Wiring Finished Houses.

Fig. 22.

On the contrary, if the burners fail to work and no sign of a short circuit can be thusobtained, it is evident that a wire is broken or a screw is loose.

To locate a break, connect up the bell as just described and attach the testing wire to the switch with all levers closed; this is actually putting the bell in series with the battery, coil, and ground. Then hunt for the break. Take a long piece of wire and fasten one end to a ground pipe. Then touch the other end to the circuit wire in the cellar as far as you can go, baring the insulation in spots, but carefully re-insulating it again. If there is no break in the cellar, the bell will ring loudly at each contact. Next, proceed to the next floor and repeat the operation, gradually workingawayfrom the battery. As soon as you pass the break, the bell will fail to respond. Two persons here are better than one, as it may be necessary to go quite a distance from the bell before finding the trouble.

Fig. 23 shows details of the wiring from the hall light to the two push-buttons. A wire is run right down from the top pushT, middle connection, past the lower pushL, where a similar branch joins it, until it reaches the section switch. The lighting and extinguishing wires from the lower push run up and arejoined on to the similar wires from the top push, which latter wires go directly through the floor and ceiling to the automatic burnerA.

Fig. 23., & Fig. 24.

Fig. 24 is the detail of the wiring for the cellar automatic burnerA, from the pushP, and is so clearly shown as not to require further explanation.

The secret of success in gas-lighting work is careful wiring. The platinum tip of the vibrating rod is often bent, either by accidental blow or by the continual hammering against the tip on the collar. This often causes an open circuit when the lighting armature refuses to buzz. Again, soot will form, causing weak action owing to imperfect contact. Examine, adjust, and clean; here, as in all electrical work, contacts must be clean.

In general wiring, use weatherproof office wire, or, better still, well-made electric light wire. For ordinary house work No. 16 B. & S. gauge is preferable; smaller wire means higher resistance and less current at burner. For braided office wire, No. 16 runs about 95 feet to the pound, No. 18 about 135 feet to the pound. The cheaper grades of wire without the patent finish or extra insulation are not worth using; sooner or later trouble will ensue,and once a house is wired, it is no pleasant job to hunt trouble, especially if the wire was put on before the plaster. In modern buildings in large cities, the use of conduit tubes has become general, but the handling of these conduits comes more under the province of the electric-light wireman and less within the scope of these pages.

In wiring new wooden buildings do not draw wires too tight; the wood may expand and either break wire or cause a weakening of the insulation. In wiring before the plaster is put on, always leave a good length free, so it will not be covered up by the plasterers.

The wire used on the gas fixture is of a special kind, being made for the purpose. It is made in two sizes, No. 22 and No. 24 B. & S. gauge, and with three windings of cotton, three outer layers of cotton and one of silk, or three windings of cotton which is soaked in fireproof preparation, and then wound with silk.

As the piece used is generally short, these small sizes are sufficient in carrying capacity. After wiring up a fixture, this fine wire can be tied on to the pipes, etc., with thread, and a good coating or two of shellac varnish applied.When this is dry, the thread can be removed and the shellac will hold the wires on to the fixture. On no account finally connect up the battery to a circuit when shellacking the wire. Wait until the shellac is thoroughly dry andhard—at least half a day, if possible.

White lead is generally used at the joints where the burner screws into the fixture, but tinfoil wrapped round the joint will give good service. It prevents leaks and ensures a good contact.

The ground connection at the battery must be first-class; do not be content with just wrapping a few turns of wire around the pipe in the cellar (assuming the battery is in the cellar), but clean and scrape the pipe; clean at least two feet of the wire, wind it tightly and evenly on the pipe andsolderit. There is a pipe-clamp made which is clamped on the pipe and the wire attached to that, but it must be properly put on a clean surface.

