CHAPTER IV CELLS AND BATTERIES

CHAPTER IV CELLS AND BATTERIESIn 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 current. Furthermore, many boys have no source of power from which to drive a small dynamo. Batteries must therefore be resorted to in the majority of cases.A number of different cells and batteries are described in this chapter. All of them are practical, but after buying zinc, chemicals, etc., for any length of time, figure out what your batteriescostyou to make. The real value is not their cost in dollars and cents but in what you havelearnedin making them. If you have a continuous use for electrical current for runningsmallelectrical devices it is cheaper to buy dry cells, or what is better, astorage battery, and have itrechargedwhen necessary.Build your own batteries first. Then after you have learned how they are made and something about their proper care buy them from some reliable electrical house.Batteries are always interesting to the average experimenter, and when properly made are one of the most useful pieces of apparatus around the home, laboratory, or shop that it is possible to construct. Many hundreds of thousands of experiments have been carried out by capable men in an effort to discover or devise a perfect battery, and the list 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 fair service, have been chosen for description.Cells are usually consideredoneelement or jar of a battery. Acellmeans only one, while abatteryis agroupof cells. It is not a proper use of the word to say "battery" when onlyonecell is implied. This is a very common error.The Voltaic cellis called after its inventor, Volta, a professor in the University of Pavia, and dates back to about the year 1786.Fig. 52.—The Voltaic Cell.Fig. 52.—The Voltaic Cell.A simple voltaic cell is easily made by placing some water mixed with a little sulphuric acid in a glass tumbler and immersing therein two clean strips, one of zinc and the other of copper. The strips must be kept separate from each other. The sulphuric acid must be diluted by mixing it with about ten times its volume of water. In mixing acid with water always remember never to pour water into acid but to perform the operation the other way and pour the acid into the water. A copper wire is fastened with a screw or by soldering to the top of each of the strips, and care must 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 kept at opposite sides of the jar.The sulphuric acid solution attacks the zinc, causing it slowly to waste away and disappear. This action is calledoxidation, and in reality is a very slow process of burning. The consumption of the zinc furnishes the electric energy, which in the case of this cell will be found to be sufficient to ring a bell or buzzer, or run a very small toy motor.As soon as the plates are immersed in the acid solution, bubbles will begin to rise from the zinc. These bubbles contain a gas called hydrogen and they indicate that a chemical action is taking place. The zinc is being dissolved and thehydrogengas is being set free from the acid. It will be noticed that no bubbles arise from the copper plate and that there is little if any chemical action there. In other words, it seems that the chemical action at one plate is stronger than that at the other.A cell might be likened to a furnace in which the zinc is the fuel which is burned to furnish the energy. We know that if the zinc is burned or oxidized in the open air it will give out energy in the form ofheat. When it is burned or oxidized slowly in acid in the presence of another metal it gives out its energy in the form ofelectricity. The acid might be likened to the fire, and the copper to a hand which dips into the cell to pick up the current and takes no part chemically.If a wire is connected to each of the plates and the free ends of the wires touched to the tip of the tongue it will produce a peculiar salty taste in the mouth indicating the presence of a current of electricity.If the wires are connected to an electric bell, the bell will ring, or, instead, the current may be used to run a small motor. If the cell is made of two zinc plates or two copper plates, the bell will not ring, because no electricity will be produced. In order to produce a current, the electrodes must be made of two different materials upon which the acid acts differently. Current may be obtained from a cell made with a zinc and carbon plate or from one with zinc and iron.Therefore, in order to make a battery it is necessary to have a metal which may be consumed, a chemical to consume or oxidize it, and an inactive element which is merely present to collect the electricity.When the wires connected to the two plates are joined together, a current of electricity will flow from the copper plate through the wire to the zinc. The copper is known as thepositivepole and the zinc as thenegative.A simple voltaic cell may be easily made by cutting out a strip of zinc and a strip of copper, each 3 1/2 inches long, and one inch wide. A small hole bored through the upper end of the strips will permit them to be mounted on a wooden strip with a screw as shown in Figure 53. The connecting wires are placed under the heads of the screws. Care should be exercised to arrange the screws used for mounting the electrodes to the wooden strip so that they do not come exactly opposite, and there is no danger of the points touching and forming a short circuit.Fig. 53.—The Elements of Simple Voltaic Cell.Fig. 53.—The Elements of Simple Voltaic Cell.Fig. 54.—A Home-Made Voltaic Cell.Fig. 54.—A Home-Made Voltaic Cell.An ordinary tumbler or jelly glass will make a good battery jar. The exciting liquid should be composed ofOne part of sulphuric acidTen parts of waterOne of the disadvantages of the voltaic cell is that it becomespolarized, that is, small bubbles of hydrogen which are liberated by the chemical action collect on the copper plate and cause the strength of the battery to fall off rapidly.There are a great number ofelements, as the zinc and copper are called, and an even greater number of different solutions orexcitantswhich can be employed in place of sulphuric acid to make a cell, forming an almost endless number of possible combinations.Leclanche Cell.One of the most common forms of cell employed for bell-ringing, telephones, etc., is called the Leclanche cell, after its inventor, and consists of two elements, one of zinc and the other of carbon, immersed in a solution ofsal ammoniacorammonium chloride. This cell has an E. M. F. of 1.4 volts, which is about half as much again as the voltaic cell.Fig. 55.—Carbon-Cylinder Cell, and Cylinder.Fig. 55.—Carbon-Cylinder Cell, and Cylinder.The most common form of Leclanche cell is illustrated in Figure 55. This type is usually known as a "carbon cylinder" cell because the positive element is a hollow carbon cylinder. The zinc is in the form of a rod passing through a porcelain bushing set in the center of the carbon cylinder. A battery of such cells can only be used successfully for open circuit work. The "open circuit" is used for bells, burglar alarms, telephone circuits, etc., or wherever the circuit is such that it is "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 of time hydrogen gas will collect on the carbon cylinder and the cell will becomepolarized. When polarized it will not deliver much current.Many methods have been devised for overcoming this difficulty, but even the best of them are only partially successful.The usual method is to employ a chemicaldepolarizingagent. Figure 56 shows a Leclanche cell provided with adepolarizer.The carbon is in the form of a plate placed in aporous cupmade of earthenware and filled withmanganese dioxide.Chemists classmanganese dioxideas anoxidizingagent, which means that it will furnish oxygen with comparative ease. Oxygen and hydrogen have a strongchemical affinityor attraction for each other.Fig. 56.—A Leclanche Cell, showing the Porous Cup.Fig. 56.—A Leclanche Cell, showing the Porous Cup.If the carbon plate is packed in manganese dioxide any hydrogen which tends to collect on the carbon and polarize the cell is immediatelyseizedby the oxygen of the manganese dioxide and united with it to form water.This form of Leclanche cell is called the disk type. It is capable of delivering a stronger current for a longer period of time than the carbon cylinder battery. The zinc is usually made in the form of a cylinder, and fits around the outside of the porous cup.Dry Cellsare used extensively nowadays for all open circuit work on account of their convenience and high efficiency.The dry cell is not, as its name implies, "dry," but the exciting agent or electrolyte, instead of being a liquid, is a wet paste which cannot spill or run over. The top of the cell is poured full of molten pitch, thus effectively sealing it and making it possible to place the cell in any position.Dry cells can be purchased from almost any electrical house or garage for twenty-five cents each. It will therefore hardly pay the young experimenter to make his owndry cells. For the sake of those who may care to do so, however, directions for building a simple but efficient dry cell of the type used for door-bells and ignition work, will be found below.Fig. 57.—A Dry Cell.Fig. 57.