Year: 1886

page_text: Date of Application, 12th June, 1886.
Complete Left, 7th Mar., 1887.
Complete Accepted, 22nd Apr., 1887.
We, RANKIN KENNEDY Electrical Engineer and ROBERT DICK, Manufacturer, both
of the Electric Lamp Works, 115 Woodside Road, Glasgow, Lanarkshire, do hereby
declare the nature of our Invention to be as follows:-
Our said invention has for its object the improvement of the carbon conductors and
fittings employed in a vacuum for the production of lights by electricity, whereby the
said lights may be used in what is known as the series order of distribution, thus
allowing of the use of comparatively small copper conductors for the supply of large
numbers of lights at a distance and from one common centre; and whereby we also
obtain an improved light both as to quantity and quality of luminosity and of any
desired size.
These electric lights or lamps made according to our improvements may also be
employed in what is known as parallel order, (that is where the lamps are grouped in
parallel arc between the leading main conductor and the return main, so that each
lamp is independent of the others if the electro-motive force of the supply is constant),
when only a few are required, say up to 100 lights from one centre, in which they
also show improved light by giving more candle power per unit of electric energy
expended.
By the improvements and to obtain the advantages of our invention, the carbon
conductor is made of low resistance and high specific resistance from its shortness in
length and increased uniform section and perfectly homogeneous nature; but although
the resistance of the carbon as a whole is low, yet per unit of its length the resistance
is high, this condition is of great importance, for example, if we take two pieces of
carbon of the same size in length and thickness, and measure their resistance
respectively, that carbon which has the highest resistance would be the best for the
purpose of this invention, it having the greatest specific resistance.
In no case,
however, is it necessary or advantageous by our improvements, to use carbons of
more than 100 ohms of current resistance; all in contradistinction to the filament
carbons used in electric lamps which require a small section and great length of
filament and requiring a high resistance to give the light. We have discovered that

page_text: carbon conductors can be made of very great resistance per inch, (taking one inch as
a unit length of carbon conductor), without at the same time having a small cross
section. In the carbon filaments employed in the well-known lamps of Edison the
resistance per inch is comparatively low, and to obtain the necessary high resistance
for such a lamp the filament is made of small cross section, and of great length from
5 to 10 inches long.
According to our invention, we adopt carbons of from 50 to 150 ohms of specific
resistance per inch, and make them of a proportionally short, thick, rigid construction
and character, giving them each a low resistance as a whole, although of high specific
resistance. And we have discovered that this carbon conductor is very suitable for
incandescent electric lamps to be used in great numbers connected in series to a central
supply, and that these carbons are much more economical and give a higher efficiency
of light than those known as carbon filaments of small cross section and long length,
having a low specific resistance with a very high current resistance.
Hitherto in making carbon conductors for incandescent lamps the practice and aim
has been to make the specific resistance low, and using long thin elastic or flexible
carbon filaments, requiring a process of depositing carbon on them, known as
Sawyer's process, in their manufacture to render these long thin carbon filaments
uniform in resistance; this depositing of graphitic carbon necessarily lowers the
specific resistance of the filaments. Whereas by our improvements we make short
rigid carbon conductors of high specific resistance and of a sufficiently uniform
resistance, so that the after process of depositing carbon on them is quite unnecessary.
This we have found to be a great advantage, as the said deposited carbon, being of a
different kind or graphite character from the filament carbon to which it is applied,
(which is of the charcoal form of carbon) destroys the homogenous nature of the
filament or carbon conductor which is a source of great evil in the lamp.
To overcome the difficulty hitherto experienced in making electric lamps of the
incandescent type, connected in series order to the supply, arising from the fact that
if any one or more lamps in the series should fail through the rupture or breaking of
the carbon conductor, the whole series would be extinguished. We construct the
lamp in such a manner that the failure of the carbon conductor automatically cross-
connects the electrodes or wires of the carbon inside the lamp or glass bulb, and thus
the circuit being maintained the current goes on uninterruped and the faulty lamp is
switched off or cut out of the series so as not to stop the others.
Having thus generally described the nature of, or the principles upon which our
new or improved incandescent electric lamp is constructed and its action and advan-
tages, we shall now proceed to describe how we carry our invention into effect or
practice. Our improved incandescent lamp consists of a carbon conductor of
short length and low current resistance (under 100 ohms), but of a high specific
resistance and homogeneous without any outer deposit of graphitic carbon, and
attached to electrodes or wires so arranged within the containing glass bulb that in
the event of the carbon conductor getting injured or failing to act, the electrodes or
wires are automatically cross-connected to prevent the interruption of the current to
and through the remaining lamps of the circuit.
«
To prepare a carbon conductor for incandescent electric lamps according to our
improvements, a carbon-forming vegetable or textile material or fibre (preferably
'Kitool," a natural grass or plant fibre) is drawn to a round or other uniform section
or thickness through cutting dies. This dressed fibre is then placed in a copper or
other ductile metal drawn tube, which loosely fits it; the copper tube is then drawn
down through the slightly decreasing holes of a draw plate until the tube compresses
the fibre; this compression of the fibre is carried on as far as possible without
breaking it; the tube is then cut into suitable lengths, and the lengths bent into the
desired shape for the carbon conductors as arranged; after shaping they are packed
into cruicibles in a muffle or other closed furnace where no air can get at them and
raised gradually to a white heat until they are quite carbonised within the tubes they
are drawn in.
The effect of the carbonisation of the fibre under this high compression is to produce

