Improvements in Carbons for Electric Arc Lamps.
Year: 1891

page_text: COMPLETE SPECIFICATION.
[Communicated from abroad by THE THOMSON-HOUSTON INTERNATIONAL
ELECTRIC COMPANY, of 620 Atlantic Avenue, Boston, Massachusetts, United
States of America.]
Improvements in Carbons for Electric Arc Lamps.
I, HENRY HARRIS LAKE of the firm of Haseltine Lake & Co. Patent Agents
45 Southampton Buildings in the County of Middlesex 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 carbons or pencils for use in electric arc lamps of the
kind in which the electrodes are presented to one another end to end and which are
fed towards one another as they are cosumed by the arc passing between them.
In electric arc lamps burning on circuits with the standard current of from eight
to ten amperes it is the practice to employ a round carbon of approximately seven
sixteenths of an inch in diameter, a dimension which has been found by long
experience to give the best results. Carbon pencils having their cross sectional
area thus proportional to the number of amperes of current employed burn away at
their tips uniformly, give a light of great steadiness and throw a minimum shadow.
They, however, waste with such rapidity that in practice they will not burn or give
a continuous service for the length of time ordinarily desired unless they are given
an excessive length such as to require unusual or cumbersome dimensions in the
lamp itself. Thus with the dimensions or proportions of carbon stated, a positive
carbon of twelve inches and a negative of six inches will give a service for approxi-
mately only seven to eight hours.
Heretofore it has been the practice to use a double carbon lamp when it was
necessary to give service for the whole night because a single pair of round carbons
cannot be made to last long enough if the carbons are of the usual length, the
positive twelve inches, the negative six inches. Attempts have been made to
construct satisfactory lamps burning positive carbons of twenty-four inches and
negative ones of twelve inches, but success has not been attained. The point of
light in such lamps sinks down about eleven inches during the night, necessitating
the employment of very long globes in order to shield the arc against the wind when
the carbons commence to burn. As the upper carbon rods and the side rods must be
made quite thick in order to be stiff enough notwithstanding their great length, such
a lamp is also heavy and costly.
Attempts have been made to secure the desired length of service by using a round
carbon of an increased cross section, but when the standard diameter or proportion
of cross section to amperes of current is much exceeded a practical difficulty
presents itself which renders such a solution of the problem unsatisfactory, riz. with
a larger carbon, the lower carbon will burn not to a point but blunt and the arc will
be caused to travel around the end giving an unsteady light.
There is also a tendency to the formation of projections on the end of the carbon near
the ends which will obscure the light. In the case of the upper cylindrical electrode,
if the same be given sufficient cross sectional area to give the desired increase of
time of service, the crater formed therein will become so deep, the walls not being
sufficiently heated to consume at the proper rate, that the passage of the light rays
outward would be seriously obstructed. The attempt to remedy such difficulty by
increasing the number of amperes of current employed would simply result in
increasing the rate of waste and the whole purpose of increasing the cross sectional
area of the round carbon would be defeated.
It has also been proposed to employ wide flat plates of carbon to give increased
length of service, but the width of such carbon has been such that a comparatively

