Mechanics of the Household / A Course of Study Devoted to Domestic Machinery and Household Mechanical Appliances

Bell-ringing Transformers.

—The general employment of alternating electricity for all commercial service requiring distant transmission is because of the possibility of changing the voltage to suit any condition. The energy transmitted is determined by the amperes of current carried by the wires and the volts of pressure by which it is impelled. The product of these two factors determines the watts of energy transmitted.

110 volts × 1 ampere = 110 watts.

If the voltage is raised to say ten times the original intensity with the same current, the quantity of energy is ten times the original amount.

1100 volts × 1 ampere = 1100 watts.

The carrying capacity of wires is determined by the amperes of current that can be transmitted without heating.

The cost of copper wire is such that the expense of large wires for carrying a large current is unnecessary where by raising the voltage a small wire will perform the same service; therefore, it is desirable to transmit electric energy at a high voltage and then transform it to suit the condition of usage.

Alternating current may be transformed to a higher or a lower voltage to suit any condition by using step-up or step-down transformers.

A transformer is a simple device composed of two coils of wire wound on a closed core of iron. The coil into which is sent the inducing current is the primary. That in which the current is induced is the secondary coil. The change in voltage between primary and secondary coils vary as the number of turns of wire which compose the coils. The house circuit may be stepped down from the customary 110 volts to a voltage such as is furnished by a single dry cell, or a battery of cells.

In principle, the action of the transformer is the same as that of the induction coil, a detailed explanation of which will be found in any text-book of physics. Each impulse of current in the primary coil of the transformer magnetizes its core and the magnetism thus excited induces a corresponding current in the secondary coil. Since alternating current in the primary coil constantly changes the polarity of the core, each change of magnetism induces current in the secondary coil.

Small transformers are frequently used for operating doorbells, annunciators, etc., in place of primary batteries. These transformers are also used to supply current for lighting low-power tungsten lamps that cannot be used with the ordinary voltages employed in house lighting. The primary wires of the transformer are attached to the service wires in the house and from the secondary wires voltages are taken to suit the desired purposes.

Fig. 250 shows such a transformer with the cover partly broken away to expose the interior construction. The wires from house mains MM lead the current to the primary coil P which is a large number of turns of fine wire wound about a soft-iron core. The induced current in the secondary coil S is taken from the contact points 1, 2, 3 and 4. The construction of the transformer coils shown in Fig. 250 indicates the primary wires at LL of Fig. 251. The wires of the primary coil are permanently attached to house wires. The reactive effect of the magnetism in the coil permits only enough current to flow as will keep the core excited. This is a step-down transformer and the secondary coil contains fewer turns of wire than the primary coil. Since the voltage induced in the secondary coil is determined by the number of turns of wire in action, this coil is so arranged that circuits formed by attachment with different contacts give a variety of voltages. The numbers on the front of Fig. 250 correspond to those of Fig. 251. The coils between contact 1 and the others 2, 3 and 4, represent different number of turns of wire and in them is induced voltages corresponding with the number of turns of wire in each.

The Recording Wattmeter.

—To determine the amount of electricity used by consumers, each circuit is provided with some form of wattmeter. These meters might be more correctly called watt-hour meters since they register the watt-hours of electrical energy that pass through the circuit.

In the common type of meter, the recording apparatus in composed of a motor and a registering dial. The motor is intended to rotate at a rate that is proportional to the amount of passing current. An example of this device is the Thompson induction meter of Fig. 252. The motion of the aluminum disc seen through the window in front indicates at any time the rate at which electricity is being used. This constitutes the rotating part of the motor. It is propelled by the magnetism, created by the passing current, and is sensitive to every change that takes place in the electric circuit. Each lamp, heater or motor that is brought into use or turned off produces a change of current in the conducting wires and this change is indicated by the rate of rotation of the disc. Each rotation of the disc represents the passage of a definite amount of electricity that is recorded on the registering dials.

The shaft on which the disc is mounted is connected with the recording mechanism by a screw which engages with the first of a train of gears. These gears have, to each other, a ratio of 10 to 1; that is, ten rotations of any right-hand gear, causes one rotation of the gear next to the left. The pointers on the dial are attached to the gear spindles. One rotation of the right-hand dial will move the pointer next to the left one division on its dial. Each dial in succession will move in like ratio.

