=A Toy Shocking Machine.=.The little shocking machine shown in Fig. 187 is a harmless toy with which you can have an endless amount of fun when entertaining friends. The shock it produces is not severe, but strong enough to make your friend's arm and wrist muscles twitch, and perhaps cause him to dance. Large shocking coils contract the muscles to such an extent that it is impossible to let go of the metal grips until the current has been shut off, but in our small shocking machine the handles can be dropped the instant the person holding them wishes to do so.

[Ill.u.s.tration: FIG. 187.--Detail of the Toy Shocking Machine.]

The shocking machine consists of an _induction-coil_, an _interrupter_, and a pair of _handles_, all of which are easy for a boy to make, and a _wet_ or _dry battery_ of one or two cells to furnish the current.

[Ill.u.s.tration: FIGS, 188-191.--Details of Induction-Coil.]

=The Induction-Coil= is the first part to make. This is shown in detail in Figs. 188 to 191. The coil has windings of two sizes of wire upon an iron core. For the core buy a 5/16-inch carriage-bolt 2-1/2 inches long, and for the wire coils get some No. 20- or 24-gauge electric-bell insulated copper wire, and some No. 30-gauge insulated magnet-wire. To keep the wire from slipping off the ends of the bolt core, cut two cardboard ends about 1-1/2 inches in diameter. Slip one of these on to the bolt next to the head, and the other one next to the nut, as shown in Fig. 188.

Three layers of the coa.r.s.e wire should be wound on first, for

=The Primary-Coil.= Pierce a hole through one cardboard end, stick the wire through it, and allow about 5 inches to project upon the outside; then commence winding the wire upon the core, placing each turn close to the preceding turn. When the opposite end of the bolt has been reached, wind back to the starting point, then work back to the other end again.

There will be in the neighborhood of 175 turns in the three layers. Cut off the wire so there will be a 5-inch projection, and stick the projecting end through a hole in the cardboard end. This completes the primary-coil (Fig. 189).

Before winding the small wire on top of the primary-coil, to form

=The Secondary-coil=, wrap the primary-coil with a layer of bicycle tape, or glue several layers of paper around the coil. Then wind on the small wire as you did the coa.r.s.er wire, being very careful to get it on evenly and smoothly. Wind eleven layers on the coil, and run the end of the eleventh layer out through the cardboard end (Fig. 190). There should be about 100 turns of this wire to the layer, or 1100 turns in all.

A crank arrangement can be rigged up to make the winding easier, but with patience, and by doing the work slowly, the wire can be wound almost as well by hand. It is difficult to keep track of each preceding turn, while winding, because of the fineness of the wire, and on this account it is a good scheme to coat each layer with bluing after it has been wound on, so that each turn of the following layer will show plainly against the stained layer beneath it. Figure 190 shows the complete induction-coil.

Cut a base block 5 inches wide and 7 inches long, bevel the top edges to give it a trim appearance, and mount the induction-coil to one side of the center (Fig. 187), strapping it in place by means of two tin straps similar to that shown in Fig. 191, cut from a tin can.

The projecting ends of the primary-coil connect with the battery, while the two ends of the secondary-coil connect with the handles. Make three binding-post plates out of folded pieces of tin, similar to plates _B_ and _C_, in Fig. 182. Tack two of these to the end of the base and connect the secondary-coil wires to them (Fig. 187), and tack the third near one end of the induction-coil and connect one primary-coil wire to it (Fig. 187).

=For the Handles= take two pieces of broom-handle 3-1/2 inches long, and cover each with a piece of tin (Fig. 192). The pattern for the tin covering (Fig. 193) shows how tabs are prepared on the ends and holes punched through them for connecting with the induction-coil. The connecting wires should be 5 or 6 feet long. Flexible wire is better than bell-wire for these, because it is more easily handled in pa.s.sing the handles around. Tack the tin covering to the pieces of broom-handle.

[Ill.u.s.tration: FIGS. 192 and 193.--Details of Shocking-coil Handles.]

The purpose of the induction-coil is to raise the voltage of the battery. The flow of current must be an interrupted one, in order to shock, and therefore

=An Interrupter= must be inserted between the battery and one of the wires leading to the primary-coil of the induction-coil. There are several ways to construct an interrupter, but the scheme which I have invented for the model of this shocking-machine (Fig. 187) serves the purpose nicely, and is a neat appearing little piece of apparatus. This interrupter is easily constructed as you will see by the working details shown in Figs. 194 to 198.

