CHAPTER XLIV

STORAGE BATTERIES

=Introduction.=—The practical development of the storage battery is comparatively recent, although a knowledge of the phenomena upon which its actions are based, dates back to 1801. In 1800, the year made memorable by Volta's discovery of the galvanic battery, Nicholson and Carlisle found that a current from Volta's cell could decompose water.

In 1801, Gautherot discovered that if two plates of platinum or silver, immersed in a suitable electrolyte, be connected to the terminals of an active primary cell and current be allowed to flow, a small current could be obtained on an outside circuit connecting these two electrodes as soon as the primary battery had been disconnected.

Erman found that the positive pole of such a cell, was the pole which had been connected to the positive pole of the battery.

In 1803, Ritter observed, with gold wire, the same phenomenon as Gautherot, and constructed the first secondary battery, by superposing plates of gold, separated by cloth discs, moistened with ammonia.

Volta, Davy, Marianini, and others added somewhat to the knowledge on the subject, and in 1837, Schoenbein found that peroxide of lead could be used in secondary batteries.

Sir William Grove next came forward with the discovery that metal plates, with a layer of oxide on them, acted better than the plain metallic plates, and Wheatstone and Siemens found still later that peroxide of lead was the best for such purposes.

In 1842, Grove constructed a gas battery, in which the electromotive force came from the oxygen and hydrogen evolved in the electrolysis of water acidulated with sulphuric acid. By means of fifty such cells, he obtained an arc light.

Michael Faraday, when electrolyzing a solution of lead acetate, found that peroxide was produced at the positive, and metallic lead at the negative pole, and in his "Experimental Researches," he comments on the high conductivity of lead peroxide, and its power of readily giving up its oxygen. Although he made no apparent use of this discovery, it may be considered as the next important step in the development of the storage battery.

According to Niblett, Wheatstone, de la Rue, and Niaudet were well aware that peroxide of lead was a powerful depolarizer, but nobody appears to have made use of this fact until 1860, when M. Gaston Plante constructed his well known cell with coiled plates. Plante's researches extended up to 1879, and practically determined the state of the art.

As to the theory at this time, it may be stated that Clerk Maxwell, although the leading electrician of his time, speaks of the storage battery as storing up a quantity of energy in a manner somewhat analogous to the ordinary condenser; hence the use of the word "accumulator" for storage battery.

In 1879, R. L. Metzer did away with the tedious forming process, by mechanically applying the active material. This important discovery was not, however, generally known, until 1881, when Camille Faure obtained important patents concerning the method of shortening the time of formation.

Charles F. Brush, working independently of either Faure or Metzer, arrived at the same result, and the United States courts have decided, after long litigation, that to him belongs the priority of invention in this country.

=Ques. To what use is the storage battery sometimes put in electric lighting or power stations?=

Ans. To carry the "peak" of the load; that excessive portion of the load which, for instance, in electric lighting stations has to be carried only for two or three hours a day. To carry the entire load at minimum hours. To act as equalizer or reservoir. Also for equipment of annex or substations.

=Theory of the Storage Battery.=—The action of the storage battery is practically the same as that of the primary battery and it is subject to the same general laws. The cells of a storage battery are connected in the same way as primary cells, and when charged is capable of generating a current of electricity in a manner similar to that of a primary battery. It differs, however, from the primary battery in that it is capable of being recharged after exhaustion by passing an electric current through it in a direction opposite to that of the current on discharge. This difference constitutes the principal advantage of the storage battery over the primary battery.

=Ques. Describe a storage cell.=

Ans. A storage cell consists of plates or of grids in an electrolyte, of such a character that the electrical energy supplied to it is converted into chemical energy (a process called charging). The chemical energy can be reconverted into electrical energy (a process called discharging).

=Ques. Describe the electrolyte generally used.=

Ans. It consists of a weak solution of sulphuric acid which permits ready conduction of the current from the primary battery, the greater the proportion of acid within certain limits, the smaller the resistance offered.

=Ques. What is the effect of the current passing through the electrolyte?=

Ans. It decomposes the water into oxygen and hydrogen; this is indicated by the formation of bubbles upon the exposed surfaces of both plates, these bubbles being formed by oxygen gas on the plate connected to the positive pole of the primary battery, and hydrogen on the plate connected to the negative pole.

Because, however, the oxygen is unable to attack either platinum or silver under such conditions, the capacity of such a device to act as an electrical accumulator is practically limited to the point at which both plates are covered with bubbles. After this point the gases will begin to escape into the atmosphere.

=Ques. What is the prime condition for operation of a storage battery?=

Ans. The resistance of the electrolyte should be as low as possible in order that the current may pass freely and with full effect between the electrodes. If the resistance of the electrolyte be too small, the intensity of the current will cause the water to boil rather than to occasion the electrolytic effects noted above.

=Ques. What happens when the charging current is discontinued, and the two electrodes joined by an outside wire?=

Ans. A small current will flow through the outside circuit, being due to the recomposition of the acid and water solution. The process is in a very definite sense a reversal of that by which the current is generated in a primary cell.

Hydrogen collected upon the negative plate, which was the cathode, so long as the primary battery was in circuit, is given off to the liquid immediately surrounding it, uniting with its particles of oxygen and causing the hydrogen, in combination with them, to unite with the particles of oxygen next adjacent. The process is continued until the opposite positive plate is reached, when the oxygen collected there is finally combined with the surplus hydrogen, going to it from the surrounding solution.

This chemical process causes the current to emerge from the positive plate, which was the anode, so long as the primary battery was in circuit. The current thus produced will continue until the recomposition of the gases is complete; then ceasing because these gases, as before stated, do not combine with the metal of the electrodes.

=Types of Storage Battery.=—There are three classes of storage cell which are commercially important:

1. Plante cells; 2. Faure cells; 3. Alkaline cells.

According to construction secondary cells may be classified as follows:

1. Lead sulphuric acid cells; 2. Lead copper cells; 3. Lead zinc cells; 4. Alkaline zincate cells.

The lead sulphuric acid type includes all those cells belonging to the Plante and Faure groups.

Lead copper cells consist of sheets of metal coated with lead oxide, serving as the positive electrode, and copper plates for the negative electrodes. These plates are immersed in a solution of copper sulphate. Cells belonging to this class are not employed in commercial practice, being useful only for laboratory experiments.

Lead zinc cells are similar to the preceding type, but differ by having zinc for the negative electrode, and zinc sulphate for the electrolyte. The voltage of these cells is slightly higher than that of the ordinary cell, and their capacity per unit of total weight is high, but they are apt to lose their charge on open circuit, besides they possess most of the disadvantages of the Plante cells.

Alkaline zincate cells have copper for the positive, and iron for the negative electrode. The electrolyte is composed of sodium, or potassium, zincate. Cells of this type are used to some extent for traction purposes.

In addition to the above there are some special forms of cell which do not belong to the four preceding types.

=Ques. Describe the Plante type.=

Ans. In the Plante type the lead is chemically attacked and finally converted into lead peroxide, probably after it has gone through several intermediate changes. The plates are all formed as positive plates first and then all that are intended for negative plates are reversed, the peroxide being changed into sponge lead.

=Ques. What is done to make the Plante plate more efficient?=

Ans. The surfaces are finely subdivided, the following methods being those common: scoring, grooving, casting, laminating, pressing, and by the use of lead wool.

=Ques. Describe the Faure or pasted type.=

Ans. This form of plate is constructed by attaching the active material by some mechanical means to a grid proper. The active material first used for this purpose was red lead, which was reduced in a short time to lead peroxide when connected as the positive or anode, or to spongy metallic lead when connected as the cathode or negative, thus forming plates of the same chemical compound as in the Plante type.

The materials used at the present time by the manufacturers for making this paste are largely a secret with them, but in general they consist of pulverized lead or lead oxide mixed with some liquid to make a paste.

=Ques. How do Faure plates compare with those of the Plante type?=

Ans. They are usually lighter and have a higher capacity, but have a tendency to shed the material from the grid, thus making the battery useless.

Many ways have been tried for mechanically holding the active material on the grid, the general method involving a special design in the shape of the grid. Some of these designs are: 1, solid perforated sheets of lattice work; 2, corrugated and solid recess plates not perforated; 3, ribbed plates with projecting portions; 4, grid cast around active material; 5, lead envelopes, and 6, triangular troughs as horizontal ribs.

=The Electrolyte.=—Sulphuric acid is generally used as electrolyte; the acid should be made from sulphur and not from pyrites, as the latter is liable to contain injurious substances.

=Ques. How is the electrolyte prepared?=

Ans. One part of chemically pure concentrated sulphuric acid is mixed with several parts of water. The proportion of water differs with several types of cell from three to eight parts, as specified in the directions accompanying the cells.

=Ques. What test is necessary in preparing the electrolyte?=

Ans. In mixing the water and acid, the hydrometer should be used to test the specific gravity[6] of both the acid and the solution. The most suitable acid should show a specific gravity of about 1.760 or 66° Baumé.

[6] NOTE.—_Specific gravity_ is the weight of a given substance relative to an equal _bulk_ of some other substance which is taken as a standard of comparison. Water is the standard for liquids. In the laboratory the _specific gravity bottle_ is often used in determining the specific gravity of a liquid. The capacity of the bottle is 1,000 grains of pure water. When it is filled with spirits of wine and weighed in a balance (together with a counterpoise for the weight of the bottle, which of course is constant), it will weigh considerably less than 1,000 grains; in fact, the bottle will contain only about 917 grains of proof spirit; therefore, taking the specific gravity of water as unity, 1 or 1.000, the specific gravity of spirits of wine is 0.917. If, on the other hand, the bottle be filled with sulphuric acid, it will weigh about 1,850 grains; hence, the specific gravity of sulphuric acid is said to be 1.850. A more convenient method for the automobilist is by the use of the hydrometer.