page_text: carbon conductors of such perfect uniformity of section, density and surface that there
are so few defects in them that the shorter lengths required may be nearly wholly
utilised with but little waste, as these carbons are not subject to the same amount of
irregularities and faults inherent in the long thin filaments made without compression
during carbonisation. Thus our improved carbons do not require filling up or re-
pairing by depositing and flashing which is absolutely necessary in the making of the
long thin filaments without compression.
The fibres are extracted from the copper tube after carbonisation by dissolving the
copper off them in a suitable acid, after which they are washed and dried and cut into
lengths ascertained by measuring their electric resistance, ranging from a quarter
of an inch to three or four inches according to the size and luminosity of light
desired.
After being thus prepared and carbonised, the carbon conductors are mounted on
platinum electrodes and tested in a partial vacuum (or in an inert gaseous atmosphere
in which the gas does not combine with them); they are afterwards sealed into bulbs
of glass which are exhausted by air and Sprengle pumps in the usual manner. When
the lamps are being exhausted vapours of chlorine are admitted in some cases to
combine with and remove any hydrogen remaining in the carbon conductors.
Our new or improved arrangement of the wires or electrodes within the glass bulbs,
for cross-connecting them or short-circuiting them in the event of the failure of an
incandescent lamp or its carbon conductor, consists in forming an easy working joint
on one or both of the wires or electrodes preferably only one wire is so jointed.
The lower part of the wire or electrode is fixed and on the end of it is jointed an L
or equivalent laterally shaped switch wire oscillating on this joint at the angle forined
by the perpendicular and horizontal branches of the shaped piece. One end of the
carbon conductor is rigidly jointed to the top of the perpendicular branch, and the
horizontal branch hangs over a lateral projection on the other electrode. So long as
the carbon is whole and sound the L shaped switch piece is fixed; but if the carbon
breaks the shaped piece falls and the horizontal branch makes contact with the
projecting piece on the opposite wire, thus short-circuiting or cross-connecting the
two wires and permitting the electric current to pass to the other lamps in series or
parallel arc.

page_text: COMPLETE SPECIFICATION.
Improvements in and Connected with Incandescent Electric Lamps.
We, RANKIN KENNEDY, Electrical Engineer, and ROBERT DICK, Manufacturer,
both of the Electric Lamp Works, 115 Woodside Road Glasgow, Lanarkshire, do
hereby declare the nature of our said invention, and in what manner the same is to
be performed to be particularly described and ascertained in and by the following
statement in writing, reference being had to the accompanying sheet of Drawings,
and to the letters and Figures marked thereon, that is to say :-
Our said invention has for its object the improvement of the carbon conductors and
fittings employed in a vacuum for the production of lights by electricity, whereby the
said lights may be used in what is known as the series order of distribution, thus
allowing of the use of comparatively small copper conductors for the supply of large
numbers of lights at a distance and from one common centre; and whereby we also
obtain an improved light both as to quantity and quality of luminosity and of any
desired size.
These electric lights or lamps made according to our improvements may also be
employed in what is known as parallel order (that is where the lamps are grouped in
parallel arc between the leading main conductor and the return main, so that each
lamp is independent of the others if the electro-motive force of the supply is constant),
when only a few are required, say up to 100 lights from one centre, in which they
also show improved light by giving more candle power per unit of electric energy
expended.
By the improvements and to obtain the advantages of our invention the carbon
conductor is made of low resistance, and high specific resistance, from its shortness
in length and increased uniform section and perfectly homogeneous nature and con-
sequent little elasticity; but although the resistance of the carbon as a whole is low,
yet per unit of its length the resistance is high, this condition is of great importance;
for example, if we take two pieces of carbon of the same size in length and thickness,
and measure their resistance respectively, that carbon which has the highest resistance
would be the best for the purpose of this invention, it having the greatest specific
resistance. In no case, however, is it necessary or advantageous by our improve-
ments to use carbons of more than 100 ohms of current resistance; all in contradis-
tinction to the filament carbons used in electric lamps, which require a small cross
section and great length of filament, and requiring a high resistance to give the light
and elasticity to prevent breakage. We have discovered that carbon conductors can
be made of very great resistance per inch, (taking one inch as a unit length of carbon
conductor) without at the same time having a small cross section. In the carbon
filaments employed in the well-known lamps of Edison the resistance per inch is
comparatively low, and to obtain the necessary high resistance for such a lamp the

