Part II
Chapter VII
ELECTRICAL RESISTANCE
The science of controlling forces is so well understood and figured out that it becomes a simple mechanical proposition to adapt the various types of controllers to any form of power that may be employed. The tremendous force stored within the mechanism of a great transatlantic liner is governed by the twist of a man’s wrist. The locomotive that will pull a hundred cars loaded with coal, representing a weight of thousands of tons, is started and stopped by a short lever that is drawn in one direction or the other by a man’s hand. Great forces of all kinds are quite as easily controlled as the supply of gas through a jet—by simply turning the key that lets out so much as may be required, no matter what the pressure is back of the flow.
This same principle applies to electricity, but the means of governing it is vastly different from the methods employed for other forces. Electricity is an unknown and unseen force, coming from apparently nowhere and returning to its undiscovered country immediately upon the completion of its work. The flow of steam, water, liquid air, gas, and compressed air through pipes is governed by a throttle or cock, which allows as much or as little to pass as may be required; and if the joints, unions, and couplings in the pipes are not absolutely tight there will be a leakage. Electricity is controlled by resistance in its passage through solid wires, rods, or bars, and cannot be confined within a given space like water, nor held in tanks or pipes as a vapor or gas. It is invisible, colorless, odorless, and occupies no apparent space that can be measured; it is the most powerful and terrible and yet docile force known to man, doing his bidding at all times when properly governed and regulated. In some respects, electricity can be compared to water stored in a tank—for instance, if you have a tank of water containing fifty gallons at an elevation of twenty-five feet, and a pipe leading down from it, the pressure of the water at the outlet of the pipe will be a given number of pounds. Now if the tank were double the size the pressure at the outlet of the pipe would be proportionately greater. Now if you have a battery made up of a number of cells they will develop a given number of volts, and if the number of the cells be doubled the voltage will be correspondingly increased. Or if you have a dynamo giving a certain number of volts, that number may be increased by doubling the size.
The water contained within the tank represents its pressure at the outlet of the pipe. The current in volts, generated in a battery or dynamo, represents its pressure on an outlet or conductor wire; and both represent the force behind their respective conductors. The valve, or faucet, at the end of the pipe plus the friction in the pipe would represent the resistance to the flow of water, while the resistance-coils or other mediums plus the size of the wire, or conductor and switch, would regulate the flow of electric current. The flow of water in a pipe under certain pressure would represent its gallons per minute or hour, while with electricity its flow in a wire or other conductor would represent its amperage. It is to govern the flow of current that resisting mediums are employed.
The resistance of electric current is measured in ohms, and it is with this phase that we are interested in this chapter. If there is only a small resistance put in the path of a current, then it requires but a small pressure or voltage to send it through the wires or circuit. This is easily understood by the boy who has experimented with small incandescent lamps in which short pieces of carbon-filament are contained. It requires the pressure of a few volts only to send the current through the carbon; but for the large carbon-filaments, measuring ten or twelve inches in length, from one hundred to five hundred volts may be necessary. The ordinary house lamps require one hundred and ten volts and half an ampere to give sixteen candle-power.
It is easily understood, then, that it requires a high pressure or voltage to force the current through the resisting carbon-filament, or across the space from one carbon to the other in the arc-lamps used for street lighting. The shorter and larger the conducting wires the less the resistance, and consequently the lower the voltage or pressure necessary to force it. Contrariwise the longer and finer the conducting wares, the greater the resistance. As copper is the best commercial conductor of electric currents, it is in universal use, and in it the minimum of resistance is offered to the current. Iron wire is a poorer conductor, and is not used for high voltage (such as trolleys or transmission of power), but is confined to telegraph and telephone lines and low-pressure work. German-silver wire, one of the poorest conductors, is not used for lines at all, but is employed solely as a resisting medium for controlling current.
Ohm’s Law
This is the fundamental formula expressing the relations between current, electro-motive force, and resistance in an active electric circuit. It may be expressed in several ways with the same result, as follows:
1. The current strength is equal to the E. M. F. (electro-motive force) divided by the resistance.
2. The E. M. F. (electro-motive force) is equal to the current strength multiplied by the resistance.
3. The resistance is equal to the E. M. F. (electro-motive force) divided by the current strength.
All these are different forms of the same statement; and when figuring electrical data, C stands for current, E for electro-motive force, and R for resistance.
Resistance-coils and Rheostats
The method by which electricity is controlled is resistance. No matter how great the voltage of a current, nor its volume in amperes, it can be brought down from the deadly force of the electric trolley-current to the mild degree needed to run a small fan-motor, an electric bell, or a miniature lamp. This is accomplished by means of resisting mediums, such as fluids or wires, which hold back the current, and allow only the small quantity to pass that may be required to operate the apparatus.
The jump from the high voltage of the trolley-current to the low one required for the electric bell, a lamp, or a small motor, is frequently made in traction-work, but in this case regular transformers are used. For the small apparatus, that may have its current supplied from a battery, or a small dynamo driven by a water-motor, the forms of resistance-coils and rheostats described on the following pages should meet every requirement.
The standard unit of resistance is called an ohm, so named after Dr. G. S. Ohm, a German electrician, whose theory on the subject is accepted as the basis on which to calculate all electrical resistance. The legal ohm is the resistance of a mercury column one square millimetre in cross-sectional area and one hundred and six centimetres in length, and at a temperature of 0° Centigrade or 32° Fahrenheit, or the freezing-point for water. The conductivity of metals is dependent greatly on their temperature, a hot wire being a much better conductor than a cold one. Since counter-electro-motive force sometimes gives a spurious resistance, the ohmic resistance is the true standard by which all current is gauged.
In technical mechanism and close readings the ohmic resistance counts for a great deal, but in the simple apparatus that a boy can make the German-silver resistance coils and the liquid resistance will answer every purpose.
To give a clearer idea of the principle of the rheostats, a short description of the mercurial column will first be presented. During the early part of the last century wires were not used as a resisting medium for electric currents. In their place, glass tubes, filled with mercury sealed at one end and corked at the other, were arranged in rows and supported in a wooden rack.
Wires led out from the top and bottom of each tube, and were brought down to metal buttons arranged in a row along the front edge of the base-plate, as shown in the illustration of a mercurial rheostat ([Fig. 1]). Each tube represented a certain resistance—one or more ohms, as required. The outlet wire was attached to the button at one end of the row, and the inlet could be moved along from button to button, until the required amount of current was obtained.
The mercurial rheostat was an expensive, cumbersome, and treacherous thing to handle; it was liable to break, and its weight often prohibited its use in places where the more convenient and easily handled German-silver rheostats are now in universal employment. Overheating the mercury in the columns caused it to expand, and sometimes, before the switch could be thrown open, an end would be forced out and the mercury would climb over the edge of the glass columns.
All metals have a certain amount of resistance for electric currents, and some have more than others. German-silver, for instance—a metal made of a mixture of other metals with about eighteen per cent. of nickel (see [Appendix])—is considered to be the best commercial resistance medium, while pure copper is regarded as the best commercial conductor. Unalloyed copper is universally employed for electric conductors of high voltage; but for telegraph and telephone work, galvanized iron wire is still used extensively.
The finer the wire, the higher is its resistance, and the more resistant the metal, the greater are the number of ohms to a given length. To nine feet and nine inches of No. 30 copper wire there is one ohm resistance, while to No. 24—which is six sizes coarser—there is one ohm to thirty-nine feet and one inch. In many cases it is necessary to use the coarser wire and greater length, as the current would superheat or burn the fine wire, while the coarser would conduct it safely.
For very high voltage and amperage—such as used in traction cars, in power stations, and in manufacturing plants—castings of German-silver are employed and linked in series. They are more easily handled than the coils of wire, and a greater number of them can be accommodated in a small space.
For light currents in experimental work, where batteries are employed, obtain a pound or two of bare German-silver wire, from Nos. 24 to 30, and wind the strands on a round piece of stick attached to a winder (see Magnets and Induction-Coils, [chapter iv.]). Make several of these coils, two or three inches long, with the wire wound closely and evenly. When pulled apart the coils will appear as shown in [Fig. 2] A, and will resemble a spiral spring. This can be made fast over a porcelain knob and the ends caught down, as shown at B in [Fig. 2], or it may be drawn over a round stick, a porcelain tube, or a lug made of plaster of Paris and dextrine (three parts of the former to one of the latter), as shown at C in [Fig. 2], and the ends securely bound with a strand or two of wire, twisted tight to keep the ends from slipping.
The lugs may be made in a mold, using as a pattern a piece of broom-handle—shellacked and oiled to prevent the plaster from adhering to it. Obtain a small square and deep box, and drop some of the wet mixture down in the bottom; on this place the broomstick, small end down (it should be slightly tapered), and around it pour in the wet plaster mixture. While it is setting, turn the stick with the thumb and fingers, so as to shape the hole perfectly then draw it out, and a true mold will be the result. When dry enough, pour some shellac down into the mold and revolve it, so that the shellac will be evenly distributed, and let it harden for a day. Then saw off the end of the mold, so that it will be open at both ends.
In order to make the lugs, pour in the plaster mixture, taking care to oil the mold before each pouring, so that the lug can be drawn out when the mixture has set. If it sticks, tap the small end gently to start it. For coils where there is little or no heat, ordinary pieces of broom-handle, or round sticks having a coat or two of shellac, will answer very well; but where the current heats the core, it must be of some material that will not char.
Another method of making resistance-coils is to measure off a length of wire; then double it, and with a small staple attach the loop end at one end of the (wooden) core. Pay out the two strands of wire an equal distance apart with the thumb and fingers, and with the other hand twist the core. At the other end of the spool catch the loose ends of the wire under small staples, taking great care not to let the staples touch or even be driven close together. This arrangement is shown at D in [Fig. 2], and for a field resistance-board any number of these coils may be made.
In [Fig. 3] the mode of connecting coils is shown. The dots represent contact-points to which the movable arm can be shifted. The wires at the bottom of coil, Nos. 1 and 2, are connected together, while those at the top of No. 2 and 3 are joined, and so on to the end. The leading-in current is connected at pole H and so on to J, while the leading-out wire is made fast to pole I. The switch-arm is moved on the first dot, or contact-point, and the current passes up wire A, down coil No. 1, up coil No. 2, down No. 3, up No. 4, and so on to No. 6, and down wire G and out at I. Supposing that this offers too much resistance, the switch-arm is moved up one point. This cuts out coil No. 1, as the current passes up wire B, through coil No. 2, down No. 3, and so on, and out through G and pole I. Another move of the switch and coil No. 2 is cut out, the current passing up wire C, down coil No. 3, up No. 4, and so on, and out at I. Each move of the switch cuts out one coil, lessening the resistance; but when moved to the last contact-point the current flows without resistance—in at H, through the switch-arm, and out at I.
The plan of arranging the coils suggested at [Fig. 2] B is shown in [Fig. 4], where four of the coils are arranged in series over porcelain knobs, and the lower ends made fast to the base-board with small staples. Small pieces of brass are used for the switch contact-plates; those are provided with one plain and one countersunk hole for a flat and round headed screw.
The screw-heads are arranged in a semicircular fashion, so that the switch-arm, attached at one end to the screw J, will touch each plate as it is moved forward or backward.
TWO SIMPLE FORMS OF RHEOSTATS
The current passing in at binding-post A travels to J and B, the latter being the resting-plate for the switch-arm. A move of the arm to C sends the current up over the first coil and down; then over the second, third, and fourth coils, and out at G; through plate H (which is the rest at the right side), and out at I.
A move of the switch-arm to D cuts out the first coil; a move to E, the first and second coils; and so on until the last plate is reached, when the current will pass without resistance in at A, through J, and out at I.
A simple arrangement for a resistance-coil is shown in [Fig. 5]. This consists of a set of small metal plates in which two holes are made, one for a screw, the other for a screw-eye (see [Binding-posts], [chapter iii.]). Two lines of steel-wire nails are driven along a board, and German-silver wire is drawn around them in zig-zag fashion, beginning at the left and going towards the right side of the board. One end of wire is made fast under the screw-head on plate A. The strand is carried out around the first nail on the lower row and over the first one on the upper row, then down, up, down until six nails have been turned. The wire is then carried down to the screw in plate B, given two turns, and carried up again and over the nail on the top row, repeating the direction of zigzag No. 1, until six of them are made. The end of the wire is then made fast to plate G, and all the screws are driven in to hold the plates and wire securely.
The inlet wire is attached to A, the outlet to G, and any degree of resistance can be had by moving the inlet wire to the various plates along the line, cutting out sections Nos. 1 to 6 as desired.
For heavier wire the arrangement as shown in [Fig. 6] should be satisfactory.
A frame twelve by fifteen inches is constructed of wood three-quarters of an inch thick and one inch and a quarter wide, having the ends securely fastened with glue and screws. Spirals are wound of German-silver wire (any size from No. 16 to 22), and drawn apart. The ends are caught to the frame with small staples, and each alternate coil-end is joined, as shown in [Fig. 6]. The leading-out wires to the contact-points on the switch should be of insulated copper, and are to run down the sides of the frame, and so to the switch-board. To clearly illustrate, however, the plan of wiring, the drawing is made so as to show the leads from the coil-ends to the switch. Care should be taken to study this drawing well, so as not to make an error in connecting a wrong end to a contact-point, thereby causing a short circuit. When properly connected the current passes in at A and out at I; but if wires are improperly connected, the current will jump when the switch-arm reaches the misconnected contact.
The switch is an important part of every rheostat, and should be carefully and accurately made. One of the simplest and most practical switches is constructed from a short, flat bar of brass or copper having a knob attached at one end and a hole provided at the other through which a screw may pass (see [Switches], [chapter iii.]). The contact-points are made from one or two copper washers, with the holes countersunk so that a machine screw of brass, with a flat head, will fit the hole snugly. The top of the head will then be flush with the top of the washer, as shown at [Fig. 7] A. The bolt is passed down through a piece of board, then slate or soapstone, and caught with a washer and nut, as shown at [Fig. 7] B. A loop of wire is passed about the bolt end, then another nut is screwed tightly over it to hold it in place, as well as to lock the first nut. The binding-posts that hold the inlet and outlet wires may be made of bolts and nuts also, as shown at [Fig. 7] B; but the bolt must be passed through the switchboard so that the head is at the rear and the ends project out to receive the nuts.
A very compact and simple rheostat and switch is shown in [Fig. 8]. It is composed of a base-board, eight blocks of hard-wood, and a top strip used as a binder to lock the upper ends of the blocks together. The hard-wood blocks are three-quarters of an inch thick, one inch and a half wide, and four inches long. A small hole is made near each end of the block and through one of them an end of the wire is passed. The wire is then wound round the block, taking care to lay it on evenly, and with about one-eighth of an inch of space between each strand. When the opposite hole is reached, pass the end of the wire through it and clip it. The block will then resemble [Fig. 7] C. There should be three or four inches of wire at each end for convenience in connection, and when the eight blocks are wound they are to be mounted on end at the rear side of a base-board measuring ten inches long, three inches wide at the ends, and nine at the middle (or across the face of the switchboard to the rear edge behind the blocks). Use slim steel-wire nails and glue to attach the blocks to the base; or slender screws may be employed. Across the top lay a piece of wood a quarter of an inch in thickness, and drive small nails or screws down through it and into the blocks.
COMPACT FORMS OF RHEOSTATS
Connect the ends of the coils together in series, as already described, and carry the wires under the base-plate in grooves cut with a V-shaped chisel. If the sunken wires are bothersome, the work may be avoided by running the wires direct to the foot of the contact-points and elevating the rheostat on four small blocks that may be screwed, or nailed and glued, under the corners, as shown in [Fig. 8]. These will raise the base half an inch or more above the table on which the rheostat will rest so as to allow room for the under wires.
A rheostat of round blocks standing on end is shown at [Fig. 9] A. These are pieces of curtain-pole, four inches long and wound with loops of No. 16 or 18 wire, as shown at [Fig. 9] B. The loop and loose ends are caught with staples, and when arranged on a base-board they are to be connected in series as before described. One long, slim screw passed up through the base-board and into the lower end of the block will hold each block securely in place. To keep it from twisting, a little glue may be placed under the blocks so that when the screw draws the block down to the base it will stay there permanently upon the hardening of the glue. The leading wires should be slipped under the washers forming the contact-points of the switch; or they may be carried under the board to the nuts that hold the lower ends of the bolts.
Another form of rheostat ([Fig. 10] A) is made by sawing a one-inch curtain-pole into four-inch lengths and cross-cutting each piece with eight or ten notches, as shown at [Fig. 10] B. These pieces are screwed and glued fast along each side of a base-board eight inches wide and fourteen inches long, so that the notches face the outer edges of the board. The strand of wire passes round these upright blocks and fits into the notches so as to prevent them from falling down.
The top end of wire at each pair of blocks is made fast by a turn or two of another piece of wire and a twist to hold it securely; then the loose end is carried down through a hole and along under the board to the foot of a contact-point.
Any number of these upright coils may be made, and on a long board the switch may be arranged at one side instead of at the end, as shown in [Fig. 10] A. When making ten or more coils it is best to use three or four sizes of wire, beginning with fine and ending with coarse. For instance, in a twelve-coil rheostat make three coils of No. 26, three of No. 22, and three of No. 18; or if coarser wire is required use Nos. 20, 16, and 12.
German-silver comes bare and insulated. It is preferable to have the fine wire insulated, but the heavier sizes may be bare, as it is cheaper; moreover, if heated too much the insulation will burn or char off. When cutting out the coils always begin at the end where the finer wire is wound; then as the current is admitted more freely the heavier wires will conduct it without becoming overheated.
For running a sewing-machine, fan, or other small direct-current motor wound for low voltage, the house current (if electric lights are used in the house) may be brought down to the required voltage with German-silver rheostats similar to these already described. Another and very simple method is to arrange sixteen-candle-power lamps in series, as shown in [Fig. 11]. Six porcelain lamp-sockets are screwed fast to a wood base and the leading in and out wires brought to binding-posts or the contact-points of a switch. The leading-in wire to the series is made fast at binding-post A, which in turn is connected with screw B, under the head of which the switch-arm is held. When the switch is thrown over to contact-point C the current passes through lamp No. 1 back to point D; through lamp No. 2 back to E; then through lamps Nos. 3, 4, 5, and 6, and out through point I to post J. A turn of the switch to D cuts out lamp No. 1, to E cuts out No. 2, and so on. The filaments of incandescent lamps in their vacuum are among the very best mediums of resistance, and with a short series of lamps a current of 220 volts can quickly be cut down to a few volts for light experimental work or to run some small piece of apparatus.
Lamps in series are often used to cut down the current for operating electric toys and trains. The adjustment of the current should never be left to children, however, but should be attended to by some one qualified to look after the apparatus. Otherwise an unpleasant or even dangerous shock may be received. Another simple form of resistance apparatus is made from the carbon pencils used for arc lights. Short pieces will answer very well, but if the long bare ones can be had they will be found preferable. Do not use the copper-plated ones as they would conduct the current too freely; they should be bare and black. Now around the ends of each piece take several turns of copper wire for the terminals and cut-out wires. Fasten those pencils down on a board (as shown at [Fig. 12]) by boring small holes through the board, passing a loop of copper wire down through the holes, and giving the ends a twist underneath. The leading wires to and from the contact-points should be insulated and may be above or below the board. From the descriptions already given, the connections of this rheostat can readily be understood.
The rheostat shown in [Fig. 13] is perhaps the most complete and practical apparatus that a boy could make or would need. It is composed of a frame, six porcelain tubes, a switchboard, and the necessary German-silver and copper wire.
From an electrical supply-house obtain six porcelain tubes fourteen by three-quarter inch. Porcelain tubes and rods warp in the firing and are seldom straight; in purchasing these select them as nearly perfect as possible in shape, size, and length.
A PANEL RHEOSTAT
Buy, also, twelve small porcelain knobs that are the right size to fit inside the large tubes. These should have holes bored through them to admit screws. Construct a frame of hard-wood to accommodate the tubes, as shown in the drawing, and leave one end loose. With slim screws make the porcelain knobs fast to the top and bottom strips of the frame, as shown in [Fig. 14]. The porcelain rods will fit over these and will thus be held securely in the frame, one small knob entering the tube at each end, as indicated by the dotted lines in [Fig. 14].
The first porcelain tube to the left is wound with No. 22 German-silver wire, the next with No. 20, the third with No. 18, then Nos. 16, 14, and 12; so that in this field a broad range can be had for a current of 110 volts.
The coils are connected in series, as explained for the other rheostats, and the leading wires brought down to the back of a switchboard of which [Fig. 13] A is the front and [Fig. 13] B the rear view. The switchboard is made of thin slate or soapstone; or a fibre-board may be employed. Fibre-board is especially made for electrical work, and can be had from a large supply-house in pieces of various thickness, three-eighths of an inch being about right for this board. Brass bolts and nuts and copper washers are used for the contact-poles, and when the ends of the leading wires are looped around the bolts the nuts are to be screwed down tightly so as to make good contacts. This rheostat may be used when lying on a table, or it can be hung up by means of two screw-eyes driven in the top of the frame, as shown in [Fig. 13] A.
A convenient form of rheostat for fine wire and high resistance is shown in [Fig. 15]. This is on the plan of the well-known Wheatstone rheostat and does not require a switchboard nor a series of coils. Two rollers, one of wood the other of metal or brass-covered wood, are set in a frame, and by means of a handle and projecting ends with square shoulders, one or the other of the rollers may be turned so that the wire on one winds up while on the other it unwinds.
The wooden roller may be made from a piece of curtain-rod one inch in diameter, and it should have a thread cut on it. This will have to be done on a screw-cutting lathe, and any machinist will do it for a few cents. There should be from twelve to sixteen threads to the inch—no more—although there may be as few as eight. Twelve will be found a good number, as that does not crowd the coils and the risk of their touching is minimized. The ends of the roller should have bearings that will fit in holes made in the end-pieces of the frame, and at one end of each roller a square shoulder is to be cut, as shown at A in [Fig. 16]. A short handle may be made from two small pieces of wood, as shown at B in [Fig. 16]. It must be provided with a square hole so that it will fit on the roller ends. The metal roller may be made from a piece of light brass tubing one inch in diameter through which a wooden core is slipped; or it can be a piece of brass-covered curtain-pole with the ends shaped the same as the wooden one. The wood roller should have a collar of thin brass or copper (or other soft metal except lead) attached to the front end; or several turns of wire may be made about the roller so as to form a contact-point. A piece of spring brass, copper, or tin rests on this collar and is held fast under a binding-post, which in turn is screwed to the wooden frame. A similar strip of spring metal is held under another post on the opposite side of the frame and bears on the metal roller.
German-silver wire is wound on the wooden roller, one end having been made fast to the metal collar; and when all the thread grooves on the wood roller are filled the opposite end of the wire is attached to the rear end of the metal roller. The current entering at binding-post No. 1 crosses on the strip of spring metal to the collar, travels along the coil of wire, and crosses to the metal roller and is conducted out at binding-post No. 2 (see [Fig. 15]). If the resistance is too great slip the handle over the end of the metal roller and give it several turns. The current will then pass with greater freedom as the wire on the wooden roller becomes shorter. This may be readily seen by connecting a small lamp in series with a battery and this rheostat. As the metal cylinder is turned the current flows more freely and the filament becomes red, then white, and finally burns to its full capacity. Take care, however, not to admit too much current as it will burn out the lamp. Some sort of adjustment should be made to prevent the rollers turning of themselves and thus allowing the wire coils to slacken. This may be done by boring the two holes for the rollers to fit in and then, with a key-hole saw, cutting the stick as shown at C in [Fig. 16], taking care not to split it at the ends. The result will be a long slot which, however, has nothing to do with the bearings. Down through the middle of the stick make a hole with an awl, so that the screw-eye will move easily in the upper half but will hold in the lower half. Under the head of the eye place a small copper washer; then with the thumb and finger drive the screw-eye down until the head rests on the washer.
A slight turn of the eye when it is in the right place will draw the upper and lower parts of the stick together and bind the wood about the bearing ends of the rollers. The rollers should not be held too tightly as that would strain the wire when winding it from one to the other. It should be just tight enough to keep the wire taut.
Two or more of these roller resistance-frames may be made and connected in series so that a close adjustment can be had when using battery currents for experimenting.
Liquid Resistance
Apart from metallic, mercurial, or carbon resistance a form of liquid apparatus is frequently used in laboratory and light experimental work.
This style of resistance equipment is the least expensive to make, and will give excellent satisfaction to the boy who is using light currents for induction-coils, lamps, galvanometers, and testing in general. The simplest form of liquid resistance is made by using a glass bottle with the upper part cut away. The cutting may be done with a steel-wheel glass-cutter. The bottle should then be tapped on the cut line until the top part falls away. Go over the sharp edges with an old file to chafe the edge and round it; then solder a tin, copper, or brass disk to a piece of well-insulated wire and drop it down in the bottom of the receptacle, as shown at [Fig. 17]. Cut a smaller disk of metal, or use a brass button, and suspend it on a copper wire which passes through a small hole in a piece of wood at the top of the jar. Notches should be cut at the under side of this wood cross-piece so that it will fit on top of the jar and stay in place. The jar is to be nearly filled with water, having a teaspoonful of sulphate of copper dissolved in it. This will turn the water a bluish color and make it a slightly better conductor, particularly when the button is lowered close to the round disk. If a high resistance is desired the copper may be omitted leaving the water in its pure state. The wires leading in and out of the jar should be connected between the apparatus and the battery so that the proper amperage can be had by raising or lowering the button. A series of these liquid resistance-jars may be made of glass tubes an inch in diameter and twelve inches long. One end of them may be stopped with a cement made of plaster of Paris six parts, ground silex or fine white sand two parts, and dextrine two parts. Mix the ingredients together when dry, taking care to break all small lumps in the dextrine; then add water until it is of a thick consistency like soft putty. Solder the ends of some copper wires to disks of copper or brass and set them on the middle of bone-buttons; these in turn are to be imbedded in the mixture after the wire has been passed through a hole in the bottom.
