This coil should
have a diameter
[Illustration: Gasoline Burner]
of only 1 in. One end of the copper tube is bent around so it will
point directly into the reamed-out hole in the end of the brass
tube, A. A nipple, N, is made by drilling a 1/8-in. hole halfway
through a piece of brass and tapping to screw on the end of the
1/8-in. copper pipe. A 1/64-in. hole is then drilled through the
remaining part of the nipple. The other end of the copper tube is
connected to the supply tank. The distance between the nipple, N,
and the ends of the tube, A, should be only 5/16 of an inch. Fig.
2 shows the end view.
** A Homemade Telephone Receiver [55]
A telephone receiver that will do good work may be built very
cheaply as follows: For the case use an ordinary 1/2-lb.
baking-powder box with a piece of heavy wire soldered on the
inside, 1-5/16 in. from the bottom. For the magnet use a piece of
round hardened steel about 3/8 in. in diameter and 1-1/4 in. long.
If desired, a piece of an old round file may be used for the
magnet core, which should be magnetized previous to assembling,
either by passing a current of electricity around it, or by direct
contact with another magnet.
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