IMPROVEMENTS IN THE PREPARATION OF MATERIALS TO RE EMPLOYED FOR THE PURPOSES OF ELECTRIC INSULATION
Year: 1881

page_text: ÜETTERS PATENT to John Ambrose Fleming of Saint John's College Cambridge
Demonstrator of Mechanism in the University of Cambridge for an Invention.
of IMPROVEMENTS IN THE PREPARATION OF MATERIALS TO RE EMPLOYED
FOR THE PURPOSES OF ELECTRIC INSULATION
PROVISIONAL SPECIFICATION left by the said John, Ambrose Fleming
at the Office of the Commisioners of Patents on the 23rd April 1881.
JOHN AMBROSE FLEMING of St John's College Cambridge Demonstrator of
Mechanism in the University of Cambridge "IMPROVEMENTS IN THE PREPARATION
OF MATERIALS TO BE EMPLOYED FOR THE PURPOSES OF ELECTRIC INSULATION
"My Invention relates to Improvements in the preparation of materials to be
employed for the purposes of electric insulation whereby advantages in economy
and facility of production are obtained.
It is well known that the insulators or insulating substances in common
use. aure
difficult. to work or fashion with tools. For example glass and porcelain and
likewise Ebonite or Vulcanite can easily be cast or moulded whilst hot but are
difficult to cut, and ebonite is in addition expensive. Now my Invention has for
its object the production of an insulating or non conducting material not permitting
of the passage of electricity through it readily, and which is capable of being very
casily cut or fashioned with edged tools, or in a lathe so as to admit of its being
worked into various forms, for insulators for telegraphic purposes, for insulating the
conductors conveying the electric current for electric lights or for any purpose in
constructing electric apparatus, in which an insulating substance is required.
In carrying out my Invention in order to effect this object I take the best
quality of wood of various descriptions which has been treated in such a manner as
to remove from it water and all acids and I then cause melted paraffin wax to be
forced into the wood under pressure. The paraffin wax solidifies in the fibre and
.converts the wood from a moderate conductor into a nearly perfect non conductor
the wood not being simply immersed in the paraffin but impregnated with it into
the interior of the wood. The material thus produced forms an electric insulator
which can be easily worked into any form. In lieu of using paraffin I may employ
mixtures of paraffin, shellac and rosin either singly or in various proportions and
I find that wood so prepared even in very thin sheets constitutes an insulator of
great value.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said John Ambrose Fleming in- the Great-Seal-Patent Office on the
19th October 1881.
JOHN AMBROSE FLEMING of St John's College- Cambridge Demonstrator of
Mechanism in the University of Cambridge "IMPROVEMENTS IN THE PREPARATION
OF MATERIALS TO BE EMPLOYED FOR THE PURPOSE OF ELECTRIC INSULATION
My Invention relates to Improvements in the preparation of materials to be
employed for the purposes of electric, insulation whereby advantages in economy
and facility of production are obtained.
It is well known that the insulators or insulating substances in common use are
difficult to work or fashion with tools, for example Glass and Porcelain and
likewise ebonite or vulcanite can easily be cast or moulded whilst hot but are
difficult to cut and ebonite is in addition expensive. Now my Invention has for
its object the production of an insulating or non conducting material not permitting
of the passage of electricity through it readily and which is capable of being very
easily cut or fashioned with edged tools or in a lathe so as to admit of its being
worked into various forms for insulators for telegraphic purposes for insulating
the conductors conveying the electric current for electric lights or for any purpose
in constructing electric apparatus in which an insulating substance is required.
In carrying out my Invention in order to effect this object I take the best
quality of wood of various descriptions which has been treated in such a manner
as to remove from it water and all acids and I then cause melted paraffin wax to
be forced into the wood under pressure. The paraffin wax solidifies in the fibre
and converts the wood from a moderate conductor into a nearly perfect non
conductor; the wood not being simply immersed in the paraffin but impregnated
with it into its interior or throughout its mass.
In carrying out the process I may employ any one of the well known types
of apparatus for extracting moisture, from wood and impregnating it with a
liquid the apparatus shown in diagram elevation on the accompanying sheet of
drawings is found convenient in practice:
A is a strong iron box in which the wood in the form of planks or blocks B is
placed when dried the box being then closed and made air tight is enclosed in an
Oven Cheated by gas or a fire to a temperature of say about 130° Centigrade.
Above the box is a Vessel D containing the melted paraffin wax which com-
municates with the box by a pipe E provided with a tap F.
From the box also passes a pipe G which is in communication. with an air
exhaust apparatus H a regulating tap G being provided, the pipe opens into a
vessel 1 for collecting water and acid which distil out from the wood and from
this Vessel extends a worm or condenser K to condense the water vapour or acid
vapours whilst beyond the condenser and communicating therewith is a tube L
filled with some hydroscopic substance such for example as chloride of calcium.
The tube L is in direct communication with the air exhaust apparatus H which
may consist of an ordinary air pump or (as indicated in the drawing) of a water
jet aspirator connected at its upper end a with a cistern of water or water supply
pipe and at its lower end b with a waste pipe.
The apparatus operates in the following manner vizt:--
The wood chosen is first air dried or dried in any convenient manner as far as
possible and is next placed in the iron box A as shewn at B. and the box, is closed
up airtight. The tap F is then closed and the tap G¹ opened and a vacuum is
produced in the box at the same time the box is heated to a temperature of say
about 120° Centigrade. Under the combined influence of the vacuum and heat

page_text: the moisture and acids are extracted from the wood and condense in the vessel 1.
The Vacuum should be of such a degree that the barometer guage provided at M
stands at a height of 28. inches.
The paraffin wax having now being melted and poured into the vessel D) in
quantity sufficient for the purpose the tap G is then closed and the tap F opened
the atmospheric pressure then forces down the melted wax into the box and
compresses it into the fibre of the wood the heat is then withdrawn and when
the apparatus is cold the box is opened and the impregnated wood cut out the
operation being then complete.
I have found that the most suitable woods for the purposes of my Invention are
Canadian poplar, pine, or white deal, as they are capable of absorbing a greater
weight of the paraffin but any other description of wood as for example
Sycamore or Hondurous or Cuba Mahogany may be employed although I prefer
those previously mentioned. In lieu of using paraffin alone I may employ mixtures
of paraffin and rosin the object of using rosin being to raise the melting point of
the impregnating material. I have found in practice that a mixture of say about
3 parts by weight of paraffin wax and one part by weight of rosin gives good
results but other proportions may be employed although in all cases I have
found that it is desirable to have an excess of paraffin wax.
The material produced in the manner hereinbefore described forms an electric
insulator which can be easily worked with tools into any required form.
Having now described and particularly ascertained the nature of my said Inven-
tion and the manner in which the same is or may be used or carried into effect I
would observe in conclusion that what I consider to be novel and original and
therefore claim as the invention secured to me by the herein before in part recited
Letters Patent is:-
The employment for the purposes of electrical insulation of wood deprived of
its moisture and impregnated with paraffin wax or with a mixture of paraffin wax
and rosin substantially as herein before described.
In witness whereof the said John Ambrose Fleming have to this my
Specification. set my hand and seal this fourteenth day of October One thousand
eighty hundred and eighty one.
TOHEN A VERDOSE EI WAING &..
TOYTEN A MERDÓSK WI WALING &