Their location can be seen in the bottom of the tubes [Fig. 18], and [Fig. 19] A is an enlarged figure drawing of the plate, button, and wire. The wires are brought out under the lower edge of the tubes, and enough of the composition is floated about the bottom and outer edge of the tube to form a base, as shown in the drawing. A base-board is made six inches wide and long enough to accommodate the desired number of tubes. Two pieces of wood one inch wide and three-quarters of an inch thick have hollow notches cut from them at one side, as shown at [Fig. 19] B. In these notches the tubes are gripped. Screws are passed through one stick and into the other so as to clamp the wood and tubes securely together. The rear stick is supported on two uprights which are made fast to the rear edge of the base-plate with screws and glue.
Along the front of the base-board small metal contact plates, or binding-posts, are arranged (see [Binding-posts], [chapter iii.]) and the wires led to them from the tubes, as shown in the drawing. The top or drop wires in the tubes are provided with metal buttons at the ends; or the end of the wire may be rolled up so as to form a little knob. The manner of connecting the wires was freely explained in the resistance-coil descriptions and may be studied out by examining the drawing closely. In this resistance-apparatus there are two ways of cutting out a medium—first, by lowering the wire in the tube so that both contact-points meet; and second, by cutting out the first tube altogether by connecting the incoming wire with the second binding-post. Then again the resistance may be regulated quite accurately by raising or lowering the wires in the liquid.
For example, there is too much resistance if the current has to travel through all the tubes. If it is too strong when one tube is cut out, the wire in tube No. 1 is lowered so that the contacts are an inch apart. Then the more accurate adjustment is made by dropping the wire in the second tube, as shown in [Fig. 18]. The wires leading out at the top of the tubes are pinched over the edge to hold them in place. They should be cotton insulated and the part that is in the liquid should be coated with hot paraffine.
The water may be made a slightly better conductor if a small portion of sulphate of zinc, or sulphate of copper, is added to each tubeful.
Hittorf’s resistance-tube is one of the oldest on these lines, and two or more of them are coupled in series, as described for this water-tube resistance; glass tubes are employed that have one end sealed with a permanent composition, as described for [Fig. 18]. A metallic cadmium electrode is placed at the bottom of the tube, and the tube is then filled with a solution of cadmium iodide one part and amylic alcohol nine parts, and then corked. A wire passing down through or at the side of the cork is attached to another small piece of metallic cadmium, which touches the top of or is suspended a short distance in the liquid.
As the alcohol is volatile the cork cannot be left out of the tube, and the wire must be drawn through the cork with a needle so that no opening is left for evaporation. A number of these tubes may be made and coupled in series and the wires led down to the contact-points of a switch.
Chapter VIII
THE TELEPHONE
For direct communication over short or moderately long distances, nothing has been invented as yet that will take the place of the telephone. A few years ago, when this instrument was first brought out, it was the wonder of the times, just as wireless telegraphy is to-day. Starting with the simple form of the two cups with membranes across the ends, and a string or a wire connecting them, we have to-day the complex and wonderful electric telephone, giving perfect service up to a distance of two thousand miles. Some day inventors in the science of telephony will make it possible to communicate across or under the oceans, and when the boys of to-day grow to manhood they should be able to transact business by ’phone from San Francisco to the Far East, or from the cities near the Atlantic coast to London, Paris, or Berlin.
It is hardly necessary to enter into the history of telephones, as this information may be readily found in any modern encyclopædia or reference work. But the boy who is interested in electricity wants to know how to make a telephone, and how to do it in the up-to-date way, with the wire and ground lines, switches, cut-outs, bell connections, and other vital parts, properly constructed and assembled. In this laudable ambition we will endeavor to help him.
The general principle of the telephone may be explained in the statement that it is an apparatus for the conveyance of the human voice, or indeed any sounds which are the direct result of vibration.
Sound is due to the vibrations of matter. A piano string produces sound because of its vibration when struck, or pulled to one side and then released. This vibration sets the air in rapid motion, and the result is the recording of the sound on our ear-drums, the latter corresponding to the film of sheepskin or bladder drawn over the hollow cup or cylinder of a toy telephone. When the head of a drum is struck with a small stick it vibrates. In this case the vibrations are set in motion by the blow, while in the telephone a similar phenomenon is the result of vibratory waves falling from the voice on the thin membrane, or disk of metal, in the transmitter. When these vibrations reach the ear-drum the nervous system, corresponding to electricity in the mechanical telephone, carries this sound to our brains, where it is recorded and understood. In the telephone the wire, charged with electricity, carries the sound from one place to another, through the agencies of magnetism and vibration.
Over short distances, however, magnetism and electricity need not be employed for the transmission of sound. A short-line telephone may be built on purely vibratory principles. Almost every boy has made a “phone” with two tomato-cans over which a membrane is drawn at one end and tied. The middle of the membrane is punctured, and a button, or other small, flat object, is arranged in connection with the wires that lead from can to can.
A Bladder Telephone
A really practical talking apparatus of this simple nature may be made from two fresh beef bladders obtained from a slaughter-house or from the butcher. You will also need two boards with holes cut in them, two buttons, some tacks, and a length of fine, hard, brass, copper, or tinned iron wire. The size should be No. 22 or No. 24. The boards should be ten by fourteen inches and half an inch in thickness. Cut holes in them eight inches in diameter, having first struck a circle with a compass. This may be done with a keyhole saw and the edges sand-papered to remove rough places. Prepare the bladders by blowing them up and tieing them. Leave them inflated for a day or two until they have stretched, but do not let them get hard or dry.
When the bladders are ready, cut off the necks, and also remove about one-third of the material, measuring from end to end. Soak the bladders in warm water until they become soft and white. Stretch them, loosely but evenly, over the opening in the boards, letting the inside of the bladder be on top, and tack them temporarily all around, one inch from the edge of the opening. Test for evenness by pushing down the bladder at the middle. If it stretches smoothly and without wrinkles it will do; otherwise the position and tacks must be changed until it sets perfectly smooth.
The bladder must now be permanently fastened to the board by means of a leather band half an inch wide and tacks driven closely, as shown in [Fig. 1]. With a sharp knife trim away the rough edges of the bladder that extend beyond the circle of leather. Attach a piece of the fine wire to a button, as shown in [Fig. 2], and pass the free end through the centre of the bladder until the button rests on its surface. Then fasten an eight-pound weight to the end of the wire and set in the sun for a few hours, until thoroughly dry, as shown at [Fig. 3].
When both drums are complete, place one at each end of a line, and connect the short wires with the long wire, drawing the latter quite taut. The course of the main wire should be as straight as possible, and should it be too long it may be supported by string loops fastened to the limbs of trees, or suspended from the cross-piece of supports made in the form of a gallows-tree or letter F. To communicate it will be necessary to tap on the button with a lead-pencil or small hard-wood stick. The vibration will be heard at the other end of the line and will attract attention.
By speaking close to the bladder in a clear, distinct tone, the sound will carry for at least a quarter of a mile, and the return vibrations of the voice at the other end of the line can be clearly recognized.
A Single (Receiver) Line
The principal parts of the modern telephone apparatus are the transmitter, receiver, induction-coil, signal-bell, push-button, batteries, and switch. The boxes, wall-plates, etc., etc., are but accessories to which the active parts are attached.
The first telephone that came into general use was the invention of Graham Bell, and the principle of his receiver has not been materially changed from that day to this, except that now a double-pole magnet and two fine wire coils are employed in place of the single magnet and one coil. A practical form of single magnet receiver that any boy can easily construct is shown in [Fig. 4], and [Fig. 5] is a sectional drawing of the receiver drawn as though it had been sliced or sawed in two, from front to rear.
It is made from a piece of curtain-pole one inch and an eighth in diameter and three inches and a half long. A hole three-eighths of an inch in diameter is bored its entire length at the middle, and through this the magnet passes. At one end of this tube a wooden pill-box (E) is made fast with glue, or a wooden cup may be turned out on a lathe and attached to the magnet tube. If the pill-box is employed it should be two inches and a half in diameter, and at four equidistant places inside the box small lugs of wood are to be glued fast. Into these lugs the screws employed to hold the cap are driven. The walls of pill-boxes are so thin that without these lugs the cap could not be fastened over the thin disk of metal (D) unless it were tied or wired on, and that would not look well. If the cup is turned the walls should be left thick enough to pass the screws into, and the inside diameter should then be one inch and three-quarters.
The cap (B) is made from thin wood, fibre, or hard rubber. It is provided with a thin rim or collar to separate its inner side from the face of the disk (D). Four small holes are bored near the edge of this cap, so that the screws which hold it fast to the cup (E) may pass through them. The magnet (M) is a piece of hard steel three-eighths of an inch in diameter and four inches and a quarter long. This may be purchased at a supply-house, and if it is not hard enough a blacksmith can make it so by heating and plunging it in cold water several times. It may be magnetized by rubbing it over the surface of a large horseshoe magnet, or if you live near a power station you can get one of the workmen to magnetize it for you at a trifling cost. Should you happen to possess a bar magnet of soft iron with a number of coils of wire, and also a storage-battery, the steel bar may be substituted for the soft iron core and the current turned on. After five minutes the steel can be withdrawn. It is now a magnet, and will hold its magnetism indefinitely.
Now have a thin, flat spool turned from maple or boxwood to fit over one end of the rod, and wind it with a number of layers of No. 36 copper wire insulated with silk. This is known in the electrical supply-houses as “phone”-receiver insulated wire, and will cost about fifty cents an ounce. One ounce will be enough for two receivers. It should be wound evenly and smoothly, like the strands of thread on a spool, and this may be done with the aid of the winder described on [page 58].
When the wire is in place a drop of hot paraffine will hold the end so that the wire will not unwind. The ends of this spool-winding should be made fast to heavier wires, which are run through small holes in the tube (A) and project out at the end, as shown at F F. The magnet, with its wire-wound spool on the end, is then pushed through the hole in A until the top end of the rod is slightly below the edges of the cup (E), so that when the metal disk (D) is laid over the cup (E) the space between the magnet and disk, or diaphragm (D), is one-sixteenth of an inch (see [Fig. 5]). Put some shellac on the magnet, so that when it is in the right place the shellac will dry and hold it fast.
The cap (B) holds the disk (D) in place, and protects the spool and its fine wire from being damaged and from collecting dust. After giving the exterior a coat of black paint and a finishing coat or two of shellac, the receiver will be ready for use.
The original telephone apparatus was made up of these receivers only—one at each of a line in connection with a battery, bell, push-button, and switch. On a window-casing, or the wall through which the wires passed, a lightning-arrester was arranged and made fast. Using receivers only, it was necessary to speak through the same instrument that one heard through, and for a few years this unhandy method of communication was the only one possible. Then the transmitter was invented.
Plan of Installation
Many of these single-receiver lines are still in use, and as they require but a small amount of constructive skill a diagram of the wiring and the plan of arrangement is shown in [Fig. 6].
At the left side, R is the receiver at one end of the line and R 2 that at the other, line No. 1 being a continuous wire between the two receivers. When the boy at R wishes to call his friend at R 2 he uses his push-button (P B), and the battery (B B) operates the electric bell (E B 2) at the other end. In order to have the bell connections operative, the switch (S 2) must be thrown over to the left when the line is “quiet,” while the switch (S) should be thrown to the right. With the switches in this position the boy at either end may call his friend at the opposite end.
With the switch (S 2) thrown to the left (the position it should be in, except when talking over the line), the boy at the other end pushes his button (P B), first throwing switch S to the left. This makes connection for the battery (B B), and the circuit is closed through wires that join line No. 1 and line No. 2 at 1 and 2. The branch lines to the bell (E B 2) join the main lines at 3 and 4, through switch S 2, when the bar is thrown to the left. The circuit being complete, the batteries (B B) at one end of the line ring the bell (E B 2) at the other end of the line.
In the reverse manner, when the switch (S) is thrown to the right, the boy at the opposite end rings the bell (E B) by pressing on the button (P B 2), first throwing switch S 2 over to the right. If the boy at the left is calling up the boy at the right, the switch (S) should be thrown to the left, and he keeps ringing until the other operator throws switch S 2 over to the right. If now he has the receiver (R) up to his ear he can hear the vibration of the bell (E B 2) ringing through the receiver (R) at his end of the line. But when the boy summoned to R 2 takes up the receiver and places it to his ear, he throws switch S 2 over to the right side, and the boy at R leaves switch S over on the left side. This brings the lines into direct connection with the receivers in series. Be careful, when setting up this line, to have the batteries (B B) in series with B 2 B 2; otherwise there would be counter-action. The carbon of one cell should be connected with the zinc of the next cell, and so on.
Another receiver is shown at [Fig. 7]. The tube (A) and the cup are turned from one piece of wood, and the cap (B) from another piece. The length of the receiver is five inches, and the cap is two inches and a half across. The shank, or handle, through which the magnet is passed measures one inch and a quarter in diameter.
These wood parts will have to be made by a wood-turner; and before the long piece is put in a lathe the hole, three-eighths of an inch in diameter, should be bored. It must be done carefully, so that the wood shell will be of even thickness all around the hole. Also two small holes should be made the entire length of the handle, through which the wires leading from the coil to the binding-posts may pass.
The spool for the fine insulated wire coil is turned from box-wood or maple, and wound as described in [chapter iv.], on Magnets and Induction-coils. Small binding-posts (F F) with screw ends should be driven down into the holes at the end of the handle and over the bare ends of the wires that project out of the holes. The magnet (M) is three-eighths of an inch in diameter, and is provided with the spool and coil (C) at the large end of the receiver.
The disk (D) is of very thin iron, and is held in place by the cap (B) and four small brass screws driven through the edge of B and into the cup end of A. A screw-eye should be driven into the small end of the receiver from which it may hang from a hook. If a double hook and bar is employed the receiver will hang in the fork, being held there by the rim of wood turned at the small end of A.
A Double-pole Receiver
Another form of receiver is shown at [Fig. 8]. This is a double-pole receiver, with the coils of fine wire arranged on the ends of a bent band of steel and located in the cup (A), so that the ends of the magnet are close to the diaphragm (D). [Fig. 8] is a sectional view of an assembled receiver, but a good idea can be had from the drawings of the separate parts. The magnet (M) is of steel one-eighth of an inch thick and five-eighths of an inch wide. A blacksmith will make this at a small cost. It should measure two and one-half inches wide, two and one-half inches long, the ends being five-eighths of an inch apart.
Thin wooden spools are made from wood or fibre to fit over the steel ends, and are wound with No. 36 silk-insulated wire. A wooden cup, or shell (A), is turned from cherry, maple, or other close-grained wood, and at the back a hole is cut just large enough for the magnet ends to slip through exclusive of the coils wound on them. A plug of wood (A A) is driven between the ends of the magnet to hold them in place. Some shellac on the edges of the hole and the plug will harden and keep the parts in place.
The coils (C C) are placed on the magnet ends, and the fine wires are made fast to the binding-posts (E E), the latter being screwed fast to the shell (A). The diaphragm (D) is then arranged in place and held with the cap (B) and the small screws which pass through it and into the shell (A).
The Transmitter
With any one of these receivers a more complete and convenient telephone can be made by the addition of a transmitter and an induction-coil.
Following the invention of the receiver, several transmitters were designed and patented, among them being the Edison, Blake, Clamond, Western Union, and Hunning. The Edison and Hunning are the ones in general use, and as either of them can easily be made by a boy a simplified type of both is shown in [Figs. 9 and 11].
SIMPLIFIED TYPE OF TRANSMITTER
Some small blocks of wood, tin funnels, small screws, granulated or powdered carbon, some thin pieces of flat carbon, and a piece of very thin ferrotype plate will be the principal things needed in making a transmitter similar to the one shown in [Fig. 9]. All that is visible from the outside is a plate of wood screwed to a block of wood, and a mouth-piece made fast to the thin board.
In [Fig. 10] an interior section is shown, which when once understood will be found extremely simple. The block (A) is of pine, white-wood, birch, or cherry, and is two inches and three-quarters square and five-eighths or three-quarters of an inch thick. A hole seven-eighths of an inch in diameter is bored in the centre of this block, half an inch deep, and a path is cut at the face of the block one inch and a half in diameter and one-eighth of an inch deep. Be careful to cut these holes accurately and smoothly, and if it is not possible to do so, it would be well to have them put in a lathe and turned out.
The face-plate (B) is two inches square, with a three-quarter-inch hole in it, and the under-side is cut away for one-eighth of an inch in depth and one inch and a half in diameter. The object of these depressions in block A and face-plate B is to give space for the diaphragm (D) to vibrate when the voice falls on it through the mouth-piece (C).
From carbon one-eighth of an inch in thickness two round buttons are cut measuring three-quarters of an inch across. A small hole is bored in the centre of each button, and one of them is provided with a very small brass screw and nut, as shown at F F. One side of the button-hole is countersunk, so that the head of the screw will fit down into it and be flush with the face of the carbon. With a small three-cornered or square file cut the surface of the buttons with criss-cross lines, as shown at F F. When the buttons are mounted in the receiver these surfaces will face each other. Cut a small washer from felt or flannel, and place it in the bottom of the hole in block A. Line the side of the hole with a narrow strip of the same goods; then place the button (F F) in the hole, pass the screw through the hole and through the block (A), and make it fast with the nut, as shown at F. Place a thin, flat washer under the nut, and twist a fine piece of insulated copper wire between washer and nut for terminal connections, taking care that the end of the wire under the nut is bare and bright, so that perfect contact is assured. Since the practice of telephony involves such delicate and sensitive vibratory and electrical phenomena, it is best to solder all joints and unions wherever practicable, and so avoid the possibility of loose connections or corrosion of united wires.
From very thin ferrotype plate cut a piece two inches square, and at the middle of it attach the other carbon button by means of a small rivet which you can make from a piece of copper wire. Or a very small brass machine screw may be passed through the button and plate; then gently tapped at the face of the plate to rivet it fast, as shown at E. Lay the block down flat and partly fill the cavity with carbon granules until the button is covered. Do not fill up to the top of the hole. Over this lay the disk (D), so that the carbon button at the under side of it will fit in the top part of the hole between the sides of felt or flannel. Make the disk fast to the block (A) with small pins made by clipping ordinary pins in half and filing the ends.
A slim bolt (G) is passed through the block (A), and a wire terminal is caught under a nut and between a washer at the back of the block, as described for F. The japan or lacquer must be scraped away from the disk (D) where the bolt-head touches it, so that perfect electrical contact will be the result.
A small tin funnel is cut and made fast to the face-plate (B), or if an electrical supply-house is at hand a mouth-piece of hard rubber or composition may be had for a few cents. The block (B) is then screwed fast to A, forming the transmitter shown at [Fig. 9]. When this transmitter stands in a vertical position the granules, or small particles of carbon, drop down between the buttons of carbon, packing closely at the bottom of the cavity. At the middle they are loosely placed, and at the top there are none. As the high or low vibrations of the voice fall on the disk (D) they act accordingly on the carbon granules, which in turn conduct the vibrations to the rear carbon button, and, by the aid of electricity reproduce the same sound, in high or low tone, through the receiver at the other end of a line.
This improved transmitter makes it possible to talk in a moderate tone of voice over distances up to one thousand miles, while with the old form of the instrument it was necessary to talk very loud in order to be heard only a few miles away. Where a portable apparatus is desired, this block may be attached to a box or an upright staff.
This transmitter will not work when on its back or so that the funnel is on top, because the particles of carbon would settle on the rear button and not touch the front one. It is essential that the carbon grains should touch both buttons at the same time, and at the lower part of the cavity they should lie quite solid. It is not necessary, however, to pack it in, for the vibratory action of the voice, or other sounds, will cause the particles to adjust themselves and settle in a compact mass.
Another Form of Transmitter
In [Fig. 11] another style of transmitter is shown. It is assembled on the front of a box. This front or cover swings on hinges, and can be opened so that the mechanism in the interior of the box may be gotten at easily.
A sectional view of this transmitter is shown in [Fig. 12]. A hole one inch and a half in diameter is cut in the cover (A). A round or square block (B) two inches and a quarter across and half an inch thick is made fast to the rear of the cover, and in this a hole is bored seven-eighths of an inch in diameter and one-quarter of an inch deep.
The sides and bottom of this hole are lined with flannel or felt, and a carbon button with roughened surface, as shown at F F, is made fast in it by a small machine screw and nut (F). A diaphragm (D) is cut from thin ferrotype plate, and a carbon button is made fast to the middle of it by a small machine screw or a rivet made from soft copper or brass. When the block (B) has been screwed fast to A, place some granules of carbon in the space (H); then lay the diaphragm over the opening, and make it fast with small screws or pins driven around the edge.
From a small tin funnel and a tin-can cap make a mouth-piece (C) by cutting a hole in the cap and slipping the funnel through it, then cutting the end of the funnel that projects through the hole and bending back the ears so that they lap on the inner side of the cap. These small ears may be soldered to the cap so as to hold the mouth-piece securely in place. From felt or flannel cut a washer the size of the can top and about three-eighths of an inch in width. Lay this over the diaphragm; then place the mouth-piece on it and fasten it to the door (A) with small screws. The use of this washer is to prevent any false vibrations in the mouth-piece affecting the sensitive diaphragm. Make a small hole through A and B and pass a bolt (E) through this hole, taking care to lap a thin piece of sheet-brass on the diaphragm (D), bending it over so that it will lie under the head of the bolt (E). The diaphragm must be scraped where the metal touches it, so as to make perfect electrical connection between D and E. At the rear end of E arrange a washer and nut (G), so that the current passing in at G travels through E and D, then through the carbon buttons and granules, and out at F.
From pine or white-wood one-quarter or three-eighths of an inch thick make a box four inches wide, six inches high, and two inches and a half deep. To the front of this attach a cover, which should measure a quarter of an inch larger all around than the width and height of the box. Use brass hinges for this work so that the cover may be opened. Fasten a transmitter to the front of the cover, or make one on the cover, as shown in [Fig. 11], and attach the box to a back-board or wall-plate five inches wide and seven inches high made of pine or white-wood half an inch in thickness (see [Fig. 13]).
At the left side of the box cut a slot through the wood, so that a lever and hook may project and work up and down. The end of this lever is provided with a hook on which a receiver may be hung, as shown in [Fig. 13], and the inside mechanism is arranged as shown at [Fig. 14]. A is an angle-piece of brass or copper, which acts as a bracket and which is screwed fast to the inside of the box. B is the lever and hook, which is cut from a strip of brass. The attached end is made wider, and an ear (C), to which a wire is soldered, projects down beyond the screw.
A view looking down on this lever and bracket is shown at [Fig. 15]. A is the bracket, B the lever, and E the screw or bolt holding the two parts together, with a thin copper washer between them to prevent friction. When the lever and bracket are made fast to the box, a spring (D) should be arranged, so that when the receiver is removed from the hook the lever will be drawn up to the top of the slot. A small contact-plate (F) is made of brass, and fastened at the lower end of the slot. On this the lever should rest when the receiver is on the hook. A contact-wire is soldered to this plate, which in turn is screwed fast to the inside of the box. This mechanism is part of a make-and-break switch to cut out and cut in the bells or telephone, and will be more clearly understood by referring to the diagram in [Fig. 17]. At the right side of the box a small push-button is made fast, and this, with two binding-posts at the top and four at the underside of the box, will complete the exterior equipment of one end of a line.
The construction of the push-button is shown in [Fig. 16], A being the box and B the button which passes through a small hole made in the side of the box. C is a strip of spring-brass screwed fast to the box. It must be strong enough to press the small bone or hard rubber button towards the outside of the box. A wire is caught under one screw-head, and another one is passed under the screw-head which holds the other spring (D) to the box. When the button (B) is pushed in, it brings spring C into contact with D, and the circuit is closed. Directly the finger is removed from B the spring (C) pushes it out and breaks the circuit. This button is used only in connection with the call-bells, and has nothing to do with the telephone. The wires leading from the interior of the box pass through the wall-plate and along in grooves to the foot of the binding-posts, which are arranged below the box on the back-board, as shown in [Fig. 13].
A buzzer or bell is made fast to the inside of the box, unless it is too large to fit conveniently, in which case it may be attached to the wall above or below the box.
The Wiring System
[Fig. 17] shows the wiring system for this outfit, which, when properly set up and connected, should operate on a circuit or line several miles in length, provided that the batteries are strong enough.
This system may be installed in the box shown in [Fig. 13], the flexible cord containing two wires being attached to the binding-posts at the top of the box and to the posts at the end of the receiver. This system differs from the one shown in [Fig. 6] only in the addition of receivers T and T 2, and in the substitution of the automatic lever-switches (L S and L S 2) for the plain switches (S and S 2) in [Fig. 6]. When the line is “quiet” the receiver (R) should be hanging on the lever-switch (L S), which rests on the contact-plate (A). At the opposite side of the line the receiver (R 2) hangs on the lever-switch (L S 2), which in turn rests on the contact-plate (A A). This puts the bell circuit in service.
PLAN OF TELEPHONE CIRCUIT, COMPRISING RECEIVERS, TRANSMITTER, ELECTRIC BUZZERS OR BELLS, LEVER-SWITCHES, PUSH-BUTTONS AND BATTERIES FOR STATIONS NOT OVER FIVE MILES APART.
