other Galvanic Cells having Mercury Electrodes.
Year: 1886

page_text: other Galvanic Cells having Mercury Electrodes.
I ALEXANDER MUIRHEAD of N° 3 Elm Court, Temple, E.C. in the City of
London Doctor of Science, Electrical 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 what are known
as Clark cells, employed as standards of Electromotive-force, and it has reference
to a modification of the mercury electrode of these cells whereby the combination is
rendered more portable.
In the drawing accompanying this Specification Figs I and II illustrate the two
principal modes of constructing Clark cells that have been adopted hitherto. Zn, is
a rod of pure zinc supported by means of a cork, C, in a glass cell or vessel; at the
bottom of the cell is a layer of pure redistilled mercury, Hg, with which connexion
is made by means of a platinum wire, Pt, either hermetically sealed into the glass
cell, as in Fig. II, or passed down a small tube attached to the side of the cell, as
in Fig. I; between the mercury and the zinc electrodes is a paste, S, composed of
mercurous sulphate (protosulphate) and saturated solution of zinc sulphate.
Both of these forms of the Clark cell, especially when newly set up, are
unsuitable for transport, the mercury being free, is apt to leave the platinum wire
contact, Pt, when the cell is inverted or upset and to fall through the paste into
contact with the zinc rod, thereby either short-circuiting the cell altogether, or
destroying the value of its electromotive-force. To remedy this defect is the object
of this invention and Figs. III IV and V illustrate the mode in which I prefer to
carry it out.
According to this invention the wire, Pt, which may be of platinum or platinum-
iridium is coiled up in such manner as to form a cylindrical cage open at one end
and terminating at the other in a flat spiral, from the centre of which the wire is
continued down the middle of the cage and brought out through the glass cell, to
form the outside connexion. This cage of platinum is fitted inside either a tubular
projection, T, made to the cell itself as in Figs. III and IV or inside a separate piece
of glass tubing, X, as shown in Fig. V.
Another way of constructing a cage or enclosure for the reception of the
mercury in these cells is to place a piece of platinum wire gauze or perforated

page_text: platinum sheet over the end of the tubular projection, T, or glass tube, X, and to
connect it by binding to the platinum wire connexion, Pt, which passes through
the glass cell.
It is found that Clark Standard cells improved in the manner above described
have the advantage of being more constant in Electromotive force when subjected
to vibration or rough treatment than those made according to Figs. I and II besides
being more portable. The mass of mercury when confined in chambers constructed
of platinum in the above manner adheres firmly to the platinum connexion and
does not separate readily from it.
This invention can also be applied to other forms of galvanic cells in which
mercury is one of the 'electrodes.
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
In Clark Standards of Electromotive-force, or other galvanic cells in which
mercury forms one of the electrodes, the method of confining the mercury in a
chamber constructed of gauze, perforated sheet, or wire of platinum, or platinum-
iridiun, substantially' as and for the purposes hereinbefore described.
Dadh xth day of Tune TRRG