The Boy Electrician - Alfred Morgan

7/14/2019 The Boy Electrician - Alfred Morgan

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BOYE L E C T R I C I A N

Practical Plans for ElectricalApparatusfi?r workandplayjvitkan explanationOf the principles oferery-day electricity.

&JILFRED PMORGXN

With illustrations gy they author^

B O S T O NLOTHROR LEE & SHEPARD CO.

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nA B O Y ' S W I R E L E S S O U T F I T M A D E U P O F T H E A P P A R A T U S D E S C R I B E D I N C H A P T F .R X I V . T H E

J U N I O R D Y N A M O A N D A C O H E R E R O U T F I T C A N B E S E E N O N T H E L O W E R P A R T O F T H E T A B L E .


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COPYRIGHT, 1913, BY LOTHROP, LEE & SHEPARD COMPANYEntered at Stationers' Hall, London

Published, July, 1014

Allrightsreserved

THE BO Y ELECTRICIAN

Q., ": 1

liortoaofc tynsaBerwick & S m i t h Co.Norwood, M B S B . , U. S. A.

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TO THE SELF-RELIANT3SO0 of Smerlca,

OUR FUTURE ENGINEERS AND SCIENTISTS, THAN WHOMNONE IN THE WHOLE WORLD ARE BETTER ABLETO WORK OUT AND SOLVE THE PROBLEMS

THAT EVER CONFRONT YOUNGMANHOOD, THIS BOOKIS CORDIALLYDEDICATED.GV3


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INTRODUCTIONO N C E upon a time, and this is a true tale, a boy had a whole rail

road system for a toy . T he train ran auto m atically , propelled bytiny electric motors, the signals went up and down, the station wasreached, a bell rang, the train moved on again and was off on itsjourney around many feet of track to come back over the old route.

Th e boy viewed his gift with rap tured eyes, and then his facechanged and he cried out in the bitternes s of his disa pp oin tm ent:" But wha t do I do? " Th e toy was so elaborate th at the boy wasleft entirely ou t of the pla y. Of course he did no t like it . H is crytells a long story.

The prime instinct of almost any boy at play is to make and tocreate. He will make things of such m aterials as he has at ha nd , anduse the whole force of dream and fancy to create something out ofno thin g. Th e five-year-old will lay half a dozen wooden blocks to gethe r with a spool on one end and tell you it is a steam tra in . And itis. H e has bo th m ade and created an engine, which he sees bu t w hichyou don't, for the blocks and spool are only a symbol of his creation.Give his older brother a telephone receiver, some wire and bits ofbra ss, and he will make a wireless telegraph outfit and listen to asteamship hundreds of miles away spell out its message to the shore.

The wireless outfit is not a symbol, but something that you canboth hear and see in operation even though you may not understandth e whispering of the dots and dashes. And as soon as the m ysteryof this modern wonder more firmly grips your imagination, you per-

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v i I N T R O D U C T I O Nhaps may come to realize that we are living more and more in theage of electricity and mechanism. Elec tricity propels our trains , lightsour houses and streets, makes our clothes, cures our ills, warms us,cooks for us and performs an innumerable number of other tasks atthe tu rnin g of a little switch. A m ere list is impossible.

Almost every boy experiments at one time or another with electricity and electrical ap pa rat us . I t is my purpose in writing thisbook to open this wonderland of science and present it in a mannerwhich can be readily understood, and wherein a boy may " do somethin g." Of course there are other books with the same pur por t, bu tthey do not accomplish their end. Th ey are not prac tical. I cansay this because as a boy I have read and studied them and theyhave fallen far short of teaching me or my companions the thingsth a t we were seeking to learn. If they have failed in this re spect,they have done so perhaps not through any inability of the author,but from the fact that they have not been written from the boy'sstandpoint. They tell what the author thought a boy ought to knowbu t not wh at he really does wa nt to know. Th e ap pa ratu s describedtherein is for the most part imaginary. Th e au tho r tho ug ht it mightbe possible for a boy to build motors, telegraph instruments, etc.,out of old bolts and tin can s, b ut he never tried to do so himself.

The apparatus and experiments that I have described have beenconstructed and carried out by boys. Their problems and theirquestions have been studied and remedied. I hav e tried to presen tpractical matter considered wholly from a boy's standpoint, and toshow the young experimenter just what he can do with the toolsand materials in his possession or not hard to obtain.

To the boy interested in science, a wide field is open . Th ere is nobetter education for any boy than to begin at the bottom of the ladder an d climb the rungs of scientific know ledge, step by ste p. I t

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I N T R O D U C T I O N viiequips him with information which may prove of inestimable worthin an opportune moment.

There is an apt illustration in the boy who watched his motherempty a jug of molasses into a bowl and replace the cork. His m othertold him not to disturb the jug, as it was empty. He persisted, however, and turned the jug upside down. No more molasses came, butout crawled a fly. New developments in science will never cease.Invention will follow invention. The unexpected is often a valuableclue. The Edisons and Teslas of to-day have not discovered everything. There is a fly in the molasses, to be had by persistence. Inspiration is but a starting-p oint. Success means work, day s, nigh ts,weeks, and years.

There can be no boy who will follow exactly any directions givento him, or do exactly as he is told, of his own free w ill. He will " bolt"a t the first opportunity. If forced or obliged to do as he is directed,his action will be accompanied by a host of " whys." Therefore inpresenting the following chapters I have not only told how to makethe various motors, telegraphs, telephones, batteries, etc., but havealso explained the principles of electricity upon which they dependfor their operation, and how the same thing is accomplished in theevery-day world. In giving directions or in making cautions, I haveusually given the reason for so doing in the hope th a t this information may be a stimulant to the imagination of the young experimenterand a useful guide in enabling him to proceed along some of thestrange roads on which he will surely go.

ALFRED P. MORGAN.UPPER MONTCLAIR, N. J.

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C O N T E N TCHAPTER I

MAGNETS AND MAGNETISMPAGE

IThe Discovery of the Magnet The Origin of the Compass Experiments with Magnetism Artificial Magnets Making a Magnet Magnetic Poles M agnetic Force Compasses Magnetic Substances Attraction through Bodies Magnetic Induction TheLaws of M agnetic Attraction Lines of M agnetic Force The Magnetic Circuit The Earth a Great Magnet Magnetic Dip ADipping Needle The Uses of Magnets Preserving a Magnet.

CHAPTER IISTATIC ELECTRICITY

The Wonderful Amber The First Observation of Electricity Benjamin Franklin's Famous Kite Lightning and Electricity Electrical Induction Two Kinds of Electricity Conductors andInsulators Electrified Writing-Paper A Surprise for the Cat Frictional Electricity Electroscopes The Pith-Ball Electroscope The Gold-Leaf Electroscope Positive and Negative Electricity The Electrophorus An Electrical Frog-Pond.

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CHAPTER IIISTATIC ELECTRIC M ACHINES . . . .

A Cylinder Electric Machine Selecting the Bottle Mountingthe Bottle The Base The " Rubber " The Prime Conductor Using the Machine The Wimshurst Machine The Glass Plates The Sectors The Bosses The Frame The Uprights The

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CONTENTSP A G EDriving-Wheels The Collectors The Neutralizes Experimentswith an Electric Machine The Leyden Jar Igniting Gunpowder

The Electric Umbrella A Lightning Board The Electric Dance The Electric Whirl Lichtenberg's Figures.CHAPTER IV

CELLS AND BATTERIES 53Build your own Batteries first The Voltaic Cell How Electricityis made with Chemicals A Simple Cell Leclanche Cell Polarization Dry Cells How to m ake a Dry Cell Recharging DryCells Wet Batteries Carbon Plates Battery Elements B i chromate Batteries Handling Acid A Plunge Battery TheEdison - Lalande Cell A Tomato-Can Battery Secondary orStorage Batteries Connecting Cells Making a Storage Battery The Plates Forming the Plates Charging a Storage Battery Ampere Hours.

CHAPTER VELECTRO - MAGNETISM AND MAGNETIC INDUCTION 82Oersted's Experiment The Magnetic Field about a Wire CarryingCurrent Field of Force The Iron Core The Principle of anElectro - M agnet Electro - Magnets Handling Steel Rails withElectro-Magnets Magnetic Induction.*

CHAPTER VIELECTRICAL UNITS 92

The Units of Electrical Measure Measuring the Current TheAmpere The Volt Electro-motive Force The Ohm Ohm'sLaw The Watt The Electrical Horse-power The Kilowatt The Coulomb The Difference between Alternating and Direct Currents The Cycle The Alternation Frequency.CHAPTER VH

ELECTRICAL APPURTENANCES 100Wires Wire' Sizes Insulators Binding-Posts Switches andCut-Outs Home-made Switches Fuses Lightning-Arresters.

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CONTENTS xiCH AP T E R VI I I

P A G EELECTRICAL MEASURING INSTRUMENTS 116Meters A Simple Voltmeter and Ammeter A Portable Voltm eter and Am m eter Calibrating the Me ters Connecting theM eters Galvanoscopes and Galvanom eters Simple Galvanoscopes

Astat ic Galvanoscope Astat ic Galvanometer How to Mak e aWh eatstone Bridge Resistance-Coi l s How to Use a Wh eatstoneBridge for Measuring Resistance.C H A P T E R I X

BELLS , A LA R MS , A ND ANNUNCIATORS . . 140How to Build an Electric Bel l An Electric Alarm An Annunciator Push-Butto ns Bell System s A Burglar Alarm .