If the boy at the left wishes to call up the boy at the right he removes the receiver (R) from the hook (L S) and presses on the button (P B). This closes the circuit through the battery (C C C), and operates the electric buzzer or bell (E B 2) at the other end of the system, through line No. 1 and line No. 2. The operation may be clearly understood by following the lines in the drawing with a pointer. The boy at the left may keep on calling the boy at the right so long as the receiver (R 2) hangs on the lever (L S 2) and holds it down against the plate (A A). But directly the receiver (R 2) is removed, the lever (L S 2) flies up—being drawn upward by the spring (D) shown in [Fig. 14]—and closes the telephone circuit through the spring-contact (B B), at the same time cutting out the bell circuit. The boy at the left having already removed his receiver, the telephone circuit is then complete through lines Nos. 1 and 2 and batteries C C C and C 2 C 2 C 2, the boys at both ends speaking into the transmitters and hearing through the receivers. The contacts B and B B are made from spring-brass or copper, and are attached inside the boxes at the back, so that when the levers are up contact is made, but when down the circuit is broken or opened. In [Fig. 18] an interior view of a box is shown, the door being thrown open and the receiver left hanging on the hook.
TELEPHONE INSTALLATION. INTERIOR VIEW OF BOX
The arrangement of the several parts will be found convenient and easy of access. E B is the electric buzzer, L S the lever-switch, P B the push-button, T the transmitter, and R the receiver. Nos. 1, 2, 3, 4, 5, 6, 7, 8 are binding-posts or terminals, and B is the spring-contact against which the lever-switch (L S) strikes when drawn up by the spring (D).
The wires that pass from 6 to 7 and from 4 to 8 should be soldered fast to one side of the hinge, and those running from the terminals or nuts at the back of the transmitter (T) to 7 and 8 should be similarly secured. Small brass hinges are not liable to become corroded at the joints, but to insure against any such possibility the ends of several fine wires may be soldered to each leaf of the hinge, so that when the door is closed the wires will be compressed between the hinge-plates. For long-distance communication it will be necessary to install an induction-coil, so that the direct current furnished by the batteries, in series with the transmitter, can by induction be transformed into alternating current over the lines connecting the two sets of apparatus. This system is somewhat more complicated and requires more care in making the connections, but once in operation it will be found far superior to either of the systems hitherto described.
A Telephone Induction-coil
It will be necessary to make two induction-coils, as described in [chapter iv.], [page 62], [Fig. 8]. A telephone coil for moderately long-distance circuits is made on a wooden spool turned from a piece of wood three inches and a half long and one inch square, as shown at [Fig. 19]. The core-sheath is turned down so that it is about one-sixteenth of an inch thick. This spool is given a coat or two of shellac, and two holes are made at each end, as shown in the drawing. The first winding or primary coil is made up of two layers of No. 20 double-insulated copper wire, one end projecting from a hole at one end of the spool, the other from a hole at the other end. This coil is given two or three thin coats of shellac to bind the strands of wire and thoroughly insulate them, and over the layer a piece of paper is to be wrapped and shellacked. The secondary coil is made up of twelve layers of No. 34 silk-insulated copper wire, and between each layer a sheet of paper should be wound so that it will make two complete wraps. Each paper separator should be given a coat of shellac or hot paraffine; then the turns of wire should be continued just as thread is wound upon a spool, smoothly, closely, and evenly, until the last wrap is on. Three or four wraps of paper should be fastened on the coil to protect it, and it may then be screwed fast inside a box. The core-hole within the coil should be packed with lengths of No. 24 soft Swedes iron wire three inches and a half long. In [Fig. 19] the wires are shown projecting from the end of a spool, and [Fig. 20] depicts a completed telephone induction-coil. The installation of the induction-coils is shown in [Fig. 21].
PLAN OF TELEPHONE CIRCUIT, COMPRISING RECEIVERS, TRANSMITTERS, ELECTRIC BUZZERS OR BELLS, LEVER-SWITCHES, INDUCTION-COILS, PUSH-BUTTONS, AND BATTERIES FOR STATIONS UP TO FIVE HUNDRED MILES APART.
The wiring is comparatively simple, and may be easily followed if the description and plan are constantly consulted when setting up the line. R and R 2 are the receivers, T and T 2 the transmitters, C 1 and C 2 the batteries, E B and E B 2 the buzzers or bells, P B and P B 2 the push-buttons, and L S and L S 2 the lever-switches. For convenience of illustration the induction-coils are separated. The primary coil (P C) is indicated by the heavy spring line and the secondary coil (S C) by the fine spring line. When the line is “dead” both receivers are hanging from the hooks of the lever-switches. If the boy at the left wishes to call the boy at the right he lifts the receiver (R) from the hook (L S) and presses the button (P B). This throws the battery (C 1 C 1 C 1) in circuit with lines Nos. 1 and 2, and operates the buzzer (E B 2). When the boy at the right lifts his receiver (R 2) from the hook (L S 2), the bell circuit is cut out and the ’phone circuit is cut in. When the lever-switches are drawn up against the contact-springs (A, B, and C and A A, B B, and C C), both batteries are thrown into circuit with the transmitters at their respective ends through the primary coils (P C and P C 2). By inductance through the secondary coils (S C and S C 2), lines Nos. 1 and 2 are electrified, and when the voice strikes the disks in the transmitters the same tone and vibration is heard through the receivers at the other end of the line. While conversation is going on the batteries at either end are being drawn upon or depleted; but as soon as the receivers are hung on the hooks and the lever-switches are drawn away from the contact-springs, the flow of current is stopped. The buzzers or bells consume but a small amount of current when operated, and in dry cells the active parts recuperate quickly and depolarize. The greatest drain on a battery, therefore, is when the line is closed for conversation.
An Installation Plan
A simple manner in which to install this apparatus in boxes is shown in [Fig. 22]. The box is depicted with the front opened and with the receiver hanging on the hook. When the lever-switch (L S) is down it rests on the contact-spring (A), thus throwing in the bell circuit. When the boy at the other end of the line pushes the button on his box it operates the buzzer (E B). This can be understood by following with a pointer the wires from the buzzer to the outlet-posts (Nos. 1 and 3) at the bottom of the wall-plate.
When the receiver (R) is lifted from the hook (L S), it cuts out the bell circuit and cuts in the telephone circuit, through the spring-contacts (B and C). This circuit may easily be followed through the wires connecting transmitter, receiver, induction-coil, and batteries. The heavy lines leading out from the induction-coil are the primary coil wires, and the fine hair lines are those forming the secondary coil. The medium lines are those that connect the binding-posts, batteries, and lines.
When the bell circuit is connected the impulse coming from the other end of the line enters through wire No. 10 to post No. 3, thence to strip E and plate G, and so on to E B, which it operates. The current then passes from E B to contact A, through L S to post No. 1, and out on wire No. 11.
To operate the buzzer at other end of the line the button (P B) is pushed in. This moves the spring (E) away from the plate (G), and brings it into contact with F. This connects the circuit through the battery wire (No. 8) to post No. 1 to line No. 11 without going into the box, and from wire No. 9 to post No. 2; thence to hinge No. 7 to plate F, through E, down to post No. 3, and out through wire No. 10. In this manner the current is taken from the batteries at the foot of wires Nos. 8 and 9, and used to ring the buzzer at the other end of the line.
When the hook (L S) is up the circuit is closed through T, I C, and battery. The current runs from the battery through wire No. 8 to post No. 1, to L S, through C and primary coil out to hinge No. 6, through transmitter to hinge No. 7, to post No. 2, and back to battery through wire No. 9.
By inductance the sound is carried over the line, in at wire No. 10, to post No. 3, through secondary coil to post No. 4, through receiver R to post No. 5, through B and L S to post No. 1, and out through wire No. 11. At the other end of the line it goes through the same parts of the apparatus.
A Portable Apparatus
For convenience it is often desirable to have a portable transmitter, and so avoid the inconvenience of having to stand while speaking. A neat portable apparatus that will stand on a ledge or table, and which may be moved about within the radius of the connecting lines, is shown in [Fig. 23].
The wooden base is four inches square and the upright one inch and a half square. The stand is twelve inches high over all, and on the bottom a plate of iron or lead must be screwed fast to make it bottom-heavy, so that it will not topple over.
The lever-switch may be arranged at the back of the upright and the push-button at the front near the base, as shown at A. The wall-box contains the buzzer and induction-coil, and within it the wiring is arranged from the portable stand to the batteries and line as shown at C. This illustration is too small, however, to show the complete wiring, and the young electrician is therefore referred to [Fig. 22]. The battery (B) is composed of as many dry or wet cells as may be required to operate the line. These must be connected in series at both ends. At D a rear view of the upright and transmitter is shown to illustrate the manner in which the wiring can be done. If a hollow upright is made of four thin pieces of wood a much neater appearance may be secured by enclosing the wires.
A PORTABLE APPARATUS
In all of these telephone systems one wire must lead to the ground, or be connected with a water-pipe, taking care, however, to solder the wire to a galvanized pipe so that perfect contact will be the result. If the wire is carried directly to the ground it must be attached to a plate, which in turn is buried deep enough to reach moist earth, as described in the chapter on Line and Wireless Telegraphs, [page 215].
Care and accuracy will lead to success in telephony, but one slip or error will throw the best system out of order and render it useless. This, indeed, applies to all electrical apparatus; there can be no half-way; it will either work or it won’t.
Chapter IX
LINE AND WIRELESS TELEGRAPHS
A Ground Telegraph
Nearly every boy is interested in telegraphy, and it is a fascinating field for study and experimental work, to say nothing of the amusement to be gotten out of it. The instruments are not difficult to make, and two boys can easily have a line between their houses.
The key is a modified form of the push-button, and is simply a contact maker and breaker for opening and closing an electrical circuit. A practical telegraph-key is shown in [Fig. 1], and in [Fig. 2] is given the side elevation.
The base-board is four inches wide, six inches long, and half an inch in thickness. At the front end a small metal connector-plate is screwed fast, and through a hole in the middle of it a brass-headed upholsterer’s tack is driven for the underside of the key to strike against. Two L pieces of metal are bent and attached to the middle of the board to support the key-bar, and at the rear of the board another upholsterer’s tack is driven in the wood for the end of the bar to strike on and make a click. The bar is of brass or iron, measuring three-eighths by half an inch, and is provided with a hole bored at an equal distance from each end for a small bolt to pass through, in order to pivot it between the L plates. A hole made at the forward end will admit a brass screw that in turn will hold a spool-end to act as a finger-piece. The screw should be cut off and riveted at the underside. A short, strong spring is to be attached to the back of the base-block and to the end of the key-bar by means of a hook, which may be made from a steel-wire nail flattened. It is bound to the top of the bar with wire, as shown in [Figs. 2] and [3].
The incoming and outgoing wires are made fast to one end of the connector-plate and to one of the L pieces that support the key. When the key is at rest the circuit is open, but when pressed down against the brass tack it is closed, and whether pressed down or released it clicks at both movements. A simple switch may be connected with the L-plate and the connection-post at the opposite side of the key-base, so that, if necessary, the circuit may be closed. Or an arm may be caught under the screw at the L-plate, and brought forward so that it can be thrown in against a screw-head on the connector-plate, as shown in [Fig. 3]. The screw-head may be flattened with a file, and the underside of the switch bevelled at the edges, so that it will mount easily on the screw.
In [Fig. 4] (page 191) a simple telegraph-sounder is shown. A base-board, four inches wide, six inches long, and seven-eighths of an inch in thickness, is made of hard-wood, and two holes are bored, with the centres two inches from one end, so that the lower nuts of the horseshoe magnet will fit in them, as shown in [Fig. 5]. This allows the yoke to rest flat on the top of the base, and with a stout screw passed down through a hole in the middle of the yoke and into the wood the magnets are held in an upright position.
From the base-block to the top of the bolt the magnets are two inches and a quarter high. The bar of brass or iron to which the armature (A in [Fig. 5]) is attached is four inches and a half in length and three-eighths by half an inch thick. At the middle of the bar and through the side a hole is bored, through which a small bolt may be passed to hold it between the upright blocks of wood. At the front end two small holes are to be bored, so that its armature may be riveted to it with brass escutcheon-pins or slim round-headed screws. The heads are at the top and the riveting is underneath. A small block of wood is cut, as shown in [Fig. 6], against which the two upright pieces of wood are made fast. This block is two inches and a half long, one inch and a quarter high, and seven-eighths of an inch wide. The laps cut from each side are an inch wide and a quarter of an inch deep, to receive the uprights of the same dimensions.
At the top of this block a brass-headed nail is driven for the underside of the bar to strike on. A hook and spring are to be attached to the rear of the sounder-bar, as described for the key, and at the front of the base two binding-posts are arranged, to which the loose ends of the coil-wires are attached.
Just behind the yoke, and directly under the armature-bar, a long screw is driven into the base-block, as shown at B in [Fig. 5]. It must not touch the yoke, and the head should be less than one-eighth of an inch below the bar when at rest. On this the armature-bar strikes and clicks when drawn to the magnets. The armature must not touch the magnets; otherwise the residual magnetism would hold it down. The screw must be nicely adjusted, so that a loud, clear click will result.
TELEGRAPH KEY AND SOUNDER
When the sounder is at rest the rear end lies on the brass tack in the block, and the armature is about a quarter of an inch above the top of the magnets. The armature is of soft iron, two inches and a half long, seven-eighths of an inch wide, and an eighth of an inch thick. These small scraps of metal may be procured at a blacksmith’s shop, and, for a few cents, he will bore the holes in the required places; or if you have a breast or hand drill the metal may be held in a vise and properly perforated.
By connecting one wire from the key directly with one of the binding-posts of the sounder, and the other with the poles of a battery, and so on to the sounder, the apparatus is ready for use. By pressing on the key the circuit is closed, and the magnetism of the sounder-cores draws the armature down with a click. On releasing the key the bar flies back to rest, having been pulled down by the spring, and it clicks on the brass tack-head. These two instruments may be placed any distance apart, miles if necessary, so long as sufficient current is employed to work the sounder. Two sets of instruments must be made if boys in separate houses are to have a line. Each one must have a key, sounder, and cell, or several cells connected in series to form a battery, according to the current required.
In the plan of the telegraph-line connections ([Fig. 7], page 196) a clear idea is given for the wiring; and if the line and return wires are to be very long, it would be best to have them of No. 14 galvanized telegraph-wire, copper being too expensive, although much better. These wires must not touch each other, and when attached to a house, barn, or trees, porcelain or glass insulators should be used. If nothing better can be had, the necks of some stout glass bottles may be held with wooden pins or large nails, and the wire twisted to them, as shown in [Fig. 8]. When the line is not in use the switches on both keys should be closed; otherwise it would be impossible for the boy having the closed switch to call up the boy with the open one. Take great care in wiring your apparatus to study the plan, for a misconnected wire will throw the whole system out of order.
To operate the line see that all switches are closed and that the connections are in good condition. When the boy in house No. 2 wants to call up his friend in house No. 1 he throws open the switchon key, as shown in the [plan], and by pressing down on the finger-key his sounder and that in house No. 1 click simultaneously. As soon as he raises or releases the key the armatures rise, making the up-click. If he presses his key and releases it quickly the two clicks on the sounder in house No. 1 are close together; this makes what is called a dot. If the key is held down longer it makes a long time between clicks, and this is called a dash. The dot and dash are the two elements of the telegraphic code. You will understand that the boy in house No. 2 hears just what the one in No. 1 is hearing, since the electric current passing through both coils causes the magnets to act in unison. So soon as the operator in house No. 2 has finished he closes his switch, and the other in house No. 1 opens his switch on the key and begins his reply. This is the simple principle of the telegraph, and all the improved apparatus is based on it, no matter how complicated. The complete Morse alphabet is appended:
The Morse Telegraph Code
Any persevering boy can soon learn the dot-and-dash letters of the Morse code, and very quickly become a fairly good operator. Telegraphic messages are sent and received in this way, and are read by the sound of the clicks. Various kinds of recording instruments are also employed, so that when an operator is away from his table the automatic recorder takes down the message on a paper tape. In the stock-ticker, employed in brokerage offices, the recording is done by letters and numerals, and the paper tape drops into a basket beside the machine, so that any one picking up the strip of paper can see the quotations from the opening of business up to the time of reading them. These quotations are sent out directly from the floor of the exchanges, and by the action of one man’s hand thousands of machines are set in operation all over the city.
Perhaps the most unique and wonderful telegraphic signal-apparatus is that located on the floor of the New York Produce Exchange and the Chicago Exchange. The dials, side by side, are operated by direct wire from Chicago. When the New York operator flashes a quotation it appears simultaneously on the New York dial and simultaneously on the Chicago dial, and vice versa.
Electrical instruments are not the only means by which the Morse alphabet may be transmitted, for in some instances instruments would be in the way, while in others the wires might be down and communication cut off.
This is interestingly illustrated by an event in Thomas A. Edison’s life. When he was a boy and an apprentice telegraph operator on the Grand Trunk Line, an ice-jam had broken the cable between Port Huron, in Michigan, and Sarnia, in Canada, so that communication by electricity was cut off. The river at that point is a mile and a half wide, the ice made the passage impossible, and there was no way of repairing the cable. Edison impulsively jumped on a locomotive standing near the river-bank and seized the whistle-cord.
He had an idea that blasts of the whistle might be broken into long and short sounds corresponding to the dots and dashes of the Morse code. In a moment the whistle sounded over the river: “Toot, toot, toot, toot,—toot, tooooot,—tooooot—tooooot—toot, toot—toot, toot.” “Halloo, Sarnia! Do you get me? Do you hear what I say?”
No answer.
“Do you hear what I say, Sarnia?”
A third, fourth, and fifth time the message went across, to receive no response. Then suddenly the operator at Sarnia heard familiar sounds, and, opening the station door, he clearly caught the toot, toot of the far-away whistle. He found a locomotive, and, mounting to the cab, responded to Edison, and soon messages were tooted back and forth as freely as though the parted cable were again in operation.
Some years ago the police of New York were mystified over a murder case. The man they suspected had not fled, but was still in his usual place, and attending to his business quite as though nothing had happened to connect him with the tragedy.
Detectives in plain clothes had been following him and watching closely his every move in and out of restaurants and shops and at social affairs; but not the slightest proof could be secured against him.
One noon-time they followed him into a café, where he had gone with a friend. The detectives took seats near him, but each of them sat at different tables in the room full of people.
When in the café the suspect sat next the wall, a habit the detectives had noticed. Consequently, only those persons who sat at one side of him or directly in front could see his face. During the time they were in the restaurant the detectives communicated with each other by tapping on the table tops with a lead-pencil; and something the man said, which the nearest detective heard, led to the climax. One detective rose, paid his check, and loitered near the door; another got up a little later and sauntered out, but returned with a cardboard sign. Going over to the table where the suspected criminal and his friend sat, he deliberately tacked it on the wall above them, then went out again, leaving the third detective to watch the face of the man as he read:
$1000 REWARD
for information leading to the arrest of the murderer of ————————
on March ————, 1876
The man cast a glance about the restaurant, then said to his companion: “Did I show any signs of agitation?” The third detective rose, stepped over to the man, tapped him on the shoulder, and said, “I want you.” There would have been a scene of violence had not the other two detectives closed in on the man, and within six months he paid the penalty of his crime.
If it had not been for the dot-and-dash alphabet, tapped out with lead-pencils, the detectives could not have communicated; but like Edison, they used the means at hand to open up and carry on a silent conversation.
Wireless Telegraphy
Everybody nowadays understands that wireless telegraphy means the transmission of electrical vibrations through the ether and earth without the aid of wires or any visible means of conductivity. The feat of sending an electrical communication over thousands of miles of wire, or through submarine cables, is wonderful enough, for all that custom has made it an every-day miracle. To accomplish this same end by sending our messages through the apparently empty air is indeed awe-inspiring and almost beyond belief. And yet we know that wireless telegraphy is to-day a real scientific fact.
At first sight it would seem that the instruments must be complicated and necessarily beyond the ability of the average boy to make, and far too expensive as well. As a matter of fact, the young electrician may construct his wireless apparatus at a very moderate cost, it being understood that the sending and receiving poles may be mounted on a housetop or barn.
But first let us consider the theory upon which we are to work. There is no doubt but that electricity is the highest known form of vibration—so high, indeed, that as yet man has been unable to invent any instrument to record the number of pulsations per second. This vibration will occur in, and can be sent through, the ordinary form of conductor, such as metals, water, fluids and liquids, wet earth, air and ice. Also through what we call the ether.
Now the ether of the atmosphere, estimated to be fifteen trillion times lighter than air, is the medium through which the electrical vibrations pass in travelling in their radial direction from a central point, corresponding to the ripples or wavelets formed when a pond or surface of still water is disturbed. Ether is so fine a substance that the organs of sense are not delicate enough to detect it, and it is of such a volatile and uneasy nature that it is continually in motion. It vibrates under certain conditions, and when disturbed (as by a dynamo) it undoubtedly forms the active principle of electricity and magnetism.
James Clark Maxwell believed that magnetism, electricity, and light are all transmitted by vibrations in one common ether, and he finally demonstrated his theory by proving that pulsations of light, electricity, and magnetism differed only in their wave lengths. In 1887 Professor Hertz succeeded in establishing proof positive that Maxwell’s theories were correct, and, after elaborate experiments, he proved that all these forces used ether as a common medium. Therefore, if it were not for the ether, wireless telegraphy, with all its wonders, would not be possible. We understand, then, that the waves of ether are set in motion from a central disturbing point, and this can be accomplished only by means of electrical impulse.
Suppose that we strike a bell held high in the air. The sound is the result of the vibrations of its mass sending its pulsating energy through the air. The length of the sound-waves is measured in the direction in which the waves are travelling, and if the air is quiet and not disturbed by wind the sound will travel equally in all directions. The sound of a bell will not travel so well against a wind as it will with it, just as the ripples on a pond would be checked by an adverse set of wavelets.
Now the ether can be made to vibrate in a similar manner to the air by a charge of electricity oscillating or surging to and fro on a wire several hundred thousand times in a second. These oscillations strike out and affect the surrounding ether, so that, according to the intensity of the disruptive charge at the starting-point, the ether waves may be made to reach near or distant points.
This is, perhaps, more clearly shown by the action of a pendulum. In [Fig. 9] the rod and ball are at rest, but if drawn to one side and released it swings over to the other side nearly as far away from its central position of rest as from the starting-point. If allowed to swing to and fro it will oscillate until at last it will come to rest in a vertical position. This same oscillation (oscillation being a form of vibration) takes place in the water when a stone has been flung into it, and in the ether when affected by the electrical discharge. In [Fig. 10] are shown the principal varieties of vibration—the oscillating, pulsating, and alternating.
It is known that if these oscillations are damped, so that the over-intense agitation of the central disturbance is lessened, a new series of vibrations, such as the pulsating or alternating, is set up, and these secondary vibrations possess the power to travel around the world—yes, and perhaps to other worlds in the planetary cosmos.
OSCILLATION AND VIBRATION
The study of ether disturbances, wave currents, oscillating currents, and the other phenomena dependant upon this invisible force is most interesting and fascinating, and were it possible to devote more space to this topic several chapters could be written on the scientific theory of wireless telegraphy.[2]
[2] For further information on this subject the student is referred to such well-known books as Signalling Across Space Without Wires, by Prof. Oliver J. Lodge, and Wireless Telegraphy, by C. H. Sewall.
The principle difference between wire, or line, and wireless telegraphy is that the overhead wire, or underground or submarine cable, is omitted. In its stead the ether of the air is set in vibratory motion by properly constructed instruments, and the communication is recorded at a distance by instruments especially designed to receive the transmitted waves.
It seems to be the popular impression that a wireless message sent from one point to another travels in a straight line, as indicated by [Fig. 11], B representing Boston, which receives the message from N. Y., or New York. As a matter of fact, if several sets of wireless receiving instruments were located on the circumference of a circle the same distance from New York in all directions, or even at nearer or farther points, they would all receive the same message. Instead of travelling in one direction, the ether waves are set in motion by the electrical disturbance, just as water is agitated by the stone thrown into it. The ripples, or wavelets, are started from the central point of disturbance and radiate out, so that instead of reaching Boston only the waves travel over every inch of ground, or air space, in all directions, and would be recorded in every town and village within the sphere of energy set up by the original force that put the ether waves in motion. The stronger this initial force the wider its field of action. This is shown at [Fig. 12], which is an area comprising Philadelphia, Pittsburg, Buffalo, Washington, and other cities. Moreover, the waves of electrical disturbance would carry far beyond in all directions, taking in the cities of the north, south, and west, and at the east, going far out to sea, beyond Boston harbor and below Cape Hatteras, where ships carrying receiving instruments could pick up the messages. Like the ripples on the water, the radiating waves, or rings, become larger as they reach out farther and farther from the centre of disturbance, until at last they are imperceptible, and lose their shape and force.
At great distances, therefore, the ether disturbance becomes so slight that it is impossible to record the vibration or message sent out; and until some improved forms of apparatus and coherer are invented, or the original disturbing force is enormously increased, it will be impossible to send messages at longer distances than four or five thousand miles from a central point. Both Marconi and De Forrest assert that they are perfecting coherers which will make it possible to girdle the earth with a message, and that within the next few years an aerogram may be sent out from a station, and, after instantly encircling the earth and being recorded during its passage at all intermediate stations, it will return and be received at the original sending-point. This, of course, is a matter of future achievement; but now that messages across the Atlantic are a commercial fact, it seems quite possible that the greater feat of overriding space and reaching any point on the earth’s surface will soon be a reality. And now to proceed from theory to the construction of a practical wireless apparatus having a radial area of action over some ten or fifteen miles.
