CHAPTER III.

ELECTRICAL APPARATUS.

FIRING-BATTERIES.

Voltaic batteries are supplied for firing torpedoes from ships and boats. A modification of the Le Clanché cell has been adopted and is now issued from the Torpedo Station. One ship‘s firing-battery of six cells is supplied to such ships as are fitted with spars. For use in boats and elsewhere, as may be necessary, two boat‘s firing-batteries of four cells each, with two spare cells for each battery, are supplied. When the guns are to be fired by electricity an additional firing-battery will be furnished for the purpose.

=_Note._=—Ships having only one torpedo launch will be supplied with but one boat‘s battery.

THE CELL.

=Plate XIII.=

The positive element is zinc in the shape of a cylinder open at both ends. Around the zinc is molded a covering of okonite, which forms the jar of the cell. A lug from the zinc cylinder projects up through the okonite covering and has soldered to it the brass negative terminal of the cell. The negative element is a thin plate of platinum enclosed in a cylindrical muslin bag filled with crushed carbon. The bottom of the bag is closed by a flat, circular piece of ebonite. The top of the bag is seized to a plug of ebonite, through which passes a platinum wire, soldered to the platinum plate and to the brass positive terminal in the top. The ebonite plug is scored to take a rubber cover, the outer edge of which fits in a groove cut around the inside of the okonite cylinder above the top of the zinc, preventing loss of the liquid by splashing, or by evaporation. A hole in the cover permits the entrance of air, which is necessary for the proper operation of the cell. A rubber ring around the lower end of the negative element prevents its contact with the zinc. The liquid is a nearly saturated solution of sal-ammoniac (ammonium chloride). This cell polarizes rapidly on a short-circuit, but recovers in a few hours if left on open circuit.

FIRING-BATTERY FOR SHIPS.

The ship‘s firing-battery consists of six cells inclosed in a box. The cells are joined up in series. The terminals are at one end of the box, on top, and are covered by a lid hinged to the cover of the box.

FIRING-BATTERY FOR BOATS.

This pattern is similar to the ship‘s battery, except that four cells only are inclosed in its box.

BATTERY TESTER.

=Plate XIV.=

This consists of a small wooden case inclosing a resistance-coil and a fuze-bridge. One end of the coil is connected to a brass spring and the other to one end of the fuze-bridge; the other end of the fuze-bridge is connected to a brass contact-piece opposite a spring at the other end of the case. When the tester is laid over the terminals of the battery and pressed down, contact is made between the contact-piece and spring, and a circuit established through the resistance-coil and bridge. If the battery is in good condition the bridge will be seen to redden, through a glass plate in the top of the case. The resistance of the coil in the tester for the ship‘s battery is 6.5 ohms and in the tester for the boat‘s battery it is 4 ohms.

Should the fine wire bridge accidentally be broken, the plug must be removed and a new one inserted. A number of plugs, with bridges, are supplied for this purpose.

MANAGEMENT AND CARE OF FIRING-BATTERIES.

=To Prepare the Liquid.=—Make a saturated solution of sal-ammoniac with rain or distilled water. The solution will be hastened by crushing the crystals of sal-ammoniac and heating the water. Allow the solution to cool and settle, and decant it carefully. Then add one-tenth its volume of distilled or rain water.

One pound of sal-ammoniac to four pints of water will give the proper degree of saturation.

=To Fill the Cells.=—Press down the edge of the rubber cover at one point and, by inserting a screw-driver at this point, pry up the cover, and lift its edge all around. Introduce the liquid through a glass funnel, being careful to spill none of it on the connections, and fill the jars to within half an inch of the top. After twenty-four hours replenish the liquid, filling the jars to the same point as before, and replace the rubber cover.

The ship‘s battery should be kept in a locker provided for it on the berth-deck, and should be kept connected with the wires leading to the firing apparatus on the spar-deck.

Neither the ship‘s nor the boat‘s firing-batteries are to be tested too frequently, nor must the duration of a test be longer than is necessary. The batteries, if kept stationary in a proper locker, need be tested but once weekly. The boat‘s battery must be tested before it is sent into the boat, and again after it is put in place in the boat.

The liquid should last from six to twelve months, according to the work done by the battery. Should the battery fail to show the proper test, search for bad or corroded connections. Test each cell separately, by touching the legs of a fuze-bridge directly to the poles of the cell. A single cell should redden the fuze-bridge when no other resistance is interposed. Faulty cells must be taken out, emptied and supplied with fresh liquid.

The batteries must be examined daily. The connections must be kept clean and free from salts and, to secure this, the liquid must not be allowed to come in contact with them. Corroded connections can be cleaned with emery cloth, or, if very badly corroded, they may be scraped with the back of a knife-blade.

