Year: 1886

page_text: I ALEXANDER MUIRHEAD of Cowley Street Westminster, S.W. Doctor of Science,
Telegraph Engineer, do hereby declare the nature of my said invention and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement :-
This invention relates to improvements in the manufacture of the new form of
Standard cells described in the Specification of the Patent No. 8376 of 1886 applied
for by me, and of which Fig. I of the drawing accompanying the present Specifi-
cation is an illustration. In these cells the mercury constituting the positive
electrode or the electro-negative metal of the combination is contained in a
cylindrical shaped cage, X, terminating at both ends in a flat or slightly curved
closely wound spiral of platinum wire. In filling the cage, X, a quantity of pure
redistilled mercury is placed in the glass cell, A, sufficient to cover the cage, X, and
heated for a few minutes almost to boiling point; on cooling, the excess of mercury
is poured off leaving the cage, X, completely filled with mercury and the portion of
the platinum wire, Pt, inside the cell well amalgamated. A clearer sketch of the
cage, X, is given below Fig. I at W.
Since the date of the above mentioned patent I have found that for most
practical purposes these cells form sufficiently reliable standards of electromotive
force even when set up without the mass of pure mercury, Hg Fig. I, in contact
with the amalgamated platinum wire connexion, Pt. The platinum, Pt, alone
answers well enough provided it be properly amalgamated with pure mercury.
That is to say, standard cells made according to this invention with merely a
surface of pure amalgamated platinum as the positive electrode, pure zinc as the
negative electrode, and a mixture of pure mercurous sulphate with saturated
solution of pure zinc sulphate as electrolyte agree closely enough in electromotive
force with one another for all ordinary electrical measurements.
The platinum for the purpose of this invention may be in sheet or foil, or
preferably of wire wound closely into a flat or slightly curved spiral, and the
amalgamation effected either by boiling it in pure mercury or by dipping it red-hot
into pure mercury. When platinum foil is employed the amalgamation is more
permanent if the surface be roughened, or the foil corrugated or grooved.
In Fig. II of the drawing accompanying this Specification is shown a Standard
cell constructed according to this invention. Y, is a flat closely wound spiral of

page_text: platinum wire which has been coated or amalgamated with pure mercury by either
of the methods above described; the continuation of the wire, Pt, is sealed into the
glass cell at w forming the outer connexion. Zn is a rod of pure zinc supported
by a cork, C, as in Fig. I. The horizontal dotted lines, which have the same
meaning in all the figures of the drawing, represent the electrolyte used in these
cells, vizt.; a paste composed of pure mecurous sulphate and saturated solution of
pure zinc sulphate.
Fig. III illustrates another mode of setting up Standard cells according to this
invention-one which is more expensive but more durable than that shown in
Fig. II. Instead of supporting the zinc electrode by means of a cork, C, as in
Figs. I and II, a platinum wire connexion, Q, is fused into the zinc rod, Zn, and
sealed into the glass tube, T, at, x, the junction of the platinum and the zinc being
protected from the electrolyte of the combination, and at the same time firmly
secured to the tube, by shellac or other suitable cement. S is the electro-negative
plate, a flat spiral of platinum wire similar to Y of Fig. II. The cell is hermetically
sealed up at R, after the introduction of the electrolytic paste of pure zinc and
mercurous sulphates.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed I declare that what
I claim is:
1. In the construction of Standard cells, the use of amalgamated platinum as one
of the electrodes, either in the form of a closely wound spiral, or cylinder of wire,
or foil preferably grooved or corrugated or with its surface roughened substantially
as herein before described.
2. The combination in a Standard cell, of platinum amalgamated with pure
mercury, and pure zinc as the electrodes with a mixture of pure mercurous sulphate
and saturated solution of pure zinc sulphate.
3. The hermetically sealed form of Standard cell substantially as above described
and illustrated in Fig. III of the drawing accompanying this Specification.
Dated this 22nd day of September 1886.