Produced by James Simmons.

This file was produced from page images at the Internet Archive.

Transcriber’s Note

This book was transcribed from scans of the original found at the Internet Archive. The page scans were done by Google. The original book was done as three volumes, but the edition I have transcribed put all three volumes together as a clothbound book. As a result it had three identical prefaces and duplicated ads. I have included one preface, at the beginning, and put the ads at the end of the book. I have rotated a couple of illustrations.

Arts and Science Series No. 7

Home-made

Electrical Apparatus

A Practical Handbook for Amateur

Experimenters

In Three Parts

*Volume I*

Second Edition

*BY*

*A. M. Powell*

PUBLISHED BY

COLE & MORGAN, Inc.

Publishers of the Arts and Science Series

P.O. BOX 473 CITY HALL STATION

NEW YORK, N. Y.

Printed in U. S. A.

Copyright 1918

by

COLE & MORGAN, Inc.

PREFACE

The purpose of this book is to aid the young experimenter in building and operating his own electrical apparatus and instruments. Every boy of now-a-days experiments with electricity and the right sort of book which furnishes him with ideas gets close to his heart. Of books upon electricity there is no end. That is granted. But there are very few practical books for the young experimenter who wishes to construct miscellaneous electrical apparatus for his own amusement and instruction which really amounts to something and which is worth his pains when the labor has been finished.

This book is therefore offered as a volume of instruction for making all sorts of batteries, rectifiers, motors, etc., which are entirely out of the toy class and yet are not so elaborate that they cannot be easily constructed at home by the average boy who is willing to put a little care into his work. The materials required are such that they can he procured without any great expense.

It has been planned to present the material in such a manner that it will aid the judgment of the young experimenter and assist him in developing his own ideas. Without exception, all of the apparatus described in the following pages has been actually constructed by the author, not only once but many times and put to a practical test before being embodied into the book. You may therefore be sure that if you follow the instructions carefully, that the result will in each case be a substantial piece of apparatus which is capable of fulfilling all of your expectations.

The drawings have all been reproduced on a large scale and in almost every case the dimensions of even the smallest details have been given. Some of the apparatus has been described in the pages of the "Boys’ Magazine" and since its publication the readers of that magazine have written to the author asking questions about the apparatus which have enabled him when rewriting the material for publication in book form to clear up many questions and further explain in a little more detail many of the problems which naturally occur to the boy who likes to build his own electrical devices.

THE AUTHOR.

PREFACE …………………………………………………..
CHAPTER I. STATIC ELECTRICAL APPARATUS ……………………….
How to Build a Wimshurst Machine. ………………………….
Experiments with Static Electrical Apparatus. ……………….
CHAPTER II. CELLS AND BATTERIES. …………………………….
The Voltaic Cell. ………………………………………..
Homemade Batteries. ………………………………………
Battery Solutions or Electrolytes. …………………………
Connecting Cells. ………………………………………..
Storage or Secondary Cells. ……………………………….
An Experimental Storage Cell. ……………………………..
A Homemade Storage Cell. ………………………………….
Recharging and Caring for Storage Cells. ……………………
CHAPTER III. HOW TO REDUCE THE 110 V. D.C. OR A.C. TO A LOWER
VOLTAGE FOR EXPERIMENTAL PURPOSES. …………………………..
CHAPTER IV. HOW AN ALTERNATING CURRENT MAY BE CHANGED INTO DIRECT
CURRENT BY MEANS OF AN ELECTROLYTIC RECTIFIER. ………………..
CHAPTER V. HOW TO BUILD A STEP-DOWN TRANSFORMER FOR REDUCING THE 110
VOLT A. C. FOR EXPERIMENTAL PURPOSES. ………………………..
CHAPTER VI. ELECTRIC MEASURING INSTRUMENTS ……………………
Galvanometers, Ammeters, Voltmeters. How to Make a Galvanometer. .
The Construction of Ammeters and Voltmeters. ………………..
CHAPTER VII. CURRENT CONTROL DEVICES. ………………………..
How to Make a Pole Changing Switch or Current Reverses How to
Reverse a Small Motor. ……………………………………
How to Make a Small Battery Rheostat for Regulating the Speed of
Small Motors, Etc. ……………………………………….
CHAPTER VIII. HOW TO MAKE A TELEGRAPH KEY AND SOUNDER AND INSTALL A
TELEGRAPH LINE. ……………………………………………
CHAPTER IX. HOW TO MAKE AND INSTALL A TELEPHONE. ………………
CHAPTER X. MEDICAL COILS AND SHOCKING COILS. ………………….
CHAPTER XI. THE CONSTRUCTION OF SPARK COILS. ………………….
Experiment 1—An Imitation Gassiot’s Cascade. ………………..
Experiment 2—A Ghostly Light ………………………………
Experiment 3—Lighting Geissler Tubes. ………………………
Experiment 4—Flickering Light. …………………………….
Experiment 5—Rotating a Geissler Tube. ……………………..
Experiment 6—Fluorescent Writing. ………………………….
Experiment 7—An Electric Bomb. …………………………….
Experiment 8—Electrifying the Garbage Can. ………………….
Experiment 9—How to Make an Electric Spark Photograph Itself. …
CHAPTER XII. HOW TO MAKE A DYNAMO-MOTOR ………………………
CHAPTER XIII. AN ELECTRIC BATTERY MOTOR. ……………………..
CHAPTER XIV. HOW TO BUILD AN ELECTRIC ENGINE. …………………
CHAPTER XV. MINIATURE BATTERY LIGHTING. ………………………
CHAPTER XVI. COHERER OUTFITS FOR WIRELESS TELEGRAPHY. ………….
CHAPTER XVII. HOW TO BUILD A TESLA HIGH FREQUENCY COIL. ………..
CHAPTER XVIII. AN EXPERIMENTAL WIRELESS TELEPHONE. …………….
CHAPTER XIX. MISCELLANEOUS EXPERIMENTS AND APPARATUS. ………….
ELECTROLYSIS. ……………………………………………
ELECTROPLATING. ………………………………………….
ELECTRIC CURRENT GENERATED BY HEAT. ………………………..
A HANDY LIGHT. …………………………………………..
AN EXPERIMENTAL ARC LAMP. …………………………………
A MAGNETIC DIVER. ………………………………………..
THE MAGNETIC FISH. ……………………………………….
A MAGNETIC CLOWN. ………………………………………..
AN ELECTRIC BREEZE. ………………………………………
A STATIC MOTOR. ………………………………………….