In wiring finished houses, especially wooden ones, the wires can be run along skirting boards, and often pushed out of sight in thespace between the floor and the skirting. This is quite permissible, as the wires, unlike electric-light wires, carry no dangerous current; but waterproof wire becomes preferable, as the water used in washing a floor will often creep under and rot the insulation. In going upstairs, wires can often be run in the fluting of a moulding along the stairway, and be quite inconspicuous; but wherever possible, fish the wires up inside the wall. The main thing to be considered in wiring is that the wires are large enough, well insulated, all joints well made and taped and put where there is no danger of injury. Rats have a habit of gnawing paraffin-coated insulation, and it is well to run such in metal tubes. In joining or splicing wires, do it in a thorough manner, and solder if possible. Never use the old bell-hanger joint—the one in which the ends of the wires are merely looped together. Strip insulation and scrape or sand-paper bright about three inches of each wire to be spliced. Then, placing the bare wires across each other about three-quarters of an inch from the insulation, tightly wind the loose bare ends of each around the bare inside portion of the one it is being spliced to. A touch of solder will prevent trouble from oxidation, after theadhesive tape has been wrapped on. Attention to details like these will often ensure the satisfactory working of the job.

A handy tool for gas-lighting wiring is shown in Fig. 25. One end is bored out to fit the small nuts on the ratchet and pendant burners, and the other is filed flat for use as a screw-driver.

Fig. 25.

A case may arise where there is electric light on the same chandelier as the gas lights, and that an insulating bushing has been screwed in between the fixture and the pipe. In this case it will be necessary to run two wires to each burner, the pipe common return being now unavailable. Another scheme is to interpose an insulating bushing under each burner; then the second or return wire need only be run from the burner to the gas pipeoutsidethe main bushing. But the local fire-insurance rules must first be consulted.

Most ceiling gas fixtures will admit of the fixture wire being run inside the brass shell,which makes a neater job. But the very best of insulation must be used, and great care be taken that it be not abraded. It should be shellacked or otherwise insulated before use. The electric-light fixture wires are admirable for use here if there is room.

For concealed work in a finished house, locate the position of the fixture under the floor of the room above by measuring both in the room where the fixture is and in the room above. Then cut out a piece of the floor, drill up from underneath through the fixture plaster-rose with a fine drill, and push the fixture wire up. The main wire can be laid under the carpet, or along the floor-crack in the upstairs room.

In wiring up wall-fixtures, push-buttons, etc., it is often possible to fish the wire up from the floor by punching a hole at the fixture and inserting a piece of chain (made for the purpose), attached to a long and stout thread. Then drill into the skirting near the floor plumb underneath the first hole and fish for the chain with a piece of wire having a hook on the end of it. Where fixtures have brass rosettes, these can be removed by (generally) unscrewing the fixture,but first shut off thegasat the meter, or plug the hole; this may seem unnecessary advice, but experience warrants its being given. When the chain is fished out, a piece of wire can be attached to the thread and pulled through in turn. In most cases its point of exit at the fixture can be concealed by the rosette, through a hole in which it passes. Take care that the edges of this hole do not cut the insulation. Care must be taken at every step in gas-lighting wiring.

In wiring up a push-button, screw all wires tightly under their respective binding screws, and then cover wherever possible with adhesive tape. As the wires must be somewhat loose to allow of the connections being made at the back of the push-button at the wall, they will have to be carefully pushed into the hole, and if they are not tightly held by screws, trouble will result. It is a good plan, when using fine enough wire, to make a sort of eye at the end of the wire and pass the screw through this, instead of merely giving the wire end a turn around the screw and then driving the screw home. Of course washers should be used wherever an ordinary screw holds a bare wire.

One of the uses to which an automatic burner can be put is in conjunction with an electric door-spring, lighting when the door is opened, but preferably extinguished by independent push. In this case, a form of trip spring should be used which would only make contact during a portion of the travel of door. Such a trip is shown in Fig. 26.

Ais automatic burner;C, the primary coil;B, the battery;T, a swinging trip piece of brass hinged in brass plate,P, which is screwed over the door in such manner that the door opening in direction of the arrow will cause the tripTto strike against the springS, and make contact. This spring is insulated from the platePby the hard rubber blockR.

On the door being opened, the trip will make contact long enough to light the burner and will then fall back as the door passes. On shutting the door, the trip will be raised and will fall as the door passes, but will not make contact. Or, if so desired, it can be made to operate a second contact to extinguish the burner by fixing a second insulated spring so it will be pressed when the top of trip makes adownward movement—as when the door passes it in shutting.

Fig. 26.

Various applications of automatic burners in connection with burglar alarms will suggest themselves, but in these cases the utmost care must be taken that the apparatus is in good working order; failure to light might cause the room to be filled with gas, and serious results ensue.

