uth of the bottle a sharp report will be heard.

If the bottle is fitted with a cork containing two wires nearly
touching, and the apparatus connected with an induction coil, in
such a manner that a spark will be produced inside the bottle, the
explosion will blowout the cork or possibly break the bottle.
Caution should be used to avoid being struck by pieces of flying
glass if this experiment is tried, and under no condition should a
lighted match or spark be brought near the end of the rubber hose
D, as the presence of a little air in the generator will make an
explosive mixture which would probably break the jar.

** Gasoline Burner for Model Work [55]

When making a small model traction engine or a locomotive the
question arises, "What shall the fuel be?" If you have decided to
use gasoline, then a suitable burner is necessary. A piece of
brass tubing about 3 in. in diameter and 6 in. long with caps
screwed on both ends and fitted with a filling plug and a bicycle
valve makes a good gasoline supply tank, says the Model Engineer,
London. The bicycle valve is used to give the tank an air pressure
which forces the gasoline to the burner.

The burner is made from a piece of brass tube, A, as is shown in
the illustration, 1/2 in. in diameter and 2-1/2 in. long, which is
plugged up at both ends, one end being drilled and reamed out to
5/16 in. Three rows of holes 1/16 in. in diameter are drilled in
the brass tube. One row is drilled to come directly on top, and
the other two at about 45 degrees from the vertical. It is then
fitted to a sheet steel base, B, by means of the clips, C C, Fig.
1. A piece of 1/8-in. copper pipe, P, is then coiled around the
brass tube, A, which forms the vaporizing coil. 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
che