Cecil Henry Bullivant

A phenomenon is always mysterious, so long as its origin remains hidden. That is to say that any event, the causes of whose manifestation are obscure, will be found to prompt some feeling of wonderment.

For this reason then—just as an automobile in motion will bewilder a savage, because he has at no time seen any but living creatures moving, and does not understand the new mechanism—so for us an electrical effect mostly presents something of a miraculous nature. To take a concrete example. Whereas the ringing of a church bell by the sexton engenders no feeling of wonderment in the average listener’s breast, the buzzing of an electric bell, which ensues upon connecting with a battery, does have this influence to a greater or less extent, because the electricity’s behavior is by no means so obvious as that of the sexton pulling the rope.

Let this character of the miraculous then, which pertains with scarcely an exception to every electrical phenomenon, stand as an excuse for the experiments to be detailed hereafter.

Electricity may be produced by a variety of methods. For commercial purposes, where unstinted supplies are necessary, mechanical energy is converted into the subtle force by means of dynamos. Exceptional sources of mechanical energy are now frequently used, as witness the Niagara Falls, where electric current is produced on the site, and whence it is conducted by cables to places of utility; and also the case of Nansen’s “Farthest North” Expedition (before Cook found the Pole!), which utilized a deck windmill for installation of electric light aboard.

Electricity is also produced when any two substances are brought into contact, and more especially if they are placed near one another, but not touching, in certain liquids, thereby forming “cells.” With these arrangements, electricity finds its source in chemical action; and, although not powerful, such cells are extensively employed, on account of reliability, in telephone and telegraph systems. No more convenient source of galvanic energy has yet been devised than a battery of “cells”—i.e. a number of cells connected together—and the type which we intend to use, and of whose construction the following is a description, is among the cheapest possible to make and maintain.

The battery is to consist of eight cells, connected together, in a manner hereafter described. For each cell procure a 1 lb. stone jar (A), and line it inside with a sheet of tin (B), which may be cut from a condensed milk can, and should be curved so as to press outwards against the jar’s inner surface (Fig. 1). A 2-inch length of copper wire (C) is soldered to its upper edge.

Fig. 1.—Making a cell.

Fig. 2.—Copper spiral surrounded by broken coke in rag or flannel bag.

The next operation is to twist an 8-inch piece of copper wire for about 6 inches of its length round a pencil, thus forming a spiral (X), round which a flannel bag (A) filled with small coke (B) is tied (Fig. 2). At least two thicknesses of flannel are advantageous, or if this be found rather expensive, flannel and rag combined, or odd pieces of rag alone may be utilized.

The chief considerations are to construct a porous wall of appreciable thickness round the coke, and to avoid colored rags if possible. The bag is to stand upright in the middle of the jar, leaving about ¹/₂-inch space all round to be packed with zinc scrap, which for convenience may well be “granulated.” To make this, melt up as much waste zinc as can be collected in a ladle and pour it in a thin stream into a large bowl of cold water, moving the ladle over the surface of the water meanwhile, in order to cool the zinc stream as suddenly as possible. The zinc which forms in a heap at the bottom of the bowl should be breakable into very small pieces, and is termed “granulated” (Fig. 3).

Fig. 3.—Granulating zinc.

Fig. 4.—Section of the complete cell.

When the cell has thus been assembled with curved tin sheet, bag of coke and broken zinc in place, it is nearly filled with strong salt solution, and above this, in order to prevent evaporation, a thin layer of melted tallow may well be poured. Fig. 4 represents a section of the complete cell, A being the flannel bag containing coke; B², wire from coke; C, wire from tin; D, layer of tallow; E, level of solution; F, the jar; G, the tin; H, the zinc.

The eight components of the battery being thus complete, nothing necessary remains but to connect them together. However, they will prove more portable and self contained if arranged in a shallow wood tray. This may be either a confectionery box—if one of suitable dimensions is obtainable—or can perhaps be constructed as indicated by the accompanying sketch, with handles at either end (Fig. 5). It should certainly be strong, as the set of jars is of considerable weight, and would, if accidentally dropped, create a pretty printers’ pi. Lastly, when the cells have been arranged in two rows of four a side, the finishing touch is to join the copper wire ends by twisting, according to the plan shown in Fig. 6, and the battery is complete. The end wires A and B will be referred to hereafter as negative and positive terminals respectively.

Experiment 1.—Connect one extremity of a straight wire with the battery’s positive terminal, and place it on the table so as to lie due north and south. Above it stand a compass, whose needle—also pointing due north and south—will be parallel to the wire (Fig. 7). Now, when the free end of the north-south conductor is connected to the battery’s other terminal so that a current may flow, the needle swings round at right angles and thus now lies east and west. Needless to add, electricity prompts the needle’s behavior, and unless such movement does take place, the cells are at fault somewhere.

