IMPROVEMENTS IN THE MANUFACTURE OF INCANDESCENT LAMPS AND IN APPARATUS THEREFOR "
Year: 1882

page_text: LETTERS PATENT to William Crookes F.R.S. of Boy Court Ludgate Hill in
the City of London for an Invention of "IMPROVEMENTS IN THE MANUFACTURE
OF INCANDESCENT LAMPS AND IN APPARATUS THEREFOR
"
PROVISIONAL SPECIFICATION left by the said William Crookes at the
Office of the Commissioners of Patents on the 6th September 1882.
WILLIAM CROOKES. F.R.S of Boy Court Ludgate Hill in the City of London.
"IMPROVEMENTS IN THE MANUFACTURE OF INCANDESCENT LAMPS AND IN APPARATUS
THEREFOR
33
This Invention has for its object improvements in the manufacture of incandescent
lamps and in apparatus therefor.
In the preparation of the carbon filaments I employ rectangular frames of copper,
nickel or other metal which will withstand the action of the chemicals employed.
I distend upon the frame the thread from which the filaments are to be made. I
then immerse the frame with the threads upon it in a bath of cuprammonia or such
other solvent as it may be intended to employ to impart to the thread a horn like
texture. The threads are dipped in acid and then washed with water whilst still
on the frame and then the frame is taken to pieces leaving the threads connected
with the two end bars. The threads are then laid around rods of glass supported
horizontally in a rack and so each portion of thread between the bars of the frame
is brought to the form which it is required to have when it becomes a finished
filament so arranged the threads are strained by a weight and while thus held they
are allowed to dry and harden.
They are then cut off from the bars and are arranged in the carbonizing box.
Flat plates of graphite are employed in the carbonizing process; such a plate
having been placed in the carbonizing box, a little powered [sic] charcoal is spread
upon it and on this the filaments are laid. A little more charcoal is sifted over the
filaments and another flat plate of graphite is placed upon them. This plate
receives another layer of filaments and so on until the box is full. The box is then
heated in the usual way. The graphite plates hold the filaments Hat during the
[Price 6d]

page_text: carbonizing process and keep them in proper form. After carbonizing the filaments
are immersed for some time in chloroform, chloride of carbon, benzol, or some
analogous liquid, to displace the occluded gas from the pores.
The ends of the filament are next inserted (with a little carbonaceous cement)
into small platinum tubes which they loosely fit and they are then ready for the
adjustment of the resistance. For this purpose the tubes carrying the filament are
placed upon a fork like instrument projecting upwards from a foot. The ends of
the fork are conducting wires and serve to apply when required a heating current
to the filament. The foot also serves as a stopper for a bottle like vessel which is
placed over it so as to enclose the filament.
A piece of wide india rubber tubing is stretched over the lower part of the
stopper to act as a washer between the stopper and the neck.
The stopper and neck are kept smeared with burnt india-rubber and so an air
tight joint is very readily made. As a further precaution I sometimes provide a
mercury trap around the neck. If it be desired to treat several filaments simul-
taneously passages are provided connecting the vessels in which the several filaments
are contained. The vessel or vessels are then attached to and exhausted by a
mercurial air pump and vapour of chloride of carbon or other suitable carbonaceous
vapour is admitted. The vapour is introduced by means of a novel mercurial
valve; there is a tube connected at its upper end with a wide cylindrical tube
about 36 inches long, the lower end of this latter tube is connected by means of an
india-rubber tube with a reservoir which can be elevated or lowered at will hence
when the apparatus is exhausted and the reservoir raised a column of mercury
stands in the tube. Below the level of the top of the mercurial column as it
normally stands another tube enters the wide one, and rising over 30 inches it is
connected with the vessel in which the carbonaceous liquid is contained.
The
mercury in the column prevents the vapour of the liquid from entering the vacuous
enclosure, for it covers the entrance, but when it is desired to admit vapour to the
filament for the purpose of depositing carbon upon it the reservoir is lowered
and the column of mercury falls by a like amount and the vapour bubbles up into
the vacuum.
On the india rubber tube between the reservoir and the wide tube is a pinch cock
which closes the tube and prevents the mercury falling when the apparatus is not
exhausted.
The heating of the filament is regulated by varying the resistance in circuit and
that this may be done readily a contact making metal ball is employed. It rolls
along two horizontal rails of brass. One of these rails is continuous the other is
divided into lengths and resistances consisting of spirals of German silver wire are
inserted between length and length. The ball completes the circuit from the con-
tinuous rail to one or other of the lengths of the divided rail. Thus the position of
the ball on the rails regulates the amount of resistance in circuit and the degree to
which the filament is heated.
