this should be done by first cleaning them in sulphuric acid and then rubbing mercury over their surface. Copper plates after much usage become so filled with salt that their effective surface is considerably lessened, they should then be replaced by new ones.

The terminal connections of the battery must be kept tightly screwed and free from creeping salts. The contact

surfaces should be made clean and bright before they are placed together. In connecting a wire to a binding post it should be bent around the screw as at A, Fig. 61, so that the nut when being screwed on will tend to draw the wire

closer to the screw and

FIG. 61. Right and Wrong Ways of Connecting a Wire to a Binding Post

not throw it out as it would if the wire be bent as at B.

Although a defective battery may usually be remedied by treating the apparent trouble, the exact working conditions of a cell can best be learned by testing its voltage with a low-reading voltmeter, Fig. 62. Comparing the reading on the scale a when the terminals of the cell are disconnected from the telephone circuit and joined by short wires to the binding posts c and s of the meter, with

the figures previously given for the electromotive force of the kind of cell tested, will show the true operating condition of the cell. A battery is often exhausted unnecessarily by the user of the telephone forgetting to replace the receiver on the hook switch when through talking. This leaves the battery circuit closed through the transmitter and primary winding of the induction coil, and makes the cells work continuously.

a

The Magneto Bell.-A thorough inspection of the magneto bell necessitates the door of the magneto box being opened and an examination made of the movement of the clapper. If the clapper clings to one gong, that gong should be moved slightly toward the other gong and against the clapper. If the ring indicates that the gongs

FIG. 62.-A Low-Reading Pocket Voltmeter for Testing Battery Cells

is not loud and clear, it are too close together. They should be so adjusted that the clapper just touches their edges when in its extreme positions. The soldered connections in the bell circuit on the door and hinges should also be carefully examined.

The Magneto Generator.-Defects in generators can usually be traced to their circuit-closing devices. In series generators the spring of the auto

matic shunt is usually the cause of the trouble; in bridging generators, the contact between the armature shaft and contact spring is often defective by reason of dust and oil accumulating thereon. A slight bending of the spring, or perhaps a new one, will be required in the former case, and the cleaning of the contact surfaces will be necessary in the latter case, to set matters right. If platinum contacts are used, unglazed writingpaper should be employed to clean them; otherwise emery cloth or sand-paper may be used. Occasionally, the permanent horseshoe magnets become weakened, preventing the development of current. This can easily be tested by placing the fingers across the terminals of the generator and turning the handle. If no shock is felt with the contacts and springs in good condition, the magnets are at fault and a new generator should be put in. An occasional oiling of the gear wheels and armature bearings is necessary to make them run smoothly.

The Hook Switch. This part of a telephone set sometimes fails by making poor connections with the contact springs. In a series set, the trouble is usually in the contact with the lower spring, in which case the bell circuit will be open when the receiver is on the hook. In a bridging set, accumulations of dust on the springs actuated by the hook switch may cause poor contacts between the springs, or they may have become slightly bent out of shape. A slight bending of the springs and

the use of unglazed writing-paper or fine sandpaper are the remedies to apply.

To Locate Trouble in a telephone station without examining each part of the apparatus separately, the inspector should proceed as follows. If the trouble is in the signaling circuit and is such that the station can be called but cannot call others, the magneto generator should first be tested. This, in case of a series set, should be done by connecting together the top binding posts of the set and turning the handle of the generator; if the bell of the set rings, the generator is all right; but if it does not ring, the generator must be examined for the defects previously suggested. In case the bell rings, the short-circuiting wire should be removed from across the top binding posts of the set and placed across the line circuit at the point of entrance to the building. The ringing of the bell now indicates that the inside wiring is all right and that the trouble is elsewhere. The ground connections might then advantageously be inspected. In case of a bridging connection, the generator, if in good order, should ring the bell of the set without any changes being made in the wiring. If it does not ring its bell, an examination should be made of the generator; but if it can do this, an inspection is necessary of the other ringers on the line to see if all of them have the same resistance.

If the station cannot be called but can call others, the bell should first be examined; in case

of a bridging bell, the generator of the set should also be inspected for a short circuit between its contact spring and the insulated pin on its armature shaft, and the resistance of the ringers on the line should be checked up.

If the trouble is in the talking circuit and is such that a message can be received but not transmitted, the battery would first be suspected; next a broken connection in the battery circuit; and finally, a damaged transmitter.

If a message can be transmitted but not received, the fault is obviously in the receiver. Weak incoming messages and signals, however, may be due to poor connections.

The Inspector's Kit should contain a screwdriver, tack hammer, file, pair of long-nosed pliers, pair of cutting pliers, trimming knife, soldering lamp and iron, solder and soldering fluid, roll of rubber tape, coil of No. 18 insulated wire, small bottle of machine oil, dust brush, candle, small low-reading voltmeter, chamois skin, cloth, and oil or paste for polishing outside of telephone set, fine sand-paper, emery cloth and unglazed writingpaper, box of nuts, screws, staples, and washers, box of granulated carbon, box of carbon buttons, receiver and transmitter diaphragms, receiver cords, magneto-box hinges, rubber bands, dampers, and contact springs. In a separate bag should be the battery supplies, comprising zincs, carbons, copper plates, porous cups, solution ingredients, or dry cells, depending upon the kind of batteries in