IMPROVEMENTS IN ELECTRIC LAMPS
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by the said Desmond Gerald Fitz-Gerald
at the Office of the Commissioners of Patents on the 8th September 1881.
DESMOND GERALD FITZ-GERALD, of Brixton, in the County of Surrey,
Electrician. "IMPROVEMENTS IN ELECTRIC LAMPS."
My Invention relates to that kind of lighting apparatus in which a filament of
carbon is maintained in an incandescent state by the passage of an electric
current.
In producing the carbon filament I treat paper or any suitable vegetable fibre,
thread, or fabric with a concentrated solution of zinc chloride, which in most cases
I prefer to use cold. The material is then thoroughly washed, first in acidulated
water or a dilute ammoniacal solution, and afterwards in water, and lastly it is
carbonised whilst protected from contact with air, as is well understood. I make
the ends of the filaments considerably thicker than their central portion by forming
these ends of several folds or thicknesses of the material.
In establishing the contact between the ends of the carbon filament and the
conductors conveying the current, I prefer to cement the ends of the filament into
two short lengths of tube, preferably of iron, copper, silver, or platinum, by means
of a mixture of finely divided carbon and platinum-black made into a paste with
water, or with a solution of sugar or starch. The filaments thus cemented into the
tubes are again exposed to a high temperature whilst protected from contact with
air, as before, one end of each tube being left free for the reception of the ends of
the conducting wires which are to convey the current. The conducting wires pass
through a cork which fits into the neck of a glass vessel, or through a plug of
earthenware or other suitable refractory material, upon which the neck of this
vessel is contracted by the application of heat. A tube or tubes for the exhaustion
of air from the vessel, or for the passage into it of cyanogen or other suitable gas
may also pass through the cork or plug. In order to render the vessel air tight I
77

page_text: use first a fusible cement, such as marine glue, and afterwards an infusible cement
formed of litharge and glycerine, which in a short time becomes very hard and
impervious.
In order to facilitate the production of a partial vacuum within the glass
containing vessel, and to effect the removal of residual oxygen, and in some cases
of residual nitrogen or of cyanogen gas, I introduce within this vessel a wire or
supplementary carbon filament, suitably mounted so as to be heated to any required
degree by the passage of a current during and sometimes also subsequently to the
period of exhaustion. This wire may be formed either of an oxidisable metal, such
as iron or zinc, in which case when sufficiently heated it effects directly the
abstraction of oxygen, or it may be of inoxidisable metal, such as platinum, in which
case it may be utilised for raising the temperature of the atmosphere within the
glass vessel during the process of exhaustion, and also for heating an oxidisable
metal, such as magnesium or other suitable oxidisable substance, such as a metallic
sulphide placed in contact with the wire, and by means of which the abstraction
of oxygen or other gaseous bodies may be effected.
Before commencing the process of rarifying the atmosphere within the glass
containing vessel, I sometimes pass a current of superheated steam through this
vessel, afterwards filling it with an atmosphere of dry cyanogen gas; or I simply
pass a current of this gas through the vessel. In either case the residual gas may
be more or less perfectly absorbed by the action of an oxidisable metal or other
substance heated directly or indirectly by the passage of a current.
In order to indicate the degree of rarifaction within the glass containing vessel,
I enclose in it a manometer, which. may be formed of a length of glass capillary
tube closed at one end, and containing a minute quantity of mercury in close
proximity to this closed end.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Desmond Gerald Fitz-Gerald in the Great Seal Patent Office on the
8th March 1882.
DESMOND GERALD FITZ-GERALD, of Brixton, in the County of Surrey,
Electrician. "IMPROVEMENTS IN ELECTRIC LAMPS."
This Invention relates to improvements in electric lamps, and especially to that
kind of lighting apparatus in which a filament of carbon is maintained in an
incandescent state by the passage of an electric current.
The accompanying Drawings are to be taken as part of this Specification.
In producing the carbon filament I heat unsized paper or any suitable
vegetable fibre, thread, or fabric with a concentrated solution of zinc chloride,
which I prefer to use cold. I make the ends of the carbon filaments thicker than
their central portion by forming these ends of several folds, or layers, or thicknesses
of the material. When working with unsized paper, such as Swedish filtering
paper, to obtain filaments of any required resistance the sheet to be treated is laid
out in either one, two, or three layers, according as the resistance is desired to be
high, medium, or low, and is then temporarily fixed to any convenient flat smooth
surface or board, while the edges to be thickened for the purpose of avoiding
excessive heating of the contacts are suitably folded fourfold, sixfold, or eightfold.
