MENTS IN THE MEANS OR APPARATUS FOR OBTAINING LIGHT BY ELECTRICITY, AND IN THE MANUFACTURE OF MATERIALS TO BE EMPLOYED THEREIN."
Year: 1879

page_text: PROVISIONAL SPECIFICATION left by St. George Lane Fox at the Office of
the Commissioners of Patents on the 20th March 1879.
"IMPROVE-
ST. GEORGE LANE Fox, of Telegraph Street, in the City of London.
MENTS IN THE MEANS OR APPARATUS FOR OBTAINING LIGHT BY ELECTRICITY, AND
IN THE MANUFACTURE OF MATERIALS TO BE EMPLOYED THEREIN."
My Invention has reference to obtaining light by the incandescence of a portion
of a continuous conductor, through which a current of electricity is made to pass,
and the improvements chiefly relate to the manufacture of the material of which
such portion of the conductor as is made incandescent is composed. For the manu-
facture of this material I employ two highly refractory materials, one of which is
a conducting material, such for example as plumbago, and the other a non conducting
or bad conducting material, such for example as magnesia, zirconia, lime, steatite,
or earthy matter. I mix or combine these materials in such proportions as to make
the whole give a specific resistance in accordance with the electro motive force
employed for producing the light. Where an electro motive force of 140 volts is
employed in order to produce a light somewhat equal in power to an ordinary gas
jet, the portion of the continuous conductor which is made incandescent, and which
portion I will call the "luminous bridge," should have a resistance of about
300 ohms or British Association units. To attain this high resistance, and keep
the bridge of small size, the quantity of non-conducting material would have to be
considerably in excess of the conducting material. If however a smaller electro
motive force is employed the conducting power, and consequently the proportion of
the conducting material, will have to be increased.
The manner in which I prefer to manufacture the luminous bridge is as follows:-
I grind or reduce the materials to impalpable or very fine powder, and then with
the aid of a little moisture I unite them into a compact piece of the required form
by means of powerful pressure. Sometimes I add a trace of a silicate or other
fusible material for the purpose of assisting in the hardening or increasing the
toughness of the combined material. Sometimes also I produce on the surface a
very hard film of carbon, and this I effect after the bridge has been made by
heating it at a high temperature with a hydro carbon; for example, by raising it
to an incandescent state by sending a current through it while immersed in a dense
hydro carbon. In order that the temperature of the luminous bridge may be as
much as possible equal throughout I make it narrower at and near the ends than in

page_text: the middle. I connect or fit each of the ends to a piece of plumbago or other con-
ducting material, and union to these pieces may be made at the time of moulding
the luminous bridge by placing powdered plumbago in parts of the mould contiguous
to the parts which receive the mixture for forming the bridge. The bridge and
plumbago pieces form what I may call an electric candle, and are held in any
suitable holder or holders. According to one method the plumbago pieces are held
by iron or other metallic clips, to which fine conducting wires are connected.
According to another method the said pieces are held loosely in metallic supports.
having sufficient elasticity to allow of the insertion of the candle between them,
electrical contact being formed by the pressure between the plumbago pieces and
the metallic supports due to the weight of the candle. According to a third
method the said pieces enter passages in a block of steatite, adamant, or other
suitable material, in which they are connected with the wires of the continuous
conductor; and in order to increase the conductivity, and to enable the plumbago
to be soldered to the conducting wires, it may be coated with copper or other
metal.
The parts before described are hermetically enclosed within a globe or other form
of glass or other suitable material, through one portion of which the conducting
wires are hermetically carried. From this globe all trace of oxygen, carbonic acid
gas, water, and any gas or vapor capable of attacking or affecting the material of
the luminous bridge when at a high temperature must be removed.