IMPROVEMENTS IN ELECTRICAL CONDENSERS OR ACCUMULATORS
Year: 1876

page_text: LETTERS PATENT to Desmond Gerald Fitz-Gerald, of Brixton, in the County
of Surrey, Electrician, for the Invention of "IMPROVEMENTS IN ELECTRICAL
CONDENSERS OR ACCUMULATORS."
Sealed the 16th March 1877, in pursuance of an Order of the Lord Chancellor, and
Sealed the 16th March 1877, in pursuance of an Order of the Lord Chancellor, and
dated the 2nd September 1870
PROVISIONAL SPECIFICATION left by the said Desmond Gerald Fitz-Gerald
at the Office of the Commissioners of Patents on the 2nd September 1876.
DESMOND GERALD Fitz-Gerald, of Brixton, in the County of Surrey, Electrician.
"IMPROVEMENTS IN ELECTRICAL CONDENSERS OR ACCUMULATORS
23
This Invention relates to improvements in electrical condensers or accumulators
used in telegraphy and for experimental purposes in electricity.
According to my Invention I use a foiled paper (ie, paper coated with a metallic
substance, as is well understood) pieferably manufactured with an uncoated margin
of paper on three sides of the sheet Such foiled paper is dipped in paraffin, wax,
or prepared with any other suitable non-conducting substance. Or instead of the
foiled paper I use sheets of any suitable insulating material similarly coated or
surfaced with plumbago or other conducting substance in powder or otherwise
After laying together any required number of these sheets of foiled paper prepared
with paraffin, or of the sheets of coated insulating material with the uncoated margin
alternately in opposite directions, and after consolidating the sheets by pressure and
heat, I expose the alternate conducting surfaces preferably by cutting a thin slice
from the two opposite ends of the slab thus formed, and I then bring each set of
alternate conducting surfaces into electrical contact by means of plumbago in powder
applied to the cut ends of the slab, or by means of an amalgam of mercury or by
both these means conjoined.
The surface exposed by cutting may if preferred be rendered conducting by means
of metallic solutions from which the metal is thrown down by chemical actinic, or
electolytic processes. Or the alternate surfaces may be brought into contact by
means of bent strips of tin foil The two sets of conducting surfaces are then
respectively connected to terminal binding-screws preferably by means of flat
insulated plates of metal applied closely to the opposite ends of the slab where the
alternate conducting surfaces have been brought into electrical contact.

page_text: Sheets of paraffined paper or of other insulating material may when desirable be
interposed between the sheets of prepared foiled paper or of coated insulating
material.
SPECIFICATION filed in pursuance of the conditions of the Letters Patent and
of an Order of the Lord Chancellor by the said Desmond Gerald Fitz-Gerald
in the Great Seal Patent Office on the 16th March 1877.
18
DESMOND GERALD FITZ-GERALD, of Brixton, in the County of Surrey, Electrician.
IMPROVEMENTS IN ELECTRICAL CONDENSERS OR ACCUMULATORS."
This Invention relates to improvements in electrical condensors or accumulators
used in telegraphy and for experimental purposes in électricity
According to my Invention I use a foiled paper (ie., a paper coated with a metallic
substance, as is well understood) preferably manufactured with an uncoated margin
of paper on three sides of the sheet. Such foiled paper is dipped in paraffin wax
or prepared with any other suitable non-conducting substance Or instead of the
foiled paper I use sheets of any suitable insulating material similarly coated or
surfaced with plumbago or other conducting substance in powder or otherwise.
After laying together any required number of these sheets of foiled paper prepared
with paraffin, or of the sheets of coated insulating material with the uncoated
margins alternately in opposite directions, and after consolidating the sheets by
pressure and heat, I expose the alternate conducting surfaces preferably by cutting
a thin slice from the two opposite ends of the "slab" thus formed, and I then bring
each set of alternate conducting surfaces into electrical contact by means of plumbago
in powder applied to the cut ends of the slab or by ineans of an amalgam of mercury,
or by both these means conjoined.
The surface exposed by cutting may if preferred be rendered conducting by means
of metallic solutions from which the metal is thrown down by chemical actinic or
electrolytic processes. Or the alternate surfaces may be brought into contact by
means of bent strips of tin foil. The two sets of conducting surfaces are then
respectively connected to terminal binding screws preferably by means of flat
insulated plates of metal applied closely to the opposite ends of the slab where the
alternate conducting surfaces have been brought into electrical contact.
Sheets of paraffined paper or of other insulating material may when desirable
be interposed between the sheets of prepared foiled paper or of coated insulating
matorial.
The following is an example of the mode in which I construct condensers by
means of paraffined paper surfaced with plumbago or other conducting substance in
powder:
Having selected a paper, preferably unbleached and unsized, and freed by washing
from salts or other substances soluble in water, this is cut into sheets of suitable and
uniform size and dried by exposure to a heated atmosphere The sheets are then
dipped into melted paraffin wax preferably contained in a water bath furnished with
an escape pipe for the steam. The paraffined sheets are then surfaced as follows:-
A wooden frame forming three sides of a box, externally of the same size as the
sheets of paper and constructed of boards equal in thickness to the breadth of the
uncoated margin to be left on three sides of the paper, is placed upon one of the
prepared sheets for the purpose of preserving this margin from contact with the
conducting powder Strips of velvet or other soft material may be glued to the edges
of this frame which come into contact with the paraffined paper in order to preserve
the surface of the latter from injury. The margin to be left uncoated being thus
protected a sufficient quantity of plumbago or other conducting powder is thrown
upon the surface of the paraffined paper and is rapidly spread over it by means of a
piece of velvet glued to a wooden handle or by any other suitable implement, and
the excess of the powder is then brushed off the paper into a receptacle placed

