IMPROVEMENTS IN INSULATING ELECTRICAL CONDUCTORS
Year: 1883

page_text: LETTERS PATENT to Alfred Julius Boult of the firm of W. P. Thompson
& Boult of 323 High Holborn in the county of Middlesex Engineer for an
Invention of "IMPROVEMENTS IN INSULATING ELECTRICAL CONDUCTORS
a communication to him from abroad by James Gardner Sanderson of New
York, United States of America
C
PROVISIONAL SPECIFICATION left by the said Alfred Julius Boult at the
Office of the Commissioners of Patents on the 17th May 1883.
ALFRED JULIUS BOULT of the firm of W. P. Thompson & Boult of 323 High
Holborn in the county of Middlesex Engineer "IMPROVEMENTS IN INSULATING
ELECTRICAL CONDUCTORS a communication to me from abroad by James Gardner
Sanderson of New York United States of America
"'
The object of the invention is to provide a compound for insulating electrical
conductors, capable of being applied to them in a liquid condition, which afterwards
solidifies or hardens, retaining at the same time a certain degree of flexibility, and
thus forms not only a superior insulating covering for the conductors, but also
affords a sufficient mechanical protection for the same, whereby the employment of
special protective devices may in many instances be dispensed with.
The essential ingredients which are employed in making this improved compound
are asphalt or bitumen or other like substance, a metallic oxide, which is a
non-conductor of electricity, and sulphur; and the method by which these
substances are combined with each other to make the product, is to melt the
asphalt or bitumen, and to mix the metallic oxide and sulphur together after
reducing each of them to a fine powder, and then incorporate them with the
melted bitumen in certain proportions after which the compound may be applied
directly to the conductors, or may be run into cakes or blocks capable of being
conveniently handled or transported, and which may be broken up and melted
when required for use.
་་་་་
In preparing the improved compound, the asphalt or bitumen is first heated
over a slow fire in a suitable kettle or boiler for a sufficient length of time to

page_text: thoroughly melt it and expel every trace of moisture. The temperature ordinarily
required for this purpose is about 300 degrees Fahrenheit. There is then, by
preference, added, to eight parts by weight of the asphalt or bitumen, three parts
of metallic oxide and three parts of sulphur. These proportions may be somewhat
varied without materially affecting the characteristics of the resultant compound;
for use under some conditions the proportion of sulphur, especially, may be
considerably reduced. The particular metallic oxide which it is preferred to use is
the sesqui-oxide of iron, which is a non-conductor of electricity. Any metallic
oxide which is a non-conductor of electricity, and is capable of being reduced to a
pulverulent condition may be employed as a substitute for the oxide of iron with
excellent results.
The metallic oxide having been ground to a fine powder and screened through a
sieve having not less than seventy meshes per lineal inch-the finer the better-
is thoroughly mixed with an equal quantity by weight of flour of sulphur, or
sulphur in a finely powdered condition. This mixture of sulphur and metallic
oxide is slowly sifted into and thoroughly incorporated with, the heated asphalt or
bitumen which should be maintained at a uniform temperature of about 300 degrees
Fahrenheit during the operation.
After the materials have been thoroughly intermingled the material is ready for
use as hereinafter directed. If not designed to be used at once it is preferable to
run it into cakes or blocks of convenient size in a suitable mould, allowing it to
cool and become hard therein. Such cakes may be handled and transported with
facility and may at any time be melted over a slow fire at about the same degree
of heat as that employed in the original process of preparation.
It may sometimes be difficult to procure asphalt or bitumen of good quality, and
in such case coal-tar may be employed in lieu thereof, in the same proportion; or
a mixture of coal-tar and bitumen may be employed, the amount of coal tar in
such case being equal or nearly so to the amount of bitumen for which it is
substituted. It will thus be understood that coal-tar and the bitumens are, for the
purpose of this invention, equivalents. Any non-conducting metallic oxide-which
is capable of being reduced to powder may in either case be substituted for the
sesqui-oxide of iron, although the latter is generally preferable.
A very convenient method of employing this improved compound for the
insulation of electrical conductors especially when placed under ground, is to
enclose the conductor or conductors within a suitable trough or other structure,
forming a mould. This trough may be of rectangular section, and partitions which
are of porcelain or other suitable non-conducting substance perforated with suitable
apertures, may be placed transversely within the trough at suitable distances apart.
Uninsulated electrical conductors are threaded through these apertures and kept
under tension. The conductors being thus supported in a position parallel to but
not touching each other, the insulating compound in a melted or liquid condition
may be poured into the trough filling it to the top. When the compound
solidifies the conductors will be embedded with it at the required distances from
each other, and efficiently insulated. The trough may be made of wood or other
cheap material and may be laid at the bottom of a trench and after the compound
has become hard may be covered with earth. The insulation of the wires will not
be affected by the decay of the trough as the compound is formed of inorganic
substances, none of which are subject to change by reason of the action of the
moisture of the earth or from other causes. In case copper conductors are
employed, their surfaces may with advantage be coated with tin to prevent any
possible chemical action upon the copper by the sulphur which forms a constituent
of the compound.
It is proposed in some cases to lay thin metal tubes in the insulating material,
through which are drawn wires, either naked or insulated; this method serving to
diminish or prevent induction..

