IMPROVEMENTS IN ELECTRIC LAMPS, AND IN THE METHOD OF MANUFACTURING THE SAME
Year: 1879

page_text: "
LETTERS PATENT to Thomas Alva Edison, of Menlo Park, in the State of
New Jersey, United States of America, for the Invention of IMPROVEMENTS
IN ELECTRIC LAMPS, AND IN THE METHOD OF MANUFACTURING THE SAME.”
PROVISIONAL SPECIFICATION left by the said Thomas Alva Edison at the
Office of the Commissioners of Patents on the 10th November 1879.
THOMAS ALVA EDISON, of Menlo Park, in the State of New Jersey, United
States of America. "IMPROVEMENTS IN ELECTRIC LAMPS, AND IN THE METHOD OF
MANUFACTURING THE SAME.”
It is necessary to practically subdivide the electric light into a great number of
luminous points, so that lamps connected in multiple may be employed without
the necessity of using conductors of great size for the current to the lamps. It is
essential that the lamps should be of great resistance. In the Provisional
Specification of Patent dated June 17th, 1879, No. 2402, I have set this forth, and
obtained lamps of great resistance by employing long lengths of platinum or
metallic wires pyroinsulated, and wound in such a manner that but small radiating
surface is exposed to the air, although a great length of wire is used.
My present Invention relates to lamps of a similar character, except that carbon
threads or strips are used in place of metallic wires. I use a block of glass, into
which are sealed two platinum wires. These wires serve to convey the current to
the electric lamp within a bulb, which is blown over the lamp and united to the
glass block.
The bulb is exhausted of air to about one millionth of an atmosphere.
Upon the ends of these wires are two clamps that secure two other platinum
wires. The burner consists of a filament or thread of carbon, preferably
coiled, with the ends secured to the platinum wires, the whole being made
as follows:-
Fibrous material, such as paper, thread, wood, or any vegetable or animal matter
which can be carbonized, has the ends secured to platinum wires, the fibre is
wound in such a shape as to expose the least amount of surface to radiation, such
as in a helix or spiral. The helix is secured to the platinum wires by plastic
carbon, and the whole is placed in a closed vessel free from air, and subjected to a
heat sufficient to fully carbonize the fibre, and leave nothing but carbon.
At the

page_text: same time the effect of the carbonization is to lock the carbon to the platinum wire,
and make good connection.
These wires are secured by the clamps to the two platinum wires in the bulb,
and the bulb is exhausted of air and sealed. Lamps of one hundred ohms resistance
may be made in this manner, from which light from the incandescent carbon is
obtained. The destruction of the fragile carbon by oxidation is prevented by the
high vacuum, which is obtained before sealing the glass bulb.
Previously to my Invention carbon sticks have been used, but they have only
had a resistance of three or four ohms, and none have been used in vacuum bulbs
composed entirely of glass, except the leading wires, hence the difficulties of
sealing leading wires into glass, which would convey a current of sufficient strength
to a lamp of but three or four ohms resistance is too great to make such a lamp
successful, but when the resistance of the lamp is 100 ohms or more the leading
wires can be very small, as they will then be a small factor in the total resistance
of the lamp, and will not heat so as to crack the glass.
Lamp black, which has been placed in sealed crucibles, and subjected to a white
heat for several hours, may be kneaded with tar until it reaches such a consistency
as to allow its being rolled out on flat plates to very thin wires, which are
sufficiently flexible to allow of coiling into helices; after they are rolled out to the
proper length and size they are coated with a non-carbonizable powder of liquid,
and wound or coiled.
The two ends are increased in size and secured to platinum wires, the whole is
then subjected to heat in a closed tube, and the volatile constituents of the tar
driven off and the balance carbonized, thus making a solid and homogeneous coil,
which can be then united to the leading wires of the lamp, and a glass bulb blown
over it and exhausted of air, and the lamp is then ready for use. The non-carbonized
material prevents the spirals from touching each other until the whole has so
stiffened sufficiently to remain in its position.
To assist in more rapidly manufacturing these spirals I sometimes wind the
flexible carbon wires between metallic spirals, which after the carbonization of the
tar are eaten away by acids, thus leaving the carbon intact. I also sometimes roll
a thread within the compound of carbon and tar, so as to allow of greater
convenience in handling the same, and the flexible carbon filament is not so liable
to crack by its own weight in the act of winding.