The meters are carefully calibrated and usually record with truthfulness the amount of electricity used. They are, however, subject to derangement that produces incorrect registration.

To Read the Meter.

—First, note carefully the unit in which the dial of the meter reads. The figures above the dial circle indicate the value of one complete revolution of the pointer in that circle. Therefore, each division indicates one-tenth of the amount marked above or below the circle.

Second, in reading, note the direction of rotation of the pointers. Commencing at the right, the first pointer rotates in the direction of the hands of a clock (clockwise); the second rotates counter-clockwise; the third, clockwise; etc., alternately. The direction of rotation of any one pointer may easily be determined by noting the direction of the sequence of figures placed around each division. The arrows (shown above) indicate the direction of rotation of the pointers when the meter is in operation.

Third, read the figures indicated by the pointers from right to left, setting down the figures as they are read, i.e., in a position relative to the position of the pointers. Note: One revolution of the first or right-hand pointer makes one-tenth of a revolution of the pointer next to it on the left. One revolution of this second pointer makes one-tenth of a revolution of the pointer next to it on the left, etc. Therefore, if, when reading the dial, it is found that the second pointer rests very nearly over one of the tenth divisions and it is doubtful as to whether it has passed that mark, it is only necessary to refer to the pointer next to it on the right. If this pointer on the right has not completed its revolution, it shows that the second pointer has not yet reached the division in question. If it has completed its revolution, that is, passed the zero, it indicates that the second pointer has reached the division and the figure corresponding is to be set down for the reading.

The foregoing also applies to the remaining pointers. When it is desired to know whether a pointer has passed a tenth division mark, it is necessary to refer only to the next pointer to the right of it.

Fourth, see if the register is direct-reading, i.e., has no multiplying constant. Some registers are not direct-reading in that they require multiplying the dial reading by a constant such as 10 or 100 in order to obtain the true reading. If the register bears some notation such as “Multiply by 100,” the reading as indicated by the pointers should be multiplied by 10 or 100 as the case may be to determine the true amount of energy consumed.

Some of the earlier forms of meters were equipped with what is known as a “non-direct-reading register.” In this case, the reading must be multiplied by the figure appearing on the dial as just explained, but the dial differs from those just described in that the multiplying constant is generally a fraction such as ½, etc., and the dial has five pointers. This older style of register reads in “watt-hours” of “kilowatt-hours.”

Fifth, the reading of the dial does not necessarily show the watt-hours used during the past month. In other words, the pointers do not always start from zero. To determine the number of watt-hours used during a certain period it is necessary to read the dial at the beginning of a period and again at the end of that period. By subtracting the first reading from the second, the number of watt-hours or kilowatt-hours used during the period is obtained.

The meter man, having in his possession a record of the readings of each customer’s meter for the preceding months, is thus able to determine the amount of energy consumed monthly.

EXAMPLES OF METER READINGS

Fig. 253a shows an example of an ordinary dial reading. Commencing at the first right-hand pointer, Fig. 253c, it is noted that the last figure passed over by the pointer is 1. The next circle to the left shows the figure last passed to be 2, bearing in mind that the direction of the rotation of this pointer is counter-clockwise. The last figure passed by the next pointer to the left is 1, while that passed by the last pointer to the left is obviously 9. The reading to be set down, therefore, is 9121.

In a similar manner the dial shown in Fig. 253b may be read. In this case, however, three of the pointers rest nearly over the divisions and care must be used to follow the direction to avoid error. Commencing at the right, the first pointer indicates 7. The second pointer has passed 9 and is approaching 0. The third pointer appears to rest directly over 0, but since the second pointer reads but 9, the third cannot have completed its revolution and hence the figure last passed is set down which in this case is 9. Similarly, the fourth or left-hand pointer appears to rest directly over 1 but by referring to the pointer next to it on the right, we find that its indication is 9 as just explained. Therefore, the fourth pointer cannot have reached 1, and so the figure last passed which is 0 is set down, which in this case is 9. Similarly, the fourth or left-hand pointer appears to rest directly over 1, but by referring to the pointer next to it on the right we find that its indication is 9 as just explained. Therefore, the fourth pointer cannot have reached 1, and so we set down the figure last passed which is 0. The figures as they have been set down, therefore, are 0997, which indicates that 997 kilowatt-hours of electricity have been used.

