Chapter XII

MISCELLANEOUS APPARATUS

The field of applied electricity is such a wide one as to preclude any exhaustive handling of the subject in a book of this size. The aim has been to acquaint the young student with the basic principles of the science, and it is his part to develop these principles along the lines indicated in the preceding pages. But there are some practical applications that may be properly grouped under the heading of this chapter. They may serve as a stimulus to the inventive faculties of the youthful experimenter, and since the pieces of apparatus now to be described are useful in themselves, the time spent in their construction will not be wasted.

A Rotary Glass-cutter

When making a circle of glass it is generally best to let a glazier cut the disk, otherwise many panes are likely to get broken before the young workman succeeds in getting out a perfect one. But with a rotary glass-cutter the task is a comparatively simple one, and the tool is really an indispensable piece of apparatus in every electrician’s kit. (See Figs. 1 and 2.)

The wooden form is turned from pine or white-wood, and is three inches in diameter at the large end, or bottom, one inch in diameter at the top, and two inches high. It is covered with felt held on with glue. Directly in the middle of the top a small hole is bored one-eighth of an inch in diameter, and in this aperture an awl or marker is placed, handle up, as shown in Fig. 2. Notice that the awl is not made fast to the form, but is removable at pleasure. A hard brass strip twelve inches long, five-eighths of an inch wide, and one-eighth of an inch thick is cut at the end to receive a steel-wheel glass-cutter, as shown at the foot of Fig. 1.

A number of one-eighth-inch holes are bored along the strip, and half an inch apart, measuring from centre to centre. To cut a disk of glass the form is placed at the centre of the pane, the latter being imposed on a smooth table-top over a piece of cloth. The strip, or arm, is laid on the form, and over a small washer, so that one of the holes lines with that in the form. The awl is passed down through the strip and into the block, and the cutter is arranged in the slot at the end of the arm. Press down lightly on the handle of the awl, to keep the form from slipping; then the cutter is drawn around the glass, describing the circle, and cutting the surface of the glass, as shown by the solid line in Fig. 4. The disk must not be removed from the pane until the margin is broken away. With a straight-edge and a cutter score the glass across the corners, as indicated by the dotted lines in Fig. 4; then tap the glass at the underside along the line and break off the corners. After the corners have been removed tap the glass again, following the line of the circle; then break away the remaining fragments and smooth the edge.

To Smooth Glass Edges

To smooth the rough edge of glass there are several methods. The simplest way is to hold the disk or straight-edge against a fine grindstone and use plenty of water. The glass must be held edgewise, as shown in Fig. 5, and _not_ flatwise, as shown in Fig. 6. To properly grind a disk two workmen are necessary, one to turn the stone, and the other to hold the disk by spreading the hands and grasping it at the middle on both sides (see Fig. 5). In this manner the glass may be held securely, and slowly turned, so that an even surface will be ground. When the flat edge is smoothed, tilt the glass first to one side and then the other, and grind off the sharp edges.

Another method is to lay the glass on a table, upon a piece of felt or cloth, and allow the edge to project over the table for two or three inches. Hold the glass down with one hand to prevent its slipping; then, with a piece of corundum, or a rough whetstone and glycerine, work down the edge until it is smooth, turning the glass continually so that the edge you are working on hangs over the table. This process of grinding is somewhat tedious, but perseverance and patience will win out.

To Cut Holes in Glass

Holes may be cut in glass in several ways by an expert, but the boy who is a novice in this line should stick to slow and sure methods and take no chances. Fortunately, glass is little used in voltaic electricity, but it is indispensable in the construction of the frictional machines, Leyden-jars, and condensers, where glass is used as the dielectric, also for the covering-plates to instruments.

The simplest method is that of rotating a copper tube forward and backward over the glass, using fine emery dust for the cutting medium and oil of turpentine as a lubricant. The copper tube must be held in a rack, so that its location will not shift during the rotating or cutting motion. The rack in which the tube is held may be of any size, but to take a disk or square of glass, twenty inches across, the frame should be twenty-two inches long, ten inches wide, and twelve inches high, as shown in Fig. 3.