FIG. 1.—A simple Wimshurst Machine which any boy can easily make. P P, Plates; BR, Neutralizes; C R, Collectors; DR, Discharge Rods; J J, Leyden Jars; H H, Insulating Handles; C, Crank; U, Upright; B, Belt. ……………………………………………………. FIG. 2.—The plates for the Static Machine are made of hard rubber and are 7 inches in diameter. Each plate carries sixteen tinfoil sectors. …………………………………………………. FIG. 3.—The details of the Tinfoil Sector. Sixteen are required for each plate. They are stuck to the plates with shellac. ………… FIG. 4.—Details of the Grooved Pulley, attached to each plate. The Pulleys are turned out of wood. …………………………….. FIG. 5.—The base of the Wimshurst Machine. All woodwork about the machine should be carefully dried and then shellaced so that it cannot absorb any moisture. ………………………………… FIG. 6.—Details of one of the Uprights which support the Plates, Driving Pulleys, etc. These, being made of wood, should also be dried and shellaced so that they cannot absorb moisture. ………. FIG. 7.—Showing the Two Uprights in position on the Base. ……… FIG. 8.—The Driving Pulleys. These are turned out of wood and mounted on a shaft having a Crank at one end. ………………… FIG. 9.—The Crank is bent out of a piece of 3/16 rod, 7 inches long, into the shape shown. ……………………………………… FIG. 10.—The Collector with the Discharge Rods, etc, in position. A is the Brass Ball forming one terminal of the gap across which the sparks jump. B is another Brass Ball screwed onto the end of the Collector Rod and having a hole in it, through which the Discharge Rod slips. CC are two threaded Washers used to clamp the Discharge Rod in place. …………………………………………….. FIG. 11.—Showing how Binding Posts may be substituted for Round Balls on the Collector Rods. ……………………………….. FIG. 12.—Details of the Discharger Rods. …………………….. FIG. 13.—The Supporting Bar upon which the Collector Rods are mounted. Made of hard rubber so as to be a perfect Insulator. ….. FIG. 14.—The Neutralizers. Two are required. They are bent out of Brass Rod and fitted with a Tinsel Tuft at each end. The centre piece upon which the Rod is mounted should be of Hard Rubber. …. FIG. 15.—Details of the Leyden Jars. They are simply small Test Tubes, coated inside and outside with tinfoil for about two-thirds their height and fitted with a Brass Rod connected with the inside coating. …………………………………………………. FIG. 16.—A Large Leyden Jar for experimental purposes. ………… FIG. 17.—Showing how to Discharge a Leyden Jar with a curved piece of stiff wire fitted to a Wooden Handle. …………………….. FIG. 18.—The "Lightning Board" is simply a Strip of Glass covered with small Tinfoil Squares. It may be insulated by mounting on a Bottle. The two Wires attached to the wide Tinfoil Strips at the ends of the "Board" are for connection to the Static Machine or Leyden Jar. ………………………………………………. FIG. 19.—A very pretty effect can be produced by arranging small tinfoil strips on the Glass in a Pattern. Each strip should be separated from the other just far enough for a Spark to pass. ….. FIG. 20.—A very pretty design made by arranging the Strips in the form of a Seven-pointed Star. Flowers, initials or almost any pattern may be made in the same way. ………………………… FIG. 21.—The Electric Parasol. The upper right-hand corner shows a piece of Tissue Paper cut into Strips. (1) Is the apparatus before the Tissue Paper is fastened to the Cork. (2) Shows the completed "Parasol" and (3), the Parasol when connected to the machine and the latter is set in operation. ………………………………… FIG. 22.—Electric Birds. The Birds are made of Tissue Paper and should be about the size and shape shown in the lower right-hand corner of the illustration above. …………………………… FIG. 23.—Electric Acrobats. The Acrobats are made of paper. The little figure in the upper right-hand part of the illustration is the proper size. ………………………………………….. FIG. 24.—The Electric Mortar. C is the Mortar, P the Powder, B a Small Ball and W W the two Wires between which the Spark igniting the powder takes place. ……………………………………. FIG. 25.—An Electric Whirligig. …………………………….. FIG. 26.—A Voltaic Cell. A Voltaic Cell consists of a Strip of Copper and a Strip of Zinc immersed in a dilute solution of Sulphuric Acid. …………………………………………… FIG. 27.—Ordinary Jelly Glasses, Tumblers, Fruit Jars, etc, make good Jars for small cells by cutting off the tops. ……………. FIG. 28.—A Simple Home-made Cell. …………………………… FIG. 29.—A Home-made Battery having two Carbon Plates with a Zinc Rod between. ……………………………………………… FIG. 30.—The Elements for a Simple Home-made Cell composed of two Carbon Rods and one Zinc Rod clamped between two Wooden Strips. … FIG. 31.—Four Carbon Rods and one Zinc Rod arranged to form the Elements of a Cell. ……………………………………….. FIG. 32.—A Battery of Three Cells arranged so that they can all be lifted out of the solution at once. …………………………. FIG. 33.—Showing how Cells are arranged when they are connected in Series. The Voltage of Six Dry Cells connected in series as above would be approximately 6 x 1.5 or 9 Volts. …………………… FIG. 34.—Showing Six Dry Cells connected in Multiple. The Voltage of such an arrangement would only be 1.5, but the Amperage available would be six times that possible from Cells connected as in Figure 33. ……………………………………………………… FIG. 35.—Showing how to connect a Battery of Cells in Series-Multiple. ………………………………………….. FIG. 36.—Battery Connectors like that shown above can be obtained for 1 1/2 cents each and will be found to be very handy. ………. FIG. 37.—A Simple Experimental Storage Battery consisting of two Lead Plates immersed in Dilute Sulphuric Acid. ……………….. FIG. 38.—Showing how to charge a Simple Storage Cell composed of two Lead Plates immersed in Sulphuric Acid by connecting it to two Bichromate of Potash Cells. ………………………………… FIG. 39.—Showing how the Plates for a Storage Cell may be made from Sheet Lead by boring it full of holes and filling with paste. ….. FIG. 40.—A set of three Plates composed of One Positive and Three Negatives assembled to form a Cell. …………………………. FIG. 41.—Glass and Rubber Storage Cell Jars which are on the market for the Electrical Experimenter and may be purchased very reasonably. ………………………………………………. FIG. 42.—An empty Storage Cell Grid and also a Pasted Plate both of which are on the market for experimenters who wish to build their own Cells. ……………………………………………….. FIG. 43.—Two Negative Plates "burned" together and the Connecting Lug used. ………………………………………………… FIG. 44.—The Elements of a Storage Cell composed of two Negative Plates and one Positive Plate in their proper position. ……….. FIG. 45.—Three different sizes of Storage Cells which may be purchased ready made or built by the experimenter out of prepared materials as explained. ……………………………………. FIG. 46.—A Hydrometer for preparing and testing the Acid Solution for Storage Batteries. …………………………………….. FIG. 47.—The proper way of Recharging Storage Cells from the 110 Volts D. C. Supply in series with a set of Lamps. …………….. FIG. 48.—A Lamp Bank consisting of a Set of 110-Volt Lamps connected Multiple and arranged to be placed in series with any device it is desired to use on the 110-Volt Current. ……………………… FIG. 49.—A Single Cell of Electrolytic Rectifier. …………….. FIG. 50.—An Electrode cut out of Sheet Metal. The top is bent over at right angles and drilled so that it can be mounted on the underside of the cover. ……………………………………. FIG 51.—A Cast Electrode will last much longer than one cut from Sheet Metal. Cast Electrodes like that above are on the market and can be purchased very reasonably. …………………………… FIG. 52.—A completed single Cell Rectifier. The right hand sketch shows how the Electrodes are mounted on the underside of the cover. FIG. 53.—A Diagram showing how a Rectifier cuts off one-half of the Alternating Current Wave and changes it into Pulsating Direct Current. …………………………………………………. FIG. 54.—Circuit showing how a Single Cell of Rectifier should be connected in series with a Lamp Bank to Recharge a Storage Cell. A is the Aluminum Plate and L the Lead or Iron Plate. …………… FIG. 55.—Diagram showing the Difference in Current after it has been passed through a Single Cell or Rectifier and after passing through a Four-Cell Rectifier. …………………………………….. FIG. 56.—Diagram showing how a Four-Cell Rectifier is connected. The Alternating Current Source is connected to C and D. The Direct Current is taken off at A and B. The Electrodes marked A, A, A, A are the Aluminum Electrodes. L, L, L, L may be Lead or Iron. …… FIG. 57—A Complete Four-Cell Rectifier connected together and Mounted in a Tray. ………………………………………… FIG. 58.—Details of the two different Pieces of Sheet Iron used in building up the Core. Sufficient of each piece are required to form a pile of each three-quarters of an inch thick. ………………. FIG. 59.—The Method used in piling up the Strips to Assemble the Core. ……………………………………………………. FIG. 60.—Assembly of the Core. ……………………………… FIG. 61.—Details of the Primary and Secondary Windings. ……….. FIG. 62.—Showing the Core completely assembled with the Primary and Secondary in position. P, P are the Primary Terminals. 1, 2 and 3 are the Secondary Terminals. ……………………………….. FIG. 63.—The Step-down Transformer mounted on a Wooden Base. …… FIG. 64.—A detailed Drawing showing how the Sides of the Case are formed by bending a long strip of Sheet Iron at four points. …… FIG. 65.—Details of the Top and Bottom of the Case. …………… FIG. 66.—The completed Transformer. …………………………. FIG. 67.—A Simple Galvanometer. …………………………….. FIG. 68.—Details of the Bobbin. …………………………….. FIG. 69.—Details of the Armature, Bearings and Pointer. ……….. FIG. 70.—A complete Voltmeter having the Scale at the top. …….. FIG. 71—An Ammeter so constructed that the Scale is at the bottom. . FIG. 72.—Showing how the Armature, Shaft and Pointer are assembled for a Meter having the Scale at the bottom. ………………….. FIG. 73.—Details of the Wooden Parts which form the Case. ……… FIG. 74.—Showing how the Apparatus is arranged and connected for calibrating the Ammeter. …………………………………… FIG. 75.—Showing how the Apparatus is arranged and connected for calibrating the Voltmeter. …………………………………. FIG. 76.—A Pole changing Switch for reversing Small Motors or the direction of an Electric Current. …………………………… FIG. 77.—Top view of a small Battery Rheostat ………………… FIG. 78.—Details of the Rheostat Base. The lower part of the illustration is a cross section. ……………………………. FIG. 79.—Looking at the Base from the bottom showing the grooves in which the Wires are laid. ………………………………….. FIG. 80.—The German-silver Resistance Wire is wound around a Fibre Strip. …………………………………………………… FIG. 81.—The Lever, Knob, Binding Posts, etc. ………………… FIG. 82.—The completed Rheostat. ……………………………. FIG. 83.—Key Frame. ……………………………………….. FIG. 84.—Sounder Frame. ……………………………………. FIG. 85.—The Electro Magnets. ………………………………. FIG. 86—The Sounder Armature. ………………………………. FIG. 87.—Sounder Frame with Lever in Position. ……………….. FIG. 88.—Top View of Completed Instrument ……………………. FIG. 89.—Side View of Key. …………………………………. FIG. 90.—Key and Circuit Closing Levers. …………………….. FIG. 91.—American Morse Code. ………………………………. FIG. 92.—Circuit for Two Instruments. ……………………….. FIG. 93.—The Wooden Back for the Telephone. ………………….. FIG. 94.—The Complete Telephone. ……………………………. FIG. 95.—Details of the Receiver Hook. ………………………. FIG. 96.—Showing how the Push Button is arranged. …………….. FIG. 97.—Circuit showing how to connect two Telephone Stations to the Line. ………………………………………………… FIG. 98.—Bobbin for Medical Coil. …………………………… FIG. 99.—Bobbin with Winding. ………………………………. FIG. 100.—Construction of the Core. …………………………. FIG. 101.—Vibrator Parts and Core Cap. ………………………. FIG. 102.—Regulator Tube. ………………………………….. FIG. 103.—The Base with Location of Holes. …………………… FIG. 104.—Top View of Finished Coil. ………………………… FIG. 105.—Side View of Completed Coil. ………………………. FIG. 106.—Vibrator Parts. ………………………………….. FIGS. 107 and 108.—Two Types of Handles. …………………….. FIG. 109.—Induction or Spark Coil. ………………………….. FIG. 110.—The Primary and Core. …………………………….. FIG. 111.—The Secondary Winding. ……………………………. FIG. 112.—The Fixed Condenser. ……………………………… FIG. 113.—Details of the Wooden Coil Heads. ………………….. FIG. 114.—Details of the Wooden Base. ……………………….. FIG. 115.—Details of the Interrupter. The Spring and Standard for the One inch coil should be made one-quarter of an inch longer. … FIG. 116.—The tube. ……………………………………….. FIG. 117.—The Bridge. ……………………………………… FIG. 118.—Section of the Spark Coil showing the arrangement of the Parts. …………………………………………………… FIG. 119.—End View of the Complete Coil. …………………….. FIG. 120.—Side View of the Completed Coil. …………………… FIG. 121.—Diagram of Connections. …………………………… FIG. 122.—Perspective view of Coil showing names of the various parts. …………………………………………………… FIG. 123—Front view of the Field Casting. ……………………. FIG. 124.—Side elevation of the Field Casting. ……………….. FIG. 125.—Details of the Armature. ………………………….. FIG. 126.—The Commutator. ………………………………….. FIG. 127.—The Armature and Commutator Assembled on the Shaft ready for winding. ……………………………………………… FIG. 128.—Details of the Wooden Base. ……………………….. FIG. 129.—Details of the Bearings. ………………………….. FIG. 130.—The Pulley. ……………………………………… FIG. 131.—The Brushes. …………………………………….. FIG. 132.—The Completed Dynamo. …………………………….. FIG. 133.—The completed Electric Motor. ……………………… FIG. 134.—Details of the Field Frame. ……………………….. FIG. 135.—The Assembled Field ready for Winding. ……………… FIG. 136.—Details of the Armature Lamination. ………………… FIG. 137.—The Armature assembled on the Shaft ready to Wind. …… FIG. 138.—The Commutator. ………………………………….. FIG. 139.—Diagram showing how the Armature Coils are connected to the Commutator Sections. …………………………………… FIG. 140.—The Bearings. ……………………………………. FIG. 141.—The Brushes. …………………………………….. FIG. 142.—The Fibre Block for supporting each Brush. ………….. FIG. 143.—Completed Electric Engine. ………………………… FIG. 144.—The Engine Base. …………………………………. FIG. 145.—Details of the Electromagnet Bobbin. ……………….. FIG. 146.—Details of the Engine Frame. ………………………. FIG. 147—The Bearings. …………………………………….. FIG. 148.—Details of the Shaft. …………………………….. FIG. 149.—The Armature, Armature Bearing and Connecting Rod. …… FIG. 150.—The Brushes. …………………………………….. FIG. 151.—A Flywheel may be cut from sheet iron. ……………… FIG. 152.—Small Tungsten Battery Lamps. ……………………… FIG. 153.—A Simple Lighting Arrangement. …………………….. FIG. 154.—Showing the differences between the Candelabra, Single Ediswan and Double Ediswan Types of Lamp Bases. ………………. FIG. 155.—Miniature Sockets of the types known as "Flat Base Porcelain," "Pin" and "Weatherproof." ……………………….. FIG. 156.—Connections for a 2.8 Volt Lamp. …………………… FIG. 157.—A Miniature Base Tungsten Filament Battery Lamp for small lighting. ………………………………………………… FIG. 158.—A Tungsten Automobile Lamp with Ediswan Base. ……….. FIG. 159.—Lamps Controlled by One Switch. ……………………. FIG. 160.—Lamps Controlled by Separate switches. ……………… FIG. 161.—Double Control System. ……………………………. FIG. 162.—The Coherer Details. ……………………………… FIG. 163.—The Complete Coherer. …………………………….. FIG. 164.—Pony Type Relay. …………………………………. FIG. 165.—Connections for the Receiving Set. …………………. FIG. 166.—Coherer, Decoherer and Relay Connections. …………… FIG. 167.—How the Transmitter is Connected. ………………….. FIG. 168.—The Complete Spark Gap. …………………………… FIG. 169.—Details of Spark Gap. …………………………….. FIG. 170.—Tesla Coil Circuits. ……………………………… FIG. 171.—Secondary Tube. ………………………………….. FIG. 172.—Details of the Secondary Heads. ……………………. FIG. 173.—Details of the Primary Head. ………………………. FIG. 174.—Primary Cross Bar. ……………………………….. FIG. 175.—Front View of the completed Tesla Coil. …………….. FIG. 176—Side View of the completed Tesla Coil. ………………. FIG. 177.—Diagram of connections for operating the Coil. ………. FIG. 178.—Plate Glass Condenser. ……………………………. FIG. 179.—When a Bar Magnet is plunged into a Hollow Coil of Wire, a Momentary Current of Electricity is Generated. ……………….. FIG. 180.—Magnetic Phantom showing the Lines of Force about a Bar Magnet. ………………………………………………….. FIG. 181.—Magnetic Phantom about a Coil of Wire carrying a current. FIG. 182.—Illustrating the Principle of the Induction Wireless Telephone. ……………………………………………….. FIG. 183.—Showing how the Coils may be formed by winding around nails set in a circle in the Floor. …………………………. FIG. 184.—Circuit Diagram showing how the Coil is connected so as to serve for either transmitting or receiving. ………………….. FIG. 185.—Apparatus for Electrolysis Experiment. ……………… FIG. 186.—Electroplating Tank. ……………………………… FIG. 187.—Generating Electric Current by Heat. ……………….. FIG. 188.—A Handy Light. …………………………………… FIG. 189.—Experimental Arc Lamp. ……………………………. FIG. 190.—The Magnetic Diver. ………………………………. FIG. 191.—The Magnetic Fish. ……………………………….. FIG. 192.—The Magnetic Clown. ………………………………. FIG. 193.—An Electric Breeze. ………………………………. FIG. 194.—The Static Motor. …………………………………