page_text: small portion of the end of the carbon would be heated by the arc the remaining
part being cold, until finally the heated portion would burn away so far that the arc
would be forced to shift itself to the cold, portion or (in some forms of lamp) the
carbons would be fed together or caused to touch at a point far removed from
the arc there burning: The service of such carbons has never proved wholly
satisfactory.
In those cases where the carbon has been allowed to drop to form the arc at a
new point, the carbon burns fitfully and the consumption of the edge is irregular ;
but in all cases of flat carbons as heretofore used there a deficient action owing
not only to the large mass of carbon which lends itself to the dissipation of heat of
the part for the time being kept hot by the arc, but also to the fact that in most
forms of lamp the arc in order to burn across the whole edge must from time to
time attack or force its way on to cold or unheated portions of carbon and heat
them up.
Other forms of carbon such as the rotating disc carbon have also been proposed
as a means of providing the desirable length of service without undue length of the
consumed electrode.
The present invention consists in forming the carbon electrode or pencil as a
flattened bar or prism thickest at the middle and becoming thinner towards the
edges, said pencil having however, the increased transverse area in cross section
necessary to give the required length of service and, in ordinary forms of arc lamp
approximately twice the area of the ordinary round carbon which would be employed
on a circuit having a current of the same number of amperes.
The preferred form employed in cross section, is that of an oval or ellipse the
shorter diameter of which if the carbon is to be used on a circuit from eight to ten
amperes, would be approximately the same as the diameter of the ordinary round
carbon employed on a circuit having the same current, that is to say, approximately
seven sixteenths of an inch, but might be somewhat less or greater, while its longer
diameter would be such as to give a mass or bulk sufficient to cause the carbon to
waste away at approximately only half the rate of the ordinary round seven
sixteenth carbon. The thickness of the elliptical carbon might be less than seven
sixteenths of an inch or might be even greater, but it is preferred not to make it
greater since the carbon does not burn so well and a deeper crater would be formed.
The necessary increase of area is obtained by giving the carbon a greater dimension
from edge to edge, and excellent results are obtained by making its dimension from
edge to edge approximately twice the thickness when the figure in cross section
is an oval.
A carbon formed in this way and proportioned in its mass, as described, with
relation to the current of the standard circuit carrying from seven to ten amperes
will burn uniformly to a point or edge substantially in the same way as the ordinary
round seven sixteenths carbon, but will at the same time waste at only about half
the rate of the seven sixteenths carbon. It will be practically free from the
irregularities which exist in the case of a round carbon of the same area burned
upon the same circuit.
In a carbon formed according to this invention with the shorter diameter of the
flattened bar or prism about seven sixteenths of an inch for carbons burning with say
ten amperes of current, the lower carbon will, by reason of such short dimension,
burn to practically. a knife edge of long taper while the upper carbon will have a
crater assuming the shape of a narrow and shallow groove instead of-the-deep crater
with light obscuring edges which would exist in the case of a carbon on the same
circuit cylindrical in form and having the necessary diameter to burn at only the
same rate. The longer axis of the ellipse when the elliptical form is employed
should be approximately seven eighths of an inch for a ten ampere current and the
increased mass provided by this larger dimension will provide the necessary increased
time of consumption, but will not permit a part of the carbon to be cold while the
remaining part only where the arc plays and burns is red hot. The carbon will
therefore, waste uniformly at a point or edge and the formations of the projections

page_text: Figure 8 shows in cross section the dimensions of the cylindrical carbon heretofore
ordinarily employed on a circuit to which the carbons illustrated in the other figures
are adapted.
=
Figure 9 shows in cross section a cylindrical carbon of increased area in cross
section heretofore employed.
With
The carbon shown in the latter figure is supposed to be about three quarters of
an inch in diameter and that illustrated in Figure 8 to be seven sixteenths.
the size shown in Figure 9, or in a larger size, burned upon the same circuit or
substantially the same circuit as that of Figure 8 the consumption is very imperfect,
an irregular wall or shell projecting towards the space between the carbons placed
end to end often resulting which intercepts a large portion of the light. Other sizes
larger than that indicated in Figure 8 have been employed for the same purpose
but have been objectionable for one reason or another. By giving however, to the
increased size of carbon to be used on the same or substantially the same circuit as
the smaller size the form of a flattened bar or prism such as is indicated in Figure 3
the objections are removed. Its greatest thickness is but little if any in excess of the
diameter of the standard carbon employed on the same circuit so that the arc is
able to keep the sides of the pencils burned away so as to maintain a uniform taper
or tip without forming projecting shells which will intercept the light. The carbons
will burn from the front and rear sides to the same extent and consequently cast no
more shadow than the standard carton. The thinning of the material towards the
edges allows it to waste away at such points sufficiently to cause or permit the uniform
consumption and continued pointing of the pencil at its end. In fact, the action
of the carbon is almost the same as that of the standard size employed on the
same circuit but its rate of consumption per unit of length is practically one
half less.
This invention is not limited to the exact relative dimensions of the large and
smaller diameters for the ellipse hereinbefore specified but the same may be
Blightly varied.
Figure 4 shows a modification in which the flattened prism or bar instead of being
curved from its centre towards its end is flat and straight thus producing approxi-
mately a diamond shaped carbon in cross section the corners being however, rounded
off or blunted. The necessary area to give the same rate of consumption is the form
shown in Figure 3, would be obtained by slightly increasing one or both of the
dimensions, thus for instance, the greatest thickness may be one half inch and the
width or longer dimension one and one eighth inches.
Other variations in the form might be employed as, for example, the carbon may
be flat on one side and rounded on the other as shown in Figure 5, or slightly

