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.
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.
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.)
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.