=Ques. In preparing the electrolyte, how should the water and acid be mixed?=

Ans. The mixture should be made by pouring the acid slowly into the water, _never the reverse_. As cannot be too strongly stated, in mixing, the liquid should be stirred with a clean wooden stick, the acid being added to the water slowly; the latter is corrosive and will painfully burn the flesh.

Distilled or rain water should be used in preparing the electrolyte. When made, the solution should be allowed to cool for several hours or until its temperature is approximately that of the atmosphere (60 being the average). At this point it should have a specific gravity of about 1.200 or 25° Baumé. If the hydrometer show a higher reading, water may be added until the correct reading is obtained; if a lower reading, dilute acid may be added with similar intent.

The electrolyte should never be mixed in jars containing the battery plates, but preferably in stone vessels, specially prepared for the purpose. Furthermore, it should never be placed in the cell until perfectly cool.

=Ques. What is the effect of mixing the acid and the water?=

Ans. The mixture becomes hot.

Before using, the mixture should be allowed to cool.

=Ques. What kind of a vessel should be used?=

Ans. The vessel should be of glass, glazed earthenware, or lead.

=Ques. At what density is the resistance of dilute sulfuric acid at a minimum?=

Ans. At 1.260.

The percentage of concentrated sulphuric acid and of water per 100 parts of the electrolyte for various specific gravities is given by the following table:

SPECIFIC GRAVITY TABLE +——————————————+————————————+————————————————+ |Sulphuric acid| Water |Specific gravity| | (Per cent.). |(Per cent.).| of Mixture. | +——————————————+————————————+————————————————+ | 50 | 50 | 1.398 | | 47 | 53 | 1.370 | | 44 | 56 | 1.342 | | 41 | 59 | 1.315 | | 38 | 62 | 1.289 | | 35 | 65 | 1.264 | | 32 | 68 | 1.239 | | 29 | 71 | 1.215 | | 26 | 74 | 1.190 | | 23 | 77 | 1.167 | | 20 | 80 | 1.144 | | 17 | 83 | 1.121 | | 14 | 86 | 1.098 | | 10 | 90 | 1.068 | +——————————————+————————————+————————————————+

The electrolyte of the desired specific gravity may be purchased ready for use, but in cases where it is desirable to save freight, the acid may be diluted at the point of installation.

=Ques. What is the effect of a deep containing vessel?=

Ans. Parts of the plate surface may do more than their share of the work due to the difference in the density of the electrolyte at the top and bottom. The containing vessel should, therefore, never be deeper than about 20 inches unless some artificial means of acid circulation be used.

=Ques. What is the effect of changes in temperature on the electrolyte?=

Ans. The resistance of the electrolyte is changed, being less for increase of temperature.

=Ques. How should the cells be filled?=

Ans. Enough of the electrolyte should be poured into the jars to completely cover the plates, or to within about a half inch of the top edge of the jar. Large cells should be filled by means of an acid proof pump and rubber hose.

=Ques. What change takes place after filling the jars?=

Ans. The specific gravity of the electrolyte will fall considerably, but will rise again when the battery is charged.

=Ques. What may be said with respect to the density of the electrolyte?=

Ans. It should never exceed 1.200 when the battery is fully charged.

=Ques. How much electrolyte is used per 100 ampere hours battery capacity, on an 8 hour rating?=

Ans. About ten pounds; in automobile batteries, about four pounds is sufficient.

=Ques. What may be said with respect to impurities in the electrolyte?=

Ans. The electrolyte should be free from chlorine, nitrates, acetates, iron, copper, arsenic, mercury, and the slightest trace of platinum.

Mercury alone has no injurious effect unless it be present in sufficient quantity to amalgamate the plates, but in combination with any other metal, may cause local action.

The following tests should be made for impurities before the electrolyte is poured in the cells:

=Chlorine.=—To a small sample of the electrolyte add a few drops of silver solution (20 grains of silver dissolved in 1,000 cu. cm. of water). A white precipitate indicates chlorine.

=Nitrates.=—Place some of the electrolyte in a test tube, and add 10 grains of strong ferrous sulphate solution. Carefully pour down the side of the test tube a small amount of chemically pure concentrated sulphuric acid. A brown stratum between the electrolyte and the concentrated acid indicates the presence of nitric acid.

=Acetic acid.=—Neutralize the electrolyte with ammonia, then add ferric chloride. If the solution turns red, and is afterwards bleached by the addition of hydrochloric acid, acetic acid is present.

=Iron.=—Neutralize a sample of the electrolyte with ammonia; boil a small portion with hydrogen peroxide, and add ammonia or caustic potash solution until the mixture becomes alkaline. If a brownish red precipitate forms, it indicates iron.

=Copper.=—If copper be present, a bluish white precipitate will be formed when ammonia solution is added to the electrolyte.

=Mercury.=—This is indicated by an olive green precipitate when a solution of potassium iodide is added to the electrolyte, or by a black precipitate when lime water is added.

=Platinum.=—A rough test for traces of platinum is made by pouring the electrolyte into a cell in which the battery plates are immersed. If gassing take place for some time on open circuit, it is an indication of the presence of platinum.

=Ques. What should be done with old electrolyte?=

Ans. When a battery is taken down the electrolyte may be saved and used when re-assembling the battery, providing great care be exercised when pouring it out of the jar, so as not to draw off with it any of the sediment. It should be stored in convenient receptacles, preferably carboys, which have been thoroughly washed and never used for any other purpose.

The electrolyte saved in this manner will not, however, be sufficient to refill the battery, and as some new electrolyte will be required, in general it is recommended that the old supply be thrown away and all new electrolyte (1.200 specific gravity) be used when re-assembling.

=Voltage of a Secondary Cell.=—This depends on the density of the electrolyte, the character of the electrodes and condition of the cell; it is independent of the size of the cell.

The voltage of a lead sulphuric acid cell when being charged is from 2 to 2.5 volts. While the cell is being discharged, it decreases from 2 to 1.7 volts. The voltage due to the density of the electrolyte may be calculated from the following formula:

V = 1.85 + .917 (S - s)

in which

V = voltage; S = specific gravity of the electrotype; s = specific gravity of water at the temperature of observation.

=Connection for Charging.=—The dynamo cable connections may be made either before or after filling the cells. In making these connections great care should be taken to be sure that the positive terminal of the battery is connected to the positive lead of the dynamo, and that the negative terminal of the battery is connected to the negative lead of the dynamo. In order to insure that the reverse connections are not made accidentally, the dynamo leads should be tested by a pole tester, and the positive and negative poles marked red and black respectively.

The polarity of the dynamo wires being determined, they may be joined to the proper terminals by means of suitable clamps or by solder.

Wherever possible the dynamo should be of the direct current, shunt wound, or special compound type, but in cases where only alternating current can be obtained, suitable rectifiers or converters should be used for changing it to direct current.

=Charging.=—Before beginning to charge a storage battery, it should be gone over carefully, and any cell that is not up to the standard should be disconnected and put in working order before being replaced. In general, if the current used in charging be too large, it will waste energy by evolving an excess of heat and gas; if too small, an insulating deposit of white lead sulphate will be formed on the positive plate, thereby preventing the formation of the proper amount of lead peroxide.

=Ques. How should a battery be charged for the first time?=

Ans. It is essential that the current be allowed to enter at the positive pole at about one-half the usual charging rate prescribed, but after making sure that all necessary conditions have been fulfilled, it is possible to raise the rate to that prescribed by the manufacturers of the battery.

=Ques. What is the usual period for charging a new battery?=

Ans. With several of the best known makes of storage battery the prescribed period for the first charge varies between twenty and thirty hours.

=Ques. How is the electrolyte affected by the first charge?=

Ans. A change of specific gravity occurs. The specific gravity should be about 1.200 when the solution is poured into the cells.

At the completion of the first charge, it should, on the same scale be about 1.225. If it be higher than this, water should be added to the solution until the proper figure is reached, if it be lower, dilute sulphuric acid should be added until the hydrometer registers 1.225.

At the first charging of a cell, when the pressure has reached the required limit, the cell should be discharged until the voltage has fallen to about two-thirds normal pressure, when the cell should again be recharged to the normal voltage (2.5 or 2.6 volts).

The manufacturers of a well known cell of the Plante genus prescribe for the first charge, half rate for four hours, after which the current may be increased to the normal power and continued for twenty hours successively.

=Ques. What strength of current should be used in charging a cell?=

Ans. It should be in proportion to the ampere hour capacity of the cell.

Thus, as given by several manufacturers, the normal charging rate for a cell of 40 ampere hours should be five amperes, or one-eighth of its ampere hour rating in amperes of charging current.

=Ques. What should be the voltage of the charging current before closing the charging circuit?=

Ans. The voltage should be at least ten per cent. higher than the normal voltage of the battery when charged.

=Ques. What indicates the completion of a charge?=

Ans. When a cell is fully charged the electrolyte apparently boils and gives off gas freely. The completion of a charge may be determined by the voltmeter, which will show whether the normal pressure has been attained.

=Ques. How should the voltage be regulated during the first charge?=

Ans. It should be allowed to rise somewhat above the point of normal pressure.