CHAPTER I. STATIC ELECTRICAL APPARATUS

*Static Electricity. How to Build a Wimshurst Machine. Experiments with
Static Electrical Apparatus.*

*Static Electricity* is an extremely interesting subject for the amateur experimenter, in view of the many spectacular experiments which may be performed with it. The number of such experiments is almost unlimited.

Static electricity was the first evidence of the wonderful force which in the present day moves trains, lights our homes, etc., to come to the notice of man. Long before the days of batteries, dynamos, telegraphs, electric lights and before, perhaps, such things were even dreamed of, static electricity absorbed the attention of scientists, and the names of some of the world’s greatest men such as for instance, Aristotle, Roger Bacon, Gilbert, Boyle, Newton, Franklin, etc., are closely linked with its history. It is probably safe to say that experiments with static electricity led the famous Italian, Galvani, to the discovery of the sort of electricity called *galvanic* currents, and to the battery. Galvanic current is the sort of electricity produced by batteries and has the same properties in many ways as that generated by huge dynamos in the power houses of to-day.

The modern boy can duplicate these old experiments far more easily and on a larger scale than any of the old scientists could, owing to the fact that he is supplied with explicit directions and can easily obtain the necessary materials at a neighboring hardware or electrical store, whereas men like Newton and Franklin not only had to *devise* or *invent* their own apparatus but make their materials as well.

How to Build a Wimshurst Machine.

Static electricity and lightning are the same thing.

A boy can produce static electricity in small quantities by rubbing a glass rod with a piece of flannel or silk.

[Illustration: FIG. 1.—A simple Wimshurst Machine which any boy can
easily make. P P, Plates; BR, Neutralizes; C R, Collectors; DR,
Discharge Rods; J J, Leyden Jars; H H, Insulating Handles; C, Crank; U,
Upright; B, Belt.]

Rub the rod briskly and then hold it over some tiny bits of paper or specks of dust and watch them jump up to meet the rod, just as if the latter were a magnet attracting small tacks or nails. It is static electricity which gives the rod this wonderful power. If you rub the rod briskly and then hold it close to your cheek, you will feel a slight tickling and hear a faint crackling sound. If this is done in the dark you may be able to see a very faint phosphorescent light or even small sparks.

The quantity of electricity produced in this manner by rubbing a glass rod is extremely limited and while a number of very interesting and instructive experiments may be performed in this manner, the most spectacular ones are only possible with the aid of a "static-machine".

[Illustration: FIG. 2.—The plates for the Static Machine are made of hard rubber and are 7 inches in diameter. Each plate carries sixteen tinfoil sectors.]

The most practical form of static machine is that known as the "Wimshurst". It consists of two circular plates made of glass or hard rubber arranged so that by turning a crank, they may be revolved in opposite directions. On these plates are a number of small strips of tinfoil. The static electricity is generated on these tinfoil strips and collected by two metal rods having small pins arranged along them in a row.

A simple form of Wimshurst machine which any boy can easily make is illustrated in Figure 1. It will generate considerable static electricity and will make sparks two inches long.

*The Plates* on these machines are hard rubber. They are illustrated in Figure 2. Glass is usually used for static machine plates, but has the disadvantage of breaking easily. It is also hard for the young experimenter to cut out circular glass plates and drill them. The author has had very good success with hard rubber.

[Illustration: FIG. 3.—The details of the Tinfoil Sector. Sixteen are required for each plate. They are stuck to the plates with shellac.]

Two plates are required for the machine. They should be in the form of circles seven inches in diameter and be perfectly true. They need to be only one-sixteenth of an inch thick. The rubber should be perfectly flat and not warped at any point.

*The Sectors*, as the tinfoil strips are called, are wedge shaped pieces having rounded ends as shown in Figure 3. They should be cut of heavy tinfoil. Thirty-two sectors are required, sixteen for each plate. They are seven-sixteenths of an inch wide at the top, one inch long and five-sixteenth of an inch wide at the bottom.

The plates should be very carefully cleaned by rubbing with a dry cloth and then laid on a flat surface all ready to receive the sectors.

The sectors should be stuck to the plates with thick shellac. They should be arranged all on one face, symmetrically and at equal distances apart, with the inner ends resting on a circle four and one-half inches in diameter. Each sector should be carefully pressed down on the rubber so that it sticks smoothly without any air bubbles or creases.

