IMPROVEMENTS IN ELECTRIC LAMPS, AND THE MATERIALS EMPLOYED IN CONSTRUCTION
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, AND
THE MATERIALS EMPLOYED IN
CONSTRUCTION."
IN
THEIR
PROVISIONAL SPECIFICATION left by the said Joseph Wilson Swan at the
Office of the Commissioners of Patents on the 27th November 1880.
JOSEPH WILSON SWAN, of Newcastle on Tyne, in the County of Newcastle,
IN THE MATERIALS
Chemist.
IN ELECTRIC LAMPS, AND
"IMPROVEMENTS
EMPLOYED IN THEIR CONSTRUCTION."
My Invention relates to electric lamps in which light is produced by passing an
electric current through a conductor of carbon so as to render it incandescent, said
carbon conductor being enclosed in an air tight and vacuous or partially vacuous
glass vessel.
It is well known that the practical efficiency of the kind of electric lamp above
described has hitherto been impaired by the want of homogeneity and compactness
in the carbon conductors, and by the imperfection of the contact betwixt it and the
metallic conductors which convey the electric current to it.
I have found that an exceedingly solid, homogeneous, and elastic form of carbon,
peculiarly adapted for the formation of arches, spirals, or other forms of conductor
for electric lamps, can be produced from cotton thread which has been subjected to
the action of sulphuric acid of such strength as to cause a similar kind of change to
take place in the thread to that which takes place in bibulous paper in the well
known process of making vegetable parchment.
A kind of cotton thread suitable for being treated in the manner above described
is known as crochet thread, but it must be understood I do not confine myself
A suitable strength of
exclusively to the use of this particular kind of thread.
sulphuric acid is formed by mixing together two parts of sulphuric acid s.g., 1845,
with one part of water. The cotton thread, after being immersed in acid of this
strength or thereabouts, and allowed to remain immersed for just sufficient time to
effect the change required, is then removed and quickly and thoroughly washed in
water so as to completely eliminate the acid.
'

page_text: To facilitate and render more perfect the contact between the conductors which
carry the electric current to and from the carbon, I take either the parchmentised
thread above described, or the thread without being previously parchmentised, and
I wrap round it at suitable intervals strips of bibulous paper so as to thicken the
thread at those places where the clips or other metallic attachments are required
to make contact with it when it is converted into carbon and placed in the lamp,
and I then treat the thread so prepared with the sulphuric acid bath above
described so as to parchmentise the paper or other suitable form of cotton wrapped
round the thread, and weld the whole into one mass, and after the required effect
has been produced I wash away the acid with water as before described. After the
parchmentised thread has been washed and dried I compress and flatten the ends so
"as further to condense them and to give them a form suitable for being held firmly
in a clip. I then take the pieces treated as above described, each with thickened
end, and shape them into arches, spirals, or other forms suitable for the lamp
required. I then bury them in powdered charcoal or other form of carbon or air-
excluding powder contained in a crucible or some suitable covered vessel of iron or
earthenware, and I subject the whole to a high temperature, such, for example, as
that of the pottery biscuit kilns. Thickening the ends of the carbon employed in
incandescent electric lamps in the manner described is obviously also applicable to
carbons formed from paper or other form of vegetable fibre. An alternative mode
of attaching the carbon conductor produced as above described to the metallic
conductors which convey the electric current to and from it, consists in, so to speak,
splicing the carbon and a wire or narrow strip of platina or other suitable metal.
This splicing I effect by laying together so that they overlap by about half an
inch, one end of the wire or strip of platina or other suitable metal and one end
of the thread out of which a carbon spiral or arch is to be formed. The wire or
strip and the thread are then bound together by a wrapping of cotton thread, or..
by wrapping round them a strip of bibulous paper, so as to form several folds,
and after both ends of the thread are so treated the whole is immersed in the bath.
of sulphuric acid, as above described, so as to parchmentise the thread and the. a
wrapping.
After washing and drying I shape the thread into the required form, and
carbonise it as above described.
-