CH AP T E R XELECTRIC TELEGRAPHS 150

Th e First Telegraph Th e Principle of th e Telegraph Th e Ke y The Sounder How to Make a Simple Ke y and Sounder Connecting the Instruments A Complete Telegraph Set H o w t oBuild a Telegraph Relay Conne cting a Relay How to Learn toTelegraph Th e Alphabet O perating.

C H A P T E R X IMICROPHONES A ND TELEPHONES 170

Microphones How to Hear a Fly 's Foo ts tep Telephones Th e Principle of the Telephone The Telephone Transm itter TheTelephone Receiver How to Bui ld a Telephone Telephone Rece ivers A Hom e-made Telephone Receiver A Hom e-made Telephone Transm itter A Com plete Telephone Instrument A Desk-Stand Type of Telephone A Telephone Induct ion Coi l Connecting the Telephones.

C H A P T E R X I IINDUCTION C OI LS 194A Me dical Coil or Sh ock ing Co il Spark Coils Th e Principle ofthe Spark Coil Building a Spark Coil The Core Th e Primary

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xii CONTENTS The Secondary Winding the Secondary The Interrupter The Condenser Finishing the Coil Experiments with a Spark Coil Electrical Hands Geissler Tubes Ghost Light PuncturingPaper A Practical Joke An Electrified Garbage-Can Photographing an Electric Discharge Jacob's Ladder X-Rays TheTube The Fluoroscope Using the Outfit.

CHAPTER XIIIT R A N S F O R M E R S 221

How Alternating Current is Transmitted An Alternating CurrentSystem The Transformer Step-Up Transformers Step-DownTransformers An Experimental Transformer The Core TheWindings Arranging the Switches Connecting and Mounting theTransformer.CHAPTER XIV

WIR ELES S TELEGRAPHY 237The Principle of Wireless Telegraphy Wireless Waves A SimpleTransmitter Waves in the Ether The Action of the ReceivingStation How to Build Wireless Instruments The Aerial Typesof Aerials Erecting the Aerial The Ground Connection TheReceiving Apparatus A Tuning Coil A Loose Coupler TheJunior Loose Coupler Detectors A Crystal Detector " Cat-Whisker " Detectors The Fixed Condenser Telephone Receivers Connecting the Receiving Apparatus The Transmitting Apparatus The Spark Coil Small Spark-Gaps The Condenser A Helix An Oscillation Helix The Aerial Switch Connecting the Transmitting Apparatus The Continental Code A Coherer Outfit The Coherer The Decoherer Building a Relay Connecting andAdjusting the Apparatus.

CHAPTER XVA WIRELESS TELEPHONE a8i

The Principle of the Wireless Telephone Experiments illustratingthe Principle of the Wireless Telephone Building a Wireless Telephone Making the Coils The Strap-Key Connecting andOperating the Apparatus.

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CONTENTS xiiiCHAPTER XVI

P A G EELECTRIC MOTORS 289Thomas Davenport The First Electric Motor A Simple ElectricMotor The Simplex Motor The Armature Making the FieldMagnet The Bearings The Commutator Core The Base Assembling the Motor Connections How to Build a Larger Motor Cutting out the Laminations Winding the Motor.

CHAPTER XVIIDYNAMOS 301

The Difficulties of Building a Dynamo The Principle of the Alter- nator and the Direct-Current Dynamo Making a Magneto into aDynamo A 10-Watt Dynamo The Field The Armature The Commutator The Windings The Base The Bearings The Brushes Assembling and Completing the Dynamo.CHAPTER XVin

AN ELECTRIC RAILWAY 318A Toy Railway Car How to Make the Running Gear Installingthe Motor Testing the Car Making the Body How to Makethe Track Track Pattern s A Cross-over A Rail Connector Making the Car Reversible A Track Bumper A Design for a Railway Bridge A Design for a Railway Station.

CHAPTER XLXMINIATURE LIGHTING 334

What it may be used for Carbon Battery Lamps TungstenBattery Lamps Lamp Bases Sockets and Receptacles TheWires used for Miniature Lighting Switches Batteries Multiple Wiring Series Wiring Three-way Wiring Lamp Brackets A Hanging Lamp Small Dry Cells An Electric Hand-Lantern A Ruby Lantern A Night Lamp A Watch-Light An ElectricScarf-Pin.CHAPTER XX

MISCELLANEOUS ELECTRICAL APPARATUS 354How Electricity may be Generated by Heat The Energy of theSun Sun-Power Apparatus How to Build a Thermopile How

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xiv CONTENTSto M ake a Reflec toscope How to Reduce the n o - v . Cur ren t so th a tit may be used for Experimenting The Induc t ion M oto r A M oto rwi thout Brushes Al terna t ing-Curren t Power M otors Elec t ro lys is Electro-Plating Copper-Pla t ing Nickel -Pla t ing How to Makea Rheo sta t How to M ak e a Pole-Changing Swi tch Revers ing aSmall M oto r A com plete Wireless R eceiving Set Th e Tesla Coil High-Frequency Cu rren ts How to M ake a Tesla Coil Experi me nts wi th High-Frequency Curr en ts Conclus ion .

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L I ST O F H A L F - T O N E IL L U S T R A T I O N S(In addition to three hundred and twenty-three text illustrations )

A Boy's Wireless Outfit Made up of the Apparatus described in ChapterXIV FrontispieceFACING P A G E

A Double L ightning Discharge from a Cloud to the E arth . . . . 20Lifting-Magnets of the Type known as Pla te, Billet, and Ingot Magnets . 88An X-Ray Photograph of the Hand 220A Double-Slider Tuning Coil 260The Junior Loose Coupler 260A Crystal Detector 260An Oscillation Helix 270An Oscillation Condenser 270The Junior Dynamo, Mounted 316Complete Wireless Receiving Set, consisting of Double-Slider Tuning Coil,Detector, and Fixed Condenser 372Complete Wireless Receiving Set, consisting of a Loose Coupler in place of

Tuning Coil, Detector, and Fixed Condenser 372A Com plete Coherer Outfit, as described on page 274 378The Tesla High-Frequency Coil 378

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3 li ^k"CHAPTER I

MAGNETS AND MAGNETISM*tM0 j

OVER two thousand years ago, in far-away Asia Minor,a shepherd guarding his flocks on the slope of Mount Idasuddenly found the iron-shod end of his staff adhering toa stone. Upon looking further around about him he foundmany other pieces of this peculiar hard black mineral, thesmaller bits of which tended to cling to the nails and studsin the soles of his sandals.This mineral, which was an ore of iron, consisting of ironand oxygen, was found in a district known as Magnesia,and in this way soon became widely known as the " Magnes-stone," or magnet./*This is the story of the discovery of the magnet. I texists in legends in various forms. As more masses of th ismagnetic ore were discovered in various parts of the world,the stories of its attractive power became greatly exaggerated , especially during the M iddle Ages. In fact, magnetic mountains which would pull the iron nails ou t of ships,or, later, move the compass needle far astray, did not losetheir place among the terrors of the sea until nearly theeighteenth century.

For many hundreds of years the magnet-stone was of

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2 THE B O Y E L E C T R I C I A Nlittle use to mankind save as a curiosity which possessedthe power of attracting small pieces of iron and steel andother magnets like itself. Then some one, no one knowswho, discovered that if a magnet-stone were hung by athread in a suitable manner it would always tend to pointN orth and S outh; and so the " M agnes-stone " becam ealso called the " lodestone," or " leading-stone."

These simple bits of lodestone suspended by a threadwere the forerunners of the modern compass and were ofgreat value to the ancient navigators, for they enabledthem to steer ships in cloudy weather when the sun wasobscured and on nights when the pole-star could not beseen.The first real compasses were called gnomons, and consisted of a steel needle which had been rubbed upon alodestone until it acquired its magnetic properties. Then itwas thrust through a reed or short piece of wood whichsupported i t on the surface of a vessel of water. If theneedle was left in this receptacle, naturally it would move

against the side and not point a true position. Thereforeit was given a circular movement in the water, and as soonas it came to rest, the point on the horizon which the northend designated was carefully noted and the ship's courselaid accordingly.The modern mariners' compass is quite a different ar

rangem ent. It consists of three pa rts , the bowl, the card,and the needle. The bowl, which contains the card andneedle, is usually a hemispherical brass receptacle, sus-

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MAGNETS AND MAGNETISM 3pended in a pair of brass rings, called gimbals, in such amanner that the bowl will remain horizontal no matterhow violently the ship may pitch and roll. Th e card, whichis circular, is divided into 32equal parts called the pointsof the compass. The needles,of which there are generallyfrom two to four, are fastenedto the bottom of the card.In the center of the card isa conical socket poised on anupright pin fixed in the bottom of the bowl, so that thecard hanging on the pin turnsfreely around its center. Onshipboard, the compass is so placed that a black mark,called the lubber's line, is fixed in a position parallel to thekeel. The po int on the compass-card which is directlyagainst this line indicates the direction of the ship's head.

