hould cover Z.

[Illustration: Fig. 9.]

(G) Connect the wires leading from Z and C to your sounder and key. (See
diagram.) The cell will be weak at first, and it may not be able to run
your sounder. If this is the case, "short-circuit" it by allowing the
current to run around and around through the sounder and key, the switch
being closed. You may also "short-circuit" the cell by joining the two
wires together. This will, in a few hours, make the dividing line
between the blue and white quite distinct, when the cell will be
stronger. If you have a short line only, the battery may be
short-circuited through your sounder or other coils of wire for 5 or 6
hours a day, without working it too much. It may be necessary to draw
off some of the clear zinc sulphate, replacing it with clear water, if
the blue line gets too low. Add water occasionally to make up for
evaporation.

14. Regulating. The two solutions are kept apart by gravity, as the
copper sulphate is heavier than the zinc sulphate. The dividing line
between the blue and white solutions is fairly clear when the battery
works well, and it should be about half way between C and Z, or about at
J, Fig. 9. Never allow the blue to get as high as Z, as this indicates
that the cell is not worked enough. The dividing line can be lowered by
allowing it to run a buzzer or bell for a few hours, or by simply
short-circuiting it. If the blue gets much below J it indicates that you
are working the cell too hard, or that you need more copper sulphate.
The harder the cell works, the more zinc sulphate is formed, and the
lower the dividing line becomes.

15. Gravity Batteries of two more cells are needed when used on
telegraph lines. You will need 1 cell to each sounder; that is, for a
short line in the house with two sounders, use 2 cells. If you use a few
hundred feet of wire running to a friend's house, use 3 cells. They must
be joined in series; that is, the copper of one to the zinc of the
other. (See diagram of complete telegraph line.) Do not use ground
connections for short lines and home-made sounders; use a return wire.
Do not use different kinds of cells upon the same line.

APPARATUS 10.

_16. Storage Battery._ To show the principle of storage batteries it is
only necessary to use two plates of lead dipped in the battery fluid of
App. 14. The cell may be made as in App. 5, Fig. 5, the only difference
being that both plates are of sheet-lead. It will be an advanta