—A Dry Cell.The principle of a dry cell is the same as that of a Leclanche cell of the disk type. The exciting solution isammonium chloride, the electrodes or elements are zinc and carbon, and the carbon is surrounded by manganese dioxide as a depolarizing agent.Obtain some sheet zinc from a plumbing shop or a hardware store and cut out as many rectangles, 8 x 6 inches, as it is desired to make cells. Also cut out an equal number of circles 2 3/8 inches in diameter.Roll the sheets up into cylinders 2 3/8 inches in diameter inside and 6 inches long. The edges are lapped and soldered. Fit one of the round circles in one end of each of the cylinders and solder them securely into place, taking care to close up all seams or joints which might permit the electrolyte to escape or evaporate.Secure some old carbon rods or plates by breaking open some old dry cells. The carbons will be in the form of a flat plate, a round rod, or a star-shaped corrugated rod, depending upon the manufacture of the cell. Any of these types of carbons will serve the purpose well, provided that they are fitted with a thumb-screw or a small bolt and nut at the top so as to make wire connections with the carbon.Make a wooden plunger of the same shape as the carbon which you may select, but make it slightly larger. Smooth it with sandpaper and give it a coat of shellac to prevent it from absorbing moisture.This wooden plunger is temporarily inserted in the center of one of the zinc cups and supported so that it will be about one-half inch above the bottom.The electrolyte is prepared by mixing together the following ingredients in the proportions shown:Sal Ammoniac. 1 partZinc Chloride. 1 partPlaster of Paris. 3 partsFlour. 3/4 partWater. 2 partsFig. 58.—The Different Operations involved in Making a Dry Cell.Fig. 58.—The Different Operations involved in Making a Dry Cell.The above paste is then firmly packed into the zinc shell around the wooden plunger, leaving a space of about 3/4 of an inch at the top. The paste can be poured in very readily when first mixed but sets and hardens after standing a short while.After it has set, withdraw the wooden plunger, thus leaving a space inside of the dry cell a little larger than the carbon. The carbon is now inserted in this hole and the surrounding space is filled with a mixture composed of:Sal Ammoniac. 1 partZinc Chloride. 1 partManganese Dioxide. 1 partGranulated Carbon. 1 partFlour. 1 partPlaster of Paris. 3 partsWater. 2 partsThe granular carbon may be had by crushing up some old battery carbons. The parts given in both of the above formulas are proportioned so that they may be measured by bulk and not by weight. An old teaspoon or a small cup will make a good measure.Each one of the zinc shells should be filled in this manner. After they have all been filled, clean off the top edge of the zinc and pour the remaining space in the cell full of molten tar or pitch so as to seal it over.Solder a small binding-post to the top edge of the zinc to facilitate connection. Then wrap the cells in several thicknesses of heavy paper to prevent them from short circuiting, and they are ready for use.A small hole bored through the sealing material after it is dry will provide a vent for the escape of gases.Recharging dry cellsis a subject that interests most experimenters.Dry cells very often become useless before the zinc shell is used up or the chemicals are exhausted, due to the fact that the water inside of the cell dries up and the resistance therefore becomes so great that it is practically impossible for the current to pass.The life of such cells may be partially renewed by drilling several holes in the cell and permitting it to soak in a strong solution of sal ammoniac until some of the liquid is absorbed. The holes should then be plugged up with some sealing wax in order to prevent evaporation.An old dry cell may be easily turned into a "wet" cell by drilling the zinc full of holes and then setting it in a jar containing a sal ammoniac solution. The battery should be allowed to remain in the solution.Wet batteriesare very much easier to make than dry batteries and are capable of delivering more current.They have the disadvantage, however, of wasting away more rapidly, when not in service, than dry cells.The Leclanche cell is the type generally first attempted by most experimenters.Carbon platesfor making such a battery are most easily and cheaply obtained from old dry cells. About the only way that a dry cell can be broken open is with a cold-chisel and a hammer. Care must be taken, however, in order not to break the carbon.Ordinary jelly-glasses make good jars for small cells. Fruit-jars may be used for larger batteries by cutting the tops off so that the opening is larger. The carbon plate contained in a dry cell is usually too long for a jar of this sort and must be broken off before it can be used. The lower end is the one which should be broken because the top carries a binding-post, with which connections can be made. A small hole is bored in the carbon rod at a distance from the bottom equal to the height of the jar which is to be used.Fig. 59.—A Zinc-Carbon Element, made from Heavy plates.Fig. 59.—A Zinc-Carbon Element, made from Heavy plates.Considerable care must be used in boring carbon because it is very brittle and easily cracks. Only very light pressure should be used on the drill. The carbon is fastened to a strip of wood, about an inch and one-quarter wide, one-half an inch thick, and a little longer than the top of the glass jar is wide.Fig. 60.—A Method of making a Cell Element from Carbon Rods.Fig. 60.—A Method of making a Cell Element from Carbon Rods.A piece of heavy sheet zinc is fastened on the other side opposite the carbon, with a screw. It is a good idea to paint the screws and the surrounding portions of both the zinc and the carbon with hot paraffin wax so that the solution will not "creep" and attack the screws. It is also a good plan first to soak the wooden strip in some hot paraffin until it is thoroughly impregnated.Ammonium chloride, or, as it is more commonly called, sal ammoniac, should be added to a jar of water until it will dissolve no more. The zinc and carbon elements may then be placed in the solution.One of the great disadvantages of the voltaic cell is that the zinc is attacked by the acid when the battery is not in use and cannot be allowed to remain in the solution without quickly wasting away. This is true in the case of the Leclanche cell only to a very small extent. The voltaic cell is more powerful than the Leclanche cell, but the elements must be carefully lifted out and rinsed with water every time that you are through using the cell. By using several carbon plates instead of one, the cell may be made more powerful. The illustrations show several ways of accomplishing this. The simplest method is to place a carbon plate on each side of the wooden strip and use a zinc in the form of a rod which passes through a hole between the two. Care must always be used to keep any screws which are used to hold the carbons or zincs in position in the cells from touching each other.Fig. 61. An Element made from two Carbon Plates and a Zinc Rod.Fig. 61. An Element made from two Carbon Plates and a Zinc Rod.In Figure 62 an arrangement of using four carbons is shown. The drawing is self-explanatory. In any of the cells using more than one carbon element, the carbons should all be connected.In discussing the voltaic cell we mentioned the fact that it becomes polarized, and explained this phenomenon as being caused by hydrogen bubbles collecting on the copper or positive pole. The same thing happens in the case of carbon or any other material which is used as a positive.Polarizationis the "bugbear" of batteries. It can be eliminated to a certain extent, however, by the use of a "depolarizer"placed in the solution. There are several such substances, the most common beingsodium bichromateandpotassium bichromate. These are used in battery preparations on the market called "Electric Sand," "Electropoian Fluid," etc.Fig. 62. A Method of Mounting four Carbon Plates.Fig. 62. A Method of Mounting four Carbon Plates.When one of these is added to a sulphuric acid solution, using zinc and carbon as the battery elements, it forms a very powerful cell, having E. M. F. of two volts.A battery solution of this kind may be prepared by adding four ounces of bichromate of potash to a solution composed of four ounces of sulphuric acid mixed with sixteen ounces of water. The battery will give a more powerful current for a longer time when this solution is used instead of the plain sulphuric acid and water or sal ammoniac.Fig. 63.—A Battery Element arranged for three Cells.Fig. 63.—A Battery Element arranged for three Cells.It might be well at this time to caution the experimenter against the careless handling of sulphuric acid. It is not dangerous if handled properly, but if spilled or spattered around carelessly it is capable of doing considerable damage to most things with which it comes in contact. Do not attempt to use it in any place but a shop or cellar. The smallest drop coming in contact with any organic matter such as woodwork, clothing, carpets, etc., will not only discolor any of the latter, but eat a hole in it. The best thing to use to counteract the effects of the acid which has been spilled or spattered is water in sufficient quantity to drench things and dilute the acid enough to render it harmless. A little strong ammonia will neutralize the acid and sometimes restore the color to clothing which has been burned by acid.Fig. 64.—A Plunge Battery, with Windlass.Fig. 64.—A Plunge Battery, with Windlass.All acid batteries of this sort have the one objection that it is impossible to leave the elements in the solution without wasting the zinc. The usual way to arrange the battery cells so that the elements may be removed from the solution most easily is to fasten the elements to a chain or cord passing over a windlass fitted with a crank so that when the crank is turned the elements may be raised or lowered as desired.A "plunge battery" of this sort is illustrated in Figure 64. The construction is so plainly shown by the drawing that it is hardly necessary to enter into the details. The crank is arranged with a dowel-pin which passes through into a hole in the frame, so that when the elements are lifted out of the solution the pin may be inserted in the hole and the windlass prevented from unwinding.Fig. 65.—A Plunge Battery adapted to a Set of Elements, as shown in Figure 63.Fig. 65.