IMPROVEMENTS IN THE CONSTRUCTION INCANDESCENT ELECTRIC AND MANUFACTURE OF APPARATUS USED THEREIN."LAMPS AND
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 CONSTRUCTION
INCANDESCENT ELECTRIC
AND
MANUFACTURE OF
APPARATUS USED THEREIN."
LAMPS, AND IN THE
PROVISIONAL SPECIFICATION left by the said William Crookes at the
Office of the Commissioners of Patents on the 6th March 1882.
WILLIAM CROOKES F.R.S. of Boy Court Ludgate Hill in the City of London
"IMPROVEMENTS IN THE CONSTRUCTION AND MANUFACTURE OF INCANDESCENT
ELECTRIC LAMPS AND IN THE APPARATUS USED THEREIN."
This invention is for improvements in various matters connected with the
construction of incandescent lamps.
For forming the carbon filaments I use instead of the vegetable matter referred
to in my former Patents animal fibres such as silk, hair, wool, silk-worm-gut or
animal matters such as horn or gelatine and parchment. I treat these with
cuprammonia and carbonize the same way as with vegetable fibre but more
slowly to prevent tumefaction. Some of the above substances are capable of being
completely dissolved in cuprammonia and can then be deposited in a filament in the
same way as cotton wool.
I find that these substances can also be used for the purpose of producing the
carbon filaments without treating them with cuprammonia by taking care that the
heat is applied with extreme slowness so as to thoroughly dessicate the substance
before any process of carbonization commences. Or the silk thread or other
substance composed of animal fibres may be passed through a saturated solution of
cotton in cuprammonia and this can be similarly carbonized to make the filaments.
Instead of the solution of cotton in cuprammonia for this purpose a solution of
any of the above substances in cuprammonia can be used. In practice I draw
them through a solution by means of clockwork the length of time during which
the substance remains in the solution being regulated so as to thoroughly change it
with the solution.
Another method of obtaining a suitable substance for carbonization into the
filaments of electric lamps is by adding an acid to a solution of cellulose silk or
any of the above substances in cuprammonia and then washing. By this means
a plastic substance is produced which may be formed into any required shape
•

page_text: either alone or with other carbonaceous substances such as starch gluten &c. to
give to it the required consistency and subsequently carbonized.
Instead of using cuprammonia for treating cellulose in the manner spoken of in
my former Patent a strong solution of chloride of zinc or of caustic alkali or other
solvent may be used.
One of the great difficulties in making incandescent lamps is the construction
of the junction between the carbon filament and the terminals of the conducting
wires by which the current is conveyed to it. I find it is disadvantageous that the
filament should be rigidly held or pressed upon directly by the metal forming the
conducting wires. Accordingly I form a receptacle for the end of the filament
either by terminating the conducting wires by a small hollow cone of platinum or a
platinum wire flattened out and bent round upon itself or a platinum wire twisted
into a cup shaped receptacle or preferably a platinum wire bent on itself three or more
times and I cement the end of the filament into this receptacle by means of a
cement composed of a mixture of ground graphite and water to which has the proper
consistency given to it by the admixture of a little sugar or similar carbonaceous
substance. I use preferably the hard graphitoidal form of carbon produced by the
decomposition of a hydrocarbon gas or vapour by intense heat.
I also sometimes
put a glass cap over the terminal to form the receptacle for the end of the filament
which is cemented into it in the way above mentioned.
These
The ends of the filament may be electro plated or not as is found convenient.
If they are electro plated they may be joined on to the terminals by little copper
tubes being pinched upon them either with or without graphite cement.
tubes may be either single or double. These tubes may also be made of platinum
iron or any suitable metal instead of copper or the platinum wire may be split at
the end and the electro plated end of the filament wedged into it.
For the above cement I prefer powdered graphite and water with a little sugar
as above described but a serviceable cement of the same kind may be made by
platinum powder and water or platinum yellow and water.
In depositing carbon upon filaments to strengthen them I find that the vapour
of either of the chlorides of carbon yields good results.
