Improvements in Incandescent Electric Lamps and Leading-in-wires therefor.
Year: 1890

page_text: Date of Application, 6th Oct., 1890
Complete Specification Left, 1st July, 1891-Accepted, 1st Aug., 1891
PROVISIONAL SPECIFICATION.
Improvements in Incandescent Electric Lamps and Leading-in-wires
therefor.
I, BENJAMIN JOSEPH BARNARD MILLS of 23 Southampton Buildings in the
County of Middlesex Patent Agent do hereby declare the nature of this invention,
communication to me from abroad by Thomas Alva Edison of Llewellyn Park,
In the County of Essex and State of New Jersey, United States of America,
Inventor, to be as follows:-
In incandescent electric lamps the incandescent filament is connected to
conductors called the "leading-in" conductors, by means of which the filament
within the sealed glass globe is connected with the circuit wires outside of said
globe. To maintain a stable vacuum it has been found best to make these leading-
in-wires of platinum, since its coefficient of expansion is so nearly that of glass
that less trouble is caused by its expansion and contraction than is experienced
with other metals.
The object of this invention is, to economise in the amount of platinum
employed, and at the same time to provide a seal around the leading-in-wires
which shall be as nearly perfect or more nearly perfect than with the constructions
hitherto employed, while at the same time an effective support for the filament is
formed.
It is usual in the manufacture of incandescent electric lamps, to introduce the
platinum leading-in-wires into a glass tube, and then to fuse and compress the tube
around the wires, thereby tightly sealing them into the glass. These wires have
necessarily been of a considerable size, not for electrical reasons, that is, in order
to be of sufficient conducting capacity to convey the current without undue
heating, but for mechanical reasons, since they are required to support the
filament, and to be of such rigidity that they will not be bent by the weight of
the filament, or by the jarring to which they are subject in use, transportation &c.
These wires are also of a considerable length, extending from the end of the
filament to a point outside the globe where they are connected with copper wires.
The use of platinum wires of such size and length obviously involves a very
considerable expense.
It has been found that wires of copper, iron, nickel, silver and other metals and
some alloys, having a greater coefficient of expansion than platinum, can be sealed
into the glass, but on cooling they contract sufficiently to permit air to pass into
the vacuum, although they will still be held mechanically rigid by the glass. I
therefore in the present invention use leading-in-wires of two metals, one section
being of a metal having substantially the same coefficient of expansion as
glass, such as platinum, the other being of a different and cheaper metal, and I
seal both of the metals into the glass. The seal will remain perfect at the
platinum sections, and it will therefore be immaterial if the copper or other wire
contracts away from the glass as described.
It is found that the best results are obtained by carrying out the invention in
the following way:
Short sections of platinum wire several times smaller in cross section than the
leading-in-wires heretofore used, are employed, and to one end of these are
attached by fusion, larger copper wires which are to be connected to the filament
and support, and convey current thereto. To the other ends of the platinum wires
are attached other copper wires which are to extend out of the lamp for connection
with the supplying circuit. The entire length of the platinum wires as well as a
portion of the wires extending from both ends thereof are sealed into the glass,

page_text: these wires being laid in the glass tube and the end of the tube softened by heat
and pressed down upon said wires to form a flat scal, as will be well understood.
It is preferred to employ platinum wire which is alloyed with iridium or other
metals of the platinum group. The preferable alloy for the purpose is one
containing about 5% of iridium.
Since the size of such wire may, as stated, be made to depend solely on the
electrical conditions, such wire may be made as small as will suffice to carry the
current for the lamp without sufficient heating to cause expansion enough to injure
the seal. While platinum has practically the same coefficient of expansion as
certain kinds of glass, the glass used for incandescent electric lamps does not
approach this quite so closely and hence the platinum seal as heretofore made with
the wire of comparatively large diameter necessary for mechanical stability has not
been absolutely perfect, the contraction of the wire being greater than that of the
glass. But by the use of the small wires, the proportion of the contraction being
diminished, and the total area available for leakage around the wires being also
decreased, this difficulty is avoided; while when the lamp is in operation the heat
due to the current causes the wire to expand strongly against the glass and so
make the seal perfect.