The side-plates are eleven inches high and ten inches wide, the top is twenty-two inches long and ten inches wide, while the under ledge is twenty and a quarter inches long by ten inches wide. This frame is put together with glue and screws. Across the back, from the corners down to the middle of the under ledge, battens or braces are made fast to prevent the frame from racking. A hole is made through the middle of the top and under ledge for the copper tube to pass through. If different-sized tubes are to be used, blocks to fit the top and under board are to be cut and bored, so that they may be held in place with screws when in use. To cut a hole in glass, place the disk or pane on a felt or cloth-covered table, and over it arrange the frame, so that the tube will rest on the spot to be drilled. Drop the copper tube down through the hole, having first spread the bottom of the tube slightly, so that it will not split the glass. Now put some emery inside the tube so that it will fall on the glass; then place a wooden plug in the top of the tube and arrange an awl, or hand-plate, so that the tube may be pressed down. Take one turn about the tube with a linen line, or gut-thong, and make the ends fast to a bow, so that it will draw the string taut but not too tight. Lubricate the foot of the tube with oil of turpentine, and draw the bow back and forth. At first the motion will cause the copper to scratch the glass, and then cut it, until finally a perfectly drilled hole is formed. During the operation both glass and frame must be held securely, and the bow drawn evenly and without any jerking motion. Holes of different sizes may be cut with tubes of various diameters. Small holes may be cut with a highly tempered steel-drill and glycerine, the drill being held in a hand-drilling tool or in a brace.

Anti-hum Device for Metallic Lines

In overhead wires, where galvanized or hard copper wire is used, the hum due to the tension of the wires, and the wind blowing through them, causes a musical vibration which becomes most annoying at times. This can be overcome by a simple device known as an “anti-hum.” It consists of a knob made of wood or rubber, through which a hole is bored, and around which a groove is cut. One end of the wire is passed through the hole and a loop formed, the loose end being wrapped about the incoming wire. The other end of the line is passed around the knob in the groove, and the end twisted about the line-wire. The knob is then an insulator and a sound-deadener at the same time. To complete the metallic circuit a loop of wire is passed under the knob, the ends of which are made fast to the line-wires, as shown at Fig. 7.

A Reel-car for Wire

It is not always convenient nor possible to carry about a heavy roll of wire when hanging a line, especially if it is No. 12 galvanized wire, of which there are from fifty to a hundred pounds in one roll. Wire should be unwound as it is paid out, and not slipped off from the coil, since it is liable to kink; therefore, some portable means of transporting it should be provided. Line-wires over long distances are paid out from a reel-truck drawn by horses. For the use of the amateur electrician the reel-car shown in Fig. 8 should meet all requirements.

The reel is made from two six-inch boards, a barrel-head or a round platform of boards, four trunk-rollers, and a bolt. From a six-inch board cut two pieces five feet long. Eighteen inches from either end cut one edge away so as to form handles, as shown at C C C C in Fig. 8, rounding the upper and under edges to take off the sharp corners. Cut four cross-pieces sixteen inches long; and from two-by-four-inch spruce joist cut four legs twelve inches long, and plane the four sides.

Nail two of the cross-pieces to the legs; then nail on the side-boards and so form the frame of the reel. Bore a half-inch hole through a piece of joist; then nail it between the remaining two cross-boards, taking care to get it in the centre, as shown at A. Arrange these pieces at the middle of the frame, making them fast with nails driven through the side-boards and into the ends of these cross-pieces. Drive some pieces of matched boards together, and with a string, a nail, and a pencil describe a circle twenty inches in diameter. With a compass-saw cut the boards on the line, and join them with four battens made fast at the underside with nails. Do not make the battens so that they will extend out to the edge of the circle, but keep them in an inch or two, so that the under edge of the turn-table will rest on four trunk-rollers screwed fast to the top edges of the side-boards and end cross-pieces, as shown at B. A half-inch bolt is passed down through a hole made at the middle of the table, and through the block. Between the block and the underside of the table several large iron washers should be placed on the bolt, so that they will keep the table slightly above the rollers, the main weight of the table and its load of wire being held by the middle cross-brace. The object of the trunk-rollers is to relieve the side strain on the bolt, and also to prevent friction between the edge of the table and the frame, in case the tension on the wire pulls it to one side. Bore six holes in the table, on a circle of twelve inches, and drive hard-wood pegs in them, as shown in Fig. 8. When a roll of wire is lying on the table two boys can easily lift and carry the car, and as they do so the wire will pay out. Give all the wood-work a coat of dark-green paint, and oil the trunk-rollers and the wood where the bolt passes through. A pair of nuts should be placed on the lower end of the bolt and a washer under its head. These lock-nuts must be screwed on with two monkey-wrenches, forced in opposite directions, so that one nut will be driven tightly against the other. This is to prevent the turning of the table from unscrewing the nuts.

