Year: 1886

page_text: Date of Application, 29th June, 1886.
Complete Left, 24th Mar., 1837.
Complete Accepted, 26th Apr., 1887
ILLIAM MAXWELL Engineer of mayor am
the nature of this invention to be as follows:-
In the preparation of carbon filament or other refractory conductors for incandescent
electric lamps a process technically known as "flashing" is employed which consists
in electrically heating the conductor in a vessel containing hydrocarbon gas or
vapour.
Coal gas is usually employed as the most convenient agent but by the ordinary
method of flashing it frequently produces a dull sooty or mottled deposit upon the
surface of the filament or conductor.
Various means have been employed to purify the gas before using but without
marked results for the faulty deposit chiefly springs from the use of a limited
atmosphere of the hydrocarbon which becoming unduly heated rapidly alters and
deteriorates during the process.
My invention is an improved process or method for producing a clean dense and
homogeneous deposit or layer of carbon upon the surface of a filament or other
refractory conductor while at a high temperature from coal gas or other hydrocarbon
gas or vapour..
I electrically heat or "flash" the filament or conductor in a current or hydro-
carbon gas or gas and vapour which has a rapidity or strength of flow sufficient to
overcome the tendency to form convection currents within the "flashing" vessel and
so prevents any return of the altered and vitiated products towards the filament or
conductor.
In order to obtain a slow and dense deposit I may dilute the hydrocarbon gas with
nitrogen hydrogen or other suitable gas which may be without injurious action upon
the substance of the conductor and lower the pressure to any required degree by means
of an air pump.
In order to obtain a quick deposit I may charge the hydrocarbon gas with a
proportion of hydrocarbon vapour and use a higher pressure or temperaturo.

page_text: I prefer to maintain the current of coal gas or other hydrocarbon gas or of hydro-
carbon gas and vapour at a low temperature and under atmospheric pressure.
In carrying out my invention I may use a close case or chamber of any suitable
construction furnished with means for observing the conductor or conductors under-
going treatment and communicating with an air or exhaust pump and with supplies
of the gases vapours etcetera required during the process.
Any usual forms of pressure guages and of electrical instruments may be employed
and also any suitable standard of light.
In order to limit or control the deposit of carbon upon the filament or conductor I
prefer to use electrical instruments or appliances-automatic or otherwise—which will
indicate the strength of current in use so that a filament or conductor of any given
quality and cross-section may be incandesced with a certain electrical current that
may be specified in amperes or in fractions of an ampere.
'
Two or more filaments or conductors may be treated together in series or in
parallel.
Conductors for Incandescent Electric Lamps.
I, WILLIAM MAXWELL 34 Claybrook Road Fulham, S.W. 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 :-
In the preparation of carbon filaments or other refractory conductors for incan-
descent electric lamps, a process technically known as "flashing" is employed, which
consists in electrically heating the conductors in the presence of a hydrocarbon gas or
vapour until a specified resistance is reached, the heating being intermitted for the
purpose of comparing the resistance attained, with a standard.
Coal gas is a convenient agent for the process, but as ordinarily used-in limited
quantity it is unsatisfactory, for this gas frequently produces upon the conductor a
deposit of carbon of variable appearance and quality, and of faulty structure, and the
walls of the flashing vessel become more or less covered and obscured by sooty
particles.
Again testing the electrical resistance of conductors thus treated does not indicate
with sufficient exactness the strength of current required for their proper incan-
descence.
My invention relates to a method of producing a pure, dense and homogeneous
deposit of carbon upon carbon filaments or other refractory conductors for incan-
descence lamps, from coal gas or other hydrocarbon gas or vapour, this method being
such that I can employ a very high temperature in flashing, without any intermittence