The principal parts of a wireless apparatus include the antennas (or receiving and sending poles with their terminal connections), the induction-coil, strong primary batteries or dynamo, the coherer and de-coherer, the telegraph key and sounder (or a telephone receiver), and the necessary connection wires, binding-posts, and ground-plates.
A large induction-coil with many layers of fine insulated wire will be necessary for the perfect operative outfit. The most practical coil for the amateur is a Ruhmkorff induction-coil. (See the directions and illustrations for constructing this coil, beginning on [page 59] of [chapter iv.])
The sending apparatus is practically the same in all outfits, and consists of a source of electrical energy, such as a battery, or dynamo, the essential induction-coil and adjustable spark-gap between the brass balls on terminal rods, and the make-and-break switch, or telegraph-key.
It is in the various forms of coherers and receiving apparatus that the different inventors claim superiority and originality. The systems also differ in their theory of harmonic tuning or vibratory sympathy. This is accomplished by means of coils and condensers, so that the messages sent out on one set of instruments will not be picked up or recorded by the receiving apparatus of competitors.
Having made or purchased an induction-coil of proper and adequate size, it will now be necessary to construct the parts so that an adjustable spark-gap may be secured.
Make a hollow wooden base for the induction-coil to rest on. It should be a trifle longer than the length of the coil and about seven inches wide. This may be made from wood half an inch thick. The base should be two inches high, so that it will be easy and convenient to make wire connections under it. Mount the induction-coil on the base and make it fast with screws, arranging it so that the binding-posts are on the side rather than at the top of the coil, as shown in [Fig. 13].
Cut a thin board and mount it across the top of the induction-coil on two short blocks, and to this attach two double-pole binding-posts (P P). The fine wires from the induction-coil are made fast to the foot of each post, and from the posts the aerial wire (A W) and ground wire (G W) lead out.
Fasten two binding-posts at the forward corners of the base, and to them make connection-wires fast to the heavy or primary wires of the coil. Wires B and C lead out from these posts to the battery and key, and to complete this part of the sending, or transmitting apparatus it will be necessary to have two terminal rods and balls attached to the top of the binding-posts (P P). This part of the apparatus is generally called the oscillator, and the rods are balanced on the posts, so that they can be moved in order to increase or diminish the space (S G), or spark-gap, between the brass balls.
When, after experiment, the proper space has been determined, the set screw at the top of the posts will hold the terminal rods securely in place.
Obtain a piece of brass, copper, or German-silver rod three-sixteenths of an inch in diameter. Now cut two short rods, each six inches long, and two inches from one end flatten the rods with a hammer, as shown at A in [Fig. 14]. Flatten the rod in two places at the other end, as shown at B B in [Fig. 14]; then bore holes through the flattened parts (A), so that the binding-screws at the top of the posts (P P) will pass through them.
Obtain two brass balls from one to one inch and a half in diameter. If they are solid or cast brass they may be attached to the ends of the terminal rods by threading, so that it will be easy to remove them. If the balls are of spun sheet-metal it will be necessary to solder them fast to the ends of the rods, and, when polishing the balls, the rods will have to be removed from the binding-posts. It is imperative that the balls should be kept polished and in bright condition at all times, to facilitate the action of the impulsive sparks.
To counterbalance these balls there should be handles at the long ends of the rods. These handles may be of wood, or made of composition molded directly on the rods. A good composition that can be easily made and molded is composed of eight parts plaster of Paris and two parts of dextrin made into a thick paste with water. The dextrin may be purchased at a paint-store, and is the color of light-brown sugar. Mix the dry plaster and dextrin together, so that they are homogeneous; then add water to make the pasty mass. Use an old table-knife to apply the wet composition to the bars. The flattened parts will help to hold the mass in place until it sets. It is best to make two mixtures of the paste and put one on first, leaving it rough on the surface, so that the last coat will stick to it. When the last coat is nearly dry it may be rubbed smooth with the fingers and a little water, or allowed to dry hard, and then smoothed down with an old file and sand-paper.
If solid brass balls are used for the terminals the composition handles may be made heavier; but in any event the proper amount of composition should be used, so that when the rod is balanced on a nail or piece of wire passed through the hole it will not tip down at one end or the other, but will remain in a horizontal position.
The overhead part of the apparatus employed to collect the electric waves is called the antennæ, and in the various commercial forms of wireless apparatus this feature differs. The general principle, however, is the same, and in [Figs. 15], [16], [17], and [18] some simple forms of construction are shown.
Great care must be taken to properly insulate the rod, wire, or fingers of these antennæ, so that the full force of the vibration is carried directly down to the coherer and sounder or receiver. For this purpose, porcelain, glass, or gutta-percha knobs must be employed.
In [Fig. 15] the apparatus consists of an upright stick, a cross-stick, and a brace, or bracket, to hold them in proper place.
Porcelain knobs are made fast to the sticks with linen string or stout cotton line. Then an insulated copper wire is run through the holes in the knobs, and from the outer knob a rod of brass, copper, or German-silver, or even a piece of galvanized-iron lightning-rod, is suspended. Care should be taken to see that the joint between rod and wire is soldered so as to make perfect contact. Otherwise rust or corrosion will cause imperfect contact of metals, and interrupted vibrations would be the result. The upright stick should be ten or fifteen feet high, and may be attached to a house-top, a chimney, or on the corner of a barn roof.
Another form of single antenna is shown in [Fig. 16]. This is a rod held fast in a porcelain insulator with cement. The insulator, in turn, is slipped over the end of a staff, or pole, which is erected on a building top or out in the open, the same as a flag-pole. Near the foot of the rod, and just above the insulator, a conducting-wire is made fast and soldered. This is run down through porcelain insulators to the apparatus.
If the pole is erected on a house-top it may be braced with wires, to stay it, but care must be taken not to have these wires come into contact with the rod, or conducting-wire.
TYPES OF ANTENNÆ
Another form of antennas is shown in [Fig. 17], where rods are suspended from a wire which, in turn, is drawn taut between two insulators. The insulators are held in a framework composed of two uprights and a cross-piece of wood.
This frame may be nailed fast to a chimney and to the gable of a roof, as shown in the [drawing]; and to steady the rods, so that they will not swing in a high wind, the lower ends should be tied together with cotton string, the ends of which should be fastened to the uprights. The leading-in wire is made fast to the top wire, from which the rods are suspended, and all the exposed joints should be soldered to insure perfect contact and conductivity. A modified form of the Marconi antennæ is shown in [Fig. 18]. This is made of a metal hoop three of four feet in diameter held in shape by cross-sticks of wood, which can be lashed fast to the ring. Leading down from it are numerous copper wires which terminate in a single wire, the whole apparatus resembling a funnel. The upper unions where the wires join the ring need not be soldered, but at the bottom, where they all come together and join the leading-in wire, it is quite necessary that a good soldered joint be made. This funnel may be hung between two upright poles on a house-top, or suspended from the towers or chimneys.
Almost any metal plate will do for the ground, or the ground-wire (G W in [Fig. 13]) may be bound to a gas or water pipe which goes down deep in the ground, where it is moist. Rust or white lead in the joints of gas-mains sometimes prevent perfect contact, but in water-pipes the current will flow readily through either the metal or the water. To insure the most perfect results, it is best to have an independent ground composed of metal, and connected directly with the oscillator, or coherer, by an insulated copper wire. A simple and easily constructed ground is a sheet of metal, preferably copper, brass, or zinc, to the upper edge of which two wires are soldered, as shown in [Fig. 19]. This is embedded in the ground three or four feet below the surface. Another ground-plate is a sheet of metal bent in V shape and then inverted. Two wires are soldered to the angle, and the ends brought together and soldered. This ground is buried three or four feet deep, and stands in a vertical position, as shown at [Fig. 20]. At [Fig. 21] a flat ground is shown. This is a sheet of metal cut with pointed ends. The ground-wire is soldered to the middle of it, and it is then buried deep enough to be embedded in moist earth.
One of the best grounds is an old broiler with a copper wire soldered to the ends of the handles, as shown at [Fig. 22]. This is buried deep in the ground in a vertical position, and the insulated copper wire is carried up to the instruments.
The most important part of the wireless telegraphic apparatus is now to be constructed, and this requires some care and patience. The coherer is the delicate, sensitive part of the apparatus on which hinges success or failure. There are various kinds of coherers designed and used by different inventors, but while the materials differ and the construction takes various forms, the same basic principle applies to all.
TYPES OF GROUNDS
The coherer can best be explained as a short glass tube in which iron or other metallic filings are enclosed. Corks are placed in both ends of the tube, and through these corks the ends of wire are passed, so that they occupy the position shown in [Fig. 23], the ends being separated a quarter of an inch. Metal filings will not conduct an electric current the same as a solid rod or bar of the same metal, but resist the passage of current.
After long periods of experimenting with various devices to detect the presence of feeble currents, or oscillations, in the ether, the coherer of metal filings was adopted. When the oscillations surge through the resonator, the pressure, or potential, finally breaks down the air film separating the little particles of metal, and then gently welds their sharp edges and corners together so as to form a conductor for the current. Before this process of cohesion takes place these fine particles offer a very high resistance to the electrical energy generated by a dry cell or battery—so much so that no current is permitted to pass. But once the oscillations in the ether cause them to cohere—presto! the resistance drops from thousands of ohms to hundreds, and the current from the dry cell now flows easily through the coherer and deflects the needle of a galvanometer. This is the common principle of all coherers of the granulated metal type, although there are many modifications of the idea.
The action of the electric and oscillatory currents on particles of metal can best be understood by placing some fine iron filings on a board, as shown at [Fig. 24], and then inserting the aerial and ground wires in the filings, but separated by an eighth or a quarter of an inch. A temporary connection may be made as shown in [Fig. 25].
A A are aerials on both instruments; C is the open coherer, or board with iron filings, in which the ends of the aerial and ground wires are embedded; D C is a dry cell; and R is a telegraphic relay, or sounder. If the wire across C was not parted and covered with filings, the dry cell would operate R, but the high resistance of the particles of metal holds back the current.
On the opposite side, I C is the induction-coil; K is the telegraphic key, or switch, which makes and breaks the current; S B is the storage-batteries, or source of electric energy; and S G the spark-gap between the brass balls on the terminal rods. By closing the circuit at K the current flows through the primary of the induction-coil, affects the secondary coil, and causes a spark to leap across the gap between the brass balls. This instantly sets the ether in motion from A on the right, and the impulse is picked up by A on the left. This oscillation breaks down the resistance of the filings at C, and the current from battery, or dry cell (D C), flows through the filings and operates the sounder, or relay (R). This operation takes place instantly, and the particles of metal are seen to cohere, or shift, so that better contact is established. But as soon as the spark has jumped across the gap the action of cohesion ceases until the key (K) is again operated to close the circuit and cause another spark to leap across the gap. The shifting of the metal particles on the board (C) is what takes place in the glass tube of the coherer, [Fig. 23], but in this confined space the particles will not drop apart again as on the flat surface, but will continue to cohere. A de-coherer is necessary, therefore, to knock the particles apart, so that the next oscillatory impulse will have a strong and individual effect. There are several forms of de-coherers in use, but for the amateur telegrapher an electric-bell movement without the bell, or, in other words, a buzzer with a knocker on the armature, will answer every purpose. (See description of [buzzer] on [page 64].) It must be properly mounted, so that on its back stroke, or rebound, the knocker will strike the glass tube and shake the particles of metal apart. For this purpose the vibrations of the armature should be so regulated as to obtain the greatest possible speed, in order that the dots and dashes (or short and long periods) will be accurately recorded through the coherer and made audible by the sounder or telephone receiver.
Another form of coherer is shown in [Fig. 26]. This is made of a small piece of glass tube, two rods that will accurately fit in the tube, some nickel filings, two binding-posts, and a base-block three inches and a half long. The two binding-posts are mounted on the block, and through the holes in the body of the posts the rods are slipped. They pass into the tube, and the blunt ends press the small mass of filings together, as shown in the drawing. By means of the binding-posts these coherer-rods may be held in place and the proper pressure against the filings adjusted; then maintained by the set-screws. The nickel filings may be procured by filing the edge of a five-cent piece. Obtain a few filings from the edge of a dime and add them to the nickel, so that the mixture will be in the proportion of one part silver to nine parts nickel. This mixture will be found to work better than the iron filings alone. The aerial and ground wires are made fast to the foot-screws of the binding-posts, and the base on which the coherer is mounted may be attached to a table or ledge on which the other parts of the receiving and recording apparatus are also installed.
Another form of coherer is shown at [Fig. 27]. This is constructed in a somewhat similar manner to the one just described. A glass tube is provided with two corks having holes in them to receive the coherer-rods. Two plugs of silver are arranged to accurately fit within the tube, and into these the ends of the coherer-rods are screwed or soldered. Between these silver plugs, or terminals, the filings of nickel and silver are placed, and the rods are pushed together and caught in the binding-posts. The aerial and ground wires are made fast to the foot-screws of the posts.
For long-distance communication it is necessary to have a condenser placed in series with the sparking or sending-out apparatus. (See the type of condenser described and illustrated in [chapter iv.], [page 72].)
An astatic galvanometer is also a valuable part of the receiving apparatus, and the one described on [page 111] will show clearly the presence of oscillatory currents by the rapid and sensitive deflections of the needle.
For local service, where a moderately powerful battery is employed, a telegraph-key, such as described on [page 190], will answer very well, but for high-tension work, where a powerful storage-battery or small dynamo is employed, it will be necessary to have a non-sparking key, so that the direct current will not form an arc between the terminals of a key. Most of the keys used for wireless telegraphy have high insulated pressure-knobs, or the make and break is done in oil, so that the spark or arc cannot jump or be formed between the points.
The plan of a simple non-sparking dry switch is shown at [Fig. 28]. This is built up on a block three inches wide and five inches long. It consists of a bar (A), two spring interrupters (B and C), a spring (D), and the binding-posts (E E). They are arranged as shown in [Fig. 28], and a front elevation is given in [Fig. 29]. The strip (B) lies flat on the block, and is connected with one binding-post by a wire attached under one screw-head and run along the under side of the base in a groove to the foot of the post. Strip C is of spring-brass, and is made fast to the base with screws. This is “dead,” as no current passes through it, and its only use is to interrupt. The bar (A) is arranged as explained for the line telegraph-key, and the remaining binding-post is connected to it by a wire run under the base and brought up to one of the angle-pieces forming the hinge. A high wood or porcelain knob is made fast at the forward end of the bar, so that when high-tension current is employed the spark will not jump from the bar to the operator’s hand. The complete key ready for operation is shown at [Fig. 30], and to make it permanent it should be screwed fast to the table, or cabinet, on which the coil and condenser rest. The plan of a “wet” key is shown in [Fig. 31], and the complete key in [Fig. 32].
DRY AND WET NON-SPARKING SWITCHES
A base of wood three by five inches is made and given several coats of shellac. Obtain a small rubber or composition pill or salve box, and make it fast to the front end of the base with an oval-headed brass screw driven down through the centre of the box. A wire leading to one binding-post is arranged to come into contact with the screw, and the other post is connected by wire to one hinge-plate supporting the bar. The long machine screw, or rivet, passed down through the knob and into the bar, extends down below the bar for half an inch or more, so that when the knob is pressed down the end of the screw, or rivet, will strike the top of the screw at the bottom of the box without the bar coming in contact with the edge of the box. When in operation the composition box is filled with olive oil or thin machinery oil, so that when contact is made by pressing the knob down the circuit will be instantly broken, the spring at the rear end of the bar drawing it back to rest. The oil prevents any sparks jumping across; and also breaks an arc, should one form between the contact-points. With the addition of a good storage-battery (the strength of which must be governed by the size of the induction-coil and the distance the messages are sent) and a dry-cell or two for the receiving apparatus, the parts of the wireless apparatus are now ready for assembling. Full directions for making storage-cells is given in [chapter ii.], [page 21], and for dry-cells in chapter ii., [page 29]. For short-distance work the plan shown in [Figs. 33] and [34] will be found a very satisfactory form of apparatus. One of each kind of instrument should be at every point where communication is to be established.
In the sending apparatus ([Fig. 33]) S C are the storage-cells, K the key, and I C the induction-coil. T T are the terminals and balls, S G the spark-gap, and P P the posts that hold the terminal rods. A W is the aerial wire running up from one post, and G W the ground-wire connecting the other terminal post with the ground-plates.
In the receiving apparatus ([Fig. 34]) C is the coherer, D C the de-coherer, T S the telegraphic sounder, or relay, and A G the astatic galvanometer. B is the dry-cell, or battery, and D C S the de-coherer switch, so that when the apparatus is not in use the dry-cell will not operate the buzzer or de-coherer. A W is the aerial wire and G W the ground-wire. Two or more storage-cells may be connected in series (that is, the negative of one with the positive pole of the other) until a sufficiently powerful source of current is secured for the transmission of messages.
To operate the apparatus, the circuit is closed with K, and the current from S C flows around the primary coil in I C and affects the secondary coil, causing the spark to leap across the gap (S G). This causes a disturbance through the wires A W and G W, and the ether waves are set in oscillatory motion from the antennæ on the house-top. This affects the antennæ at the receiving-point, and the impression is recorded through the coherer (C) on the telegraphic sounder or relay (T S), which is operated by the current from dry-cell or battery (B), since the oscillations have broken the resistance of the filings in the coherer (C). The instant that the current passes through the coherer and operates T S, the astatic galvanometer indicates the presence of current by the deflected needle.
When the apparatus is in operation D C S is closed, so that the current from B operates the coherer (D C). Directly communication is broken off, the switch (D C S) should be opened; otherwise the buzzer would keep up a continuous tapping. For long-distance work a more efficient sending apparatus is shown in [Fig. 35]. This is composed of an induction-coil, with the terminal rods and brass balls forming the spark-gap, an oil key (K), and three or more large storage-cells, or a dynamo (if power can be had to run it). A condenser is placed in connection with the aerial and ground wires, so that added intensity or higher voltage is given the spark as it leaps across the gap. In operation this apparatus is similar to the one already described. Where contact is made with K the primary coil is charged, and by induction the current affects the secondary coil, the current or high voltage from which is stored in the condenser. When a sufficient quantity is accumulated the spark leaps across S G and affects wires A W and G W. This action is almost instantaneous, and directly the impulse sets the ether in motion the same impulse is recorded on the distant coherers and sounders.
There are a great many modifications of this apparatus, but the principles are practically the same, and while the construction of this apparatus is within the ability of the average boy, many of the more complicated forms of coherers and other parts would be beyond his knowledge and skill. Marconi has realized his ambition to send messages across the ocean without wires, and is now doing so on a commercial basis, and at the rate of twenty-five words a minute. It is but the next step to establish communication half-way around the world, and finally to girdle the earth.
Chapter X
DYNAMOS AND MOTORS
To adequately treat of dynamos and motors, a good-sized book rather than this single chapter would be necessary, and only a general survey of the subject is possible. Its importance is unquestionable; indeed, the whole science of applied electricity dates from the invention of the dynamo. Without mechanical production of electricity there could be no such thing as electric traction, heat, light, power, and electro-metallurgy, since the chemical generation of electricity is far too expensive for commercial use. Surely it is a part of ordinary education nowadays to have a clear and definite idea of the principles of electrical science, and in no department of human knowledge has there been more constant and rapid advance. It is only a truism to assert that the school-boy of to-day knows a hundredfold more about electricity and its varied phenomena than did the scientists and philosophers of old—Volta and Galvani and Benjamin Franklin. Yet it was for these forerunners to open and blaze the way for others to follow. A beginning must always be made, and the Marconis and Edisons of to-day are glad to acknowledge their indebtedness to the experimenters and inventors of the past. And now to our subject.
All dynamos are constructed on practically the same principle—a field of force rapidly and continuously cutting another field of force, and so generating electric current. The common practice in all dynamos and motors is to have the armature fields revolve within, or cut the forces of the main fields of the apparatus. There are many different kinds of dynamos generating as many varieties of current—currents with high voltage and low amperage; currents with low voltage and high amperage; currents direct for lighting, heating, and power; currents alternating, for high-tension power or transmission, electro-metallurgy, and other uses. It is not the intention in this chapter to review all of these forms, nor to explain the complicated and intricate systems of winding fields and armatures for special purposes. Consequently, only a few of the simpler forms of generators and motors will be here described, leaving the more complex problems for the consideration of the advanced student. For his use a list of practical text-books is appended in a foot-note.[3]
[3] First Principles of Electricity and Magnetism, by C. H. W. Biggs; The Dynamo: How Made and Used, by S. R. Bottone; Dynamo Electric Machinery, by Professor S. P. Thompson; Practical Dynamo Building for Amateurs, by Frederick Walker.
The Uni-direction Dynamo
The uni-direction current machine is about the simplest practicable dynamo that a boy can make. It may be operated by hand, or can be run by motive power. The field is a permanent magnet similar to a horseshoe magnet. This must be made by a blacksmith, but if a large parallel magnet can be purchased at a reasonable price so much the better, as time and trouble will be saved. This magnet should measure ten inches long and four inches and a half across, with a clear space seven inches long and one inch and three-quarters wide, inside measure. The metal should be half an inch thick and one inch and a quarter wide. A blacksmith will make and temper this magnet form; then, if there is a power-station near at hand where electricity is generated for traction or lighting purposes, one of the workmen will magnetize it for you at a small cost; or it can be wound with several coils of wire, one over the other, and a current run through it. When properly magnetized it should be powerful enough to raise ten pounds of iron. This may be tested by shutting off the current and trying its lifting power. If the magnet is too weak to attract the weight the current should be turned on and another test made a few minutes later.
Before the steel is tempered there should be four holes bored in the magnet and countersunk, so that screws may be passed through it and into the wooden base below, as shown at [Fig. 1]. This wooden base is fourteen inches long, eight inches wide, and one inch in thickness. It may be made of pine, white-wood, birch, or any good dry wood that may be at hand. The blocks on which the magnet rests are an inch and a quarter square and seven inches long. The magnet is mounted directly in the middle of the base, an equal distance from both edges and ends, as shown in the plan drawing ([Fig. 10]). The blocks are attached with glue and brass screws driven up from the underside of the base.
From a brass strip three-eighths of an inch wide and one-eighth of an inch thick cut a piece six inches long, and bore holes at either end through which long, slim, oval-headed brass screws may pass. Use brass, copper, or German-silver for this bar, and not iron or steel. To the underside, and at the middle, solder or screw fast a small block of brass, through which a hole is to be bored for the spindle or shaft. This finished bar is shown in [Fig. 2]. When mounted over the magnet and held down with brass screws driven into the wood base, its end view will appear as shown in [Fig. 3], A being the bar, B B the screws which hold it down, D the base into which they are driven, and C C the blocks under the magnet (N S). The object of this bar is to support one end of the armature shaft. From brass one-eighth of an inch thick bend and form two angles, as shown at [Fig. 4]. Two holes for screws are to be drilled in the part that rests on the base, and one hole, for the shaft to pass through, is bored near the top of the upright plate. The centre of this last hole must be the same height from the base as is the hole in the bar ([Fig. 2]) when mounted over the magnet, as shown at [Fig. 3]. The location of these plates is shown in the plan ([Fig. 10]). There is one plate at each end of the base, as indicated at B and B B, the shaft passing through the hole in the brass block at the underside of the bar (C). These angles are the end-bearings for the armature shaft, and should be accurately centred so that the armature will be properly centred between the N and S bars of the magnet.
DETAILS OF UNI-DIRECTION DYNAMO
The armature is made from soft, round iron rod one inch and a half in diameter and five inches long. A channel is cut all around it, lengthwise, five-eighths of an inch wide and half an inch deep, as shown in [Fig. 5]. This will have to be done at a machine-shop in a short bed-planer, since it would be a long and tedious job to cut it out with a hack-saw. The sharp corners should be rounded off from the central lug, so that they will not cut the strands of fine wire that are to be wound round it.
Two brass disks, or washers, are to be cut, one inch and a half in diameter and from one-eighth to one-quarter of an inch thick, for the armature ends. A quarter-inch hole is to be made in the centre of each for the shaft to fit in, and two smaller holes must be drilled near the edge, and opposite each other, so that machine-screws may pass through them and into holes bored and threaded in the ends of the armature, as shown at [Fig. 5]. These ends will appear as shown at [Fig. 6], and the middle hole should be threaded so as to receive the end of a shaft. When the shaft is screwed in tight the end that passes through the brass disk must be tapped with a light hammer to rivet the end, and so insure that the shaft will not unscrew.
The shafts should be of hard brass or of steel. The one at the front should be one inch and a half in length, and that at the rear six inches long, measuring from the outer face of the brass end to the end of the shaft. From boxwood or maple turn a cylinder three-quarters of an inch in diameter and an inch long, with a quarter-inch hole through it. Over this slip a piece of three-quarter-inch brass or copper tubing that fits snugly, and at opposite sides drill holes and drive in short screws that will hold the tube fast to the hub. They must not be so long as to reach the hole through the centre. Place this hub in a vise, and with a hack-saw cut the tube across in two opposite places, so that you will have the cylinder with two half-circular shells or commutators screwed fast to it, as shown at [Fig. 7]. This hub will fit over the shaft at the front end of the armature, and will occupy the position shown at F in [Fig. 10].