If, for example, the reading of this meter for the preceding month was 976 kilowatt-hours, the number of kilowatt-hours used during that month would be 997-976 = 21 kilowatt-hours.

State Regulation of Meter Service.

—Electric wattmeters are subject to errors that may cause them to run either fast or slow. Complaints made of inaccurate records or readings are usually rectified by the electric company. In many States all public utilities are governed by laws that are formulated by public utilities commissions or other bodies from which may be obtained bulletins fully describing the conditions required of public service corporations or owners of public utilities. The following quotation from Bulletin No. V., 233 of the Railroad Commission of Wisconsin, will give an illustration of the requirement in that State.

Rule 14.—Creeping Meters.—No electric meter which registers upon “no load” shall be placed in service or allowed to remain in service.

This means that when no electricity is being used in the system the motor disc should remain stationary and if it shows any motion under such condition it is not recording accurately.

PERIODIC TESTS

Electric Batteries.

—Electric batteries are composed of electric cells that are made in two general types: the primary cell, in which electricity is generated by the decomposition of zinc; and the secondary cell or storage cell in which electricity from a dynamo may be accumulated and thus stored. Electric cells are the elements of which electric batteries are made; a single electric cell is often called a battery but the battery is really two or more cells combined to produce effects that cannot be attained by a single element.

Both primary and secondary batteries form a part of the household equipment but the work of the secondary battery is used more particularly for electric lighting, the operation of small motors and for other purposes where continuous current is required. It will, therefore, be considered in another place.

Primary batteries are used to operate call-bells, table pushes, buzzers, night latches and various other forms of electric alarms besides which they are used in gas lighters, thermostat motors and for many special forms, all of which form an important part in the affairs of everyday life. Primary battery cells for household use are made to be used in the wet and dry form, but the dry cell is now more extensively used than any other kind and for most purposes has supplanted the wet form.

Formerly all primary cells were made of zinc and copper plates placed in a solution called an electrolite, that dissolved the zinc and thus generated electricity, the electrolite acting as a conductor of the electricity to the opposite plate. In later electric cells the copper was replaced by plates of carbon and from the zinc and carbon cell was finally evolved the present-day dry cell. When the use of electric cells reached a point where portable batteries were required, a form was demanded from which the solution could not be lost accidentally. The first electric cells in which the electrolite was not fluid was, therefore, called a dry cell. These cells are not completely dry. The electrolite is made in the form of a paste that acts in the same manner as the fluid electrolite and is only dry in that it is not fluid.

In construction the dry cell is shown in Figs. 254 and 255, the former showing its exterior and the latter exposing its internal construction. The container is a zinc can which is lined with porous paper to prevent the filler from coming into contact with the zinc. The zinc further is the active electrode, the chemical destruction of which generates the electricity. The parts enclosed in the container are: a carbon rod, which acts as the positive pole; and the filler, composed of finely divided carbon mixed with manganese dioxide and wet with a solution of salammoniac. The composition plug, made of coal-tar products and rosin, is intended to keep the contents of the can in place and prevent the evaporation of the moisture. Binding posts attached to the carbon rod and soldered to the can furnish the + and-poles.

In the action of cell, the salammoniac attacks the zinc in which chemical action electricity is evolved. The electricity is conducted to the carbon pole through the carbon and the salammoniac solution which in this case is the electrolite. In the dissolution of the zinc, hydrogen gas is liberated which adds to the resistance of the cell and thus reduces the current. The presence of the hydrogen is increased when the action of the cell is rapid and the decrease in current is said to be due to polarization. The manganese dioxide is mixed with the filler in order that the free hydrogen may combine with the oxide and thus reduce the resistance. This process is known as depolarization. The combination between the hydrogen and the oxide is slow and for this reason the depolarization of batteries sometimes require several hours. Dry cells are usually contained in paper cartons to prevent the surfaces from coming into contact and thus destroying their electrical action.