To increase the resistance of the lamp black tar compound I sometimes work it
into a volatile powder, such as powdered camphor, oxide zinc, but to make the
light insensitive to variations of the current a considerable mass of matter should
be used, in order that the specific heat of the lamp may be increased, so that it
takes a long time to reach its full brilliancy, and also to die away slowly. To do
this it is better to have the carbon as homogeneous as possible, and obtain the
requisite resistance by employing a filament several inches long, and winding
the same in a spiral form, so that the external radiating surface shall be small.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Thomas Alva Edison in the Great Seal Patent Office on the 10th
May 1880.
"
THOMAS ALVA EDISON, of Menlo Park, in the State of New Jersey, United
States of America. IMPROVEMENTS IN ELECTRIC LAMPS, AND IN THE METHOD OF
MANUFACTURING THE SAME.'
»
The object of this Invention is to produce electric lamps giving light by
incandescence, which lamps shall have high resistance so as to allow of the
practical subdivision of the electric light.
The Invention consists in a light giving body of carbon wire, or sheets coiled or
arranged in such a manner as to offer great resistance to the passage of the electric
current, and at the same time present but a slight surface from which radiation
can take place.
The Invention further consists in placing such light giving body of great
resistance in a nearly perfect vacuum, to prevent oxidation and injury to the
conductor by the atmosphere.
The current is conducted into the vacuum bulb through platina wires sealed into
the glass.
The Invention further consists in the method of manufacturing carbon conductors
of high resistance, so as to be suitable for giving light by incandescence, and in the
manner of securing perfect contact between the metallic conductors or leading
wires, and the carbon conductor.
Heretofore light by incandescence has been obtained from rods of carbon of one
to four ohms resistance placed in closed vessels, in which the atmospheric air has
been replaced by gases that do not combine chemically with the carbon. The
vessel holding the burner has been composed of glass cemented to a metallic base.
The connection between the leading wires and the carbon has been obtained by
clamping the carbon to the metal.
The leading wires bave always been large, so that their resistance shall be many
times less than the burner; and in general the attempts of previous persons has
been to reduce the resistance of the carbon rod. The disadvantages of following
this practice are, that a lamp having but one to four ohms resistance cannot be
worked in great numbers in multiple arc without the employment of main
conductors of enormous dimensions, that owing to the low resistance of the lamp
the leading wires must be of large dimensions and good conductors, and a glass
globe cannot be kept tight at the place where the wires pass in and are cemented,
hence the carbon is consumed because there must be almost a perfect vacuum to
render the carbon stable, especially when such carbon is small in mass, and high in
electrical resistance.
In the use of a gas in the receiver at the atmospheric pressure, which, although
not attacking the carbon, serves to destroy it in time by "air washing" or the
attrition produced by the rapid passage of the air over the slightly coherent highly
heated surface of the carbon.
I have reversed this practice. I have discovered that even a cotton thread
properly carbonized, and placed in a sealed glass bulb exhausted to one millionth of
an atmosphere, offers from one hundred to five hundred ohms resistance to the
passage of the current, and that it is absolutely stable at very high temperatures;
that if the thread be coiled as a spiral, and carbonized, or if any fibrous vegetable
substance which will leave a carbon residue after heating in a closed chamber be so
coiled, that as much as two thousand ohms resistance may be obtained without
presenting a radiating surface greater than three sixteenths of an inch; that if
such fibrous material be rubbed with a plastic compound composed of lamp-black
and tar, its resistance may be made high or low according to the amount of lamp-

page_text: black placed upon it. I have also discovered that carbon filaments may be made
by a combination of tar and lamp-black, the latter being previously ignited in a
closed crucible for several hours, and afterwards moistened and kneaded until it
assumes the consistency of thick putty. Small pieces of this material may be
rolled out in the form of wire as small as seven one thousandths, 7/1000, of an
inch in diameter, and over a foot in length, and the same may be coated with a
non-conducting non-carbonizable substance, and wound on a bobbin, or as a spiral,
and the tar carbonized in a closed chamber by subjecting it to high heat, the
spiral after carbonization retaining its form. I sometimes roll a thread within the
compound of lamp-black and tar, so as to allow of greater convenience in handling
the same; and the flexible carbon filament is not so liable to crack by its own
weight in the act of winding.