[Ill.u.s.tration: FIG. 194.--Interrupter for Shocking-coil.]

Cut the base block _A_ 1-1/2 inches wide and 2-1/2 inches long. Make the shaft _B_ 2-3/4 inches long and of a diameter equal to the hole in a thread spool; and prepare the crank _C_ to fit on the end, and drive a brad into it for a handle. Fasten the crank to the shaft with glue, or by driving a small brad through the two. The shaft supports _D_ should be prepared as shown in Fig. 196, 1-1/4 inches wide across the bottom, 5/8 inch wide at the top, and 1-3/4 inches high. Bore a hole through each, a little below the top, and large enough so the shaft will turn easily, and fasten these supports with brads to the sides of base _A_.

Drive eight brads into a thread spool, s.p.a.cing them equidistant from one another, and mount this spool upon the shaft (_E_, Fig. 194), first slipping the shaft through one support, then through the spool, and then through the other support. Drive the spool brads a trifle into the shaft to hold the spool in position.

The projecting arm _F_ (Fig. 194) is a strip of tin cut from a can, and must be long enough so each nail-head will strike its end when spool _E_ is revolved. Drive a nail into base _A_, at _G_, and, after bending strip _F_ as shown in Fig. 198, fasten it with brads upon the top of an upright made similar to _H_ (Fig. 197), and nail this upright to the end of base _A_. The upper end of strip _F_ must be bent so it will bear down upon the head of nail _G_.

The wire from the primary-coil which is as yet not connected should be attached to nail _G_, and one battery wire should be connected to a binding-post plate _I_ fastened to the lower end of strip _F_. Figure 198 shows how the binding-post plate is made out of a doubled piece of tin, with a hole punched through it for a small binding-screw.

This completes the interrupter. Mount it beside the induction-coil upon the base block, and connect it with the battery and the induction-coil, as shown in Fig. 187. Connect the battery cells in series. Two cells will be enough.

[Ill.u.s.tration: FIGS. 195-198.--Details of Interrupter.]

=How the Interrupter Works.= When you turn the crank of the interrupter, each nail in spool _E_ raises the end of strip _F_, in pa.s.sing it, thus breaking the electrical contact between it and the head of nail _G_. If the strip has been bent properly, it will spring back into contact with the head of nail _G_, and each time the contact is made, the person holding the handles will receive a shock. The strength of the current can be regulated somewhat by the speed with which the interrupter crank is turned. The shocks are stronger and more distinct when the crank is turned slowly.

Home-made electrical toys of a light construction are easily operated by a toy motor, when the motor and battery cell are not carried by the toy; but when both are transported, as in the case of a wagon, the construction must be very carefully worked out, or the motor will not be powerful enough to drive the wheels.

=The Toy Electric Motor Truck= shown in Fig. 199 is of light construction, the axle bearings produce very little friction, and the battery is light and of a powerful type.

[Ill.u.s.tration: FIG. 199.--A Toy Electric Motor Truck.]

Get an oblong shaped cigar-box for the _bed_ and _sides_ of the truck, several large thread spools for _wheels_ and _pulleys_, two small silk-thread spools, four lead-pencils, or sticks whittled perfectly round and 1/4 inch in diameter, for _axles_, _belt-shaft_, and _steering-wheel post_, and six screw-eyes 5/16 inch in diameter for the _bearings_.

First, place the cigar-box in a wash-boiler or wash-tub of hot water, and allow it to remain there until the paper labels have soaked off or loosened sufficiently so they can be sc.r.a.ped off with a knife.

[Ill.u.s.tration: FIG. 200.--Top view of Electric Motor Truck.]

Then, after the box has thoroughly dried, cut the two strips _A_ (Fig.

208), and fasten them to the bottom, one at each side. Screw the screw-eye axle bearings into these strips. Place them at equal distances from the ends of the strips.

=The Wheels= are made from the f.l.a.n.g.e ends of the large spools. Figure 202 shows the front pencil axle. Slip the center portion of one of the large spools on to this for a pulley, then stick the pencil ends through the screw-eyes in strips _A_, and glue the spool-end wheels on to them. The rear axle is like the front one, with the spool pulley omitted (Fig. 203).