Electrical Data Edison Cell +——————————————————————————————————————————————————————————————+ | =B-2= =B-4= =B-6=| |Normal output, ampere hours 40 80 120 | | | |Maximum output, ampere hours 48 95 142 | |Normal rate of discharge, amperes for | | five hours 8 16 24 | | | |Average voltage on normal discharge 1.2 1.2 1.2 | | | |Normal rate of charge, amperes for | | seven hours 8 16 24 | | | |Maximum rate of "boosting charge" | | (for short time only) 50 100 140 | | | |Length of containing can (determined | | by number of plates) 1½ 2⅝ 3-13/16 | | | |Width of containing can 5⅛ 5⅛ 5⅛ | | | |Height " " " 7-15/16 7-13/16 7¾ | | | |Height over all 8¾ 8¾ 8⅞ | | | |Weight of each cell alone, lbs. 4.6 7.4 10.5 | | | |Average weight per cell of battery, | | assembled in trays 5.5 8.7 11.8 | +——————————————————————————————————————————————————————————————+

=Ques. How often should a battery be charged?=

Ans. At least once in two weeks, even if the use be only slight in proportion to the output capacity.

In charging a storage battery, it is essential to remember the fact that the normal charging rate is in proportion to the voltage of the battery.

Thus, a 100 ampere hour battery, charged from a 110 volt circuit at the rate of ten amperes per hour, would require ten hours to charge, and would consume in that time an amount of electrical energy represented by the product of 110 (voltage) by 10 (amperes) which would give 1,100 watts, or 1⅒ kw.

=Ques. If in charging a battery, one or more of the cells do not boil at the completion of the charge, or fail to show the proper voltage, what should be done?=

Ans. The charging must be continued until the cadmium test shows the required voltage, but if the prolonging of the charge be liable to damage the plates in the other cells, the defective cell or cells should be cut out of circuit when the battery discharges and then placed in circuit again when the battery is recharged. If the desired result cannot be attained by this method, the plates which require additional charging may be charged in a separate cell.

=Ques. How is the cadmium test made?=

Ans. A plate of cadmium is mounted in a hard rubber frame and immersed in the electrolyte. The test consists in taking voltage readings between the cadmium plate and the positive or negative plates of the cell. During charge the cadmium plate reads negative to the negative plate, until the cell is about full, when the reading should be zero; the charge should be continued until the cadmium reads 0.2 volt positive to the negative while charging at the normal rate.

=Ques. Name some portable instruments that should be provided for testing batteries.=

Ans. 1, a hydrometer syringe (specific gravity tester); 2, an acid testing set (can be used instead of the syringe); 3, a low reading voltmeter; 4, suitable prods, and 5, a thermometer.

=Ques. What precaution should be taken in charging a battery?=

Ans. Care should be taken not to have a naked flame anywhere in its vicinity.

To either charge or discharge a battery at too rapid a rate involves the generation of heat. Thus, while this is not liable to result in a flame under usual conditions, the battery may take fire, if it be improperly connected or improperly used.

=Ques. What is the effect of varying the charging current?=

Ans. In charging a storage cell, particularly for the first time, a weaker current than that specified may be used with the same result, provided the prescribed duration of the charge be proportionally lengthened. The battery may also be occasionally charged beyond the prescribed voltage, ten or twenty per cent. overcharge effecting no injury, although if frequently repeated, it shortens the life of the battery.

=Ques. What are the charge indications?=

Ans. The state of the charge is not only indicated by the density of the electrolyte and the voltage of the cell, but also by the _color of the plates_, which is considered by many authorities as one of the best tests for ascertaining the condition of a battery.

=Ques. What are the colors of the plates?=

Ans. In the case of formed plates, and before the first charging, the positives are of a dark brown color with whitish or reddish gray spots, and the negatives are of a yellowish gray. The whitish or reddish gray spots on the positive plates are small particles of lead sulphate which have not been reduced to lead peroxide during the process of forming, and represent _imperfect sulphation_.

As a general rule, the first charging should be carried on until these spots completely disappear. After this the positive plates should be of a dark red or chocolate color at the end of the discharge, and of a wet slate or nearly black color when fully charged. A very small discharge is sufficient, however, to change them from black to the dark red or chocolate color.

If the battery has been discharged to a pressure lower than 1.8 volts, the white sulphate deposits will reappear, turning the dark red color to a grayish tint in patches or all over the face of the plate, or in the form of scales of a venetian red color.

_The formation of these scales_ while charging indicates that the maximum charging current is too large and should be reduced until the scales or white deposits fall off or disappear, after which the current can be increased again.

During charging, the yellowish gray color of the negatives changes to a pale slate color which grows slightly darker at the completion of the charge. The color of the negatives always remains, however, much lighter than that of the positives.

=Ques. How are the best results obtained in charging?=

Ans. The rate of charge should be normal, except in cases of emergency. At such a rate, unless the constant voltage method be employed, the cell may be considered full when the voltmeter reads 2.5 volts during charge. The electrolyte should be kept at uniform density throughout the cell; when water is added, because of evaporation, it should be added by means of a funnel reaching to the bottom of the cell. Care should be taken never to add acid after evaporation; otherwise the electrolyte will be too heavy. Hydrometer readings should be taken regularly; the reading is an excellent indication of the amount of charge in the battery. Hydrometer readings are useless, however, unless the precaution be taken to keep the electrolyte of uniform density.

=Ques. What voltage should be used in charging?=

Ans. At the beginning of the charge the voltage should be about 5 per cent. higher than the normal voltage of the battery, unless the latter has been overdischarged, in which case the difference of pressure should not exceed 2 per cent., otherwise the current might be too large.

=Ques. In what two ways may batteries be charged?=

Ans. They may be charged either at constant current or at constant voltage.

Although the latter method is considered the better one by many authorities, it is a fact, nevertheless, that if the charging current be normal at the beginning of the charge, and no means be provided for keeping it constant, it will diminish as the charging progresses, thereby greatly increasing the length of the time required for charging, and resulting in serious injury to the plates.

=Ques. How may the charging current be kept constant?=

Ans. Its voltage should be gradually increased, first to about 10 or 15 per cent. above the voltage of the battery, and kept at that point nearly to the end of the charge, where in consequence of the rapid rise of pressure in the battery it might become necessary to increase the voltage of the current to 30 or 40 per cent. above the normal of the battery.

=Ques. What tests should be made while charging?=

Ans. Occasional voltage and cadmium readings of each cell should be taken for the purpose of ascertaining their condition and the behavior of the separate plates.

=Ques. What tests should be made after charging?=

Ans. Each cell should be tested with a low reading voltmeter and hydrometer about once a week. If any cell read low, it should be cut out and examined to see if any material has been introduced which would cause a short circuit. If this trouble do not exist, the cell should be given an independent charge.

=Charge Indications.=—The state of the charge is not only indicated by the density of the electrolyte and the voltage of the cell, but also by the _color of the plates_, which is considered by many authorities as one of the best tests for ascertaining the condition of a battery.

In the case of formed plates, and before the first charging, the positives are of a dark brown color with whitish or reddish gray spots and the negatives are of a yellowish gray. The whitish or reddish gray spots on the positive plates are small particles of lead sulphate which have not been reduced to lead peroxide during the process of forming, and represent _imperfect sulphation_.

As a general rule the first charging should be carried on until these spots completely disappear. After this, the positive plates should be of a dark red or chocolate color at the end of a discharge and of a wet slate or nearly black color when fully charged. A very small discharge is sufficient, however, to change them from black to the dark red or chocolate color.

If the battery has been discharged to a pressure lower than 1.8 volts, the white sulphate deposits will reappear turning the dark red color to a grayish tint in patches or all over the surface of the plate, or in the form of scales of a venetian red color.

The _formation of these scales_ during charging indicates that the maximum charging current is too large and should be reduced until the scales or white deposits fall off or disappear, after which the current can be increased again.

=Ques. Describe the behavior of the electrolyte during discharge.=

Ans. There is a definite change in the density of the electrolyte for a given amount of discharge.

The density of the electrolyte is, therefore, one of the best indications of the state of charge, provided, of course, no internal discharge due to local action takes place. If, when the cell is charged, it show a density of 1.200, and when discharged 1.130, the difference .07 represents the total charge. If at any time the density be 1.165, then just one half the amount of capacity has been taken from the cell.

It is necessary to stir the electrolyte well, in order for these observations to be reliable.

If the discharge has taken place at a high rate, the cell must stand for an hour or more before the electrolyte will completely diffuse so that the density readings are correct.

=Ques. Define the term "boiling."=

Ans. Boiling means the rapid evolution of gas when a cell is nearly charged.

=Ques. What causes boiling?=

Ans. The amount of sulphate to be converted into peroxide becomes less and less as the charge progresses and the plates therefore become virtually smaller, so that the current becomes too large for the work demanded of it. The result is, that part of the current not actually used in the formation of peroxide decomposes the electrolyte into its constituent elements.

=Ques. Why do the gases evolved produce a less milky appearance of the electrolyte when a battery has been in use for a considerable time?=

Ans. The plates are better formed; consequently a larger charging current can be used without producing "boiling".

=Ques. What may be said of charging a battery as quickly as possible?=

Ans. As a general rule, such a procedure should not be adopted unless the battery be thoroughly discharged.

=Ques. What precaution should be taken?=

Ans. The danger to be avoided in rapidly charging a cell is its tendency to heat.

=Ques. What apparatus is necessary in charging a battery?=

Ans. The battery may be charged from direct current mains having the proper voltage. A current as near uniform as possible is required, and existing conditions must be met in each separate case. Sometimes a motor dynamo set with a regulating switchboard is used. Such an apparatus consists of a direct current dynamo, driven direct from the shaft of a motor, which, in turn, is energized by current from the line circuit.

With a direct current on the line, a direct current dynamo may be used; but with an alternating current an induction motor is required. The speed of the motor is governed by a rheostat, and the output of the dynamo is thus regulated as desired.

=Charging Through the Night.=—If an electric vehicle, after a late evening run, is to be used in the morning, the battery may be charged during the night without an attendant being present; but in doing this great care must be taken not to excessively overcharge.

A careful estimate of the amount of current required should be made and the rate of charge based on this estimate.