Experiments with MagnetismThe phenomena of magnetism and its laws form a veryimportant branch of the study of electricity, for they playan important part in the construction of almost all electrical apparatus.Dynamos, motors, telegraphs, telephones, wireless apparatus, voltmeters, ammeters, and so on through a practicallyendless list, depend upon magnetism for their operation.,

FIG. 1. The Card of a Mariners'Compass, Showing the " Points."

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4 THE BOY ELECTRICIANArtificial Magnets are those made from steel by the a p

plication of a lodestone or some other magnetizing force.The principal forms are theBar and Horseshoe, so called_ . , from their shape. The proc-FIG. 2. A Bar Magnet. c ress of making such a mag

net is called Magnetization.Small horseshoe and bar magnets can be purchased attoy-stores. They can be used to perform a num ber ofvery interesting and instructive experiments.Stroke a large darning-needle from end toend, always in the same direction, with oneend of a ba r magnet. Then dip th e needlein some iron filings and it will be found thatthe filings will cling to the needle. Theneedle has become a magnet.Dip the bar magnet in some iron filingsand it will be noticed that the filings clingto the magnet in irregular tufts near the ends, FlG; 3-T,A Horse~. shoe M agnet.with few if any near the middle.This experiment shows that the attractive power of awm-

SMUIU^O. X g i p f t j J : - ' BAR MAGNET

FIG. 4. A Magnetized Needle and a Bar Magnet whichhave been dipped in Iron Filings.

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MAGNETS AND MAGNETISM 5magnet exists in tw o opposite places. These are called thepoles.There exists between magnets and bits of iron and steela peculiar unseen force which can exert itself acrossspace.

The power with which a magnet attracts or repels another magnet or attracts bits of iron and steel is calledMagnetic Force. The force exerted by a magnet upon abit of iron is not the same a t all distances. The force isstronger when themagnet is near thei ron and weakerwhen it is farther

away.Place some smallcarpet-tacks on apiece of paper andhold a magnet abovethem. Gradua l ly

BAR MdOKCT

FIG. 5- The Lifting Power of a Bar Magnet. Itmust be brought closer to the nails than the tacksbecause they are heavier.

lower the magnet until the tacks jump up to meet it.Then try some nails in place of the tacks. The nails areheavier than the tacks, and it will require a greater forceto lift them . Th e magnet will have to be brought muchcloser to the nails than to the tacks before they are lifted,showing that the force exerted by the magnet is strongestnearest to it.Magnetize a needle and lay it on a piece of cork floatingin a glass vessel of water . I t will then be seen th a t the

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THE BOY ELECTRICIANneedle always comes to rest lying nearly in a north andsouth line, with the same end always toward the north.The pole of the magnet which tends to turn towards thenorth is called the

north-seeking poleand the opposite oneis called the south-seeking pole.The name is usually abbreviated tosimply the north andsouth poles. The north pole of a magnet is often indicatedby a straigh t line or a letter N stamped into the metal.

A magnetized needle floating on a cork in a basin ofwater is a simple form ofCompass. Figure 7 shows several other different ways

A Simple Compass.

, IIU n s \ "" ~. ~ * P 1 M ^ MAGNCTIZ

FIG. 7. Several Different M ethods of Making a Simple Compass.of making compasses. The first method is to suspend amagnetized needle from a fine silk fiber or thread.

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MAGNETS AND MAGNETISM 7The second method illustrates a very sensitive compass

made from paper. Two magnetized needles are stuckthrough the sides with their north poles both at the sameend . The paper support is mounted upon a third needlestuck through a cork.A compass which more nearly approaches the familiartype known as a pocket compass may be made from a small

piece of watch-spring or clock-spring.The center of the needle is annealed or softened by holding it in the flame of an alcohol lamp and then allowing itto cool.Lay the needle on a piece of soft metal such as copperor brass, and dent it in the center with a punch.Balance the needle on the end of a pin stuck through thebottom of a pill-box.Magnetic Substances are those which are attracted by amagnet. Experiment with a num ber of different m aterials,such as paper, wood, brass, iron, copper, zinc, rubber, steel,chalk, etc. I t will be found tha t only iron and steel arecapable of being attracted by your magnet. Ordinarymagnets at tra ct bu t very few substances. Iron, steel,cobalt, and nickel are about the only ones worthy of mention.Attraction through Bodies. A magnet will a tt ract a nailor a tack through a piece of paper, just as if nothingintervened.It will also attract through glass, wood, brass, and allother substances. Through an iron pla te, however, the

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8 THE BOY ELECTRICIAN

PANI Or O L A 5 3 .

FIG. 8. The Attraction of an IronNail through Glass.

attraction is reduced or entirely checked because the irontakes up the magnetic effect itself and prevents the forcefrom passing through and reaching the nail.

A number of carpet-tacks m aybe supported from a magnet inthe form of a chain. Each individual tack in the series becomes a temporary magnet byinduction.

If the tack in contact withthe magnet be taken in thehand and the magnet suddenly withdrawn, the tacks willat once lose their magnetism and fall apart.It will furthermore be found that a certain magnet willsupport a certain number of tacksin the form of a chain, but that if asecond magnet is placed beneath thechain, so th a t its south pole is underthe north pole of the original magnet, the chain may be lengthened bythe addition of several other tacks.

The reason for this is that the magnetism in the tacksis increased by induction.Magnets will Attract or Repel each other, depending uponwhich poles are nearest.Magnetize a sewing-needle and hang it from a thread.Bring the north pole of a bar magnet near the lower end of

BA R MMSNKT 1B*n MAANCT

FIG. 9. A Magnetic Chain.

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MAGNETS AND MAGNETISM 9the needle. If the lower end of the needle happens tobe a south pole it will be attracted by the north poleof the bar m agnet. If, on the other hand , it is a northpole, it will be repelled and you cannot touch it withthe north pole of the bar magnet unless you catch it andh61d it.

This fact gives rise to the general law of magnetism:Like poles repel each other and unlike poles attract each other.

FIG. 10. An Experiment Illustrating tha t Like Poles Repel EachOther and Unlike Poles Attract.

Another interesting way of illustrating this same law isby making a small boat from cigar-box wood and laying aba r magnet on it. Place the north pole of the ba r magnetin the bow of the boat.Floa t the boat in a basin of water. Bring the south poleof a second magnet near the stern of the boat and it will

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IO THE BOY ELECTRICIAN

S A S I N or

sail away to the opposite side of the basin. Present the n o r thpole of the magnet and it will sail back again.If the south pole of the magnet is presented to the bow

of the boat the little ship will followthe m a g n e t ailaround the basin.The repulsion ofsimilar poles may* be also illustratedby a number ofmagnetized sewing-needles fixed in small corks so that theywill float in a basin of water with their points down.

FIG. I I . A Magne t i c Boa t .

FIG. 12 . Repulsion between Similar Poles, Shown byFloat ing Needles .The needles will then arrange themselves in differentsymmetrical groups, according to their number.A bar magnet thrust among them will attract or repelthem depending upon its polarity.

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MAGNETS AND MAGNETISM * 11The upper ends of the needles should all have the same

polarity, that is, all be either north or south poles.Magnetism flows along certain lines calledLines of Magnetic Force. These lines always form closedpaths or circuits. The region in the neighborhood of amagnet through which these lines are passing is called thefield of force, and the path through which they flow is calledtheMagnetic Circuit. The paths of the lines of force can beeasily demonstrated by placing a piece of paper over a

FIG. 13. A Magnetic " Ph antom ," Showing the Field of Forceabout a Magnet.

bar magnet and then sprinkling iron filings over the paper,which should be jarred slightly in order that thefilingsmaybe drawn into the magnetic paths.The filings will arrange themselves in curved lines, diverging from one pole of the magnet and meeting again atthe opposite pole. The lines of force are considered as extending outward from the north pole of the magnet, curving

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FIG. 14. Magnetic Phantom showing the Lines of Force about a HorseshoeMagnet

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MAGNETS AND MAGNETISM 13around through the air to the south pole and completingthe circuit back through the magnet.Figure 14 shows the lines of force about a horseshoemagnet. I t will be noticed that the lines cross directlybetween the north and south poles.

The difference between the magnetic fields produced bylike and unlike poles is shown in Figure 15.A study of this illustration will greatly assist the mind in

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FIG. 15. Lines of Force between Like and Unlike Poles.conceiving how attraction and repulsion of magnetic polestake place.It will be noticed the lines of force between two northpoles resist each other and meet abruptly at the center.The lines between a north and a south pole pass in regularcurves. -The Earth is a Great Magnet. The direction assumed bya compass needle is called the magnetic meridian.The action of the earth on a compass needle is exactlythe same as tha t of a permanent magnet. The fact tha t amagnetized needle places itself in the magnetic meridianis because the earth is a great magnet with lines of forcepassing in a north and south direction.

The compass needle does not generally point exactlytoward the true N or th. This is because the magnetic pole

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1 4 THE BOY ELECTRICIANof the earth toward which the needle points is not situatedat the same place as the geographical pole.Magnetic Dip. If a sewing-needle is balanced so as to beperfectly horizontal when suspended from a silk threadand is then magnetized, it will be found th at it has lost i t sbalance and that the north end points slightly downward.

This is due to the fact that the earth is round and thatthe magnetic pole which is situated in the far North istherefore not on a horizontal linewith the compass, but below sucha line.