I prefer to arrange the successive layers thus formed in gradation, so that when the
filaments are cut from this sheet the cross section increases gradually towards the
extremities, consequently giving a low resistance actually in the metal contact-
tube, while the number of layers diminish step by step to the normal thickness
where the light is required. Next, the sheet is to be rolled or pressed, and having
obtained sheets of the required form, viz., thin over the central portion and thick
at the edges, gauged strips can be conveniently cut, placed over a mould, and
directly treated with the zinc chloride solution by immersing them (while secured
by thread or otherwise to the mould) in a vessel containing the solution; but the
operation of cutting the gauged strips may be advantageously carried out after the
unsized paper or any suitable vegetable fabric has been treated with the zinc
chloride solution. The specific gravity of the zinc chloride solution used should be
1-876 or thereabouts, and in order to prevent disintegration or loss of substance the
material should be removed from the solution as soon as the process of gelatinisation
is complete.
When the material has been thus treated and sufficiently gelatinised it is
thoroughly washed, first in water slightly acidulated with hydrochloric acid, next
with a dilute solution of ammonia, and lastly, in water; then it is left to
thoroughly dry, becoming when ready for use very tenacious. Or after the
material has been partially dried it may advantageously be subjected to pressure
between plates or slabs of porous material (such as lithographic stone) shaped or
rubbed down so as to give the required difference of thickness between the ends
and the central portions of the strips.
When a thread (for instance of crotchet cotton) is used for the production of the
filament the ends may be thickened either by their being "croched" or by wrapping
them with other thread. When natural fibres are used they may be diminished in
the central portions by scraping or other suitable means. Both the thread and the
natural fibre are treated by the zinc chloride in the manner already described, but
the pressure may be omitted.
The filaments produced as described are now carbonised whilst protected from
the air. This is effected by placing a number of them on a mould of graphite

page_text: or other material of suitable form, and being secured loosely near their ends with
thread or other suitable means, they can be placed in a crucible packed with fine
carbon and completely covered with the same, so that no air can attack them when
the crucible or vessel is closed, and the whole is then placed in a furnace and raised
to a very high temperature.
In establishing the contract between the ends of the carbon filament A (see
Figures 2, 5, and 6 of the accompanying Drawings) and the conductors conveying
the current, I prefer to cement the ends of the filament into two short lengths of
tube B, preferably of copper, but iron, silver, or platinum may be used (experience
has shewn that, in the case of copper, the tubes should not be less than of an
inch in length) by means of a mixture of finely divided carbon and a small propor-
tion of platinum-black (C) made into a paste with water, or a solution of sugar,
starch, or other like suitable material.
The filaments A thus cemented into the tubes B by tightly packing the paste C
around their ends within the tubes are allowed to stand until the paste is dry,
when they are again exposed to a temperature not exceeding 1900° F. in the case
of copper, whilst protected from contact with air as before, one end of each tube
being left free for the reception of the ends of the conducting wires D, E, which
are to convey the current. The actual mounting of the carbon filaments in their
tubes, carbonising and attaching to the conductors by means of a slot-catch F, is
effected in the following manner:-The metal tubes B of the stated required
length are firmly bound with copper wire to a graphite or other block G, Figure 7,
having slots at opposite points in its longest diameter, such slots receiving the said
tubes Band keeping them rigidly parallel and at the required distance apart; this
block serves also as a holder, whilst the carbon filaments A are being cemented
into the tubes, and if fixed so as to allow the ends of the metal tubes to project
at least a of an inch beyond the mould, also aids in the manipulation during the
final establishment of contact between the wire conductors D, E, and the said
metal tubes B. The method of establishing contact is very simple. Having
plugged up half the lengths of the interior of the tubes with the extremities of a
U shaped pieces of wire H, preferably of copper, and of the requisite diameter,
thus allowing the tubes to be placed and maintained parallel, the tubes should be
reduced in thickness around one third of their outer circumference, very near the
ends which have to receive the conductors, as at F, so that the thin scales of metal
thus left after filing can easily be depressed into corresponding nicks in the
-conductors-when-they-are-insorted-after-the-removal-of-the-plugs. If_the_
conductors are much smaller than the bore of the tubes the difference may be
supplied by a plug forming a suitable bed for the conductor to rest against. When
a good contact is secured the block G can be slipped away without straining the
carbon filament. The conducting wires (when they by reason of their. length
require such support) should have a bridge of porcelain (not shewn) or other suitable
material attached to fix them rigidly together before the filament of carbon is
mounted.
