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starting as the car gains momentum. This condition of sudden and wide fluctuations in the load imposes the need of very sensitive and quick-acting engine governors, as the dynamo speed must be kept constant.

Line and Track Construction. The single overhead trolley system has, with a very few exceptions, been generally adopted in the U. S. and Canada. In this system the current is led from one pole of the dynamo to a single wire suspended over the centre of the track, and reaches the car motors through the trolley-wheel and arm, whose upward pressure keeps it constantly in contact with the overbead wire. From the motor the circuit is completed to the other pole of the dynamo through the car-wheels and the track, which acts in the same capacity as the overhead conductor. Trolley lines are constructed with either hard drawn copper or silicon bronze wire of from a quarter to half an inch in diameter, and are supplemented by parallel feeder wires, with which they are connected at regular intervals. By dividing the overhead lines into two or more parallel strands it permits the trolley wire to be divided into sections or blocks, any of which can be disconnected from the system and repaired in case of accident without affecting any other sections of the road. The trolley wire is insulated by the hangers which support it, the bodies of which are composed of various insulating materials, such as moulded mica, porcelain, etc. The tracks, which are used as conductors, are connected so as to form a continuous metallic circuit from the car-wheels to the dynamos at the station, and as the rail-joints cannot be relied upon to make a good electrical connection, on account of the non-conducting rust which forms on the surfaces in contact, it is necessary to either bond or weld the tracks. Bonding is the general practice, and consists of riveting a wire at the ends of two rails, so as to form a by-path around the joint. The two parallel tracks are also cross-connected by bonds at intervals of the length of a rail. The tracks thus connected are supplemented by ground wires correspovding to the feeders for the trolley wire. Since the introduction of electric welding several attempts have been made to weld the ends of the rails together, making a single unjointed rail of the entire length of the road. This method has been only partially successful, as there is a tendency to breaking at the welds, due to the expansion and contraction of the track at different seasons. The best results with welding have been obtained with deep rails, in which the greater surface is under ground,

Several other methods have been employed for distributing the current to the cars, but none of them have attained much prominence. The double overhead trolley system, in which the second wire corresponds to the track circuit, described above, is still in use on a very few roads, but is undesirable on account of the crossing of wires of opposite polarities at switches, track-crossings, etc., and the liability of short circuits from falling telephone and telegraph wires. A number of conduit systems have also been devised, all of which may be divided into two classes-open or slotted conduits and closed conduits. In all conduit systems the chief obstacles lie in the expense of construction and the difficulty of securing proper drainage. Either one trolley wire and a track return or two trolley wires may be used with the open conduits. A successful example of the latter construction is the street-car system of over twenty-five miles in Budapest, which has been in operation for several years. Closed conduit systems are those in which, by electromagnetic switches or other automatic devices, the current is supplied only to the section of the conductor directly beneath the car. One arrangement of this kind, which will illustrate the object in view, was to place a bare conductor in a rubber tube, similar to a hose pipe, upon the upper side of which was placed a line of contact points, fixed like rivets through the tube. As the trolley traveled along the tube, which was flattened by its weight, these contacts were pressed down upon the inclosed bare conductor, and the current was thus led to the motors. The tube springing back to its normal shape only delivered current at the point where it was pressed down by the trolley. A great deal of attention is being given to the subject of closed conduits.

Car Equipment.--One or more electric motors geared to the car axles and a controlling switch on each platform constitute the principal parts of a motor-car equipment. Instead of having the journal boxes attached to the car frame, as in horse cars, the motors and running gear are attached to a car truck, on which the car body rests. The remarkable improvement which has been made in the design of street-car motors within the last four or five years is the principal cause of the success of electric railways. The first car motors were entirely too light mechanically and of too small capacity. From a single fifteen horse-power motor driving one car axle, the capacity of the car equipments has been gradually increased up to the present practice of using two twenty horse power motors, one geared to either axle, A marked improvement has also been made in the reduction of armature speeds, so that the use of a double reduction in speed by means of a countershaft and two pairs of gears between the armature shaft and the car axle is almost obsolete. Gearless motors, in which the armature is built on the car axle, have been introduced by one manufacturer, but single-reduction motors having the armature shaft geared directly to the car axle are most commonly used at present. Almost all modern car motors are of the multi-polar type instead of the bi-polar, as formerly, and tle reduction in armature speeds is due to this change of design. The severe service to which street-car motors are subject has led to making them very substantial in design, in order to avoid mechanical injury, and so-called ironclad (can refer to illustration under magneto-electric machines of Westinghouse Ironclad Car Motor) Electro-Chemistry. motors, in which the field magnets form a closed iron box, are largely used to prevent short-circuiting by water or by nails or scraps of iron picked up by the magnets. Most of the single-reduction, four-pole motors are supported on one side on the car axles by journals set in projecting lugs at each end of the motor frame, the armature shafts being parallel to the car axles. The opposite sides of the motors are connected to the frame of the car truck by means of springs, and a pinion on each armature shaft meshes with a gear wheel on either axle. The function of the springs is to avoid a shock on starting the car, by permitting the motors to turn through a small arc about the axles. In gearless motors the armature shaft is a hollow tube, through which the car axle passes, and to which it is flexibly connected by means of springs. Another method in use with some geared motors is to place the motor on the truck with its shaft at right angles to the car axles. The shaft carries a bevel pinion at each end which mesh with bevel gears on both of the car axles. With this system a single motor of large capacity is used. A number of attempts have been made from time to time to connect the armature shaft and the axle by belts, sprocket chains, friction clutches, etc., none of which has been able to stand the service.

