IMPROVEMENTS IN APPLIANCES OR APPARATUS FOR OR APPERTAINING TO THE PREPARATION OF CARBON FILAMENTS
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by Alexander Ritchie Leask and
Frederick Peter Smith at the Office of the Commissioners of Patents on the
30th June 1882.
ALEXANDER RITCHIE LEASK and FREDERICK PETER SMITH, both of Holborn
Viaduct in the City of London. "IMPROVEMENTS IN APPLIANCES OR APPARATUS
FOR OR APPERTAINING TO THE PREPARATION OF CARBON FILAMENTS.”
Carbon filaments require to be specially treated after they are made to regulate
the amount of their resistance to the current and to make them of even resistance
throughout their length. This is usually done by placing them in a vessel con-
taining carburetted hydrogen gas and passing a current through them-technically
known as "flashing." Our improvements relate to the appliances or apparatus to
be employed in the "flashing" process.
The whole is by preference arranged something after the manner of a pedestal
office desk at which the operator can sit the apparatus being almost entirely closed
in. The materials and exact form may in most cases be varied but the following
may be taken as a description of the apparatus in a workable form: A glass vessel
is provided into which leads a pipe for the gas supply and from it leads another
pipe to take off the waste gas. A regulator with index and sector or equivalent
is provided upon or in connection with the supply pipe to regulate the quantity of
gas within the vessel. There is a suitable aperture in the top of the vessel through
which the tongs or tool which holds the filament to be tested is inserted; a rubber
plug closes the aperture. This tool consists of two rods having a spring catch to
each somewhat like the keys of a flute for holding the ends of the filament and
the springs are adjusted so as not to crush the filament, as often happens with the
screw-clip previously used. Each rod carries a projection which presses upon and
makes contact with a spring forming the end of the lead and return wires which
convey the current, so that when the tool is pushed into the vessel contact is made
and a current passes through the filament, and when withdrawn, contact is broken.
An ordinary arrangement of battery galvanometer and testing bridge is employed
which, being well understood by persons skilled in the art, does not require special
description here.
When the current is passed through the filament the gas in the vessel is decom-
posed and a deposit of carbon takes place upon the filament and since the

page_text: resistance is greatest where the filament is thinnest a greater amount of heat is
generated at that part and a greater deposit of carbon takes place there thus
tending to equalize the thickness of the filament throughout its length. A piece of
coloured glass is inserted in the wall of the vessel (or it may be made entirely of
coloured glass) to observe the filament through and a switching or shunting device,
preferably operated by means of a foot pedal is employed so that when the pedal
is moved one way contact is made with the wires from and to the dynamo-machine
for "flashing and when moved in the opposite way contact is made with the
battery system and galvometer for testing the resistance of the filament. An
electro magnet is placed upon dynamo return wire and a contact breaker kept
out of contact by a spring except when pressed, is placed in connection with the
same wire. This consists of an iron jar or vessel open at the top to which the wire
is connected; in this jar is a little water and into this a plunger (when pressed by
the operator) dips, but is usually kept clear by means of the spring; the return
wire is attached to this plunger. The water serves to prevent the escape of gases,
which were a great source of annoyance and injurious to health under the old plan
of making contact by means of a soldering bit and a plate of zinc.
The apparatus is used as follows. The filament is placed in the clips and
inserted into the vessel containing the gas and the tool pressed in till contact is
made with the springs, the treadle is moved and contact made by the shunting
device with the current from the dynamo which is not strong enough to flow
steadily through the filament and the plunger of the contact breaker being.pressed
in and the resistance being less than that of the filament the current flows through
the contact breaker, but the plunger being suddenly released, flies up and the
reaction of the electro-magnet sends a "flash" through the filament. The pedal
being again moved the current from the dynamo is cut off. and that from the
battery is connected with the filament which can now be tested. As many flashes
are employed as is necessary to cause a sufficient deposit of carbon upon the
filament to bring it down to the required resistance.