If, say, 72 ampere hours be required to recharge, and the time available is nine hours, the average rate of charge must be 8 amperes.

If charging from a 110-volt circuit, the rate at the start should be about 10 amperes; if from a 500-volt circuit, about 9 amperes; as, in charging from a source with constant voltage, such as a lightning or trolley circuit, the rate into the battery will fall as the charge progresses. This also applies if the charging be done from a mercury arc rectifier without attendance.

=Ques. What precautions should be taken in charging a battery out of a vehicle?=

Ans. When a battery is being overhauled, the cells must be connected together in series and to the charging source in relatively the same manner as if they were in the vehicle; that is, the positive (+) terminal of one group of cells must be connected to the negative (-) terminal of the next group, and the two free terminals, one positive and the other negative, must be connected respectively to the positive and negative terminals of the charging circuit, but not until all of the groups have been connected in series. Great care must always be taken to have the polarities correct and the wire or cable for the connections of ample size to carry, without heating, the heaviest current used in charging.

=Charging Small Cells.=—For cells of the portable type, having capacities from 10 to 100 ampere hours, the normal charging and discharging rate should be about one-tenth the stated capacity, but the discharging rate may be increased to double this value, in case of necessity.

If the cells be provided with formed plates and not charged, the jars should be filled with the proper electrolyte, and then charged for at least 10 hours steady, or until they boil, then they may be discharged.

In the case of unformed plates, the charging should be from 30 to 40 hours, until the cells boil, and the plates assume their proper color.

=Ques. How are small cells easily charged from 110 or 220 volt circuits?=

Ans. This may be conveniently done by inserting in one of the charging leads an incandescent lamp which will pass the required quantity of current. If the current required be as large as 10 amperes, a suitable resistance or 10 lamps in parallel, each passing one ampere, may be used. Great care should be taken to see that the battery is connected properly.

=Period of Charging a New Battery.=—In the case of batteries provided with formed plates, the first charge should extend over a period of not less than 30 consecutive hours, without stopping, if possible, or for periods of not less than 10 hours a day for three consecutive days. The electrolyte will then commence to "boil" or "gas," assuming a milky appearance due to the ascending bubbles of gas. At this stage the density of the electrolyte as shown by the hydrometer placed in each cell should be at least 1.200; it is essential that the charging should be continued until every cell boils equally. From this point the charging should be prolonged until the pressure, as determined by a voltmeter or a cadmium tester, rises to about 2.55 volts.

The charging of unformed plates is similar in all respects to that of formed plates, except that the first charging should extend over a period of at least 70 consecutive hours without stopping, at the end of which time the plates should have the characteristic colors of those of a fully charged battery. If they do not, the charging should be prolonged and the cell tested for density of electrolyte, and voltage, as already described until the desired conditions are attained. Then the battery may be discharged and recharged.

It is probable that a total of 300 to 400 hours of charging with intervening discharges will be required to form the plates until they acquire a good color, and the density of the electrolyte becomes stable.

In regular charging, the rate should be rapid when the battery is nearly exhausted, but it should be greatly reduced at the end of the charge after passing the point of boiling. Charging at too low a rate is always injurious.

=Ques. What may be said with respect to the capacity of a new battery?=

Ans. A new battery will never give its full capacity till after about twenty discharges. During this time it should be given about 25% overcharge. After that, 10% overcharge, that is, 10% more charge than was taken out, will be sufficient for ordinary work.

=High Charging Rates.=—Occasionally it is desirable to charge a battery as quickly as possible. As a general rule, such a procedure should not be adopted unless the battery be thoroughly discharged, and not then, unless done by a person who thoroughly understands what he is about; battery makers will always furnish data and directions to meet emergencies.

In charging a battery at a high rate, the danger to be avoided is the tendency of the cells to heat. The troubles that might arise from this cause may be prevented by immediately reducing the current strength. The proper rate of charge for a given battery of cells may be thus discovered by experiment. A battery should never be charged at a high rate unless it be completely exhausted, since it is a fact that the rate of charge that it will absorb is dependent upon the amount of energy already absorbed.

For rapid charging, when a battery has to be charged in four hours, the current should vary about as follows:

40 per cent. of total 1st hour 25 " " " " 2nd " 20 " " " " 3rd " 15 " " " " 4th "

For quick charging in three hours the rates should be: 50 per cent. 1st hour; 33⅓ per cent. 2nd hour; 16⅔ per cent. 3rd hour.

=Mercury Arc Rectifier.=—This is a device for obtaining direct current from alternating current for use in charging storage batteries. The transformation is obtained at a low cost, because the regulation is obtained from the alternating side of the rectifier, while the current comes from the direct current side.

The theory is as follows: In an exhaust tube having one or more mercury electrodes, ionized vapor is supplied by the negative electrode or cathode, when the latter is in a state of "excitation." This condition of excitation can be kept up only as long as there is current flowing toward the negative electrode.

If the direction of the voltage be reversed, so that the formerly negative electrode is now positive, the current ceases to flow, since in order to flow in the opposite direction it would require the formation of a new negative electrode, which can be accomplished only by special means. Therefore, the current is always flowing toward one electrode—the cathode, which is kept excited by the current itself. Such a tube would cease to operate on alternating current voltage after half a cycle if some means were not provided to maintain a flow of current continuously towards the negative electrode.

=Ques. Describe the construction and operation of a mercury arc rectifier.=

Ans. Fig. 1,135 is an elementary diagram of connections. The rectifier tube in an exhausted glass vessel in which are two graphite anodes A, A´, and one mercury cathode B. The small starting electrode C is connected to one side of the alternating circuit, through resistance; and by rocking the tube a slight arc is formed, which starts the operation of the rectifier tube. At the instant the terminal H of the supply transformer is positive, the anode A is then positive, and the arc is free to flow between A and B. Following the direction of the arrow still further, the current passes through the battery J, through one-half of the main reactance coil E, and back to the negative terminal G of the transformer. When the impressed voltage falls below a value sufficient to maintain the arc against the reverse voltage of the arc and load, the reactance E, which heretofore has been charging, now discharges, the discharge current being in the same direction as formerly. This serves to maintain the arc in the rectifier tube until the voltage of the supply has passed through zero, reversed, and built up such a value as to cause the anode A to have a sufficiently positive value to start the arc between it and the cathode B. The discharge circuit of the reactance coil E is now through the arc A'B instead of through its former circuit. Consequently the arc A'B is now supplied with current, partly from the transformer, and partly from the reactance coil E. The new circuit from the transformer is indicated by the arrows enclosed in circles.

=Ques. How is a mercury arc rectifier started?=

Ans. A rectifier outfit with its starting devices, etc., is shown in figs. 1,132 to 1,134. To start the rectifier, close in order named line switch and circuit breaker; hold the starting switch in opposite position from normal; rock the tube gently by rectifier shaker. When the tube starts, as shown by greenish blue light, release starting switch and see that it goes back to normal position. Adjust the charging current by means of fine regulation switch on the left; or, if not sufficient, by one button of coarse regulation switch on the right. The regulating switch may have to be adjusted occasionally during charge, if it be desired to maintain the charging current approximately constant.

=Capacity.=—The unit of capacity of a storage cell is the _ampere hour_, that is, the ability to discharge one ampere continuously for one hour. For instance, a 100 ampere hour battery will give a continuous discharge of 12½ amperes for eight hours. It should theoretically give a discharge of 25 amperes continuously for four hours, or 50 amperes for two hours, but in reality, the ampere hour capacity decreases with an increase of discharge rate.

It requires, theoretically .135 ounces of metallic lead on either element reduced to sponge lead or to lead peroxide to produce one ampere hour; in practice, from four to six times this amount is required.

The reason for this is because it is impossible to reduce all the active material, to bring every particle in contact with the electrolyte, or to cause every part to be penetrated by the current.

Experiments show that from .5 to .8 ounces of sponge lead, and from .53 to .86 ounces of metallic lead converted into peroxide, are required on their respective elements to produce a discharge of one ampere hour at ordinary commercial rates.

The capacity increases with the temperature, being about one per cent. for each degree Fahr. increase in temperature.

Battery capacity depends on the size and number of plates; the quantity of active material present, and the quantity of electrolyte.

For an eight hour rate of discharge and 60 degrees temperature, the capacity of American batteries varies from 40 to 60 ampere hours per square foot of positive plate surface ( = 2 × number of positive plates in parallel × length × breadth).

The following table gives the variation of capacity for different rates of discharge:

Capacity Variation for Different Discharge Rates

+——————————-+——————————————————————+ | Discharge | Per cent of capacity | | rate | at 8 hour rate | +——————————-+——————————————————————+ | | =Plante= | =Faure= | | 8 hour | 100% | 100% | | 6 hour | 96% | 96% | | 4 hour | 80% | 88% | | 2 hour | 61% | 70% | | 1 hour | 56% | 48% | +——————————-+——————————+——————————-+

=Ques. How may the capacity of a battery be increased?=

Ans. By mixing organic materials with the lead oxide, _but any such mixture is always accompanied by a rapid deterioration of the plates_.

=Discharging.=—In discharging a battery its voltage should never be allowed to fall below 1.8 volts, under load, thus leaving about 30 per cent. of the total capacity unused. The normal discharging current may be equal to the normal charging current, but a discharge equal to 3 or 4 times the normal may be given without injury to the plates. Some types may be discharged at even six or seven times the normal rate. In such cases, however, the capacity will be reduced in the same proportion, as before explained in the paragraph dealing with battery capacities.

=Ques. What is the effect of discharging too rapidly?=

Ans. It tends to break the plates, and in the case of pasted plates, a very sudden discharge will dislodge the paste.