The best cell is that which gives the greatest amount of current for the longest time. Under any condition the working value of a cell is determined by the number of amperes of current it can furnish. The current is measured by a battery tester such as Fig. 257. The + connection of the tester is placed in contact with the + pole of the cell or battery and the other connection placed on the-pole. The pointer will immediately indicate the current given out by the battery. A new dry cell will give 20 or more amperes of current for a short time but if used continuously the quantity of current will be reduced by polarizing until but a very small amount is generated. A cell that indicates less than 5 amperes should be replaced. If short-circuited, that is if the poles are connected without any intervening resistance, a large amount of current will be given but the cell will soon wear out and possibly be ruined. A cell should, therefore, never be allowed to become short-circuited. The voltage of a cell is practically continuous and should be from 1.5 to 1 volt. It is quite possible that a cell may possess its normal voltage and yet deliver little current; the voltage of a cell does not indicate its working property. In order to be assured of active cells they should be tested at the time of purchase with an ammeter.

The moisture in the paste of a cell is that which forms the circuit between the zinc and the carbon elements. If the paste has dried out its resistance is increased and the cell generates little current. The voltage of such a cell may be normal while the amperage is very low. Cells in this condition may be revived by adding moisture to the paste as a temporary remedy. This may be accomplished by puncturing the can with a nail and adding water. A solution of salammoniac may be used instead of water and the cell soaked to accomplish the same purpose; this, however, is only a temporary expedient.

Temperature influences the working properties of an electric cell in pronounced manner. The moisture contained in the cell is composed of ammonium chloride and zinc chloride and consequently the resistance of the cell increases with the fall of temperature; the effect of the resistance thus added is a decrease in the flow of current. Batteries should be kept in a temperature as nearly as possible that of 70°F. The battery regains its normal rate of discharge when the temperature is restored.

The normal voltage and amperage for a given make of cell is practically the same for all. The size of the cell does not in any way influence the voltage. Small cells and large cells are the same. The large cells are advantageous only in that they give out a greater number of ampere-hours of energy. All batteries are rated in the number of ampere-hours of current they are capable of furnishing. The ampere-hour represents an ampere of current for one hour. On this basis all batteries are rated for the total amount of energy they are capable of producing. If the battery is worked at a high current, its life is short; if however, it is discharged at a low rate, its life should be long. In all cases the product of the number of amperes and the number of hours constitute the ampere-hours of energy produced.

Battery Formation.

—For ordinary household work as that of operating doorbells, etc., the cells which form a battery are joined in series, that is the positive or carbon pole of one cell is joined to the zinc or negative pole of the next. The cells so connected are placed in circuit with the bell and push button. If by accident the two cells of a battery are joined with both carbon poles or both zinc poles together the battery will give out no current because the voltage is opposed.

In the use of batteries for ignition as for gasoline engines, automobiles, etc., the arrangement of the cells has frequently a decided influence on the effect produced. In Fig. 256 A is represented four cells joined in series, that is the carbon or + poles are joined with the zinc or-poles, alternately. Connected in this manner if each cell gives 1.5 volts the battery will give 4 × 1.5 = 6 volts; the current, however, will remain as that of a single cell. If the cells singly give 20 amperes, the battery will give 20 amperes. When cells are connected in this form the current passes through each cell in turn and is as much a part of the circuit as the wires. Should one of the cells be “dead”—that is delivering no current—it will act as additional resistance and the current is reduced.

When joined in multiple or parallel connection as in Fig. 256 B, in which all similar binding posts are connected, the effect is decidedly different. In the multiple connection all of the zincs are joined to act as a single zinc and all of the carbons are likewise joined and act as a single carbon. In such a combination the voltage will be that of a single cell 1.5 volts, but the amperage will be four times that of a single cell or 80 amperes.

The diagrams and following descriptions of possible combinations were taken from a bulletin on battery connections issued by the French Battery and Carbon Co.

By combining the series and multiple connections, as shown in Fig. C, both the voltage and current can be increased over that delivered by one cell. Referring to the figure, it is seen that in each of the two rows of four cells the cells are connected in series. This would produce 6 volts and 20 amperes for the series of four which may now be assumed as a unit, so that the two rows can be imagined as two large cells, each of which has a normal output of 20 amperes at 6 volts. Now by connecting the similar poles of two such large cells they are in multiple and we get an increased current or 40 amperes and 6 volts, which is the capacity of the eight cells connected as shown in the figure. This is commonly designated as a multiple-series battery.