A magnetic needle mounted soas to move freely in a verticalplane, and provided with a scalefor measuring the inclination, iscalled aDipping Needle. A'dipping needlemay be easily made by thrustinga knitting-needle through a corkbefore it has been magnetized.A second needle is thrust through at right angles to thefirst and the arrangement carefully balanced, so that it willremain horizontal when resting on the edge of two glasses.Then magnetize the first needle by stroking it with a barmagnet. When it is again rested on the glasses it will befound th at the needle no longer balances, but dips downw ard.Permanent Magnets have a number of useful applicationsin the construction of scientific instruments, voltmeters,

FIG. 16. A Simple DippingNeedle.

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M A G N E T S AND M A G N E T I S M 15ammeters, telephone receivers, magnetos and a number ofother devices.In order to secure a very powerful magnet for some purposes a number of steel bars are magnetized separately, andthen riveted together. A magnet made in this way is calleda compound magnet, and may have either a bar or a horseshoe shape.

Magnets are usually provided with a soft piece of ironcalled an arma ture or " keeper." The " keeper " is laidacross the poles of the magnet when the latter is not in useand preserves its magnetism.A blow or a fall will disturb the magnetic arrangement ofthe molecules of a magnet and greatly weaken it. The mostpowerful magnet becomes absolutely demagnetized at ared heat, and remains so after cooling.Therefore if you wish to preserve the strength of a magnetic appliance or the efficiency of any electrical instrumentprovided with a magnet, do not allow it to receive roughusage.

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CHAPTER IISTATIC ELECTRICITY

I F you take a glass rod and rub it with a piece of flannelor silk, it will be found to have acquired a property whichit did not formerly possess: namely, the power of attractingto itself such light bodies as dust or bits of thread a n dpaper.

Hold such a rod over some small bits of paper and watchthem jump up to meet it, just as if the glass rod werea magnet attracting small pieces of iron instead ofpaper.' The agency at work to produce this mysterious power iscalled electricity, from the Greek word " Elektron," which

means amber. Amberwas the first substancefound to possess thisproperty.

The use of amberbegins with the dawnof civilization. Am berbeads have been foundFIG. 17. An Electrified Glass Rod will Attrac t in t h e r o y a l t o m b s a tMycenae and at vari-

16Small Bits of Paper.

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S T A T I C E L E C T R I C I T Y 17ous places throughout Sardinia, dating from at least twothousand years before our era.Amber was used by the ancient world as a jewel and fordecoration.The ancient Syrian woman used distaffs made of amberfor spinning. As the spindle whirled around it often rubbedagainst the spinner's garments and thus became electrified,as amber always does when it is rubbed . Then on nearingthe ground it drew to itself the dust or bits of chaff or leaveslying there, or sometimes perhaps attracted the fringe ofthe clothing.

The spinner easily saw this, because the bits of chaffwhich were thus attracted would become entangled in herthread unless she were careful. The amber spindle was,therefore, called the " ha r pa ga " or " clu tcher," for itseemed to seize such light bodies as if it had invisible talons,which not only grasped but held on.

This was probably the first intelligent observation of anelectrical effect.In the eighteenth century, when Benjamin Franklinperformed his famous kite experiment, electricity was believed to be a sort of fiery atmospheric discharge whichcould be captured in small quantities and stored in receptacles such as Leyden jars.Franklin was the first to prove that the lightning discharges taking place in the heavens are electrical.The story of his experiment is very interesting.He secured two light strips, of cedar wood, placed cross-

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18 T H E B O Y E L E C T R I C I A Nwise and covered with a silk handkerchief for a ki te . Tothe top of the upright stick of the kite was fastened a sharpwire about a foot long. The twine was of the usual kind,but was provided with a short piece of silk ribbon and akey. The purpose of the ribbon was possible protectionagainst the lightning running through his body, silk beinga " non-conductor," as will be explained a little farther on.The key was secured to the junction of the silk ribbonand the twine, to serve as a convenient conductor fromwhich to draw the sparks if they came. He did not haveto wait long for a thunderstorm, and as he saw it gatheringhe went out with his son, then a young man twenty-twoyears of age. The great clouds rolled up from the horizon,and the gusts of wind grew fitful and strong. The kite felta swishing blast and began to rise steadily, swooping thisway and tha t as the breeze caught it. The thunder m uttered nearer and nearer and the rain began to patter on thegrass as the kite flew higher.

The rain soon began to fall heavily, compelling Franklinand his son to take refuge under a near-by shed. The heavykite, wet with water, was sailing sluggishly when suddenlya huge low-lying black cloud traveling overhead shot fortha forked flame and the flash of thunder shook the very-earth. The kite moved upward, soaring straight intothe black mass, from which the flashes began to comerapidly.Franklin watched the silk ribbon and the key. Therewas no t a sign. H ad he failed? Suddenly the loose fibers

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S T A T I C E L E C T R I C I T Y 19of the twine erected themselves. The moment had come.Without a tremor he advanced his knuckle to the key.And between his knuckle and the key passed a spark! thenanother and another. They were the same kind of littlesparks th at he had made hundreds of times with a glasslube.

And then as the storm abated and the clouds swept offtowards the mountains and the kite flew lazily in the blue,the face of Franklin gleamed in the glad sunshine. Thegreat discovery was complete, his name immortal.

The cause of lightning is the accumulation of the electriccharges in the clouds, the electricity residing on the surfaceof the particles of water in the cloud. These charges growstronger as the particles of water join together and becomelarger. As the countless multitude of drops grows larger andlarger the " potential" is increased, and the cloud soon becomes heavily charged.

Through the effects of a phenomenon called indtiction,and which we have already stumbled against in the experiment with the tacks and the magnetic chain, the forceexerted by the charge grows stronger because of a chargeof the opposite kind on a neighboring cloud or some objecton the earth beneath. These charges continually striveto burst across the intervening air.

As soon as the charge grows strong enough a vivid flashof lightning, which may be from one to ten miles long, takesplace. The heated air in the path of the lightning expandswith great force; but immediately other air rushes in to

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20 THE BOY ELECTRICIANfill the partia l vacuum , thus producing the terrifying soundscalled thunder.In the eighteenth century, electricity was believed to bea sort of fiery atmospheric discharge, as has been said.Later it was discovered that it seemed to flow like waterthrough certain mediums, and so was thought to be a fluid.Modern scientists believe it to be simply a vibratory motion, either between adjacent particles or in the ether surrounding those particles.

It was early discovered that electricity would travelthrough some mediums bu t not through others. Thesewere termed respectively " conductors " and " non-conductors " or insulators. M etals such as silver, copper, gold,and other substances like charcoal, water, etc., are goodconductors. Glass, silk, wool, oils, wax, etc., are nonconductors or insulators, while many other substances,like wood, marble, paper, cotton, etc., are partial conductors.

There seems to be two kinds of electricity, one called" static " and the other " curren t " electricity. The formeris usually produced by friction while the latter is generatedby batteries or dynamos.

A very simple and well-known method of generatingstatic electricity is by shuffling or sliding the feet overthe carpe t. Th e body will then become charged, and if theknuckles are presented to some metallic object, such as agas-jet or radiator, a stinging little spark will jump out tomeet it.

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From the author's " Wireless Telegraphy and Telephony," by permission.A D O U B L E L I G H T N I N G D I S C H A R G E F B O M A C L O U D TO T H E E A R T H .


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S T A T I C E L E C T R I C I T Y 21The electricity is produced by the friction of the feet

sliding over the carpet and causes the body to becomeelectrified.Warm a piece of writing-paper, then lay it on a woodentable and rub it briskly with the hand. I t soon will becomestuck to the table and will not slide along as it did at first.If one corner is raised slightly it will tend to jump right

back. If the paper is lifted off the table it will tend to clingto the hands and the clothing. If held near the face itwill produce a tickling sensation. All these things happen

FIG. 19. A Piece of D ry Writing-Paper m ay be Electrifiedby Rubbing.

because the paper is electrified. I t is drawn to the otherobjects because they are neutral, that is, do not possess anelectrical charge.All experiments with static electricity perform better inthe winter time, when it is cool and clear, than in the summ er. The reason is that the air in winter is drier than insummer. Summer air contains considerable moisture andwater vapor. W ater vapor is a partial conductor of electricity, and the surrounding air will therefore conduct the

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2 2 THE BOY ELECTRICIANstatic electricity away from your apparatus almost as fastas it can be produced in the summer time.Some day during the w inter time, when it is cool and clear,and the cat is near a fire or a stove, stroke the cat rapidlywith the hand . The fur will stand up towards the handand a faint crackling noise will be heard . The cracklingis caused by small sparks passing between the cat and the

FIG. 20. A Surprise for the Cat.hand . If the experiment is performed in a dark room, thesparks may be plainly seen. If you present your knuckleto the cat's nose a spark will jump to your knuckle andsomewhat surprise the cat.

If the day is brisk and cool, so that everything outside isfrozen and dry, try combing the hair with a rubber comb.Your hair will stand up all over your head instead of lying

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STATIC^ ELECTRICITY 23down flat , and the faint crackling noise, showing thatsparking is taking place as the comb passes through thehair , will be plainly hea rd. T he electr icity is pr od uc ed bythe fr ict ion between the hair and the comb.