=Ques. How is the discharge capacity of a storage battery stated?=

Ans. In ampere hours. This, unless otherwise specified, refers to its output of current at the eight hour rate. Most manufacturers of automobile batteries specify only the amperage of the discharge at three and four hours. Thus, at the eight hour rate, a cell which will discharge at ten amperes for eight hours is said to have a capacity of eighty ampere hours. It does not follow that eighty amperes would be secured if the cell were discharged in one hour. It is safe to say that not more than forty amperes would be the result with this rapid discharge.

As a general rule, the one hour discharge rate is four times that of the normal, or eight hour discharge, and considerations of economy and prudence suggest that it should never be exceeded, if, indeed, it ever be employed. The three hour discharge, which is normally twice that of the eight hour, is usually the highest that is prudent, while the four hour discharge is the one most often employed in vehicles for the average high speed riding.

=Ques. What should be the maximum rate of discharge?=

Ans. The one-hour rate; this when used, should not extend over fifteen or twenty minutes. In the case of regulating batteries a forty-five minute rate of discharge may be allowed for one or two minutes during great fluctuations of load.

=Ques. How does the capacity decrease?=

Ans. It decreases with the increase in current output.

An 80 ampere hour cell, capable of delivering 10 amperes for 8 hours, would, when discharged at 14 amperes, have a capacity of 70 ampere hours; when discharged at 20, its capacity would be 60; and when discharged at 40, its capacity will have decreased from 80 to 40 ampere hours.

=Ques. What, in general, are the indications of the quantity of electricity remaining within a cell?=

Ans. The voltage, and the density of the electrolyte.

=Ques. What should be done after discharging?=

Ans. Whenever possible the battery should be immediately charged.

=The Battery Room.=—Precautions should be taken to prevent any direct sunlight falling on the battery cells in glass jars, as the breakage of such jars due to unequal expansion of the different portions of the glass, is a source of constant trouble and danger.

The exclusion of direct sunlight also tends to keep the evaporation of the electrolyte at a minimum.

Operation of Edison Rectifier

The operation of the Edison rectifier may be explained as follows with the aid of figs. 1,154 to 1,156 (the parts being uniformly lettered in the figures): The primary circuit taken from the alternating current mains by the cord B, embraces the primary winding of the transformer T, a condenser C, and the coils P, of the vibrating units, fig. 1,155.

The secondary circuit from the transformer embraces the massive carbon and copper contacts (N and O, fig. 1,156) which pass only the positive waves of the alternating current, for charging batteries or other duty.

An ammeter and rheostat may be placed in this charging circuit if the current is to be varied, or a fixed connection may be substituted on the base of the rectifier if it is to be used for the maximum duty of 8 or 16 amperes.

The vibrating unit (fig. 1,155), which operates in a manner similar to the well known action of a polarized relay, includes a permanent magnet M; the coil in the primary circuit P; the vibrating armature of steel with removable carbon contact N; the stationary copper contact with comb top for heat radiation O, and the screw Q for adjusting the amplitude of the armature vibration.

The vibrating armature of each unit is divided into two parts, which gives flexibility, affords increased current capacity and minimizes sparking, the two leads shown being connected together in one circuit.

A primary relay and a secondary switch (E and F, figs. 1,154 and 1,156), close their contacts when current is flowing.

Upon failure of the main alternating current line they operate to open the charging circuit. A storage battery is thus prevented discharging through the rectifier.

Upon resumption of the main alternating current, the rectifier starts automatically.

Every battery room should be provided with a water tap and sink. The floor should be paved with vitrified brick, preferably blue or yellow in color, of diamond pattern and sloping in all directions toward suitable drains. A floor of this type can be easily washed by flooding with water, and its patterns tend to keep it dry under foot at all times. Wooden floors are rotted very quickly by acid spillings and by the spray.

The room should be kept absolutely clear of everything, which may be injured, by the sulphuric acid fumes and it should be well ventilated to insure the safety and good health of the attendants.

A battery, even at rest, gives off hydrogen which when diluted with air forms a mixture which is very liable to explode if brought in contact with any kind of flame. Unless proper ventilation be provided, the breaking of the connection when a current is flowing, or the lighting of a bare flame lamp in the battery room would be dangerous.

=Battery Attendants and Workmen.=—Those employed in setting up batteries are liable to suffer from soreness of hands and the destruction of clothing unless proper precautions be taken to prevent the same. In order to avoid these troubles, the boots should be painted with paraffine mixed with an equal quantity of beeswax.

The clothing should be of woolen material, which, unlike cotton, is practically unaffected by the acid. If cotton shirts be worn, they should be dipped in a strong solution of washing soda and then rough dried.

An apron of sacking, backed with flannel should be worn over all the other clothes. A bottle of strong ammonia should be kept in the battery room at all times, and in case of an accidental splash of acid on the clothes, the immediate application of a small quantity of the ammonia, by means of the stopper, will at once neutralize the acid and prevent it burning a hole in the material. A pail containing water made strongly alkaline with washing soda should also be kept conveniently at hand during all operations in the battery room. The hands should be dipped occasionally in this water in order to prevent the skin smarting and becoming sore under the action of the acid.

If a splash of acid should happen to enter the eye, it should be washed at once with clean water, warm water preferably, and then put one or two drops of olive oil into the eye. If olive oil be not immediately available, any kind of engine oil is better than none at all.

=Points on Care and Management.=—In setting up storage cells, they should be placed in as few tiers as possible, and in such a manner that the direct rays of the sun are not allowed to fall upon the cells. The rays of the sun are likely to crack the glass. This is probably due to the unequal expansion of the glass, for it has been found that jars which are carefully annealed never crack in this manner. Of course, the latter precaution does not apply to large batteries, where lead lined wooden tanks or solid lead boxes are used.

In installing plants where expert attendance is not to be had, it is well to place in the circuit two magnetic cut outs, one set for maximum current, and the other for minimum voltage, so that the battery cannot be discharged too low.

=Ques. How should the cells be placed?=

Ans. They should be placed as shown in fig. 1,151, on insulators A, resting on wooden stringers B, and supporting pieces C placed on the floor. The insulators are usually of glass or porcelain, which in certain patterns may be filled with oil, to insure better insulation as shown in figs. 1,165 and 1,166.

In setting up a battery, it should be remembered that plates deteriorate on standing exposed to the air. They should, therefore, be unpacked and set up immediately on arrival. When they are entirely connected up, they are ready for the addition of the electrolyte, and for the forming charge, which they should receive immediately.

=Ques. How should the wooden stringers, shelves, cell boards, and trays be treated?=

Ans. They should be thoroughly varnished to insure cleanliness as well as good insulation.

Outside of each cell and close to the mouth, melted paraffine should be applied by means of a brush, so as to form a band about an inch wide, for the purpose of preventing the electrolyte creeping over the top of the jar, wetting the outside, and thereby impairing the insulation.

=Ques. What should be done to avoid waste of current by leakage?=

Ans. Each cell of the battery must be thoroughly insulated.

=Ques. What is the effect of verdigris which forms on the terminals?=

Ans. It is a poor conductor and should therefore be removed and the terminals kept bright and clean to insure the proper flow of the current.

=Ques. What precautions should be taken in unpacking cells?=

Ans. The plates should be handled carefully. When they are sent out from the factory already built into sections, they should be unpacked without disturbing a single plate. In all cases, every particle of packing, straw, hay and any chips and bits of parts should be carefully removed, and all the dust should be blown out of the spaces between the plates by means of a bellows or other similar device.

NOTE.—_Champion directions for repairs._ To replace broken jars in a battery remove the lid and lift out elements bodily. Empty the good jars with a syringe or by tilting the battery over. Never put the acid in any vessel except glass, stone or lead. Put new jars in place same as others and run melted paraffine around the edges. The wax must be broken off the elements that are to go into new jars and be poured on again. Fill the jars with acid to ¾" from tops. Melt the broken wax in a tin ladle and pour over the acid about ½" thick. Do not fill with wax to tops of jars. When the wax gets cold it will be found to have shrunk away from the edges of the jars. Fill up the opening with a little melted paraffine wax by means of a squirt can. Cut a small hole in the middle of the wax seal for a vent. Smear the brass posts and terminals and inside of case with vaseline to prevent creeping of the acid. The "6-25-G" requires one-half gallon of acid and the "6-50-G" one gallon.

Although such particles are good non-conductors, the action of the sulphuric acid electrolyte carbonizes them, giving them conducting properties which tend to produce leakage.

=Ques. How should the cells be assembled?=

Ans. In placing the plates or plate sections in the containing jars or tanks, care should be taken to see that the supporting frame of paraffined wood bears evenly on the bottom of the jar. If they do not, wedges of paraffined wood should be placed under the frame, so as to distribute the weight of the section equally. Each section should be lowered gently into the jar until it rests fairly upon the frame, and care should be taken to see that none of the plates have shifted, and that the section is situated centrally in the jar, with a small clear space all around.

=Ques. How should the cells be arranged?=

Ans. They should be so placed that the battery attendant can see the edges of the plates and consequently the spaces between them at the same time.

=Ques. Describe the method of connecting the cells.=

Ans. This is accomplished by means of solder, bolts and nuts, or clamps, according to circumstances. The use of solder is not essential if there be a good surface of the lead strip of one cell in contact with that of the next, and provided these contact surfaces have been well cleaned. Usually, the ends of the lead strips are turned up so that the junction of two cells takes the form of an inverted T as shown in fig. 1,162.

=Ques. What precaution should be taken in joining the terminals of the cells?=

Ans. The contact at the junctions should be very thorough, otherwise they will become heated when a current is flowing, and it is desirable that the connections should include as little lead strip in the circuit as possible, thereby reducing the amount of useless resistance.