Experiment 2.—Having decided by the compass’s behavior that the battery is actually efficient, bring the terminal wires into contact in the dark, and notice the slight spark (Fig. 8). Next obtain a spare bobbin from an old electric bell (Fig. 9), and pass the current round the coils whilst making the spark. This should now be more distinct—thicker, and brighter, though not so frequent—owing to induction taking place between the wire coils.

Experiment 3.—Repeat the previous experiment whilst using pieces of carbon, round which the free wire ends (D and E, Fig. 9) are twisted, to bring into contact with one another (Fig. 10). The spark obtained is very bright, and may possibly by careful handling be maintained for a moment or two; if the current is more powerful, the spark does keep constant, even though the carbons be drawn apart considerably, and thus forms in principle such an arc lamp as floods the streets of towns with their dazzling rays. The pieces of carbon may frequently be picked up beneath arc light standards, after the electrician has gone on his rounds “trimming” the lamps.

Experiment 4.—Again repeat the No. 2 experiment, but insert a rough file in the circuit and drag the free end of a wire from the battery up and down its surface (Fig. 11). Sparks in plenty, but apparently frail and resembling those thrown off by squib fireworks, are produced in this manner.

Experiment 5.—If a few iron filings (A, Fig. 12) be scattered evenly on a sheet of paper (C, Fig. 12) and a horse-shoe magnet (B, Fig. 12) approached from beneath, the filings arrange themselves in a curious design, which really maps out the magnetic lines of force. Now, if this experiment is repeated whilst using the bell-bobbin in place of the permanent horse-shoe magnet, and a current passed round the coils, the same disposition of the filings ensues, showing that the bobbin’s iron cores have been magnetized. In Fig. 13, A is the filings; B, the wire from negative terminal battery; C, the sheet of paper; and D, the wire from positive terminal.

Experiment 6.—“Flax” wire, whose core consists of about forty fine copper filaments stranded together, may often be had in scrap lengths at electricians’ shops, as it finds wide employment in lighting installations. The silk and rubber insulation should be ignited and allowed to burn, any residue being carefully wiped off with rag, after which two lengths of, say, three strands apiece are separated from the wire core. These are very flexible, so that when attached to the battery terminals and magnet wires the bobbin, being extended as shown by a silk strand, is able to revolve freely in any direction. As a matter of fact, whilst the current is flowing the bobbin sets itself north and south like any other magnet—a very ordinary performance, the reader may remark! But, on the other hand, if the flexible wires be changed over so that the one previously connected to the battery’s positive terminal is now connected to the negative and vice versa, with the result that the current travels round the bobbin coils in an opposite direction, the electro-magnet swings half a turn, and comes to rest with its pole that was towards the north now pointing south. So that the bobbin resembles a weathercock, except in so far as it changes with the current instead of the wind (Fig. 14).

Experiment 7.—The number “7” has been regarded among races of men as peculiarly fortunate. Perhaps happily, therefore, it falls to this experiment, which, indeed, is rather the construction of new than the arrangement of old apparatus. The magnetic properties of a bell-bobbin may be utilized in constructing a primitive electro-motor. Decapitate four 1¹/₂-inch nails, and, having bent ¹/₈-inch of both ends of each at right angles, mount them equal distances apart round the circumference of a thread reel (Fig. 15).

Next plug the center hole of this reel with hard wood, and bore another hole through of smaller diameter, so as to slide stiffly on a straight piece of ¹/₈-inch brass wire. About 1 inch from the cotton reel is to be soldered a ³/₈-inch square of tin or copper sheet, having a hole at its center through which the brass spindle passes (Fig. 16). Two small brass standards, for which straightened curtain-rod clips may well be employed, are screwed about 3¹/₂ inches apart to a wooden baseboard, and have a hole drilled near their top edges to accommodate the spindle (B, Figs. 16 and 17). This being placed in position, should be provided near the bearings with washers (E, Fig. 17) and beads (D, Fig. 17), the washers being soldered in order to prevent lateral movement of the shaft. Lastly, with a view to realistic appearance, solder a small tin fan (C, Fig. 17) to one projecting end of the spindle, and enamel or paint it gray. The arrangements of these fittings are made quite clear by the diagram.

By now the most difficult part of our task has been attempted, so that if the reel and spindle revolve “sweetly” in the bearings, no doubt need be entertained as to whether the motor will ever reach completion.

The bell-bobbin must be mounted with its magnet faces as near the reel circumference as possible, and with their centers the same height above the baseboard as the spindle. A piece of wood beneath the bobbin, of such thickness as to keep it at the right height, and another strip across the top, through the ends of both of which screws are driven into the baseboard, will secure the magnet firmly in position (Fig. 18). The next operation is to bend a springy strip of brass to the shape shown in F, Fig. 19, and fix it immovably by the screw G—round which one free end of the bobbin wire (L) has been twisted several turns—to the baseboard, so that its top portion misses the metal square or contact-breaker (P) on the spindle by about ¹/₄ inch. Now drive a second screw (R) carefully into the wood through another hole in the strip, until this latter presses lightly against each point of the contact-breaker successively as the spindle revolves.