Both plates should be treated in the same manner.

[Illustration: FIG. 4.—Details of the Grooved Pulley, attached to each plate. The Pulleys are turned out of wood.]

*The Pulley* illustrated in Figure 4 is one inch in diameter and eleven-sixteenths of an inch thick. Two of these pulleys will be required. The hole through the centre should be about three-sixteenths of an inch in diameter. One pulley should be attached to each of the rubber plates. The large face of the pulley should be against the face of the plate upon which the tinfoil sectors are mounted. The hole in the centre of the pulley should line up perfectly with a hole of the same size in the centre of each one of the plates. The plates are fastened to the pulleys by three small brass nails driven into the wood through small holes in the rubber.

*The Base* of the machine is a rectangular shaped piece of wood six inches long, four inches wide and three-quarters of an inch thick. A notch, one inch wide and one-half an inch deep is cut in the centre of the front and back as shown in Figure 5. The purpose of these notches is to receive the uprights.

*The Uprights* are strips of wood, seven inches long, one inch wide and one-half an inch thick. The tipper end of each of the uprights is rounded as shown in Figure 6.

[Illustration: FIG. 5.—The base of the Wimshurst Machine. All woodwork about the machine should be carefully dried and then shellaced so that it cannot absorb any moisture.]

Two holes should be bored through each of the uprights from front to back. The lower hole is three-sixteenths of an inch in diameter and two and one-quarter inches from the bottom. The upper hole is six and one-half inches from the bottom and is between one-eighth and three-sixteenths of an inch in diameter so that a three-sixteenth rod driven into it will fit tightly.

The uprights should be mounted in position in the base and fastened with screws.

The plates are mounted between the upper ends of the uprights in the position shown in Figure 1, by driving a short piece of 3/16 round brass rod through the uprights into the holes in the centre of the pulleys. The rod used to mount the back plate should be one and one-half inches long and that used for the front plate one and five-eighths inches long. The 3/16 hole in the pulleys should be large enough so that the latter will revolve freely.

The plates are revolved by two driving pulleys provided with a crank for turning.

*The Driving Pulleys* are shown in Figure 8. They are not so easy to make as the small pulleys attached to the plates. They are turned out of wood and should be both alike. The exact shape and dimensions are shown in the illustration. The hole through the centre should be a scant three-sixteenths of an inch so that the pulleys will force onto a 3/16 rod very tightly.

*The Crank* is bent out of a piece of brass or steel rod about seven inches long. The straight portion, forming the shaft upon which the pulleys are mounted, is three and seven-eighths inches long. The portion at right angles to this, forming what is known as the "throw" of the crank, is one inch and seven-eighths. The part forming the crank handle is one inch and one-quarter long.

[Illustration: FIG. 6.—Details of one of the Uprights which support the Plates, Driving Pulleys, etc. These, being made of wood, should also be dried and shellaced so that they cannot absorb moisture.]

The driving pulleys are placed between the two standards with the small projecting portions or "bosses" nearest the uprights. The straight portion of the crank should then be slipped through the hole in the front upright and driven tightly into the driving pulleys. The driving pulleys should fit so tightly onto the shaft that they will not slip. The end of the shaft should project through the pulleys far enough so that is rests in the hole in the rear standard.

The holes in the uprights or standards should be just large enough so that the shaft will turn freely. The driving pulleys should be lined up so that the groove in each comes directly under the groove in the corresponding pulley attached to the plate above.

*The Belts* consist simply of heavy cotton cord. The rear belt should be crossed so that the rear plate runs in the opposite direction from the front plate when the crank is turned.

The electricity is collected from the sectors on the plates by two

*Collectors.* These are illustrated in Figure 10 and consists of a piece of 5/32 brass rod, about six inches long, bent into the shape shown. Two small tufts of "tinsel" are soldered to the U-shaped portion of the collector so that when the latter is placed in its proper position on the machine, they will brush against the tinfoil-sectors as they pass when the plates revolve.

[Illustration: FIG. 7.—Showing the Two Uprights in position on the
Base.]

The other end of the rod is threaded to fit into a hole in a small brass ball about three-eighths or one-half inch in diameter. Many experimenters may have difficulty in securing a suitable brass ball for this purpose. An ordinary binding post may be used instead. The hole in the bottom of a binding post is usually threaded to fit an 8-32 screw. The end of the rod is just the right size to receive an 8-32 thread and so there should be no trouble in getting the parts to fit. The brass ball is marked "A" in the illustration. The ball is preferable to the binding because it has no sharp corners from which the electricity might leak. Static electricity leaks from sharp edges or corners and they must always be avoided as far as possible in the construction of static apparatus.

The end of the rod where it screws into the ball or binding post should be threaded back for a distance of about three-quarters of an inch and two brass nuts screwed onto the rod. These nuts are marked "C" in the illustration.

[Illustration: FIG. 8.—The Driving Pulleys. These are turned out of wood and mounted on a shaft having a Crank at one end.]

The collectors are held in position by the supporting bar illustrated in Figure 13. This bar is made of a strip of hard rubber, five and one quarter inches long, five-eighths of an inch wide and three-sixteenths of an inch thick.

Three holes, each five-thirty-seconds of an inch in diameter, should be bored in the bar. One hole should be exactly in the centre and the other holes seven-sixteenths of an inch back from the end.

The centre hole is slipped over the end of the shaft which projects through the front standard supporting the plate and the bar fastened across the support at right angles like a cross by driving in two small brass nails or screws through holes made in the rubber for that purpose.

The threaded portion of the collector rods should be slipped through the holes near the ends of the hard rubber bar and clamped firmly in position by placing one of the nuts "C" on the back and the other on the front and tightening them up.

The exact position of the collectors is best understood from Figure 1. They are lettered C R in the illustration. The brass balls B are screwed onto the ends of the rods after the nuts have been tightened. Each of these balls should have a hole, one-eighth of an inch in diameter drilled through it at right angles to the collector rod. The hole provided in the binding post for the accommodation of the wire may be used in case binding posts are employed instead of the rods.

These holes are to accommodate the Discharge Rods, which are two round brass rods, one-eighth of an inch in diameter and three and one-half inches long. One end of each of the rods is fitted with a small brass ball.

[Illustration: FIG. 9.—The Crank is bent out of a piece of 3/16 rod, 7 inches long, into the shape shown.]

The other end of each is provided with a small insulating handle. A No. 8003 Electrose Knob is just the thing. These knobs are provided with a threaded bushing so that they may be screwed onto the rod.

The proper position for the discharge rods is shown in Figure 1. By sliding the rods back and forth in the balls on the ends of the collectors, the distance between the balls on the ends of the rods may be varied.

The spark discharge from the machine, when the latter is completed, takes place between these balls.

The machine still remains to be fitted with the "neutralizers" and a set of Leyden jars.

*The Neutralizers* are illustrated in Figure 14. Two are required. They consist of a piece of one-eighth inch brass rod, six inches long, having the ends bent over at right angles so as to form a shallow U. The distance between the ends when bent should be about three and five-eights inches. A tuft of tinsel should be soldered to the ends of each of the neutralizers.

[Illustration: FIG. 10.—The Collector with the Discharge Rods, etc, in position. A is the Brass Ball forming one terminal of the gap across which the sparks jump. B is another Brass Ball screwed onto the end of the Collector Rod and having a hole in it, through which the Discharge Rod slips. CC are two threaded Washers used to clamp the Discharge Rod in place.]

Each neutralizer rod is supported by a hard rubber washer three-quarters of an inch in diameter and five-sixteenths of an inch thick. In the centre of the washer a hole should be drilled, which will fit snugly onto the rods upon which the plates are mounted and revolve. The neutralizer rod passes through a hole in the upper part of the washer as shown in the illustration.

Before the neutralizers can be put into position it will be necessary to pull out the rods which support the plates so that the plates can be removed. The hard rubber washers supporting the neutralizers are then slipped over the rods so that one will come between each support and plate when the latter is put back into position. The rods should be turned so that the tinsel tufts touch the sectors. The rubber washers should fit snugly on the rods so that the neutralizer will stay in any position in which it is placed. The proper position for the front neutralizer is a little less than half way between vertical and horizontal as shown in Figure 1. The neutralizer behind the rear plate should be at right angles to that in front.

[Illustration: FIG. 11.—Showing how Binding Posts may be substituted for
Round Balls on the Collector Rods.]

The machine is now all ready for operation. In order for it to operate satisfactorily it is necessary for it to be warm and dry. It is, therefore, a very good idea to thoroughly dry the woodwork and give it a coat of varnish or shellac so that it cannot absorb any moisture. It may be necessary to start the machine by rubbing a glass rod with a piece of flannel or silk and then touching the rod to some of the sectors. The handle of the machine should be turned from left to right, that is, in such a direction that the front plate revolves in the same direction as the hands of a clock.

If the machine is in proper working order a stream of small sparks should flow between the spark balls on the ends of the discharger rods, provided they are not over a half inch apart, when the crank is turned.

The spark can be intensified and lengthened by fitting the machine with two small Leyden jars.

*The Leyden Jars* are made from small test tubes three inches long. The inside of the tube should be coated with tinfoil to within about one inch from the top. The outside of the tube should be coated in the same manner for the same distance. The tinfoil can be secured to the glass with shellac.

The top of the Leyden jars is closed with an ordinary cork. A piece of heavy brass wire bent into the form of a hook should pass through the cork and make connection with the tinfoil on the inside of the tube. One Leyden Jar should be hung over each of the collector rods by means of the hook. The tinfoil coatings on the outside of the jars should be connected together by a piece of wire running across from one tube to the other.