The conducting wires B, preferably of platinum, pass into a hollow glass stopper I,
shewn in elevation, Figure 1, and are sealed by fusion of the glass directly into
suitable arms J, K, projecting therefrom. A third like arm L with its wire M
sealed therein and passing through projects likewise from the stopper. This is for
à supplementary filament or wire N, which is introduced (for the absorption of
residual gases) between its wire and the wire of one of the other conductors
(shewn attached to D). This arrangement will be found more fully described herein-.
after. When the filament A is mounted on these conductors and the supple-
mentary fibre is also mounted, the stopper I is introduced into the neck of a glass
vessel or bulb O (Figure 3) and hermetically sealed (by fusion) towards its base (as
seen at Figure 2). A tube leading from the top of the bulb serves to connect it to
the exhaust apparatus. The base of the lamp or hollow plug may be filled in first
partially with a minute quantity of fusible cement, such as gum copal, introduced

page_text: as a powder and afterwards heated, and then with an infusible cement Q composed
of litharge and of glycerine diluted with about two thirds its volume of water,
which mixture rapidly becomes very hard and impervious.
In order to facilitate the production of a partial vacuum within the glass
containing vessel, and to effect the removal of residual oxygen, and in some cases
of residual nitrogen or cyanogen gas, I introduce within this vessel as before stated
a wire or supplementary carbon filament or wire N suitably mounted so as to be
heated to any required degree by the passage of a current during, and sometimes
also subsequently to, the period of exhaustion. This wire may be formed either
of oxidisable metal, such as iron, or zinc, in which case, when sufficiently heated, it
effects directly the abstraction of oxygen; or it may be of inoxidisable metal, such
as platinum, in which case it may be utilised for raising the temperature of the
atmosphere within the glass vessel during the process of exhaustion, and also for
beating an oxidisable metal, such as magnesium or other suitable oxidisable
substance (see magnesium coil P, Figures 2 and 4) placed in contact with the wire,
and by means of which the abstraction of oxygen or other gaseous bodies may be
completely effected. Of these methods I prefer to use iron wire surrounded with
magnesium ribbon. I connect one of the conducting wires D with fine wire N of
iron, covered spirally with magnesium ribbon P to a third current conveying
conductor M. Experiment has shewn that the length of iron wire used should not
exceed 1 inches. The magnesium ribbon may be inch in length. It is found
that every trace of oxygen is absorbed by the magnesium on the wire.
While the lamp is under the action of the mercury pump a current is passed
through the wire filament N of sufficient strength to produce a low red heat; at
the same time external heat may be applied to prevent any of the magnesia formed
from cracking the glass should it fall away from the heated wire. When the
magnesium has absorbed all the residual oxygen the connections are shifted to the
two main conductors D, E, and the carbon filament is raised to the required
temperature, thus driving out any occluded gases which will be carried away by
the action of the pump. The auxiliary fibre may again be connected to the battery
or other electro motor and heated, when the magnesium will absorb any trace of-
oxygen that may have been left and also as it would appear some portion of the
residual nitrogen. Having obtained the required vacuum the glass vessel is
hermetically sealed by fusing the tube at the top of the lamp.
In order to indicate the degree of rarifaction within the glass containing vessel
I enclose in it a manometer (not illustrated) which may be formed of a length of
capillary tube closed at one end and containing a minute quantity of mercury in
close proximity to this sealed end. This tube may be bent into convenient lengths
for economy of space, and the unsealed end has a small bulb with a short neck
placed over it, but not fitting tightly enough to prevent the passage of air. This
bulb prevents the mercury from being drawn entirely out of the capillary tube by
the exhaustion into the glass containing vessel. The manometer for convenience
of fixing is bound onto one of the conducting wires in one or two places.
I claim as my Invention to be secured by the herein before in part recited Letters
Patent,―
1. In the manufacture of carbons for electric lighting, the use of a concentrated
solution of zinc chloride, substantially as and for the purpose or purposes herein-
before set forth and described.
2. The use of a cement composed of finely divided carbon and platinum-black,
substantially as and the purpose or purposes hereinbefore set forth and described.
3. The combination for or complete system of attaching the carbon filaments to
the metal current conductors, substantially as and for the purpose or purposes
herein before set forth and described and illustrated in the accompanying Drawings.
4. For facilitating the production of a vacuum and the complete absorption
of oxygen within the glass containing vessel of electric lamps, the use of a
supplementary filament or wire oxidisable or non-oxidisable and either of these in

page_text: combination with an oxidisable metal, substantially as and for the purpose or
purposes hereinbefore set forth and described.
5. The use of a manometer in a glass containing vessel of an electric lamp,
substantially as and for the purpose or purposes hereinbefore set forth and
described.
In witness whereof, I, the said Desmond Gerald Fitz-Gerald, have hereunto
set my hand and seal, this Eighth day of March, in the year of our Lord
One thousand eight hundred and eighty-two.
Witness,
JOHN W. GRAY, C.E.,
Patent Agent,
27, Southampton Bldgs.,
W.C.
DESMOND G. FITZ-GERALD. (LS.)