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 24th May
1881.
JOSEPH WILSON SWAN, of Newcastle on Tyne, in the County of Northumberland,
Chemist. "IMPROVEMENTS IN ELECTRIC LAMPS, AND IN THE MATERIALS
EMPLOYED IN THEIR CONSTRUCTION."
My said Invention relates to that class of electric lamps in which light is
produced by passing an electric current through a conductor of carbon, so as to
render it incandescent, the said carbon conductor being enclosed in a glass chamber
or bulb from which the air has been exhausted.
In carrying out my said Invention I form the carbon conductor from cotton
thread which has been subjected to the action of sulphuric acid of such a strength
as to cause a change or conversion to take place in the thread of a similar character
to that which is produced by the treatment of bibulous paper with sulphuric acid,
according to the well known process of making vegetable parchment. A suitable
strength of sulphuric acid for the purpose is formed by mixing together about two
volumes of sulphuric acid of a specific gravity of 1845 with about one volume of
water. The cotton thread after being immersed in this solution and allowed to
remain therein for a sufficient time to effect the required conversion is removed
from the solution and washed with water until the whole of the acid is eliminated,
after which it is dried and carbonized by any of the suitable well known means.
The description of cotton thread most suitable for treatment in the manner
hereinbefore described is that known as crotchet thread, but other kinds of cotton
thread may be employed.
The accompanying Sheet of Drawings illustrates by way of examples the
application of the prepared cotton thread to two lamps of the class hereinbefore
.referred to.
Figures 1 and 2 represent respectively vertical sections taken at right angles to
each other of a lamp having a single carbon; and Figures 3 and are similar
views of another lamp in which multiple carbons are employed.
Referring to Figures 1 and 2, a is the carbon formed of the prepared cotton
thread, which is bent round and gripped at its two extremities by clips b, to which
the upper ends of the metal conductors c are attached; the carbons thus arranged,
together with a convenient length of the metal conductors c, are surrounded by a
glass bulb or receptacle d, and the lower ends of the said metal conductors which
pass through the bottom of the glass receptacle d may be sealed into the same, but
when metal conductors of large sectional area are employed I prefer to secure
their lower ends to platinum caps e, which are attached to the bottom of the glass
receptacle d by fusing the glass around the said caps, the metal conductors either
passing through the caps or terminating in them, as desired, all as described in the
Specification to former Letters Patent granted to me, dated the 20th January 1880,
No. 250.
When such platinum caps are employed it is not indispensable to form the con-
ducting wires of platinum, but these may in that case be of copper, iron, silver, or
other suitable metal.
The carbons are thickened at their ends with a wrapping of cotton or other
suitable material, which is united to the cotton thread by immersion in sulphuric
acid in the manner herein before described, the increased thickness at the termi-
nations facilitating the attachment of the carbons to their holding clips, and
preventing them from becoming heated in use. This method of obtaining increased
thickness is also applicable when the carbon is formed from paper or cardboard.

page_text: In my Drawings the metal conductors c are represented as being each surrounded
with a glass tube f, a little larger in the bore than the wire, for the purpose of
steadying and giving rigidity to the metal conductor.
Figures 3 and 4 represent a lamp of otherwise similar construction to the lamp
hereinbefore described with reference to Figures 1 and 2, but arranged for the
reception of a number of carbons to be used simultaneously.
It is found advantageous to exhaust the air from the glass bulb or receptacle d
whilst the carbon contained within it, is raised (by the passage of a current of
electricity) to the same degree of incandescence as or to a higher degree of incan-
descence than that ultimately required to be produced in using the lamp as
described in the Specification to former Letters Patent granted to me, dated the
2nd January 1880, No. 18.
Having now described and particularly ascertained the nature of my said
Invention, and the manner in which the same is or may be used or carried into
effect, I would observe in conclusion that what I consider to be novel and original,
and therefore claim as the Invention secured to me by the hereinbefore in part.
recited Letters Patent is,-
First. Forming the carbon or carbons of an electric lamp from cotton thread,
converted by the action of sulphuric acid and carbonized, substantially as herein-
before described.
Second. In carbons formed from cotton thread, paper, or cardboard, constructing
the carbons with thickened ends by uniting the thickening material to the cotton
thread, paper, or cardboard by the action of sulphuric acid, substantially as herein-
before described.
In witness whereof, I, the said Joseph Wilson Swan, have to this my
Specification set my hand and seal, this Twenty fourth day of May, One
thousand eight hundred and eighty one.