page_text: being required for testing, while great accuracy can be attained in manufacturing a
number of lamps for incandescence in parallel or series.
Having ascertained the sectional area of the filament or conductor for treatment, I
electrically heat or "flash" it to a high incandescence in a vessel through which a
stream of coal gas or other hydrocarbon at reduced pressure is caused to flow with
such velocity that there is practically no circulation due to convection currents within
the vessel, such as might bring portions of the altered or vitiated atmosphere back to
the conductor. I determine the extent of the deposit by ascertaining the strength of the
electric current required to maintain the conductor at a standard incandescence, and
when I find that the electric current has attained the desired strength I open the
circuit and remove the heated conductor. I vary the treatinent according to the
nature of the conductor; for example, in heating carbon fibres or filaments of dense
structure and small cross-section, I sometimes mix and dilute the hydrocarbon gas
with nitrogen, hydrogen or other gas or gases that will not act injuriously upon the
substance of the conductor, and I maintain the atmosphere in the vessel at a low
pressure by continuous exhaust. The carbon deposit is thus slowly formed and is of
great density.
In treating carbon conductors of large size and open structure, and especially for
the formation of junctions or "mounts," it is sometimes preferable to use the hydro-
carbon gas in admixture with a carbonaceous vapour from a volatile liquid, such as
Benzole or Carbon bisulphide. The gas forms a suitable vehicle for the vapour,
effecting its transference through the depositing vessel at a more rapid rate than-
could be otherwise attained. By this means a homogeneous deposit of carbon can be
quickly produced.
In carrying out the process, I use an air-tight case which can be conveniently made
in the following manner. On a base of insulating material, through which the
necessary pipes and electric connections pass air-tight, is placed a tall narrow glass or
metal bell or receiver, the joint between it and the base being made tight by a
caoutchouc ring. The gas supplied enters the vessel at the base and passes from the
top through a pipe connected with the exhaust, the rapidity of flow, and the pressure,
being regulated by taps on the entrance and exit pipes.
Owing to the extreme brilliancy of the conductor during the process of deposition,
it is necessary to protect the eyes of the operator and to obscure the light to such a
degree that it may be conveniently compared with a standard.
The vessel, when it is of glass, should therefore be furnished with an opaque cover,
this cover or the vessel when it is itself opaque having a sight hole fitted with a dark
glass, or a cell containing dark liquid such as iodine solution.
The obscuration may be such that the incandescent conductor shall appear to have
a certain low degree of luminosity such as may be compared with a suitable standard
of light; or the obscuration may be so great as to render. comparison unnecessary,
the fact of the conductor becoming visible indicating that tho required incandescence
is attained. As the operation proceeds, the electrical current is increased so as to
maintain the apparent luminosity, and when the desired limit of current is reached,
the circuit is opened either by a switch worked by hand or automatically by an
electric or magnetic "cut-out." Although this mode of testing is of advantage,
obviously the usual testing for resistance may be applied either separately or conjointly
with the testing for current.
I sometimes connect in series with the filament for treatment a glow lamp having a
conductor that will attain a low degree of incandescence when the electric current
reaches the specified limit; when this lamp glows, it is known that the deposition has
been carried to the desired limit.
Two or more filaments may be connected either parallel or in series and treated at
the same time.
To facilitate observation and comparison, it is advisable to carry out the process in
a dark or artificially illumined chamber.
In applying the process described to the manufacture of electric lamps which are to
have a certain candle power whether they are connected parallel or in series, I select

page_text: a number of filaments or conductors of similar quality, the sectional dimensions of
which correspond, as ascertained by a micrometer gauge or otherwise; I electrically
heat these to a certain standard of light or incandescence in the vessel having a
stream of gas, containing hydrocarbon flowing through it, and I continue this heating
until the electric current passing through each is of the required strength, I then
open the circuit, remove the heated filaments, and cut and mount them in equal
lengths.
Throughout the process the conductor heated should be flashed to a high incan-
descence, while the pressure and temperature of the gaseous fluid passing through the
vessel should be maintained low and constant. In treating fine filaments, the pressure
may best be from one twentieth to one fifth of an atmosphere, for coarser conductors
the pressure may be higher.
The gas employed should be dry and may if required be kept cool by using a
refrigerator.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed, I declare that what I claim is :-
1. In the preparation of carbon filaments or other conductors for incandescent
electric lamps, electrically heating them in a vessel through which continuously during
the process is caused to flow a stream of coal gas, or equivalent hydrocarbon fluid at
a reduced pressure and constant temperature, substantially as described.
2. The herein described method of controlling the deposit of carbon on a conductor
for an incandescent lamp by first gauging its sectional area and then depositing
carbon on the conductor while it is electrically heated to a standard incandescence
until the electric current required attains a predetermined strength.
Dated this 24th day of March 1987
ABEL & IMRAY,
Agents for the Applicant.