Battery, Marié Davy's.
A two fluid porous cup battery with carbon negative plate, zinc positive
plate, and mercury sulphate, a nearly insoluble salt, as depolarizer and
excitant. Mercurous or mercuric sulphates have been used in it. Its
electromotive force is 1.5 volts. The local action and waste, owing to
the slight solubility of the mercury compounds, is very slight. If used
on close circuit it becomes polarized. It is also subject under extreme
circumstances to reversal of polarity, zinc becoming deposited upon the
carbon, and there forming a positive electrode.
In using the cells in series the level of liquid in all must be the
same, otherwise the cell in which it is lowest will become polarized and
exhausted.
Modifications of this battery on the lines of the gravity battery have
been constructed.
Synonym--Sulphate of Mercury Battery.
Battery, Maynooth's.
A battery of the Bunsen type, with cast iron negative plate. The iron
takes the passive form and is not attacked.
Battery, Medical.
A term applied very indiscriminately to medical current generators, and
to medical induction coils, or to any source of electricity, static or
current, for medical application.