—A Plunge Battery adapted to a Set of Elements, as shown in Figure 63. They may be lifted out and placed on the "Arms" to drain.A somewhat easier method of accomplishing the same result is that shown by Figure 65. In this, the elements are simply raised up out of the jars and laid across the two "arms" to drain.The Edison-Lalandecell employs a block of pressed copper oxide as the positive element, while two zinc plates form the negative. The exciting liquid is a strong solution of caustic soda.Fig. 66.—An Edison-Lalande Cell.Fig. 66.—An Edison-Lalande Cell.The copper oxide acts both as the positive element and as a depolarizer, for the oxygen of the oxide immediately combines with any hydrogen tending to form on the plate.This type of cell has some advantages but also many disadvantages, chief among which is the fact that the E. M. F. is very low. It is used principally for railway signal work, slot-machines, etc.A Tomato-Can Batteryusing caustic soda as the exciting liquid is a simple form of home-made battery whose only disadvantage is the low voltage that it delivers.Fig. 67.—A Tomato-Can Cell; Sectional View.Fig. 67.—A Tomato-Can Cell; Sectional View.Fig. 68.—The Tomato-Can Cell Complete.Fig. 68.—The Tomato-Can Cell Complete.The cell is liable to polarization, but the large surface of its positive elements protects it to some extent.The positive element and the outer vessel is a tomato can. Within it is a porous cup made out of blotting paper or unglazed earthenware such as a flower pot.The space between the can and the porous cup is filled with fine scrap-iron such as borings and turnings. A zinc plate is placed in the porous cup.The cell is filled with a ten-per-cent solution of caustic soda.The following table gives the names, elements, fluids, voltage, etc., of the most useful batteries, all of which may be easily constructed by the experimenter.Table of Useful BatteriesSecondary or Storage BatteriesThe storage battery is a very convenient means of taking energy at one time or place and using it at some other time or place.Small storage batteries are used in automobiles to supply current for the headlights and spark-coils. Many automobiles are now equipped with "electric starters," consisting of a dynamo-motor and a storage battery. Throwing a switch will cause the current from the storage battery to drive the motor and "crank" the engine. After the engine is started, the motor acts as a dynamo and generates a current for recharging the storage battery.Storage batteries are also used to drive electric vehicles and cars.Many central lighting and power stations employ storage batteries to supply the extra current demanded during rush hours. In the middle of the day, when the "load" is light, the surplus current of the dynamos is used to recharge the storage batteries.What is really effected in the storage battery is the electrical storage ofenergy, not the storage of electricity. Properly speaking, the energy is put into the form of chemical energy, and there is reallyno more electricity in the cellwhen it is charged than after it is discharged.Fig. 69.—Two Methods of Connecting Cells so as to obtain Different Voltage and Amperage Values.Fig. 69.—Two Methods of Connecting Cells so as to obtain Different Voltage and Amperage Values.Storage batteries are made up of plates of lead (the electrodes) or an alloy of lead cast into a "grid" or framework.The framework may be one of a large number of patterns, but usually consists of a set of bars crossing one another at right angles, leaving a space between.The spaces are filled with a paste oflead oxide. They are then "formed" by placing in a tank of acid solution and connected to a source of electric current.Fig. 70.—Small Storage Cells.Fig. 70.—Small Storage Cells.The plate connected to the positive wire gradually turns dark-brown in color, due to the changes in the paste, which gradually turns intolead peroxide. The paste in the negative plate becomes gray in color and changes into a form of metallic lead calledspongy lead.The positive and negative plates are placed in a bundle after the forming process has been completed. They are kept apart by strips of wood or rubber called separators.The negative plates of one cell are all connected in parallel at one end of the cell. The positive plates are connected at the other end. The liquid surrounding the plates is diluted sulphuric acid.When the battery has been exhausted, it is charged by connecting a dynamo with the terminals of the battery and sending a current through it. This current reverses the chemical action, which goes on during the discharge of the battery.A Storage Batteryfurnishes the most convenient source of current for performing all sorts of electrical experiments. It is capable of giving more current for a longer period than dry cells and is not expensive, for it merely requires recharging and does not have to be thrown away each time the current is used up.The storage cell described below is made in a very simple manner and will well repay any time or expense spent in its construction.Fig. 71.—How to make the Plates for a Storage Cell.Fig. 71.—How to make the Plates for a Storage Cell.The plates are cut out of a large sheet of lead, one-quarter of an inch thick. They may be made any convenient size to fit the jars which the experimenter may have at hand. We will assume that they are to be made two and seven-eighths inches wide and three and one-half inches long. They will then fit the rectangular glass storage cell which is already on the market and can be procured from dealers in electrical supplies.A long terminal or lug is left projecting from the plate as shown in Figure 71.Any number of plates may be placed in a single cell, depending of course upon the size of the glass jar. We will suppose that three will just fit the jar nicely. An odd number of plates should always be used, so that a positive plate may come between two negatives.Each cell will give two volts regardless of the number of plates. Increasing the number of plates, however, will give the cell a greater amperage capacity and make the charge last longer. Three cells (six volts) will form a convenient set for running small fan-motors, miniature lights, etc.Cut out nine plates and pile them up in sets of three with a piece of thin wood (cigar-box wood) between each pair of plates. Clamp them together in a vise and bore full of one-quarter-inch holes.The plates are now ready for pasting. They are placed on a smooth slab of stone or glass and pasted with a stiff mixture of red lead and sulphuric acid (two parts water to one part acid). The paste must be pressed carefully into the recesses of the plates with a flat stick. They are then laid aside to dry and harden.Fig. Fig. 72.—The Wood Separator.Fig. 72.—The Wood Separator.After they have thoroughly dried they should be assembled as in Figure 73 with one positive plate between two negative ones. The wooden "separators" are easily cut out of wood with a saw and penknife. The thin wood used in the construction of peach baskets is the best for the purpose. The separators should be made the same size as the lead battery plates.Each group of plates is then placed in a jar containing a mixture of sulphuric acid and water (4 parts water to one part acid). In mixing the acid be very careful to pour the acid into the water, stirring the mixture slowly at the same time, and not the water into the acid.Fig. 73.—The Complete Element for a Storage Cell.Fig. 73.—The Complete Element for a Storage Cell.The plates are now ready for "forming." The binding-posts on the lugs of the plates may be secured from the carbons of some old dry cells. The simplest method of "forming" the plates is to use four gravity cells and "form" one storage cell at a time.Fig. 74.—A Battery of Home-Made Storage Cells.Fig. 74.—A Battery of Home-Made Storage Cells.Connect the positive pole (copper) of the gravity battery to the positive pole (center-plate) of the storage cell and the negative (zinc) of the gravity battery to the negative (outside plates) of the storage cell. Allow the current to flow through the storage battery for several days or until the positive plate turns to a dark chocolate-brown color and the negatives to a gray-slate.Fig. 75.—Gravity Cells.Fig. 75.—Gravity Cells. These consist of zinc and copper elements, immersed in a zinc-copper sulphate solution. They cannot be easily made, and are best purchased. The illustration also shows the star-shaped copper and "crowfoot" zinc element used in a gravity cell.After the cells have once been "formed" all that they require is occasional recharging from gravity cells or from a dynamo, by connecting the positive pole of the charging current to the positive plates of the storage cells and the negative pole to the negative plates.When the cells are fully charged, bubbles of gas will rise freely from the plates. If a dynamo is used it must be "shunt" wound and not a "series" machine. Recharging will only require about one-quarter of the time consumed in forming.It is a very good plan to connect twelve gravity cells in series and use them to recharge the storage battery. The gravity cells can always be kept connected to the storage cells when the latter are not in use and thus remain fully charged and ready to supply their maximum current.After the cells have been in use for some time, it is a good plan to lift out the plates and remove all sediment which has settled to the bottom of the jars.A set of three such storage cells will have an E. M. F. of over six volts. Any number may be connected up in series in order to obtain a higher voltage.Storage batteries are usually rated in "ampere hours." An ampere hour is the amount of current represented by one ampere flowing for one hour. A ten-ampere-hour storage battery will deliver:One ampere for ten hoursTwo amperes for five hoursFive amperes for two hoursTen amperes for one hourIn other words, the result obtained by multiplying the number of amperes by the time in hours is theampere hour capacity.A dynamo must have an E. M. F. of about ten volts in order to charge a three-cell storage battery.ELECTRO-MAGNETISM AND MAGNETIC INDUCTION

