Improvements in Standards of Electromotive Force.
Year: 1893

page_text: Date of Application, 9th Oct., 1893--Accepted, 11th Nov., 1893
COMPLETE SPECIFICATION.
Improvements in Standards of Electromotive Force.
We, ALEXANDER MUIRHEAD, of No. 2 Princes Street, Storey's Gate, in the
City of Westminster, Doctor of Science, Electrical Engineer, and JOSEPH
ARTHUR LOVEL DEARLOVE, of No. 4 Great Winchester Street, in the City of
London, Assoc. Inst. Elec. Engineers, do hereby declare the nature of this inven-
tion and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement :-
This invention has for its object the construction of standards of electromotive
force having amalgams of cadmium as the negative electrode and of making the
same portable.
In the case of standard cells in which cadmium is the negative electrode we
find that the electro-motive force is dependent upon the proportions of cadmium
and mercury in the amalgam used.
The following table shows the electro-motive force of cells set up with different
amalgams of cadmium, the electrolyte being a saturated solution of cadmium
sulphate and mercurous sulphate and the positive electrode pure mercury.
It is important, therefore, in the construction of standards of electromotive force
with cadmium as negative electrode that the amalgam employed be of definite
composition.
In substituting an amalgam of cadmium for the pure metal itself as the negative.
electrode of a standard cell made in accordance with the Specification of Letters
Patent granted to one of us dated 22nd September A.D. 1886 and numbered 12,059 it
is necessary, in order to make the combination portable, that the amalgam be cast in
the shape of a rod. For giving strength to this rod we sometimes embed in it a
length of amalgamated platinum wire either straight or wound in a spiral, or
sometimes we cast the amalgam round a rod of cadmium. In order to strengthen
the rods of amalgam so formed still further we sometimes cast the amalgam in a
tube of glass or porcelain. The amalgam whilst warm can be pressed into a
perforated glass or porcelain tube or into a slotted porcelain tube, the operation
being performed in a tightly fitting mould.
The amalgam of cadmium we prefer to use is composed of one part of cadmium
to seven parts of mercury which gives an electro-motive force of 1.0192 volts.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that we are
well aware that it has been suggested to construct voltaic cells of cadmium
amalgam and mercury as electrodes but such cells cannot be taken as standards of
electromotive force unless the amalgam employed is of the definite composition
above stated, as, until this proportion of mercury and cadmium is reached, the
г.
71

page_text: electromotive force of the combination is both unstable and variable.
claim is ;-
What we
1. In standard cells, the use, as the negative electrode of the combination, of
amalgams of cadmium cast in the shape of a rod strengthened by means of a length
of amalgamated platinum wire either straight or wound in a spiral and by a glass
or equivalent tube substantially as set forth.
2. The combination, in standard cells, of amalgamated platinum and an amalgam
of cadmium of definite composition with a saturated solution of pure mercurous
sulphate in saturated solution of cadmium sulphate respectively as set forth.
Dated this 9th day of October 1893
A. F. SPOONER,
124, Chancery Lane, W.C., Agent for the Applicants.