Improvements in the Manufacture of Filaments for Incandescent Electric Lamps.
Year: 1889

page_text: Date of Application, 9th Apr., 1889
Complete Specification Left, 15th Aug., 1889-Accepted, 28th Sept., 1889
New York, United States of America, Clergyman.]
Improvements in the Manufacture of Filaments for Incandescent
Electric Lamps.
I, HENRY HARRIS LAKE, of the firm of Haseltine, Lake & Co., Patent Agents.
Southampton Buildings, in the County of Middlesex, do hereby declare the nature of
this invention to be as follows:-
This invention relates to an improved method of manufacturing filaments for
incandescent electric lamps, which includes the process of treating the carbonized
filament for the purpose of strengthening and toughening it and the various steps
and manipulation of the product substantially as hereinafter more fully described.
In carrying the said invention into practice I take any of the usual forms of
carbon, such as are derived from baking various vegetable fibres, among which
linen thread, tampico, or cocoa fibre are examples. After these fibres have been
carbonized by baking them at a very high heat (between 1500° and 2000° C.)
I dip or soak them in a saturated solution of tungsten trioxide dissolved in aqua
ammonia or in any of the fixed alkalies. The filaments thus treated are dried and
then subjected to a high heat by incandescing them electrically in the presence of
dry hydrogen gas. Or the carbonized filaments may be connected to a negative pole
of a battery and suspended in an electrolyte,composed of soluble tungsten compound in
an aqueous solution and depositing the metal tungsten on the filament by immersing an
anode of platinum in the solution and causing the electric circuit to be completed.
The filament is withdrawn after a sufficiently heavy coat of the metal has been
deposited and then dried and finally incandesced electrically in an atmosphere of
hydrogen as before, resulting in both cases, in a coating of tungsten metal on the
carbon fibril. More or less of the tungsten is deposited in with the carbon thus
filling up the pores which appears to produce in the filament a property similar to
that conferred on steel by the addition of tungsten namely, a great increase in strength
and elasticity. Obviously the soaking, drying and subsequent reduction of tungsten
compounds to the metal may be repeated several times until sufficient quantity of
tungsten has been incorporated with and deposited on the carbon.
I do not confine myself to any particular period in the process for impregnating
the fibrils with a tungsten compound nor to the particular compound herein described
as others are available.
I also do not confine myself to any particular electrolytic bath in which to
deposit the tungsten on the fibrils by electrolysis.
Dated this 9th day of April 1889.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Filaments for Incandescent
Electric Lamps.
I, HENRY HARRIS LAKE, of the firm of Haseltine, Lake & Co., Patent 'Agents,
Southampton Buildings, in the County of Middlesex, do hereby declare the nature of
this invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
This invention relates to an improved method of manufacturing filaments for
incandescent electric lamps.

page_text: An important feature of the said invention consists in a novel process of treating
the carbonized filaments for the purpose of rendering the same stronger and tougher
than heretofore.
The said invention moreover comprises other improvements hereinafter set forth.
In carrying my said invention into practice, I employ any of the usual forms of
carbon, such as are derived from various vegetable fibres as for example linen-thread.
tampico, or cocoa fibre. The said fibres having been first carbonized by baking them
at a very high temperature (say between 15000 and 2000° C.) the resulting filaments
of carbon are dipped or soaked in or moistened with a saturated solution of tungsten
trioxide dissolved in aqua ammonia or in any of the fixed alkalies. The filaments
thus treated are dried and then highly heated or rendered incandescent by means of
electricity in an atmosphere of dry hydrogen gas, whereby the tungsten compounds
are reduced and the pores of the filament are filled with metallic tungsten.
In some cases the said carbonized filaments are connected to the negative pole of a
battery and suspended in an electrolyte composed of an aqueous or other suitable
solution of a tungsten compound and the metal tungsten is deposited on the filament
by immersing an anode of platinum in the solution and causing the electric circuit to
be completed. The filament is withdrawn when a sufficiently heavy coat of the metal
has been deposited thereon and is then dried and finally, rendered incandescent by
means of electricity in an atmosphere of hydrogen gas as herein before mentioned.
The result in both cases is that a coating of tungsten metal is deposited upon the
carbon filament. More or less of the tungsten penetrates into the pores of the
carbon and thus fills up the said pores, thereby imparting to the filament a property
analogous to that conferred on steel by the addition of tungsten, namely, a great
increase in strength and elasticity.
It is obvious that the hereinbefore mentioned soaking and drying of the tungsten
compounds and their subsequent reduction to the metal may be repeated several times
until a sufficient quantity of tungsten has been incorporated with and deposited upon
the carbon.
It is obvious moreover, that the duration of the above described process may be
varied according to circumstances, and that any suitable tungsten may be used or any
suitable electrolytic bath employed to deposit the tungsten on the filaments by
electrolysis.
i
In the accompanying drawing is shown a diagram illustrating one method of
carrying the said invention into practice.
A is a chamber in which is placed the filament intended to be treated, B is an air
pump, C is a retort, D, D¹, are dynamo-electric machines.
The air-pump B is connected by means of a suitable pipe a with the chamber A.
is a stop cock or valve for cutting off the connection with the air pump B when
required.
The retort C is provided with a lamp c or other means for heating the same and is
connected with a chamber d in which is situated a coil d formed of suitable wire
which is connected by means of wires or conductors d with the dynamo-electric
machine D and is heated by means of an electric current therefrom. The chamber d
communicates by means of a pipe e with the pipe a and through this pipe with the
filament chamber A. el is a stop cock or valve provided in the said pipe e for
controlling the flow of hydrocarbon when necessary. f is another stop cock or valve
for the admission of air to the chamber A when necessary. g is the filament to be
treated which is placed in the said chamber A. and is connected by means of wires or
conductors with the dynamo-electric machine D¹.
The improved manufacture is carried on by means of the said apparatus as follows,
that is to say:-The filament g to be treated is first dipped or soaked in a saturated
solution of tungsten trioxide dissolved in aqua ammonia or in any of the fixed alkalies.
The said filament g is then dried placed in the chamber A and is subjected to a high
heat, or rendered incandescent by means of a current from the dynamo electric
machine D in the presence of pure dry hydrogen gas. This hydrogen gas is
produced in the retort C by subjecting some pure hydrocarbon such as naphthaline