[Illustration: FIG. 12.—Details of the Discharger Rods.]

The machine is now complete and ready for performing a number of very interesting experiments.

Experiments with Static Electrical Apparatus.

*A Leyden Jar* is a very simple device for accumulating and storing static electricity. It consists simply of a wide mouthed jar or bottle coated with tinfoil part way up on both the outside and the inside in exactly the same manner as the small test tubes used on the static machine.

Not all glass jars are suitable for making Leyden Jars. The quality of the glass varies considerably and some will be found far superior to the rest.

The glass vessels used by chemists and called "beaker glasses" usually make excellent Leyden Jars.

It is not very difficult to make a good Leyden Jar. After you have selected the jar or bottle you wish to use, clean and dry it very thoroughly. Then give the inside a thorough brushing over with shellac. Cut a strip of tinfoil which is long enough to go all the way around the inside of the jar and about two-thirds its height. Before the shellac is thoroughly dry but is still sticky, insert the tinfoil strip carefully into the jar and press it smoothly against the glass.

[Illustration: FIG. 13.—The Supporting Bar upon which the Collector Rods are mounted. Made of hard rubber so as to be a perfect Insulator.]

The outside of the jar should also be given a coat of shellac and covered with tinfoil in exactly the same manner. The tinfoil on the outside of the jar should be the same height as that on the inside. The bottom of the jar should be coated, both inside and out by cutting two circular pieces out of the tinfoil and sticking them on with shellac.

The jar should be provided with a wooden cover which will fit snugly into the top. The wood should be dried and then given a coat of shellac so that it cannot absorb any moisture.

[Illustration: FIG. 14.—The Neutralizers. Two are required. They are bent out of Brass Rod and fitted with a Tinsel Tuft at each end. The centre piece upon which the Rod is mounted should be of Hard Rubber.]

It may perhaps be well at this point to emphasize how highly important it is to always keep all static electrical apparatus thoroughly dry and to construct it so that it will not collect or absorb any moisture.

A small hole should be bored through the centre of the cover so as to permit a brass rod to pass through. A piece of spring wire bent into a spiral should be attached to the lower end of the rod. When the cover is in position, the spring wire should make contact with the tinfoil on the inside of the jar.

It is a very good idea to fit the top of the rod with a small brass ball. This will prevent the electricity from "leaking" from the sharp corners on the end of the rod. Static electricity leaks very easily from sharp corners or points, but does not escape so readily from round corners or balls.

[Illustration: FIG. 15.—Details of the Leyden Jars. They are simply small Test Tubes, coated inside and outside with tinfoil for about two-thirds their height and fitted with a Brass Rod connected with the inside coating.]

The Leyden jar may be "charged" with electricity from the static machine by connecting a wire from one of the discharge rods to the outside tinfoil coating on the jar. Another wire should be connected from the other discharge rod to the rod on the jar which connects with the inside tinfoil coating.

Turning the handle of the machine rapidly for ten or fifteen seconds will charge the jar. Disconnect the wires as promptly as possible so that the electricity in the jar will not have a chance to leak back into the machine. Be very careful while doing this, however, because if you should happen to touch the tinfoil on the outside of the jar and the rod which connects with the inside coating at the same time you will get one of the surprises of your life.

[Illustration: FIG. 16.—A Large Leyden Jar for experimental purposes.]

The shock won’t really hurt you any but it will be very uncomfortable and somewhat surprising.

You can discharge a Leyden jar by bringing a piece of wire which is connected to the outside coating, near to the knob on the rod. When the wire is close to the ball the electricity will jump across the space in the shape of a snapping white spark.

The Leyden jar can be used in connection with a number of experiments described later on.

[Illustration: FIG. 17.—Showing how to Discharge a Leyden Jar with a curved piece of stiff wire fitted to a Wooden Handle.]

*Bottled Lightning.* A very pretty effect can be obtained by passing the spark from a Leyden jar or a static machine over a "lightning board." A "lightning board" consists of a pane of glass having a number of small squares of tinfoil stuck on it so that when the electrical discharge is passed over it, sparks take place between the little tinfoil squares and produce an effect something like miniature lightning.

A lightning board suitable for the static machine just described may be made from a strip of ordinary window glass about nine inches long and two inches wide.

Clean the glass thoroughly and then give it a coat of shellac on one side. As soon as the shellac becomes sticky, lay on a strip of tinfoil the same size as the glass and rub it down smoothly. When the shellac has thoroughly dried so that the tinfoil is stuck tightly to the glass, the board is ready to be cut up into squares. This can be best accomplished by means of a sharp knife and a ruler. Use care in doing the work so as not to tear the tinfoil and be sure that the knife cuts all the way through to the glass. Leave two solid strips of tinfoil at each end to which to make connections.

[Illustration: FIG. 18.—The "Lightning Board" is simply a Strip of Glass covered with small Tinfoil Squares. It may be insulated by mounting on a Bottle. The two Wires attached to the wide Tinfoil Strips at the ends of the "Board" are for connection to the Static Machine or Leyden Jar.]

The lightning board should be mounted by cementing it in a slot in a cork in a bottle so that the glass bottle serves as an insulated support.

If one of the tinfoil strips left solid at the end of the board is connected to one of the discharge rods on the static machine and the other end is connected likewise to the other discharge rod innumerable little sparks will zig-zag between the tinfoil squares when the machine is set in operation. The effect is quite pretty if the experiment is performed in a dark room.

The Leyden jar can be charged by the static machine and discharged through the lightning board. The sparks produced by the Leyden jar will be much more brilliant than those of the static machine above.

A very pretty effect can be produced by arranging the tinfoil in the form of a pattern or design as for example that illustrated in Figure 19. A strip of glass about the same size as that used for the lightning board may be employed. The glass is coated with shellac and as soon as it becomes sticky, small rectangular pieces of tinfoil arranged in a zig-zag pattern and having small spaces between them, are stuck in position. The end pieces are made larger than the other strips so as to afford means for connecting the wires. The strip should then be insulated and mounted by cementing it in a slot in the cork of a glass bottle.

[Illustration: FIG. 19.—A very pretty effect can be produced by arranging small tinfoil strips on the Glass in a Pattern. Each strip should be separated from the other just far enough for a Spark to pass.]

The apparatus shown in Figure 20 is made according to the same plan but the glass in this case is in the form of a square instead of a strip. The tinfoil strips are arranged in the form of a seven pointed star or any other pattern which may be desirable. The two large strips A and B are the ones to which the wires should be connected.

*The Electric Parasol* is illustrated in Figure 21. It is made by pasting some narrow strips of tissue paper, about three-sixteenths of an inch wide and three or four inches long, to a small cork which has previously been covered with tinfoil. The strips can be made most easily by cutting a small sheet of tissue paper into strips like the teeth of a comb as shown in the upper right hand corner of Figure 21. The tinfoil covered cork should be mounted on the upper end of a stiff copper or brass wire supported in a bottle.

If this wire is then connected to one of the discharge rods on the static machine and the hand held to the other, the paper strips will spread out like a parasol or umbrella, as soon as the machine is set in operation.

[Illustration: FIG. 20.—A very pretty design made by arranging the Strips in the form of a Seven-pointed Star. Flowers, initials or almost any pattern may be made in the same way.]

A novel experiment somewhat similar in principle to the "electric parasol" is that shown in Figure 22.

Three small paper birds about the size of that shown at the right hand side of the illustration should be cut out of tissue paper and each one attached to a piece of cotton thread about six inches long. The threads are then tied to one end of a T-shaped frame bent out of copper wire and supported on a bottle.

If the wire frame is then connected to one of the discharge rods and the hand held to the other while the machine is set in operation, the birds will rise in the air and fly around as far as the threads will let them.

[Illustration: FIG. 21.—The Electric Parasol. The upper right-hand corner shows a piece of Tissue Paper cut into Strips. (1) Is the apparatus before the Tissue Paper is fastened to the Cork. (2) Shows the completed "Parasol" and (3), the Parasol when connected to the machine and the latter is set in operation.]

*Electric Acrobats.* The apparatus shown in Figure 23 consists of a circular metal plate about four inches in diameter suspended by a wire from a wire "T" stuck in a cork in a bottle. Another circular metal plate of the same size is laid on the table below the other. The distance between the two plates should be about one inch or an inch and one-half.

Cut three or four little figures, the same size as that shown in the upper right hand part of the illustration, out of tissue paper and lay them on the bottom plate.

[Illustration: FIG. 22.—Electric Birds. The Birds are made of Tissue Paper and should be about the size and shape shown in the lower right-hand corner of the illustration above.]

The circular metal plates may be made of sheet tin, copper, brass or galvanized iron. Even cardboard, provided that it is covered with tinfoil, will serve.

The upper plate should be connected to one discharge rod on the static machine and the lower plate to the other. Then as soon as the machine is set in operation the little paper figures will begin to dance up and down, stand on their heads, hang by one foot or hand, turn somersaults and perform all sorts of stunts.

*Gunpowder* may be ignited by the spark from a Leyden jar. A miniature mortar may be made from a piece of broom handle about an inch and one-half in diameter with a hole one inch deep in one end as shown by C Figure 24. The mortar should be fastened to a small wooden base which will support it in an inclined position as in the illustration.

[Illustration: FIG. 23.—Electric Acrobats. The Acrobats are made of paper. The little figure in the upper right-hand part of the illustration is the proper size.]

Bore two small holes through the wall of the mortar, near the bottom and exactly opposite to each other Insert two short pieces of coper wire, W, W, in the holes and fasten them tightly in position. The ends of the wires should be about one-eighth of an inch apart.

