takes place with the ordinary forms
of battery between the experiments is prevented. This saving is of such
extent, that I estimate the zinc in the new form of battery to be thrice as
effective as that in the ordinary form. vii. The importance of this saving
of metal is not merely that the value of the zinc is saved, but that the
battery is much lighter and more manageable; and also that the surfaces of
the zinc and copper plates may be brought much nearer to each other when
the battery is constructed, and remain so until it is worn out: the latter
is a very important advantage (1148.). viii. Again, as, in consequence of
the saving, thinner plates will perform the duty of thick ones, rolled zinc
may be used; and I have found rolled zinc superior to cast zinc in action;
a superiority which I incline to attribute to its greater purity (1144.).
ix. Another advantage is obtained in the economy of the acid used, which is
proportionate to the diminution of the zinc dissolved. x. The acid also is
more easily exhausted, and is in such small quantity that there is never
any occasion to return an old charge into use. The acid of old charges
whilst out of use, often dissolves portions of copper from the black
flocculi usually mingled with it, which are derived from the zinc; now any
portion of copper in solution in the charge does great harm, because, by
the _local_ action of the acid and zinc, it tends to precipitate upon the
latter, and diminish its voltaic efficacy (1145.). xi. By using a due
mixture of nitric and sulphuric acid for the charge (1139.), no gas is
evolved from the troughs; so that a battery of several hundred pairs of
plates may, without inconvenience, be close to the experimenter. xii. If,
during a series of experiments, the acid becomes exhausted, it can be
withdrawn, and replaced by other acid with the utmost facility; and after
the experiments are concluded, the great advantage of easily washing the
plates is at command. And it appears to me, that in place of making, under
different circumstances, mutual sacrifices of comfort, power, and economy,
to obtain a desired end, all are at once obtained by Dr. Hare's form of
trough.

1133. But there are some disadvantages which I have not yet had time to
overcome, though I trust they will finally be conquered. One is the extreme
difficulty of making a wooden trough constantly water-tight under the
alternations of wet and dry to which the voltaic instrument is subject.