Fig. 256 D illustrates a multiple-series connection made in a different manner, but which produces the same voltage and current as the above mentioned. In Fig. D, two cells at a time are connected in multiple, and these sets are then connected in series. The capacity of each set of two is 40 amperes at 1½ volts, and as these four sets are connected in series the total output of the eight cells combined is 6 volts and 40 amperes, the same as that produced by the connections shown in Fig. C.

Fig. E shows the multiple-series connection illustrated in Fig. D, applied to twelve cells in which four sets of three cells each are wired in series, the three cells of a set being in multiple so that the capacity of a set is 1½ volts and 60 amperes. By connecting the four sets in series as shown, the total capacity will be 60 amperes at 6 volts.

The use of the series-multiple connection is a distinct step forward in dry-cell use. The arrangement of cells shown in Figs. C or D is better than the arrangement in Fig. A, in just the same way that a team of horses is better than a single horse. One horse pulling a load of 2 tons may become exhausted in one hour, but two horses pulling that same load may work continuously for six hours. It is true that in Fig. C there are twice as many cells used as in Fig. A, but the eight cells in Fig. C will do from three to four times as much work as the four cells in Fig. A. In other words, while more cells are used in the multiple-series arrangement, the amount of service per cell is greater and the service is, therefore, cheaper in the multiple-series arrangement.

Some battery manufacturers sell their batteries put up in boxes, the cells being connected up in multiple-series and surrounded by pitch or tar to keep out the moisture. This has certain advantages as well as certain disadvantages. One of the objections to this method of putting up dry cells is that if by any chance one cell out of the eight or twelve which are buried in the pitch is defective it will run all of the cells down, and being buried offers no means of detection or removal. It is not possible to guarantee absolutely that a weak cell will not be occasionally included in a large number, so dry cells may be expected to vary to some degree among themselves.

It is interesting to know the effect of one weak cell on a series-multiple arrangement. If, for example, in Fig. C or Fig. D, the dotted line connecting (a) and (b) be used to indicate a cell which is partly short-circuited by internal weakness or external defect the result is as follows:

In the arrangement shown in Fig. C, where one cell of the upper four is short-circuited, the lower four will discharge through the upper four even though the external circuit is not closed; that is, one short-circuited cell will cause a run-down in all of the cells. In Fig. D, however, one short-circuited cell will influence not the entire set but the other one to which it is directly connected. There is thus seen to be an advantage in the arrangement of Fig. D and Fig. E, over the arrangement in Fig. C.

In making connections between cells insulated wire should be used, or special battery connectors are preferably employed. The ends of the wires or connectors and the binding posts must be scraped clean so that good electrical connection can be made between the two, and the knurled nuts should be screwed tight into place. Care must also be taken that the pasteboard covering around the battery is not torn. This would allow contact between the zinc containers, and thus short-circuit the cells. The batteries should be placed so that the zinc cans and the binding posts of any cell do not come into contact with any other cell. Vibration might cause enough motion for the brass terminal to wear through the pasteboard of the neighboring cell and make contact with the zinc can.

Different classes of work require different amounts of current at different voltages and by choosing the proper combination of series, multiple, or series-multiple connections practically every requirement can be fulfilled. For electric bells, telegraph instruments, miniature lights, toy motors with fine wire windings, etc., series connection is recommended for the reason that the resistance of the external circuit is high and a large voltage is necessary. For spark coils, magnets and toy motors with large wire windings, multiple or series-multiple connection of batteries should be used as a high voltage is not required.

For some work, gas-engine ignition especially, it is economical to have two complete sets of batteries, either of which can be thrown into the circuit at will, so that while one set is delivering current the other is recuperating. It has been estimated that by using two sets of batteries, properly connected to give the desired current, the life of each set is increased about four times. Thus it is seen that a saving of 50 per cent. is effected in the cost of the batteries.

Battery Testers.