Cut two small blocks of wood for the brushes and binding-posts, and bore a hole through them, so that the foot-screw of a binding-post may pass through the block and into the post, as shown at [Fig. 8]. From thin spring copper cut a narrow strip and bend it over the block, catching it at the top with a screw and lapping it under the binding-post at the outside.
From boxwood or maple have a small wooden pulley turned, with a groove in it and a quarter-inch hole through the centre. This pulley should be half an inch wide and one inch and a half in diameter, as shown at [Fig. 9]. This is to be attached at the end of the long shaft, where it will occupy the position shown at E in [Fig. 10].
All the parts are now ready for assembling except the armature, which must be wound. Before laying on the turns of wire the channel in the iron must be lined with silk, held in place with glue or shellac. A band of silk ribbon is given two turns about the centre of the iron, and the sides are so completely covered with silk that not a single strand of wire will come into direct contact with the iron. Great care must be taken, when winding on the wire, not to kink, chafe, or part the strands. The channel should be filled but not overcrowded, and when full several wraps of insulating tape should be made fast about the armature to hold the wire firmly in place and prevent it from working out at the centre when the armature is driven at high speed. The armature, when properly wound and wrapped, will appear as shown at A in [Fig. 11], and it is then ready to have the ends screwed on. Several sizes of wire may be used to wind the armature, according to the current desired, but for general use it would be well to use No. 30 silk-insulated copper wire.
PLAN OF THE UNI-DIRECTION DYNAMO
About four ounces should be enough for this armature, and the ends are to be passed through small holes in the brass end (B); see [Fig. 11]. One end must be soldered to one commutator, the other end to the other commutator. The end-piece (B) is attached to the iron armature (A) with machine-screws; then C is to be made fast in a similar manner.
When putting the parts together, it would be well to use some shellac on the wooden cylinder and driving-wheel to make them hold to the shaft.
By following the plan in [Fig. 10], it will be an easy matter to put the parts together; when they are assembled the complete machine will appear as shown in the drawing ([Fig. 12]).
The driving-wheel should be of wood five-eighths of an inch thick and six inches in diameter, and held in the frame of wood and metal brackets by a bolt. A short handle can be arranged with which to turn the wheel, and a small leather belt will transmit the power to the small wheel on the armature shaft. As the armature is revolved the lines of force are cut and the current is carried out through the wire attached to the binding-posts on the blocks (G G).
Considerable current may be generated if the armature is driven at higher speed than the hand-wheel will cause it to revolve. This can be accomplished by running the belt over a larger wheel, such as the fly-wheel of a sewing-machine, or connecting it to a large pulley on a water-motor. The latter may be attached to a faucet in the wash-tub if there is pressure enough to do the work.
A Small Dynamo
All dynamos are constructed on the same general principle as that of the uni-direction machine just described; but they differ in their windings, the quantities of metal electrified, the sizes and lengths of wire wound on both armature and field, and in their shape and speeds.
In large dynamos it is impossible to employ steel magnets of the required size. In place of them soft iron cores are used and magnetized by external electric current; or the wiring is done in “series” or “shunt,” so that the fields will be self-exciting once the machine has been properly started.
The principal difference in dynamos is, perhaps, more clearly illustrated by the diagrams shown in [Figs. 13], [14], [15], and [16]. In [Fig. 13] the arrangement of armature and field-magnet is the same as in the uni-direction machine, the field (F) being of magnetized steel, while the armature (A) is of soft iron wound with coils of fine wire, the ends of which are brought out at the commutators (C), through which the current is carried to the brushes (B and B B). If, however, the soft iron cores are used, a separate magnetizing electric current must be passed through the coils of wire wound about the field-pieces, so that they will become temporary magnets—the same as the cores of an electric bell movement, a telegraph-sounder, or the induction-coil core when a current is passed through the primary coil. The armature (A) is then driven at high speed by power, and the current is taken off for use through wires that lead from B and B B.
In all of these figures the armatures rotate, in the space between the large pole-pieces of the field-magnets, in the same direction as the hands of a clock move. In these figure drawings the field-magnets, commutators, and brushes only are shown, the armature being indicated by the circle (A).
[Figure 13] represents a dynamo, the field-magnets of which are excited by a separate battery or generator. This is known as a “separately excited” machine, and is employed for various uses. The brushes (B and B B) are connected to the external circuit—that is, with the motor or other apparatus for which current is to be generated. The magnetic field in which the armature rotates will be constant if the exciting current is constant, like the magnetism in the magnet of the uni-direction current machine.
The induced electro-motive force (which depends upon the rate at which the lines of force are cut) will be constant for the given speed at which the armature rotates. This action is the same as that described for the uni-direction current machine.
[Figure 14] is the diagram of a “series”-wound dynamo. The field and armature are soft gray iron, and are wound in series—that is, one end of the magnet-winding is made fast to the brush B, the other to the brush B B, and the apparatus to be operated by the current is let in between B B and the magnet, as shown by the indicated electric arc-light in the illustration. The field-magnet coils, the armature, and the external conductors are in series with each other, forming a simple circuit. When the armature is driven at high speed the field-magnets become self-exciting, with the result that current is generated. Its simple course is through B B to commutators on the hub, thence through one winding on the iron armature A, to B, through field F, and back to B B again, operating in its course any pieces of equipment designed for electric impulse, such as motors, or lamps, trolley-cars, trains, or electric machinery.
The third type, shown in [Fig. 15], is known as “shunt”-winding. The field-magnet coils and the external resistance are in parallel, or shunt with each other, instead of in series. The brushes are connected with the external circuit, and also with the ends of the field-magnet coils. This is clearly shown in the drawing. The ends of the field-coils are connected with brushes B and B B, and the external circuit wires are connected also with the same brushes, and pass down to such an apparatus as a plating bath, in which the current runs through the electrode, the electrolyte, and the cathode, most of the current generated passing through the external circuit. The field-coils are of fine wire, and when the armature is rotated there will always be a current through the field-magnets, whether the external circuit is complete or not. If a break occurs in the external circuit, a more powerful current will consequently pass through the field-magnets.
In [Fig. 16] a “compound”-wound dynamo is shown. It is a combination of the series and the shunt machine. The field-magnet coils are composed of two sizes of wire. There are comparatively four turns of stout wire and many turns of fine wire, the ends of both being connected, as shown in the drawing. The stout wire leads out to lamps which are arranged in series, as shown at the foot of the drawing. The current developed by this dynamo is one of “constant potential,” and is used almost exclusively for incandescent lamps, the “constant” current from the series-wound machine being used for arc-lamps, power, and other commercial purposes.
It will not be necessary to use the first or last systems, nor to experiment with the alternating current, with its phases and cycles. All that a boy wants is a good direct-current machine that will light lamps, run sewing-machines or motors, and furnish the power for long-distance wireless telegraphy and other apparatus requiring considerable current.
To begin with, it would be better to make a small dynamo and study its principles as you progress; then it will be a great deal easier to construct a larger one. It will be necessary to have the iron parts made at a blacksmith-shop, since the various cutting, threading, and tapping operations call for the use of special iron-working tools. Soft iron should be used, and if a piece of cast-iron can be procured for the lugs or magnet ends it will give better service than wrought-iron.
From three-quarter-inch round iron cut two cores, each three inches and a half long, and thread them at both ends, as shown at B B in [Fig. 17]. From band-iron five-eighths of an inch thick and one inch and a half wide cut a yoke (A), and bore the indicated holes two inches and three-quarters apart, centre to centre. These should be threaded so that the cores (B B) will screw into them. From a bar of iron cut off two blocks one inch and a half by one inch and a half by two inches for the lugs. Now, with a hack-saw and a half-round file, cut out one side of each lug, as shown at C. These lugs are to be bored and threaded at one end, so that they can be screwed on the lower ends of the cores (C C).
For a larger dynamo the yoke should be made six inches long, one inch thick, and two inches and a half wide. The cores should be of one-inch iron pipe. These will be hollow, as shown at B B in [Fig. 18]. For the ends cast-iron blocks must be made or cast from a pattern two inches and three-quarters square and four inches high, as shown at C. The yoke (A) and the lugs (C) are bored and threaded to receive the one-inch pipe, and when set up this will constitute an iron field-magnet six inches wide, two inches thick, and nine inches high. This, if properly wound, should develop a quarter of a horse-power.
The parts shown in [Fig. 17], when screwed together, will give you a field-magnet two by one and a half by five and three-quarter inches high, and will appear as shown in [Fig. 19], A being the yoke at the top, B B the cores, C C the lugs, and D a strip of brass screwed fast across the back of the lugs (C C), and in which a hole is bored to act as a bearing for one end of the armature shaft. Between the lugs and the strip (D) fibre washers three-eighths of an inch in thickness are placed to keep the strip away from the lugs. A hole is bored directly through the middle of each lug, from front to rear, and it is threaded at each end so that a machine-screw will fit in it. The brass strip (D) is five-eighths of an inch wide, three-sixteenths of an inch thick, and four inches long. Copper or German-silver may be used in place of brass, but iron or steel must not be employed, since these metals are susceptible to magnetism. Two holes should be made in the bottom of each lug, and threaded, so that machine-screws may be passed through a wooden base and into them in order to hold the dynamo on the base.
[Figure 20] is an end view of the field-magnets showing the yoke at A, the core at B, the lug at C, and the bearing and binding-strip of yellow metal at D. Two blocks of hard-wood, an inch square and one inch and a half long, are cut and provided with holes, so that they can be fastened to the lugs C C with long, slim machine-screws, as shown at E E in [Fig. 21]. This is a view looking down on the magnets, blocks, and straps. These blocks are to support the brushes and terminals, and should be linked across the face with a brass strap G, so that the other end of the armature shaft may be supported. Care must be taken, when setting straps D and G, to have them line. The holes, too, must be centred, since the armature must revolve accurately within the field-lugs (C C) without touching them, and there is but one-sixteenth of an inch space between them.
From hard-wood half an inch in thickness cut a base, six by seven inches, and two strips an inch wide and five inches long. With glue and screws driven up from the underside of the strips fasten them to the base, as shown at [Fig. 22]. Then make the field-magnets fast to the base with long machine-screws, using washers under the heads at the underside of the base-board. The mounting should then appear as shown in [Fig. 28].
From steel, half an inch in diameter, cut a shaft five inches long. Have it turned down smaller at one end for three-eighths of an inch, and at the other end for a distance of one inch and a half, as shown at [Fig. 23]. This is for the armature, and it should fit between D and G in [Fig. 21], and should revolve easily in the holes cut to receive it in both straps, with not more than one-eighth of an inch play forward or backward. The long, projecting end should be at the rear, and should extend beyond strip D for three-quarters of an inch, so that the driving-pulley can be made fast to it.
The armature is made up of segments or laminations of soft iron and insulated copper wire. The laminated armature works much better than does the solid metal ring or lug, and a pattern may be made from a piece of tin from which all the sections can be cut. With a compass, strike a two-inch circle on a clear piece of tin; then mark it off, as shown at [Fig. 24], and cut it out with shears. The hole at the centre of the pattern need not be bored, but a small pinhole should be made so that a centre-punch can be used to indicate the middle of each plate for subsequent perforation. Ordinary soft band iron may be employed for this purpose, and the sections should not be more than one-sixteenth of an inch in thickness.
It will take some time to cut out the required number of pieces for this small armature. When they are all ready they should be slipped over the shaft, and if they have been properly matched and cut, they should appear as a solid body, one inch and a half long.
Arrange these laminations on the armature shaft so that when the shaft is in position the mass of iron will be within the lugs of the field-magnets. The holes through the iron plate should be so snug as to call for some driving to put them in place. Each disk of iron should be given a coat of shellac to insulate it, and between each piece there should be a thin cardboard or stout paper separator to keep the disks apart. These paper washers should be dipped in hot paraffine, or thick shellac may be used to obtain a good sticking effect and so solidify the laminations into a compact mass. When this operation is completed the armature core should appear as shown in [Fig. 25].
From maple, or other hard-wood with a close grain, make a cylinder three-quarters of an inch long and one inch in diameter to fit the shaft. Over this drive a piece of copper or brass tubing, and at four equal distances, near the rear or inner edge, make holes and drive small, round-headed screws into the wood. Then, with a hack-saw, cut the tube into four equal parts between the screws. This is the commutator. In order to hold the quarter circular plates fast to the cylinder, remove one screw at a time, and place thick shellac on the cylinder. Then press the plate firmly into place and reset the screw. Repeat this with the other three, and the armature will be ready for the winding.
The voltage and amperage of a dynamo is reckoned by its windings, the size of wire, the number of turns, and the direction. This is a matter of figuring, and need not now concern the young electrician, since it is a technical and theoretical subject that may be studied later on in more advanced text-books.
For this dynamo use No. 22 cotton-insulated copper wire for the armature, and No. 16 double cotton-insulated copper wire for the field. The armature, when properly wound and ready for assembling with the brushes and wiring, will appear as shown in [Fig. 26].
A small driving-wheel two inches in diameter and half an inch thick must now be turned from brass and provided with a V-shaped groove on its face. The hub, at one side, is fitted with a set-screw, so that it can be bound tightly on the shaft. This pulley is made fast to the shaft at the rear of the dynamo, and on the opposite end to where the commutator hub is attached.
A diagram of the wiring is shown in [Fig. 29], and in [Fig. 30] the mode of attaching the ends of the coil wires to the commutators is indicated. Two complete coils of wire must be made about each channel of the armature, as illustrated on the drum of [Fig. 30]. These are separated by a strip of cardboard dipped in paraffine and placed at the centre of a channel while the winding is going on. In some armatures the coils are laid one over the other; but with this construction, and in the case of a short-circuit, a broken wire, or a burn-out, it is impossible to reach the under coil without removing the good one.
Begin by attaching one end of the fine insulated wire to commutator No. 1; then half fill the channel, winding the wire about the armature, as indicated in [Fig. 30]. When the required number of turns has been made, carry the end around the screw in commutator No. 2, baring the wire to insure perfect contact when caught under the screw-head. From No. 2 carry the wire around through the channel at right angles to the first one, and after half filling it bring the end out to commutator No. 3. Carry the wire in again and fill up the other half of the first channel, and bring the end out to commutator No. 4. Fill up the remaining half of the second channel; then attach the final end to commutator No. 1, and the armature winding will be complete without having once broken the strand of wire.
To keep the coils of wire in place, and to prevent them from flying out, under the centrifugal force of high speed, it would be well to bind the middle of the armature with wires or adhesive tape.
After driving down the small screws over the leading-in and leading-out wires the armature will be ready to mount in the bearings. As the blocks that support the brushes and binding-posts partly close the opening to the cavity at the front, the armature will have to be inserted from the back into the strip (G) in [Fig. 21]. Then the back strip (D) is screwed in place. The armature, when properly mounted, should revolve freely and easily within the field-lugs without friction, and the lugs must by no means touch the armature. From thin spring-copper brushes may be cut and mounted on the block under the binding-posts, so that one will rest on top of the commutators while the other presses up against the underside. The wiring is then to be placed on the field-magnets. This is carried out as described for the electric magnets on [pages 54-58] of chapter iv., each core receiving five or seven layers, or as much as it will hold without overlapping the lug or yoke. The ends of the wires are connected as shown at [Fig. 14] or [Fig. 15], the ends being carried down through the base and up again in the right location to meet the foot of a binding-post. The complete dynamo will appear as shown in [Fig. 28].
Before the dynamo is started for the first time it would be well to run a strong current through the field coils. The residual magnetism retained by the cores and iron parts will then be ready for the next impulse when the dynamo is started again. Larger dynamos may be made of this type. With an armature, the core of which is four inches in diameter and six inches long, having eight instead of four channels, and placed within a field of proportionate size, the dynamo will develop one horse-power.
A Split-ring Dynamo
Another type of dynamo is shown in [Fig. 31]. This is composed of a wrought or cast iron split-ring wound for the field, an armature made up of laminations, and the necessary brushes, posts, commutators, and wire.
Have a blacksmith shape an open ring of iron, in the form of a C, three-eighths of an inch thick and four inches wide. The opening should be three inches wide, as shown in [Fig. 32]. This ring should measure five inches on its outside diameter, and the ends are to be bored and threaded to receive machine-screws. Two lugs are to be made from wrought-iron to fit on these ends. These should be four inches long, an inch and a half high, and three-quarters of an inch thick at top and bottom. They should be hollowed out at the middle, so that an armature two inches in diameter will have one-eighth of an inch play all around when arranged to revolve within them. Holes are made through the lugs to receive machine-screws, which are driven into the holes in the ends of the iron (C). Wrought-iron L pieces are made one inch and a half high and an inch across the bottom, and with machine-screws they are made fast to the backs of the lugs to act as feet on which the field-magnet may rest, as shown in [Fig. 33]. Across the back of the lugs, and set away from them by fibre washers, a strap of brass is made fast. This measures three-quarters of an inch wide and a quarter of an inch thick, and at the middle of it a three-eighth-inch hole is bored to receive the rear end of the armature shaft. This is shown in [Fig. 34], which is a front view of the field, or C, iron, the lugs (L L) and feet (F F), the armature bearing (S), and the base (B), of three-quarter-inch hard-wood. The field-magnet is bolted to the base with lag-screws, so that it will be held securely in place.
The laminations for the armature core are two inches in diameter, and are cut from soft iron one-sixteenth of an inch thick. They have eight channels, as shown in [Fig. 35], and the tubing on the commutator hub is divided into four parts so that the terminals from each coil can be brought to a commutator, as described for [Fig. 30]. In the eight-channel armature, however, there is but one coil of wire in each channel.
DETAILS OF SPLIT-RING DYNAMO
In [Fig. 36] a plan of the armature is shown, S representing the shaft, B B the bearings, L the laminations, C the commutators and hub, P the driving-pulley, and N N the nuts that hold the laminations together and lock them to the shaft. The shaft is half an inch in diameter, the laminations four inches thick, and the commutator barrel one inch in diameter and three-quarters of an inch long. The shaft is turned down from the middle to where P and C are attached; then at the front end it is made smaller, where it passes through the front bearing.
With the detailed description already given for the construction of the small dynamo, it should be an easy matter to carry out the work on this one, and a quarter horse-power generator should be the result. The field-magnet is wound with five or seven layers of No. 16 double cotton-insulated wire, and the armature with No. 22 silk or cotton-covered wire. The connections may be made for either the series or the shunt windings shown in [Figs. 14 and 15]. Another type of field is shown in [Fig. 37], where two plates of iron are screwed to one core, and the lugs are, in turn, made fast to the inner sides of the plates within which the armature revolves. The “Manchester” type is shown in [Fig. 38], where two cores, constructed by a top and bottom yoke, are excited by the coils, and the lugs are arranged between the cores, so that the armature revolves within them.
A Small Motor
The shapes, types, powers, and forms of motors are as varied and different as those of dynamos, each inventor designing a different type and claiming superiority. The one common principle, however, is the same—that of an armature revolving within a field, and lines of force cutting lines of force. A motor is the reverse of a dynamo. Instead of generating current to develop power or light, a current must be run through a motor to obtain power.
Motors are divided into two classes: the D C, or direct current, and the A C, or alternating current. For the amateur the direct-current motor will meet every requirement, and since the battery, or dynamo current, that may be available to run a motor, is in all probability a direct one, it will be necessary to construct a motor that is adapted to this source of power and for the present avoid the complications of the alternating current both in generation and in use.
The direct-current motor is an electrical machine driven by direct current, the latter being generated in any desired way. This current is forced through the machine by electro-motive force, or voltage; the higher the pressure, or voltage, the more efficient the machine. Be careful lest too much current (amperage) is allowed to flow, for the heat developed thereby will burn out the wiring.
Motors are so constructed that when a current is passed through the field and armature coils the armature is rotated. The speed of the armature is regulated by the amount of amperage and voltage that passes through the series of magnets, and this rotating power is called the torque.
Torque is a twisting or turning force, and when a pulley is made fast to the armature shaft, and belted to connect with machinery, this torque, or force, is employed for work.
The speed of an armature when at full work is usually from twelve hundred to two thousand revolutions a minute. As few machines are designed to work at that velocity, a system of speeding down with back gears, or counter-shafts and pulleys, is employed. The motor itself cannot be slowed down without losing power. The efficiency of motors is due to the centrifugal motion of the mass of iron and wire in the armature and the momentum it develops when spurred on by the magnetism of the field-magnets acting upon certain electrified sections of the armature. The armature of a working motor is usually of such high resistance that the current employed to run it would heat and burn out the wires if the full force of the current was permitted to flow through it for any length of time. As the armature rotates it has counter electro-motive force impressed upon it. This acts like resistance, and reduces the current passing through. The higher the speed the less current it takes, so that after a motor has attained its highest, or normal speed, it is using less than half the current required to start it.
Reduction of current in the armature reduces torque, so that the turning force of the armature is reduced as its speed of rotation increases. On the other hand, the momentum, or “throw,” produces power at high speed, together with an actual saving of current. An armature revolving at sixteen hundred revolutions, and giving half a horse-power on a current of five amperes, is more economical than one making three to five hundred revolutions, and giving half a horse-power on a current of fifteen to twenty amperes. Thus, a slowly turning armature takes more current and exerts higher torque than a rapidly rotating one.
To protect the fine wire on the armature from burning, in high-voltage machines a starting-box, or rheostat, is employed. The motor begins working on a reduced current, and as it picks up speed more current is let in, and so on until the full force of the current is flowing through the motor. It is then turning fast enough to protect itself through the counter electro-motive force. This can be understood better after some practical experience has been had in the construction and running of motors. Of the various forms of motors but three will be illustrated and described; but the boy with ideas can readily design and construct other types as he comes to need them.
The Flat-bed Motor
The simplest of all motors is the flat-bed type, illustrated in [Fig. 39]. This is composed of a magnet on a shaft revolving before a fixed magnet attached to the upright board of the base. Where space is no object, this motor will develop considerable power from a number of dry-cells or a storage-battery. Now, in the section relating to dynamos, four different systems of wiring were shown. In motors of the direct-current type but one system will be described—that of the series-winding, illustrated in [Fig. 40]. The current, entering at A, passes to the brush (B), thence through the commutator (C) and the armature coils. It runs on through the brush (B B), the field-coils (F), and out at D. This is the same course the current takes in the series-wound dynamo illustrated in [Fig. 14], page 241, and with such a dynamo current could be generated to run any series-wound, direct-current motor.
A FLAT-BED MOTOR AND PARTS
From hard-wood half an inch thick cut a base-piece six inches and a half long by three inches and a half wide. Arrange this base on cross-strips three-quarters of an inch wide and half an inch thick, making the union with glue and screws driven up from the underside. To one end of this base attach an upright or back two inches and three-quarters high, and allow the lower edge to extend down to the bottom of the cross-strip, as shown at the left of [Fig. 39]. Make this fast to the end of the base and side of the cross-strip with glue and screws; then give the wood a coat of stain and shellac to properly finish it.
Now have a blacksmith make two U pieces of soft iron for the field and armature cores, as shown in [Fig. 41]. These are of quarter-inch iron one inch and a half in width. They are one inch and three-quarters across and the same in length. One of them should have a half-inch hole bored in the end (at the middle), and above and below it smaller holes for round-headed screws to pass through. By means of these screws the U is held to the wooden back. The other U is to have a three-eighth-inch hole bored in it so that it will fit on the armature shaft. Wind the U irons with six layers of No. 20 cotton-insulated wire, having first covered the bare iron with several wraps of paper. Use thick shellac freely after each layer is on, so that the turns of wire will be well insulated and bound to each other. Follow the wiring diagram shown in [Fig. 40] when winding these cores, and when the field is ready, make it fast to the back with three-quarter-inch round-headed brass screws.
Directly in the middle of the hole through the field iron bore a quarter-inch hole for the armature shaft to pass through; then make an L piece, of brass, two inches high, three-quarters of an inch wide, and with the foot an inch long, as shown at [Fig. 42]. Two holes are made in the foot through which screws will pass into the base, and near the top a quarter-inch hole is to be bored, the centre of which is to line with that through the back, at the middle of the field core. The shaft is made from steel three-eighths of an inch in diameter and six inches and a half long. One inch from one end the shaft should be turned down to a quarter of an inch in diameter, and one inch and a quarter from the other end it must be reduced to a similar size. The short end mounts in the back and the long one receives the pulley, after the latter passes through the L bearing. A piece of three-eighth-inch brass tubing an inch long is slipped over the shaft two inches from the pulley end and secured with a flush set-screw. This tubing is then threaded and provided with two nuts, one at either end, so that when the armature U is slipped on the collar the nuts can be tightened and made to hold the magnet securely on the shaft. This shaft is clearly shown in the sectional drawings [Fig. 43].
At the left side the shaft (S) passes into the wood back through the quarter-inch hole. At the outside a brass plate with a quarter-inch hole is screwed fast and acts as a bearing. The shaft does not touch the field-magnet (F M), because the hole is large enough for the quarter-inch shaft to clear it. A fibre washer (F W) is placed on the shaft before it is slipped through the back. This prevents the shaft from playing too much, and deadens any sound of “jumping” while rotating.
At the middle the shaft (S) passes through the brass collar on which the threads are cut. A M represents the armature magnet, and W W the washers and nuts employed to bind it in place. At the right, S again represents the shaft, B the bearing, C the commutator hub, and P the pulley, while R is the small block under the hub to which the brushes and binding-posts are attached.
From the descriptions already given of dynamos, and with these figure drawings as a guide, it should be an easy matter to assemble this motor.