A small pinch of gunpowder is then placed in the bottom of the mortar.

Charge the Leyden jar and then discharge it through the mortar by connecting it to the two wires W, W. As soon as the spark passes, the powder will explode. An experiment such as this should be performed cautiously and the face and hands should be kept away from the powder. Do not put more than a pinch of powder in the mortar at a time and by all means keep the reserve supply out of the way so that there will be no danger of exploding it by accident.

*An Electric Whirligig* is an interesting piece of apparatus which may be built by following the suggestions contained in Figure 25.

[Illustration: FIG. 24.—The Electric Mortar. C is the Mortar, P the Powder, B a Small Ball and W W the two Wires between which the Spark igniting the powder takes place.]

Mount four pieces of dowel about three inches long at the corners of a wooden base about eight inches long and two inches wide so that they form four vertical posts as shown by A, B, C, D.

The dowels, as well as the wooden base should be carefully dried and shellaced so that they will not absorb any moisture.

Stretch two pieces of straight stiff wire between the posts A C and B D, near the top. The wires should be perfectly straight and level.

The whirligig itself is made by passing a sewing needle through the axis of a small cork. Four small wires having the ends bent over at right angles should then be stuck in the cork as shown in the upper left hand part of Figure 25. All of the wires should point in the same direction.

[Illustration: FIG. 25.—An Electric Whirligig.]

The four wires should all be the same length so that the whirligig is perfectly balanced. The cork is then covered with tinfoil so that there will be an electrical connection between the four small wires and the needle forming the shaft.

The two wires A C and B D are connected together by a wire A B and a piece of flexible wire led to the Wimshurst machine. The opposite side of the Wimshurst machine is then grounded or touched with the hand. If the whirligig is laid on the wires A C and B D as shown in the illustration and it is perfectly balanced it will commence to revolve and roll along the wires just as soon as the Wimshurst machine is set in operation. It is the escape of the electricity from the points of the four wires on the whirligig which causes this.

Other interesting experiments in static electricity may be performed with the aid of a Wimshurst machine and the experimenter who is sufficiently interested to continue farther is referred to any good book on physics or some such volume as "The Boy Electrician".

CHAPTER II. CELLS AND BATTERIES.

Sources of Current. One of the chief difficulties of the average young experimenter is to secure a satisfactory source of current for operating his apparatus.

There are three means at his disposal and he may draw his electricity from

1. A power or lighting circuit;
2. A dynamo;
3. Batteries.

[Illustration: FIG. 26.—A Voltaic Cell. A Voltaic Cell consists of a
Strip of Copper and a Strip of Zinc immersed in a dilute solution of
Sulphuric Acid.]

Only those who are so fortunate as to live in a house wired for light and power service and supplied from the street mains, are likely to be able to utilize the first named. Those experimenters who live in towns where there are no commercial power wires or whose homes are not wired for such service will have to therefore depend upon a dynamo or a battery.

A dynamo is a very satisfactory source of current, provided some sort of power, such as a windmill, water motor or small engine is available for driving it. A hand dynamo is unsatisfactory for some purposes because the experimenter is usually unable to drive the dynamo and attend to other work at the same time.

Batteries are the most expensive source of current but for many reasons, as explained above, are all that is available to the average experimenter.

There are two classes of batteries, known as

1. Primary batteries; 2. Secondary or storage batteries.

*Primary Batteries* are those which generate their own current by the action of some chemical such as, for example, an acid upon a metal.

*Secondary Batteries* derive their current from a dynamo or other source of electricity and store it away in the form of *Chemical energy* until it is used up. A storage battery might be likened to a pail, which can be carried to a dynamo and filled full of electricity. Those who possess a storage battery can recharge it themselves from the 110-volt lighting or power circuit, from a dynamo or by taking it to an automobile garage where recharging is done.

Homemade batteries are not as practical as those which can be purchased ready made, but the knowledge and experience gained in making your own are so valuable that every experimenter is urged to start in this way.

Various materials such as zinc, copper, carbon, etc., can be used to make some very interesting and valuable batteries.

One of the most common mistakes made in reference to cells and batters is in calling a single cell a *battery*. One cell is a cell. More than one cell connected together is a *battery of cells* or simply a *battery*.

The Voltaic Cell.

The first practical cell was invented in 1786 by an Italian professor named Volta and it is, therefore usually called the Voltaic cell.

A Voltaic cell may be easily made by the experimenter, by placing some water, mixed with sulphuric acid, in a glass tumbler or a jelly jar and then immersing therein a strip of zinc and a strip of copper, each about four inches long and one inch wide. The strips must be kept separate from one another and should be scraped clean and bright before they are placed in the solution. A copper wire is fastened to the top of each one of the strips. The acid solution should be composed of one part of acid, mixed with ten parts of water.

When mixing acid and water, always remember to pour the acid into the water and never pour water into acid. Otherwise the solution will suddenly become very hot and is liable to crack the jar. Acid should always be mixed in a glass or earthenware vessel and never in any sort of a wooden or metal receptacle, because it will attack and dissolve metals and wood.

As soon as the acid has been prepared for the Voltaic cell fill a tumbler about three quarters full and then immerse the zinc and copper strips therein. As soon as the strips are in the acid, bubbles will commence to rise from the zinc. These bubbles are a gas called hydrogen and are evidence of a chemical action which takes place in a battery. The zinc is being dissolved by the acid and during the process, sets free hydrogen gas.

It will probably be noticed that very few bubbles arise from the copper plate and that there seems to be little chemical action there.

It will also be noticed that if the two wires connected to the strips are brought together the bubbles will arise from the zinc much faster than before. That is because, when the wires are connected together, a complete electrical circuit is formed: The zinc is really being oxidized or slowly burned. If zinc is burned in the open air or in a fire it will give out its energy in the form of heat but when it is burned in an acid solution in the presence of another metal it gives out its energy in the form of electricity.

The zinc strip in a Voltaic battery is known as the *negative* pole or cathode, and the copper strip, as the positive pole or anode. When the electrical circuit is completed by touching the two wires connected to the poles together, the current is supposed to flow from the positive pole through the wires and back into the solution through the negative pole.

If the two wires, instead of being connected together, are connected to an electrical instrument called a voltmeter the needle or pointer on the meter will swing over and point to about one volt.

*A Voltmeter* is an instrument for measuring electrical pressure or *potential*. The pressure of an electric current is measured in *volts* just as the pressure of water may be measured in *pounds*.

If the copper strip is lifted out of the solution and a carbon plate or rod also having a wire attached is substituted in its place it will be found that the voltage or potential has increased to one and one-half volts. Zinc and carbon are said to have a greater potential difference than zinc and copper and inasmuch as it is usually desirable for a battery to have the greatest potential difference possible, zinc and carbon are employed in the batteries of to-day instead of zinc and copper.

If the wires are then disconnected from the voltmeter and connected to an electrical instrument called an *ammeter*, the needle or pointer will probably swing over until it indicates a current of perhaps ten amperes. An *ammeter* is an instrument for measuring the volume of an electric current. An *ampere* is a unit of current and is used to designate the rate of flow just as feet per second are used to denote rate of flow in the case of water in a pipe.

If the meter is allowed to remain connected to the cell for a short time it will be noticed that the pointer will commence to slowly drop back towards zero.

The cell is then becoming *polarized*, which is to say that small bubbles of hydrogen which are liberated by the chemical action, collect on the carbon and cause the strength of the battery to fall off. If the battery is agitated or the carbon is lifted out and scraped it will be found that the current will immediately rise again to its first strength.

It would be a nuisance if it were continually necessary to scrape the carbon or shake the battery so as to avoid *polarization* and so another means is employed to secure the desired result.

This is accomplished by introducing certain chemicals into the solution which will give forth *oxygen*. When oxygen and hydrogen meet under proper conditions they combine and form ordinary *water*.

*Bichromate of potash* or as it is also often called *potassium bichromate* is the chemical most commonly employed for this purpose.

[Illustration: FIG. 27.—Ordinary Jelly Glasses, Tumblers, Fruit Jars, etc, make good Jars for small cells by cutting off the tops.]

Homemade Batteries.

*The materials* required for making batteries, suitable as a source of current for the experimenter, will not be found expensive in most cases.

*Carbon rods* and *plates* may be purchased from an electrical supply house but they can also be easily and cheaply obtained from old dry cells. Dry cells may be split open with a cold chisel and a hammer. Care should be exercised not to break the carbon in removing it.

The round carbon rods used in arc lamps may be used for making batteries provided that if they are copper plated, the copper is first removed by immersing the rod in a bath of nitric acid. If this precaution is not taken there will be a "local action" set up between the copper and the carbon and the battery will not be as efficient as it will be if the copper is removed.

Carbon rods and plates are easily drilled with an ordinary hand drill. Carbon is quite brittle and breaks easily, therefore only very light pressure should be used.

While zinc rods and plates may also be purchased they are easily made by the experimenter who possesses a little ingenuity. The melting point of zinc is quite low. It can be melted in a small iron pot and cast into the form of rods or plates in plaster-of-Paris moulds. Plates may also be cut out of heavy sheet zinc.

[Illustration: FIG. 28.—A Simple Home-made Cell.]

Ordinary jelly-glasses, tumblers, fruit jars, etc., make good jars for small cells. The tops of fruit jars and batteries can be cut off so as to make the opening larger.

The cutting can be done with an ordinary glass cutter or by filling a scratch completely around the jar or bottle, at the place it is desired to cut it off, with a three cornered file. If a hot poker or wire is then held against the scratch it will commence to crack along the line and follow the hot poker as it is drawn around.

[Illustration: FIG. 29.—A Home-made Battery having two Carbon Plates with a Zinc Rod between.]