—The “strength” of a cell is determined by the amperes of current it is capable of producing; therefore, a meter that will indicate the amount of current being produced is used to test the current strength of the cell. Battery testers are made to indicate voltage or amperage and sometimes the instrument is made to indicate both volts and amperes. As explained above, the voltage of a cell is not a true indicator of its strength. The ampere meter or ammeter, as it is termed, is the proper indicator of the strength of the cell.

The common battery tester does not always give the exact number of amperes of current, but it indicates the relative strength which is really the thing desired. When the current from an active cell is once shown on the dial of the tester, any other cell of the same intensity will be indicated in like amount.

Electric Conductors.

—Covered wire for carrying electricity is made in a great variety of forms and designated by names that have been suggested by their use. These wires are made of a single strand or in cables, where several wires are collected, insulated and formed into a single piece. Cables may contain any number of insulated wires.

The sizes of wires are determined by a wire gage. In the United States the B. & S. gage is used as the standard for all wires and sheet metal. The gage originated with the Brown & Sharp Mfg. Co. of Providence, R. I., and has become a national standard by common consent. The numbers range from No. 0000 to No. 60. The size of wire for household electrical service ranges from No. 18 which is 0.04 inch in diameter to No. 8 which is 0.128 inch across. The carrying capacities in amperes of wires, as given by the Underwriters’ table of sizes from No. 8 to No. 18, are as follows:

Portable Cord.

—This is a term used to designate reinforced lamp cord. The wires are laid parallel and are covered as with a supplementary insulation of rubber. The additional insulation and the braided covering assumes a cylindrical form. The covering is saturated with weatherproof compound, waxed and polished.

An electric generating system is commonly termed an electric plant. It consists of an engine for the development of power, a dynamo for changing the power into electricity and—to be of the greatest service—a storage battery for the accumulation of a supply of energy to be used at such times as are not convenient to keep the dynamo in active operation.

Such a combination, each part comprised of mechanism with which the average householder is unfamiliar, seems at first too great a complication to put into successful practice. Such, however, is not the case. The operation of small electric generating plants is no longer an experiment. Their general use testifies to their successful service. The working principles are in most cases those of elementary physics combined with mechanism, the management of which is not difficult to comprehend. Such plants are made to suit every condition of application and at a cost that is condusive to general employment.

In a brief space it is not possible to enter into a detailed discussion of the gasoline engine, the electric dynamo, and the storage battery with the various appliances necessary for their operation; it is, therefore, intended to give only a general description of the leading features of each. The manufacturers of such plants furnish to their customers and to others who are interested detailed information with explicit instructions for their successful management.

The first private lighting plants were made up of parts built by different manufacturers and assembled to form generating systems with little regard to their adaptability. A gasoline engine belted to a dynamo of the proper generating capacity supplied the electricity. Neither the engines nor the dynamos were particularly suited to the work to be performed, yet these combinations were sufficiently successful to command a ready sale. The energy thus generated was accumulated in a storage battery from which was taken the current for a lighting and heating device. Besides the generating and storage apparatus there is required in such a system, a switchboard, to which are attached the necessary meters and switches that are required to measure and direct the current to the various electric circuits.

Foresighted manufacturers, comprehending the probable future demand, began the construction of the various parts, suited to the work and the conditions under which they were to be employed. The manufacture of apparatus, designed for the special service and composed of the fewest possible parts, has reduced the operating difficulty to a point of relative simplicity. Experience in the use of a large number of these plants has revealed to the maker the course of many minor difficulties of operation and the means of their correction. The mechanism has been improved to prevent possible derangement and to simplify the means of control, until the private electric plant is successfully employed by those who have had no former experience with power-generating machines.

As an example of the private electric plant Fig. 258 shows the apparatus included in a combined engine, dynamo and switchboard, connected with a storage battery. The relative size of the machine is shown by comparison with the girl in the act of starting the motor. This plant is of capacity suitable for supplying an average home with electricity for all ordinary domestic uses. A nearer view of the generating apparatus is given in Fig. 259 in which all of the exterior parts are named. An interior view of the generating apparatus is given in Fig. 260, in which is exposed all of the working parts. The right-hand side of the picture shows all of the parts of the gasoline engine that furnishes the power for driving the generator. This is an example of an air-cooled gasoline engine in which the excess heat developed in the cylinder is carried away by a drought of air. The air draft is induced by the flywheel of the engine, which is constructed as a fan. The blades of the fan, when in motion, are so set as to draw air into the top of the engine casing and exhaust it from the rim of the wheel. The air in passing takes up the heat in excess of that necessary for the proper cylinder temperature. This form of cylinder cooling takes the place of the customary water circulation and thus eliminates its attending sources of trouble. In principle the engine is the same as is employed in automobiles and other power generation.

