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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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:

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:

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.

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.

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.

If they require forming, they must be put through the same forming process which has already been described.

The finished cells when sealed will appear like those shown in Figure 45, according to the sizes of plates and jars used.

Recharging and Caring for Storage Cells.

Storage cells are especially affected by the usage given them. If they are mistreated they will quickly go to pieces, whereas, on the other hand if well treated they will last indefinitely.

It is important that the electrolyte used in the cells should always be of the proper strength. The only accurate method of preparing the electrolyte is with the aid of a hydrometer. A hydrometer is an instrument for determining the specific gravity of solutions.

It is a little device which looks somewhat like a thermometer. It is placed in the solution and allowed to float. There is a numbered scale along the upper part of the hydrometer and the specific gravity or strength of the solution is indicated on the scale by the point which is level with the surface of the solution.

The normal specific gravity for a storage battery solution should be about 1.250. The strength can be increased by adding more acid and decreased by adding water.

Ordinary commercial or technical grades of sulphuric acid and ordinary water are satisfactory for primary batteries, but the acid and water used in making the electrolyte for storage cells must be chemically pure if you wish to obtain good results and desire your batteries to hold their charge while standing.

Storage cells can be recharged with DIRECT current only. A dynamo for recharging storage cells must be SHUNT wound. The voltage of the charging current must be greater than that of the storage cells. About three volts of charging current will be required for each cell of the storage battery. Cells may be connected in multiple when recharging so as to bring the voltage of the cells below that of the charging current. It will of course, however, take much longer to recharge cells connected in multiple than the same cells connected in series, provided that the amperage of the current is the same.

Storage cells must not be recharged too rapidly. It is better to recharge them slowly rather than too rapidly. Two amperes is plenty for small cells of 10-15 ampere hours capacity. Three amperes is sufficient for cells of 15-25 ampere hours capacity. Five to six amperes is the right charging rate for a 40 ampere hour battery and 8 amperes in the case of a 60 ampere hour battery.

Storage cells should never be allowed to stand discharged for any length of time or the plates are liable to become hardened and "sulphated." They turn white when they are sulphated. It will take a great deal of charging and recharging to get them back in shape when once they get in that condition.

Never short circuit a storage cell or discharge it too rapidly.

Whenever any great amount of sediment collects in the bottom of the jars, pour out the acid solution and wash the cell out thoroughly with some pure water.

The plates of a storage cell should always be raised up off the bottom of the jar, so that any sediment which collects will fall below.

It is a very good plan to keep the terminals of a storage cell or battery smeared with vaseline so that they will not become corroded.

You can tell when a storage cell or battery is fully recharged by the color of the plates. The positives will in that case be a dark chocolate brown and the negatives a light slate gray color.

A cell which is fully recharged will indicate 2 1/2 volts on a voltmeter connected across its terminals while the charging current is still on.