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Alfred Julius Boult in the Great Seal Patent Office on the
17th November 1883.
ALFRED JULIUS BOULT of the firm of W. P. Thompson and Boult of
323, High Holborn in the county of Middlesex Engineer." "IMPROVEMENTS IN
INSULATING ELECTRICAL CONDUCTORS A communication to me from abroad by
James Gardner Sanderson, of New York, United States of America.
The object of the invention is to provide a compound for insulating electrical
conductors capable of being applied to them in a liquid condition which afterwards
solidifies or hardens, retaining at the same time a certain degree of flexibility, and
thus forms not only a superior insulating covering for the conductors, but also
affords a sufficient mechanical protection for the same, whereby the employment of
special protective devices may in many instances be dispensed with.
The essential ingredients which are employed in making this improved compound
are asphalt or bitumen or other like substance, a metallic oxide, which is a non-
conductor of electricity, and sulphur; and the method by which these substances
are combined with each other to make the product, is to melt the asphalt or
bitumen, and to mix the metallic oxide and sulphur together after reducing each
of them to a fine powder, and then incorporate them with the melted bitumen in
certain proportions, after which the compound may be applied directly to the
conductors; or may be run into cakes or blocks capable of being conveniently
handled or transported, and which may be broken up and melted when required
for use.
In preparing the improved compound, the asphalt or bitumen is first heated over
a slow fire in a suitable kettle or boiler for a sufficient length of time to thoroughly
melt it and expel every trace of moisture. The temperature ordinarily required
for this purpose is about 300 degrees Fahrenheit. There is then, by preference,
added, to eight parts by weight of the asphalt or bitumen, three parts of metallic
oxide and three parts of sulphur. These proportions may be somewhat varied
without materially effecting the characteristics of the resultant compound; for use
under some conditions the proportion of sulphur, especially,, may be considerably
reduced. The particular metallic oxide which it is preferred to use is the sesqui-
oxide of iron, which is a non-conductor of electricity. Any metallic-oxide which
is a non-conductor of electricity, and is capable of being reduced to a pulverulent
condition may be employed as a substitute for the oxide of iron with excellent
results.
The metallic oxide having been ground to a fine powder and screened through a
sieve having not less than seventy meshes per lineal inch-the finer the better-is
thoroughly mixed with an equal quantity by weight of flour of sulphur, or
sulphur in a finely powdered condition. This mixture of sulphur and metallic
oxide is slowly sifted into and thoroughly incorporated with, the heated asphalt or
bitumen which should be maintained at a uniform temperature of about 300 degrees
Fahrenheit during the operation.
After the materials have been thoroughly intermingled the material is ready for
use as hereinafter directed. If not designed to be used at once it is preferable to
run it into cakes or blocks of convenient size in a suitable mould, allowing it to
cool and become hard therein. Such cakes may be handled and transported with
facility and may at any time be melted over a slow fire at about the same degree
of heat as that employed in the original process of preparation.
It may sometimes be difficult to procure asphalt or bitumen of good quality, and

page_text: in such case coal-tar may be employed in lieu thereof, in the same proportion; or a
mixture of coal-tar and bitumen may be employed, the amount of coal-tar in such
case being equal or nearly so to the amount of bitumen for which it is substituted.
It will thus be understood that coal-tar and the bitumens are, for the purpose of
this invention, equivalents. Any non-conducting metallic oxide which is capable
of being reduced to powder may in either case be substituted for the sesqui-oxide
of iron, although the latter is generally preferable.
A very convenient method of employing this improved compound for the
insulation of electrical conductors especially when placed underground, is to enclose
the conductor or conductors within a suitable trough or other structure, forming a
mould. This trough may be of rectangular section, and partitions which are of
porcelain or other suitable non-conducting substance perforated with suitable
apertures, may be placed transversely within the trough at suitable distances apart..
Uninsulated electrical conductors are threaded through these apertures and kept
under tension. The conductors being thus supported in a position parallel to but
not touching each other, the insulating compound in a melted or liquid condition
may be poured into the trough, filling it to the top. When the compound solidifies
the conductors will be embedded with it at the required distances from each other,
and efficiently .insulated. The trough may be made of wood or other cheap
material and may be laid at the bottom of a trench and after the compound has
become hard may be covered with earth. The insulation of the wires will not be
affected by the decay of the trough as the compound is formed of inorganic
substances, none of which are subject to change by reason of the action of the
moisture of the earth or from other causes. In case copper conductors are
employed, their surfaces may with advantage be coated with tin to prevent any
possible chemical action upon the copper by the sulphur which forms a constituent
of the compound.
It is proposed in some cases to lay thin metal tubes in the insulating material,
through which are drawn wires, either naked or insulated, this method serving to
diminish or prevent induction.
Having now described the invention as communicated to me, I wish it to be
understood that what I desire to protect under the Letters Patent is :-
1. The herein before described method or process of making an insulating compound
for electrical conductors which consists in forming a mixture of non-conducting
metallic oxide and sulphur in a pulverulent condition, and incorporating said
mixture with melted bitumen, substantially as set forth.
2. The herein before described compound for insulating electrical conductors,
consisting of bitumen, non-conducting metallic oxide and sulphur, combined
substantially in the proportions set forth.
In witness whereof I the said Alfred Julius Boult have hereunto set my hand
and seal this seventeenth day of November in the year of our Lord one thousand
eight hundred and eighty three.
ALFRED J. BOULT (L.S.)