page_text: filament is made of small cross section, and of a length from 5 to 10 inches long
requiring great elasticity to give endurance and length of life to the fine filament.
According to our invention we adopt carbons of from 50 to 150 ohms of specific
resistance per inch and make them of a proportionally short, thick, rigid construction
and character, giving them each a low resistance as a whole, although of high specific
resistance. And we have discovered that this carbon conductor is very suitable for
incandescent electric lamps to be used in great numbers connected in series order to a
central supply, and that these carbons are much more economical and give a higher
efficiency of light than those known as carbon filaments of small cross section and
long length, having a low specific resistance with a very high current resistance.
Hitherto in making carbon conductors for incandescent lamps the practice and aim
has been to make the specific resistance low, and use long thin elastic or flexible
carbon filaments, requiring a process of depositing carbon on them, known as
Sawyer's process, in their manufacture, to render these long thin carbon filaments
uniform in resistance; this depositing of graphitic carbon necessarily lowers the
specific resistance of the filaments. Whereas by our improvements we make short
rigid carbon conductors of high specific resistance and of a sufficiently uniform
resistance, so that the after process of depositing carbon on them is not absolutely
necessary. This we have found to be a great advantage, as the said deposited carbon,
being of a different kind or graphite character from the filament carbon to which it is
applied, (which is of the charcoal form of carbon) lessens or destroys the homogeneous
character or nature of the filament or carbon conductor which is a source of great evil
in the lamp.
To overcome the difficulty hitherto experienced in making electric lamps of the
incandescent type whether fitted with filaments or other carbon conductors, connected
in series order to the supply, arising from the fact that if any one or more lamps in
the series should fail through the rupture or breaking of the carbon conductor, the
whole series would be extinguished. We construct any of these incandescent lamps
in such a manner as shown in the Drawings, that the failure of the carbon conductor
automatically cross connects the electrodes or wires of the carbon inside the lamp or
glass bulb, and thus the circuit being maintained the current goes on uninterupted
and the faulty lamp is switched off or cut out of the series so as not to stop the
others.
Having thus generally described the nature of, or the principles upon which our
improvements are applied to incandescent electric lamps and their action and advan-
tages, we shall now proceed to describe how we carry our invention into effect or
practice.
Cur first improvement in incandescent lamps, consists of a carbon conductor of
short length and low current resistance (under 100 ohms), but of a high specific
resistance and homogeneous without any outer deposit of graphitic carbon, and
attached to electrodes or wires so arranged within the containing glass bulb in
accordance with our second improvement that in the event of the carbon conductor
getting injured or failing to act, the electrodes or wires are automatically cross-
connected to prevent the interruption of the current to and through the remaining
lamps of the circuit.
To prepare a carbon conductor for incandescent electric lamps according to our
first improvement, a carbon-forming vegetable or textile material or fitre (preferably
Kitool," a natural grass or plant fibre) is drawn to a round or other uniform section
or thickness through cutting dies. This dressed fibre is then placed in a copper or
other ductile metal drawn tube, which loosely fits it; the copper tube is then drawn
down successively through the slightly decreasing holes of a draw plate until the tube
compresses the fibre within it; this compressing of the fibre is carried on as far as
possible without breaking it by the excessive drawing of the copper tube. The tube
is then cut into suitable lengths, and the lengths bent into the desired shape of the
carbon conductors as required; after thus shaping these they are packed into
|cruicibles in a muffle or other closed furnace where no air can get at theui and raised