In exhausting the lamps and standardizing the resistance of the filaments I find
it convenient to have a vessel forming part of the pump in which there is a mixture
or compound which is fixed at ordinary temperatures but gives off a vapour of
hydrocarbon when heated. As type of three different classes of substances which
are suitable for this purpose I may mention india rubber or a mixture of benizoate
of lime or baryta with quick lime or of acetate of soda and soda lime or charcoal
Buturated with benzole. When the vacuum is good I evolve vapour from one of
the above mixtures by heating the vessel in which it is contained and when the
gauge has been lowered in this way for a few millimetres I pass the current
through the filament until the resistance is equal to that adopted as the standard
and then by withdrawing the heat I stop the evolution of vapour and complete the
exhaustion heating the filaments and lamps during the process to drive off the
occluded vapour as well as the vapour which adheres to or is condensed upon
the surface of the glass or that of other portions of the lamp. I find that the
resistances of several lamps may be equalized at the same time in one operation by
The lowest
arranging them in a series and passing a current through them.
resistance gets hottest and gets the heaviest deposit upon it and so becomes level
with the others and thus the resistance of all can be brought to the required
point. In regulating the resistance of lamps I arrange an automatic cut off which
I work by a bridge galvanometer the resistances being as adjusted that when the
resistance of the lamp attains the standard a relay is brought into action and cuts
off the main current or diverts it to another lamp or set of lamps.
I sometimes leave a little mercury vapour in the lamps in order to prevent
any oxygen remaining therein as it forms a non-volatilizeable compound therewith.

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 September 1882.
WILLIAM CROOKES F.R.S. of Boy Court Ludgate Hill in the City of London
" IMPROVEMENTS IN THE CONSTRUCTION AND MANUFACTURE OF INCANDESCENT
ELECTRIC LAMPS AND IN THE APPARATUS USED THEREIN
"
This Invention is for improvements in various matters connected with the
construction of incandescent lamps.
For forming the carbon filaments I use instead of the vegetable matter referred
to in my former patents animal fibres such as silk hair wool silkworm gut or
animal matters such as horn or gelatine and parchment. I treat these with
cuprammonia and carbonize the same way as with vegetable fibre but more slowly.
to prevent tumefaction.
The following method for which I have applied for Letters Patent will be found
very suitable, I take a rectangular frame of copper nickel, or other suitable
material not acted on by the cuprammonia, so constructed that the sides and enda
can readily be separated and in this frame I stretch a number of the threads which
I desire to employ, parallel the one to the other.
The dimensions of the frame are
such that it will conveniently hold as many threads as are to be operated on at
one time and that each thread crossing it may be amply long enough to form a
filament for the lamp. Threads of white floss silk put together with little twist to
the substance desired form a very suitable material.
The frame with the threads thus stretched upon it is placed in a dipping vessel
containing cuprammonia. The cuprammonia may be prepared in the usual way
by the action of strong ammonia upon copper turnings or leaf. I use a solution
containing from one and a half to two per cent of copper. After about from 4 to
ten minutes in the solution I withdraw the frame with the threads upon it, and
having washed well in dilute nitric or sulphuric acid and then in water, I take the
frame to pieces, the threads remaining upon the end bars of the frame.
To bring the threads to the forms which I desire for the carbon filaments of my
lamps, I lap them around glass rods suitably held I use five parallel horizontal
glass rods, a central rod and four other others equidistant from it, two above and
two below. The thread may be traced from either bar of the frame up between the
two lower glass rods then outwards over the upper rod and descending beneath
the centre rod. The form thus given to the threads is U like in the middle with
a descending limb on either side. These limbs being the parts immediately
attached to the side copper bars of the frame.-A weight is attached to the side
bars to keep the threads distended around the glass rods whilst they dry. The
weight should be as heavy as the threads will carry without risk of breaking.
When the threads are thoroughly dry they will keep their form and they are then
cut off from the metal bars.
The threads are now ready to be carbonized, I arrange them for this purpose in
an iron or nickel box laying them in layers separated by finely powdered charcoal
sifted over them. When the box is full its cover is put on and secured and a gas
pipe is connected leading coal gas into the box. The box with its contents is then
heated to a white heat in a furnace a slow current of coal gas passing into the box,
and when cold it is opened and the carbon filaments are taken out.
Some of the above substances are capable of being completely dissolved in
cuprammonia aud can then be deposited in a filament in the same way as cotton
wool.
Thus for example silk may be dissolved in cuprammonia and the clear solution

page_text: on evaporating to dryness leaves a film or thin sheet from which threads may be
cut and these threads can be treated in the same way as the strained threads
already described after leaving the cuprammonia bath.
Or the silk thread or other substance composed of animal fibres may be passed
through a saturated solution of cotton in cuprammonia and this can be similarly
carbonized to make the filaments.