For those persons who use gas stoves and are mechanically inclined, an arrangement of an alarm clock with an automatic burner will enable them to light up without getting out of bed, or perhaps even waking up.

To construct a primary coil such as used with pendant or automatic burners presents no difficulty. The most convenient sizes are those 8 to 10 inches in length and about 3 inches in diameter. It is quite common to speak of these coils as8 or 10 inch coils; to the writer’s knowledge this has been taken to mean a Ruhmkorff or double-wound induction coil, giving a free 8 or 10 inch spark.

Fig. 27.

To make such a coil (Fig. 27), proceed as follows: Prepare a spool by gluing a paper or fibre tube 3/4 inch in outside diameter by about 1-16 inch thick into square or roundspool ends three inches square, one-half inch thick, and having each a centre hole just large enough to admit of the tube being held tightly. These ends should be firmly fixed on the tube; a pin or two driven through tube into end will assist in strengthening the joint. Now wind on the tube about 3 pounds No. 12 B. & S. cotton-covered magnet wire. This will give about six layers of 80 turns each, nearly 500 turns in all, a total length of, say, 150 feet, measuring .25 ohm. The ends of the wire are to be brought out through holes drilled in the spool ends, and can be fixed to brass binding posts on those ends.

Into the paper tube push as many iron wires 8 inches long by No. 22 B. W. gauge as will fill it. These iron wires can be tightened finally by driving in at each end, a stout wire nail.

Although not absolutely necessary, a coat or two of shellac varnish applied to the windings will make a better insulation. Shellac varnish is readily made by dissolving one part gum shellac in four parts of alcohol. For coils which are likely to be in damp places, a good saturation with insulating compound, such as P. & B. paint, will render them waterproof.The need for good insulation in these primary coils is not so urgent as in Ruhmkorff coils, owing to the lower potential of the current.

A smaller coil can be made with No. 14 B. & S. wire where the battery is of higher resistance (or gives less than ten amperes on short circuit). The remarks on battery selection on another page will be found to meet application here.

Where there are a number of burners to be installed in different parts of a house, it becomes desirable to wire in a number of circuits. As one end of the circuit is already grounded, a second ground will cause material injury to the battery if not detected in time. It becomes, therefore, necessary to be able to open a grounded circuit without affecting all the lights in a house. This is possible with the multiple circuit arrangement by using a switch, either automatic or operated by hand.

The simplest form of danger signal is the relay electric bell attachment, which device is mounted on the end of the gas-lighting coil.It consists of an armature which closes a circuit when attracted by the coil core, in which circuit are included a battery and electric bell.

Now when an ordinary pendant or ratchet burner is pulled, it only sends a momentary current through the coil, enough to magnetize the core, but not enough to attract the armature sufficiently long for the bell to ring. But if a short circuit or ground should occur, the armature is held against the contact long enough to cause the bell to ring and give warning. In some cases a constant ringing attachment is added, in which case the bell rings until some one stops it.

This is a most ingenious device for opening a short circuit, depending on its action upon the sluggish movement of glycerine (Fig. 28).

A sealed glass tube pivoted near its centre contains a portion of glycerine sufficient to considerably overbalance it and keep one end down. A soft iron armature is attached to this tube in such manner that each time a current flows through a pair of electro-magnets, the attraction of the armature causesthe tube to tilt and the glycerine flows along to the other end. Now it will be readily seen that if the tube is only tilted for a second or so, the slow-moving glycerine will not have flowed sufficiently to the end to overbalance it, but it requires an attraction of the armature for a considerable period. This electro-magnet is in circuit with the gas-lighting wires, the tube being provided with contacts in such manner that, when fully tilted, the circuit is broken. The momentary jerks imparted to the armature by the operation of a pendant or automatic burner will not be enough to permanently tilt the tube and breakcontact, but a short circuit will hold the armature tight down, until the increasing weight of glycerine causes the tube to open the circuit.

Fig. 28.

Fig. 29.

Fig. 30.

