AN IMPROVEMENT IN THE HOUSING AND INSULATION OF ELECTRICAL WIRES BENEATH THE SURFACE OF THE GROUND
Year: 1883

page_text: LETTERS PATENT to Herbert John Allison, of the firm of Allison Brothers,
Patent Agents, of Southampton Buildings, London, for an Invention of
"AN IMPROVEMENT IN THE HOUSING AND INSULATION OF ELECTRICAL WIRES
BENEATH THE SURFACE OF THE GROUND" communicated to him from abroad
by Charles Carroll Gilman, of Eldora, Iowa, United States of America.
COMPLETE SPECIFICATION filed by the said Herbert John Allison at the
Office of the Commissioners of Patents on the 20th November 1883.
""
HERBERT JOHN ALLISON, of the firm. of Allison Brothers, Patent. Agents, of
Southampton Buildings, London, "AN IMPROVEMENT IN THE HOUSING AND
INSULATION OF ELECTRICAL WIRES BENEATH THE SURFACE OF THE GROUND
communicated to me from abroad by Charles Carroll Gilman, of Eldora, Iowa,
United States of America.
My invention relates to the protection and insulation underground of electrical
conductors.
I use as the material for the construction of a protecting and insulating under-
ground enclosure, terra cotta composed of clay and made porous or cellular by the
means and in the manner described in British Letters Patent N° 4634 dated
October 22nd, 1881, namely by mixing with the clay in its preparation, one or two
parts by measure of resinous wood saw dust, or equivalent comminuted combustible
matter which is consumed in the burning of the ware, leaving it of a highly
cellular structure, forming an earthenware that will receive and take up into itself
mineral bitumen so as to become saturated therewith and thus be rendered
impervious throughout to water, and also having a structure into or through
which spikes or nails may be driven without fracturing it. This ware when made
of clay free from grit, is susceptible after firing also of being sawed or dressed
with edge-tools into boards or planks and other desired forms, and such forms
fitted together to make close joints as wood may be wrought.

page_text: I construct from the said cellular terra cotta an underground enclosure in
which to lay electrical conductors, for example, telegraph wires, preferably as
follows:-
I prepare slabs or planks of the above described cellular terra cotta of suitable
size and form a section of a trough or conduit of the desired dimensions to contain
the insulated electric conductors, which I design to place in it; they may be for
example from twelve to twenty four inches wide, two inches thick, and from three
to four feet long.
I saw or plane them to a uniform thickness and preferably tongue and groove
their edges and ends so that they inay be jointed together. When thus prepared
I plunge them into highly heated mineral asphaltum, or its equivalent, and allow
them to remain therein until the pitch has penetrated and permeated the cellular
structure of the terra cotta to such an extent that the pitch cannot be detached or
separated from the terra cotta without destroying or breaking up the terra cotta
itself. If planks of one or two inches in thickness are allowed to remain in the
heated pitch, a sufficient length of time, say from one to two hours, they will be
permeated and saturated through and through with the pitch, but if the pitch
penetrates the terra cotta to the extent of one fourth to one half an inch that is
usually sufficient for the present purpose.
After these slabs or planks are sufficiently saturated with the hot pitch, they are
removed therefrom with their surfaces covered with the pitch that adheres to them.
In this condition and while the pitch is still hot, the planks are to be put together
to form a casing or conduit, laid in a trench in the ground or sheathing in the form
of an underground tunnel.
Tongued and grooved joints with the surfaces covered with the hot asphaltum
may be formed both at the adjacent edges and ends of the planks, and the planks
may be nailed or spiked together as wooden planks can be to form a closed
indestructible, water and air tight underground enclosure for the conductors. The
conductors may be insulated from one another within the conduit by being
suspended on insulating brackets or in any other desired way. I prefer however
to employ for the purpose the above described cellular terra cotta saturated with
asphaltum.
To this end I cut channels in the surface of plates of the terra cotta before
dipping them into the heated asphaltum, and lay these plates while the asphaltum
is hot within the above described case or conduit, one upon another, with the
conductors laid in the channels and embedded therein in the asphaltum. The
conduit may be filled with successive layers of these plates enclosing the conductors
between them.
It is preferable to saturate the terra cotta slabs or planks at the manufactory at
which they are made, before being transported to the place where they are to be
used. When this is done, they must be again dipped in hot pitch before being put
together to form the conduit, in order that the joints where the planks come
together may be hermetically sealed by the pitch.
In the accompanying drawings I represent one form of conduit or enclosure for
electric conductors which may be constructed of the described cellular terra cotta
saturated with asphalt, but I do not of course intend to limit myself to the special
form shown. Any suitable form and size of conduit may be constructed and used.
Figure 1 is a longitudinal view of the outside of such a conduit; Figure 2 is a
vertical section of the same on line x, x, Figure 1, showing the frame work of the
interior with brackets in which the wires may be carried; Figure 3 represents a
longitudinal section of three of the described cellular terra cotta planks grooved
for the reception of the wires and laid one upon another, the same being intended
to be saturated and covered with bitumen as before described, and Figure 4
represents a single slab of the said terra cotta showing grooves for the wires.
I have thus described what I regard as the preferable method of supporting and
insulating from one another the conductors within the enclosure. But I do not
limit myself to the method described. Any other suitable mode may be adopted,

page_text: one of which would be after placing the conductors in the enclosure separated from
each other, to pour in melted pitch to fill the enclosure in which the conductors
will then be embedded.
What I claim as my invention and desire to secure by Letters Patent is :—
An underground insulating watertight conduit composed of the described cellular
terra cotta saturated with asphaltum, enclosing and insulating one or more wire
electrical conductors as described.
In witness whereof, I, the said Herbert John Allison, have hereunto set my
hand and seal, this twentieth day of November in the year of our Lord one
thousand eight hundred and eighty-three.
HERBERT. J. ALLISON. (L.S.)