Instead of the solution of cotton in cuprammonia for this purpose a solution of
any of the above substances in cuprammonia can be used.
I place the threads upon a copper frame as before and dip them, the only
difference being that in place of cuprammonia in a state to dissolve cellulose, I now
employ cuprammonia which is already saturated with cellulose or organic matter.
The after processes are as already described.
Another method of obtaining a suitable substance for carbonization into the
filaments of electric lamps is by adding an acid to a solution of cellulose silk or
any of the above substances in cuprammonia and then washing. By this means a
plastic substance is produced which may be formed into any required shape either
alone or with other carbonaceous substances such as starch gluten &c. to give to it
the required consistency and subsequently carbonized.
When a bath of cuprammonia, by use as already described has become saturated
with cellulose or organic matter, I precipitate it by the addition of acid and I wash
the precipitate well upon a filter. I then knead the precipitate and so obtain a
dough like mass which on drying hardens. It may be cut into threads to form
filaments as already described, or moulded into sticks for the manufacture of
carbons for are lights or it may be used as a cement to thicken the ends of
filaments or to aid in forming the connection between filaments and their conducting
wires and holders.
Instead of using cuprammonia for treating cellulose in the manner spoken of in
my former Patent a strong solution of chloride of zinc or of caustic alkali may be
used and the same is the case in respect to silk and animal fibre.
One of the great difficulties in making incandescent lamps is the construction of
the junction between the carbon filament and the terminals of the conducting
wires by which the current is conveyed to it. I find it is disadvantageous that
the filament should be rigidly held or pressed upon directly by the metal forming
the conducting wires. Accordingly I form a receptacle for the end of the filament
either by terminating the conducting wires by a small hollow cone of platinum or
a platinum wire flattened out and bent round upon itself or a platinum wire
twisted into a cup shaped receptacle or preferably a platinum wire bent on itself
three or more times and I cement the end of the filament into this receptacle by
means of a cement composed of a mixture of ground graphite and water which has
the proper consistency given to it by the admixture of a little sugar or similar
carbonaceous substance.
I use preferably the hard graphitoidal form of carbon produced by the decom-
position of a hydrocarbon gas or vapour by intense heat.
In some cases I form the cup like receptacle of platinum foil and insert the
platinum wire conductor through the bottom of the cup and secure it by riveting.
The dimensions of the cup may be 3 millimetres in depth and 2 millimetres in
diameter, this is for a filament of which the thickness at the end is about four
tenths of a millimetre so that the filament drops quite freely into the cup. The
cement which I employ I make from the carbon deposit which accumulates upon
the sides of the box in which the filaments are carbonized and which results from
the decomposition under the high heat of the coal gas which as already described
is supplied to the box in order to exclude air therefrom. I take this graphitoidal
carbon and grind it as pigments are ground, very fine and I mix it with very
dilute syrup to a state which admits of its being laid on freely with an artist's
brush. I apply the cement with the brush so as well to fill the cup like
receptacle. The filament is then ready for the further treatment by which it is
prepared for use,

page_text: This graphitoidal carbon makes a better electrical connection than cements which
contain carbon in other forms,
The graphitoidal carbon is a good conductor and inalterable.
Or a very simple and good method for forming the connection between the
conducting wire and the filament is to bend the wire upon itself to and fro so as
to form three vertical fingers, parallel and equidistant and each about 2 or 3
millimetres long. The end of the carbon filament is introduced between these
fingers and by pressing very lightly upon it they retain it in place. I then apply
the cement with a brush both over the fingers and the end of the filament. Thus
I produce a very good electrical connection whilst the filament is so lightly held
that it is not exposed to strains liable to produce fracture. I also sometimes put a
glass cap over the terminal to form the receptacle for the end of the filament which
is cemented into it in the way above mentioned.
When I employ a glass cup the conducting wire is sealed into the bottom of the
cup, its end projecting up within the cup. The dimensions of the cup may be a
little in excess of those already specified so that the end of the filament may enter
the cup freely by the side of the conducting wire. The cup is then filled with the
cement in the manner described.
The ends of the filament may be electro plated or not as is found convenient.
If they are electro plated they may be joined on to the terminals by little copper
tubes being pinched upon them either with or without graphite cement. These
tubes may be either single or double. These tubes may also be made of platinum
nickel iron or any suitable metal instead of copper or the platinum tube may be
split at the end and the electro plated end of the filament wedged into it.
