Improvements in Standard Cells for Small Electric Currents.
Year: 1898

page_text: Date of Application, 28th Sept., 1898
Complete Specification Left, 24th June, 1899-Accepted, 29th July, 1899
PROVISIONAL SPECIFICATION.
Improvements in Standard Cells for Small Electric Currents.
'
We, SIEMENS BROTHERS & Co. LIMITED, of 12, Queen Anne's Gate, West-
minster, S.W., Electrical Engineers, and EUGENE FREDERICK AUGUST OBACIL,
of 113, Victoria Road, Old Charlton, Kent, Analytical Chemist and Electrician,
do hereby declare the nature of this invention to be as follows;-
-
The standard cells hitherto proposed all possess one or several of the following
disadvantages. They are either not sufficiently portable and permanent and have
to be set up from time to time, or they possess such extremely high internal
resistances and polarize so strongly when delivering the smallest currents, that
they can only be used for electrostatic or nil methods of measurements.
The present invention relates to a standard cell which is free from these
defects.
In the construction of the improved cell advantage is taken of the fact that
it is possible to reduce the electrical potential of a mixture of depolarising salt
and conducting carbon, for example plumbago, surrounding a carbon electrode,
exactly to that of the metal forming the electropositive component of the de-
polarising salt with which it is surrounded by the addition of a certain per centage
of the metal in a finely divided state to the mixture of depolarising salt and
plumbago.
By the use of a carbon electrode and of finely divided carbon mixed with the
depolarising agent, the contact surface between the electrode and the depolariser
is largely increased and consequently the internal resistance is greatly diminished
while at the same time the depolarising action takes place more promptly. The
following is an example of the treatment of the carbon electrode of a Clark cell,
according to this invention. Mercurous sulphate, plumbago and finely divided
metallic mercury are intimately mixed, and the mixture, made into a stiff pasto
by adding an aqueous solution of zinc sulphate, is spread over the carbon electrode
and held on it by binding round with calico or other suitable fabric.
This mode of construction may be applied to any type of cell such as the Clark
cell consisting of zinc, zinc sulphate mercurous sulphate and mercury; the
Watson cell consisting of cadmium, cadmium sulphate mercurous sulphate and
mercury a modified form of the De la Rue cell consisting of zinc potassium
chloride, silver chloride and silver, and the like.
Dated this 28th day of September 1898.
ABEL & IMRAY,
Agents for the Applicants.
Improvements in Standard Cells for Small Electric Currents.
We, SIEMENS BROTHERS & Co., LIMITED, of 12, Queen Anne's Gate, West-
minster, S.W., Electrical Engineers, and EUGENE FREDERICK AUGUST OBACH,
Price 8d1

page_text: of 113, Victoria Road, Old Charlton, Kent, Analytical Chemist and Electrician,
do hereby declare the nature of this invention and in what manner the same is
to be performed, to be particularly described and ascertained in and by the
following statement:
-
The standard cells hitherto, proposed all possess one or several of the following
disadvantages. They are either not sufficiently portable and permanent and have
to be set up from time to time, or they possess such extremely high internal
resistances and polarize so strongly when delivering the smallest currents, that
they can only be used for electrostatic or nil methods of measurement.
The present invention relates to a standard cell which is free from these
defects.
In the construction of the improved cell advantage is taken of the fact that it
is possible to reduce the electrical potential of a mixture of depolarising salt
and conducting carbon, for example plumbago, surrounding a carbon electrode,
exactly to that of the metal forming the electropositive component of the de-
polarising salt with which it is surrounded by the addition of a certain per centage
of the metal in a finely divided state to the mixture of depolarising salt and
piumbago.
By the use of a carbon electrode and of finely divided carbon mixed with the
depolarising agent, the contact surface between the electrode and the depolariser
is largely increased and consequently the internal resistance is greatly diminished
while at the same time the depolarising action takes place more promptly.
The following is an example of the treatment of the carbon electrode of a
Clark cell, according to this invention. Mercurous sulphate, plumbago and finely
divided metallic mercury are intimately mixed, and the mixture, made into a
stiff paste by adding an aqueous solution of zinc sulphate, is spread over the
carbon electrode and held on it by binding round with calico or other suitable
fabric.
This mode of construction may be applied to any type of cell such as the Clark
cell consisting of zinc, zinc sulphate, mercurous sulphate and mercury; the
Watson cell consisting of cadmium, cadmium sulphate, mercurous sulphate and
mercury; a modified form of the De la Rue cell consisting of zinc, potassium
chloride, silver chloride, and silver, and the like.
On the accompanying drawing is shewn by way of example one form of standard
cell constructed according to the above described invention.
Fig. 1 shews a longitudinal section and Fig. 2 a transverse section of the cell.
Within the outer casing B are the zine or cadmium electrodes Z embedded in
the exciting material E which may consist of a paste of plaster of Paris and
flour mixed with a concentrated solution of zinc or cadmium sulphate, or potassium
chloride, according to whether the "Clark," Weston " oľ De la Rue" type
of cell is intended. The carbon electrode C consists of a carbon plate having
a number of large holes, preferably symmetrically distributed and filled with
plugs of the depolarising mixture.
"
Connection between the carbon plate and terminal T is made by means of a cast
lead cap L provided with plugs pp of an expanding alloy so as to insure intimate
contact between the carbon and the lead.
The zinc electrodes Z are in connection with terminal T¹; a wood distance
piece W separates the carbon and zinc electrodes.
D is the layer of depolarising material surrounding the carbon electrodes.
This material, in the case of a Clark" cell consists of an intimate mixture
of equal parts by weight of neutral mercurous sulphate (free from mercuric
salt) and purified plumbago, and a small quantity such as 5 per cent. of
powdered gum tragacanth. This is made into a stiff paste with a saturated
solution of zinc sulphate, and pure metallic mercury in a fine state of division
is then uniformly distributed throughout the mass.
In setting up the cell the depolarising paste is first rammed into the holes of
the carbon plate, and the latter is then surrounded with a layer of the paste,

page_text: say about th in. in thickness pressed on as tightly as possible, such layer
being kept in position on the carbon by a layer of calico or other suitable fabric,
bound round with tape. The zinc electrodes are so arranged relatively to the
carbon electrode thus covered that a space of about 1/8th inch intervenes between
them and the surface of the depolarising coating.
The element is then completed and closed up in the known manner.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed we declare that what we
claim is:-
In a standard cell, the use in combination with the positive electrode, of a
layer of depolarising compound consisting of a mixture of a depolarizing salt
with carbon, and a per centage of the metal forming the electro-positive com-
ponent of the depolarizing salt in a finely divided state substantially as des-
cribed.
Dated this 24th day of Tune 1800
ABEL & IMRAY,
Agents for the Applicants.