The ends of the field and armature magnets should be separated an eighth of an inch. The hub for the commutators is three-quarters of an inch long and three-quarters of an inch in diameter. The commutators are made as described for the uni-direction current machine, care being taken to keep the holding screws from touching the shaft. A three-quarter-inch cube of wood is mounted on the base, under the commutator hub, and to this the brushes and binding-posts are made fast, as shown in [Fig. 39]. Unless the armature happens to be in a certain position this motor is not self-starting, but a twist on the pulley, as the current is turned on, will give it the necessary start. Its speed will then depend on the amount of current forced through the coils.
Another Simple Motor
Another type of motor is shown in [Fig. 44], where one field-winding magnetizes both the core and the lugs. The frame of this motor is made up of two plates of soft iron a quarter of an inch thick, six inches long, and two inches and a half wide. Each plate is bent at one end so as to form a foot three-quarters of an inch long, and a half-inch hole is drilled one inch and a quarter up from the bottom, at the middle of each plate. Through this hole pass the machine-screws which hold the iron core in place between the side-plates. The core is made of three-quarter-inch round iron two inches and three-quarters long, and drilled and threaded at each end to receive the binding machine-screws.
Two lugs are cut from iron, and hollowed at one side so that an armature two inches in diameter will rotate within them when made fast to the side-plates. The lugs are two inches and a half long, an inch wide, and two inches and a half high.
From iron five-eighths of an inch wide and one-eighth of an inch thick make two side-strips with L ends. These are four inches long, and are provided with two holes so that the machine-screws which hold the lugs to the inside plates will also hold these strips in place, at the outside, as shown in [Fig. 45]. At the rear these strips extend half an inch beyond the frame. Across the back a brass strip of the same size as the iron strips is arranged. It is held at the ends by screws, or small bolts, made fast to the L ends of the side-strips. Directly in the middle of the back-strip a hole is made for the armature shaft, and beyond it the pulley is keyed or screwed fast to the shaft.
At the front a similar strip is made and attached. This latter has a small hole in the middle of it to serve as a bearing for the forward end of the shaft. Across the top of the motor a brass strip or band is made fast with machine-screws; and at the angles formed by the front ends of the side-strips and the front cross-strips hard-wood blocks are attached. To these the brushes and binding-posts are made fast, so that one brush at the top of the left-hand block rests on the top of the commutator. The one at the underside of the opposite block must rest on the underside of the commutator.
The armature core is made up of laminations as described for the dynamo armatures. In a really efficient motor the armature should have eight or more channels.
The other parts of the motor may be assembled and wired as described on the preceding pages. The armature should be wound with No. 20 or 22 insulated copper wire, and the field with No. 16 or 18. For high voltage, however, the armature should be wound with finer wire and a rheostat used to start it.
A Third Type of Motor
The third type is but a duplicate of the series-wound dynamo, the general plan of which is shown in [Fig. 40].
This motor can be made any size, but as its dimensions are increased the weight of the field-magnets and armature must be proportionately enlarged. For an efficient and powerful motor, the field should stand ten inches high and six inches broad. The iron cores are five inches long and one inch and a half in diameter. These should be made by a blacksmith and bolted together. The armature is three inches in diameter and four inches long, and should develop two-thirds of a horse-power when sufficient current is running through the coils to drive it at sixteen hundred revolutions.
The wiring is carried out as shown in [Fig. 40], and the armature hung and wound as suggested for the dynamo shown in [Fig. 28], [page 246].
Chapter XI
GALVANISM AND ELECTRO-PLATING
Simple Electro-plating
To the average boy experimenter, electro-plating is one of the most fascinating of the uses to which electricity may be put. In scientific language the process is known as electrolysis, and involves the separation of a chemical compound into its constituent parts or elements by the action of an electric current and the proper apparatus. Electrolysis cannot take place, however, unless the liquid in the tank, commonly called the electrolyte (no relation to electric light), is a conductor.
Water, or water with mixtures of chemicals, such as sulphate of copper, sulphate of zinc, chloride of nickel, cyanide and nitrate of silver, or uranium and other metallic salts, are good conductors. Oil is a non-conductor, and a current will not pass through it, no matter what the pressure may be. The simplest electro-plating outfit, and the one that a boy should start with, is the sulphate of copper bath, such as is commonly employed by makers of electrotypes, and which is in extensive use by refiners of copper for high-grade electrical use.
More than half of the total output of copper in the world is used for electrical work—conductors, switches, and all sorts of parts—and since any impurity in the copper interferes with its conducting powers, it is most important that it should be free from any traces of carbon or arsenic. The electrolytic refining of copper is now a very important process in connection with electric work, and about half a million tons of copper are treated annually to free it from all impurities. Moreover, the gold, silver, and other valuable metals which may be found in copper-ore are thus recovered.
The electro-plating, electrotyping, and refining operations are one and the same thing; but in the first instance the object to be plated is left in the solution only a short time or until a blush of copper has been applied. In the second process the wax mold is left in long enough for a thin shell of copper to be deposited; and in the third, the kathodes are immersed until they are heavily coated with copper. To carry on any of these operations it will be necessary to have a small tank or glass jar to hold the plating-bath or electrolyte. Preferably it should be of a square or oblong shape. But a serviceable tank may be constructed from white-wood, pine, or cypress, if proper care is taken in making and water-proofing ([Fig. 1]). For experimental purposes a tank eighteen inches long, ten inches wide, and twelve inches deep will be quite large enough to use as a copper bath. For silver, nickel, or gold, smaller tanks should be employed, as they contain less liquid, or electrolyte, which in the more valuable metals is expensive.
Obtain a clear plank twelve inches wide, well seasoned, and free from knots or sappy places. Cut two sides twenty inches long and two ends eight inches long. With chisel, saw, and plane shape the ends of the side planks as shown at [Fig. 2]; or if there is a mill at hand it would be well to have the ends cut with a buzz-saw, thus insuring that they will be accurate and fit snugly. Screw-holes are bored with a gimlet-bit, and countersunk, so that screws will pass freely through them and take hold in the edges of the boards. Screws and plenty of white-lead, or asphaltum varnish, should be used on these points to make them water-tight; then the lower edge of the frame is prepared for the bottom board. Turn the tank bottom up, and, with a fat steel-wire nail and a hammer, dent a groove at the middle of the edge of the planks all around, as shown in [Fig. 3]. It will not do to cut this out with a gouge-chisel, because it is intended that the wood should swell out again if necessary. The object of driving the wood down is to form a valley into which a line of cotton string-wicking, soaked in asphaltum varnish or imbedded in white-lead, may be laid. This should be done (as shown in [Fig. 4]) before the bottom is screwed on, so that afterwards (in the event of the joint leaking) the wood will swell and force the wicking out, and thus properly close the fissure.
The bottom board should be provided with holes all around the edge, not more than two inches apart, through which screws can be driven into the lower edge of the tank. Treat the wood, both in and outside, to several successive coats of asphaltum varnish, and as a result you will have a tank resembling [Fig. 1].
Two shallow grooves are to be cut in the top of each end board of the tank, for the cross-bars to fit in immovably. These bars should be about three inches apart; and the ones holding the anodes, or flat copper plates, should be close to one side, leaving plenty of room for objects of various sizes to be properly immersed.
Another manner in which the bottom of the tank can be attached is shown in [Fig. 5], which is a view of the tank sides turned bottom up. A rabbet is cut from the lower edges of the sides and ends, before they are screwed together, and a bottom is fashioned of such shape as to accurately fit in the lap formed by the rabbet. This rabbet and the outer edge of the bottom plank should be well smeared with white-lead, and all put together at the same time, driving the screws into the edge of the bottom plank, through the lower edges of the sides and bottom, and also through the bottom board into the lower edges of the sides and ends ([Fig. 6]).
Still another and stronger way in which to make a tank for a large bath is to cut the planks as shown at [Fig. 7]. The sides are then bolted together, locking the ends and bottom, so that they cannot warp or get away. The bolts are of three-eighth-inch round iron-rod, threaded at both ends and provided with nuts. Large washers are placed against the wood and under the nuts, so that when the nuts are screwed on tightly they will not tear the wood, but will bear on the washers. The points are all to be well smeared with white-lead or acid-proof cement (see Formulæ) before the parts are put together and bolted, so as to avoid any possibility of leakage. ([Fig. 8] shows the completed tank.)
TANK FOR ELECTRO-PLATING
Now obtain two copper rods long enough to span the tank, with an inch or two projecting beyond the tank at either side. At one end of these attach binding-posts, to which the wires from a battery can be connected, leaving the opposite ends free, as shown at [Fig. 9] (see [page 275]). Anodes, or pure soft copper plates, are hung on the positive rod, while on the negative one the objects to be plated, or kathodes, are suspended on fine copper wires just heavy enough to properly conduct the current. The positive wire leads from the carbon, or copper pole, of the battery, while the negative one is connected with the zinc. The anodes are plates of soft sheet or cast copper, and should be as nearly pure as possible for electrolytic work; but if they are to be re-deposited, to free them from impurities, they may be in thin ingot form, just as the copper comes from the mines.
The general principle of electro-refining of copper is very simple. A cast plate of the crude copper is hung from the positive pole in a bath of sulphate of copper, made by dissolving all the sulphate of copper, or bluestone, that the water will take up. Drop a few lumps on the bottom of the tank to supply any deficiency, then add an ounce of sulphuric acid to each gallon of liquid, to make it more active and a better conductor.
The crude copper plate is to be the leading-in pole for the current, while a thin sheet of pure copper, no thicker than tissue-paper, is suspended from the opposite rod for the leading-out pole; or in place of the thin sheet, some copper wires may be suspended from the rod. The electrodes—that is, the copper plate and the thin sheet or wires—are placed close together, so that the current may pass freely and not cause internal resistance in the battery. The electric current, in its passage from the crude copper plate to the pure copper sheet or wires, decomposes the sulphate of copper solution and causes it to deposit its metallic copper on the sheet or wires; and at the same time it takes from the crude copper a like portion of metallic copper and converts it into chemical copper. The electric current really takes the copper from the solution and adds it to the pure copper sheet, while the remaining constituents of the decomposed solution help themselves to some copper from the crude plate. In this way the crude copper diminishes and the pure copper sheet increases in size, the impurities as well as the salts of other metals being precipitated to the bottom of the tank, or mingled with the solution, which must be purified or replaced from time to time by fresh solution. This is the process of copper-plating, and any metal object may be properly cleansed and coated with copper by suspending it in the bath and running the current through it.
When the refining process is employed, any metal will answer as a depository for the copper, but as the intention is to produce a pure copper plate which can be melted and cast into ingots, it is of course necessary to have the original kathode of the same metal; otherwise an impure mixture will be the result. If, for example, a piece of cast-iron be used upon which to deposit the copper, then the iron will be enclosed in a deposit of pure copper; in other words, the result will be a heavily copper-plated piece of iron, and the smelting process will bring about a fusion of the two metals. It is not necessary to have absolutely pure copper for the anodes when copper-plating or electrotyping; but the purer the copper the less the solution is fouled, and it will not require replenishing so often.
An object intended to receive a plating of copper need not be of metal at all; it may be of any material, so long as it possesses a conducting surface. A mold or a cast made of any plastic material, such as wax or cement, may have its surface made conductive by the application of graphite, finely pulverized carbon, or metal dusts held on by some medium not soluble in water. The wax molds, or impressions of type and cuts, are dusted with plumbago, and then suspended in the copper solution. A wire from the negative pole is connected so as to come in contact with the plumbago, and the copper deposit immediately begins to form on the face of the wax. When the film of copper has become heavy enough, the mold is drawn out of the solution, and the thin shell of metal removed from the wax and cut apart, so that each shell is separated from its neighbor and freed from marginal scraps. Flowers, leaves, laces, and various other objects can be given a coat of copper by thus preparing their surfaces, and some most beautiful effects may be secured by copper-coating roses; then placing them for a short time in a gold bath, and afterwards chemically treating the surface plating so as to imitate Roman, Tuscan, or ormolu gold, in bright or antique finish. Coins, medallions, bas-reliefs, medals, and various other things are reproduced by the electro-plating process, and their surfaces finished in gold, silver, bronze, or other effects. Years ago this was not possible, because the old method was to make a fac-simile cast in metal of the object desired, and then chase or refinish the surface. This was a costly and tedious task. When Brugnalelli, an Italian electrician, electro-gilded two silver coins in 1805, he laid the foundation for the modern process, but it did not come into general use until about 1839, when electro-plating and the electro-depositing of metals was begun on a practical scale. Before the invention of the dynamos for generating current, batteries had to be employed, and this made the process somewhat more expensive than the present method. Our boy amateurs, however, will have to be content with the battery system, since they are not supposed to have access to direct-current power, such as is used for arc or street lighting.
Various forms of batteries may be used for this work, and they will be described in detail. For the copper-plating bath it will be necessary to have the anodes of soft, cast, or sheet, copper sufficiently heavy so as not to waste away too quickly. These should be of the proper size to fit within the bath, and either one large one or several small ones may be employed. Stout copper bands should be riveted to the top of the plates, by means of which they may be hung on the bar and so suspended in the solution ([Fig. 10]). The contact-points should be kept clean and bright, so that the current will not meet with any resistance in passing from the rod to the plates.
In [Fig. 9] a complete outfit is shown for any plating process, the difference being only in the solution and anodes. For silver-plating a silver solution and silver anodes are required, while for gold the gold solution and gold anodes will be necessary. In this illustration, A represents the tank, B the battery, C C the anodes, D D D the kathodes, or articles to be plated, E the positive rod, F the negative, and G, H the leading-in and leading-out wires.
There is often a doubt in a boy’s mind as to how the battery is to be connected up to the bath and the articles suspended in it. But there will be no difficulty about it once that the principle of the process is thoroughly understood.
It is well to remember that the electro-plating bath is just the reverse of a battery in its action. The process carried on in a battery is the generation of electricity by the action of the acid on the positive metal, accompanied by the formation of a salt on one of the elements; while in the plating-bath the current from an external source (the battery or dynamo) breaks up the salts in solution and deposits the metal on one of the elements (the kathode).
The remaining element in the solution attacks the salts, in chemical lumps or granular form, and dissolves them to take the place of the exhausted salts; or it attacks the metal anode from which these salts were originally made, and eats off the portion necessary to replace the loss caused by the action of the current in depositing the fruits of this robbery in metallic form upon the article to be plated (the kathode). There should be no confusion in the matter of properly connecting the poles if one remembers that the current is flowing through the battery as well as through the wires and the solution in the tank.
Get clearly in your mind that the current originates in the battery of zinc and carbon or zinc and copper. The zinc is electro-positive to carbon or copper, and at a higher electric level the current flows from the zinc plate inside the cell to the carbon or copper; therefore, the zinc is the positive pole. Now the current, having flowed through the battery from zinc to carbon, or the negative plate, is bound to flow out of the battery from the carbon through the apparatus and back again to the zinc in the battery. Therefore, the wire (G) attached to the carbon of the battery leads a positive or + current, although the carbon is negative; in the battery, and the wire (H) leading out is negative, or -, although it returns the current to the positive pole of the battery.
This is the simple explanation of the circulation of current; but to cut it down still more, always remember to attach the wire from the anode rod to the carbon, or copper, of the battery, and the kathode rod to the zinc of the battery.
In copper-plating this is easy to determine without any regard to wires, because if the wires are misconnected there will be no deposit, and the kathode will turn a dark color. If everything is all right a slight rose-colored blush of copper will appear at once on the kathode. Too little current will make the process a long and tedious one, while too much current will deposit a brown mud on the kathode, which will have to be washed off or removed and the article thoroughly cleansed before a new action is allowed to take place.
With a series of cells it is an easy matter to properly govern the current by cutting out some of the cells or by using resistance-coils (see [chapter vii.] on Electrical Resistance).
Cells and batteries for electro-plating may be made or purchased, and primary batteries should be used. The use of the secondary or storage-battery is not necessary for plating purposes, since no great volume of current is needed, and it can be generated in a battery of cells while the work is going on.
One of the best primary batteries is the Benson cell, shown in connection with the [plating-bath], and also in [Fig. 11]. It consists of an outer glass jar (G J), which contains a cylinder of amalgamated zinc (Z +, or positive) covered with diluted sulphuric acid—one part acid to three parts water. An inner porous cup (P C) contains concentrated nitric acid, into which the carbon (C -, or negative) is plunged. The liquid in the inner cup and glass cell should be at the same level.
THE BENSON CELL PRIMARY BATTERY
There is no polarizing in this cell, for the hydrogen liberated at the zinc plate, in passing through the nitric acid on its way to the carbon-pole, decomposes the nitric acid and is itself oxidized. A cell with a glass jar six inches in diameter and eight inches high will develop about two volts of electro-motive force; and as its internal resistance is very low it will furnish a steady current for several hours. Any number of these cells may be made and connected in series; but when not in use it would be well to remove and wash the zincs. Any bichromate battery will answer very well for plating, the Grenet being an especially good one. A well-amalgamated zinc plate forms one pole, and a pair of carbon plates, one on each side of the zinc and joined at the top, make up the other pole. When not in use the entire plunge part should be removed from the bichromate solution, rinsed off in water, and laid across the top of the jar, ready for its next employment. The zinc and carbons must be joined together so that they are well insulated, and with no chance of the zinc coming into contact with the carbons. This may be done with four pieces of hard-wood soaked in hot paraffine and then locked together with stove-bolts and nuts, as shown at [Fig. 12]. Holes must be made in the top corners of the carbons and zinc, and with small bolts and nuts the connecting wires can be made fast.
To charge this battery, add five fluid ounces of sulphuric acid to three pints of cold water, pouring the acid slowly into the water and stirring it at the same time with a glass or carbon rod. When this becomes cold, after standing a few hours, add six ounces of finely pulverized bichromate of potash. Mix this thoroughly, and pour some of the solution into the glass cell until it is three-fourths full; then it will be ready to receive the carbons and zinc. When arranging the wood-clamps on the carbon and zinc plates it would be well to make two of the clamps longer than the others so that they will extend out far enough to rest on the top edge of the jar. To keep them in position at the middle of the jar, notches should be cut at the underside of these clamps, so that they will fit down over the edge of the jar. Any number of these cells may be connected together to obtain the desired amount of current, or electro-motive force.
Other batteries suitable for electro-plating are the Edison primary, Taylor, Fuller, Daniell, gravity, Groves, and Merdingers. All of these may be purchased at large electrical equipment or supply houses.
The Cleansing Process
One of the most important operations of the plating process is to properly cleanse the articles to be plated before they are placed in the bath. When once cleaned the surfaces of these objects must not be touched with the fingers, or any dusty or greasy object; otherwise the electro-deposited metal will not hold on the surface, but will peel off, in time, or blister. A very small trace of foreign matter is sufficient to prevent the deposit from adhering to the surface to be plated; therefore, great care must be taken to eliminate all trace of anything that would interfere with the perfect transmission of metallic molecules to the prepared surfaces. Acids are chiefly employed to remove foreign matter from new metallic surfaces; and for copper, brass, iron, zinc, gold, and silver a table is given on [page 281] which will show the right proportion of acids to water in order to cleanse the various metals. In the following scale the numerals stand for parts. For example: the first one means 100 parts water, 50 parts nitric acid, 100 parts sulphuric acid, and 2 parts hydrochloric acid—making in all 252 parts. These can be measured in a glass graduate.
| Water | Nitric Acid | Sulphuric Acid | Hydrochloric Acid | |
|---|---|---|---|---|
| Copper and brass | 100 | 50 | 100 | 2 |
| Gold | 100 | ... | ... | 15 |
| Silver | 100 | 10 | ... | ... |
| Wrought-iron | 100 | 2 | 8 | 2 |
| Cast-iron | 100 | 3 | 12 | 3 |
| Zinc | 100 | ... | 10 | ... |
Twist a piece of fine copper wire about part of the object to be cleaned and plated; then dip it in the acid and rinse off in clean warm or hot water, and rub the surface briskly with a brush dipped in the liquid. Dip it again several times, and rinse in the same manner; then, when it is bright and clean, place it in the bath, twist the loose end of the wire around the negative rod, and start the current flowing, taking care that the object is thoroughly immersed.
Tarnished gold or silver articles may be cleaned by immersing them in a hot solution of cyanide of potassium; or a strong warm solution of carbonate of ammonia will loosen the tarnish on silver, so that it can be brushed off. Corroded brass, copper, German-silver, and bronze should be cleansed in a solution composed of sulphuric acid, three ounces; nitric acid, one and three-quarters ounces; and water, four ounces. This soon loosens and dissolves the corrosion; then the article should be brushed off, dipped in hot water, and rinsed. Then replace it in the solution for a minute or two and rinse again, when it will be ready for the plating-bath.
Corroded zinc should be immersed in a solution of sulphuric acid, one ounce; hydrochloric acid, two ounces; and distilled or rain water, one gallon. It should be well brushed after the acid has bitten off the corrosion.
Rusty iron or steel should be pickled in a solution of sulphuric acid, six ounces, hydrochloric acid, one ounce, and water, one gallon. When the rust has been removed, immerse the object in a solution composed of sulphuric acid, one pint, and distilled water, one gallon. Before the acid is added to the water dissolve one-quarter-pound of sulphate of zinc in the water; then add the acid, pouring it slowly and stirring the water.
Lead, tin, pewter, and their compounds may be cleansed by immersing them in a hot solution of caustic soda or potash, then rinsing in hot water. Take great care if caustic is used, as it will burn the skin and tissues of the body. Do not let the fingers come into contact with any cleansed article, because the oily secretions of the body will stick to the metal and cause the coat of deposited metal to strip off or present a spotted appearance.
The Plating-bath
The object to be plated should not touch the bottom or sides of the plating-vat, and it should be far enough away from the anodes to avoid any possibility of coming into contact with them. It will not do to place the anode and kathode too close together, as the plate will be deposited unevenly; the thicker coating will appear on the parts closest to the anode. Neither should they be separated too far, as the resistance of the cell is thereby increased, and of course this means a waste of energy. The knowledge of how to arrange the anode and kathode is a matter to be learned by experience, but by carefully watching the deposit it will not be a difficult matter to determine the proper positions.
For many reasons the glass tank is preferable for amateur electro-plating work, since the objects may be watched without disturbing their electric connections and without removing them from the liquid. A very good plan for the copper bath, when spherical, cylindrical, or hollow objects are to be plated, is to line the inside of the tank with strips or a sheet of copper, hung on hooks that will catch on the sides; then connect the positive wire directly to these strips. With this arrangement but one rod, the negative, is in use, and the objects to be plated are suspended from it. It follows that the objects will take up the copper deposit from all sides, and a more evenly distributed coating will be the result.
It is better to start up the current gradually, rather than to put on at the beginning a large amount of electro-motive force. By watching the character of the deposit you can soon tell if you have the proper strength of current. If everything is working properly the copper deposit will have a beautiful flesh tint; but if the current is too strong it takes on a dark-red tone and resembles the surface of a brick. This is not right, and the object must be removed and washed off, the current reduced, and the object replaced in the bath.
When a sufficiently heavy coating of the copper has been applied, remove the object and wash thoroughly in running or warm water to free it from any remaining copper fluid. If this is not done the surface, in drying, will turn a dull brown, and will have to be bitten off with the acid solution for cleansing copper.
The finer the copper deposit the better and smoother it will be; the grain will be smaller, and it will not present a rough surface, which is always difficult to plate over with silver or gold, unless a frosted effect is desired. Non-conducting objects are usually plated with copper first, and then replated with the metal desired for the final finish.
To make the surface conductive, finely powdered black-lead, or plumbago of the best kind, or finely pulverized gas-carbon is brushed over the surface. This must be thoroughly done; and if the deposit is slow about appearing at any spot it may be hastened by touching it with the end of an insulated wire attached to the main conductor. This, of course, will only answer for objects strong enough to stand the brushing treatment; it will not do for flowers, insects, and other delicate things, that are to be silver or gold plated. These should be given a film of silver by soaking in a solution of alcohol and nitrate of silver, made by shaking two parts of the chemical into one hundred parts of grain-alcohol, with the aid of heat and in a well-corked bottle. When dry, the object should be subjected to a bath of sulphuretted hydrogen gas under a hood. The sulphuretted hydrogen is made by bringing a bar of wrought-iron to a white-heat in the kitchen range or furnace fire, and touching it with a stick of sulphur. The iron will melt and drop like wax. These drops should be collected in a bottle. Now pour over them diluted sulphuric acid, one part acid to three parts water, and the gas will at once rise. It will be quickly recognized by its odor, which is similar to that of over-ripe eggs. It can be led off through a tube to the place where you wish to use it, and when through, the operation of gas-generation may be stopped by pouring off the liquid.
All objects prepared in this way should be given a preliminary coating of thin copper before they are plated with any other metal.
Silver-plating
Plating in silver is done in practically the same way as described for the coppering process. Thin strips or sheets of pure silver are used for the anodes, and the electrolyte is composed of nitrate of silver, cyanide of potassium, and water.
Dissolve three and one-half ounces of nitrate of silver in one gallon of water; or if more water is needed to fill the tank, add it in the proportion of three and one-half ounces of the nitrate to each gallon of water. Dissolve two ounces of cyanide of potassium in a quart of water, and slowly add this to the nitrate solution. A precipitate of cyanide of silver will be formed. Keep adding and stirring until no more precipitate is formed, but be careful not to get an excess of the cyanide in the solution.
Gather this precipitate, and wash it on filtering-paper by pouring water over it. The filter-paper should be rolled in a funnel shape thus permitting the water to run away and leaving the precipitate in the paper. This precipitate is to be dissolved in more cyanide solution, and added to the quantity in the tank. There should be about two ounces of the potassium cyanide per gallon over and above what was originally put in.