For the cement I prefer powdered graphite and water with a little sugar as
above described but a serviceable cement of the same kind may be made by
platinum powder and water or platinum yellow and water or a mixture of either
of these with the graphite cement.
†
I prefer the following method; I use platinum tubes of the following
dimensions 0.8 millimetre outside diameter. 5 millimetre long drawn down from
foil 0.3 millimetre thick and 3.7 millimetre wide having the internal bore just
large enough to allow the end of the filament to slip freely into it. These can be
attached to the platinum wire conductors of the lamp by slipping the tubes over
the wires till the latter reach about half way up the tubes. A nip with a pair of
pincers will then make a firm and electrically sound joint.
The open ends of the tubes are then filled with thin cement applied by a small
brush and then the bare ends of the filament are inserted.
Another very convenient method is to form an open jointed tube of thin sheet
copper nickel iron, platinum or other metal about one centimetre long and of a size
to embrace tightly the end of the filament. The filament is prepared by depositing
a coating of copper upon its end for a length of about 5 millimetres.
The conducting wire is inserted into the metal tube at one end and the filament
at the other so that they meet in the middle. The metal tube is then nipped in
tightly upon the conducting wire and the same pressure will tighten it upon the
end of the filament without injuring it.
The carbon cement may be applied with a brush to the joint or it may be
dispensed with.
Sometimes I make a double tube by bending a piece of thin sheet copper
to a figure of eight form. I then insert the conducting wire into one passage and
the end of the filament into the other. The connecting tube may also be made in
other ways.
In all these cases the ends of the filaments may be electro plated or not with
copper as may be found convenient If they are to bear compression or pinching
it will be safer to electro-plate them.
In depositing carbon upon filaments to strengthen them I find that the
vapour of either of the chlorides of carbon yields good results as also does

page_text: chloroform which is mentioned in the Specification of a former Patent granted
to me.
This operation may be performed in the manner described in the specifications
of my former Specifications Nos. 2612 and 3799 in the year 1881 the filaments
being heated electrically in a chamber from which the air is exhausted and into
which the vapour is given off.
Or a very convenient method is to heat the filaments electrically whilst
immersed in the liquid chloride of carbon or chloroform. Thus the use of an air
pump in this part of the process is rendered unnecessary.
The process is
continued until the resistance of the filament has been brought down to the amount
desired.
A great advantage derived from the use of chloride of carbon in this process is
that chlorine is evolved and this chlorine at the high temperature forms volatile
products with any impurity the carbon filament may contain and so the impurity
is eliminated.
The use of chloroform is advantageous for the same reason. Bromides of carbon
which closely resemble the chlorides operate in a similar manner and the Bromine
given off forms volatile products with the impurites of the carbon.
In exhausting the lamps and standardizing the resistance of the filaments I find
it convenient to have a vessel forming part of the pump in which there is a
mixture or compound which is fixed at ordinary temperatures but gives off a
vapour of hydrocarbon when heated. As type of three different classes of
substances which are suitable for this purpose I may mention india rubber or a
mixture of benzoate of lime or baryta with quick line or of acetate of soda and
soda lime or charcoal saturated with benzole. When the vacuum is good I evolve
vapour from one of the above mixtures by heating the vessel in which it is
contained and when the gauge has been lowered in this way for a few millimetres
I pass the current through the filament until the resistance is equal to that adopted
as the standard and then by withdrawing the heat I stop the evolution of vapour
and complete the exhaustion heating the filaments and lamps during the process to
drive off the occluded vapour as well as the vapour which adheres to or is
condensed upon the surface of the glass or that of other portions of the lamp.
By the use as a source of carbonaceous vapour in this operation of finally
adjusting the resistance of the filaments of a substance which at ordinary temperature
gives off no vapour the operation is brought under easy control and the required
vacuum is easily obtained.
Fine india rubber is a very suitable material to employ, a small piece of it is
placed in a glass vessel connected with the air pump.
When the vacuum is
obtained in the lamp or vessel containing the filament, the electric current is passed
through and the resistance is measured. Heat is then carefully and intermittently
applied to the vessel containing the india rubber.
Gradually the resistance of the filament decreases and when by measurement it
is found to be what is required the heat is withdrawn and the current is
taken off.
I find that the resistances of several lamps may be equalized at the same time
in one operation by arranging them in a series and passing a current through them.
The highest resistance gets hottest and gets the heaviest deposit upon it and so
becomes level with the others and thus the resistance of all can be brought to the
required point.
