Part 118 (1/2)

Insert the short end of the tube in the cork and place the other end in a test tube that is placed in water as shown. The globe may be fastened in position by a wire pa.s.sed through the cork and tied to a ring stand. If you do not have a ring stand, suspend the globe by a wire from a hook that is screwed into any convenient place.

A neat alcohol lamp may be made of an old ink or muscilage bottle.

Insert a wick in a piece of the gla.s.s tubing and put this through a hole bored in a cork and the lamp is ready to burn alcohol or kerosene. Alcohol is cleaner to use as a fuel. Fill the globe about two-thirds full of water or other liquid and apply the heat below as shown. The distilled liquid will collect in the test tube.

--Contributed by Clarence D. Luther, Ironwood, Mich.

** Old-Time Magic

** Balancing Forks on a Pin Head [427]

Two, three and four common table forks can be made to balance on a pin head as follows: Procure an empty bottle and insert a cork in the neck. Stick a pin in the center of this cork so that the end will be about 1-1/2 in. above the tap. Procure another cork about 1 in. in diameter by 1-3/4 in. long. The forks are now stuck into the latter cork at equal distances apart, each having the same angle from the cork. A long needle with a good sharp point is run through the cork with the forks and 1/2 in. of the needle end allowed to project through the lower end.

The point of the needle now may be placed on the pin head. The forks will balance and if given a slight push they will appear to dance. Different angles of the forks will produce various feats of balancing.

--Contributed by O. E. Tronnes, Wilmette, Ill.

[Ill.u.s.tration: Balanced Spoons]

** The b.u.t.toned Cord [427]

Cut a piece of heavy paper in the shape shown in Fig. 1 and make two cuts down the center and a slit as long as the two cuts are wide at a point about 1 in. below them. A string is put through the slit, the long cuts and back through the slit and then a

[Ill.u.s.tration: Removing the String]

b.u.t.ton is fastened to each end. The small slit should not be so large as the b.u.t.tons. The trick is to remove the string. The solution is quite simple. Fold the paper in the middle and the part between the long cuts will form a loop. Bend this loop down and pa.s.s it through the small slit. Turn the paper around and it will appear as shown in Fig. 2. One of the b.u.t.tons may now be drawn through and the paper restored to its original shape.

** Experiment with an Incandescent Lamp [427]

When rubbing briskly an ordinary incandescent lamp on a piece of cloth and at the same time slightly revolving it, a luminous effect is produced similar to an X-ray tube. The room must be dark and the lamp perfectly dry to obtain good results. It appears that the inner surface of the globe becomes charged, probably by induction, and will sometimes hold the filament as shown in the sketch.

--Contributed by E. W. Davis, Chicago.

[Ill.u.s.tration: Lamp]

** How to Make a Small Motor [428]

The accompanying sketch shows how to make a small motor to run on a battery of three or four dry cells and

[Ill.u.s.tration: Details of Small Electric Motor]

with sufficient power to run mechanical toys. The armature is constructed, as shown in Figs. 1 and 2, by using a common spool with 8 flat-headed screws placed at equal distances apart and in the middle of the spool. Each screw is wound with No. 24 gauge iron wire, as shown at A, Fig. 1. The commutator is made from a thin piece of copper, 1 in. in diameter and cut as shown in Fig.

3, leaving 8 points, 1/8 in. wide and 1/8 in.- deep. The field is built up by using 8 strips of tin, 12 in. long and 2 in. wide, riveted together and shaped as shown at B, Fig. 4. Field magnets are constructed by using two 3/8-in. bolts, 1-1/2 in. long. A circular piece of cardboard is placed on each end of the bolt, leaving s.p.a.ce enough for the bolt to pa.s.s through the field B, and to receive a nut. Wind the remaining s.p.a.ce between the cardboards with 30 ft. of No. 22 double-wound cotton-covered copper wire. A light frame of wood is built around the magnets, as shown at C, Fig. 4. Holes are made in this frame to receive the axle of the armature. Two strips of copper, 1/4 in. wide and 3 in. long, are used for the brushes. The armature is placed in position in its bearings and the brushes adjusted as shown in Fig. 4, one brush touching the shaft of the armature outside of the frame, and the other just touching the points of the commutator, which is placed on the shaft inside of the frame. Connect the outside wire of one magnet to the inside wire of the other, and the remaining ends, one to the batteries and back to the brush that touches the shaft, while the other is attached to the brush touching the commutator.