Brass or gun metal clamps may be kept clean by brushing them over with melted paraffin after they have been screwed up tightly. When thus treated they serve to indicate points of bad contact by heat, generated at such points, when the current is flowing, softening the paraffin and changing its normal color. Vaseline and different kinds of anti-sulphuric acid varnishes, or preparations that are not attacked by the electrolyte, may also be used for this purpose. It is a good plan to color the varnish with vermillion or lamp black and paint the positive connections red and the negative connections black, and also other parts of the installation for distinguishing the polarities.

=Cell Connections.=—The cells may be connected together either in series or parallel, or in parallel-series or series-parallel combinations, according to the requirements, but in all cases it is best to use the simplest arrangement practicable.

For instance: if the cells employed in an installation requiring 110 volts, have only half the capacity required, and 55 cells give the desired voltage, then the number of cells must be increased to 110, and theoretically the required number of amperes hours at 110 volts may be obtained in one of two ways: 1, by connecting the cells in pairs in parallel and then coupling the pairs together in series, and 2, by arranging the 110 cells in two complete batteries of 55 cells each connected in series, then coupling the two batteries in parallel.

The first method is quite impracticable, however, as the slightest difference between the voltages of the two cells of any pair will result in the one having the greater pressure discharging into the other, thereby causing the entire battery to quickly deteriorate.

NOTE.—_To determine the positive wire._ Without a voltmeter, the positive terminal of the charging circuit can be determined by attaching a piece of clean lead to each wire which is to be connected to the battery, and immersing them, without touching each other, in a glass or other insulating vessel containing water to which is added a drop or two of sulphuric acid. After the current has passed through the circuit for a short time, the positive lead will commence to discolor, and, if left long enough, will turn brown. Bubbles will arise from the two terminals immersed, the larger and more frequent ones being from the negative, the smaller ones from the positive.

NOTE.—_Method of disconnecting "National" cells._ There are two methods of disconnecting the cells employing link connectors. First a ⅝ inch bit or twist drill may be used, boring down into the top of the posts about ¼ inch. The link will then be loosened and can be removed. This leaves the link, as well as the post, in good condition for reburning. Second the link may be cut in the center. A flame should be played on the top of the post, at the same time grasping the end of the half link firmly with pliers. When the connection has become warmed (care being taken not to melt the lead) the half link can be twisted loose from the port. New links may be used if desired in re-assembling the cells. It is not necessary to remove the covers from the element, the links may be cut in the center and the plates removed from the jars without removing the links from the ports. The links can be afterwards reburned together in the center. When the cells are equipped with "T" or "L" straps, they should be cut apart with hack saw or chisel midway between the cells, and in re-assembling, burned together at this point.

=Battery Troubles.=—To successfully cope with faults in storage batteries, there are two requisites: 1, a thorough knowledge of the construction and principle of operation of the battery, and 2, a well ordered procedure in looking for the source of trouble. The faults which are usually encountered by those who operate storage batteries are here given.

=Short Circuiting.=—A form of derangement that may occasionally affect storage batteries is short circuiting. It may be caused by some of the active material—if the cell be of the pasted variety—scaling off and dropping between the plates, or by an over collection of sediment in the bottom of the cell.

Should the operator suspect trouble with his battery he may discover a short circuited cell by the marked difference in color of the plates or of the specific gravity of the electrolyte, as compared with the other cells. No particular damage will be caused, if the trouble be discovered and removed before these symptoms become too marked.

If a foreign substance has become lodged between the plates, it may be removed by a wood or glass instrument.

If some of the active material has scaled off, it may be forced down to the bottom of the jar. If excessive sediment be found, the jar and plates should be washed carefully, and reassembled.

A cell that has been short circuited may be disconnected from the battery and charged and discharged several times separately which may remedy the trouble.

=Ques. How are internal short circuits indicated?=

Ans. Short circuits in a cell are indicated by short capacity, low voltage and low specific gravity, excessive heating and evaporation of the electrolyte.

=Ques. How are internal short circuits located?=

Ans. If the trouble cannot be located by the eye, the battery should be connected in series and discharged at the normal rate through suitable resistance. If a suitable rheostat be not available, a water resistance may be used.

This consists of a receptacle (which must not be of metal) filled with very weak acid solution, or with salt water in which are suspended two metal plates, which are connected by wires through an ammeter. The current may be regulated by altering the distance between the plates, or by varying the strength of the solution. As the discharge progresses the voltage will gradually decrease, and it should be frequently read at the battery terminals; as soon as it shows a sudden drop, the voltage of each cell should be read with a low reading voltmeter.

While the readings are being taken, the discharge rate should be kept constant and the discharge continued until the majority of the cells read 1.70 volts; those reading less should be noted. The discharge should be followed by a charge until the cells which read 1.70 volts are up, then the low cells should be cut out, examined, and the trouble remedied.

=Overdischarge: Buckling.=—On account of unequal expansion of the two sides of a plate, or certain portions thereof, the strains thus set up may distort it and cause it to assume a buckled shape, that is, bent so one side is concave.

Buckling is due always to over discharge on either the whole, or some portion of the plate. Occasional buckling may occur with too rapid charge and discharge.

=Sulphation of Plates.=—During discharge a storage cell deteriorates on account of the formation of lead sulphate over the surface of the plates. This lead sulphate is the product of the chemical combination of active material with the electrolyte. It is a non-conductor, white in color and of greater volume, in proportion than the active material. When the discharge is over prolonged, sulphation is evidenced by the electrodes becoming lighter in color, because of the sulphate which lessens the active surface.

=Ques. Name some causes of sulphation.=

Ans. It is sometimes caused by a too weak or too strong acid solution, but more generally by continued over discharging, or too rapid discharging of the batteries, or by allowing them to remain uncharged for long periods of time.

=Ques. What is the effect of sulphation?=

Ans. It tends to cause shedding of the active material, buckling of plates, loss of capacity, increase of resistance and consequent reduction of efficiency, and increase of temperature with flow of current. A sufficient amount of lead peroxide and sponge lead must be retained on the plates to reduce this resistance, otherwise the charging current cannot flow through the active material and regenerate the battery.

=Ques. What should be done in case of sulphation?=

Ans. Charge the battery below the maximum rate, necessarily prolonging the charge, until the plates assume the proper color. This is a tedious task, but it must not be hastened, as rapid charging will cause serious buckling.

* * * * *

NOTE.—_How to destroy acid vapor in storage battery rooms_: The best remedy is a good system of thorough and rapid ventilation; failing this the evil effect of the acid may be minimized by the fumes of a powerful alkali such as ammonia, which will readily combine with the sulphuric acid to form sulphate of ammonia, an inert and harmless salt. If the use of liquid ammonia be objectionable, the granulated carbonate of ammonia will do equally well. The ammonia fumes are best obtained by placing dilute ammonia in shallow dishes, so that an extensive evaporating surface is obtained. In the same way the corroding dew which is so frequently deposited on the lugs and connectors of storage battery elements may readily be neutralized by the application of a solution of ammonia, or even common washing soda. A good method of protecting metal work in battery rooms is to smear it over evenly with vaseline.

The charging should be done at low rates. Discharge should not be carried below 1.8 volts per cell, and the charging current should be stopped when each cell shows 2.4 volts.

If the plates be in a very bad condition, a little of the white sulphate deposit on each of the positive plates may be removed with a stick, thus exposing a part of the good surface to the action of the electrolyte.

If the positive plates cannot be restored to their proper color as directed, it is cheaper to replace them by a new set, rather than to attempt their recovery by means of reversals.

Electrical Data on "National" Cells (Size of plate 4⅞" × 8⅝")

======================================+=======+=======+========+======== Number of Plates per cell | 5 | 7 | 9 | 11 ——————————————————————————————————————+——————-+——————-+————————+———————— {for 4 hours |12 |18 | 24 | 30 Discharge in amperes {for 5 hours |10¼ |15¼ | 20½ | 25½ {for 6 hours | 9¼ |13¾ | 18½ | 23 | | | | {at 4 hour rate|48 |72 | 96 |120 Ampere hour capacity {at 5 hour rate|51 |76 |102 |127 {at 6 hour rate|55 |83 |110 |138 | | | | Outside measurements of rubber {Length| 1⅞ | 2⅝ | 3⅜ | 4-3/16 jar, in inches {Width | 5-5/16| 5-5/16| 5-5/16| 5-5/16 {Height|11¾ |11¾ | 11¾ | 11¾ | | | | Weight of cell complete, in lbs |14¼ |19¼ | 24¼ | 29¾ | | | | Weight of electrolyte, in lbs | 1 | 2 | 3½ | 5 ——————————————————————————————————————+——————-+——————-+————————+————————

=Lack of Capacity.=—This is usually due to the clogging of the pores in the plate with sulphate which is invisible because the surface of the plate is maintained in proper condition but the interior portions of the active material have not been thoroughly reduced. To correct this condition, the battery should be given a prolonged overcharge at low current rates, say about one fourth the normal 8 hour charging rate.

NOTE.—_Oxide of lead_, _litharge_, or _plumbic oxide_ is sometimes found native as lead ochre, and may be artificially made by heating the carbonate or nitrate. It is usually prepared on a larger scale by heating the lead in air. When the metal is only moderately heated, the oxide forms a yellow powder which is known as massicot, but at a higher temperature the oxide melts, and on cooling, it forms a brownish scaly mass, which is called flake litharge. The scaly pieces are afterwards ground between stones under water, forming buff or levegated litharge. The litharge of commerce often has a reddish yellow color, due to the presence of some of the red oxide of lead, and frequently from one to three per cent. of finely divided metallic lead is found mixed with it. When heated to dull redness litharge assumes a dark brown color, and becomes yellow again on cooling. At a bright red heat it fuses and readily attacks clay crucibles, forming silicate of lead. Litharge is a most powerful base, and has a strong tendency to form basic salts. Hot solution of alkalies, as potash or soda, readily dissolve it, and on cooling, it crystalizes out in the form of beautiful pink crystals.