This cut-out, Fig. 29, is representative of the class which use clockwork, and is both simple and reliable. The house circuit is in series with an electro-magnet which controls a clockwork having a long pinion shaft. This clockwork starts and runs while the house circuit is closed, as on operating a burner, but stops when the circuit is opened and flow of current ceases. The wires leading to different circuits in the building run through a number of contact springs mounted on sliding rods, which have teeth cut on the under side (Fig. 30). These rods have soft iron armatures on the opposite ends from the contact springs, which rest over electro-magnets, also connected to the house circuits. When the clockwork starts, the pinion shaft revolves, but does not engage in any of the sliding rods, asthey just clear it. Should a heavy or continuous current pass through one of the electro-magnets, it attracts the armature on the corresponding rod (Fig. 31), and the turning pinion engages in the teeth, drawing up the rod and breaking contact.

Fig. 31.

Fig. 32 is a form of battery protector which works on the gravity principle. Here each section is governed by a rocking contact, operated by two glass bulbs partially filled with a volatile fluid (such as ether), and joined by a glass tube. In one of these bulbs is a platinum wire which is included in the circuit and heats upon the passage of a strong or continuous current. If the circuit is closed too long, the heating of the platinum wire causes the fluid to flow into the upper bulb, and, as the bulbs are pivoted, the increased weight of the upper bulb now overbalances the rocker and breaks the circuit on that section.

Fig. 32.

The jump spark system is used where it is desired to light clusters of gas jets situated in inaccessible places, or a number of them simultaneously. The spark from a Ruhmkorff coil, being made by a contact broken at the coil and not at the burner, can be divided up among a number of simple burners placed in series. One of the burners used and known as the Smith jump spark burner is shown in Fig. 33. The wires from the coil are attached to the electrodes shown on each side of the burner, and the spark jumps across the gap, situated nearly over the burner orifice. There is a guard-flange of mica round the lower part.

Fig. 34 shows the manner in which the jump spark is applied to a Welsbach burner. A small porcelain clip carrying the spark-gap wires is held on the top of the burner chimney. The electrodes project down into the chimneyso that a draught of air cannot carry the stream of gas away from the spark-gap.

Fig. 33., Fig. 34. & Fig. 35

Fig. 35 shows a burner intended for the stage of a theatre, or where the lights are located in dangerous and inaccessible places. The burner is made of porcelain upon which are spun the metal top and bottom. Oneelectrode is also clamped around it, allowing of adjustment and better insulation.

Fig. 36.

These burners are used in series, as shown in Fig. 36.B B Bare the burners;S S, the secondary wires from the Ruhmkorff coil,I;P P, the primary coil wires from battery, opened and closed by means of the key,K.

It is often possible to place plain burners close enough so that they can ignite by contagion. In this case one of the plain burnersis removed and replaced by a multiple burner, as above.

It is customary to allow sixteen burners to one inch of spark, in which case the spark gaps are adjusted about one-sixteenth of an inch apart. A coil giving a 2-inch spark would operate 32 burners, but actually it would be found preferable to omit a few, so as to make allowance for any slight leak. A spark of over 2 inches is hard to handle, although often used; it is better to make up a number of circuits of, say, 30 burners each, and operate them alternately by a suitable switch.

The wire used to connect the burners is generally bare, although an insulated wire is sometimes used. But the electromotive force of a 2-inch spark is so high that it is better to run the wires so they do not come near anything liable to cause a leak. The remarkable tendency of these high-tension currents must be most carefully guarded against; indeed, it is what makes this style of gas lighting so often unsuccessful. A damp wall, gilt wall-paper, a gas pipe hidden in the plaster, will often lead off the current. The wires should be at least 50 per cent. further offfrom any object than the spark length; that is, a 2-inch spark circuit should be at least 3 inches away from a wall, and the further the better. It cannot be too strongly urged that every precaution be taken to keep the wires away from objects other than their insulators.

Fig. 37.

Fig. 37 shows the special form of insulator used. It is made of the highest grade glaze filled porcelain, and the screw is passed into it and holds against the lower end as far away from the wire as possible.

Glass tubes should be passed over the wireswherever they come near any metallic object, that is, within sparking distance.

This system differs from the foregoing in that the spark-gaps are connected in multiple, instead of series, and each burner is provided with a small but efficient condenser.

Fig. 38.

It prevents trouble should a wire break between burners, in which event only one burner would be out of commission, whereas in the first method, the whole number in that series would suffer. It is also more sure in action and presents less liability of the spark jumping to the ground. The burner pillars need not be made of porcelain or lava; in fact, the electrodes can be readily attached to the existing burner. Fig. 38 is a condenser consistingof a small oval piece of mica, on each side of which is fastened, with insulating varnish, a spatula-shaped piece of tinfoil. One foil sheet is attached to the line, the other to the burner electrode. These condensers must not be allowed to get wet or their efficiency will be impaired.