For a lamp taking ampère of current, platinum wires 5000 of an inch in
diameter can be employed, which is evidently a very important saving. The
saving in length is also of great importance. The bit of platinum wire used need
only be long enough to make it practicable to attach the other sections of wire to
it; this being done preferably by fusion. A wire of an inch in length is found
to make a perfect seal.
It is found that copper is the preferable metal to use in practice for the terminal
wires; silver would be preferred because it does not oxidize, but on account of its
low melting point it is difficult to handle in making the lamp, it is therefore
preferred to use copper. This wire contracts in cooling but not sufficiently to
remove from it the mechanical support afforded by the glass.
The copper wires may be of such size as to give the same mechanical support
for the filament as has heretofore been afforded by those of platinum.
It will be seen therefore that by the present invention as so far described equal
mechanical advantages and a better scal are obtained for an enormously decreased
cost in material.
There is another way in which the invention may be carried out which effects a
large saving of platinum though not so large as that which I have just described.
In this arrangement the copper wire is attached to one end only of the platinum
wire and the platinum wire is attached directly to the filament and such wire is
caused to extend down to a point within the glass seal from which point the copper
wire extends to the outside of the lamp. In this case the platinum wire has to be
large enough to support the filament so there is no saving as regards thickness of the
wire. But the length of platinum wire employed is reduced about one half so that
the cost of platinum for the lamp is reduced to one half of what is now incurred.
Dated October 6th 1890.
COMPLETE SPECIFICATION.
Improvements in Incandescent Electric Lamps and Leading-in-wires
therefor.
I, BENJAMIN JOSEPH BARNARD MILLS, of 23 Southampton Buildings, in the
County of Middlesex, Patent Agent, do hereby declare the nature of this invention,
a communication to me by Thomas Alva Edison, of Llewellyn Park, in the County
of Essex, and State of New Jersey, United States of America, Inventor, and in what

page_text: manner the same is to be performed to be particularly described and ascertained in
and by the following statement :-
In incandescent electric lamps the incandescent filament is connected to conductors
called the "leading-in" conductors, by means of which the filament within the
sealed glass globe is connected with the circuit wires outside of said globe.
To maintain a stable vacuum it has been found best to make these leading-in
wires of platinum, since its coefficient of expansion is so nearly that of glass that
less trouble is caused by its expansion and contraction than is experienced with
other metals.
The object of this invention is, to economise in the amount of platinum
employed, and at the same time to provide a seal around the leading-in-wires
which shall be as nearly perfect or more nearly perfect than with the constructions
hitherto employed, while at the same time an effective support for the filament is
formed; and to this end the invention consists in the novel devices and combinations
of devices hereinafter described and claimed.
In the accompanying drawings which illustrate the improvements,
Figure 1 is a central section of an incandescent lamp embodying the invention;
Figure 2 a section of a part of a lamp showing a modified arrangement of the
leading-in wires; and
Figure 3 a similar view showing the arrangement usually heretofore employed,
for the purpose of comparison.
It is usual in the manufacture of incandescent electric lamps, to introduce the
platinum leading-in-wires, marked 1 in Figure 3, into a glass tube, and then to fuse
and compress the tube around the wires, thereby tightly sealing them into the glass.
These wires have necessarily been of a considerable size, not for electrical reasons,
that is, in order to be of sufficient conducting.capacity to convey the current without
undue heating, but for mechanical reasons, since they are required to support the
filament, and to be of such rigidity that they will not be bent by the weight of
the filament, or by the jarring to which they are subject in use, transportation clc.
These wires are also of a considerable length, extending as shown in Figure 3,
from the end of the filament at 2, to point 3, where they are connected with
copper wires.
The use of platinum wires of such size and length obviously involves
a very considerable expense.
