IMPROVEMENTS IN THE CON- STRUCTION OF ELECTRIC LAMPS AND APPARATUS FOR ELECTRIC LIGHTING
Year: 1881

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 CON-
STRUCTION OF ELECTRIC LAMPS AND APPARATUS FOR ELECTRIC LIGHTING."
PROVISIONAL SPECIFICATION left by the said William Crookes at the
Office of the Commissioners of Patents on tho 15th June 1881.
WILLIAM CROOKES, F.R.S., of Boy Court, Ludgate Hill, in the City of London.
"IMPROVEMENTS IN THE CONSTRUCTION OF ELECTRIC LAMPS AND APPARATUS FOR
ELECTRIC LIGHTING."
This Invention has for its object improvements in the construction of electric
lamps and apparatus for electric lighting.
My electric lamp is of the class in which a carbon filament is enclosed in a
vacuous glass vessel, and rendered incandescent by the passage of an electric
current.
In the construction of an electric lamp, I take paper, cotton, linen, or cellulose in
other convenient form, and having purified it by means of hydrofluoric acid, I treat
it with a solution of ammoniacal oxide of copper, which as is well known has a
solvent effect upon cellulose.
The material paper by preference having been so prepared is thereby rendered
more dense, and the carbon filament which it yields has also a firmer consistency.
The prepared paper is punched out to the form of a horse shoe or other suitable
form and then carbonized. I obtain a good electrical connection between the film
and the conductors by means of which the current is to be passed through it by
the electro deposit of copper or other metal upon both the film and the conductor
at the point of junction, or where the two come together.
I afterwards improve the state of the carbon film by igniting the film electrically
in a vacuous vessel, also containing a hydro carbon, of which the boiling point is
high and the vapour tension at ordinary temperatures very low. The effect is
similar to that obtained when the more volatilo hydro carbons are employed and
introduced in minute quantity into the oxhausted receiver; but my process is
Price &71

page_text: simpler and much more convenient. Electrical ignition also expels the trace of
copper originally contained in the carbon film, or it may have been previously
extracted by means of solvents.
The film is enclosed for use within a glass enclosure within which a high vacuum
is obtained. For the purpose of turning the current onto and from the lamp I
employ a plug similar in some respects to the plug of an ordinary cock, and I have
a series of contact springs which in one position of the plug all bear upon it; the
current is then full on to the lamp. The plug however is so formed that as it is
turned round it passes out of contact first with one spring and then with anothor
until it leaves all of them, and then the lamp circuit is broken.
So long as the plug remains in contact with one or more of the springs, although
it is out of contact with some of them, the circuit is not broken, but the current
has to pass through resistances which are interposed between the springs. Thus by
turning the plug the amount of electricity passing through the lamp can be varied
and the light adjusted as may be desired.

