
carbons for use in electric arc lamps.
:
In the course of experiments with carbon rods each pierced with a longitudinal
hole in which is inserted a freely movable but well fitting solid cylinder of
refractory oxide, I have found that when such an improved carbon is used in
an arc lamp the electric arc is sometimes a little unsteady, the arc wandering
round, and although the light giving power of the arc is increased, the light is
fluctuating at times. I have however discovered that this defect may be
remedied by the employment of carbon rods bored through longitudinally with
two or more holes, each hole being fitted with an easily-fitting cylinder of refrac-
tory oxide. I manufacture these improved carbons in the following way. A
carbon rod is formed by pressing carbon paste in the usual manner through a
die so that the carbon has an elliptical or oval section, and is perforated longi-
tudinally by two holes. Or I may make a carbon of trefoil section having
three longitudinal holes, or one of quadri-lateral section having four holes;
and so on.
The carbon rod so formed resembles a gun barrel with 2, 3, 4 or more
barrels all welded together. In these apertures are placed easily-fitting cylinders
formed of magnesia, lime, or mixtures of these with other refractory oxides.
The carbon so formed is used as the upper carbon in an ordinary vertical open
or enclosed arc lamp. As a lower carbon I prefer to use a carbon rod of similar
shaped section to the upper but rather smaller diameter. So that an upper
two-hole elliptical sectioned carbon would have a lower solid elliptical-sectioned
carbon, but of rather smaller diameter. In any case the lower carbon must
be of such size that when the upper carbon is lifted by the arc lamp mechanism
to strike the arc the cylinders of refractory oxide fall down and rest on the
bottom carbon. These cylinders then bridge across the arc and become rapidly
heated to incandescence. I find that by the use of two or more cylinders the
electric are keeps quite steady and does not wander round. The oxide cylinders
volatilize at a slow rate and as they do so they are continually forced down by
their own weight, always bridging across the gap between the carbons. The
oxide cylinders become heated by the are and themselves become luminous,
greatly contributing to the light of the arc. The utility of the improved carbon
depends upon the free.mobility of the cylinder of refractory oxide in the interior
of the carbon rod. In those cases in which horizontal or inclined carbons must
be used the oxide cylinders may be pushed by a spring instead of by their own
weight.
Dated this 2nd day of June 1899.

page_text: I, JOHN AMBROSE FLEMING, Professor of Electrical Engineering in University
College, Gower Street, in the County of London, do hereby declare the nature
of this invention and in what manner the same is to be performed to be particu-
larly described and ascertained in and by the following statement: —
It has been proposed to make the carbon of an electric lamp with an internal
core or an external sleeve of some material such as a refractory oxide, which,
when heated by the arc produced on first putting the lamp in circuit, should
become so far conductive that the circuit, instead of forming an are between
the carbons, should pass through this core or sleeve heating it to incandescence,
the lamp being no longer of the arc kind but of the glow kind.
My invention relates to the application of refractory cores or rods of special
kind to the carbons of an electric arc lamp in such a manner that they, instead
of becoming heated, so as to become conductive, by the passage of current through
them and then becoming farther heated so as to glow, are heated by the are
itself which is maintained between the carbons, and by their brilliant incan-
descence largely increase the illuminating power of the lamp.
For this purpose, I make and arrange the carbons as I shall describe referring
to the accompanying drawings.
Fig. 1 is a side view partly sectional shewing an arrangement of the carbons
of a lamp according to my invention. Figs. 2 and 3 are sectional plans of the
two carbons respectively. I make the one carbon a with two parallel holes or
bores extending along it, and into these bores I place loosely, cores, which are
conveniently made in separate pieces in the following manner.
I subject pure
dry magnesia to great endways pressure in a tubular mould and thus form it
into a stick or pencil which I then heat to the highest attainable temperature in
an electric furnace. The pencils thus prepared are exceedingly hard and of
high electrical resistance. They are made of such diameter that they can slide
quite freely in the bores of the carbon so that when this carbon is vertical or
not much inclined from the vertical, they can slide down by gravity and lodge
on the lower carbon. When the carbon thus cored is horizontal or so far inclined
that the cores cannot descend by gravity, they may be urged forwards by springs
or otherwise so as to bear always against the other carbon. The carbon a as
well as the other carbon d is preferably made of section having straight sides
and ends rounded as indicated by the dotted arcs in Fig. 2, so that these ends in
the act of moulding the upper carbon, are sufficiently strong to be cored; but
after the carbons are baked, the rounded edges are to a great extent ground
off, leaving only a very thin wall of carbon outside the refractory cores. The
lower carbon is made of nearly the same sectional form as the upper carbon but
without the bores and not so wide.
The carbons being fed and regulated by any of the known arrangements for
that purpose employed in arc lamps, the operation is as follows:-
-
When the lamp is out of circuit the carbons are in contact, and when it is
put in circuit, the regulating apparatus separates the carbons, striking the arc,
out leaving the two cores of the one carbon bearing against the other carbon.
The arc, which is formed mostly in the space between the two cores, and remains
steadily in that position heats the cores to brilliant incandescence. The feeding
and regulation of the carbons go on in the usual way, the two cores remaining
in position, and as they gradually waste away, fresh lengths of them are pro-
truded from the bores of a, so as always to bear on the end of d however the
carbons themselves are moved or consumed.

page_text: Owing to the very small body of carbon outside the refractory cores, the arc
remains almost constantly in the middle between those rods, for the moment it
strays towards either side, the thin wall of carbon is at once consumed, causing
the arc to return to the middle.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:
An electric arc lamp having two refractory cores or rods sliding freely in
bores of one of the carbons and presenting themselves one on each side of the
are which is regulated in the usual way and heats the cores or rods to brilliant
incandescence, substantially as described with reference to the drawings.
This 1..1 da of Mak 1000
ABEL & IMRAY,
Agents for the Applicant.