It has been found that wires of copper, iron, nickel, silver and other metals and
some alloys, having a greater coefficient of expansion than platinum, can be scaled
into the glass, but on cooling they contract sufficiently to permit air to pass into
the vacuum, although they will still be held mechanically rigid by the glass. I
therefore in the present invention use leading-in-wires of two metals, one section
being of a metal having substantially the same coefficient of expansion as glass,
such as platinum, the other being of a different and cheaper metal, and I scal both
of the metals into the glass.
The seal will remain perfect at the platinum sections, and it will therefore be
immaterial if the copper or other wire contracts away from the glass as described.
Two ways of scaling in the wires are illustrated in the drawings.
In Figure 1, 4 are short sections of platinum wire several times smaller in cross-
section than the leading-in wires heretofore used. To these platinum wires are
connected larger copper or other wires 5, which support and conduct the current
to the filament 6. To the other end of the platinum wires are connected
conductors 7. which lead to the supply circuit. The entire length of the platinum
wires 4, as well as a portion of the conductors 5 and 7, are sealed into the glass, as
shown, these wires being laid in the glass tube and the end of the tube softened by
heat and pressed down upon said wires to form a flat seal, as will be well
understood.
It is preferred to employ platinum wire which is alloyed with iridium or other
metals of the platinum group. The preferable alloy for the purpose is one
containing about % of iridium.
Since the size of such wire may, as stated, be made to depend solely on the

page_text: electrical conditions, such wire may be made as small as will suffice to carry the
current for the lamp without sufficient heating to cause expansion enough to injure
the seal. While platinum has practically the same co-efficicnt of expansion as
certain kinds of glass, the glass used for incandescent electric lamps does not
approach this quite so closely and hence the platinum seal as heretofore made with
the wire of comparatively large diameter necessary for mechanical stability has
not been absolutely perfect, the contraction of the wire being greater than that of
glass. But by the use of the small wires the proportion of the contraction being
diminished, and the total area available for leakage around the wires being also
decreased, this difficulty is avoided; while when the lamp is in operation the heat
due to the current causes the wire to expand strongly against the glass and so
make the scal perfect. For a lamp taking ampere of current, platinum wires
of an inch in diameter can be employed which is evidently a very important
saving. The saving in length is also of great importance. The bit of platinum
wire used need only be long enough to make it practicable to attach the other
sections of wire to it-this being done preferably by fusion. A wire of an inch
in length is found to make a perfect seal.
It is found that copper is the preferable metal to use in practice for the terminal
wires; silver would be preferred because it does not oxidize but on account of its
low melting point it is difficult to handle in making the lamp, it is therefore
preferred to use copper. This wire contracts in cooling but not sufficiently to
remove from it the mechanical support afforded by the glass. The copper wires
may be of such size as to give the same mechanical support for the filament as has
heretofore been afforded by those of platinum.
It will be seen therefore that by the present invention as so far described equal
mechanical advantages and a better seal are obtained, for an enormously decreased
cost in material.
The arrangement in Figure 2 is slightly different from that above described.
The platinum wires 4 are of the same size as those heretofore used, since in this
case they support the filament, but are of less length since they extend only from
the end of the filament at 2 to the point 3 within the body of the glass, while the
copper or other conductors 9 extend from that point to the outside of the lamp.
Although this arrangement effects a great saving, it is not as great as in the
form first described.
By comparing Figures 1 and 2 with Figure 3, it will be seen that in the first
form the platinum used is a very small fraction of that used in the old lamp, being
both shorter and finer; while in the lamp illustrated in Figure 2 the amount of
platinum is reduced about one-half, since the wire is reduced in length about
one-half.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that
what I claim is :-
An incandescent electric lamp having leading-in wires composed of sections of
different metals, there being a section of platinum or other metal whose co-efficient
of expansion is nearly the same as that of glass, and a section or sections of
cheaper metal, and the sections of both metals being sealed into the glass of the
vacuum chamber, substantially as hereinbefore described.
1001
Dated July
1001
1st 100.
B. J. B. MILLS.
By Harris & Mills,
23, Southampton Buildings, London, Agents.