To increase the resistance of the compound of lamp black and tar I sometimes
work into it a volatile powder, such as powdered camphor, oxide zinc, but to make
the light insensitive to variations of the current a considerable mass of matter
should be used in order that the specific heat of the lamp may be increased, so that
it takes a long time to reach its full brilliancy and also to die away slowly.
All
To do this it is better to have the carbon as homogeneous as possible, and obtain
the requisite resistance by employing a filament several inches long and winding
the same in a spiral form so that the external radiating surface shall be small.
these forms are fragile and cannot be clamped to the leading wires with sufficient
force to ensure good contact and prevent heating. I have discovered that if
platinum wires are used and the plastic lamp-black and tar material be molded
around it that in the act of carbonization there is an intimate union by combination
and by pressure between the carbon and platina, and nearly perfect contact is
obtained without the necessity of clamps, hence the light giving body and the
platina wires are connected and ready to be placed in the vacuum bulb.
When fibrous material is used the plastic lamp black and tar is employed to
secure it to the platina wires before carbonizing. By using the carbon wire of such
high resistance I am enabled to use fine platinum wires for leading wires, as they
will have a small resistance compared to the light giving body, hence will not heat
and crack the sealed vacuum bulb.
Platina can only be used, as its expansion is nearly the same as that of glass.
By using a considerable length of carbon wire and coiling it in such a manner that
only a small portion of its entire surface radiates light, I can raise the specific heat
of the whole and thus prevent the rapid reception and disappearance of the light,
which on a plain wire is prejudicial as it shows the least unsteadiness of the current
by the flickering of the light, but if the current is steady the defect does not show.
I have carbonized and used cotton and linen thread, wood-splints, paper coiled in
various ways, also lamp-black, plumbago, and carbon in various forms mixed with
tar and kneaded so that the same may be rolled out into wires of various lengths
and diameters, each wire however is to be uniform in size throughout. If the
carbon thread is liable to be distorted during carbonization it is to be coiled
between a helix of copper wire. The ends of the carbon or filament are secured to
the platina leading wires by plastic carbonizable material and the whole placed in
the carbonizing chamber. The copper which has served to prevent distortion of
the carbon thread is afterwards eaten away by nitric acid, and the spiral soaked in
water and then dried and placed in the glass holder, and a glass bulb blown over
the whole with a leading tube for exhaustion by a mercury pump. This tube when
high vacua has been reached is hermetically sealed.
With substances which are not greatly distorted in carbonizing they may be
coated with a non-conducting non-carbonizing substance, which allows one coil or
turn of the carbon to rest upon and be supported by the other.
In the Drawing Fig. 1 shows the lamp sectionally. a is the carbon spiral or
thread; c, c¹, are the thickened ends of the spiral formed of the plastic compound
of lamp-black and tar; d, d', are the platina wires; h, h, are the clamps which
serve to connect the platina wires cemented in the carbon with the leading

page_text: wires x, x, sealed in the glass vacuum bulb; e, e, are copper wires connected just
outside the bulb to the wires x, x; m is the tube, shown by dotted lines leading to
the vacuum pump, which tube is hermetically sealed near the glass bulb after the
bulb has been exhausted of air, as aforesaid.
Fig. 2 represents the plastic material before being wound into a spiral.
Fig. 3 show the spiral after carbonization ready to have a bulb blown over it.
I claim as my Invention,-
First. An electric lamp for giving light by incandescence consisting of a filament
of carbon of high resistance, made as described and secured to metallic wires, as
set forth.
Second. The combination of a carbon filament within a receiver made entirely of
glass, through which the leading wires pass and from which receiver the air is
exhausted, for the purposes set forth.
Third. A coiled carbon filament or strip arranged in such a manner that only a
portion of the surface of such carbon conductor shall radiate light, as set forth.
Fourth. The method herein described of securing the platina contact wires to the
carbon filament and carbonizing of the whole in a closed chamber, substantially as
set forth.
In witness whereof, I, the said Thomas Alva Edison, have hereunto set my
hand and seal, this 20 day of April. A.D. 1880.
Witnesses,
CHA5. H. SMITH, 140, Nassau St., N.Y.
GEO. T. PINCKNEY,
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THOMAS ALVA EDISON. (L.S.)