The starting and regulation of speed of the car is effected by means of the controlling switches on the car platforms. The methods of regulation of the different electric railway systems are too numerous to be described in detail, but the same general plan is common to them all. Series machines are always used in railway work, and the field windings are wound in a number of separate sections, the ends of which are carried to contact pieces in the controlling switches. In addition to the resistance of the field winding a resistance box is also used. The contact pieces in the controller press against corresponding rows of metal plates, each row having its plates connected so as to vary the connections of the wires from the motor. In starting the car, the resistance box, sections of the field coils and armature are all in series to prevent a too large passage of current through the armature. The next turn of the switch cuts out more or less of the resistance box circuit, allowing more current to pass, and by successive movements of the switch the field coils pass through various combinations, from all in series to all in multiple, the latter corresponding to the highest car speed. To stop the car, the switch is reversed, making the same combinations in reverse order. To change the direction of the car, u separate switch is generally provided, which changes the direction of the current through the armature with reference to its direction through the fields. In systems where there is no commutation of the field coils, the changes in speed depend entirely upon the variable amounts of extra resistance thrown into the circuit. The cars used on electric railways vary from 16 feet to 35 feet long, and weigh 6 to 11 tons.

ELECTRO-CHEMICAL ORDER OF THE ELEMENTS. When two metals are placed in contact and immersed in a solution capable of acting on one of them, an electric current is produced, positive electricity passing from the metal acted on, through the liquid, to the metal unacted on. The former metal is said to be electro-positive to the latter. By experimenting with different pairs, we can arrange the metals in electro-chemical order. This order depends upon the readiness with which the metals are acted upon by the solution, and is not the same for all solutions.

The following is the electro-chemical order of the more common metals, the liquid being dilute sulphuric or hydrochloric acid : Sodium, magnesium, zinc, iron, copper, silver, platinum. When a compound of two elements is electrolyzed, the electro-positive element appears at the negative electrode, and the electro-negative element at the positive electrode. It is impossible to make a single table of the electro-chemical order of the elements, as this is not the same under all circumstances, but it may be generally stated that oxygen is the most electro-negative element, and that next to it are the elements chlorine, bromine, fluorine, sulphur, etc., which form stable compounds with the metals.

ELECTRO-CHEMISTRY, OR ELECTROLYTICS. The name electrolysis (brex king up by electricity) is given to the process of transmission of the electric current through liquids, when accompanied by the disruption of the molecules composing the circuit; the constituent radicals of the molecules being set free at the two poles.

The plates in the decomposition cells are called electrodes (electric ways); the plate connected to the + pole of the battery, usually copper, platinum, or carbon, is the anode (way up, as carrying the current out of the battery); the plate connected to the — pole of the battery (the zinc) is the cathode (downward way).

The liquid undergoing decomposition is the electrolyte. The molecules of an electrolyte break up into two radicals, which are called ions (indicating individuality, and in another sense meaning “going"). Those ions which turn towards the anode are called anions. They are electro-negative or acid radicals, such as oxygen and chlorine. Those which turn towards the cathode are called cations. They are electro-positives or basic radicals, as hydrogen and metals. The same ion may belong at different times to each of these classes if united to one having a higher individuality in either direction, for there is no direct attraction between the electrodes and the ions themselves, but the relation depends simply upon the temporary polarity they assume in the circuit.