Insulators

For telegraph and telephone lines, where pole, tree, or building attachments are necessary, insulators must be used to carry the wires without loss of current. The regular glass, porcelain, or hard rubber insulators, made for pole and bracket use, are of course the best. They can be purchased at any supply-house for a few cents each, but there are other devices which will answer equally well and which will cost little or nothing.

Obtain some bottles of stout glass, the green or dark glass being the toughest; then carefully break the bottle part away. In doing this hold the bottle by the neck, with a piece of old cloth wrapped about it, to prevent the glass chips from flying. Save all of the neck and part of the shoulder, as shown in Fig. 9, so that the wire and its anchoring loop will not slip off and fall down on the peg or cross-tree.

Hard-wood pegs cut from sticks one inch and a half square should be whittled down so that they will fit in the neck and come up to the top. The pegs should be long enough at the bottom to permit of their being fastened to the supporting poles, trees, or building. In Fig. 10 three ways of attaching insulators are shown. At A the peg is nailed to the top of a pole, or a hole is bored in the pole and the peg driven down in it. At B two sticks with peg ends are nailed to a pole in the form of a [V], and across the sticks a cross-brace is made fast to prevent the sticks from spreading or dropping down. This cross-brace is made fast to both the sticks and the pole so as to form a rigid triangle. At C the usual form of cross-tree, or [T] brace, is shown. The pegs may be nailed to the face of the cross-plate, or holes may be bored in the top and the pegs driven down into them. If the cross-piece is more than two feet long, bracket-iron should be screwed fast to the pole and brace at both sides, as shown at C. Where a cross-plate is made fast to a pole, a lap should be cut out so that the plate can lie against a flat surface rather than on a round one (see D in Fig. 10).

The shoulder of the bottle-necks must not rest on a cross-piece, or touch anything that would lead to the ground or to other wires. The shoulder acts as a collar, and so sheds water that in wet weather the current cannot be grounded through the rain. The underside of the collar should always be dry, and also that part of the peg protected by the collar, thereby insuring against the loss of current. The relative position of insulator and peg is shown at Fig. 9, and if the pegs are cut carefully the bottle-necks should fit them accurately.

Joints and Splices

It is essential in electrical work to have joints, splices, unions, and contacts made perfectly tight, so that the current will flow through them uninterruptedly. A poor contact or weak joint may throw a whole system out of order. For this reason all joints should be soldered wherever practicable. In line work, however, this is impossible, except where trolley-wires are joined, and these are brazed in the open air by an apparatus especially designed for the purpose. In telegraph and telephone lines perfect contact is absolutely necessary, and where attachments are made to insulators the main-line should never be turned around the insulator. The wire is brought up against the insulator, and with a [U] wire the main-line is tightly bound to it, as shown at Fig. 11. If it is necessary to bind the main-line more securely to the insulator, one or two turns may be taken around the insulator with the [U] or anchoring wire; then with a pair of plyers a tight wrap is made.

When joining two ends of wire together, never make loops as shown in Fig. 12 A. This construction gives poor contact, for the wire loops will wear and finally break apart. Moreover, the rust that forms between the loops will often cause an open circuit and one difficult to locate. Care must be taken to make all splices secure and with perfect contact of wires, and the only manner in which this can be done is to pass the ends of wires together for three or four inches, as shown in Fig. 12 B.

Grasp one wire with a pair of plyers, and with the fingers start the coil or twist, then with another pair of plyers finish the wrapping evenly and snugly. Treat the other end in a similar manner, and as a result you will have the splice pictured in Fig. 12 B, the many wraps insuring perfect contact. This same method is to be employed for inside wires, and after the wrap is made heat the joint and touch it with soldering solution. The solder will run in between the coils and permanently unite the joint. The bare wires should then be covered with adhesive tape.

Avoid sharp turns and angles in lines, and where it is not possible to arrange them otherwise it would be well to put in a curved loop, as shown at Fig. 13. A represents a pole, B B the line, and C the quarter-circular loop let in to avoid the sharp turn about the insulator. The current will pass around the angle as well as through the loop, but a galvanometer test would show that the greater current passed through the loop and avoided the sharp turn.

“Grounds”

In the chapter on wireless telegraphy several good “grounds” were described, any one of which would be admirably adapted to telegraph or telephone circuits. In Figs. 14, 15, and 16 are illustrated three other “grounds” that can easily be made from inexpensive material. The first one, Fig. 14, is an ordinary tin pan with the wire soldered to the middle of the bottom. The wire must be soldered to be of use, as the pan would soon rust around a simple hole and make the “ground” a high-resistance one. If the pan is buried deep enough in the earth, and bottom up, it will last for several years, or so long as the air does not get at it to induce corrosion.