The silver anodes show the condition of the fluid. If the solution is in good order they will have a clear, creamy appearance, but will tarnish or turn pink if there is not sufficient free cyanide in the solution.
The proper strength of current is indicated by the appearance of the plated objects. A clear white surface shows that everything is all right, the solution in proper working order, and the proper current to do the work. Too much current will make the color of the kathodes yellow or gray, while too little current will act slowly and require a long time to deposit the silver.
The adhesion of silver-plate is rendered more perfect by amalgamating the objects in a solution of nitrate of mercury, one ounce to one gallon of water. After the objects have been properly cleansed they are immersed in this solution for a minute, then placed in the silver-bath and connected with the negative-rod, so that the electro-depositing action begins at once.
Gold-plating
The gold-bath is made in the same manner as the silver one just described, with the exception that chloride of gold is used in place of the nitrate of silver in the first solution. This solution must be heated to 150° Fahrenheit when the process is going on; or a cold bath may be made of water, 5000 parts; potassium cyanide, one hundred parts; and pure gold, fifty parts. The gold must be dissolved in hydrochloric acid, and added to the water and potassium.
Very pretty effects may be obtained in gold-plating by changing the tones from yellow to a greenish hue by the addition of a little cyanide of silver to the solution, or by the use of a silver anode. A reddish tinge may be had by adding a small portion of sulphate of copper to the solution, or hanging a small copper anode beside the gold one. In the hot gold-bath the articles should be kept in motion, or the solution stirred about them with a glass rod.
When the solution is perfectly balanced and working right the anodes should be a clear dead yellow, and the articles in process of plating should be of the same hue.
A gold-plating outfit is shown in [Fig. 13], and consists of the tank and bath, a cell, and a resistance-coil (R), through which the strength of the current is regulated.
The current, passing out of the cell from the carbon (C), is regulated through the resistance-coils (R) by the switch (S). From thence it passes to the rod from which the anode (A) is suspended, across the electrolyte (E) to the kathode (K), on which the metal is deposited, and then returns through the negative wire to the zinc (Z) in the cell. If the hot bath is used the gold solution may be contained in a glazed earthen jar or a porcelain-lined metal jar or kettle. But if the latter is used care must be taken to see that none of the enamel is chipped, or a short-circuit will be established between the rods. This jar or kettle may then be placed on a gas-stove, and a thermometer should be suspended so that the mercury bulb is half an inch below the surface of the liquid, as shown at T in [Fig. 13]. As the liquid simmers or evaporates away a little water should be added from time to time to keep the bulk of the liquid up to its normal or original quantity.
Nickel-plating
The nickel-plating process is similar, in a general way, to the others; it is carried on in a cold bath—that is, at the normal temperature, without being heated or chilled artificially.
There are a great many formulæ for the nickel as well as for the other baths, but the generally accepted one is composed of double nickel ammonium-sulphate, three parts; ammonium carbonate, three parts; and water, one hundred parts. Another good one is composed of nickel sulphate, nitrate, or chloride, one part; sodium bisulphate, one part; and water, twenty parts.
Nickel anodes are used in bath to maintain the strength, and great care must be taken to have the bath perfectly balanced—that is, not too acid nor too alkaline.
To test this, have some blue-and-red litmus paper. If the blue paper is dipped in an acid solution, it will turn red; and back to blue again if placed in an alkaline solution. If the nickel solution is too strong with alkali, a trifle more of the nickel salts must be added, so that both the red-and-blue litmus paper, when dipped in the liquid, will not change color. If the bath is too alkaline, it will give a disagreeable yellowish color to the deposit of metal on the kathode; and if too acid, the metal will not adhere properly to the kathode, and will strip, peel, or blister off.
Finishing
When the articles have been plated they will have a somewhat different appearance to what may have been expected. For instance, copper-plated articles will have a bright fleshy-pink hue; silver, an opaque creamy-white; gold, a dead lemon-yellow color, and nickel much the appearance of the silver, but slightly bluer in its tone. Articles removed from the bath should be shaken over the bath so as to remove the solution; then they should be immediately plunged into hot water, rinsed thoroughly, and allowed to dry slowly.
When a silvered or gilded object is perfectly dry it should be rubbed rapidly with a brush and some fine silver-polishing powder until the opaque white or yellow gives place to a silver or gold lustre. It will then be ready for burnishing with a steel burnisher, or the article may be left with a frosted silver or gold surface. Steel burnishers can be had at any tool-supply house, and when used they should be frequently dipped in castile soapy water to lubricate them. They will then glide smoothly over the surface of the deposited metal, driving the grain down and making it bright at the same time. If the soapy water were not used the action of the hard burnisher over the plate would have a tendency to tear away the film of deposited metal. The burnisher must always be clean and bright, otherwise it would scratch the plated articles; and, when not in use, keep the bright polishing surfaces wrapped in a piece of oiled flannel.
Small articles, such as sleeve-buttons, rings, studs, and other things not larger than a twenty-five-cent piece, may be polished by being tumbled in a sawdust bag. A cotton bag is made, three feet long and six inches in diameter, closed at one end and half-filled with fine sawdust. The articles are then put in the bag and the end closed. Grasp the ends of the bag with both hands, as if to jump rope with it; then swing it to and fro, until the articles have had a good tumbling. Look at them to see if they are bright enough; if not, keep up the tumbling.
When old work is to be re-plated, or gone over, it will be necessary to remove all of the old plate before a really good job can be done. In some cases it may be removed with a scratch-brush or pumice-stone; but, as a rule, it can be removed much quicker and more satisfactorily with acids.
Silver may be removed from copper, brass, or German-silver with a solution of sulphuric acid, with one ounce of nitrate of potash to each two quarts of acid. Stir the potash into the acid, then immerse the article. If the action becomes weak before the silver is all off, then heat the solution and add more of the potash (saltpetre). Gold may be removed from silver by heating the article to a cherry-red, and dropping it into diluted sulphuric acid—one part acid to two parts water. This will cause the gold to peel and fall off easily.
Electrotyping
The term electrotyping is interpreted in several ways, but, in general, it means the process of electro-plating an article, or mold, with a metal coating, generally copper, of sufficient thickness, so that when it is removed, or separated from its original, it forms an independent object which, to all appearances, will be a fac-simile of the original.
To obtain a positive copy a cast has to be taken from a negative or reverse. This negative is called the mold or matrix, and can be of plaster, glue, wax, or other compositions. There are a number of processes in use, but the Adams process (no relation to the author) will give a boy a clear idea of this electro-chemical and mechanical art. This process was patented in 1870, and is said to give a perfect conduction to wax and other molds, with greater certainty and rapidity than any other, and will accomplish in a few minutes that which plumbago (black-lead) alone would require from two to four hours to effect.
As applied to the electrotyping of type, and cuts for illustration, the warm wax impression is taken by pressing the chase or form of type into a bed of wax by power or hydraulic pressure. Then remove it, and while the wax is still warm, powdered tin, bronze, or white bronze powder is freely dusted all over it with a soft hair-brush, until the surface presents a bright, metallic appearance. The superfluous powder is then dusted off, and the mold is immersed in alcohol, and afterwards washed in water to remove the air from the surface. It is then placed in the copper bath and the connection made from the negative pole to the face of the mold, so that the current will flow over its entire surface. A deposit of copper will quickly appear, and become heavier as the mold is left in longer.
When a mold has received the required deposit it should be taken from the bath and the copper film removed from it. This is done by placing the mold in an inclined position and passing a stream of hot water over the back of the copper film. This softens the wax and enables one to strip the film off, taking care at the same time not to crack or bend the thin copper positive.
The thin coating of wax, which adheres to the face of the copper, can be removed by placing it, face up, on a wire rack and pouring a solution of caustic potash over it, which, in draining through, will fall into a vessel or tank beneath the rack.
The potash dissolves the wax in a short time, and the electro-deposited shell may then be rinsed in several changes of cold water, or held under the faucet until thoroughly freed from the caustic.
As many, if not all, of the chemicals used in the various plating processes, and also the cleaning fluids, are highly poisonous, great care should be taken when handling them. Do not let the fingers or hands come in contact with caustic solutions or cyanide baths.
Never use any of these solutions if you have recently cut your fingers or hands, and do not allow the cyanides or caustics to get under the finger-nails. Never add any acid to liquids containing cyanide or ferro-cyanide while in a closed room. This should always be done in the open air, where the fumes can pass away, for the gases which rise from these admixtures are poisonous when inhaled.
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.
GLASS-CUTTING APPLIANCES
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.
Chapter XIII
FRICTIONAL ELECTRICITY
Frictional electricity is high potential, current alternating, and of high voltage but very low amperage. Apart from certain uses in laboratory and medical practice, it is valueless. In its greater volume it is akin to the lightning-bolt and is dangerous; but in its smaller volume it is a comparatively harmless toy. From the glass rod, or the amber, rubbed on a catskin to the modern static machines is a long jump, and the period of exploitation covers centuries of interesting experiments, most of which, however, have been practically useless for any commercial purpose.
Static or frictional electricity is generated by friction only, without the aid of magnets, coils of wire, or armatures rotating at high speed. The simple process of the glass and catskin has been variously modified, until at last Wimshurst invented and perfected what is known as the “Wimshurst Influence Machine.” It is self-charging, and does not require “starting.” It will work all the year round in any climate and temperature, and is the greatest improvement ever made in static electric machines.
Apart from its efficiency under all conditions, it is the simplest of all machines to make, and can easily be constructed by a boy who is handy with tools, and who can obtain the glass and brass parts necessary in its construction. The principal parts of an influence machine are the glass disks, wooden bosses, driving pulleys and crank, glass standards, brass arms with the spark-balls at the ends, and the base with the uprights on which these parts are built up and held in position.
A Wimshurst Influence Machine
Obtain a stiff piece of brown paper twenty inches square, and with a compass describe a circle twenty inches in diameter. Inside of this circle make another one fourteen inches in diameter, and near the centre a third circle six inches in diameter. Another circle four inches in diameter should be drawn inside of the six-inch circle, so that when the bosses are made fast to the glass plates they can be properly centred. Also mark sixteen lines radiating from the centre, equal distances apart, as shown in [Fig. 1].
From a dealer in glass purchase two clear, white panes of glass eighteen inches square. Be careful not to get the green glass, as this is not nearly so good as the white for static machine construction. If it is possible to get crystal plate so much the better. The panes should be thin, or about one-sixteenth of an inch in thickness, and free from bubbles, wavy places, scratches, or other blemishes.
From these panes cut two disks sixteen inches in diameter with a rotary cutter, as described in the chapter on Miscellaneous Apparatus, [page 294], and rub the edges with a water-stone (see chapter on Formulæ, [page 330].)
From flat, thin tin-foil cut thirty-two wedge-shaped pieces four inches long. They should be one inch and a half wide at one end and three-quarters of an inch at the other, as shown at [Fig. 2] A. Give each plate of glass two thin coats of shellac on both sides; then lay one on the paper pattern ([Fig. 1]) so that the outside edge of the glass will lie on the largest circle. Place a weight at the middle of the glass to hold it in place; then make sixteen of the tin-foil sectors fast to the plate, using shellac as the sticking medium. But first give one side of each sector a thin coat of shellac, allowing it to dry; then give it another coat when applying it to the glass. The sectors are to be symmetrically arranged on the glass, using a line of the pattern as a centre for each piece (as shown at A in [Fig. 1]), and the fourteen and six inch circles as the outer and inner boundaries. Each piece, as it is applied, should be pressed down upon the glass, so that it will stick smoothly, without air bubbles or creases. A very good plan is to lay a piece of soft blotting-paper over the sector and drive it down with a small squeegee-roller such as is used in photography, taking care, however, not to shift the sector from its proper position. When all the sectors are on, the plate should appear as shown in [Fig. 2]. After the shellac, which holds the sectors to the glass, is dry, run a brush full of shellac around the inner and outer extremities of the tin-foil strips for half or three-quarters of an inch in from the ends. The shellac will hold the sectors firmly to the glass, and will slightly insulate them as well, thereby preventing the escape of electricity. Apply the remaining sectors to the other plate of glass in a similar manner; and as a result two disks of glass, with the applied strips, will be ready to mount in the frame.
DETAILS OF WIMSHURST INFLUENCE MACHINE
A hole three-quarters of an inch in diameter should be made in each glass plate, so that a three-eighths spindle may pass through them and into the bosses, so as to keep them in proper line. It is preferable, however, not to bore these holes if bosses and accurately bushed holes can be made in the uprights of the frame which support these disks.
At a wood-working mill have two bosses made that will measure four inches in diameter at the large end, and one inch and a half at the small one. They should be of such length that when the plates and two bosses are arranged in line (to appear as shown in A A at [Fig. 9]) they will fill the entire space between the uprights B B. Near the small end a groove is turned in each boss, so that a round leather belt will fit in it, as shown in [Fig. 3].
The base is made from pine, white-wood, cypress, or any other wood that is soft and easily worked. It is composed of two strips twenty-four inches long, three inches wide, and one inch and a quarter in thickness, and two cross-pieces fourteen inches long, three inches wide, and one inch and a half thick.
These are put together with glue and screws, and at both sides of the base notches are cut to accommodate the feet of the uprights. The uprights are seventeen inches high, three inches wide, and one inch and a half thick. The notch at the foot of each one is cut so that, when fitted in place, the foot of the upright will rest on a table on a line with the bottom of the end cross-pieces under each corner. At the foot of the uprights a piece of sheet rubber should be made fast, with glue or shellac, so that when in operation the machine will not move about or slide.
A groove is cut at one side of each upright six inches above the bottom, as shown at [Fig. 4] A. In this groove the driving-wheel axles fit, and near the top holes are made in the uprights through which the spindles pass, which in turn support the bosses and glass disks.
At the middle of each cross-piece forming the ends of the base a one-inch hole, for the glass standard rods, is bored through the wood, as shown at [Fig. 4] B B. After attaching the uprights to the base with glue and screws, and giving all the wood-work several successive coats of shellac, the frame will be ready for its mountings.
The driving-wheels are of wood seven-eighths of an inch thick and seven inches in diameter; they should be turned on a lathe and a groove cut in the edge so that a round leather belt will fit in it. These wheels are mounted on a wooden axle that can be made from a round curtain-pole, with a half-inch hole bored through its entire length. The axle is as long as the distance between uprights B B in [Fig. 9]. The wheels are to be arranged and glued fast to the axle, so that the grooves will line directly under those in the bosses, as shown in [Fig. 9]. A half-inch axle is driven through the hub, and at one end it is threaded and provided with two washers and nuts; or a square shoulder and one washer and nut may be used, so that a crank and handle may be held fast. Shellac should be put on the shaft to make it hold fast in the hub.
The complete apparatus of wheels, axle, hub, and handle is shown at [Fig. 5], and in the frame this is so hung that the iron axle rests in the grooves cut in the uprights. To hold this in place two metal straps, as shown in [Fig. 6], are made and screwed fast to the wood. When finally adjusted the driving-wheels should rotate freely whenever the crank is turned. The wooden bosses, [Fig. 3], are given two or three coats of shellac; then they are made fast to the glass disks on the same side to which the tin-foil sectors are attached. The disks should be placed over the paper plan, [Fig. 1], and so adjusted that the outer line tallies with the large circle. Acetic glue[4] is then applied to the flat surface of the boss, and the latter is placed at the middle of the disk to line with the small circle. Place a weight on the end of the boss to hold it down, and leave it for ten or twelve hours or until thoroughly dry.
[4] See [Formulæ, Chapter xiv.], for the recipe of [acetic glue].
Both bosses should be set at the same time so that they may dry together.
If the bosses are turned on a lathe a hole should be made in each one about half-way through from the small end. This, in turn, should be bushed or lined with a piece of brass tube, which should fit snugly in the hole. A little shellac painted on each piece of tube will make it stick. Pieces of steel rod that will just fit within the tubing are to be cut long enough to enter the full length of the hole, pass through the holes made in the top of the uprights, and extend half an inch beyond, as shown in [Fig. 9]. The bosses and axles will then appear as shown in [Fig. 7].
Flat places should be filed on each rod where it passes through the wood upright; a set-screw will then hold it fast and keep it from revolving. When the hole, or tubing, is oiled so that the boss and disk will revolve freely on the axle, the disks, bosses, and axles are ready to be mounted in the frame.
A red fibre washer, such as is used in faucets, should be made fast to one glass disk at the centre, so as to separate the disks and prevent them from touching when they are revolving in opposite directions. These fibre washers can be had from a plumber or purchased at a hardware store. Shellac or acetic glue will hold the washers in place.
Mount one disk by holding the boss with the small end opposite a hole in one upright, and slip an axle through from the outside of the upright. Hold the other disk in place, and slip the remaining axle through the other upright and into the boss. When both plates are in place and centred, turn the set-screws down on the flattened axles to hold them in place.
To reduce the friction between the bosses and the uprights it would be well to place a fibre washer between them. A few drops of oil on these washers will lubricate them properly, and allow the machine to run easier. An end view of the apparatus, as so far assembled, will appear as shown in [Fig. 9], A being the disks, bosses, and axles, B B the uprights supporting them, C the hub, and D D the driving-wheels. The handle and crank (E) extends out far enough from the side to allow a free swinging motion without hitting the upright or base. Having arranged these disks and wheels so as to revolve freely, it will now be necessary to construct and add the other vital parts and the connecting links in the chain of the complete working mechanism.
From a supply-house obtain two solid glass rods an inch in diameter and fifteen inches long. These fit in the holes (B B) bored in the end-pieces of the base, [Fig. 4]. Procure two brass balls, two or two and a half inches in diameter, such as come on brass beds, and two short pieces of brass tubing, one inch inside diameter, that will fit over the ends of the rods. These tubings are to be soldered fast to the balls so that both tubes and balls will remain at the top of the glass rods.
From brass rod three-sixteenths or a quarter of an inch in diameter make two forks, as shown at [Fig. 8], and solder small brass balls at the ends of the rods. The prongs of the fork are six inches long and the shank four inches in length. Along the inside of the forks small holes are bored, and brass wires, or “points,” are soldered fast. These extend out for half an inch from the rods, and are known as the “comb,” or collectors. The forks should be so far apart that when mounted with the glass disks revolving between them the points will not touch or scratch the tin-foil sectors, and yet be as close to them as possible. A hole should be bored in the brass balls, and the shank of the fork passed through and soldered in place, as shown in [Fig. 10].
A three-eighth-inch hole is bored directly in the top of each brass ball to hold the quadrant rods, which extend over the top of the disks.
In the illustration of the complete machine ([Fig. 12]) the arrangement of the glass pillars, balls, combs, and quadrant rods is shown. The rods are three-eighths of an inch in diameter and are loose in the holes at the top of the balls, so that they can be moved or shifted about, according as to whether it is a left or a right handed person who may be turning the crank.
At the upper end of each rod a brass ball is soldered, one being three-quarters of an inch in diameter, the other two inches. The projecting ends of the forks should be provided with metal handles or brass balls, as shown in [Fig. 12]; these may be slipped over the end or soldered fast. Obtain two small brass balls with shanks, such as screw on iron bed-posts, and have the extending ends of the axles that support the bosses threaded, so that the balls will screw on them. Bore a quarter-inch hole through each ball, and slip a brass rod through it and solder it fast. Each end of these rods should be tipped with a bunch of tinsel or fine copper wires. These are the “neutralizers,” and the ends are curved so that the brushes of fine wires will just touch the disks when the latter are revolved, as shown in [Fig. 12]. The ball holding the rod is to be screwed fast to the axle; then the axle is pushed back into the boss and made fast in the head of the upright with the set-screw.
The rod-and-ball at the opposite side of the disks is arranged in a similar manner, but the rod points in an opposite direction to that on the first side. Cord or leather belts connect the driving-pulleys and bosses, the belt on one side running up straight over the boss and down again around the driving-pulley. The belt at the opposite side is crossed, so that the direction of the boss is reversed; and in this manner the disks are made to revolve in opposite directions, although the driving-pulleys are both going in the same direction.
A portion of the sectors are omitted in the illustration ([Fig. 12]) so that a better view of the working parts may be had. When the disks are revolving the accumulated electricity discharges from one ball to the other, above the plates, in the form of bright blue sparks sufficiently powerful to puncture cardboard if it is held midway between the balls.
A Large Leyden-jar
When experimenting with this machine it would be well to have one or more Leyden-jars to accumulate static charges. A large one of considerable capacity is easily made from a battery jar, tin-foil, brass rods and chain, and some other small parts.
Obtain a bluestone battery jar, and after heating it to drive all moisture from the surface, give it a coat of shellac inside and out. With tin-foil, set with shellac, cover the bottom and inside of the jar for two-thirds of its height from the bottom, as shown in [Fig. 11]. Cover the outside and bottom in a similar manner, and the same height from the bottom, and provide a cork, or wooden cap, for the top. If a large, flat cork cannot be had, then make a stopper by cutting two circular pieces of wood, each half an inch thick, the inner one to fit snugly within the jar, the other to lap over the edges a quarter of an inch all around. Fasten these pieces together with glue, as shown at [Fig. 13], and give them several good coats of shellac. Make a small hole at the middle of this cap and pass a quarter-inch rod through it, leaving six inches above and below the cap. To the top of the rod solder a brass ball. At the foot a piece of brass chain is to be made fast, so that several links of it rest on the tin-foil at the bottom of the jar.
To charge a jar from the Wimshurst machine, stand the jar on a glass-legged stool, and connect a copper wire between one of the overhead balls on the machine and the ball at the top of the rod in the stopper of the jar. Make another wire fast to the other ball at the top of the machine, and place it under the jar so that the tin-foil on the bottom touches it. By operating the machine the jar is charged.
To discharge the jar make a T-yoke, as shown at [Fig. 14], by nailing a brass rod fast to a wooden handle and soldering brass knobs, or hammering a lead bullet, on the ends of the rod. Hold one knob against the top knob of the jar and bring the other near the foil coating at the outside, when a spark will jump from the foil to the knob with a loud snap.
A Glass-legged Stool
One of the most useful accessories in playing with frictional electricity will be a glass-legged stool. A stool with glass feet is perhaps too expensive for a boy to purchase, but one may be made at little or no cost from a piece of stout plank, four glass telegraph line-insulators, and the wooden screw-pins on which they rest when attached to a pole.
The general plan of the stool is shown at [Fig. 15], and the top measures twelve by fifteen by two inches. Under each corner a screw-pin is made fast by boring a hole in the wood and setting the pin in glue. The pins are cut at the top, as shown in [Fig. 16], and when they are set in place the glass insulators may be screwed on. The wood-work should be given a few coats of shellac to lend it a good appearance and help to insulate it.
There are a great many interesting experiments that may be performed with static or frictional electricity, and these may be looked up in the text-books on electricity used in school. A word of caution will not be misplaced. Remember that the current, in large volume, is dangerous. For example, a series of charged Leyden-jars may contain enough electricity to give a very severe shock to the nervous system of the person who chances to discharge it. Its medical use should be under the advice and supervision of a physician.
Chapter XIV
FORMULÆ
In the construction of electrical apparatus there are many things, such as paint, cement, non-conducting compounds, and acid-proof substances, that are necessary in assembling the parts which make up complete working outfits. Accurate formulas and directions for these things will save the amateur trouble and expense, since they indicate the materials which have been put to the test of time and wear by others who have had abundant experience along these lines.
The amateur will not need a large number of compounds, but such as are necessary should be of the best. Those which are described in this chapter can be relied upon to give working results.
Acid-proof Cements
One of the best acid-proof cements is made by adding shellac, dissolved in grain alcohol, to red-lead until it is at the right consistency. It can be used in liquid form or in a putty-like paste. The consistency is governed by the amount of shellac added to the red-lead. The lead should be pulverized and free from lumps. This cement can be mixed in a small tin cup or on a piece of glass, with a knife having a thin blade.
It should be used as soon as it is mixed, since it “sets” as quickly as shellac, and then dries from the outside towards the middle. In a week or two it will become dry and hard like stone.
Another cement, which will also dry as hard as a stone and will hold soapstone slabs together as if they were of one solid piece, is made of litharge (yellow lead) and glycerine. The glycerine is added to the pulverized litharge to make a paste, or it can be mixed and kneaded like thin putty. It should be used very soon after mixing, as it sets rapidly.
Hard Cement
A medium hard cement is made from plaster of Paris, six parts; silex, or fine sand, two parts; dextrine, two parts (by measure). Mix with water until soft; then work with a trowel or knife.
Soft Cement
A good soft cement is made of plaster of Paris, five parts; pulverized asbestos, five parts (by weight). Add water enough to make a soft paste, and use with a trowel or knife. This is a heat-proof compound and is commonly known as asbestos cement.
Very Hard Cement
One of the hardest cements that can be made is composed of hydraulic cement (Portland or Edison), five parts; silex, or white sand, five parts (by measure). Mix with water and use like plaster with a trowel or spatula.
Care must be taken when the parts are combined to see that the cement is free from lumps. These must be broken before the silex, or sand, and water are added. Then the two parts should be mixed together at first and moistened afterwards. The proper way is to place some water at the bottom of a pan; then add the dry mixture by the handfuls, sprinkling it around so that the water can enter into it without forming lumps. Keep adding and mixing until the mass is at the right consistency to work.
All these cements are acid-proof.
Clark’s Compound
For exterior insulation, where the parts are exposed to the weather, a superior compound is made up of mineral pitch, ten parts; silica, six parts; tar, one part (all parts by weight). This is called Clark’s compound, after the man who invented it and used it successfully.
It is heated, thoroughly mixed, and used with a brush or spatula.