Ions or radicals may be single atoms or compounds, which act as radicals chemically, and these may even be incapable of actual separate existence as far as present knowledge goes. Hydrochloric acid is an electrolyte composed of two single atoms. In sulphuric

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acid two atoms of hydrogen form one ion, and the compound radical, SO,, the other. This radical cannot exist uncombined, so that sulphuric acid is an electrolyte only when in presence of something it can react on and combine with, such as water, although water itself is not an electrolyte. Ammonium, NH,, is also a compound ion strongly resembling potassium in its properties; it also cannot exist free, but breaks up into NH, ammonia) and hydrogen, giving an apparent exception to the law of equivalence, by producing two free substances, each equivalent to the current producing them; but it must be considered that ammonia is not really a radical, for NH, may be considered as the equivalent of a complete molecule and is not capable of replacing hydrogen in salts.

We must regard the circuit as consisting of chains of molecules, some metallic, as in the plates and conductors ; some liquid, as in the cells; and the transmission of electricity, is consisting of a motion of each molecule in the chain, accompanied with the breaking in halves of a molecule wherever the current passes from metal to liquid, or vice versa. We shall thus understand why there is equal current, equal quantity of electricity, or equivalent chemical action at every section of the circuit. Because there are the same number (or value, as will be seen presently) of molecular actions effected at every part, however the molecules themselves may differ in nature. Each cell is, therefore, a section of the conductor, and each has its own specific resistance, just as the wire portion has. But the cells are of two orders in one respect.

(1) Generating cells, in which energy is set free by chemical actions, and becomes electro-motive force, setting up the current. These are battery cells, represented by E in electrical formulæ. (2) Decomposition cells, in which energy is absorbed in doing chemical work. These may be simple resistances, where no ultimate change is made in the solution ; such are most electro-plating and electro-metallurgical processes where the same metal is dissolved from the anode as is set free at the cathode. But if any ions are actually set free by the current, they tend to recumbine and act as a cell of the first order, with their electro-motive force opposed to that of the battery. This “counter E M F” is represented in formulas by – e, as is the electro-motive force of secondary batteries. See ELECTRICITY, STORAGE OF. The feeblest electro-motive orce will send a current through the first of these classes of decomposition cells, bul the second class require an E M F greater than that of opposition set up by the action itself, or electrolysis cannot take place, for the reason that no current will be produced if stopped by this counter E MF, as it is called. Except for this distinction of generating and decomposing, all the cells are under the same conditions. In each cell there is a + plate or element, the zinc in the battery cells and the anode in the decomposition cells, and if the latter can unite to the chlorous radical of the electrolyte, it dissolves, just as the zinc does in the battery cells. In each cell there is the electrolyte which gives up its chlorous or - ion, at the + plate, and transmits the molecular motion, which constitutes the current to the — plate where it also gives up its + ion. The - plate then continues as the + pole or anode to the next cell, and ultimately to the — pole or terminal zinc of the battery to complete the circuit. In fact, each pair of connecting plates in separate cells acts as though it were a metallic partition separating the two liquids with which the plates are in contact. In such a plate or conducting partition, one side would be + and the other side and the two plates in different cells correspond to these two sides, united by a connecting wire instead of by the mass of metal of the plate itself. Ic is of the utmost importance to bear in mind this distinction of plates or elements related to the liquid within their own cell, and of poles or electrodes related to another cell, and to the direction of the polarity they set up, or the current they transmit. Leaving out of sight the distinction of cells, as those setting up and those absorbing energy, that plate in each cell which is + to its own liquid, or the positive plate of the cell, is the anode or + electrode of the cell to which it is connected, and completes the circuit from the

- plate of this cell. Hence it is that the anode in the decomposition cell represents the zinc in the battery cell, for, like the zinc, it is + to the liquid, and gives up energy to the liquid (though that energy is derived from the current itself in this cell), and, like the zinc, it dissolves if made of materials which can combine with the negative or - radical of the solution. For this reason some prefer to call the anode the zincode. The laws of electrolysis usually accepted are those of Faraday, who also originated the terms described. These laws are:

1. No elementary substance can be an electrolyte. That is to say, the two ions must be differently composed.

2. Electrolysis occurs only while the body is in the liquid state. This state may be due to either fusion or solution ; in the latter case many substances which are not electrolytes of themselves may become electrolytes by a secondary action.

3. During electrolysis the components of the electrolyte are resolved into two groups ; one group takes a definite direction towards one of the electrodes, the other group takes a course towards the other electrode. They turn towards the several electrodes in polar order, but are not attracted or moved towards them by a direct attraction of the polar electrodes. Faraday held that only substances containing single equivalents of each radical could act as electrolytes, but this is now superseded by more general conceptions.

4. The amount as well as the direction of electrolysis is definite, and is dependent upon the degree of action in the battery being directly proportional to the quantity of electricity in

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