The telegraph manual: a complete history and description of the semaphoric, electric and magnetic telegraphs of Europe, Asia, Africa, and America, ancient and modern.

90 VOLTAIC ELECTRICITY.
Batteries in which graphite is substituted for plates of copper, have been introduced by Mr. C. V. Walker in working the
electric telegraphs of the Southeastern Railway Company,
and with very good results. One of these batteries of twelve
pairs, of which a record was taken, was kept in daily action
for ninety-seven weeks without having been washed or having
the sand changed. It was supplied with about a dessert-spoonful of acid-water twenty-one times during the period it was in
action, and six times with merely warm water. In one instance it did duty for seventy-seven days without having been
touched.
Dr. Wollaston contrived the arrangement shown in fig' 8
for obtaining the greatest
Fig. 8. amount of power from a given
- ~I ^ _ _ -surface of zinc. The copper
t::-=1 ~ plates c c c are doubled, so
as to expose a conducting
surface to both sides of the
zinc plates, p B Br Theplates
are also brought as close
I ~ ~ Miis together as possible without
actual contact. They are
~liable t[secured to a bar of wood, and
acn of are kept apart by pieces of
cork. With a battery of this
kind, consisting of a few pairs of large plates, prodigious heating power is produced, though the intensity of the electricity
is too feeble to communicate a shock.
THE DANIELL VOLTAIC BATTERY.
The battery invented by Professor Daniell, is constructed on
a different principle. It is found in the voltaic arrangements,
that the zinc and copper plates immersed in the same cell are
liable to hav e their ac ttion imp eded, and ultmately altogether
arrested, by the transfer of zinc to the copper surface. The
action of the conducting plate is also greatly retarded by the
accumulation of hydrogen gas; so much so, indeed, that very
frequently, after the first minute the battery has been put in
action, not more than one tenth of the original power is obtained. In Professor Daniell's battery the zinc and copper
plates are kept apart by means of porous earthenware cells, or
by pieces of animal membrane, which, though sufficient to
prevent the passage of metallic particles, do not materially interrupt the voltaic action.