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 15th
December 1881.
WILLIAM CROOKES, F.R.S., of Boy Court, Ludgate Hill, in the City of London.
"IMPROVEMENTS IN THE CONSTRUCTION OF ELECTRIC LAMPS AND APPARATUS FOR
ELECTRIC LIGHTING."
This Invention has for its object improvements in the construction of electric
lamps and apparatus for electric lighting on the incandescent principle, viz., thoso
in which a carbon filament is enclosed in a vacuous glass vessel and rendered
incandescent by the passage of an electric current.
The chief difficulty in such lamps is to form a filament of homogenous carbon
which shall be capable of sustaining the intense temperature necessary for the
economical working of such lamps, and to join such a filament to the conducting
wires by which the electric current is brought to it.
In order to obtain such a filament, I take some convenient form of cellular tissue
or cellulose, such as paper, linen, or cotton thread, the pith of certain plants
or cotton wool, and having purified it if necessary from silica by the uso of hydro-
fluoric acid, according to my Patent, No. 1422, A.D. 1881, I treat it with a solution
or compound of oxide of copper in ammonia (called cuprammonia) which, as is well
known, has a solvent effect upon cellulose. In this way I wholly or partially
destroy the structure of the cellulose, and subsequently by permitting the ammonia
and water to evaporate and oxtracting the copper I obtain cellulose in a dense and
almost structureless form.
The material to be operated upon may conveniently be in the form of paper,
linen, cotton, thread, or other like forms, in which the cellulose has sufficient strength
and continuity. The cotton or thread may be twisted, crocheted, or plaited with
any convenient number of strands, so as to form a band with cylindrical or flat or
any other convenient section. The material is then passed through or dipped into
the cuprammonia liquid, and left there for a few moments until the cellulose is
acted upon to such an extent as wholly or partially to destroy its intimate structure,
but not sufficiently to produce disintergration of the substance or complete solution
of the substance in the liquid. Sometimes before bringing the thread or other form
of cellulose into contact with the cuprammonia I saturate it with strong ammonia,
which expels the air from its pores. It is not necessary that the whole of the
material should be rendered completely structureless, as it is often convenient for
the purpose of manufacturo to leave the core of the thread comparatively
unchanged. When the cuprammonia has acted sufficiently, the thread or other
form of cellulose is taken out of it, and the ammonia and water are allowed to
evaporato. Before allowing the ammonia to evaporato I sometimes give a
preliminary wash with alcohol, which removes some of the ammonia without
exercising any other solvent action.
To extract the copper that remains after the evaporation of the ammonia and
water, I use dilute nitric sulphuric or other suitable acid, and then wash the
substance thoroughly with water, and let it dry either stretched out or under
pressure between sheets of absorbent material such as blotting paper. The copper
may also but less conveniently be extracted after carbonization, either by the use
of nitric or other acids, or by being volatilized by the passage of a strong electric
current through the filament so as to raise it to a sufficiently high temperature in
a vacuum on a gas not capable of acting upon the carbon.
Where thread, cotton, or other like form of cellulose is used, I can either twist
or plait or crochet it before soaking it in the cuprammonia solution, or after.it has

page_text: been soaked in the cuprammonia solution and dried, or after it has been soaked
and dried, and the copper has been removed from it by acids, as above described.
Another very convenient process for making carbon filaments by this my
Invention, is to take a loose form of cellulose, such as cotton, wool, or Swedish
filtering paper, and to allow it to remain in the cuprammonia solution until it
is entirely dissolved, or nearly so; the liquid is then poured out into a very shallow
dish with an accurately levelled plane bottom; the ammonia and water are allowed
to ovaporate, leaving a film or skin of cupric cellulose covering the bottom of the
dish, the thickness of this film depending on the original depth of the fluid and
the per centage of the dissolved cellulose therein. This film or skin when it has
acquired a sufficient consistency by the evaporation of the ammonia and water is
treated with dilute nitric, sulphuric, or other acid to extract the copper, and is
then thoroughly washed with water and dried under pressure between sheets of
absorbent material, such as blotting paper, as above described.
In some instances I find it advantageous to take a cuprammonia solution of the
kind above described, which has already celluloso dissolved in it, and to allow
paper, thread, cotton, linen, or other convenient form of cellulose to soak in this
solution for some time until the pores are saturated and filled up with the solution
of the celluloso. This is then dried and purified from copper as before.
It is not necessary to extract the copper from the portions of the carbon filament
at and near the junctions of the filament with the conducting wires, as its presence
improves the conductivity of the filament and diminishes the heating there, which
is so destructive to incandescent lamps. The ends of the filaments may also
advantageously be improved and strengthened by the electro deposition of copper,
nickel, platinum, or other suitable metal thereon. Sometimes also I coat the
junctions between the filaments and the conducting wires with a thick syrupy
solution of cellulose in the cuprammonia solution above described, so as to form
after the aminonia has evaporated a good junction, which after carbonization shall
possess good conductivity.
If the carbon filaments are made out of sheets, whether of paper, linen, cotton,"
or wholly dissolved cellulose, I cut or punch out pieces of a convenient form from
the sheet before carbonization. Sometimes I find it convenient to cut or punch
out a thin strip from the sheet before it is quite dry and to twist it several times
so as to make a thread, or to bend the narrow strip into the shape of an elongated U,
or to fold it so as to form a right angle at each of two points near the centre, so
that the main part of it consists of two equal legs parallel to and at a short
distance from one another. Either shapes may be adopted, the folding being dono
when necessary before the material is fully dry, in which caso it readily adopts
and retains almost any desired shape.
The carbonization of the filament prepared by the above process should be
effected slowly; it may be done by any of the ordinary methods, preferably in a
gas muffle furnace. Air must be wholly excluded, and the filaments should be
placed under moderate pressure between blotting paper in such a way as to cause
the resulting carbon to retain the shape originally impressed on the filaments
before carbonising, allowance being made for shrinkago.
Thus enveloped I pack the filaments in a metal box with pounded charcoal, and
excludo air by admitting coal gas or other similar gas or vapour to the box
throughout the operation:
0
In case the filament after carbonization does not possess the right resistance or
is imperfect, I improve it by heating it electrically in a vacuous vessel which
contains a hydrocarbon compound of which the boiling point is high, and the
vapour tension at ordinary temperaturos very low. Naphthaline or zylol is a very
suitable material, so also is chloroform, as stated in my Provisional Specification,
No. 3799, in the present year. These matters although present in quantity emit
an attenuated vapour, which is slowly decomposed and deposits carbon on or in
the pores of the filament in a good conducting graphitoidal form. Carbon deposited
rapidly on the filament is a bad conductor and unsuitable. The effect when using

