Battery, Water.
A voltaic battery, whose exciting fluid is water. They are used for
charging quadrant electrometer needles and similar purposes. They
polarize very quickly and are of high resistance. Hence very small
plates in large number can be used without impairing their advantage.
Rowland's water battery dispenses with cups and uses capillarity
instead. The zinc and platinum or copper plates of a couple are placed
very close together, while the couples are more distant. On dipping into
water each couple picks up and retains by capillarity a little water
between its plates, which forms the exciting fluid. Many hundred couples
can be mounted on a board, and the whole is charged by dipping into
water and at once removing therefrom. It then develops its full
potential difference.
Fig. 55. SECTION OF WOLLASTON BATTERY.
Fig. 56. PLATES OF WOLLASTON'S BATTERY.