Battery Fluid
A depolarizing solution for use in zinc-carbon batteries like the Grenet is composed as follows:
Dissolve one pound of bichromate potash or soda in ten pounds of water (by weight). When it is thoroughly dissolved add two and one-half pounds of sulphuric acid, slowly pouring it into the bichromate solution and stirring it with a glass rod. The addition of the acid will heat the solution. Do not use it until it has entirely cooled.
Glass Rubbing
To rub the edges of glass, such as the disks for Wimshurst machines, obtain a piece of hard sandstone, such as is used for sharpening knives or scythes. The glass is placed on a table so that the edge extends beyond. Oil of turpentine is rubbed or dropped on the surface of the stone, and the edge of the glass is moistened with a rag soaked in the turpentine. Hold the glass down securely with one hand, and with the other grasp the stone and give it a forward and backward motion, grinding the glass along its edge and not crosswise. With care and patience a rough edge can soon be brought to a smooth one, and a soft, rounded corner substituted for the hard, angular, cutting edge that makes the glass a difficult thing to handle. Use plenty of lubricant in the form of oil of turpentine to make the work easy.
Acetic Glue
One of the best glues for glass and wood or glass and fibre is made by placing some high-grade glue (either flake or granulated) in a cup or tin and covering it with cold water. Allow it to stand several hours until the glue absorbs all the water it will and becomes soft; then pour the water off, and add glacial acetic acid to cover the glue. The proportion should be eighteen parts of glue to two of acid. Heat the mass until it is reduced to liquid, stirring it until it is thoroughly mixed. When ready for use it should be poured into a bottle and well corked to keep the air away from it.
Insulators
Apart from glass and porcelain, insulators can be made from non-conducting compounds, the best of which is molded mica. Ground mica or mica dust is mixed with thick shellac until it is in a putty-like state. It may then be forced into oiled molds of any desired shape. Hydraulic pressure is employed for almost every form of molded mica that is made for commercial purposes; but as a boy cannot employ that means to get the best results, he must use all the pressure that his hands and a flat board will give.
Another compound is made from pulverized asbestos and shellac, with a small portion of ground or pulverized mica added, in the proportion of asbestos, six parts; mica, four parts. Shellac is added to make a pasty mass, which is kneaded into a thick putty and forced into oiled molds until it sets. It is then removed and allowed to dry in the open air, and the mold used for more insulators.
Non-conductors
When working in different materials that seem adapted to electrical apparatus, it is necessary to know whether they can be used safely or not. Often a material seems to be just the thing, but if it should be a partial conductor, when a non-conductor is desired, it would be hazardous to use it. A list of non-conductors is therefore valuable to the amateur. Some of the principal non-conductors, among the many, are as follows: glass, porcelain, slate, marble, hard stone, soapstone, concrete (dry), hard rubber, soft rubber, composition fibre, mica, asbestos, pitch, tar, shellac, cotton, silk; cotton, silk and woollen fabrics, transite (dry), electrobestus (dry), duranoid; celluloid, dry wood (well seasoned), paper, pith, leather, and oil.
While this account of formulæ and material might be extended, this is not necessary inasmuch as the formulæ and practical directions which have been given will answer all usual practical requirements.
Insulating Varnish
There are several good insulating varnishes that can be used in electrical work, the most valuable being shellac dissolved in alcohol and applied with a brush. To make good shellac, purchase the orange-colored flake shellac by the pound from a paint-store, place some of it in a wide-necked bottle, and cover it with alcohol; then cork the bottle and let it stand for a few hours. Shake the bottle occasionally until the shellac is thoroughly dissolved. It can be thinned by adding alcohol. Always keep the bottle corked, taking out only what is necessary from time to time.
Another varnish can be made by dissolving red sealing-wax in alcohol and adding a small portion of shellac. This can be applied with a soft brush, and is a good varnish. When colors are to be applied to distinguish the poles, red is used for the positive current-poles and blue or black for the negative, if they are colored at all.
A very good black varnish is made by adding lampblack to shellac; another consists of thick asphaltum or asphaltum varnish. This is waterproof, and dries hard, yet with an elastic finish.
Battery Wax
For the upper edges of glass cells, such as the Leclanché or other open-circuit batteries, there is nothing superior to hot paraffine brushed about the upper edge to prevent the sal-ammoniac or other fluids from creeping up over the top. The paraffine can be colored with red-lead, green dust, or powders of various colors if desired, but generally the paraffine is used without color, so that it has a frosted-glass appearance when it is cool and dry.
A black wax for use in stopping the tops of dry cells and coating the tops of carbons is composed of paraffine, eight parts; pitch, one part; lampblack, one part. Heat the mixture and stir it until thoroughly mixed; then apply with a brush, or dip the parts into the warm fluid.
Another good black wax is composed of tar and pitch in equal parts. They are made into a pasty mass with turpentine heated over a stove, but not over an open flame, because the ingredients are inflammable. The compound should be like very thick molasses, and can be worked with an old table-knife.
Chapter XV
ELECTRIC LIGHT, HEAT, AND POWER
For the use of the cuts in this chapter, the Publishers desire to acknowledge the courtesy of the General Electric Company, the Thomson Electric Welding Company, and the Cooper Hewitt Electric Company.
With the discovery of the reversibility of the dynamo, the invention of the telephone, and the improvements in the electric light began the great modern development of electricity which proved that marvellous agent to be a master-workman.
Many of the things electrical that we ordinarily think of as modern inventions are merely modern applications of phenomena that were discovered many years ago. The pioneers in the science of dynamic electricity performed their experiments with the electric light, electro-magnets, etc., by using galvanic batteries. But for practical purposes the consuming of zinc and chemicals in such batteries was too expensive a way to generate electricity, and prevented any commercial use of the results of their experiments until cheaper electricity could be had.
The Work of the Dynamo
The invention of the dynamo, with which we obtain electricity from mechanical power, changed all that. Instead of consuming zinc in primary batteries, men could obtain it by burning coal, which is much cheaper, under the boiler of a steam-engine used to drive the dynamo. Thus it is that modern electricity comes from mechanical power. It is really the energy of a steam-engine or a water-wheel, or some other “prime mover,” working through the medium of electricity, that is transmitted to a distance and distributed over wires. The electricity may then be transmuted into light, heat, or chemical energy as the case may be, to light our electric lamps, develop the intense heat of the electric furnace, and charge storage-batteries.
Moreover, some time after the invention of the dynamo it was found that the mechanical power put into one of these machines could be transmitted electrically and reproduced as mechanical power. In other words, a dynamo could be made to revolve and give out power, as a motor, by supplying it with current from another dynamo. This showed the way to transmute electricity back again into mechanical power, to run our electric cars and trains, and all kinds of machinery in our factories and elsewhere. Nowadays the dynamo is used to generate nearly all the electricity that we need. Even in such comparatively old electrical applications as electro-plating and the telegraph and telephone, primary batteries are being supplanted by motor dynamos, which we shall learn about later.
It is from the invention of the dynamo and the discovery that it was reversible that we date the beginning of what are known as heavy electrical engineering applications, including electric light, heat, and power. In this closing chapter it is purposed to learn a little about these applications, and in so doing to summarize briefly the things that we have already studied.
The Electric Light
In the [chapter] on Electrical Resistance we learned that an electric current always encounters a resistance in passing through a conductor, and that when the current is strong enough the conductor is heated up. The electric light is produced by the heating of a conductor of one kind or another to incandescence by the electrical friction of the current passing through it.
The first electric light was made by Sir Humphry Davy over a hundred years ago. He discovered that when a current from a great many cells of battery was interrupted the spark did not simply appear for an instant and then go out, as it does when only a few cells are used, but remained playing between the terminals of the circuit. He found by experiment that if pieces of carbon are used as the terminals—or “electrodes,” as they are called—the electricity passes between them in an intensely hot flame, or “arc.” The latter, which is due to the electrical resistance of the vapor of carbon, heats up the carbon-points so that they give a brilliant white light.
Fig. 1
Fig. 2
Before the dynamo came into use, the electric light was rarely seen, except as a philosophical experiment; but as soon as cheap electricity became available, commercial electric arc-lamps were made by many inventors and have been continually improved. [Fig. 1] shows one form of modern arc-lamp, with its case removed to show the interior mechanism. In most arc-lamps the lamp itself consists of a pair of carbon or other electrodes in the form of long rods arranged vertically, with their tips normally in contact. When the current is turned on, the mechanism lifts the upper electrode away from the lower one. The interruption of the circuit thus caused “strikes the arc” between the tips, and the mechanism keeps the arc-distance unchanged as the carbons burn away. Some arc-lamps are made to burn on continuous-current, and others on alternating-current circuits. When continuous current is used, the upper (or positive) carbon burns away about twice as fast as the lower one, forming a cup, or “crater,” from which most of the light comes.
Uses of the Arc-Light
The first commercial use of the arc-light on a large scale was for street-lighting, to replace the old-fashioned gas-lamps. But another important use is in search-lights, in which the arc-lamp is fitted with a powerful reflector for throwing a very bright light to a distance. [Fig. 2] is a view of a search-light arranged to go on top of a ship’s pilot-house. In war-time the ships carry search-lights to help them find the enemy’s ships and repel attack; and they are used in the army also, by having a portable dynamo and engine drawn by horses. The arc is also employed in projectors for lecture-rooms, and sometimes for the headlights of steam and electric locomotives and interurban electric cars.
Incandescent and Other Lamps
The arc-lamp came into wide use for lighting large spaces like streets, stores, and public halls, but was found to be too intense for lighting smaller places like private houses. After many experiments, Edison succeeded in subdividing the electric light into the small pear-shaped “incandescent” lamps that we now see everywhere. In this kind of electric lamp the light comes from a thin “filament” of carbon, contained in a glass globe from which all air has been removed. Since there is no oxygen to support combustion, the filament may be heated white-hot by the current without being consumed.
Fig. 3
In certain other forms of incandescent lamps that are just coming into use, the filaments are made of rare metals—osmium, tantalum, etc.—that will stand a high temperature without melting. The Nernst lamp has a filament consisting of a mixture of certain materials that has to be heated before it will conduct electricity.
Then there are the so-called “vapor” lamps, consisting of a glass tube full of conducting metallic vapor which gives out light when a current is passed through it. The best-known form is the Cooper Hewitt mercury vapor-lamp shown in [Fig. 3], which gives a peculiar greenish light.
From the point of view of efficiency, the electric light, wonderful as it is, leaves much to be desired. The light always comes from a hot resistance; and whether this resistance is a mass of conducting vapor, as in the arc and vapor lamps, or a solid conducting filament, as in the so-called “incandescent” lamps, much more heat than light is produced. A needed improvement, therefore, is in the direction of obtaining a greater percentage of light for a given amount of electrical energy.
Electric Heat
The generation of heat in electrical devices usually means wasted energy—sometimes a very serious waste, as we have just seen. There are certain kinds of electrical apparatus, however, that are designed to transform all of the electrical energy delivered to them into heat, for various industrial and household purposes.
Fig. 4
Electric Furnaces
By far the most important application of electric heat, as such, is in electric furnaces, by means of which we attain the highest temperatures known to man. The electric furnace consists of a chamber of “refractory” material, containing the substances to be acted upon by the heat, with a pair of big carbon electrodes thrust into the centre, as shown in [Fig. 4], which is a picture of Moissan’s electric furnace for the distillation of metals, and supplied with heavy continuous or alternating currents. The apparatus is therefore a sort of gigantic electric arc-lamp, so enclosed that the whole of the intense heat of the arc is confined and concentrated on the smelting or other work. In many places where cheap electric power is to be had—as in the vicinity of the great Niagara Falls power-plants—electric furnaces are employed in what are known as electrometallurgical and electrochemical manufacturing processes. By their aid many metals and other substances that were formerly scientific curiosities, or entirely unknown, are produced commercially; such as aluminum, certain rare metals, and calcium carbide, from which that wonderful illuminant, acetylene-gas, is obtained.
Welding Metals
Another useful application of electric heat is in the welding of metals. Instead of heating the pieces to be welded in a forge, their ends are simply butted together and the electricity—generally from an alternating-current transformer—turned on. The heat developed by the “contact resistance” between the pieces quickly softens the metal so that the pieces may be forced together, forming a perfect weld in a few minutes without any hammering. [Fig. 5] is a view of one form of electric welding-machine in which this is accomplished. The electric process can weld certain metals that cannot be joined securely by ordinary welding methods, and is used in several special arts.
Welding is also performed by the heat of a special electric arc-lamp, which a workman holds in his hand like a blow-pipe or torch. This process is especially useful in joining the edges of sheet-steel, in making tanks for electric “transformers,” etc. The workmen have to wear smoked glasses in order to protect their eyes from the intense glare of the arc.
Fig. 5
Electric Car-heaters
Perhaps the simplest and best-known application of electric heat is the electric car-heater, consisting of coils of high-resistance wire—such as iron or German-silver wire—mounted on an insulating, non-combustible frame which is placed under the seats of the car. Part of the current from the trolley wire or third rail passes through the resistance-coils, heating them up and thereby warming the air in the car.
Household Uses
Nowadays electric heat is being more and more widely utilized in what are known as household electric heating-appliances. One of the most useful of these is the electric flat-iron, shown in [Fig. 6]. This flat-iron is designed to do away with the use of a hot stove of any kind, and is internally heated by means of a resistance-coil of peculiar shape placed in the bottom of the iron close against its working face. The iron is connected to an electric-light socket by means of an attaching plug on the end of a long, flexible cord. It takes only a few minutes to get hot, and its use saves much time and labor.
The list of special heating-appliances that are now made includes curling-iron heaters; heating-pads, for taking the place of hot-water bags in the sick-room; cigar-lighters, in which a little grid “resistance” is made incandescent by pressing a button; foot-warmers; and radiators to dry wet shoes or skirts on rainy days. For industrial use there are glue-pots, for bookbinders and pattern-makers; large flat-irons, for tailor-shops and laundries; and electric ovens, for drying certain parts of electrical machines and for cooking various kinds of “prepared foods.”
Many electric cooking-utensils are made for the household, such as coffee-percolators, egg-boilers, ovens, disk stoves, etc. Each one is equipped with a resistance-coil like that in the electric flat-iron just described, so that it contains its own source of heat, which is under perfect control by means of a switch. An “electric kitchen” consists of a number of these utensils, wired to a convenient table or stand, as shown in [Fig. 7].
Fig. 6
Fig. 7
Electric Power
We have seen that the modern way to generate electricity is from mechanical energy applied through a dynamo, and that the “electric power” thus generated may be transmitted over wires to a distance and there transformed into other forms of energy, such as light, heat, and chemical energy, or reproduced again as mechanical energy. The last mentioned of these transformations is the most important of them all, because it is the one that means the most for the advancement of civilization. Before the invention of the dynamo and the discovery that it was reversible, mechanical power could be employed only in the place where it was generated, so that its use was restricted; whereas nowadays the field of power is broadened and its cost reduced by electrical transmission and distribution.
In the [chapter] on Dynamos and Motors we learned how to make and use those machines. Let us review, very briefly, just what happens in the double transformation—of mechanical energy into electricity and then back again at the end of a line of wires—that we call electric-power transmission. In the dynamo, the power of the water-wheel, or whatever other prime mover is used, is exerted in generating electricity by forcing the electric conductors of the machine through a magnetic field. The electricity is led away to a distance—a hundred miles, perhaps—by wires and allowed to enter another machine similar to the dynamo, but operating as a motor. Here the first process is reversed: the electricity passing through the conductors of the motor reacts upon its magnetic field, causing the machine to revolve and thus generating mechanical power again. The line-wires carry the power just as positively as though a long shaft ran from the prime mover to the receiving end of the line, and much more economically. The action that goes on is similar to the operation of the telephone—which is indeed a special case of electric-power transmission—as already explained in a former chapter: the sound of the voice being transformed, at the telephone-transmitter, into electrical energy in the form of alternating currents, then carried as such over the line and finally reproduced as sound again at the receiver.
Power from Water-wheels
“Hydro-electric” transmissions—i. e., electric transmissions of power from a water-wheel as prime mover—are the most important because they bring into use cheap water-power that formerly ran to waste. There are many hydro-electric transmissions in this country, Mexico, and Canada, some of them utilizing the power of waterfalls or rapids located in mountainous and inaccessible parts. The alternating current is nearly always used because by it men can much more easily and safely generate, transmit, and receive the high voltages that have to be used than by the continuous current. The machinery at the “main generating station” consists of big alternating-current dynamos, which sometimes have vertical shafts instead of horizontal ones, so that they may be driven directly by turbines. The current is generated at a moderate potential, which is then “stepped-up,” by “static transformers,” to the comparatively high-line voltage that is required in long-distance transmissions.
Fig. 8
Transformers
[Fig. 8] is a view of a very large transformer of over 2500 electrical horse-power capacity. In the picture the containing-tank is represented as transparent, so as to show the transformer proper inside. The latter is really a special kind of induction-coil, with primary and secondary windings, and a core, weighing many tons, built up of thin sheets of steel. In this kind of transformer, the tank is filled with oil, to keep the transformer cool in operation, and to help insulate it against the high potential to which it is subjected. At the receiving end, or “sub-station,” the high-voltage electric power enters a set of “step-down” transformers, from which it is delivered again, at moderate potential, to the motors.
Sometimes power is distributed from a single great generating station to several sub-stations. In the Necaxa transmission, in Mexico, over 35,000 horse-power is taken from a waterfall in the mountains and transmitted at 60,000 volts potential to Mexico City, 100 miles away, and to the mining town of El Oro, seventy-four miles farther on.
Several kinds of motors are used at the receiving end of electric-power transmission-lines, according to the work that they are called upon to do. For “stationary” work, like driving the machines in mills and factories, two principal kinds of alternating-current motors are employed—synchronous and induction motors. The former are built just like alternating-current dynamos, and when they are running they keep “in step” with the dynamo at the other end of the line; i. e., the motion of their field windings relatively to their armatures keeps exact pace with the same motion at the dynamo, just as though a long shaft ran from one machine to the other instead of the electric wires of the transmission-line. A motor of this type, at work driving an air-compressor, is shown in [Fig. 9]. The induction-motor is really a sort of transformer, the primary winding of which is the fixed part, or field, and the secondary winding the rotating armature. It does not keep in step with the dynamo, like the synchronous motor, but adapts its speed to the “load,” or amount of work that it is called upon to do, like a continuous-current motor.
Fig. 9
Rotary Converters
Sometimes alternating-current electric power is transformed at the sub-station into continuous-current power. This is done by a special kind of transformer called a “rotary converter.” The static transformers of which we have just been speaking are built, like ordinary reduction-coils, with no moving parts, and operate by taking in alternating currents at a given potential and giving out alternating currents at a different potential, higher or lower as the case may be. The rotary converter, however, is built something like a dynamo, with a stationary field and a revolving armature, and ordinarily operates by receiving an alternating current at a given potential and delivering a continuous current of the same or a different potential. This kind of transformation is employed wherever it is desired to obtain any large amount of continuous current from an alternating-current transmission-line; and especially to obtain “500-volt continuous current” for operating street and interurban electric railways, as we shall see under the [next heading]. [Fig. 10] shows one form of rotary converter built for supplying continuous current for trolley service.
Fig. 10
Oftentimes the sub-station of a transmission system contains both static transformers and rotary converters, to supply both alternating current and continuous current from the same high-voltage alternating-current line. When the continuous current has to be transformed from one voltage to another, a “motor dynamo” is used, consisting of an electric motor driving a dynamo on a common shaft.
One of the most interesting features of electric-power transmission is the care that is taken to avoid the terrible danger from the high potentials, and at the same time prevent loss of power on the way. The electricity in the machinery and in the line-wires that extend across the country is veritable lightning, and has to be carefully guarded from doing any damage or escaping. To prevent leakage, the insulation of all of the station machinery and apparatus is made extra good, with “high dielectric strength,” so that it will not be punctured by the high voltage; and the line-insulators are made very large, and electrically and mechanically strong—quite unlike the ordinary-sized glass or porcelain insulators that are employed for telegraph and telephone lines. Each insulator before being put up is tested under a “breakdown voltage” much higher than it is to stand in actual service.
Oil-switches
The switching of high-voltage electric power is a knotty problem. The circuit cannot be interrupted by “air-break” switches, such as are used in ordinary electric-light stations, for any attempt to do so would result in a destructive arc many feet long, that could not be extinguished. Therefore “oil-switches” are always used to control the line-circuits at the main generating station and the sub-stations. In these oil-switches—which are designed to be operated from a distance, by hand-levers, or sometimes by electric motors—the circuit is made and broken under the surface of oil, which prevents the formation of an arc. Moreover, the switchboard attendant does not have to come anywhere near the deadly high-voltage wires, but can make the necessary connections at a safe distance.
Electric Traction
The use of the electric motor to propel vehicles of all kinds is called electric traction. It is, of course, a branch of electric power, which we have just been considering; and it is in many respects the most important branch. The wealth of a country is largely built up and maintained by its facilities for transportation, such as its canals, highways, railroads, and street and interurban car-lines.
In this field electric power is playing a most important part, although it was not many years ago that the first experimental electric cars were put in to replace horses on the street-railways of our cities. The change was found to be so successful that the field of the trolley-car was widened and extended very rapidly, until now we have our great suburban and interurban electric railways, with cars almost or quite as big as those on the steam-railroads and running at even higher speeds. During the last few years, also, the sphere of the steam-railroad itself has been invaded by electricity, by the construction of powerful electric locomotives to draw passenger and freight trains.
The Trolley-car
Let us consider just what it is that makes a trolley-car go. Since electric power is only mechanical energy in another form, we know that the motionless copper trolley-wire, suspended over the track in our streets, is the means of propelling the car just as truly—though in a different way—as if it were a moving steel cable to which the car was attached. We must keep in mind the fact that the electricity is not itself the source of power, but only the medium of transmission. The engine in the power-house, by turning a dynamo there, maintains a constant electric pressure, or “constant potential,” as it is termed, in the trolley-wire. This pressure of electricity forces the power through the motors of the car as soon as the motorman makes the connection to them by turning the handle of his “controller.”
Fig. 11
The Continuous-current Motor
[Fig. 11] is a view of one form of continuous-current motor. There is not much of the motor itself to be seen, because it is entirely enclosed in a cast-iron case. The shaft of the motor has a small “spur gear” fixed on one end, driving a gear-wheel which is fixed on the car axle. By this arrangement more than one revolution of the motor armature is required to make one revolution of the car-wheel, which multiplies the force exerted in turning the wheel.
Fig. 12
The Controller
[Fig. 12] is a view of a type of controller that is used on the platform of trolley-cars. The cover is removed to show the contacts, inside, by which the electric power is turned on gradually by the controller handle. The trains of electric cars that run on the elevated structures and in the subways of our large cities are supplied with power from a “third rail” placed by the side of the track, on insulating supports, and the motors on all the cars are controlled from a single “master-controller” on the front platform of the forward car. This system of control, known as the “multiple-unit” system, gives electric trains several advantages over the old kind, drawn by steam-locomotives; such as they used to have on the New York elevated roads, for example. For one thing, the train can be started much more quickly, since all the motors begin to turn the car-wheels at the same instant. Then again, the system enables a long train of cars to be controlled as easily as a single car, and better “traction” between wheels and track is obtained.
Electric Locomotives
Several of the great steam-railroads are now adopting the electric locomotive to draw their trains. [Fig. 13] is a view of one of the great continuous current electric locomotives that are used by the New York Central Railroad to handle many of its passenger-trains in and out of the Grand Central Station, in New York city. The motors of this powerful electric engine, unlike those of trolley-cars, are “gearless”; that is, their armatures are fixed directly on the locomotive axles so that they revolve at the same speed as the driving-wheels.
Fig. 13
All of the railway motors considered thus far have been of the continuous-current type, although the current to operate them is often obtained from alternating current transmission-systems, through rotary converters, as described above. The alternating current is also beginning to be employed to drive cars and trains. One type of alternating current railway motor, designed for “single-phase” operation, is in use on several interurban systems in this country, running on high-voltage alternating current most of the time, but on continuous current when within the city limits.
Other Forms of Electric Traction
Electric traction also includes electric automobiles, supplied by storage-batteries; a slow-speed electric locomotive for drawing canal-boats, and called “the electric mule”; and an ingenious gasolene-electric outfit for driving cars by electric motors without any trolley, third rail, or storage-battery. The last-mentioned arrangement consists of a set of electric car-motors mounted on the trucks in the usual way, but supplied with current by a dynamo mounted on the car itself and driven by a gasolene-engine. Thus the car carries its own power-station about with it, and is independent of any outside source of electricity.
The old alchemists sought to transmute matter from one form to another; and especially lead and other “base metals” into gold, in order that they might grow rich by concentrating the precious metal in their own selfish hands. The modern miracle that electricity works for us, the transmutation of energy, is a higher and broader thing, because it multiplies and distributes the world’s good things.
APPENDIX
A DICTIONARY OF ELECTRICAL TERMS AND PHRASES
Everybody is interested in electricity, but the ordinary reader, and particularly the boy who attempts to use this manual intelligently, will come across many technical words and terms that require explanation. It would be impossible to incorporate all needful definitions in the text proper, and the reader is therefore referred to the technical dictionary on the succeeding pages.
Care has been taken in its compilation to make the definitions complete, simple, and concise. Some of the more advanced technical terms have been purposely omitted as not necessary in a book dealing with elementary principles. The student in the higher branches of the science will consult, of course, the more advanced text-books. But for our practical purposes this elementary dictionary should answer every requirement. To read it over is an education in itself, and the young experimenter in electrical science should always refer to it when he comes across a word or phrase that he does not fully understand.