for the part, and
the top of the stage is marked X. The stage is made of 2 by 4-in.
stock. The height may vary, according to the requirements. If the
affair is set up on a barn or shed, the staging will be sufficient
to support the device. But if the stage is constructed direct from
the ground, it will be necessary to use some long timbers to get
the wheel up high enough to receive the benefit of the force of
the wind. Proceeding on the plan of the derrick stand, as shown in
Fig. 6, a stage of considerable height can be obtained.

** To Renew Old Dry Batteries [401]

Remove the paper that covers the cell and knock several good-sized
holes in the zinc shell. Place the battery in a glass jar, fill it
two-thirds full of strong sal ammoniac (or salt) solution and
connect the terminals to whatever apparatus the current is to be
used for. A few drops of sulphuric acid quickens and improves the
action. The output of the cell will be nearly as great as when the
battery was first bought.
--Contributed by C. W. Arbitt, Austin, Texas.

** Blue Dye[401]

Prussian blue and Chinese blue are both the same chemically but
they do not cut or look the same.

** Acetylene lamp [401]

When an acetylene lamp is in good order it will light up slowly
with a hissing noise followed by a pure white flame. Should the
lamp light up quickly with a yellowish flame, it is a sign of a
leak somewhere.

** Another Electric Motor [401]

This form of electric motor is used largely in England in the form
of an indicator. It is very easily made and

[Illustration: Electric Motor]

if you have an old electro-magnet will cost practically nothing.

A large soft-iron wheel is mounted on an axle with a pulley-wheel
on one end and a circuit breaker on the other end. The teeth on
the circuit-breaker must be the same number as on the soft-iron
wheel.

The electro-magnet is mounted so that its core is level with the
axle and in a line with the wheel. One wire from it is attached to
one binding screw and the other end is grounded to the iron frame
that supports it. This frame is connected to the frame supporting
the wheel. A small brush presses on the circuit-breaker and is
connected to the other binding screw.

In the diagram A represents the iron wheel; B, the brush; C, the
circuit breaker; D, the magnet. The wire connecting the two frames
is shown by a dotted line.

To start the motor, attach your battery to the screws and turn