Filament or filaments during this operation form one of the sides of a Wheatstone
Bridge arrangement and a galvanometer or indicator shews when the proper
resistance is attained.
The filament is then ready to go into the lamp. During the final exhaustion of
the lamp the filament is heated and resistances arranged as already described
regulate the heating current.
To complete the stem or foot of the lamp it is adjusted in a temporary holder
with the stem upwards and this enters a cylindrical socket-like mould open at the
top. Two pieces of thin sheet brass are placed opposite to each other in this mould,
they are bent to the curvature of the mould they line its sides and each extends
over about a third of the circumference. The straight sides are bent inwards about
2 millimetres and serrated. The conducting wires of the lamp are then soldered
to these pieces, one to each, and then the mould is filled with plaster of Paris.
The lamp when required for use is placed with its stem within a socket having
springs within it on opposite sides. These springs terminate the conductors by

page_text: which the current is brought to the lamp and they make contact with the brass
plates on either side of the lamp foot.
Sometimes I make lamps containing two or more filaments. After plating up
as already described the filaments having been mounted in the lamp are connected
in series and during the final exhaustion a little carbonaceous vapour is admitted
into the lamp whilst the filaments are strongly ignited by the current. This brings
the filaments accurately to the same resistances. The lamp is then sealed off in the.
usual way and afterwards the connections are changed and the filaments are coupled'
in parallel arc.
In lamps made in this way the filaments when the lamps are in use become
equally heated and give a similar light which otherwise is difficult to obtain.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said William Crookes in the Great Seal Patent Office on the 6th March
1883.
WILLIAM CROOKES F.R.S. of Boy Court Ludgate Hill in the City of London
"IMPROVEMENTS IN THE MANUFACTURE OF INCANDESCENT LAMPS AND IN APPARATUS
THEREFOR
"
This Invention has for its object improvements in the manufacture of incandescent
lamps and in apparatus therefor.
In the preparation of the carbon filaments I employ rectangular frames of copper,
nickel or other metal which will withstand the action of the chemicals employed.
I distend upon the frame the thread from which the filaments are to be made. I
then immerse the frame with the threads upon it in a bath of cuprammonia or such
other solvent as it may be intended to employ to impart to the thread a horn-like
texture. The threads are dried dipped in acid and then washed with water whilst
still on the frame and then the frame is taken to pieces leaving the threads
connected with the two end bars. The threads are then laid around rods of glass
supported horizontally in a rack and so each portion of thread between the bars of
the frame is brought to the form which it is required to have when it becomes a
finished filament. So arranged the threads are strained by a weight and while
thus held they are allowed to dry and harden.
Figure 1 is a front view of the metal frame. a a are the top and bottom bars
and b b are the side bars secured to the bars a a by pins c c. The top and bottomn
bars a a are notched as shown to receive the thread or cord. d is a double hook to
suspend the frame when immersed in the liquid of the baths.
Figure 2 is a perspective view of the drying frame. Figure 3 is a vertical section
of the same. e is the base board and ff are standards fixed upon it. Each standard
is perforated with three holes to receive the glass rods g 9 g. These rods are easily
removed to facilitate placing the threads or cords in the frame as the drawing
shows. The threads still remain on the bars a a and these are brought together
beneath the glass rods g. h h are hooks attached to blocks which are inserted
between the bars a and studs upon the blocks enter the holes in the ends of the
bars aa which previously received the pins c c. i is a weight suspended from
the hooks and serving to strain the threads or cords.
The dried threads are then cut off from the bars and are arranged in the
carbonizing box. Flat plates of graphite are employed in the carbonizing process,
such a plate having been placed in the carbonizing box a little powdered charcoal
is spread upon it and on this the filaments are laid. A little more charcoal is sifted
over the filaments and another flat plate of graphite is placed upon them. This
plate receives another layer of filaments and so on until the box is full. The box
is then heated in the usual way. The graphite plates hold the filaments flat during
the carbonizing process and keep them in proper form
After carbonizing the filaments are immersed and kept until required for use in
chloroform, chloride of carbon, benzol, or some analogous liquid; this displaces the
occluded gas from the pores. I usually employ benzol.
The ends of the filament are next inserted (with a little carbonaceous cement)
into small nickel or platinum tubes which they loosely fit and they are then ready
for the adjustment of the resistance. For this purpose the tubes carrying the
filament are placed upon a fork like instrument projecting upwards from a foot.
