IMPROVEMENTS IN ELECTRIC LAMPS
Year: 1880

page_text: LETTERS PATENT to Joseph Wilson Swan, of Newcastle-on-Tyne, in the
County of Newcastle, Chemist, for an Invention of "IMPROVEMENTS IN
ELECTRIC LAMPS."
PROVISIONAL SPECIFICATION left by the said Joseph Wilson Swan at the
Office of the Commissioners of Patents on the 20th January 1880.
JOSEPH WILSON SWAN, of Newcastle-on-Tyne, in the County of Newcastle,
Chemist. "IMPROVEMENTS IN ELECTRIC LAMPS."
My Invention refers to that kind of electric lamp in which light is produced by
the incandescence of a continuous conductor of carbon enclosed in an exhausted
glass bulb, and provides means for increasing their durability. The first part of
my Invention has for its object to prevent the cracking and leakage of the bulbs in
consequence of the heating and cooling of the conducting wires, which when
simply sealed into the glass globe cause it to crack and leak at or near the junction
of the wires and glass. The means I use for obtaining the object described is the
employment of caps of platinum as an attachment to the bulb at the places where
the conducting wires enter it. The caps are attached by the fusion of the glass
around their rim. The conducting wires pass through the centres of the caps,
and the junction of the wires and caps is secured airtight by soldering or other
means.
The second part of my Invention has for its object to prevent the rupture of the
carbon within the exhausted bulb as the result of its unequal contraction.
I have found that when the carbon employed within the lamp is an arch or
horseshoe shaped plate produced by cutting out the arch or horseshoe shaped piece
from a sheet of cardboard, and afterward carbonizing it by heat, that the arch or
horeshoe shaped carbon so produced is liable to become distorted and ultimately to
break in consequence of the unequal contraction caused by the unequal heating of
the inner and outer portions of the arch during the use of the lamp. This defect I
remedy by forming the carbon to be made incandescent of a strip of cardboard or
paper bent into the form of a hoop or loop; the front view of such hoop or loop

page_text: shewing the section or thickness of the strip, and the side view its width. The
strip of cardboard or paper bent as aforesaid I subject to a white heat in a closed
vessel containing powdered carbon or other suitable air excluding powder. I mount
one or more of the loops or hoops formed, as above described, within a glass bulb
by clipping the ends of the loops or boops between forceps of platinum or other
suitable metal attached to conducting wires, which pass through the caps before
described.
The third part of my Invention has for its object the prevention of the evolution
of gas occluded by the conducting wires within the lamp, and this object I
accomplish by coating the conducting wires within the lamp with glass or enamel.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Joseph Wilson Swan in the Great Seal Patent Office on the 20th July
1880.
JOSEPH WILSON SWAN, of Newcastle-on-Tyne, in the County of Newcastle,
Chemist. "IMPROVEMENTS IN ELECTRIC LAMPS."
My Invention relates to that kind of electric lamp in which light is produced by
the incandescence of continuous conductor of carbon enclosed in an exhausted
glass bulb, and provides means for increasing its durability.
The first part of my Invention has for its object to prevent the cracking and
leakage of the glass bulb or enclosing vessel in consequence of the heating and
cooling of the conducting wires, which when simply sealed into the glass globe
caused it to crack and leak at or near the junction of the wires and glass. The
means I use for obtaining the object described is the employment of a pair of caps
of platinum as an attachment to the lamp' globe, or a tube proceeding from it at the
places where the conducting wires enter the lamp enclosure. Each cap is attached
by the fusion of the glass around its rim. The conducting wires pass through or
into the caps, and the junction of the wires and caps is secured airtight by soldering,.
or where the wire does not pass through the cap but into it soldering is not
essential; a firm contact of the conducting wires with the interior of the caps is in
that case sufficient. The forms of caps I prefer to use are shewn in the annexed
Drawings, Figure 1 and Figure 2. Figure 1 shews a section through its axis of the
kind of cap I use where the wire passes through the cap, and is soldered into it,
and Figure 2 shews a section through its axis of the kind of cap I use where the
wire only enters the inside of the cap but does not pass through it. The size and
figure of the cap may be varied to some extent without detriment to the object in
view, and I therefore do not limit myself strictly to the exact size or form indicated
by the Drawings.
The second part of my Invention has for its object to prevent the rupture of the
carbon within the exhausted glass bulb as the result of its unequal contraction. I
have found that when the carbon employed within the lamp is an arch or horse-
shoe shaped plate produced by cutting out the arch or horseshoe shaped piece from
a sheet of cardboard, and afterwards carbonising it by heat, that the arch or
horseshoe shaped carbon so produced is liable to become distorted and ultimately to
break in consequence of the unequal contraction caused by the unequal heating of
the inner and outer portion of the arch during the usage of the lamp. This defect
I remedy by forming the carbon to be made incandescent of a strip of cardboard or
parchment paper (sometimes called vegetable parchment) produced in the well
known usual manner by immersing bibulous paper in sulphuric acid diluted with
water in the proportion of two parts sulphuric acid and one part water, and allowing
it to remain until the required effect is produced, and then washing with water until
the whole of the acid is eliminated and drying, after which it is bent into the form
of an arch or hoop. The front view, Figure 3, of such arch or hoop shows the
thickness of the card or parchment paper, and the side view, Figure 4, its width.
The strip of cardboard or parchment paper, after being bent as aforesaid into the
required form I subject to a white heat in a close vessel of suitable material, such
as fire clay, containing powdered charcoal or other suitable air excluding powder.
I mount one or more of the curved carbon strips, formed as above described, within
a glass. bulb forming the enclosure above mentioned by clipping the ends of the said
curved carbon strips between forceps of platinum, or an alloy of platinum and
iridium attached to the conducting wires, which pass through or into the caps as
before described.
The third part of my Invention has for its object the prevention of the evolution
of gas occluded by the conducting wires within the lamp, and this object I

page_text: accomplish by coating the conducting wires within the lamp with glass or enamel.
The form of the caps above described is shewn in Figure 1 and Figure 2, Figure 1
being a longitudinal section of the kind of cap employed when the conducting wire
passes through it, and Figure 2 shewing a longitudinal section of the kind of cap
used when the conducting wire is fixed within the cap, but without passing through
it; Figures 3 and 4 represent the arch or hoop formed as above described,
Figure 3 being a front view, and Figure 4 a side view thereof.
Figures 5 and 6 shew front and side views of the lamp with the arch and caps
in situ; Figures 7 and 8 shew front and side views of a multiple carbon lamp.
Having stated the nature of my Invention and the manner in which I carry it
into effect, I claim as new and useful,―
First. The use of caps of platinum fused to the glass of the lamp as a means
of preventing the fracture of the glass by the heating of the conducting wire.
Second. Forming carbons for incandescent electric lamps in the manner described,
in which a strip of paper or card bent to the required form is carbonised by
subjecting it to heat in a vessel containing charcoal or other form of carbon in
powder.
Third. Forming the carbon for incandescent electric lamps by carbonising
vegetable parchment of the required form, in the manner described.
Fourth. Employing several carbon arches in each lamp, as described.
Fifth. Preventing the evolution of gas occluded by the conducting wires within
the lamp, by coating the conducting wires within the lamp with glass or enamel.
In witness whereof, I, the said Joseph Wilson Swan, have hereunto set my
hand and seal, this Third day of July, in the year of our Lord One thousand
eight hundred and eighty.
Witness,
HUGH RIDDELL.
JOSEPH WILSON SWAN. (L.S.)