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80 THE BOY ELECTRICIAN

negative (zinc) of the gravity battery to the negative (out-
side plates) of the storage cell. Allow the current to flow
through the storage battery for several days or until the
positive plate turns to a dark chocolate-brown color and the
negatives to a gray-slate.

After the cells have once been “formed ” all that they
require is occasional recharging from gravity cells or from a

   

ZINC COPPER

FIG. 75. — Gravity Cells.

These consist of zinc and copper elements. immersed in a zinc-copper sulphate solution. They
cannot be easily made, and are best purchased. The illustration also shows the star-shaped copper
and “ crowfoot ” zinc element used in a grawty cell.

dynamo, by connecting the positive pole of the charging
current to the positive plates of the storage cells and the
negative pole to the negative plates.

When the cells are fully charged, bubbles of gas will rise
freely from the plates. If a dynamo is used it must be
“ shunt ” wound and not a “ series ” machine. Recharging
will only require about one-quarter of the time consumed
in forming.

It is a very good plan to connect twelve gravity cells in
series and use them to recharge the storage battery. The
gravity cells can always be kept connected to the storage

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