The ends of the fork are conducting wires and serve to apply when required a
heating current to the filament. The foot also serves as a stopper for a bottle like

page_text: vessel which is placed over it so as to enclose the filament. A piece of wide india
rubber tubing is stretched over the lower part of the stopper to act as a washer
between the stopper and the neck. The stopper and neck are kept smeared with
burnt india rubber and so an air tight joint is very readily made. As a further
precaution I sometimes provide a mercury trap around the neck. If it be desired
to treat several filaments simultaneously passages are provided connecting the
vessels in which the several filaments are contained. The vessel or vessels are then
attached to and exhausted by a mercurial air pump and vapour of chloride of carbon
or other suitable carbonaceous vapour is admitted. The vapour is introduced by
means of a novel mercurial valve; there is a tube connected at its upper end with
a wide cylindrical tube about 36 inches long, the lower end of this latter tube is
connected by means of an india rubber tube with a reservoir which can be elevated
or lowered at will, hence when the apparatus is exhausted and the reservoir raised
a column of mercury stands in the tube. Below the level of the top of the
mercurial column as it normally stands another tube enters the wide one and
rising over 30 inches it is connected with the vessel in which the carbonaceous
liquid is contained. The mercury in the column prevents the vapour of the liquid
from entering the vacuous enclosure, for it covers the entrance, but when it is desired
to admit vapour to the filament for the purpose of depositing carbon upon it the
reservoir is lowered and the column of mercury falls by a like amount and the
vapour bubbles up into the vacuum.
On the india rubber tube between the reservoir and the wide tube is a pinchcock
which closes the tube and prevents the mercury falling when the apparatus is not
exhausted.
The heating of the filament is regulated by varying the resistance in circuit and
that this may be done readily a contact making metal ball is employed. It rolls
along two horizontal rails of brass. One of these rails is continuous the other is
divided into lengths and resistances consisting of spirals of German silver wire are
inserted between length and length. The ball completes the circuit from the
continuous rail to one or other of the lengths of the divided rail. Thus the position
of the ball on the rails regulates the amount of resistance in circuit and the degree
to which the filament is heated.
The filament or filaments during this operation form one of the sides of a
Wheatstone Bridge arrangement and a galvanometer or indicator shows when the
proper resistance is attained.
The filament is then ready to go into the lamp. During the final exhaustion of
the lamp the filament is heated and resistances arranged as already described
regulate the heating current.
Figure 4 shows a vertical section of the apparatus which I employ in adjusting
the resistance of the filaments.
a is a base board or table, b is a foot attached to the board and adapted to
receive upon it the glass bottle like vessel c. The foot is of wood, it is rendered
impermeable by means of any suitable cement and a vulcanized india rubber
ring b is placed in a groove around it. The ring is smeared with burnt india
rubber and when the bottle c is put in place as the drawing shows a perfectly air
tight joint is obtained. Nevertheless I may provide a rim d around the foot into
which for extra security mercury may be poured. There are four glass tubes
inserted air tight through the foot, into two of these conducting wires e e are
sealed and these wires are led to binding screws ff by which the wires e e may be
coupled in the electric circuit. The wires terminate in points upon which the
little tubes previously attached to the ends of the filament are placed. g is a pipe
leading to the air pump and a pipe by which carbonaceous vapour can when
desired be admitted. Two, three, or more of these instruments are conveniently
mounted on the same table and the connections made so as to pass the current
through the filaments in series so far as the electro-motive force employed will
permit. The pipes g and h then have branches passing to each enclosure.-This

page_text: inverted bottle and cork like arrangement of the apparatus is very convenient in
practice and the joints give no trouble.
Figure 5 shows the apparatus used to admit carbonaceous vapour to the apparatus
represented in Figure 4.
a is a tube connected at its upper end with a wide cylindrical tube b and at its
lower end with the flexible pipe c leading to the mercury bottle or reservoir d. A
pinch cock not shown in the drawing is provided upon the pipe c. e is a glass tube
attached to b at the side and near the lower part it rises over 30 inches so that
when air is admitted to b a mercury column will stand in the tube e.
f is a vessel communicating with e in it chloride of carbon or other carbonaceous
liquid which I employ is contained. g is a tube passing from the top of b to the
apparatus shown at Figure 4 or to other apparatus where the carbonaceous vapour
is required for use.
When this apparatus is exhausted the mercury falls in the tube e until in con-
sequence of the vapour tension it stands lower in e than in b. Then if the mercury
bottle & be gradually lowered the vapour from the vessel passes up through the
mercury in b and so into the apparatus Figure 4. This takes place without the
lower end of the tube e being uncovered and air cannot enter the vessel f.