page_text: these hydrocarbon compounds is similar to that obtained when the more volatile
hydrocarbons are employed and introduced in minuto quantities into the exhausted
receiver, but my process is much more simple, certain, and convenient. The hydro-
carbon compound may be contained in a vessel in connection with the pump, so
that when sufficient carbon has been deposited upon the filament by the decom-
position of the hydro carbon compound, the process may be stopped by a tap
without interrupting any testing or other operations to which the filament is being
subjected in the receiver.
In order to make clear what I claim as my Invention I hereby declare that I
claim,
First. The preparation of filaments used in incandescent lamps by carbonizing
cellulose that has been dissolved or acted on by a solution of cuprammonia,
substantially as herein described.
Second. The preparation of carbon filaments from paper, linen, cotton, thread,
or other form of cellulose treated prior to carbonization with a solution of
cuprammonia, for the purpose of rendering the carbon produced therefrom closer
in texture, denser, and more elastic and homogenous, substantially as herein
described.
Third. The preparation of carbon filaments used in incandescent lamps from
paper, linen, cotton, thread, or other form of fibrous cellulose treated prior to
carbonization with a solution of cellulose in cuprammonia, substantially as
described.
Fourth. The manufacture of carbon filaments for uso in incandescent lamps
from a thread, film, or skin prepared from cellulose dissolved in cuprammonia
and deposited on the evaporation of the solvent, substantially as herein described.
Fifth. The carbon filaments for use in incandescent lamps prepared from celluloso
which has been dissolved in or treated with cuprammonia, and from which the
copper has been extracted at the central portion of the filament but left at the
ends, substantially as herein described.
Sixth. The method of making a strong and electrically efficient junction between
the ends of the filamonts in an incandescent lamp and the conducting wires by
painting the junctions with a solution of cellulose in cuprammonia and subsequent
carbonization, substantially as herein described.
Seventh. The method of improving the state of carbon filaments for use in
incandescent lamps by depositing upon them graphitoidal carbon by electrically
heating them in an exhausted vessel containing (or in connection with another
vessel which contains) a hydro-carbon compound, whoso boiling or volatilizing
point is so high that although the substance is present in quantity the vapour is
attenuated, substantially as herein described.
In witness whereof, I, the said William Crookes, have hereunto set my hand
and seal, this Seventh day of December, in the year of our Lord Ono
thousand eight hundred and eighty one.
WILLIAM CROOKES. (L.S.)