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 current. Furthermore, many boys have no source of power from which to drive a small dynamo. Batteries must therefore be resorted to in the majority of cases.

A number of different cells and batteries are described in this chapter. All of them are practical, but after buying zinc, chemicals, etc., for any length of time, figure out what your batteriescostyou to make. The real value is not their cost in dollars and cents but in what you havelearnedin making them. If you have a continuous use for electrical current for runningsmallelectrical devices it is cheaper to buy dry cells, or what is better, astorage battery, and have itrechargedwhen necessary.

Build your own batteries first. Then after you have learned how they are made and something about their proper care buy them from some reliable electrical house.

Batteries are always interesting to the average experimenter, and when properly made are one of the most useful pieces of apparatus around the home, laboratory, or shop that it is possible to construct. Many hundreds of thousands of experiments have been carried out by capable men in an effort to discover or devise a perfect battery, and the list 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 fair service, have been chosen for description.

Cells are usually consideredoneelement or jar of a battery. Acellmeans only one, while abatteryis agroupof cells. It is not a proper use of the word to say "battery" when onlyonecell is implied. This is a very common error.

The Voltaic cellis called after its inventor, Volta, a professor in the University of Pavia, and dates back to about the year 1786.

Fig. 52.—The Voltaic Cell.Fig. 52.—The Voltaic Cell.

Fig. 52.—The Voltaic Cell.

A simple voltaic cell is easily made by placing some water mixed with a little sulphuric acid in a glass tumbler and immersing therein two clean strips, one of zinc and the other of copper. The strips must be kept separate from each other. The sulphuric acid must be diluted by mixing it with about ten times its volume of water. In mixing acid with water always remember never to pour water into acid but to perform the operation the other way and pour the acid into the water. A copper wire is fastened with a screw or by soldering to the top of each of the strips, and care must 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 kept at opposite sides of the jar.

The sulphuric acid solution attacks the zinc, causing it slowly to waste away and disappear. This action is calledoxidation, and in reality is a very slow process of burning. The consumption of the zinc furnishes the electric energy, which in the case of this cell will be found to be sufficient to ring a bell or buzzer, or run a very small toy motor.

As soon as the plates are immersed in the acid solution, bubbles will begin to rise from the zinc. These bubbles contain a gas called hydrogen and they indicate that a chemical action is taking place. The zinc is being dissolved and thehydrogengas is being set free from the acid. It will be noticed that no bubbles arise from the copper plate and that there is little if any chemical action there. In other words, it seems that the chemical action at one plate is stronger than that at the other.

A cell might be likened to a furnace in which the zinc is the fuel which is burned to furnish the energy. We know that if the zinc is burned or oxidized in the open air it will give out energy in the form ofheat. When it is burned or oxidized slowly in acid in the presence of another metal it gives out its energy in the form ofelectricity. The acid might be likened to the fire, and the copper to a hand which dips into the cell to pick up the current and takes no part chemically.

If a wire is connected to each of the plates and the free ends of the wires touched to the tip of the tongue it will produce a peculiar salty taste in the mouth indicating the presence of a current of electricity.

If the wires are connected to an electric bell, the bell will ring, or, instead, the current may be used to run a small motor. If the cell is made of two zinc plates or two copper plates, the bell will not ring, because no electricity will be produced. In order to produce a current, the electrodes must be made of two different materials upon which the acid acts differently. Current may be obtained from a cell made with a zinc and carbon plate or from one with zinc and iron.

Therefore, in order to make a battery it is necessary to have a metal which may be consumed, a chemical to consume or oxidize it, and an inactive element which is merely present to collect the electricity.

When the wires connected to the two plates are joined together, a current of electricity will flow from the copper plate through the wire to the zinc. The copper is known as thepositivepole and the zinc as thenegative.

A simple voltaic cell may be easily made by cutting out a strip of zinc and a strip of copper, each 3 1/2 inches long, and one inch wide. A small hole bored through the upper end of the strips will permit them to be mounted on a wooden strip with a screw as shown in Figure 53. The connecting wires are placed under the heads of the screws. Care should be exercised to arrange the screws used for mounting the electrodes to the wooden strip so that they do not come exactly opposite, and there is no danger of the points touching and forming a short circuit.

Fig. 53.—The Elements of Simple Voltaic Cell.Fig. 53.—The Elements of Simple Voltaic Cell.

Fig. 53.—The Elements of Simple Voltaic Cell.

Fig. 54.—A Home-Made Voltaic Cell.Fig. 54.—A Home-Made Voltaic Cell.