page_text: concave on one side and convex on the other as shown in Figure 6, or flat on one
side and angular on the other as shown in Figure 7. These forms are merely
suggested as possible variations all alike however, in the fact that the carbon is
formed as a flattened bar or prism thickest at its middle and becoming thinner or
tapering towards the edges the total cross sectional area being, however, made much
greater and preferably twice as great as that of the ordinary standard carbon of
cylindrical form ordinarily employed on a circuit carrying the same number
of amperes.
This invention is distinguished in result from prior attempts to provide carbons
sufficiently massive so that a single pair will burn as long as two pairs of ordinary
carbons by the avoidance of projecting portions of dull carbon which intercept the
light,and cast irregular shadows around the lamp. As such shadows are most
objectionable when cast from projections on the lower or negative carbon, it is most
important that the lower carbon be constructed in accordance with this invention,
although preferably both carbons are so constructed. Thus the invention may be
in part availed of by using a lower carbon of the essential shape and proportions
specified in connection with the upper carbon of any other practical shape and
affording sufficient mass to maintain the arc for the requisite time. For this
reason this invention is not limited to the use of both carbons of like shape and
proportions it being sufficient if one of the carbons conforms to the conditions of the
invention.
No claim is made to elliptical or otherwise flattened carbons for arc lamps
generally, but only for those wherein the carbons are burned end to end, are fed
together by suitable feeding mechanism as they are consumed, and having an area
of cross section proportioned, as described, to that of ordinary carbons for burning
with the same volume of current.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed as communicated to
me by my foreign correspondents, I declare that what I claim is :-
First. In an electric arc lamp burning its carbons end to end and provided with
means for feeding them towards one another as they consume by the arc, pencils
or electrodes formed each as a flattened bar or prism thickest at its middle and
becoming thinner towards the edges and having a total cross sectional area
approximately twice that of the round carbon ordinarily employed on a circuit
carrying the same current.
Second. A pair of carbon pencils for an electric arc lamp burning two and only
two pencils by holding them in line end to end and having a feed mechanism
adapted to adjust the pencils towards one another as they are consumed, said
pencils having each a transverse area double that of the ordinary cylindrical lamp
carbons commonly employed on circuits carrying the same number of amperes,
and at least one of them formed as a flattened bar or prism of a thickness approxi-
mately equal to the diameter of the ordinary cylindrical single lamp carbon and of
a width approximately twice its thickness and tapered or thinned from its middle
towards its edge.
Third. A pair of carbon pencils for an electric arc lamp burning the pencils
by holding them in line end to end and having a feed mechanism adapted to adjust
the pencils towards one another as they are consumed, formed each with a total
cross-sectional area approximately twice that of the round carbons ordinarily
employed on a circuit carrying the same current, and at least one of them formed
as a flattened bar or prism of elliptical cross-section with a thickness at the inner
axis approximately equal to the diameter of an ordinary round carbon.
Fourth. A pair of carbon pencils for an electric arc lamp adapted to be
presented to one another end to end and to be adjusted towards one another as
they are consumed by an arc passing between them, formed each with an elliptical
or oval figure in cross section the minor diameter of which is approximately that
of the round carbon ordinarily employed on a circuit having the same current

page_text: while its major diameter is sufficient to give the increased mass in cross section
required to diminish the rate of consumption to the desired degree.
Fifth. A pair of carbon pencils for an arc lamp adapted to be presented to one
another end to end and to be adjusted towards one another as they are consumed
by an arc passing between them formed each as a flattened bar or prism thickest
at the middle and becoming thinner towards the edges as and for the purpose
described.
Sixth. A pair of carbon pencils for an arc lamp adapted to be presented to one
another end to end and to be adjusted toward one another as they are consumed
by an arc passing between them formed each with an elliptical or oval figure in
cross section as and for the purpose described.
Dated this 15th day of October 1891.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.