irs of the new arrangement were used, the consumption of
zinc at each plate was 6.76 equivalents, or 67.6 for the whole. With ten
pairs of the common construction, in a porcelain trough, the zinc oxidized
was, upon an average, 15.5 equivalents each plate, or 155 for the entire
trough.

1131. No doubt, therefore, can remain of the equality or even the great
superiority of this form of voltaic battery over the best previously in
use, namely, that with double coppers, in which the cells are insulated.
The insulation of the coppers may therefore be dispensed with; and it is
that circumstance which principally permits of such other alterations in
the construction of the trough as gives it its practical advantages.

1132. The advantages of this form of trough are very numerous and great. i.
It is exceedingly compact, for 100 pairs of plates need not occupy a trough
of more than three feet in length, ii. By Dr. Hare's plan of making the
trough turn upon copper pivots which rest upon copper bearings, the latter
afford _fixed_ terminations; and these I have found it very convenient to
connect with two cups of mercury, fastened in the front of the stand of the
instrument. These fixed terminations give the great advantage of arranging
an apparatus to be used in connexion with the battery _before_ the latter
is put into action, iii. The trough is put into readiness for use in an
instant, a single jug of dilute acid being sufficient for the charge of 100
pairs of four-inch plates, iv. On making the trough pass through a quarter
of a revolution, it becomes active, and the great advantage is obtained of
procuring for the experiment the effect of the _first contact_ of the zinc
and acid, which is twice or sometimes even thrice that which the battery
can produce a minute or two after (1036. 1150.). v. When the experiment is
completed, the acid can be at once poured from between the plates, so that
the battery is never left to waste during an unconnected state of its
extremities; the acid is not unnecessarily exhausted; the zinc is not
uselessly consumed; and, besides avoiding these evils, the charge is mixed
and rendered uniform, which produces a great and good result (1039.); and,
upon proceeding to a second experiment, the important effect of _first
contact_ is again obtained. vi. The saving of zinc is very great. It is not
merely that, whilst in action, the zinc performs more voltaic duty (1128.
1129.), but _all_ the destruction which