In regulating the resistance of lamps I arrange an automatic cut off which I
work by a bridge galvanometer the resistances being so adjusted that when the
resistance of the lamp attains the standard a relay is brought into action and cuts
off the main current or diverts it to another lamp or set of lamps.
A dynamo electric machine may conveniently be employed in this operation
A large number of filaments are arranged in series, as many as the machine can
operate upon and arrangements are made as already described for the production
of a deposit of carbon upon the filaments from a carbonaceous vapour. The

page_text: filaments form one side of a Wheatstone bridge and a large resistance such as
6000 Ohms another. The machine is connected between the two. The other sides
of the bridge may be a small resistance such as five Ohms and a variable resistance
which is adjusted according to the resistance to which the filaments are to be
finished. The other terminal of the machine is connected between these sides of
the bridge so that the machine current has two courses, one through the filaments
in series and the five Ohms, the other through the 6000 Ohms and the variable
resistance. In the cross connection of the bridge, is a galvanometer. So long as
the resistance of the filaments is greater than is required the needle of the galva-
nometer will be deflected, it ceases to be so when the required adjustment of the
resistance is effected. I cause the needle as it returns to fall against a stop and
complete a local circuit. The current in this circuit excites an electro-magnet and
this attracts its armature thereby separating parts through which the main current
flows. The arrangement may thus be made automatic or an attendant may open
the main circuit when the indicator shows that the operation is complete.
I sometimes leave a little mercury vapour in the lamps in order to prevent
any oxygen remaining therein as it forms a non-volatilizable compound
therewith.
Having thus described the nature of my said invention and the manner of
performing the same I would have it understood that I claim :-
First. The production of carbon filaments for incandescent lamps from animal
fibres such as silk, hair, wool, silk-worm gut, or animal matters such as horn or
gelatine and parchment by treating such materials with cuprammonia or other
solvent and then carbonizing them.
Second. The production of carbon filaments for incandescent lamps by the car-
bonization of cellulose or like matter precipitated from solution in cuprammonia
or other solvent.
Third. The method of forming the junction between the carbon filament and the
conducting wires by the use of a cement of graphitoidal carbon.
Fourth. The method of forming the junction between the carbon filament and
the conducting wires, by terminating the wire in a cup shaped receptacle, placing.
the end of the filament loosely in the cup and completing the connection with a
cement of graphitoidal carbon.
Fifth. The method of forming the junction between the carbon filament and the
conducting wires, consisting in bending the wire on itself so as to form a clip in
which the filament is held by a light pressure at three or more points around its
end and completing the connection with a carbonaceous or other conducting
cement.
Sixth. The method of forming the junction between the carbon filament and
the conducting wires, consisting in causing the conducting wire to terminate
within a cup of glass, into which also the end of the filament is loosely placed and
the connection completed by filling the cup with carbonaceous or other conducting
cement.
Seventh. The method of forming the junction between the carbon filament and
the conducting wires consisting in electro plating the extremities of the filament,
and then inserting them, with or without cement, into metal tubes or sockets in
which the conducting wires are terminated.
Eighth. The method of forming the junction between the carbon filament and
the conducting wires consisting in terminating the conducting wires of the lamp
in metal tubes or sockets nipped on to them or otherwise attached and inserting
the ends of the finally carbonised filament with cement into such tubes or
sockets.
Ninth. The process of improving and strengthening carbon filaments by
depositing carbon thereon from a chloride of carbon or it may be a bromide of
carbon.
Tenth. The method of finally adjusting the resistance of carbon filaments by
exhausting the lamps or vessels in which they are contained, then evolving

page_text: carbonaceous vapour to pass into contact with the filaments by the application of
heat to a body which is non-volatile at ordinary temperatures and withdrawing the
heat as the resistance desired is attained.
Eleventh. The method of equalizing the resistance of a number of carbon
filaments by heating them in contact with a carbonaceous vapour by a current of
electricity passing through the filaments in series.
Twelfth. The method of at one operation equalising and measuring the resistance
of carbon filaments, by arranging them in series and coupling them with resistances
in a Wheatstone bridge arrangement then applying an electric current by which
the filaments are raised to incandescence in contact with carbonaceous vapour and
continuing the current until it appears by the indicator of the arrangement that a
balance has been obtained.
In witness whereof I the said William Crookes have hereunto set my hand
and seal this second day of September in the year of our Lord One thousand
eight hundred and eighty two.