Fig. 39. & Fig. 40

Figs. 39 and 40 are the most generally used burners, the wire from the condenser being attached to the lug or top electrode, which is insulated from the burner by means of the mica plate to which it is riveted. The burner pillars are of course grounded through theirbeing screwed into the gas pipe. The circuit is shown in Fig. 41.Iis the induction or Ruhmkorff coil, in the primary circuit of which is the key,K, controlling the current from the battery,B, and across which is bridged thecondenser,C C. When the coil vibrator is used, the condenserC Ccan be omitted, that of the coil itself serving instead.Sis the wire leading from the secondary terminal of the coil to the burner condenser,C, which, in turn, are connected to the electrodes on the burners,P P, as before noted. The other secondary wire is grounded preferably to the gas pipe itself.

Fig. 41.

Where a lot of burners are placed together, as in a ring, it is often feasible to light them by contagion, one tip only being connected to the coil circuit, the others lighting from it and conveying the flame around to the rest. This avoids multiplicity of circuits, or, perhaps, too many burner gaps on one circuit; but the one burner may fail to light, whereas, where all are fitted, the chances of failure are less, especially in the Edwards condenser system.

In a switch for controlling the current of the secondary coil it will be evident that the utmost attention must be paid to matters of insulation. The object of such a switch is to control a number of circuits; for example,as it is not advisable to put more than 20 to 25 burners on one circuit, a case requiring the lighting of 100 burners would necessitate some means of passing the current to each circuit in turn. This is shown in Fig. 42, in whichSis a hard rubber plate, provided with a revolving metal arm and handle,H, and four contact points,P, which latter receive the ends of the wires from the groups of burner condensersBby means of nuts or binding posts. The wire from the secondary of the coil is run to the switch-handle,H, great care being taken that it does not pass near to the circuit wires, or contact points. Revolving the switch-handle connects the secondary wire to each circuit in turn. It will be noticed that, unlike a battery switch, this one has a large base, long switch-arm, contact points situated far apart, and every precaution taken to control the passage of the high-tension current. The base should always be of rubber or glass. Shellacked-wood, or such substitutes, are productive of trouble.

Fig. 42.

When it is desired to light automatically a number of burners from a distance, the Trailer (Fig. 43), is used. This is a switch similar to above, but the arm is revolvedby means of toothed wheels by the electro-magnet shown on the back. As it is never desirable to unnecessarily prolong the secondary wires, this device admits of the switch being put near the circuits, and yet being operated from afar.

Fig. 43.

Fig. 44 shows a diagram of a Ruhmkorff coil, the letters referring as follows:

Cthe iron core,Pthe primary coil wires,Ithe insulating tube between primaryPand the secondary coilS. In small coils this may be dispensed with, and a heavy layer of paraffin wax laid over the primary coil.D Dare the ends of the secondary, showing sparking taking place between a pair of balls (or between the electrodes of a gas burner);Ris a stiff spring fastened to the coil base and carrying a soft iron hammer, which is attracted toward the iron core,C, when current passes through the primary coil and magnetizes it.Lis a battery,J, a condenser, to be more fully described later on. When the springRtouches the adjustment screwAatB, as they are insulated from each other, contact is made and reference to circuit will show that the current from batteryLflows through primary coil, magnetizing the core and attracting soft iron hammer onR. As this bends forward, it breaks contact atB, the core loses its magnetism and the spring fliesback, to again make contact. This is repeated many times per second.

Fig. 44.

As a heavy spark occurs atBon the break of contact, the condenser,J, is attached atM K. This is a series of insulated tinfoil sheets, which has the property of nullifying the spark atB, and so preventing the waste of platinum with which both adjustment screwAand springRare equipped.

A Ruhmkorff coil differs from a simple primary coil in three main points. Two separate coils instead of one; high insulation, and a primary coil of few turns. In the simple coil we desired self-induction; here, we desire to avoid it as much as possible.

The average size Ruhmkorff coil, for jump spark work, would be one giving a 2-inch spark, specifications for which are as follows:

Spool—Nine inches long by one inch in diameter. End cheeks 4 inches high by 3 inches wide.

