AN IMPROVED ELECTRICAL CONDUCTING MATERIAL
Year: 1885

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I, CHARLES SCHANCK. BRADLEY, of Yonkers, in the County of Westchester, and
State of New York, United States of America, Electrician do hereby declare the
nature of my invention for "AN IMPROVED ELECTRICAL CONDUCTING MATERIAL
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 a composition of matter, being a substance which is a
conductor of electricity, impervious to liquils or gases, unaffected by water,
solutions of salts, acids, &c, and which is at the same time a material well
adapted to being rolled, cut, pressed, moulded, or otherwise worked into any desired
form.
This composition consists of gas-retort carbon, or its equivalent, and gutta-
percha or india-rubber.
The ingredients of the composition may be used in various proportions, and
various methods of mixing them may be employed; but I have found that excellent
results are obtained in the following way: I take from one to ten parts of finely
ground gas-retort carbon, and one part of gutta-percha or india-rubber, and
thoroughly incorporate these ingredients by rolling in the well-known manner in
which gutta-percha and rubber are usually worked. The mixture having been
properly made, the resulting material may then be pressed into the required form
in suitable moulds, it being made plastic for this purpose by slightly heating it.
In order to harden and strengthen the material, it may be vulcanized by any of
the well-known processes employed for gutta-percha and rubber. For example,
sulphur or some of the substances containing sulphur that are commonly employed
in vulcanizing may be added to the carbon and gutta-percha or rubber when they
are mixed together, and the subsequent heat and pressure to which the material is
subjected in order to bring it into the desired form will also vulcanize it.
Instead of using sulphur in the solid state, the vulcanization may be effected by
the use of liquids containing sulphur-such as chloride of sulphur, &c. For some
purposes, to be hereinafter pointed out, I prefer to vulcanize my material with
bromine, which is a well-known vulcanizing agent, instead of sulphur. The
bromine may be put in with the other ingredients when they are mixed, or it may
be applied in solution or in the vapour form. In fact any of the methods of
vulcanizing commonly made use of in the arts may be adopted,

page_text: The percentage of carbon in the material of course determines its electrical
conductivity, the greater the percentage of carbon the greater, of course, the
conductivity; but since the gutta-percha or rubber is the cement or binder which
holds the particles of carbon together, it is not advisable to attempt to increase the
conductivity by increasing the proportion of carbon, and consequently decreasing
the proportion of binder, beyond a certain limit, because beyond that point the
material becomes brittle, crumbly, and porous, so that it is no longer impervious to
liquids and gases. The relative proportions of carbon and gutta-percha or rubber
will depend upon the conditions in each particular case, varying from about equal
-parts of each to eight or ten parts of carbon to one of gutta-percha or rubber. The
mean between these limits-i. e., about three parts of carbon to one of gutta-percha
or rubber-will be found to be a very good mixture for general purposes, where
the maximum strength and electrical conductivity compatible with each other are
required.
The herein-described electrical conducting material possesses many decided
advantages over the ordinary baked carbon, which is used in the form of plates
and sticks in primary and secondary batteries, as well as for other electrical
purposes. First, my material is impervious to liquids and gases, hence it can be
used as a vessel or receptacle to contain them, which in many cases is a great
convenience. The imperviousness of my material also prevents liquids from
creeping up by capillary action and corroding the metallic connections, which
causes so much trouble in the case of porous carbon electrodes; second, the material
can be softened by slightly heating it, and while in that condition it may be rolled,
pressed, or moulded into any desired shape. In the same way two pieces may be
united so as to make an absolutely perfect joint; third, the material is strong and
tough, especially when vulcanized, whereas the ordinary baked carbon is weak and
brittle; fourth, the material will not disintegrate under the action of liquids as
ordinary carbon does.
It is well known that ordinary carbon is particularly apt to disintegrate when it
is employed as an electrode in electrolysis, because the carbon being porous the
metal or gas, as the case may be, set free by the electrolytic action forms to a
certain extent beneath the surface of the electrode, and acts mechanically to force
off particles of carbon; but my material, being non-porous, is free from this
trouble.
The herein-described material is useful for a great many electrical purposes; but
I have found it to be especially applicable in cases where a conductor of electricity
is required which is exposed to corrosive liquids or gases, conditions under which
no metals, except certain very expensive ones-such as platinum-can be employed.
One of the substances which compose the material is carbon, which at tem-
peratures below a red heat is as little affected by chemical action as any known
substance; and the other ingredient is gutta-percha, (which is preferable to india-
rubber for resisting chemical action,) which is used for making vessels to hold the
strongest acids.
In a secondary battery which I have invented, and described' in the speci-
fication of an application for Letters Patent bearing even date herewith N° 2463,
24 February 1885, electrodes are required which will withstand the action of
bromine which is set free when the battery is charged. I have used for this
purpose electrodes composed of the material which is the subject of the present
application and found them to be perfectly satisfactory; but I do not here claim
the application of this material to the above battery, as it is claimed in the
specification of my said application No 2463 A.D. 1885. Where my material is
used in the presence of bromine the gutta-percha is of course vulcanized with
bromine.
I am aware that it is old in the arts to inix clay, chalk, sand, and like substances
with gutta-percha and rubber in order to make a harder and cheaper material; but
this is essentially different from my invention, because all the ingredients and the
resulting compositions are non-conductors of electricity.

page_text: I am also aware that a mixture of graphite and india-rubber has been used for
packing and for journals; but this, strange to say, is not a conductor of electricity
either. For example, a mixture consisting of three parts, by weight, of graphite
and one of gutta-percha has a specific resistance over a million times as great as
that of graphite alone. This apparent anomaly is due to the fact that graphite is
soft, and each particle of it becomes coated with a film of rubber, which is an
electrical insulator, and prevents the particles from making contact, whereas gas-
retort carbon is hard and sharp. It has a grit, and the points of the particles cut
through the rubber and touch each other, making electrical connection.
A mixture of gas carbon and gutta-percha of a similar composition to the
graphite mixture referred to above (three parts of carbon to one of gutta-percha)
has a specific resistance only a few times greater than that of the gas carbon alone.
Thus graphite, which is essentially non-gritty in its nature, being a lubricator,
makes, when mixed with gutta-percha or rubber in any proportions that can be
practically used, a non-conductor of electricity, while gas carbon, coke, or other
carbon which is hard and gritty, produce, when mixed with gutta-percha or
rubber, a conducting material having the useful properties and advantages herein-
before set forth.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is
1. The herein-described electrical conducting material, consisting of gas-retort
carbon or other carbon which is hard and sharp, and gutta-percha or india-rubber.
2. The herein-described electrical conducting material, consist of gas-retort
carbon or other carbon which is hard and sharp, and gutta-percha or india-rubber,
said gutta-percha or india-rubber being vulcanized.
3. The herein-described electrical conducting material, consisting of gas-retort
carbon or other carbon which is hard and sharp, and gutta-percha or india-rubber,
said gutta-percha or india-rubber being vulcanized with bromine.
4. The herein-described electrical conducting material, consisting of ground
gas-retort carbon or other carbon which is hard and sharp, and gutta-percha or
india-rubber, said ingredients being mixed together by rolling.