Fig. 54.—A Home-Made Voltaic Cell.

An ordinary tumbler or jelly glass will make a good battery jar. The exciting liquid should be composed of

One part of sulphuric acidTen parts of water

One part of sulphuric acid

Ten parts of water

One of the disadvantages of the voltaic cell is that it becomespolarized, that is, small bubbles of hydrogen which are liberated by the chemical action collect on the copper plate and cause the strength of the battery to fall off rapidly.

There are a great number ofelements, as the zinc and copper are called, and an even greater number of different solutions orexcitantswhich can be employed in place of sulphuric acid to make a cell, forming an almost endless number of possible combinations.

Leclanche Cell.One of the most common forms of cell employed for bell-ringing, telephones, etc., is called the Leclanche cell, after its inventor, and consists of two elements, one of zinc and the other of carbon, immersed in a solution ofsal ammoniacorammonium chloride. This cell has an E. M. F. of 1.4 volts, which is about half as much again as the voltaic cell.

Fig. 55.—Carbon-Cylinder Cell, and Cylinder.Fig. 55.—Carbon-Cylinder Cell, and Cylinder.

Fig. 55.—Carbon-Cylinder Cell, and Cylinder.

The most common form of Leclanche cell is illustrated in Figure 55. This type is usually known as a "carbon cylinder" cell because the positive element is a hollow carbon cylinder. The zinc is in the form of a rod passing through a porcelain bushing set in the center of the carbon cylinder. A battery of such cells can only be used successfully for open circuit work. The "open circuit" is used for bells, burglar alarms, telephone circuits, etc., or wherever the circuit is such that it is "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 of time hydrogen gas will collect on the carbon cylinder and the cell will becomepolarized. When polarized it will not deliver much current.

Many methods have been devised for overcoming this difficulty, but even the best of them are only partially successful.

The usual method is to employ a chemicaldepolarizingagent. Figure 56 shows a Leclanche cell provided with adepolarizer.

The carbon is in the form of a plate placed in aporous cupmade of earthenware and filled withmanganese dioxide.

Chemists classmanganese dioxideas anoxidizingagent, which means that it will furnish oxygen with comparative ease. Oxygen and hydrogen have a strongchemical affinityor attraction for each other.

Fig. 56.—A Leclanche Cell, showing the Porous Cup.Fig. 56.—A Leclanche Cell, showing the Porous Cup.

Fig. 56.—A Leclanche Cell, showing the Porous Cup.

If the carbon plate is packed in manganese dioxide any hydrogen which tends to collect on the carbon and polarize the cell is immediatelyseizedby the oxygen of the manganese dioxide and united with it to form water.

This form of Leclanche cell is called the disk type. It is capable of delivering a stronger current for a longer period of time than the carbon cylinder battery. The zinc is usually made in the form of a cylinder, and fits around the outside of the porous cup.

Dry Cellsare used extensively nowadays for all open circuit work on account of their convenience and high efficiency.

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

Dry cells can be purchased from almost any electrical house or garage for twenty-five cents each. It will therefore hardly pay the young experimenter to make his owndry cells. For the sake of those who may care to do so, however, directions for building a simple but efficient dry cell of the type used for door-bells and ignition work, will be found below.

Fig. 57.—A Dry Cell.Fig. 57.—A Dry Cell.

Fig. 57.—A Dry Cell.

The principle of a dry cell is the same as that of a Leclanche cell of the disk type. The exciting solution isammonium chloride, the electrodes or elements are zinc and carbon, and the carbon is surrounded by manganese dioxide as a depolarizing agent.

Obtain some sheet zinc from a plumbing shop or a hardware store and cut out as many rectangles, 8 x 6 inches, as it is desired to make cells. Also cut out an equal number of circles 2 3/8 inches in diameter.

Roll the sheets up into cylinders 2 3/8 inches in diameter inside and 6 inches long. The edges are lapped and soldered. Fit one of the round circles in one end of each of the cylinders and solder them securely into place, taking care to close up all seams or joints which might permit the electrolyte to escape or evaporate.

Secure some old carbon rods or plates by breaking open some old dry cells. The carbons will be in the form of a flat plate, a round rod, or a star-shaped corrugated rod, depending upon the manufacture of the cell. Any of these types of carbons will serve the purpose well, provided that they are fitted with a thumb-screw or a small bolt and nut at the top so as to make wire connections with the carbon.

Make a wooden plunger of the same shape as the carbon which you may select, but make it slightly larger. Smooth it with sandpaper and give it a coat of shellac to prevent it from absorbing moisture.

This wooden plunger is temporarily inserted in the center of one of the zinc cups and supported so that it will be about one-half inch above the bottom.

The electrolyte is prepared by mixing together the following ingredients in the proportions shown:

Sal Ammoniac. 1 partZinc Chloride. 1 partPlaster of Paris. 3 partsFlour. 3/4 partWater. 2 parts

Sal Ammoniac. 1 part

Zinc Chloride. 1 part

Plaster of Paris. 3 parts

Flour. 3/4 part

Water. 2 parts

Fig. 58.—The Different Operations involved in Making a Dry Cell.Fig. 58.—The Different Operations involved in Making a Dry Cell.

Fig. 58.—The Different Operations involved in Making a Dry Cell.

The above paste is then firmly packed into the zinc shell around the wooden plunger, leaving a space of about 3/4 of an inch at the top. The paste can be poured in very readily when first mixed but sets and hardens after standing a short while.

After it has set, withdraw the wooden plunger, thus leaving a space inside of the dry cell a little larger than the carbon. The carbon is now inserted in this hole and the surrounding space is filled with a mixture composed of:

Sal Ammoniac. 1 partZinc Chloride. 1 partManganese Dioxide. 1 partGranulated Carbon. 1 partFlour. 1 partPlaster of Paris. 3 partsWater. 2 parts

Sal Ammoniac. 1 part

Zinc Chloride. 1 part

Manganese Dioxide. 1 part

Granulated Carbon. 1 part

Flour. 1 part

Plaster of Paris. 3 parts

Water. 2 parts

The granular carbon may be had by crushing up some old battery carbons. The parts given in both of the above formulas are proportioned so that they may be measured by bulk and not by weight. An old teaspoon or a small cup will make a good measure.

Each one of the zinc shells should be filled in this manner. After they have all been filled, clean off the top edge of the zinc and pour the remaining space in the cell full of molten tar or pitch so as to seal it over.

Solder a small binding-post to the top edge of the zinc to facilitate connection. Then wrap the cells in several thicknesses of heavy paper to prevent them from short circuiting, and they are ready for use.

A small hole bored through the sealing material after it is dry will provide a vent for the escape of gases.

Recharging dry cellsis a subject that interests most experimenters.

Dry cells very often become useless before the zinc shell is used up or the chemicals are exhausted, due to the fact that the water inside of the cell dries up and the resistance therefore becomes so great that it is practically impossible for the current to pass.

The life of such cells may be partially renewed by drilling several holes in the cell and permitting it to soak in a strong solution of sal ammoniac until some of the liquid is absorbed. The holes should then be plugged up with some sealing wax in order to prevent evaporation.

An old dry cell may be easily turned into a "wet" cell by drilling the zinc full of holes and then setting it in a jar containing a sal ammoniac solution. The battery should be allowed to remain in the solution.

Wet batteriesare very much easier to make than dry batteries and are capable of delivering more current.