The star-shaped “ground” is cut from a piece of sheet zinc, copper, or brass, and is about twelve inches in diameter. The wire is soldered to the middle of it, and it is buried four feet deep, lying flat at the bottom of the hole.

In Fig. 16 a pail or large tin can is shown with the wire passing down through the interior and finally reaching the bottom, where it is soldered fast. The can is filled with small chunks of carbon, or charcoal, and some holes are punched around the outer edge and bottom to let the water out. The can is then buried three or four feet in the ground. Use nothing but copper wire for “grounds,” and it should be heavy--nothing smaller than No. 14. The wire should be well insulated down to and below the surface for a foot or two, so that perfect action will take place and a complete “ground” secured.

The Edison Roach-killer

When Edison was a boy he invented the first electrocution apparatus on record. At a certain station on the Grand Trunk Railroad, where Edison was employed as a telegraph operator, the roaches were so thick that at night they would crawl up the partition between the windows and reach the ceiling, where they would go to sleep. During the day they were apt to become dizzy, lose their footing, and drop down on the heads of the operators. This did not suit young Edison, so he devised a scheme for their destruction. While watching a piece of telegraph apparatus one day, he saw a roach try to step from a bar charged with positive electricity to one through which a negative current flowed. The insect’s feet were moist and so made a connection between the two bars. As a consequence a short-circuit of high tension passed through its body and it dropped dead. This put an idea into Edison’s head, and the electrocution apparatus was soon in working order. The “killer” was the most simple device one could imagine, and was composed of two long, narrow strips of heavy tin-foil pasted side by side on a smooth board, with a space of one-eighth of an inch between them, as shown at Fig. 17. To one strip a positive wire was connected, while to the other a negative or ground was made fast. High-tension current, or that from an induction-coil, was connected with the wires, and the resulting voltage was strong enough to give one a severe shock if the fingers of one hand were placed on one plate and those of the other hand on the other plate.

This device was arranged across the window-casing in the path the roaches were accustomed to travel on their nightly trips up the side wall. It was not long after dark before roach number one sauntered up the wall, crossed the under strip, and stepped over on the upper one. But he went no farther, and he, with many of his friends and relations, were gathered up in a dust-pan the next morning and thrown into the stove.

In electricity, as in many other things, simplicity is the key-note of success; and from this little device to employ the alternating current for ridding a house of an insect nuisance sprang the grim apparatus known as the “death chair,” used in the execution of first-degree criminals in the State of New York. Many people think the mechanism for electrocution is a complicated one, but it is quite as simple as the Edison roach-killer. One pole is placed at the head of the criminal and the other at the feet, the latter being bound fast so that perfect contact can be had. Then an alternating current of fifteen hundred to two thousand volts is run through the body, and death is instantaneous and void of pain.

An Electric Mouse-killer

A modification of the simple roach-killer was recently used by the author in his laboratory to get rid of some troublesome mice. A piece of board was cut twelve inches square, the edges being bevelled so that it would be an easy matter for the mice to climb up on it. An inch-wide circle of sheet brass was prepared measuring eleven inches outside diameter and nine inches inside. Another circle was cut measuring eight inches and a half outside and six inches inside diameter. Both circles were attached to the board with copper tacks and polished as bright as possible, the finished board appearing as shown in Fig. 18.

Wires were soldered to each strip, and these in turn were connected to a high-tension current of several thousand volts. Crumbs and small pieces of meat were placed on the board inside the circles, and the trap was set in a convenient place on the floor of the laboratory.

The next morning several mice lay dead on the floor, but at some distance from the board, and this seemed a little mysterious. The following night the author worked late in the laboratory. After finishing what he had on hand, he turned down the lights and sat down and watched the trap. Presently Mr. Mouse appeared from somewhere. He sniffed the air, then approached closer to the board, sniffed again, and, evidently concluding that he was on the right trail, he climbed up the side of the board and stood on the outer strip. He placed one fore-foot on the inner strip, and, bang! up he went in the air, and landed on the floor a foot or more away. His jump into space was due to the electric action on his muscles, for the current literally tore his nervous system into shreds.

Mr. Mouse lost a great many friends and relatives that season in the same manner, and the apparatus is confidently recommended as a certain and humane agent for the destruction of all small vermin.