The little motor is now complete, except, perhaps, for the addition of two terminal screws, one of which is joined with the remaining free bobbin wire, and the other by a short length of wire to either of the bearings. The entire connections are shown in the accompanying sketch (Fig. 20). Now for working! Connect the battery wires to the motor terminals, and adjust the spindle so that one corner of the contact-breaker is fairly touching the vertical brass strip. A current should now be flowing round the bobbins, which consequently become magnetized and attract the nearest iron nail fastened to the thread reel. If the iron is not sufficiently near to be under the magnet’s influence, turn the reel on the shaft until it is in the proper position. The motor, with a little adjustment, ought to run merrily, as the bell-bobbin—alternately magnetized and demagnetized—attracts and releases the short iron bars.

Experiment 8.—Connect the battery terminals together by means of some thin iron wire such as is used for wiring flowers, and twist it into a spiral so that it may rest comfortably in a cup of cold water (A, Fig. 21). Stand also therein a thermometer (B, Fig. 21). The water’s temperature will be observed to rise steadily, showing that the passage of the electric current heats the iron wire (C, Fig. 21), which in turn imparts some warmth to the surrounding liquid.

Experiment 9.—The previous experiment showed that an electric current heats a material through which it passes. If the thin iron wire be shortened to a length of about ¹/₂-inch, our battery will probably bring it to red-heat, thus demonstrating the principle of electric incandescent lamps. The difference between theory and practice, however, in this case consists in the use of carbon, or, very rarely, platinum, in place of the iron filament, and of inclosing this in a glass bulb free of air, so that combustion cannot proceed rapidly.

Experiment 10.—Immerse two wires from the battery terminals at some little distance apart in a glass of water, which has been slightly soured with sulphuric acid or spirits of salt. The weak acid readily conducts the electric current, which decomposes the water into its chemical constituents, hydrogen and oxygen, the former gas coming off in bubbles at the wire which leads from the battery tins, and the oxygen round the other conductor (Fig. 22). The hydrogen bubbles may perhaps be ignited as they are evolved by holding a lighted match just near the water’s surface; or another method is to seal the wires into separate glass tubes, so that both dip beneath the water, and light the hydrogen gas as it escapes from the tube’s upper end (Fig. 23). In this case great care must be taken to allow time for the expulsion of all air from the tube, because hydrogen and air in certain proportions form a very explosive mixture.

Experiment 11.—Repeat the foregoing experiment, using copper sulphate solution in place of the acidified water. After the current has passed for some time, one of the wires will be noticed to have become thicker whilst the diameter of the other has decreased. This behavior is owing to deposit of copper from the solution on the one conductor and abstraction of metal from the other, whose bulk diminishes in automatically maintaining the solution’s strength (Fig. 24). In this reaction is seen the basis of commercial electroplating—silver and nickel solutions being mostly employed instead of the copper bath, since these are the metals with which those of a baser nature are more frequently plated.

Experiment 12.—Electrotyping is a modification of electro-plating, where a mold of wax coated with some conducting substance like graphite is used to deposit the metal upon. Melt some quantity of sealing-wax on to a piece of cardboard, so that it spreads out slightly larger in diameter than a fifty-cent piece, and when just plastic press the “head” surface of the new coin into the wax, so that an exact replica is obtained. Fasten a copper wire by some extra wax to the cardboard disc (as in Fig. 25), and carefully cover the whole matrix with powdered blacklead, working it well into the crevices and up to the copper conductor, with a camel-hair brush. Hang this in a jar containing saturated copper sulphate solution—the copper wire being connected to the negative battery terminals (A, Fig. 26), whilst a sheet of copper or coil of wire is suspended in the solution some little distance from the sealing-wax mold, with a wire connecting to the other battery terminal (B, Fig. 26).

So long as the current continues flowing a reddish deposit will form on the blacklead surface, and if the action be allowed to continue until a fair thickness of metal is secured, the wax may be carefully melted off, leaving an exact relief of a fifty-cent piece’s reverse side in a copper. Any medal or seal may be used in place of the silver piece to obtain a first mold, but the coin has been mentioned as being probably the most suitable article near at hand.

With this example of electrotyping, our series of descriptions must terminate. But the embryo scientist, who has traveled thus far, need not cast his apparatus to the winds and henceforward forsake electrical matters. He may arrange various combinations of wines and liquids—such, for example, as passing the current through water to his motor, and noting the decrease in speed, or insert various lengths of iron wire in the circuit. Possibly the batteries will betray exhaustion, and they may then be reinstated by discarding the old salt solution, rinsing and replenishing the granulated zinc, and washing the flannel bags in permanganate of potash solution. These batteries are, in fact, a real asset, as they can be used—three or four together—in setting up an electric-bell installation, and are easily replenishable, when at length their life begins to ebb.

An endless fund of amusement—less expensive and more instructive than many—awaits those who explore the realms of the pygmy lightning spark.