They have the disadvantage, however, of wasting away more rapidly, when not in service, than dry cells.

The Leclanche cell is the type generally first attempted by most experimenters.

Carbon platesfor making such a battery are most easily and cheaply obtained from old dry cells. About the only way that a dry cell can be broken open is with a cold-chisel and a hammer. Care must be taken, however, in order not to break the carbon.

Ordinary jelly-glasses make good jars for small cells. Fruit-jars may be used for larger batteries by cutting the tops off so that the opening is larger. The carbon plate contained in a dry cell is usually too long for a jar of this sort and must be broken off before it can be used. The lower end is the one which should be broken because the top carries a binding-post, with which connections can be made. A small hole is bored in the carbon rod at a distance from the bottom equal to the height of the jar which is to be used.

Fig. 59.—A Zinc-Carbon Element, made from Heavy plates.Fig. 59.—A Zinc-Carbon Element, made from Heavy plates.

Fig. 59.—A Zinc-Carbon Element, made from Heavy plates.

Considerable care must be used in boring carbon because it is very brittle and easily cracks. Only very light pressure should be used on the drill. The carbon is fastened to a strip of wood, about an inch and one-quarter wide, one-half an inch thick, and a little longer than the top of the glass jar is wide.

Fig. 60.—A Method of making a Cell Element from Carbon Rods.Fig. 60.—A Method of making a Cell Element from Carbon Rods.

Fig. 60.—A Method of making a Cell Element from Carbon Rods.

A piece of heavy sheet zinc is fastened on the other side opposite the carbon, with a screw. It is a good idea to paint the screws and the surrounding portions of both the zinc and the carbon with hot paraffin wax so that the solution will not "creep" and attack the screws. It is also a good plan first to soak the wooden strip in some hot paraffin until it is thoroughly impregnated.

Ammonium chloride, or, as it is more commonly called, sal ammoniac, should be added to a jar of water until it will dissolve no more. The zinc and carbon elements may then be placed in the solution.

One of the great disadvantages of the voltaic cell is that the zinc is attacked by the acid when the battery is not in use and cannot be allowed to remain in the solution without quickly wasting away. This is true in the case of the Leclanche cell only to a very small extent. The voltaic cell is more powerful than the Leclanche cell, but the elements must be carefully lifted out and rinsed with water every time that you are through using the cell. By using several carbon plates instead of one, the cell may be made more powerful. The illustrations show several ways of accomplishing this. The simplest method is to place a carbon plate on each side of the wooden strip and use a zinc in the form of a rod which passes through a hole between the two. Care must always be used to keep any screws which are used to hold the carbons or zincs in position in the cells from touching each other.

Fig. 61. An Element made from two Carbon Plates and a Zinc Rod.Fig. 61. An Element made from two Carbon Plates and a Zinc Rod.

Fig. 61. An Element made from two Carbon Plates and a Zinc Rod.

In Figure 62 an arrangement of using four carbons is shown. The drawing is self-explanatory. In any of the cells using more than one carbon element, the carbons should all be connected.

In discussing the voltaic cell we mentioned the fact that it becomes polarized, and explained this phenomenon as being caused by hydrogen bubbles collecting on the copper or positive pole. The same thing happens in the case of carbon or any other material which is used as a positive.

Polarizationis the "bugbear" of batteries. It can be eliminated to a certain extent, however, by the use of a "depolarizer"placed in the solution. There are several such substances, the most common beingsodium bichromateandpotassium bichromate. These are used in battery preparations on the market called "Electric Sand," "Electropoian Fluid," etc.

Fig. 62. A Method of Mounting four Carbon Plates.Fig. 62. A Method of Mounting four Carbon Plates.

Fig. 62. A Method of Mounting four Carbon Plates.

When one of these is added to a sulphuric acid solution, using zinc and carbon as the battery elements, it forms a very powerful cell, having E. M. F. of two volts.

A battery solution of this kind may be prepared by adding four ounces of bichromate of potash to a solution composed of four ounces of sulphuric acid mixed with sixteen ounces of water. The battery will give a more powerful current for a longer time when this solution is used instead of the plain sulphuric acid and water or sal ammoniac.

Fig. 63.—A Battery Element arranged for three Cells.Fig. 63.—A Battery Element arranged for three Cells.

Fig. 63.—A Battery Element arranged for three Cells.

It might be well at this time to caution the experimenter against the careless handling of sulphuric acid. It is not dangerous if handled properly, but if spilled or spattered around carelessly it is capable of doing considerable damage to most things with which it comes in contact. Do not attempt to use it in any place but a shop or cellar. The smallest drop coming in contact with any organic matter such as woodwork, clothing, carpets, etc., will not only discolor any of the latter, but eat a hole in it. The best thing to use to counteract the effects of the acid which has been spilled or spattered is water in sufficient quantity to drench things and dilute the acid enough to render it harmless. A little strong ammonia will neutralize the acid and sometimes restore the color to clothing which has been burned by acid.

Fig. 64.—A Plunge Battery, with Windlass.Fig. 64.—A Plunge Battery, with Windlass.

Fig. 64.—A Plunge Battery, with Windlass.

All acid batteries of this sort have the one objection that it is impossible to leave the elements in the solution without wasting the zinc. The usual way to arrange the battery cells so that the elements may be removed from the solution most easily is to fasten the elements to a chain or cord passing over a windlass fitted with a crank so that when the crank is turned the elements may be raised or lowered as desired.

A "plunge battery" of this sort is illustrated in Figure 64. The construction is so plainly shown by the drawing that it is hardly necessary to enter into the details. The crank is arranged with a dowel-pin which passes through into a hole in the frame, so that when the elements are lifted out of the solution the pin may be inserted in the hole and the windlass prevented from unwinding.

Fig. 65.—A Plunge Battery adapted to a Set of Elements, as shown in Figure 63.Fig. 65.—A Plunge Battery adapted to a Set of Elements, as shown in Figure 63. They may be lifted out and placed on the "Arms" to drain.

Fig. 65.—A Plunge Battery adapted to a Set of Elements, as shown in Figure 63. They may be lifted out and placed on the "Arms" to drain.

A somewhat easier method of accomplishing the same result is that shown by Figure 65. In this, the elements are simply raised up out of the jars and laid across the two "arms" to drain.

The Edison-Lalandecell employs a block of pressed copper oxide as the positive element, while two zinc plates form the negative. The exciting liquid is a strong solution of caustic soda.

Fig. 66.—An Edison-Lalande Cell.Fig. 66.—An Edison-Lalande Cell.

Fig. 66.—An Edison-Lalande Cell.

The copper oxide acts both as the positive element and as a depolarizer, for the oxygen of the oxide immediately combines with any hydrogen tending to form on the plate.

This type of cell has some advantages but also many disadvantages, chief among which is the fact that the E. M. F. is very low. It is used principally for railway signal work, slot-machines, etc.

A Tomato-Can Batteryusing caustic soda as the exciting liquid is a simple form of home-made battery whose only disadvantage is the low voltage that it delivers.

Fig. 67.—A Tomato-Can Cell; Sectional View.Fig. 67.—A Tomato-Can Cell; Sectional View.

Fig. 67.—A Tomato-Can Cell; Sectional View.

Fig. 68.—The Tomato-Can Cell Complete.Fig. 68.—The Tomato-Can Cell Complete.

Fig. 68.—The Tomato-Can Cell Complete.