Electr ici ty may be produced by fr ict ion between a number of sub stan ces . A ha rd rub be r rod, a glass rod, a rub be rcomb or a stick of sealing-wax may be very easily electrified by rubbing them briskly with a piece of dry, warmflannel.

Electroscopes are devices for detecting the presence ofstat ic electr ici ty.

A very simple form of electroscope may be made in muchthe same manner as the paper compass described in the

^ ' l " 1 1 ' " " ^ P A P E RFIG. 21. A Paper Electroscope.

last ch apte r . I t m ay be cut ou t of wri t ing-paper an dm ou nt ed on a pin stuck thro ug h a cork. If an electrifiedrod is held near the electroscope i t may be made to whirlaro un d in the same m ann er as a compass needle when a ba rmagnet is brought to i t .

The Pith-Ball Electroscope is a very simple device, inwhich a ball of cork or elder pith is hung by a fine silkthr ea d from a n insulated sup port . A sui table electroscope

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24 THE BOY ELECTRICIANmay be made from a glass bottle having a piece of wire th rustinto the cork to support the pith ball. When the electrified rod is presented to the pith ball, it will fly out towardsthe rod.

If the pith ball is permitted to touch the glass rod, thelatter will transfer some of its electricity and charge theball. Almost immediately the pith ballwill fly away fromthe glass rod, andno matter how nearthe rod is brought,it will refuse to betouched again.This a c t i o n ismuch the same asthat of the magnetized n e e d l e suspended from a thread when the similar pole of the magnetis presented to it.When the rod is first presented to the pith ball, the latteris neutral and does no t possess an electrical charge. Whenthe rod has touched the ball, however, some of the electricity from the rod passes to the ball, and after this they willrepel each other.

The reason is that the rod and the ball are similarlycharged and similarly charged bodies will repel each other.If you are a good observer you might have noticed when

FIG. 22. A Pi th- Ba ll Electroscope.

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STATIC ELECTRICITY 25

FIG. 23. A Double Pith-Ball Electroscope.

experimenting with an electrified rod and the small bits ofpaper, tha t some of the little papers were first at tracted andflew upwards to therod, bu t having oncet o u c h e d it, w erequickly repelled.

The repulsion between two similarlye lec t r i f i ed bod iesmay be shown by adouble electroscope.A double electroscope is made byhanging two pithballs on two silk threads from the same support.Electrify a glass rod and touch it to the pith balls. They

will imm ediately fly apa rtbecause they are electrified with the same kindof electricity.The Gold-leaf Electroscope is one of the mostsensitive means whichcan be employed to detect small amounts ofstatic electricity.It is a very simple in-A couple of

GL TUBE

GOLDLEAF

FIG. 24. A Gold-Leaf Electroscope.strument and is easily made in a short time

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26 THE BOY ELECTRICIANnarrow strips of the' thinnest tissue paper, or, better still,two strips of gold leaf, are hung from a support in a wide-mouthed glass bottle which serves at once to insulate andprotect the strips from draughts of air.

The mouth of the jar is closed by a plug of paraffin wax,through the center of which passes a small glass tube. Astiff copper wire passes through the tube. The lower end ofthe wire is bent at right angles to furnish support for thestrips of gold leaf. A round sheet metal disk about the sizeof a quarter is soldered to the upper end of the rod.

If an electrified stick of sealing-wax or a glass rod is presented to the disk of the electroscope, the strips will repeleach other very strongly. If the instrument is sensitive,the strips should begin to diverge some time before the rodreaches the disk. It is possible to make an electroscope sosensitive that chips formed by sharpening a pencil willcause the strips to diverge.There are two kinds of static electricity. Rub a glassrod with a piece of silk and then suspend it in a wire stirrupas shown in Figure 25. Excite asecond rod also with a piece ofsilk and bring it near one end ofthe suspended one. The suspendedrod is repelled and will swing awayfrom the one held in the hand.

Now rub a stick of sealing-waxwith a piece of flannel until thesealing-wax is electrified. Then

FIG. 25.Method of Suspending an Electrified Rod in aWire Stirrup.

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STATIC ELECTRICITY 27bring the stick of sealing-wax near the end of the suspendedrod . The rod will be attracted to the sealing-wax.If you experiment further you will find that two sticksof sealing-wax will repel each other.This experiment indicates that there are two kinds ofelectrification: one developed by rubbing glass with silk

C L A S S nao

G L A S S ROD

S E A L I N G W A X

FIG. 26. Similarly Electrified Bodies Repel Each Other. D i s - 'similarly Electrified Ones Attract Each Other.and the other developed by rubbing sealing-wax withflannel.In the first instance, the glass rod is said to be positivelyelectrified, and in the latter case the sealing-wax is negatively electrified.

The same law that applies to magnetism also holds truein the case of static electricity, and similarly electrifiedbodies will repel each other and dissimilar ones attract.The Electrophoms is an instrument devised by Volta in1775 for the purpose of obtaining static electricity.

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28 THE BOY ELECTRICIAN

FIG. 27. The Electrophorus.

It is easily constructed and will furnish a source of electricity for quite a num ber of interesting experiments. Anelectrophorus consists of two parts, a round cake of resinous material cast ina metal dish or pan,and a round metaldisk which is pro

vided with an insulating handle.To make an electrophorus, first procure an old cake orpie tin , and fill it with bits of resin or sealing-wax. Placethe pan in a warm spot upon the stove where the resin willmelt, taking care not to overheat or it will spatter and possibly take fire. As the resin melts, add more until the panis nearly full. When all is melted, remove from the fire an dset it away where it may cool and harden in the pan without being disturbed.Cut a circular disk out of sheet tin, zinc, or copper, ma

king the diameter about two inches less than that of thepie pa n. Solder a small cylinder of tin or sheet brass tothe center of the disk to aid in supporting the handle. Thelatter is a piece of glass tubing about three-quarters of aninch in diameter and four or five inches long, placed in thecenter of the cylinder and secured with molten sealing-wax.In order to use the electrophorus the resinous cake mustfirst be beaten or briskly rubbed with a piece of warm

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STATIC ELECTRICITY 2Qwoolen cloth or flannel. Then place the disk on the cakeholding the insulating handle w ith the right hand. Touchthe cover or the disk momentarily with the forefinger ofth e left hand . After the finger is removed, raise the diskfrom the cake by picking it up with the glass insulatinghandle. The disk will now be found heavily charged withpositive electricity, and if the knuckles are presented tothe edge, a spark will jump out to meet them.

The cover may then be replaced, touched, and once moreremoved. I t will yield any num ber of sparks, the resinous

E L E C T R O P H O R U S

FIG. 28. An Electric Frog-Pond.cake only needing to be recharged by rubbing once in a longwhile.

An Electric Frog-Pond may be experimented with bycutting out some small tissue-paper frogs. M oisten thema little and lay them on the cover of the electrophorus.Touch the electrophorus with the finger and then raise itw ith the insulating hand le. If the " frogs " are not too wetthey wifl jump from the cover upon the table as soon as thecover is raised.

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I t ICHAPTER II I

STATIC ELECTRIC MACHINES

A Cylinder Electric MachineTHE electrophorus described in the last chapter is capable

of furnishing sufficient electricity for many interesting experiments, but for the purpose of procuring larger suppliesof electricity, a static electric machine is necessary.An electric machine is composed of two parts, one forproducing the electricity by the friction of two surfacesrubbing against each other, and the other an arrangement

for collecting the electricity thus formed.The earliest form of electric machine consisted of a ballof sulphur fixed upon a spindle which could be rotatedby means of a crank. When the dry hands were pressedagainst the sulphur by a person standing on a cake ofresin, which insulated him, sparks could be drawn fromhis body.Later a leather cushion was substituted for the hands, anda glass cylinder for the ball of sulphur, so that the frictionalelectric machine now consists of a cylinder or a disk of glassmounted upon a horizontal axis capable of being turned bya handle. A leather cushion, stuffed w ith horsehair andcovered with a powdered amalgam of zinc or tin, pressesagainst one side of the cylinder. A " prime " conductor in

3o

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STATIC ELECTRIC MACHINES 3 1

l l J O f

RueeesCOLLECT

the shape of an elongated cylinder presents a row of finemetal spikes, like the teeth of a rake, to the opposite side.A flap of silk attached to the leather cushion passes overthe cylinder and covers the upper half.

When the handle of the machine is turned, the frictionproduced between the leather cushion and the glass generates a supply of positive electricity on the glass, which iscollected, as the cylinder revolves, bythe row of sharppoints, and transferred to the primeconductor.The first thing required in the construction of an electric machine is alarge glass bottle having a capacity of from two to fourquarts.The insulating power of glass varies considerably. Com

mon green glass (not white glass colored green by copper,but glass such as the telegraph insulators are made from)generally insulates the best. Some sorts of white glass, theBohemian especially, are good insulators, but this qualitywill not usually be found in ordinary bottles.Select a smooth bottle which has no lettering embossed

upon it, and stand it upon a piece of white paper. Traceon the paper a line around the circumference of the bottle

FIG. 29. Fron t View of a Cylinder ElectricMachine.