When chloride of carbon is employed it is necessary to interpose between the
plating up apparatus Figure 4 and the mercury pump a tube or vessel containing
a substance such as lime or soda-lime capable of absorbing the chlorine which is
liberated. If this is not done the chlorine fouls the mercury and interferes with
the proper working of the pump.
Figure 6 is an elevation of the apparatus which I employ to regulate the current
when heating the filament either to deposit carbon upon it or during the exhaustion
prior to sealing up the lamp.
a is a continuous rail of brass attached to the front edge of a narrow wooden
board b. c is another rail of brass attached to the back of the board b and
standing up from it somewhat higher than the rail a. The rail c is in separate
pieces numbered 1, 2 &c which have no direct electrical communication, d is a
similar divided rail fixed at a distance above the rail c. There are metal studs
fixed in both the rails c and d and wires e and fare distended between them, so
that through these wires electrical communication is established from end to end
of the divided rails. The wires e e are spirals of German silver or iron wire is
suitable if the spirals be made longer. ff are lengths of copper wire offering no
appreciable resistance to the current or these may if desired be replaced by other
spirals. This apparatus is placed in circuit with the filament to be heated, it is
connected at the points marked + and. the one on the rail a and the other on the
divided rail c. g is a brass ball which placed as shown closes the circuit and by
rolling the ball along the rails a and c the resistance the current has to overcome
is varied and the heating of the filament adjusted as desired.
-
To complete the stem or foot of the lamp it is adjusted in a temporary holder
with the stem upwards and this enters a cylindrical socket like mould open at the
top. Two pieces of thin sheet brass are placed opposite to each other in this
mould, they are bent to the curvature of the mould, they line its sides and each
extends over about a third of the circumstance. The straight sides are bent
inwards about 2 millimetres and serrated. The conducting wires of the lamp are
then soldered to these pieces, one to each and then the mould is filled with plaster
of paris. The mould opens to release the lamp
The lamp when required for use is placed with its stem within a socket having
springs within it on opposite sides. These springs terminate the conductors by
which the current is brought to the lamp and they make contact with the brass
plates on either side of the lamp foot.
Sometimes I make lamps containing two or more filaments after plating up as
already described. The filaments having been mounted in the lamp are connected

page_text: in series and during the final exhaustion a little carbonaceous vapour is admitted
into the lamp whilst the filaments are strongly ignited by the current.
Figure 7 shows two filaments mounted in a lamp. The foot contains three
platinum wires A, B, C. One wire B receives an end of each filament and the
other wires A and C receive the other ends. They are then connected up in series
by making the two outer platinum wires A and C the terminals. They are then
plated up as already described. This brings the filaments accurately to the same
resistances. The lamp is then sealed off in the usual way and afterwards the
connections are changed and the filaments are coupled in parallel arc.
The wires A and C are twisted together and form one terminal whilst the wire B
forms the other terminal.
Three or more filaments may be mounted and enclosed in the lamp and plated up
in an analogous way to this by obvious modifications.
In lamps made in this way the filaments when the lamps are in use become
equally heated and give a similar light which otherwise is difficult to obtain.
What I claim is :-
First. Means and apparatus for the preparation of the filaments for incandescent
lamps substantially as described in respect to Figures 1, 2 and 3 of the annexed
drawings.
Second. The apparatus to be used in depositing carbon upon the filament
substantially as described in respect to Figure 4.
Third. The apparatus for admitting vapour or gas to a vacuous enclosure
substantially as described in respect to Figure 5.
Fourth. The apparatus for regulating the current by which the filament is
heated-such apparatus consisting of the continuous rail a, the divided rail the
resistance spirals c and the metal ball & substantially as described in respect to
Figure 6.
Fifth. The method of forming the foot of an incandescent lamp, by attaching the
conducting wires to two side plates which are inserted into a mould together with
the stem of the lamp, and plaster or cement filled into the mould to connect the
parts solidly together.
Sixth. The process in the construction of lamps containing two or more
filaments of heating the filaments in presence of carbonaceous vapour by an electric
current passed through the filaments in series, then sealing off the lamp and altering
the connections placing the filaments in parallel arc substantially as described in
respect to Figure 7.
In witness whereof I the said William Crookes have hereunto set my
hand and seal this fifth day of March in the year of our Lord One thousand
eight hundred and eighty three.
WILLIAM CROOKES. (L.S.)