The cell is liable to polarization, but the large surface of its positive elements protects it to some extent.

The positive element and the outer vessel is a tomato can. Within it is a porous cup made out of blotting paper or unglazed earthenware such as a flower pot.

The space between the can and the porous cup is filled with fine scrap-iron such as borings and turnings. A zinc plate is placed in the porous cup.

The cell is filled with a ten-per-cent solution of caustic soda.

The following table gives the names, elements, fluids, voltage, etc., of the most useful batteries, all of which may be easily constructed by the experimenter.

Table of Useful Batteries

Secondary or Storage BatteriesThe storage battery is a very convenient means of taking energy at one time or place and using it at some other time or place.Small storage batteries are used in automobiles to supply current for the headlights and spark-coils. Many automobiles are now equipped with "electric starters," consisting of a dynamo-motor and a storage battery. Throwing a switch will cause the current from the storage battery to drive the motor and "crank" the engine. After the engine is started, the motor acts as a dynamo and generates a current for recharging the storage battery.Storage batteries are also used to drive electric vehicles and cars.Many central lighting and power stations employ storage batteries to supply the extra current demanded during rush hours. In the middle of the day, when the "load" is light, the surplus current of the dynamos is used to recharge the storage batteries.What is really effected in the storage battery is the electrical storage ofenergy, not the storage of electricity. Properly speaking, the energy is put into the form of chemical energy, and there is reallyno more electricity in the cellwhen it is charged than after it is discharged.Fig. 69.—Two Methods of Connecting Cells so as to obtain Different Voltage and Amperage Values.Fig. 69.—Two Methods of Connecting Cells so as to obtain Different Voltage and Amperage Values.Storage batteries are made up of plates of lead (the electrodes) or an alloy of lead cast into a "grid" or framework.The framework may be one of a large number of patterns, but usually consists of a set of bars crossing one another at right angles, leaving a space between.The spaces are filled with a paste oflead oxide. They are then "formed" by placing in a tank of acid solution and connected to a source of electric current.Fig. 70.—Small Storage Cells.Fig. 70.—Small Storage Cells.The plate connected to the positive wire gradually turns dark-brown in color, due to the changes in the paste, which gradually turns intolead peroxide. The paste in the negative plate becomes gray in color and changes into a form of metallic lead calledspongy lead.The positive and negative plates are placed in a bundle after the forming process has been completed. They are kept apart by strips of wood or rubber called separators.The negative plates of one cell are all connected in parallel at one end of the cell. The positive plates are connected at the other end. The liquid surrounding the plates is diluted sulphuric acid.When the battery has been exhausted, it is charged by connecting a dynamo with the terminals of the battery and sending a current through it. This current reverses the chemical action, which goes on during the discharge of the battery.A Storage Batteryfurnishes the most convenient source of current for performing all sorts of electrical experiments. It is capable of giving more current for a longer period than dry cells and is not expensive, for it merely requires recharging and does not have to be thrown away each time the current is used up.The storage cell described below is made in a very simple manner and will well repay any time or expense spent in its construction.Fig. 71.—How to make the Plates for a Storage Cell.Fig. 71.—How to make the Plates for a Storage Cell.The plates are cut out of a large sheet of lead, one-quarter of an inch thick. They may be made any convenient size to fit the jars which the experimenter may have at hand. We will assume that they are to be made two and seven-eighths inches wide and three and one-half inches long. They will then fit the rectangular glass storage cell which is already on the market and can be procured from dealers in electrical supplies.A long terminal or lug is left projecting from the plate as shown in Figure 71.Any number of plates may be placed in a single cell, depending of course upon the size of the glass jar. We will suppose that three will just fit the jar nicely. An odd number of plates should always be used, so that a positive plate may come between two negatives.Each cell will give two volts regardless of the number of plates. Increasing the number of plates, however, will give the cell a greater amperage capacity and make the charge last longer. Three cells (six volts) will form a convenient set for running small fan-motors, miniature lights, etc.Cut out nine plates and pile them up in sets of three with a piece of thin wood (cigar-box wood) between each pair of plates. Clamp them together in a vise and bore full of one-quarter-inch holes.The plates are now ready for pasting. They are placed on a smooth slab of stone or glass and pasted with a stiff mixture of red lead and sulphuric acid (two parts water to one part acid). The paste must be pressed carefully into the recesses of the plates with a flat stick. They are then laid aside to dry and harden.Fig. Fig. 72.—The Wood Separator.Fig. 72.—The Wood Separator.After they have thoroughly dried they should be assembled as in Figure 73 with one positive plate between two negative ones. The wooden "separators" are easily cut out of wood with a saw and penknife. The thin wood used in the construction of peach baskets is the best for the purpose. The separators should be made the same size as the lead battery plates.Each group of plates is then placed in a jar containing a mixture of sulphuric acid and water (4 parts water to one part acid). In mixing the acid be very careful to pour the acid into the water, stirring the mixture slowly at the same time, and not the water into the acid.Fig. 73.—The Complete Element for a Storage Cell.Fig. 73.—The Complete Element for a Storage Cell.The plates are now ready for "forming." The binding-posts on the lugs of the plates may be secured from the carbons of some old dry cells. The simplest method of "forming" the plates is to use four gravity cells and "form" one storage cell at a time.Fig. 74.—A Battery of Home-Made Storage Cells.Fig. 74.—A Battery of Home-Made Storage Cells.Connect the positive pole (copper) of the gravity battery to the positive pole (center-plate) of the storage cell and the negative (zinc) of the gravity battery to the negative (outside plates) of the storage cell. Allow the current to flow through the storage battery for several days or until the positive plate turns to a dark chocolate-brown color and the negatives to a gray-slate.Fig. 75.—Gravity Cells.Fig. 75.—Gravity Cells. These consist of zinc and copper elements, immersed in a zinc-copper sulphate solution. They cannot be easily made, and are best purchased. The illustration also shows the star-shaped copper and "crowfoot" zinc element used in a gravity cell.After the cells have once been "formed" all that they require is occasional recharging from gravity cells or from a dynamo, by connecting the positive pole of the charging current to the positive plates of the storage cells and the negative pole to the negative plates.When the cells are fully charged, bubbles of gas will rise freely from the plates. If a dynamo is used it must be "shunt" wound and not a "series" machine. Recharging will only require about one-quarter of the time consumed in forming.It is a very good plan to connect twelve gravity cells in series and use them to recharge the storage battery. The gravity cells can always be kept connected to the storage cells when the latter are not in use and thus remain fully charged and ready to supply their maximum current.After the cells have been in use for some time, it is a good plan to lift out the plates and remove all sediment which has settled to the bottom of the jars.A set of three such storage cells will have an E. M. F. of over six volts. Any number may be connected up in series in order to obtain a higher voltage.Storage batteries are usually rated in "ampere hours." An ampere hour is the amount of current represented by one ampere flowing for one hour. A ten-ampere-hour storage battery will deliver:One ampere for ten hoursTwo amperes for five hoursFive amperes for two hoursTen amperes for one hourIn other words, the result obtained by multiplying the number of amperes by the time in hours is theampere hour capacity.A dynamo must have an E. M. F. of about ten volts in order to charge a three-cell storage battery.ELECTRO-MAGNETISM AND MAGNETIC INDUCTION

The storage battery is a very convenient means of taking energy at one time or place and using it at some other time or place.