Falling off in the capacity may be caused by a dry cell, due to a leaking jar; some or all of the cells may be in a state of incomplete charge, due to the battery having been run too low and not sufficiently charged; or the plates may be short circuited, either by the sediment (deposit in the bottom of the jar) getting up to the bottom of the plates or by something that has fallen into the cell.

Electrical Data on "American" Cells

+————————+——————————————————————————————————————————-+ | Normal | Number of 30 volt Tungsten lamps that can | |Capacity| be run with 16 cells in series for | | | 2, 4, 6 or 8 hours | +————————+——————————+——————————+——————————+——————————+ | Ampere | | | | | | hours | 2 hours | 4 hours | 6 hours | 8 hours | | 40 | 14 | 9 | 8 | 7 | | 60 | 17 | 14 | 12 | 10 | | 80 | 28 | 18 | 15 | 14 | | 120 | 42 | 27 | 24 | 21 | | 160 | 57 | 37 | 31 | 28 | | 200 | 71 | 45 | 40 | 35 | | 250 | 88 | 56 | 50 | 44 | | 300 | 106 | 70 | 60 | 52 | | 350 | 124 | 81 | 71 | 62 | | 400 | 142 | 91 | 81 | 71 | +————————+——————————+——————————+——————————+——————————+

=Ques. What action takes place when a battery stands idle for some time?=

Ans. It loses part of its charge, due to local losses in the cells.

=Ques. How should batteries be treated, when used but occasionally?=

Ans. If a battery is not to be used for several days, it should first be fully charged before standing; if it continue idle, a freshening charge should be given every two weeks, continuing the charge when the cells begin to gas freely.

=Ques. What should be done in case of lack of capacity?=

Ans. If the current consumption be normal, there may be poor connections or trouble in the battery; there may be a dry cell, due to a leaking jar; some or all of the cells may be in a state of incomplete charge, due to the battery having been run too low and not sufficiently charged, or the plates may be short circuited, either by the sediment (deposit in the bottom of the jar) getting up to the bottom of the plates or by something that has fallen into the cell.

Electrical Data on "Autex" Cells (Standard plates; size, 5¾" x 8⅝")

+————————————————————————————————+————————+————————+————————+————————+ |Number of Plates | 7 | 9 | 11 | 13 | +————————————————————————————————+————————+————————+————————+————————+ |Discharge in Amperes for 4 hours| 21 | 28 | 35 | 42 | +————————————————————————————————+————————+————————+————————+————————+ | {Length | 2¾ | 3½ | 4¼ | 5 | |Outside Measurements { +————+————+————+————+ | {Width | 6⅛ | 6⅛ | 6⅛ | 6⅛ | |Rubber Jars in inches. { +————+————+————+————+ | {Height | 12⅜ | 12⅜ | 12⅜ | 12⅜ | +————————————————————————————————+————————+————————+————————+————————+ | {Element | 15¾ | 20¼ | 24¼ | 29¾ | | { +————————+————————+————————+————————+ |Weight in Pounds {Electrolyte | 4½ | 5 | 5¾ | 6¼ | | { +————————+————————+————————+————————+ | {Complete Cell | 22 | 28 | 34¼ | 40½ | +————————————————————————————————+————————+————————+————————+————————+

Electrical Data on "Autex" Cells(continued) (Standard plates; size, 5¾" x 8⅝") +————————————————————————————————+————————+————————+————————+————————+ |Number of Plates | 15 | 17 | 19 | 21 | +————————————————————————————————+————————+————————+————————+————————+ |Discharge in Amperes for 4 hours| 49 | 56 | 63 | 70 | +————————————————————————————————+————————+————————+————————+————————+ | {Length | 5¾ | 6½ | 7¼ | 8 | |Outside Measurements { +————————+————————+————————+————————+ | {Width | 6⅛ | 6⅛ | 6⅛ | 6⅛ | |Rubber Jars in inches. { +————————+————————+————————+————————+ | {Height | 12⅜ | 12⅜ | 12⅜ | 12⅜ | +————————————————————————————————+————————+————————+————————+————————+ | {Element | 34 | 38½ | 43 | 47½ | | { +————————+————————+————————+————————+ |Weight in Pounds {Electrolyte | 7 | 7¾ | 8½ | 9¾ | | { +————————+————————+————————+————————+ | {Complete Cell | 47 | 53¼ | 59½ | 66 | +————————————————————————————————+————————+————————+————————+————————+

NOTE.—_Peroxide of lead, pure oxide or plumbic dioxide_ is the true active material in all forms of lead storage cell. This lead salt is found native as the mineral plattnerite. It is a heavy lead ore, forming black, lustrous, six sided prisms. It may be prepared from the red oxide by boiling it in fine powder, with nitric acid diluted with five parts of water, or by treating the carbonate when suspended in water with a stream of chlorine gas, and then thoroughly washing and drying it. It is reduced to a lower oxide on heating or by exposure to bright sunlight. This salt readily imparts oxygen to other substances; it becomes heated to redness when thrown into sulphuric dioxide, and takes fire when triturated with sulphur—hence this oxide is a common ingredient in lucifer match composition. When used in primary or secondary batteries it readily imparts its oxygen to nascent hydrogen, forming water, and thus it acts as a powerful depolarizer. When robbed of its oxygen, it readily becomes reoxidized, if subjected to the action of nascent oxygen liberated by the electrolytic decomposition of water.

If the trouble cannot be located by the eye, connect the battery in series, and discharge it at the normal rate, through suitable resistance. If a suitable rheostat be not available, a water resistance may be used.

This consists of a receptacle (which must not be of metal) filled with very weak acid solution or salt water in which are suspended two metal plates, which are connected, by wires through an ammeter.

Electrical Data on "Autex" Cells (Light weight plates; size, 5¾" × 8⅝")

——————————————————————————+——————————+————————-+——————————+————————+————————-+ Number of Plates | 7 | 9 | 11 | 13 | 15 | ——————————————————————————+——————————+————————-+——————————+————————+————————-+ Discharge in Amperes for | | | | | | 5 hours | 15¾ | 21 | 26¼ | 31½ | 36¾ | ——————————————————————————+——————————+————————-+——————————+————————+————————-+ Outside {Length | 1-29/32 | 2-7/16 | 3-31/32 | 3½ | 4-⅟32 | Measurements { +——————————+————————-+——————————+————————+————————-+ {Width | 6⅛ | 6⅛ | 6⅛ | 6⅛ | 6⅛ | Rubber { +——————————+————————-+——————————+————————+————————-+ Jars in in. {Height | 12⅜ | 12⅜ | 12⅜ | 12⅜ | 12⅜ | ——————————————————————————+——————————+————————-+——————————+————————+————————-+ Weight {Element | 11½ | 14¾ | 18 | 21¼ | 24½ | in { +——————————+————————-+——————————+————————+————————-+ Pounds {Electrolyte | 2¼ | 2½ | 3 | 3¾ | 4¼ | { +——————————+————————-+——————————+————————+————————-+ {Comp. Cell | 15¾ | 20 | 24¼ | 28½ | 33¼ | ——————————————————————————+——————————+————————-+——————————+————————+————————-+

——————————————————————————+——————————+————————-+——————————+————————+————————-+ Number of Plates | 17 | 19 | 21 | 23 | 25 | ——————————————————————————+——————————+————————-+——————————+————————+————————-+ Discharge in Amperes for | | | | | | 5 hours | 42 | 47¼ | 52½ | 57¾ | 63 | ——————————————————————————+——————————+————————-+——————————+————————+————————-+ Outside {Length | 4-9/16 | 5-3/32 | 5⅜ | 6-5/32| 6-11/16 | Measurements { +——————————+————————-+——————————+————————+————————-+ {Width | 6⅛ | 6⅛ | 6⅛ | 6⅛ | 6⅛ | Rubber { +——————————+————————-+——————————+————————+————————-+ Jars in in.|{Height | 12⅜ | 12⅜ | 12⅜ | 12⅜ |12⅜ | ——————————————————————————+——————————+————————-+——————————+————————+————————-+ Weight {Element | 27¾ | 31 | 34¼ | 37¼ | 40½ | in { +——————————+————————-+——————————+————————+————————-+ Pounds {Electrolyte | 4¼ | 5½ | 6 | 6¾ | 7¼ | { +——————————+————————-+——————————+————————+————————-+ {Comp. Cell | 38 | 42 | 46¼ | 51½ | 56 | ——————————————————————————+——————————+————————-+——————————+————————+————————-+

The current may be regulated by altering the distance between the plates or by varying the strength of the solution. As the discharge progresses, the voltage will gradually decrease and it should be frequently read at the battery terminals. When it shows a sudden drop, the voltage of each cell should be read with a low reading voltmeter.

While the readings are being taken, the discharge rate should be kept constant and the discharge continued until the majority of the cells read 1.70 volts; those reading less should be noted. The discharge should be followed by a charge until the cells which read 1.70 volts are up; then the low cells should be cut out, examined and the trouble remedied.

NOTE.—_How to prevent lead poisoning._ Workmen employed in the manufacture of lead or lead salts are always liable to lead poisoning, both by inhaling the dust and by contact of the materials with the hands. Various preventives for this have been employed, and of these, the most simple seems to be a careful washing of the hands in petroleum. It is said that three washings a day are sufficient to prevent all serious danger of poisoning. The benzole in the petroleum appears to scour the skin and remove the loose lead dust, and the fatty substance in the oil fills up the pores of the skin and prevents the absorption of the deleterious salts. The employment of petroleum has given such good results that it has been proposed to use this material as a guard against poisoning in other industries where the salts of copper or mercury are employed.