=The Upper Shaft= shown in Fig. 201 supports a spool pulley like the one on the front axle, and its screw-eye bearings should be screwed into the top edge of the sides of the box (Fig. 200), directly over the front axle. Slip a silk-spool on to each end of this shaft to keep its ends from slipping out of the screw-eyes.

[Ill.u.s.tration: FIGS. 201-203.--Details of Axle and Belt Shaft.]

=The Belts.= As you will see by Figs. 200 to 202, the upper large pulley is belted to the motor pulley, and another belt extends from the upper shaft down to the pulley on the front axle. Rubber-bands make the best belts. Cut a hole through the bottom of the cigar-box for the belt extending from the upper shaft to the front axle to pa.s.s through. Screw the toy motor to the cigar-box with its pulley directly in line with the upper shaft pulley. Wrap the spool pulleys with bicycle-tape, to keep the rubber-band belts from slipping.

=The Battery.= A dry battery is too heavy for the motor truck to carry; so we must make a special two-cell battery like that shown in Fig. 204.

Two gla.s.s tumblers to hold the solution, a pair of battery zincs, a pair of carbons, and a bi-chromate of potash solution, are needed. Old battery zinc pencils with several inches of the eaten end cut off (Fig.

206) will do for the zincs, and the carbons from worn-out dry-battery cells cut to a corresponding length will do for the carbons. Fasten together the zincs and carbons with rubber-bands, as shown in Fig. 207, after wrapping a piece of bicycle-tape around the upper end of the carbon and inserting a small wad of it between the lower ends of the carbons and zincs, to keep them from touching one another.

[Ill.u.s.tration: FIG. 204.--Two Home-made Battery Cells Connected in Series.]

Figure 205 shows a completed cell, and Fig. 204 how the two cells are connected in _series_, that is, with the carbon of one connected to the zinc of the other. Twisting the connecting wires into coils, as shown, is a good method of taking up the slack.

[Ill.u.s.tration: FIG. 205.--A Single Cell.]

[Ill.u.s.tration: FIGS. 206 and 207.--Details of Zinc and Carbon.]

=The Bi-chromate Battery Fluid= is made up of bi-chromate of potash, sulphuric acid, and water, in the following proportions:

4 ounces of bi-chromate of potash 4 ounces of sulphuric acid 1 quart of water

In making up this solution, first add the acid to the water,--_never add the water to the acid_--and then, when the solution is nearly cool, add the bi-chromate of potash. Pour the acid into the water slowly, because the combination of the two creates a great deal of heat, and if the heat forms too quickly your gla.s.s bottle is likely to split. Label the bottle in which you put this solution POISON.

As the bi-chromate solution attacks the zinc element of a cell even when the current is not being drawn upon, the zinc should be removed when the cell is not in use.

=Amalgamating a Zinc Pencil.= To reduce the eating away of a zinc pencil used in a bi-chromate solution, the zinc should be amalgamated by rubbing a thin coat of mercury over its surface. Dip the zinc into the solution, first, then with a rag dipped in the solution rub the mercury on to it.

Cut an opening through the cigar-box large enough for the two tumblers to set in. Then cut a strip of tin about 1 inch wide and 8 inches long, and bend it into a U-shaped hanger, to support the tumbler bottoms. Slip the hanger ends under strips _A_, bend them against the sides of the box, and fasten with tacks (Figs. 208 and 209).

[Ill.u.s.tration: FIG. 208.--Plan of Motor Truck Bottom.]

[Ill.u.s.tration: FIG. 209.--Section through Bottom.]

Figure 200 shows how the battery cells are connected. A small switch can be fastened to the side of the truck to shut off and turn on the current, but, instead, you can simply withdraw one pair of elements from its tumbler to shut off the current. When through playing with the truck, however, it is important to remove both pairs of elements and wash them off, because the bi-chromate solution attacks the zinc elements even when the current is not in use. As the bi-chromate solution stains very badly, it is advisable to operate the motor truck only where there is no danger of ruining anything in case some of the solution spills, as in the bas.e.m.e.nt or workshop. If you wish to use a dry-cell instead of the pair of bi-chromate cells, you can place the cell upon the floor and make the wires connecting it to the motor long enough so the truck can run back and forth across a room.