page_text: conveniently in front of the operator. The wooden frame being then removed the
coated sheet is transferred to another table preferably so placed as to be traversed
by a slight draught of air in a direction such as to protect the sheet from any of the
conducting dust that might otherwise become deposited upon the uncoated margin.
A second sheet being similarly coated is laid upon the first sheet in one of two ways
which I will term a and b.
a, the uncoated surface of the second sheet is laid upon the coated surface of
the first sheets, i.c., both coated surfaces are placed uppermost The uncoated
margins are placed in opposite directions, ie, if the uncoated margin of the first
sheet be in the direction away from the operator the margin of the second sheet
must be in the direction towards the operator. This plan is adopted when the object
is to obtain a great capacity in small space rather than great perfection of insulation.
The third sheet is placed similarly to the first, the fourth similarly to the second,
and so on alternately until a sufficient number of sheets to constitute the required
condenser have been superposed. b, the coated surface of the second sheet is laid
upon the coated surface of the first sheet, the uncoated margins being also in juxta-
position or in the same direction. The third sheet is then superposed with its
coated surface uppermost but with its margin in the direction opposite to that of
the margin in the two first sheets, the fourth sheet has its coated surface and margin
facing those of the third sheet, and so on in duplicate alternation. One or more
sheets of uncoated paraffined paper may be placed between each pair of sheets of
which the coated surfaces are in contact This plan is adopted when the object is
to obtain great perfection of insulation rather than great capacity in small space.
The stacks thus formed of the prepared sheets are subjected in a press to gradually.
increased pressure at a temperature which may be raised to 100° Fah. when the
paper is prepared with pure paraffin wax. In this case care must be taken not to
allow the temperature to rise to 110° F., which is the melting point of some varieties
of paraffin.
For condensers required for use in hot climates, or which for any other reason
may be required to withstand a high temperature, I prepare the paper by saturating
it in a fused mixture of paraffin with any suitable resin, such as purified colophony
or gum dainmar
The pressure at an elevated temperature may advantageously be continued for
several days or even weeks, but must be relaxed should any signs be observed of
the exudation of paraffin round the edges of the slab formed by the compressed
sheets.
The slabs having been allowed to cool, a slice is removed by means of a book-
binder's knife or other suitable means from the two opposite ends formed by the
coated edges of the prepared sheets. The alternate conducting surfaces are thus
exposed, and by rubbing some plumbago or other conducting powder on to the
freshly cut edges of the paper these surfaces become conductively connected in two
sets, so that when the wires from a battery aro respectively brought into contact
with any two points on the cut and prepared edges of the slab the whole of the
surfaces become instantaneously charged.
Each slab forming a condenser may then be placed in its containing box, for
which purpose one side of the latter is 10moved. Several sheets of paraffined paper
are first placed inside the box to insulate the condenser from the remaining side of
the box To the two ends of the box corresponding to the cut and prepared edges
of the slab may be fitted plates of ebonite, to which are cemented plates of metal
equal in size to theso cut edges. These plates of metal are connected by means of
insulated wires to two binding screws insulated by ebonite. One cut edge of the
slab is applied closely to one of the plates of metal, and the other plate of metal
with the ebonite attached to it is then wedged or forced by means of screws passing
through the end of the box into contact with the other cut edge of the slab The
empty spaces within the box may be filled up with melted or softened paraffin, and
lastly, the upper side of the box is placed in position and screwed down.
I sometimes give to the condensers a cylindrical form by rolling upon a central

page_text: -
.cylinder a compound sheet of considerable length formed of two coated sheets having
their uncoated margins at opposite ends of the cylinder These may be employed
in conjunction with one or more uncoated sheets for the purpose of increasing the
dielectric resistance between the conducting sui faces. In this case contact is made
'with the coatings by means of two metal plates, one at each end of the cylinder,
these ends being rendered conducting by means of plumbago
I sometimes employ any amalgam of mercury which hardens after it has been
some time inade, for the purpose of insuring contact between the plates of metal
and the conducting surface of the condensor.
For certain purposes I prefer to include together in one box a number of separate
.condensers of small capacity. These condensers are separated from each other by
several sheets of paraffined paper or other insulating inaterial. One set of conducting
'surfaces at least in each condenser is brought into contact with a separate binding
screw connected with a separately insulated strip of metal which bears against one
of the cut ends of the slab to which plumbago in powder or other conducting
material has been applied as aforesaid. These binding screws may then be connected
externally by means of wires having any required resistance, for which purpose the
screws may be arranged alternately at opposite ends of the rectangle formed by the
top of the box containing the condensers.
The other sets of conducting surfaces may either be similarly connected with
insulated screws, or they may be brought directly into conductive contact with each
other by means of a single strip of metal bearing against all the remaining cut and
prepared edges of the slabs and connected with a binding screw.
In witness whereof, I, the said Desmond Gerald Fitz-Gerald have hereunto
set my hand and seal, this Second day of March, in the year of our Lord
One thousand eight hundred and seventy-seven.
DESMOND G. FITZ-GERALD. (L.S:)
Witness,
JOHN W GRAY, CE.,
Patent Office,
16, Southampton Buildings,
W.C.