They
[Illustration: Setting Up a Gravity Battery]
follow directions carefully and then fail to get good results.
The usual trouble is not with the battery itself, but with the
circuit. A gravity battery is suitable only for a circuit which is
normally closed. It is therefore undesirable for electric bells,
induction coils and all other open-circuit apparatus. The circuit
should also have a high resistance. This makes it impractical for
running fan motors, as the motor would have to be wound with fine
wire and it would then require a large number of batteries to give
a sufficiently high voltage.
To set up a gravity battery: Use about 3-1/2 lb. of blue stone, or
enough to cover the copper element 1 in. Pour in water sufficient
to cover the zinc 1/2 in. Short-circuit for three hours, and the
battery is ready for use. If desired for use immediately, do not
short-circuit, but add 5 or 6 oz. of zinc sulphate.
Keep the dividing line between the blue and white liquids about
1/2 in. below the bottom of the zinc. If too low, siphon off some
of the white liquid and add the same amount of water, but do not
agitate or mix the two solutions.
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