Small storage batteries are used in automobiles to supply current for the headlights and spark-coils. Many automobiles are now equipped with "electric starters," consisting of a dynamo-motor and a storage battery. Throwing a switch will cause the current from the storage battery to drive the motor and "crank" the engine. After the engine is started, the motor acts as a dynamo and generates a current for recharging the storage battery.

Storage batteries are also used to drive electric vehicles and cars.

Many central lighting and power stations employ storage batteries to supply the extra current demanded during rush hours. In the middle of the day, when the "load" is light, the surplus current of the dynamos is used to recharge the storage batteries.

What is really effected in the storage battery is the electrical storage ofenergy, not the storage of electricity. Properly speaking, the energy is put into the form of chemical energy, and there is reallyno more electricity in the cellwhen it is charged than after it is discharged.

Fig. 69.—Two Methods of Connecting Cells so as to obtain Different Voltage and Amperage Values.Fig. 69.—Two Methods of Connecting Cells so as to obtain Different Voltage and Amperage Values.

Fig. 69.—Two Methods of Connecting Cells so as to obtain Different Voltage and Amperage Values.

Storage batteries are made up of plates of lead (the electrodes) or an alloy of lead cast into a "grid" or framework.

The framework may be one of a large number of patterns, but usually consists of a set of bars crossing one another at right angles, leaving a space between.

The spaces are filled with a paste oflead oxide. They are then "formed" by placing in a tank of acid solution and connected to a source of electric current.

Fig. 70.—Small Storage Cells.Fig. 70.—Small Storage Cells.

Fig. 70.—Small Storage Cells.

The plate connected to the positive wire gradually turns dark-brown in color, due to the changes in the paste, which gradually turns intolead peroxide. The paste in the negative plate becomes gray in color and changes into a form of metallic lead calledspongy lead.

The positive and negative plates are placed in a bundle after the forming process has been completed. They are kept apart by strips of wood or rubber called separators.

The negative plates of one cell are all connected in parallel at one end of the cell. The positive plates are connected at the other end. The liquid surrounding the plates is diluted sulphuric acid.

When the battery has been exhausted, it is charged by connecting a dynamo with the terminals of the battery and sending a current through it. This current reverses the chemical action, which goes on during the discharge of the battery.

A Storage Batteryfurnishes the most convenient source of current for performing all sorts of electrical experiments. It is capable of giving more current for a longer period than dry cells and is not expensive, for it merely requires recharging and does not have to be thrown away each time the current is used up.

The storage cell described below is made in a very simple manner and will well repay any time or expense spent in its construction.

Fig. 71.—How to make the Plates for a Storage Cell.Fig. 71.—How to make the Plates for a Storage Cell.

Fig. 71.—How to make the Plates for a Storage Cell.

The plates are cut out of a large sheet of lead, one-quarter of an inch thick. They may be made any convenient size to fit the jars which the experimenter may have at hand. We will assume that they are to be made two and seven-eighths inches wide and three and one-half inches long. They will then fit the rectangular glass storage cell which is already on the market and can be procured from dealers in electrical supplies.

A long terminal or lug is left projecting from the plate as shown in Figure 71.

Any number of plates may be placed in a single cell, depending of course upon the size of the glass jar. We will suppose that three will just fit the jar nicely. An odd number of plates should always be used, so that a positive plate may come between two negatives.

Each cell will give two volts regardless of the number of plates. Increasing the number of plates, however, will give the cell a greater amperage capacity and make the charge last longer. Three cells (six volts) will form a convenient set for running small fan-motors, miniature lights, etc.

Cut out nine plates and pile them up in sets of three with a piece of thin wood (cigar-box wood) between each pair of plates. Clamp them together in a vise and bore full of one-quarter-inch holes.

The plates are now ready for pasting. They are placed on a smooth slab of stone or glass and pasted with a stiff mixture of red lead and sulphuric acid (two parts water to one part acid). The paste must be pressed carefully into the recesses of the plates with a flat stick. They are then laid aside to dry and harden.

Fig. Fig. 72.—The Wood Separator.Fig. 72.—The Wood Separator.

Fig. 72.—The Wood Separator.

After they have thoroughly dried they should be assembled as in Figure 73 with one positive plate between two negative ones. The wooden "separators" are easily cut out of wood with a saw and penknife. The thin wood used in the construction of peach baskets is the best for the purpose. The separators should be made the same size as the lead battery plates.

Each group of plates is then placed in a jar containing a mixture of sulphuric acid and water (4 parts water to one part acid). In mixing the acid be very careful to pour the acid into the water, stirring the mixture slowly at the same time, and not the water into the acid.

Fig. 73.—The Complete Element for a Storage Cell.Fig. 73.—The Complete Element for a Storage Cell.

Fig. 73.—The Complete Element for a Storage Cell.

The plates are now ready for "forming." The binding-posts on the lugs of the plates may be secured from the carbons of some old dry cells. The simplest method of "forming" the plates is to use four gravity cells and "form" one storage cell at a time.

Fig. 74.—A Battery of Home-Made Storage Cells.Fig. 74.—A Battery of Home-Made Storage Cells.

Fig. 74.—A Battery of Home-Made Storage Cells.

Connect the positive pole (copper) of the gravity battery to the positive pole (center-plate) of the storage cell and the negative (zinc) of the gravity battery to the negative (outside plates) of the storage cell. Allow the current to flow through the storage battery for several days or until the positive plate turns to a dark chocolate-brown color and the negatives to a gray-slate.

Fig. 75.—Gravity Cells.Fig. 75.—Gravity Cells. These consist of zinc and copper elements, immersed in a zinc-copper sulphate solution. They cannot be easily made, and are best purchased. The illustration also shows the star-shaped copper and "crowfoot" zinc element used in a gravity cell.

Fig. 75.—Gravity Cells. These consist of zinc and copper elements, immersed in a zinc-copper sulphate solution. They cannot be easily made, and are best purchased. The illustration also shows the star-shaped copper and "crowfoot" zinc element used in a gravity cell.

After the cells have once been "formed" all that they require is occasional recharging from gravity cells or from a dynamo, by connecting the positive pole of the charging current to the positive plates of the storage cells and the negative pole to the negative plates.

When the cells are fully charged, bubbles of gas will rise freely from the plates. If a dynamo is used it must be "shunt" wound and not a "series" machine. Recharging will only require about one-quarter of the time consumed in forming.

It is a very good plan to connect twelve gravity cells in series and use them to recharge the storage battery. The gravity cells can always be kept connected to the storage cells when the latter are not in use and thus remain fully charged and ready to supply their maximum current.

After the cells have been in use for some time, it is a good plan to lift out the plates and remove all sediment which has settled to the bottom of the jars.

A set of three such storage cells will have an E. M. F. of over six volts. Any number may be connected up in series in order to obtain a higher voltage.

Storage batteries are usually rated in "ampere hours." An ampere hour is the amount of current represented by one ampere flowing for one hour. A ten-ampere-hour storage battery will deliver:

One ampere for ten hoursTwo amperes for five hoursFive amperes for two hoursTen amperes for one hour

One ampere for ten hours

Two amperes for five hours

Five amperes for two hours

Ten amperes for one hour

In other words, the result obtained by multiplying the number of amperes by the time in hours is theampere hour capacity.

A dynamo must have an E. M. F. of about ten volts in order to charge a three-cell storage battery.

ELECTRO-MAGNETISM AND MAGNETIC INDUCTION

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