page_text: gradually to a white heat until the conductors are quite carbonised within the tubes
they are so drawn and shaped in.
The effect of the carbonisation of the fibre under this high compression within the
tube is to produce carbon conductors of such perfect uniformity of section, density
and surface that there are so few defects in them that the shorter lengths required
may be nearly wholly utilised with but little waste, as these carbons are not subject
to the same amount of irregularities and faults inherent in the ordinary long thin
filaments made with little or no compression during carbonisation. Thus our improved
carbons do not require filling up or repairing by depositing and flashing which is
absolutely necessary in the making of the said ordinary long thin filaments.
The fibres are extracted from the copper tube after carbonisation by dissolving the
copper off them in a suitable acid, after which they are washed and dried and cut
into lengths ascertained by measuring their electric resistance, ranging from a quarter
of an inch to three or four inches according to the size and luminosity of light
desired.
After being thus prepared and carbonised, the carbon conductors are mounted on
platinum electrodes in a usual manner and tested in a partial vacuun (or in an inert
gaseous atmosphere in which the gas does not combine with them); they are
afterwards sealed into bulbs of glass which are exhausted by air and Sprengle pumps
in the usual manner. When the lamps are being exhausted, in some cases vapours of
chlorine are admitted to combine with and remove any hydrogen remaining in the
carbon conductors.
The second improvement of our invention relating to the arrangement of the wires
or electrodes within the glass bulbs of any form of incandescent electric lamp whether
fitted with filament or rigid carbon conductor, for automatically cross-connecting
them or short-circuiting them, when placed in series working order in the circuit, in
the event of the failure of an incandescent lamp or its carbon conductor, consists in
forming an easy working joint lever on one or it might be both of the wires or
electrodes; so that it will fall and complete the circuit when either limb of the carbon
filament or conductor breaks.
And in order that this second part of our invention and the manner of performing
or carrying the same into effect or practice may be properly understood, we have
hereunto appended an explanatory Sheet of Drawings, in which the same reference
letters are used to indicate corresponding parts in all the figures where shown.
Figure 1 shows an Elevation of an incandescent or glow lamp A, suited for being
placed in series order, constructed in accordance with the improvements of our
invention with the electrodes a, a¹, and switch lever B, B₁, all ready for use.
And Figure 2 is an enlarged view of the electrodes separate from the glass
globe A, to show the construction of the switch lever B B', more clearly with our new or
improved short thick carbon conductors C, as broken and the switch lever B, B', as
fallen and completing the circuit through the electrodes a, a¹; and Figure 3 shows
our switch wire or lever B B' applied to an incandescent lamp fitted with an ordinary
carbon filament c, for working in series order.
Referring to these Drawings,-On the lower part of one of the fixed wires or
electrodes a an L-bellerank, or other equivalent switch lever or wire B, B', is jointed,
and oscillates on this joint at the angle formed by the perpendicular and horizontal
branches B, B1, respectively of the shaped wire. One end of the carbon filament
or conductor C is rigidly jointed to the end of the perpendicular branch B, which
is the lower end as shown in the Drawings, but would be the top when the lamp was
inverted, and the horizontal branch B', hangs over a lateral projection which is
preferably made in the form of a small loop on the other electrode a¹.
So long as
the carbon C, is whole and sound the shaped switch piece B, B', is fixed or
maintained in the position shown in Figure 1, so that it does not touch the lateral
projection or loop 6; but if the carbon C breaks, the L shaped piece falls and the
horizontal branch B¹ makes contact with the projecting piece 6 on the opposite wire a',
as shown in Figure 2, and thus short-circuits or cross-connects the two wires a, a³,

page_text: and permits the electric current to pass to the other lamps in series, or parallel arc,
although the switch is not really necessary for working with the lamps ranged in
parallel arc. And it will be seen that this switch connection B, B1, b, may be equally
applied to any form of the electrodoes, or filaments C, in incandescent or glow lamps
placed in series order.
Having thus described our said invention and the manner of performing or carrying
the same into effect or practice we have to state that we do not confine ourselves to
the precise details which we have herein described, and shown in the Drawings, that
is to say the length and thickness of the rigid carbon conductors C, may be very
considerably varied, and the form and construction of the switch lever B, B', b,
without departing from the nature of the Invention; but what we claim is :-
First. The manufacture or construction of carbon conductors of less than 100 Ohms
current resistance, and from 50 to 150 Ohms specific resistance per inch, and their use
in incandescent or glow electric lamps, substantially as herein described.
Second. In incandescent or glow electric lamps, the forming of a switch lever or
levers, on the electrodes within the globe for automatically short-circuiting or cross
connecting these on the failure of a lamp, substantially as and for the purposes and
advantages herein Described in reference to and shown in the accompanying
Drawings.