Core—Sufficient soft iron wires, 9 inches long by No. 22 B. W. gauge as will fill the spool tube.

Primary—Two layers No. 14 B. & S. gauge cotton-covered copper wire.

Secondary—Two and one-half pounds No. 36 B. & S. gauge double cotton or silk-covered magnet wire wound in four sections (or more than four sections, if feasible).

Condenser—Seventy sheets tinfoil 4 by 7-1/2inches; 80 sheets condenser paper 5 by 8 inches.

This should be made up of a fibre tube 9 inches in length by about 1/16 inch thick, and should be firmly fixed into the spool ends. If it be glued in it should also be pinned as well; it is easily possible to drive in a few screws passing through the tube into the spool ends, particularly as the soft iron core, being of loose wires, will adapt itself to the slightly projecting screw-heads. Remember that this spool must be made strong; if it comes apart during the winding process, much trouble will ensue, and perhaps all the wires lost or ruined. For reasons to be seen later, do not affix the right-hand spool end yet, but have it ready. The core consists of as many fine iron wires, say of No. 22 B. W. gauge, as can be forced into the tube, but the core can better be added after the windings are all in; that is, in such cases where a rigid spool tube is used.

This consists of two layers of No. 14 B. & S.gauge cotton (or silk) covered copper magnet wire, and should be evenly and tightly laid on. For winding coils, a lathe is a most handy machine, or the spool can be mounted on a spindle and rotated by hand. It is not feasible here to give all details of coil-construction; reference should be made to the many excellent works on the subject. The two ends are brought out through holes in the spool ends, as indicated for the simple primary coil before described. After winding, the wire is to be well basted with melted paraffin wax until it is saturated, any excess being scraped off so as to leave a smooth cylindrical surface for the secondary coil. Half a dozen turns of stout paper or oiled silk is now to be wound on, and enough paraffin wax added to leave an insulation at least one-quarter of an inch around the outside of the winding. The right-hand end of spool, where the end was not attached, will require a little care that the wire does not run off; but, as only two layers are to be wound, it is an easy thing to do.

When the primary coil is finished off, cut three pieces of hard rubber four inches square, with a central hole just big enough that theymay be slipped on over the primary coil to form divisions into which the secondary wire goes. These can be fixed equal distances apart by means of removable wooden blocks, which are taken off as each section is wound.

The secondary coil consists of about 2-1/2 pounds No. 36 B. & S. gauge silk or cotton-covered magnet wire, wound evenly in layers in the sections on the primary coil. Before any wire goes into a section, it must be seen that the division fits tight to the primary coil. It will be best to pour around the coil some melted paraffin wax so as to form an insulating ring, and prevent any possibility of the spark creeping under the section division into the next. The actual operation of winding presents no difficulty other than those of keeping the wire from damage and getting as even layers as possible. If each layer is separated from its neighbor by a strip of paraffined paper, it makes even winding easier, and better insulation. As to the insulating of the secondary coil, it can be done in a variety of ways. The coil can be soaked in moltenparaffin until saturated, or the wire can be made to pass through a dish of molten paraffin while on its way from the wire reel to the coil. In the latter case the wire must be guided by means of glass rollers, as the wax would harden rapidly if touched by the fingers. In connecting up the sections, the similar ends are to be joined; that is, the inside ends to inside ends, and outside ends to outside ends, as per diagram (Fig. 45). This will bring two outside ends free for attachment to binding posts. Fig. 46 shows direction of winding and connecting the two middle coils,A Cbeing the inside layers next to primary andB Dthe outside layers.

Fig. 45.

An outside coat of paraffin wax is now given to the coil and a wrapping of waxedpaper laid on. Then, if desired, a cover of sheet-rubber or a layer of cloth can be put on over all, to finish the job.

Fig. 46.

The base for a Ruhmkorff coil generally resembles an oblong shallow box. The coil is mounted on the lid, and the condenser inside the box, the connections being made on the lower side of the lid. It is preferable, except for appearance’ sake, to make all connectionsoutside the box, but this is left to the worker’s choice.

Fig. 47.

The Condenseris made up of 70 sheets of tinfoil each about 4 inches by 7-1/2, and 80 sheets of clean white paper 5 by 8 inches placed alternately, and saturated with paraffin wax. The tinfoil sheets are laid so that about 1/2 inch projects out of the paper sheets at each end, the alternate sheets coming out at the same end, and the projecting pieces being bent together gives the effect of a pair of tinfoil sheets insulated from each other, aggregating the sum of all the small ones.