Figure 28 shows a simple arrangement consisting of a carbon and a zinc plate mounted upon a wooden strip. The strip is used to support the plates and rests across the top of the jar so that the plates hang below in the solution. Most chemicals attack wood and for that reason it is well to dip the strip in some hot paraffin. The carbon and zinc plates are fastened on opposite sides of the wooden strip by means of a round headed screw and a washer. A wire lead should be placed under the washer on each plate. If the screw and washer are then smeared with some hot paraffin or vaseline they will be protected from corrosion.

Care should be used so that the two screws employed to fasten the plates to the strip do not touch each other in the wood. If they should, the battery will be "short circuited" and the current will flow through the screws instead of the wires.

Figure 29 shows an arrangement consisting of two carbon plates mounted upon a wooden strip. The zinc element consists of a rod set in a whole in the strip between the two carbon plates.

It will be found that two carbon plates will form a better cell than one with only one plate or rod.

The arrangement illustrated in Figure 30 shows two carbon rods and one zinc rod clamped between two wooden strips. The zinc rod is placed in the center and the carbons to either side.

[Illustration: FIG. 30.—The Elements for a Simple Home-made Cell composed of two Carbon Rods and one Zinc Rod clamped between two Wooden Strips.]

The wooden strips are cut away a bit at the points where they clamp the rods so as to form sort of a groove into which the rods fit without slipping or twisting. The strips are drawn together tightly at the ends by two wood screws.

When more than one carbon rod or plate is used in a cell, the carbons should all be connected together so as to form a single unit.

The drawing in Figure 30 shows a wire twisted around the carbons so as to connect them together but it would be a far better connection if the wire was clamped between the carbons and the wood so that it is held firmly.

Four carbon rods may be utilized by following the suggestion shown by the drawing in Figure 31.

This consists of a square piece of wood about 4 x 4 inches and one-half of an inch thick.

[Illustration: FIG. 31.—Four Carbon Rods and one Zinc Rod arranged to form the Elements of a Cell.]

A zinc rod is set in a hole in the center. Four carbon rods are set in a circle around the zinc and held in place by screws. All the carbon rods should be connected together. The wooden top not only serves to support the carbon and zinc rods, but will also act as a cover for the cell and prevent the solution from evaporating.

Battery Solutions or Electrolytes.

It has already been shown how cells become "polarized" when the solution consists simply of sulphuric acid and water. An ordinary acid solution also has the further disadvantage that the zinc element is continually consumed by the acid when it is in the solution, regardless of whether current is being drawn from the cell or not. It is of course consumed more rapidly when the circuit is complete and current is flowing than when it is not, but the action is still nevertheless sufficiently rapid to entirely consume the zinc even in the latter case in a very short time. If an ordinary acid solution is used therefore as the liquid or *electrolyte*, as it is technically termed, it is always necessary to lift the elements out of their solutions whenever the cells are not in use. They should be lifted out and carefully washed so as to remove all traces of acid.

[Illustration: FIG. 32.—A Battery of Three Cells arranged so that they can all be lifted out of the solution at once.]

A milder chemical which does not attack the zinc so rapidly as an acid is often used wherever a battery is to be employed for ringing bells, operating sounders, telephoning, etc., and only a small amount is required.

Sal-ammoniac or chloride of ammonium, as it is also called, is a good chemical for this purpose. It is very cheap and only requires to be dissolved in water. A good strong solution should be made and an element consisting of several carbons and one zinc such as those shown in Figures 29, 30 and 31 used.

Such a cell will give about 1.5 volts and 3 or 4 amperes. If the current is drawn from the battery continuously or too rapidly, it will also *polarize* and the current will begin to fall off. The advantage of a sal-ammoniac cell is that the elements may be left in the solution when the cell is not in use, without appreciable waste of the zinc.

A very powerful cell of the non-polarizing type capable of delivering a heavy current and having an E. M. F. of two volts can be made by adding some potassium bichromate to a sulphuric acid solution.

An electrolyte of this sort may be prepared by dissolving four ounces of bichromate of potash in sixteen ounces of water. Add to this, four ounces of sulphuric acid. The acid should be added slowly and the solution stirred at the same time.

This solution will be found an excellent one to use with cells having carbon and zinc elements. The current and voltage are much higher than those of an ordinary acid solution.

This type of cell also has the disadvantage that the zincs waste away rapidly when in the solution, regardless of whether current is being drawn or not. This can be partly overcome by *amalgamating* the zincs with mercury. In order to amalgamate your battery zincs, procure a little *mercuric nitrate* from a druggist or chemical house. Dissolve the mercuric nitrate in a small amount of water and then rub the zincs with a wad of cotton or cloth which has been dipped in the mercuric nitrate solution.

The arrangement shown in Figure 32 is a very convenient one to follow in arranging a battery of three or more cells. The elements of three cells are all mounted upon a strip of paraffined wood and connected in series. The three battery jars are placed in a row so that each pair of elements will dip into their proper jar when the strip is laid across the tops.

Such an arrangement is not only more compact than one having the elements composing each cell mounted upon separate strips, but will be found very convenient when an electrolyte composed of bichromate of potash and acid is used, because all the elements may then be raised out of the solutions at the same time.

It is possible to place the jars in a frame and arrange a windlass fitted with a crank so that the elements may be easily raised or lowered from and to the solution. Such an arrangement is called a "plunge battery."

Connecting Cells.

Cells may be connected either in *series*, in *multiple*, or in *series-multiple*, depending upon the number of cells to be used and the amperage and voltage desired.

[Illustration: FIG. 33.—Showing how Cells are arranged when they are connected in Series. The Voltage of Six Dry Cells connected in series as above would be approximately 6 x 1.5 or 9 Volts.]

Cells are in series when they are connected with a wire leading from the negative pole of one of the positive pole of another, so that the current flows through each one in turn. Figure 33 shows six cells connected in series. Cells are placed in series when voltage is the most important factor. The total voltage of the battery is then equal to the sum of the voltages of the cells. For example, the voltage of the ordinary dry cell is about 1.5 and therefore if four dry cells are connected in series the total voltage of the battery will be six. If six dry cells are connected in series the voltage at the terminals will be about nine.

When a heavy amperage is desired, cells are connected in multiple. Figure 34 shows six cells connected in multiple. It will be noticed that all the negative poles are connected together to form one terminal, while all the positive poles form another. The amperage of the average dry cell is about 20. The amperage of a battery of cells connected in multiple is equal to the sum of the amperages of the separate cells. The amperage of four cells connected in multiple will be about 80 and about 120 in the case of six cells.

[Illustration: FIG. 34.—Showing Six Dry Cells connected in Multiple. The
Voltage of such an arrangement would only be 1.5, but the Amperage
available would be six times that possible from Cells connected as in
Figure 33.]

The life of the average dry cell is about twenty ampere hours under normal conditions. If however the cell is discharged at a high rate, say for instance, five amperes, it will be found that the life is less than twenty ampere hours. On the other hand, if the discharge rate is very low, as for example, one-quarter of an ampere, the capacity of the cell will be greater. In order to get the most economical service from a battery it is therefore advisable to lighten the load as far as possible, and cells are consequently often connected in *series-multiple* with that result in view. In a case, for illustration, where it might be desirable to secure a current 4 1/2 volts and five amperes from dry cells, the series-multiple arrangement could be recommended. Three dry cells connected in series will furnish 4 1/2 volts and five amperes, but by using two sets as in Figure 35, the load is divided between them and each set will only have to furnish amperes to the circuit. *Two sets of cells used in series-multiple will therefore last more than twice as long as either set would alone.*

The series-multiple arrangement is recommended where cells are to be used for operating toy trains, induction coils, motors, etc., as being the most economical.

Always be sure to use large wire in connecting cells. Fine wire offers considerable resistance to the electrical current and the full benefit of the batteries cannot be secured when it is used.

[Illustration: FIG. 35.—Showing how to connect a Battery of Cells in
Series-Multiple.]

Use care to scrape all connections so that they are clean and bright. Tighten the binding posts with a pair of pliers so that there is no chance of their becoming loose.

Another wise precaution is to always arrange batteries so that there is a small space between two cells and no likelihood of any of the wires or binding posts coming into contact with one another so as to form a short circuit.

After the connections have been carefully made a little vaseline smeared over them will prevent corrosion.

[Illustration: FIG. 36.—Battery Connectors like that shown above can be obtained for 1 1/2 cents each and will be found to be very handy.]

Storage or Secondary Cells.

Storage or secondary cells (also sometimes called accumulators), differs from primary cells in that they will not give forth an electric current until they have been *charged* by passing an electric current through them.

[Illustration: FIG. 37.—A Simple Experimental Storage Battery consisting of two Lead Plates immersed in Dilute Sulphuric Acid.]

The Storage Cell is therefore a very convenient means of taking electric energy at one time or place and storing it up for future use. From this it must not be implied that electricity is actually stored in such a battery. The energy of the electric current is really changed into chemical energy and this energy produces electricity when the cell is again discharged.

The superiority of the storage cell over any other form of battery is universally recognized. The dry cell has an E. M. F. of only 1.5 volts and deteriorates rapidly with age. The E. M. F. of a storage cell is 2 volts, or 33 1/3 per cent higher. Storage cells will operate almost any electrical device with increased power over any other form of battery. A wireless set will send farther, lamps will turn steadier and a motor will give more power.

[Illustration: FIG. 38.—Showing how to charge a Simple Storage Cell composed of two Lead Plates immersed in Sulphuric Acid by connecting it to two Bichromate of Potash Cells.]