On the left-hand side is seen the dynamo and switchboard. The dynamo armature is attached to the crankshaft of the engine by which it is rotated in a magnetic field to produce the desired amount of electricity. The brushes, in contact with the commutator, conduct the electricity as it is generated in the armature, which after passing through the switchboard is made available from the two wires at the top of the board marked “light and power wires.” These wires are connected with the storage battery and also to the house circuits through which the current is to be sent.

Referring to the switchboard of Fig. 259, the three switches and the ammeter comprise the necessary accessories. The starting switch is so arranged that by pressing the lever a current of electricity from the storage battery is sent through the dynamo. The dynamo acting as a motor starts the engine. When the engine has attained its proper speed its function as a dynamo overcomes the current pressure from the battery and sends electricity into the cells to restore the expended energy, or if so desired the current may be used directly from the dynamo for any household purpose. The box enclosing the switch contains a magnetic circuit-breaker so constructed that when the battery is completely charged the switch automatically releases its contact and stops the engine.

The “stopping switch” at the right of the board and the “switch for light and circuit” on the left are used respectively for stopping the engine and for opening and closing the house circuits.

The meter performs a multiple function, in that it shows at any time the condition of charge in the storage battery, the rate at which current is entering or leaving the battery and also acts to stop the engine when the battery is charged. At any time the pointer reaches the mark indicated in the picture, the ignition circuit is automatically broken and the engine stops. The fuses on the board in this case perform the same function as those already described.

Storage Batteries.

—These batteries have already been mentioned as secondary batteries. They are sometimes called electric accumulators. The electricity is stored or accumulated, not by reason of the destruction of an electrode as in the primary cell but by the chemical change that takes place in the plates as the charging current is sent through the cell. When the battery is discharged, the current from the dynamo is sent through the battery circuit in the reverse direction to that of the discharge and the plates are restored to their original condition. The action that takes place in charging and discharging is due to chemical changes that take place in the plates and also in the solution or electrolyte in which the plates are immersed.

There are two types of storage batteries, those made of lead plates immersed in an acid electrolyte and the Edison battery which is composed of iron-nickel cells immersed in a caustic potash electrolyte. The former type is most commonly used and is the one to be described.

The lead-plate cell illustrated in Fig. 262 shows all of the parts of a working element. The plates are made in the form of lead grids which when filled to suit the requirements of their action, form the positive and negative electrodes. The negative plates are filled with finely divided metallic lead which when charged are slate gray in color. The positive plates are filled with lead oxide. When charged they are chocolate brown in color. In the figure there are three positive and four negative plates which together form the element, then with their separators are placed in a solution of sulphuric acid electrolyte. The separators are thin pieces of wood and perforated rubber plates that keep the positive and negative plates from touching each other and keep in place the disintegration produced by the electro-chemical action of the cell.

The unit of electric capacity in batteries is the ampere-hour. The cell illustrated will accumulate 80 ampere-hours of energy. It will discharge an ampere of current for 80 hours. If desired it may be discharged at the rate of two amperes for 40 hours, or four amperes for 20 hours, or at any other rate of amperes and hours, the product of which is 80. The number of ampere-hours a cell will accumulate will depend on the area of the positive and negative plates; large cells will store a greater number of ampere-hours than those of small size.

The cells, no matter what size, give an average electric pressure of 2 volts.

The plates are joined by heavy plate-straps connecting all of the positives on one end and all of the negative kind on the opposite end. To insure rigidity the two sets are secured to the rubber cover by locknuts. In this cell the plates are suspended from the cover. The plate terminals are made of heavy lead connectors that when formed into a battery are joined together with lead bolts and nuts.