Fig. 48.

The coil can now be attached to the base by means of screws passing through the lid into the coil ends. If a vibrating contact breaker be desired, reference to Fig. 44 will show method of connection. Fig. 47 shows details of a contact breaker of similar design.Ris hammer head of soft iron,Sa spring about thickness of clock spring and 3/8 inch wide or more.Bis contact point, both spring and adjustment screwAbeing fitted with platinum contacts.Cis a check nut, to holdAfrom turning.Iis an adjustment to tighten orloosen springS, by means of a lug which it carries on its shaft. It is well insulated from pillar carryingA, by the hard rubber bushing,I.

The condenser is laid in the box under the coil and attached as in Fig. 44; that is, one set of sheets to the contact pillar, and the other set to the adjustment screw.

For gas-lighting work, it is generally preferable to use a contact or strap key (Fig. 48), instead of a vibrator. The key can be mounted on coil base, in which case the condenser will be attached in same manner as for the vibrator.

Before entering into a description of the various batteries used in electric gas lighting, it will be well to briefly consider a few simple electrical rules bearing upon the subject.

A current of electricity haselectromotive force, ordifference of potentialfigured involts, andcurrentfigured inamperes.

For example we will use thewateranalogy (Fig. 49). Two tanks,AB, on the same level, are connected by a pipeC.

Supposing tankAbe filled with water and the pipe,C, to be opened; the water will flow alongCintoBuntil the level in each tank is equal. So long as there is a difference of level, there will be a pressure inC, owing to the water behind it.

Replacing the tanksAandBby unequally electrified bodies, and the pipeCby a conductor of electricity, the flow of water is representedby the tendency of the electrified bodies to equalize themselves by a flow of current along the conductor,C.

To sum up: The difference of level is now difference of potential, the pounds pressure along the pipe being expressed as electromotive force involts.

Fig. 49.

The quantity of water flowing along the pipe is measured, as electricity, in amperes. As the quantity of water passing in a given time is regulated by the size of the pipe and its own pressure, so the quantity of electricity is also regulated. A conductor of electricity offers resistance to the flow of current according to its sectional area and the material of which it is composed, this resistance being expressed inohms. The greater the voltage and lower the resistance, the more current. Thislaw, and its kindred applications, are expressed as follows:

C = E/R.

Cis current in amperes,Eelectromotive force in volts, andRresistance in ohms.

Thus a wire with a resistance of 50 ohms would pass 2 amperes with an electromotive force of 100 volts. To find resistance when other two factors are known, the formula is

R = E/C.

In selecting a battery for work, regard must be made to the current required, and its period of flow. For energizing a gas lighting primary coil, the current must be large, but is only required occasionally, the battery standing idle for long periods. In this case the class called open circuit cells are preferable, as they contain no strong acids and do not deteriorate to any extent when not in use. Of such class is the Leclanche-Samson, Monarch, carbon cylinder, and most so-called dry cells. As the resistance in a conductoraffects the current flow, so it does in a battery cell; the internal resistance of a battery is determined by its size, proximity of the elements, etc. Cells with small zincs and porous cups are of high internal resistance, those with large sheet zincs and big carbon surfaces, of low internal resistance. As the primary coil used in gas lighting is never much over one ohm, a cell of low internal resistance should be selected. But as the wires leading to the burners must be taken into account, a number of cells should be used to produce enough electromotive force to overcome the added resistance. Now battery cells can be arranged in a variety of ways—in series for higher electromotive force, and in multiple—for greater current.

Fig. 50.

Fig. 50 represents the series arrangement; here the zinc of one cell is connected to the carbon of the next; this adds the electromotiveforces together and thus gives greater ability to overcome resistance, but it also adds together the resistance of each cell. Thus 4 cells, each 2 volts and of one-half ohm internal resistance, would, in series, have an E. M. F. of 8 volts and an internal resistance of 2 ohms, current 4 amperes. Fig. 51 shows four cells in multiple, the zinc of each cell and the carbons of each cell are connected. Here the result would be but 2 volts, but the internal resistance would be only one-quarter, viz: one-eighth of an ohm, current 16 amperes.

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