If properly cared for, a storage cell will last indefinitely. It may be recharged an unlimited number of times and is exactly as good as new each time. A dry cell must be thrown away when discharged.

Storage cells are rated by their output in *Ampere Hours.* An *Ampere Hour* is the amount of current represented by one ampere flowing for one hour. A 10 ampere hour cell will give 2 amperes for five hours, 1 ampere for 10 hours, 1/2 ampere for 20 hours, etc. The ampere hour capacity of a cell divided by the amount of current being used will determine how long that current can be drawn before recharging is necessary.

Storage cells may be recharged from any source of *direct* current, that is, from the lighting circuit, in series with a lamp, from a small shunt wound dynamo, from dry cells or other primary batteries, or from alternating current by using a *Rectifier*.

An Experimental Storage Cell.

Storage cells consist of lead plates immersed in an electrolyte of dilute sulphuric acid.

Cut two strips, one inch wide and five inches long, out of sheet lead about one-eighth of an inch thick.

Attach a wire to each one of the plates and then immerse them in a jar full of *electrolyte* composed of:

1. Ten parts of water.
2. One part of sulphuric acid.

Connect the wire leading from the plates to a voltmeter and you will notice that the pointer will not move away from zero.

Disconnect the wires and mark one plate as the *positive*, by means of a little cross; mark the other plate *negative*, with a straight line.

Connect two good bichromate cells in series and lead the positive terminal to the lead plate marked with a cross. Connect the negative pole of the battery to the other lead plate. Bubbles of gas will immediately begin to arise from the lead plates. Let the batteries remain connected for about five minutes and then remove them. If you then connect the two lead plates to the voltmeter again you will find that the needle now swings nearly to two volts.

You will also find that your storage cell, for the two lead plates are now a storage cell, will also ring a bell or run a small motor for a few seconds.

The two lead plates became *charged* when the current from the bichromate cells was passed through them. This little experiment illustrates the principle of the storage cell very well.

A storage cell made of lead plates in the manner just described would not possess sufficient capacity to make it worth while as a practical cell. It has been found that if instead of a solid flat plate, a framework or grid is used, consisting of a set of bars crossing one another at right angles, leaving spaces between, which are filled with a paste made of lead oxides, there will be a considerable gain in the capacity of the cell.

A Homemade Storage Cell.

The storage cell illustrated in the accompanying illustrations is very simple to make and a battery of them capable of delivering six or eight volts will prove a very convenient source of current for performing all sorts of electrical experiments.

[Illustration: FIG. 39.—Showing how the Plates for a Storage Cell may be made from Sheet Lead by boring it full of holes and filling with paste.]

The plates are cut from sheet lead from one-quarter to five-sixteenths of an inch thick. The height and width will depend upon the size of the jars used. There are several sizes of rectangular glass storage cell jars on the market, and if the plates are made about three inches wide and three and one-half inches high, they will fit the smallest size of jar. A lug about one inch and one-half long and three-quarters of an inch wide is left projecting at the top.

Three plates are used in each cell. Each cell will have an E. M. F. of two volts when fully charged. In order therefore to have a battery capable of delivering six volts, three cells will be necessary. Nine plates will be required for three cells.

The body of the plates should then be drilled full of holes about one-eighth of an inch in diameter as shown by B in Figure 39.

The plates are now ready for pasting. Select three of the plates and mark them with a small cross. These are to be *positive* plates when finished. The paste for these plates is made by mixing red lead with diluted sulphuric acid. The paste should form a good stiff mixture. Lay the three plates upon a smooth board and press the paste carefully into the holes with a flat stick. They are then laid aside to dry and harden.

[Illustration: FIG. 40.—A set of three Plates composed of One Positive and Three Negatives assembled to form a Cell.]

The six remaining plates are to be *negatives* when finished and they are pasted in identically the same manner as the positives except that the paste is made of a mixture of yellow lead and dilute sulphuric acid instead of red lead.

A pasted plate is shown at the right in Figure 39.

Cut six rectangular pieces, three by three and one-half inches, of heavy blotting paper or thin whitewood. The thin wood used in the construction of fruit baskets may be used for this purpose. These rectangles are to be used as "separators" between the plates.

[Illustration: FIG. 41.—Glass and Rubber Storage Cell Jars which are on the market for the Electrical Experimenter and may be purchased very reasonably.]

The plates should then be assembled in groups of three, as shown in Figure 40. The positive plate is placed in the centre with a separator on either side. Two negative plates are then placed on the outside. The lugs on the negative plates should come opposite to each other. A square lead block having a hole bored through the centre may be placed between the two negative lugs. The lugs are then clamped together with a binding post and a screw. The plates are held in a compact bundle by two heavy rubber bands passing around them.

Each group of plates is then placed in its proper jar and the jar filled full of a mixture composed of:

1. Four parts of water, and 2. One part of sulphuric acid.

The plates are now ready for forming.

The cells are connected in series by leading a wire from the negative of one to the positive of another and so on.

The terminals of the battery are then connected to a steady source of direct current of at least ten volts. The positive pole of the battery should be connected to the positive of the current source and the negative to the negative.

The source of current may be (1) the 110 volt D. C. supply in series with a lamp bank as described in Chapter IV; (2) the 110 volt A. C. supply after it has passed through a rectifier; (3) another battery, or (4) a shunt wound dynamo.

[Illustration: FIG. 42.—An empty Storage Cell Grid and also a Pasted Plate both of which are on the market for experimenters who wish to build their own Cells.]

The current passed through the storage cells during the forming process should be about one ampere for cells of the size described above. As soon as the positive plates of the storage cells have changed to a dark chocolate-brown color and the negatives to a gray-slate, disconnect the storage battery from the source of current and proceed to use it just as you would any ordinary battery. Use it until it is exhausted and then connect to the charging current again, taking care to make certain that the positive pole of the battery is connected to the positive pole of the current source.

After the cells have been recharged and discharged in this manner about ten times they will be completely "formed" and ready for permanent service.

Complete directions for recharging storage cells and instructions for their care and maintenance will be found further on.

The only objection to the storage cells just described is that the paste is liable to fall out of the plates in time. The plates or "grids" as they are called used in commercial storage cells are cast in elaborate moulds which make it possible to overcome this difficulty. Such grids cannot however be made by the experimenter.

Jars, pasted plates and empty grids may be purchased from well known firms dealing in apparatus for the experimenter, and with their aid it is possible to construct a very substantial and durable storage cell at home.

The empty grids or fully formed plates may be purchased in the following sizes:

───────────────────────────────────────────────────────────────── Positive or Negative Plate, size 2 7/8 x 2 1/2 ───────────────────────────────────────────────────────────────── " 3 1/8 x 2 7/8 ───────────────────────────────────────────────────────────────── " 3 5/8 x 5 3/4 ───────────────────────────────────────────────────────────────── " 4 3/4 x 2 7/8 ───────────────────────────────────────────────────────────────── " 4 3/4 x 5 3/4 ─────────────────────────────────────────────────────────────────

Glass jars will be found satisfactory for stationary batteries. Rubber jars are however advisable for portable batteries. Jars of the following sizes may be easily obtained:

────────────────────────────────────────────────────────────────── Glass Jar, outside 3 3/4 x 4 x 1 1/2 inches ────────────────────────────────────────────────────────────────── Glass Jar, outside 3 3/4 x 5 x 1 1/2 inches ────────────────────────────────────────────────────────────────── Hard Rubber Jar, outside. 6 1/2 x 3 1/2 x 1 1/2 inches ────────────────────────────────────────────────────────────────── Hard Rubber Jar, outside. 6 1/2 x 6 1/2 x 1 1/2 inches ──────────────────────────────────────────────────────────────────

If the empty grids are purchased, they should be pasted in the same manner as those plates just described. An empty grid of this type is shown in Figure 42. A pasted plate is shown along side of it.

The two negative plates in cells of this type are fastened together by "burning" into a lug, The lugs for this purpose may also be purchased and will be found inexpensive.

The long lugs on the negative plates are cut off so that they will only just project through the rectangular holes in the "connecting lug" when the latter is in place, as shown by A in Figure 43.

The plates are "burned" into the connecting lug by using a red hot soldering iron to melt the lead until they flow together at those points. This is a job requiring a little skill and the experimenter had better practice burning some odd bits of lead together first so as to avoid all possibility of spoiling his plates.

[Illustration: FIG. 43.—Two Negative Plates "burned" together and the
Connecting Lug used.]

The positive plate is placed in position, as shown in Figure 44.

Wooden separators of the same size as the plates are placed between the plates and the whole strapped together with heavy rubber bands near the top and bottom.

The cells are then placed in their jars and the latter poured full of electrolyte, providing that the batteries are to be of the stationary or open type.

If it is desirable that they be portable and arranged so that the acid will not easily spill, it will be necessary to seal them at the top.

The sealing is accomplished by cutting a "cover" strip out of thin wood which will slip down over the lugs into the jar so that it comes about one-half an inch below the top. A small hole should be bored in the centre of the cover strip to receive a short piece of hard rubber or lead tubing, which will act as a vent and permit the gases formed during charging to escape or the electrolyte to be emptied at will.

[Illustration: FIG. 44.—The Elements of a Storage Cell composed of two
Negative Plates and one Positive Plate in their proper position.]

The cover strip should fit into the jar tightly so that when the sealing mixture is poured in it will not run down around the plates or into the jar.

The top of the battery is then poured full of a molten compound of asphaltum and pitch.

No attempt should be made to seal the batteries when they contain acid.
The inside of the jar should be clean and dry.

After the cells are sealed and filled with electrolyte they are ready for either forming or charging, depending upon whether the empty grids were purchased and pasted by the experimenter or the plates were bought already pasted and formed.