=Ques. What causes low specific gravity when there are no short circuits?=

Ans. 1, sloppage or a leaky jar (the loss having been replaced with water alone), 2, insufficient charge, 3, over discharge, or 4, a combination of these abuses. Any of these mean that there is acid in combination with the plates.

In this case the acid should be brought out into the electrolyte by a long charge at a quarter of the normal discharge rate.

=Ques. How should weak cells be treated?=

Ans. They should be grouped by themselves and charged as a separate battery, care being taken that the positive strap of one cell, is connected to the negative strap of the adjoining cell and that the charging connections are properly made. If there be not sufficient resistance in the charging rheostat to reduce the current to the proper point, a water resistance should be used.

NOTE.—_Pole testing paper._ Make a thin solution of white starch and soak strips of thin white blotting paper in it, and set aside in a clean, dry place to dry. Dissolve ½ oz. of potassium iodide in one pint of water. Immerse the strips in the solution for a few seconds and again dry. This paper, when moistened and used in the usual way, turns violet at the positive pole.

While a cell is being treated, when possible, the cover should be removed (if sealed, the compound can be loosened by using a hot putty knife).

=Disconnecting Cells.=—The best method of disconnecting cells assembled with pillar straps, for the purpose of replacing broken jars, cleaning or taking out of commission, is to use a five-eighth inch twist drill, in a carpenter's brace, boring down into the top of the pillar about one-quarter inch; then pull off the connector sleeve from the pillar. By following this method, all parts may be used again.

When cells are equipped with top straps, the straps should be cut with a sharp knife or chisel midway between the cells.

=Taking Batteries out of Commission.=—Where a battery is to be out of service for several months, and it is not convenient to give it the freshening charge every two weeks, it should be taken out of commission.

COMPARISON OF THE BAUMÉ AND SPECIFIC GRAVITY SCALES AT 60° FAHRENHEIT +————————-+——————————+————————-+——————————+————————-+——————————+————————-+——————————+ |_Degrees_|_Specific_|_Degrees_|_Specific_|_Degrees_|_Specific_|_Degrees_|_Specific_| | _Baume_ |_Gravity_ | _Baume_ |_Gravity_ | _Baume_ |_Gravity_ | _Baume_ |_Gravity_ | +————————-+——————————+————————-+——————————+————————-+——————————+————————-+——————————+ | 0 | 1.000 | 17 | 1.133 | 34 | 1.306 | 51 | 1.542 | | 1 | 1.007 | 18 | 1.142 | 35 | 1.318 | 52 | 1.559 | | 2 | 1.014 | 19 | 1.151 | 36 | 1.330 | 53 | 1.576 | | 3 | 1.021 | 20 | 1.160 | 37 | 1.342 | 54 | 1.593 | | 4 | 1.028 | 21 | 1.169 | 38 | 1.355 | 55 | 1.611 | | 5 | 1.036 | 22 | 1.179 | 39 | 1.368 | 56 | 1.629 | | 6 | 1.043 | 23 | 1.188 | 40 | 1.381 | 57 | 1.648 | | 7 | 1.051 | 24 | 1.198 | 41 | 1.394 | 58 | 1.666 | | 8 | 1.058 | 25 | 1.208 | 42 | 1.408 | 59 | 1.686 | | 9 | 1.066 | 26 | 1.218 | 43 | 1.421 | 60 | 1.707 | | 10 | 1.074 | 27 | 1.229 | 44 | 1.436 | 61 | 1.726 | | 11 | 1.082 | 28 | 1.239 | 45 | 1.450 | 62 | 1.747 | | 12 | 1.090 | 29 | 1.250 | 46 | 1.465 | 63 | 1.768 | | 13 | 1.098 | 30 | 1.261 | 47 | 1.479 | 64 | 1.790 | | 14 | 1.107 | 31 | 1.272 | 48 | 1.495 | 65 | 1.812 | | 15 | 1.115 | 32 | 1.283 | 49 | 1.510 | 66 | 1.835 | | 16 | 1.124 | 33 | 1.295 | 50 | 1.526 | | | +————————-+——————————+————————-+——————————+————————-+——————————+————————-+——————————+

NOTE.—The characteristic properties of concentrated sulphuric acid are very marked. Its freedom from odor, oily appearance, and its great weight, distinguish it from other liquids. The pure concentrated commercial acid has a density which usually reaches 1.842, and its boiling point is about 640° F. The absolutely pure acid is perfectly colorless, but usually even that used in laboratories has a peculiar grayish color, due to slight traces of organic matter. Sulphuric acid is exceedingly hydroscopic, and when exposed to the air it rapidly increases in bulk, owing to absorption of atmospheric moisture.

NOTE.—Clamps not made of metal similar to that of the connecting strips, frequently give trouble from the galvanic action due to the contact of dissimilar metals in the presence of moisture which causes the destruction of either the connecting strip or the clamp. Such troubles can be avoided by placing a thin strip of sheet zinc between the lead strip and the clamp. Under these circumstances the zinc will crumble away, and can be replaced without much inconvenience and very little expense, while the clamps and connecting strips will remain uninjured.

Strength of Dilute Sulphuric Acid of Different Densities at 59° Fahr. +————————————————+——————————+————————————————+——————————+ | Per cent. | Specific | Per cent. | Specific | | of | | of | | | Sulphuric Acid | Gravity | Sulphuric Acid | Gravity | +————————————————+——————————+————————————————+——————————+ | 100 | 1.842 | 23 | 1.167 | | 40 | 1.306 | 22 | 1.159 | | 31 | 1.231 | 21 | 1.151 | | 30 | 1.223 | 20 | 1.144 | | 29 | 1.215 | 19 | 1.136 | | 28 | 1.206 | 18 | 1.129 | | 27 | 1.198 | 17 | 1.121 | | 26 | 1.190 | 16 | 1.116 | | 25 | 1.172 | 15 | 1.106 | | 24 | 1.174 | 14 | 1.098 | +————————————————+——————————+————————————————+——————————+

=Ques. Describe the method of taking a battery out of commission.=

Ans. The battery is charged in the usual manner, until the specific gravity of the electrolyte of every cell has stopped rising over a period of one hour (if there be any low cells, due to short circuits or other cause, they should be put in condition before the charge is started, so that they will receive the full benefit of it). The cells may now be disconnected and covers and elements removed from the jars, (if sealed, the compound is loosened with a hot putty knife). The elements are placed on their sides with the plates slightly spread apart at the bottom, the separators withdrawn, and the positive and negative groups pulled apart. The electrolyte is washed off with a gentle stream of water and the plates allowed to drain and dry.[7] The positive plates are ready to be put away. When dry, the negatives are completely immersed in electrolyte (of about 1.275 specific gravity), and allowed to soak for three or four hours. The jars may be used for this purpose. After rinsing and drying, they are ready to be put away; wash also the rubber separators.

[7] NOTE.—If the active material in the negative plates extend beyond the ribs of the grid (the supporting frame), it should be at once pressed back into place, care being taken to prevent the plates drying before this is done. The most suitable and convenient method for pressing, is to place between the plates smooth boards of a thickness equal to the distance between the plates and then put the groups under pressure.

Wood separators, after having been in service, will not stand much handling and had better be thrown away. If it be thought worth while to keep them, they must be immersed in water or weak electrolyte, and in re-assembling, the electrolyte must be put into the cells immediately, as wet wood separators must not stand exposed to the air.

=Ques. What precaution should be taken with the jars?=

Ans. They should be thoroughly cleaned with fresh water, no sediment being allowed to remain.

=Putting Batteries into Commission.=—When re-assembling a battery, it should be treated in the same manner as if it were new and the regular instructions for assembling and putting a new battery into commission followed.

=Cleaning Jars.=—The jars should be thoroughly cleaned with fresh water, no sediment being allowed to remain.

Table of Voltage Change as Affected by Discharge Rate[8]

[8] NOTE.—The voltage increase or decrease with change in current is practically constant in a given type of cell for any size of cell when the current is referred to a given time rate of charge or discharge; that is, the drop in a large cell or in a small cell, when each is discharged at its four, six or eight hour rate, will be the same. The drop varies somewhat for the condition of the battery charge. For batteries which are one-third discharged, the temperature 60° Fahr., and plates in good condition, the changes in pressure which may be expected between open circuit voltage and the voltage on charge or discharge are given in the above table.

8 hour rate .05 volt 6 " " .065 " 4 " " .09 " 3 " " .11 " 2 " " .14 " 1½ " " .18 " 1 " " .21 "

=Condensed Rules for the Proper Care of Batteries.=—The following general instructions should be followed in the care and maintenance of batteries:

1. A battery must always be charged with "direct" current and in the right direction.

2. Be careful to charge at the proper rates and to give the right amount of charge; do not undercharge or overcharge to an excessive degree.

3. _Do not bring a naked flame near the battery while charging or immediately afterwards._

4. Do not overdischarge.

5. Do not allow the battery to stand completely discharged.

6. Voltage readings should be taken only when the battery is charging or discharging; if taken when the battery is standing idle they are of little or no value.

7. Do not allow the battery temperature to exceed 110° Fahr.

8. Keep the electrolyte at the proper height above the top of the plates and at the proper specific gravity. Use only pure water to replace loss by evaporation. In preparing the electrolyte _never pour water into the acid_.

9. Keep the cells free from dirt and all foreign substances, both solid and liquid.

10. Keep the battery and all connections clean; keep all bolted connections tight.

11. If there be lack of capacity in a battery, due to low cells, do not delay in locating and bringing them back to condition.

12. Do not allow sediment to get up to the plates.