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32 THE* BOY ELECTR ICIANso th a t the circle thus formed is of the same size as th ebottom of the bo ttle. Lay a carpenter's square on thecircle so that the point C just touches the circumference.Draw a line from A to B where the sides of the square cut

P A P E RFIG. 30. M etho d of Findin g th e Ce nter of a Circle .

the circumference. The point in the middle of this line isthe center of the circle.Place the paper on the bottom of the bottle so that thecircle coincides with the circumference, and mark the centerof the bottle.The bo ttle must now be drilled. This is accomplishedwith a small three-cornered file, the end of which has beenbroken off so as to form a ragged cu tting edge. The file is

set in a brace and used like an ordinary drill. During theboring process the drill must be frequently lubricated with

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STATIC ELECTRIC MACHINES 33a mixture of gum camphor and turpen tine . The drilling,which will require alm ost an hour before the glass is pierced,if the bottle is a thick one, should be performed slowly andcarefully, so as to avoid all danger of cracking the glass.The hole, when finished, should be from one-quarter tothree-eighths of an inch in diameter.

After the hole has been bored, fit a wooden plug into theneck of the bottle and cement it there with a mixture composed of one-half a pound of resin, five ounces of beeswax,one-quarter of an ounce of plaster of Paris, and three-quarters of an ounce of red ocher, melted together over amoderately warm stove. D ip the plug in the molten cementand force it into the neck of the bo ttle. When the cementdries it w ill be impossible to remove it.The sizes of bottles vary, so that it is quite impossible togive dimensions which m ust be closely followed in constructing the machine. Those in the text are approximate. Th edrawings have been made to scale so as to show the proportions the parts bear to each other.A heavy wooden base will be required to mount the

machine on. Two uprights are mounted on the base tosupport the axis of the bott le. Through one of these borea hole of the same diameter as the wooden plug fitted inthe neck of the bottle . Th e end of the wooden plug projecting through the upright is notched and fitted with acrank so th a t the bo ttle m ay be revolved. Th e handle ofthe crank is an ordinary spool having one flange cut off andmounted with a screw and a washer.

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34 THE BOY ELECTRICIANThe machine is now ready for the " rubber " and " primeconductor." The rubber is a piece of wood one inch squareand from six to eight inches long. A piece of undressedleather is tacked on as shown in the illustration and stuffed

with horsehair. The wood isshellacked and covered with tinfoil previous to tacking on theleather. A strip of wood, twoinches wide and one-half an inchthick, is fastened to the backof the rubber. The strip shouldbe just long enough so th at whenthe lower end rests on the basethe rubber is level with the axisof the bottle . The lower endmay be fastened to the base bymeans of a small brass hinge.

FIG. 31. The "R ubb er." _ , , , ,Two rubber bands stretch fromhooks between the rubber and the base so as to pull theformer tigh tly against the bo ttle. The illustration showsa method of mounting the rubber on a foot-piece held tothe base with a thumb-nut so that it may be slid back andforth and the pressure varied at will.The prime conductor is formed from a piece of curtain-pole two inches in diameter and eight inches long. Theends are rounded with a rasp and then smoothed with sandpaper. The whole surface is then shellacked and covered witha layer of tinfoil. The heads of a number of dressm aker's

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STATIC ELECTRIC MACHINES 35pins are cut off, and the pins forced into th e side of the primeconductor with a pair of pincers. They should form a rowlike the teeth of a rake about three-eighths of an inch apart.A hole is bored in the center of the under side of the primeconductor to receive a glass rod one-half inch in diameter.A second hole of the same size is bored in the base in such aposition that when the glass rod is in place, the teeth onthe prime conductor are on a level with the axis of thebottle, and their points about 3-32 of an inch away fromthe glass. The glass rod must be used in order to insulatethe prime conductor and prevent the escape of the electric ity . I t is secured with someof the cement described on page33. A piece of water-gaugeglass may be used in place of aglass rod.

A strip of oiled silk, or in itsplace a strip of silk which hasbeen shellacked, eight or nineinches wide, and long enoughto reach half-way around the bottle, is tacked to the rubber so that the silk covers the upper half of the cylinderand comes over to within one-quarter of an inch of thesteel points.The machine is now complete, and when the handle isturned rapidly, you will be able to draw sparks from theprime conductor. The sparks will probably be very short,

FIG. 32.The Pr ime Conduc to ror Collector.

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36 TH E BOY ELECTRICIANabout one-half of an inch long. These can be increased ,however, to three inches, if the glass is of the right quality,by treating the rubber with amalgam.

The amalgam is formed by melting one ounce of tin andadding to it one ounce of zinc in small bi ts. As soon a sthe zinc has also melted add to the mixture two ounces ofmercury which has been previously warm ed. Be carefulnot to inhale any of the vapor during this operation. Pou rthe mixture into a vessel of cold water, which will reducethe metal to small grains. Pour off the water and grindthe amalgam to a powder by pounding the grains with ahammer.

The leather rubber should be thinly smeared with lardand the powdered amalgam rubbed on it.In order to obtain the greatest effect from an electricmachine, it must be carefully freed from dust and particlesof amalgam adhering to the glass, and the insulating columnrubbed w ith a warm woolen cloth. The best results areobtained by placing the machine near a stove or radiatorwhere it is warm.

A Wimshurat MachineThe Wimshurst Machine consists of two varnished glassplates revolving in opposite directions. On the outside ofeach of these plates are cemented a number of tinfoil" sectors," arranged radially. Two conductors a t rightangles to each other extend obliquely across the plates, one

at* the back and the other a t the front. These conductors

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o

.GLASS CYLINDER O I L E D SILK

COLLECTOR

SPARK BALL

REAR UPRIGHT

FIG. 33. The Com plete Cylinder Electric Machine.

HANDLE

FRONT UPRIGHT


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38 THE BOY ELECTRICIANeach terminate in brushes of tinsel which electrically excitethe " sectors " as the plates revolve. The elec tricity iscollected by a set of " collectors " arranged in a somewhatsimilar manner to the collector on the cylinder electricmachine.The Glass Plates are each eighteen inches in diameter.Purchase two panes of clear glass twenty inches square

FIG. 34. Paper Pattern for laying out the Plates.from a glass dealer. The white glass is far preferable to thegreen glass and will make the best electric machine. Theplates should be of the thickness known as " single light "and should be perfectly free from wavy places, bubbles, orother imperfections.

The work is first laid out on a piece of stiff paper twenty

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STATIC ELECTRIC MACHINES 39inches square as a p at te rn . De scribe a circle four inches indiam eter. Using the same center , draw other circles , m akingthem respectively eight, sixteen, and eighteen inches indiam eter. T he n ma rk sixteen radial l ines, from the center ,making them equal dis tances apart , as shown in Figure 34.

P L A T E S E C T O R ;FIG. 35. Plate w ith Sectors in Position, and a Pa ttern for the Sectors.Lay one of the glass panes over the pat tern and cut out aglass circle eighteen inches in diameter, or perhaps you maybe able to have a glazier do the cutt ing for you and so saveconsiderable trouble an d possible bre ak age . Tw o suchplates should be made.

The Sectors are cut from heavy flat tinfoil according to

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4o THE BOY ELECTRICIANthe pattern shown in Figure 35. They should be made oneinch and one-half wide at the wide end and three-quartersof an inch at the other end. They are each four incheslong. Th irty-two such sectors are required. The easiestway to make them is to cut out a pattern from heavy cardboard to serve as a guide.

Clean and dry both of the glass plates very carefully andthen give them each two thin coats of white shellac. Afterthey have been dried, lay one of the plates on the paperpattern so that the outside of the plate will coincide withthe largest circle on the paper.

Then place a weight in the center of the plate so that itwill not move, and stick sixteen of the tinfoil sectors on theplate with thick shellac. The sectors are arranged sym metrically on the plate, using the eight-inch and sixteen-inchcircles and th e radial lines as guides. Both pla tes shouldbe treated in this manner. Each sector should be carefully pressed down on the glass, so that it will sticksmoothly withou t air-bubbles or creases. When all thesectors are in place the plates will appear like that shownin Figure 35.

The Bosses will have to be turned out at a wood-workingmill or a t some place where they have a turning-lathe. Thebosses are four inches in diameter at the large end and oneinch and one-half at the other. A groove is turned nearthe small end of each to accommodate a round leatherbelt.A hole should be made in each boss about half-way

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STATIC ELECTRIC MACHINES-^ :.; /;.. :.; *


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*/: : T3HE BOY ELECTRICIAN,-. .XheYglue^must now. bejkept in the dark, for sunlight will"i *t"-''th6'glue:so.t&3t:it:becomes insoluble.: The-jFrape: of "*the machine is composed of two stripstwfirity'five*inched'long, three inches wide, and an inch and

FIG. 37. The Frame.one-half in thickness, and two cross-pieces of the samethickness and width fifteen inches long.

Notches are cut at both sides of the base to admit thefeet of the uprights.

The Uprights are seventeen inches long, three inches wide,and one and one-half inches thick.

The notch at the foot is cut the same width as the thickness of the long members of the frame and is arranged so

that when fitted inplace, the foot of theupright will rest onthe table in line with

Fio.38.-Th/e7Up"ST" " " " t h e b o t t m f t h ecross-pieces.