page_text: of
crystals (C₁ Hg) to destructive distillation which causes all the carbon contained in
such compound to be removed as a bulky black powder leaving pure hydrogen behind,
in a gaseous state. A suitable quantity of the hydrocarbon to be distilled is placed
in the retort C and subjected to heat by means of the lamp c. The resulting vapors
of hydrocarbon are passed into the chamber d in which is contained the coil
wire, which is heated to bright redness by means of the dynamo electric machine D.
The hydrocarbon vapor liberated from the retort C on passing through the chamber d
containing the red hot coil d' is decomposed and the carbon is deposited upon the said
coil in the form of lamp black. When it is certain that the hydrocarbon gas or
vapors have become thoroughly decomposed and nothing but pure dry hydrogen in a
gaseous form remains, the said hydrogen is admitted into the chamber A wherein
the incandescent filament is situated.
The result is that the tungsten compound in the filament is reduced or decomposed
into its elements, and the tungsten inetal remains in and on the carbon filament.
The carbon filament itself at the high temperature to which it must be subjected
becomes partially soft, and on cooling shrinks so as to form a very dense and tough
fibre which is a good conductor of electricity.
By alternately treating the filament with a solution of a tungsten compound and
drying the same and subsequently rendering it incandescent by means of electricity
in pure hydrogen as described, the electrical conductive power of the filament can be
regulated, at the same time ensuring density and toughness of the filament and
thorough incorporation of the tungsten with the carbon.
I am aware that there are less costly methods of producing hydrogen, for instance
by dissolving zinc or iron in dilute hydrochloric or sulphuric acid, but the hydrogen
obtained by such means always contains more or less admixture of acid or aqueous
vapors which would be highly injurious, inasmuch as the said vapors would act on
the incandescent filament so as to instantly oxidize portions of it thus causing weak
spots with the result that an imperfect filament is produced.
The hydrogen obtained from the destructive distillation of a hydrocarbon is
absolutely free from such objections, and should a trace of carbon vapor enter into the
chamber wherein the filament is placed, the only damage it could do would be to
combine with the tungsten that rests on the surface of the filament to form tungsten
carbide which would simply flake off doing no further damage, in this case the
exterior tungsten can be easily replaced by a subsequent treatment of the filament as
above described.
Instead of the process above described the raw or unwrought fibres may be
saturated with a tungsten compound before baking, or carbonizing and be then
placed in a crucible packed with carbon dust and subjected to an intense white heat.
The result in this case is also to reduce the tungsten compound to metallic tungsten
which is incorporated in the carbon filament.
I do not confine myself to any particular period in the process for impregnating
the fibres or filaments with a tungsten compound or solution.
Having now particularly described and ascertained the nature of the said invention
and in what manner the same is to be performed, as communicated to me by my
foreign correspondent I wish it understood that I claim :-
First. The improved method or process of manufacturing filaments for incandescent
electric lamps, consisting in saturating a carbon filament with a tungsten compound,
and reducing such compound to metal tungsten, or incorporating with the carbon
filament and coating the same with tungsten by electrolysis, substantially as herein-
before described.
Second. The improved process consists in electrically heating a carbon filament
impregnated with a tungsten compound in an atmosphere of pure dry hydrogen
obtained from the destructive distillation of a hydrocarbon, substantially as herein
before described and for the purpose specified.
Third. The improved process consisting in impregnating a carbon filament with a
solution of a tungsten compound, drying the same, and then subjecting it by means of

page_text: electricity whilst in an atmosphere of dry hydrogen obtained from the destructive
distillation of a hydrocarbon to a temperature at which the carbon becomes partially
soft, substantially as and for the purpose set forth.
Fourth. The improved process consisting in regulating the electrical conductive
power of a carbon filament by alternately submitting the same to a bath containing a
tungsten compound, drying the same, and then subjecting the same by means of
electricity to a high temperature while enclosed in a chamber containing pure dry
hydrogen prepared by the destructive distillation of a hydrocarbon, substantially as
described, and for the purpose specified.
Fifth. A filament for an incandescent electric lamp composed of metal tungsten
and carbon, substantially as herein before described.
Dated this 15th day of August 1889
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.