The Driving-Wheels are turned out of wood on a lathe.They are seven inches in diameter and seven-eighths of aninch thick. A groove should be turned in the edge to carrya small round leather belt. The wheels are mounted on a

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STATIC ELECTRIC MACHINES 43wooden axle made from a round curtain-pole. They areglued to the axle and arranged so that the grooves will falldirectly underneath the pulleys turned in the bosses.

CftMS 3KCTIONFIG. 39. The Driving-Wheels and Axle.

The ends of the axle pass through the up righ ts, five inchesabove the bottom.The front end of the axle is fitted with a crank and a handle .The plates are mounted on short iron axles passing throughthe top of th e upright into the brass bushings. One end ofeach of the axles isfiled flat where itpasses through thewood upright so thatit may be firmly heldby a set-screw andprevented from revolving.Fasten a small fiber washer to the center of one glass diskso that it will separate the plates and prevent them fromtouching when revolving.

6H00V.CJ

AXLE

FIG. 40. The Boss and Axle.For sate of clearness, the Plate is not shown.

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44 THE BOY ELECTRICIANThe collectors, qu ad rant rods, etc ., are m oun ted on glass

rods one inch in diameter. The bottom s of the rods fit inholes (HH) bored in the cross-pieces of the base, Figure 37.The upper ends are each fitted with a brass ball two inchesin diameter. Th e balls are mounted on the rods by soldering a piece of brass tubing to the ball and slipping it overthe rod. Th e rods shouldbe of the proper length tobring the center of the ba llson a line with the center ofthe plates.

M ake two forks as shownin Figure 42 out of brassrod, three-sixteenths of aninch in diameter and solderbrass balls at the ends.The forks are eleven inchesFIG. 41. Showing how the Ball, Comb, l o n ( ?etc., are mounted on the Glass Rod. A number of small holes

must be bored in the " prongs " and pins made by cuttingordinary dressmakers' pins in half and soldering them inplace. These pins, mounted on the forks, form the combsor collectors.Bore a horizontal hole through each of the brass rods onthe top of the glass rods and pass the shanks of the forksthrough and solder them in place.One of the shanks may be provided with a discharge ballat the end as shown by DB in Figure 44. The other is

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STATIC ELECTRIC MACHINES 45provided with a hard rubber handle made from a piece ofrod. Bore a three-eighths hole directly in the top of eachbrass ball to receive the quadrant rods forming the spark-gap.

The quadrant rods extend over the top of the plates andare three-eighths of an inch in diam eter. Th ey are looseC_J l 1 1 1 l 1 ^ ^ ^

^Q 1 1 1 1 1 1 \^yFIG. 42. A Comb or Collector.

in the tops of the balls so that they may be moved about orremoved entirely.A small brass ball three-quarters of an inch in diameter

should be soldered to the top of one of the quadrant rodsand a similar ball two inches in diameter to the other. > A

i . < * \_ T W * S a HUSH MFIG. 43. Showing how the Tinsel Brushes are arranged on the " Neutralizer "Rods.Two large brass balls, two inches in diameter, are fittedover the ends of the axles, which project through the uprights. Bore a one-quarter-inch hole through each ball a t

right angles to the axle and slip a one-quarter-inch brassrod through and solder it fast.

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46 THE BOY ELECTRICIANThe ends of the rods should be tipped with a bunch oftinsel or fine copper wires and be curved so that the brushes

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FIG. 44. The Complete Wimshurst Electric Machine. B B B B , Brushes. C C,Combs. D B, Discharge Ball. I I , Glass Rods. H,Bandle. Q Q , Quadrant Rods.S S S S S, Sectors. S G, Spark-Gap. P P , Driving-Wheels.For the sake of clearness, several of the sectors are not shown.

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STATIC ELECTRIC MACHINES 47so formed will just touch the sectors on the disks when thelatter are revolved.These are.the neutralizes and are arranged in the approximate positions shown in Figure 44.

The driving-wheels are connected to the bosses by meansof small round leather belts. Th e belt at the rear of themachine is crossed in order to make the plates revolve inopposite directions.If the machine has been properly buil t it is now ready foroperation. I t may be necessary to charge the machine thefirst time that it is used by touching several of the sectorswith the charged cover of an electrophorus. Th en if thehandle is turned the accumulated electricity should discharge across the spark-gap at the top of the machine inthe form of bright blue sparks.

Experiments with an Electric MachineMany interesting experiments can be performed with anelectric machine. Th e number is almost unlimited. A fewof the most instructive ones are described below. Otherscan be found in almost any text book on physics.The Leyden jar consists of a glass jar coated with tinfoilpart way up on both the outsid* and inside. Through thewooden stopper passes a brass rod or a heavy copper wirewhich connects with the inner coating of tinfoil by meansof a small brass chain. Th e upper and outside end of the

rod usually terminates in a brass ball or knob.It is a very simple matter to make a good Leyden jar.

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4 8 THE BOY ELECTRICIANThe jar must be thoroughly cleaned and dried before coating. The inside is then given a thorough brushing over withshellac or varnish. Before it is dry, carefully insert the t in foil and press it smoothly against th e glass. The ou tsideof the jar is treated and coated in the same manner. T h e

BALL ^ .BRASS ROD

COVER

TINFOILCOATINGCHAIN

FIG. 45. Th e Leyde n Jar.

inside and outside of the bottom are also coated by cuttingthe tinfoil in circular pieces and shellacking them on.In order to charge the Leyden jar, grasp it in the handnear the bottom and hold the knob against the prime conductor while turning the handle of the machine.Igniting gunpowder. Bore a hole one-half inch in diam eter and one inch deep in a block of hardwood. Pass twosmall brass wires through holes in the sides, letting the ends

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STATIC ELECTRIC MACHINES 49

M O L E

FIG. 46. A Wooden Mortar for IgnitingGunpowder.

of the wires be about one-eighth of an inch ap ar t. Poura little gunpowder in loosely over the wires. Tie a pieceof thoroughly moistened cotton twine, three inches long, toone of the wires andattach it to the outs i d e c o a t i n g o f acharged Leyden jar.Connect the knob ofthe jar to the otherwire. The gunpowder will imm ediately explode. Keep the face and handsaway from the gunpowder when performing this experiment.

Electric Umbrella. The repulsion of similarly electrifiedbodies which was illustratedby the action of the pith ballelectroscope may be better illustrated by pasting some narrowstreamers of tissue paper aboutone-eighth of an inch wide andfour inches long to a small corkcovered with tinfoil. The corkis mounted on the upper end ofa stiff copper wire supported ina bo ttle. When the wire is connected to the prime conductor and the machine set inmotion, the strips will spread out like an umbrella.

Lightning Board. A pane of glass is thoroughly cleaned

FIG. 47 . An Electric Umbrella.

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So THE BOY ELECTRICIANand then given a coat of shellac or varnish. Before th evarnish is dry, press on a piece of tinfoil large enough tocover one side of the glass and rub it down smoothly.

After the shellac or varnish is dry, cut the tinfoil up intoinnumerable little squares with a sharp knife and ruler,

co RH 1 V G L A S S P L A T ETINFOIL 3auA*eaFIG. 48. A Lightning Board.

leaving two solid strips of tinfoil at the ends of the glasspane.The pane is mounted by cementing it in a slot in the corkof a bo ttle . Connect one of the tinfoil strips to the primeconductor and the other to the ear th or the body. W henthe machine is turned, innumerable little sparks will passbetween the tinfoil-squares and give an appearance verysimilar to that of lightning.The Electrical Dance. A number of lit tle balls of corkor pi th are enclosed in a cylinder of glass about two and one-half or three inches high formed by cutting off the top of alamp chimney. Th e top and bottom of the cylinder areclosed by two circular pieces of sheet brass or copper. T he

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STATIC ELECTRIC MACHINES Si

UPPffl DISK .

.GLASS c r im o iR

FIG. 49. An Electric Dance.

top disk is connected to the prime conductor while thebottom one is connected to the rubber. When the machineis set in motion, the littleballs will dance up anddown. Bits of feather orpaper cut to represent figures of men and womenmay be used as well as pithor cork balls.The Electric Whirl. Thew h i r l c o n s i s t s of an Sshaped piece of brass wire,pointed at both ends and supported on a needle by alittle conical depression made in the center with apunch.The needle is stuck in a cork in the top of a bottleand connected withthe prime conductor ofthe electric machine.When the latter is set

in motion, the whirlwill commence to revolve at a high rate ofspeed.Lichtenberg's Figures

W H I R L

FIG. SO.1 BOTTLEAn Electric Whirl.

can be produced by charging a Leyden jar by connectingthe knob or inside coating with the prime conductor andholding the outside coating in the hand.

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52 THE BOY ELECTRICIANThen trace a small circle on the electrophorus bed withthe knob.Charge a second Leyden jar by connecting the outsidecoating with the prime conductor.The inside coating should be connected to the rubber

by means of a wire fastenedto the knob . The same resu ltm ay be obtained by connec tingthe outside coating with theprime conductor and touchingthe knob with the hand.Then trace a cross on theel ec t ro ph or us bed with theknob, making the cross insideof the circle.Shake a mixture of red leadand sulphur through a muslin bag from a height of severalinches over the electrophorus.

The red lead will accumulate around the cross and thesulphur around the circle.

FIG. 51. Lichtenberg's Figures.

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*" RCHAPTER IV

CE L L S AN D B AT T E RI E S

IN order that the young experimenter may obtain electricity for driving his various electrical devices it is necessary to resort to batteries, a small dynamo, or the house-lighting current.

All houses are not supplied with electric curren t. Fu rthermore, many boys have no source of power from which todrive a small dynamo. Ba tteries must therefore be resorted to in the majority of cases.A number of different cells and batteries are described inthis chapter. All of them are practica l, bu t after buyingzinc, chemicals, etc., for any length of time, figure out whatyour batteries cost you to make. Th e real value is no t theircost in dollars and cents but in what you have learned inmaking them . If you have a continuous use for electricalcurrent for running small electrical devices it is cheaper tobuy dry cells, or what is better, a storage battery, and haveit recharged when necessary.

Build your own batteries first. Then after you have learnedhow they are made and something about their proper carebuy them from some reliable electrical house.Batteries are always interesting to the average experi-

53

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54 THE BOY ELECTRICIANmenter, and when properly made are one of the most usefulpieces of apparatus around the home, laboratory, or shopth at it is possible to construct. M any hundreds of tho usands of experiments have been carried out by capable menin an effort to discover or devise a perfect battery, and thelist of such cells is very great.

Only the most common forms, which are simple and inexpensive to construct but will at the same time render fairservice, have been chosen for description.Cells are usually considered one element or jar of a battery. A cell means only one, while a battery is a group ofcells. I t is no t a proper use of the word to say " battery "

when only one cell is implied. Thisis a very common error.The Voltaic cell is called after itsinventor, Volta, a professor in theUniversity of Pavia, and datesback to about the year 1786.A simple voltaic cell is easilymade by placing some water mixedwith a little sulphuric acid in a glasstumbler and immersing therein twoclean strips, one of zinc and theother of copper. The strips must be kept separate fromeach other. The sulphuric acid must be diluted by mixingit with about ten times its volume of water. In mixing acid

with water always remember never to pour water into acidbut to perform the operation the other way and pour the

Copper

FIG. 52.The Voltaic Cell.

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CELLS AND BATTERIES 55acid into the water. A copper wire is fastened with a screwor by soldering to the top of each of the strips, and caremust be exercised to keep the wires apart.As has been said, the zinc and copper must never be allowed to touch each other in the solution, but must be keptat opposite sides of the jar.The sulphuric acid solution attacks the zinc, causing itslowly to waste away and disappear. This action is calledoxidation, and in reality is a very slow process of burning. The consum ption of the zinc furnishes the electricenergy, which in the case of this cell will be found to besufficient to ring a bell or buzzer, or run a very small toymotor.

As soon as the plates are immersed in the acid solution,bubbles will begin to rise from the zinc. These bubblescontain a gas called hydrogen and they indicate that achemical action is taking place. The zinc is being dissolvedand the hydrogen gas is being set free from the acid. I t willbe noticed that no bubbles arise from the copper plate andth a t the re is little if any chemical action there . In otherwords, it seems that the chemical action at one plate isstronger than that at the other.A cell might be likened to a furnace in which the zinc isthe fuel which is burned to furnish the energy. We knowthat if the zinc is burned or oxidized in the open air it willgive out energy in the form of heat. When it is burned oroxidized slowly in acid in the presence of another metal itgives out its energy in the form of electricity. The acid

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56 TH E BOY ELECTR ICIANmight be likened to the fire, and the copper to a hand whichdips into the cell to pick up the current and takes no partchemically.

If a wire is connected to each of the plates and the freeends of the wires touched to the tip of the tongue it willproduce a peculiar salty taste in the mouth indicating thepresence of a current of electricity.If the wires are connected to an electric bell, the bell willring, or, instead, the current may be used to run a smallmotor. If the cell is made of two zinc pla tes or two copperplates, the bell will not ring, because no electricity will beproduced. In order to produce a curren t, the electrodesmust be made of two different materials upon which theacid ac ts differently. Current may be obtained from a cellmade with a zinc and carbon plate or from one with zinc andiron.Therefore, in order to make a battery it is necessary tohave a metal which may be consumed, a chemical to consume or oxidize it, and an inactive element which is merelypresent to collect the electricity.When the wires connected to the two plates are joinedtogether, a current of electricity will flow from the copperplate through the wire to the zinc. The copper is known asthe positive pole and th e zinc as the negative.A simple voltaic cell may be easily made by cutting ou t astrip of zinc and a strip of copper, each 3 ^ inches long, and

one inch wide. A small hole bored through the upper endof the strips will permit them to be mounted on a wooden

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C E L LS A N D B A T T E R I E S 57strip with a screw as shown in Figure 53. The connectingwires are placed under the heads of the screws. Care shouldbe exercised to arrange the screws used for mounting theelectrodes to the wooden strip so that they do not come

W0"'"*T*,*

F I G . 53.

^COPPEK

- The Elements of SimpleVoltaic Cell.TUMBLCR

FIG. 54. A Home-MadeVoltaic Cell.exactly opposite, and there is no danger of the pointstouching and forming a short circuit.An ordinary tumbler or jelly glass will make a good battery ja r. The exciting liquid should be composed of

One part of sulphuric acidTen parts of waterOne of the disadvantages of the voltaic cell is that itbecomes polarized, that is, small bubbles of hydrogen which

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58 THE BOY ELECTRICIANare l iberated by the chemical action collect on the copperplate and cause the strength of the battery to fall offrapidly.

There are a great number of elements, as the zinc andcopper are called, an d an even g rea ter nu m be r of differentsolutions or excitants which can be employed in place ofsulphuric acid to make a cell , forming an almost endlessnumber of possible combinat ions.

Leclanche Cell. One of th e m os t com m on forms of cellem ploye d for bell-ringing, telep hon es, etc ., is called th eLe clan che cell, after its in ve nto r, an d consists of two elements, one of zinc and the other of carbon, immersed in asolution of sal ammoniac or ammonium chloride. This cellhas an E. M. F. of 1.4 volts, which is about half as muchagain as the voltaic cell .

The most common form of Leclanche cell is i l lustratedin Fig ure 55. Th is typ e is usual ly kno w n as a " carbon cyl in

der " cell because the posit iveelement is a hollow carboncylinder. T h e zinc is in th eform of a rod passing througha porcelain bushing set in thecenter of the carbon cylinder.

A battery of such cells canFIG. 55- Carbon-Cylinder Cell, and 0nly be used successfully for

" open circuit " wo rk. T h e" open circuit " is used for bells, burglar alarms, telephonecircuits, etc., or wherever the circuit is such that i t is

CELL CARBON

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CELLS AND BATTERIES 59" open " most of the time and current is only drawn occasionally and then only for short periods.If the current is drawn for any appreciable length oftime hydrogen gas will collect on the carbon cylinder andthe cell will become polarized. When polarized it will notdeliver much current.

M any m ethods have been devised for overcoming this difficulty, bu t even the best of them are only partia lly successful.The usual method is to employ a chemical depolarizingagent. Figure 56 shows a Leclanche cell provided with adepolarizer.The carbon is in the form of a plate placed in a porouscup made of earthenware and filled with manganese dioxide.

Chemists class manganese dioxide as an oxidizing agent,which means that it will furnishoxygen with comparative ease.Oxygen and hydrogen have astrong chemical affinity or attraction for each other.If the carbon plate is packedin manganese dioxide any hydrogen which tends to collect onthe carbon and polarize the cellis immediately seized by theoxygen of the manganese dioxide .and united with it to formwater.This form of Leclanche cell is called the disk type. It iscapable of delivering a stronger current for a longer period

POSITIVECELLFIG. 56. A Leclanche Cell,showing the Porous Cup.

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6o THE BOY ELECTRICIANof time than the carbon cylinder ba ttery . The zinc is usually made in the form of a cylinder, and fits around the outside of the porous cup.Dry Cells are used extensively nowadays for all open circu itwork on account of their convenience and high efficiency.

The dry cell is not, as its name implies, " dry," but theexciting agent or electrolyte, instead of being a liquid, is awet paste which cannot spill or run over.The top of the cell is poured full of moltenpitch, thus effectively sealing it and making it possible to place the cell in anyposition.

Dry cells can be purchased from almostany electrical house or garage for twenty-five cents each. I t will therefore hard lypay the young experimenter to make hisown dry cells. For the sake of those whomay care to do so, however, directions forbuilding a simple but efficient dry cell ofthe type used for door-bells and ignitionwork, will be found below.The principle of a dry cell is the sameas th a t of a Leclanche cell of the disk type. The excitingsolution is ammonium chloride, the electrodes or elementsare zinc and carbon, and the carbon is surrounded bymanganese dioxide as a depolarizing agent.

Obtain some sheet zinc from a plumbing shop or a hardware store and cut out as many rectangles, 8x 6 inches,

For Ignition*< ^ A m p e r a ge

FIG. 57.A Dry Cell.

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CELLS A N D BA TTERIES 61as it is desired to make cells. Also cut out an equal num berof circles 2^i inches in diameter.Roll the sheets up into cylinders 2^i inches in diameterinside and 6 inches long. The edges are lapped and soldered. F it one of the round circles in one end of each of thecylinders and solder them securely into place, taking careto close up all seams or joints which might permit the electrolyte to escape or evaporate.

Secure some o

The Boy Electrician - Alfred Morgan

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