Boat‘s batteries must be habitually examined after use in boats and any liquid that may have splashed about them be carefully wiped off.

It sometimes happens that, from long use and impoverishment of the liquid, crystals of zinc-ammonium-chloride form in the cell, attaching themselves to the muslin bag and to the zinc. Sometimes these crystals build across from the bag to the zinc and prevent the ready removal of the negative element. When this occurs no effort should be made to remove it by force, for such a proceeding is liable to brake the platinum wire, or tear the thin platinum plate. To remove the negative element, take off the rubber cover and pour out the liquid, which should not be used again. Fill the cell with warm water and allow it to stand, full of water, for several hours. The crystals are but slightly soluble, but prolonged soaking will detach them sufficiently to permit the removal of the negative element. When this can be done the crystals are to be carefully picked off the muslin and scraped off the zinc. If such crystals are found in a cell, at any time, they must at once be removed and the liquid renewed.

These batteries require but little care, but this little they must have. Systematic attention to them will be well repaid by their good performance and their constant readiness for use.

Before the firing-batteries are returned into store at the end of the cruise, or before transportation to distant points, the negative elements must be removed from the cells, thoroughly soaked in fresh water and dried. The jars must be washed out and drained and all metal parts wiped perfectly dry.

HAND-FIRING KEY.

=Pattern B.—Plate XV.=

This consists of two pieces of hickory, shaped to fit the hand, and joined together at the smaller end. Each piece is fitted with a brass contact stud projecting from its inner face at a short distance from the larger end. The natural spring of the wood keeps the two parts separated and maintains, normally, a break between the studs. A hole, bored longitudinally in each part, permits the entrance of a leading-wire, the bared end of which is secured by a screw to the contact stud. A rubber cot is seized over the key to prevent the closing of the circuit by sea-water. A safety-pin, attached to the key by a laniard, is habitually kept between the two parts to prevent accidental closing.

The hand-firing key, introduced in an electrical circuit, provides a break that can be closed at will.

THE TESTING-MAGNETO.

This is a small magneto-electric machine, sending alternating currents into the external circuit. The circuit from the magneto includes an electro-magnet with a vibrating armature.

The magneto will actuate this armature vigorously as a sounder, or rattler, through about 1000 ohms resistance. It may be used for testing the continuity of torpedo and other circuits, or for testing the insulation of the permanent and other leading-wires.

=For Testing Continuity.=—The poles of the magneto are connected with the ends of the circuit to be tested and the crank turned. If the armature rattles it indicates a continuous circuit. The failure of the armature to rattle will show a break in the circuit.

=For Testing the Insulation of the Permanent Wires.=—Connect one pole of the magneto with the wire to be tested and the other pole to earth; or, if a cross with some other wire is suspected, the other pole is connected with that wire. If the armature rattles vigorously when the crank is turned, a leak of less than about 1000 ohms resistance is indicated; if not, the insulation resistance of the wire is about 1000 ohms.

=To Test the Insulation of a Leading-Wire.=—Attach one end of it to one pole of the magneto, the other pole of which is connected by a short length of wire to an earth-plate placed in a tub of sea-water. Keeping the two ends of the wire to be tested out and dry, pay it into the tub gradually, turning the crank of the magneto meanwhile. Should there be a fault in the insulation, its existance and locality will be indicated by rattling of the armature when it reaches the water.

FARMER‘S DYNAMO-ELECTRIC MACHINE, PATTERN A, AND FIRING-KEY.

=Plate XVI.=

For a full description of the electric machine, see “A Lecture on Galvanic Batteries, Part III” published by the Bureau of Ordnance, 1875.

In general, pattern A may be considered as having an electro-motive force of sixteen to eighteen volts and a resistance of five ohms and to be capable of firing from twenty to twenty-five detonators arranged in series, or five to six arranged in as many branch circuits, or a single detonator through 1½ miles of cable such as is now issued, or through twenty ohms resistance.

It is unnecessary to give more than three or four turns of the crank in order to generate sufficient current to fire; but these revolutions must be with the sun and continuous up to and including the moment of firing. In general, as more work is required from the machine, greater speed and longer time will be necessary to get the machine up to its maximum power; this time, however, is very limited and the rapid turning of the crank for half a minute may be considered sufficient. With a single detonator in circuit and a moderate amount of leading-wire, one-quarter of a turn of the crank will usually be sufficient to fire.

=Testing the Machine.=—To test the machine, connect the binding-screws by a piece of metal, ship the crank and turn it with the sun. If it turn hard the machine is in good order; if it turn as easily as before the binding-screws were connected the machine is out of order.

In case the machine is out of order it should be removed from the outer case and the cause sought out and remedied. There are no delicate parts or mechanism and the machine may be examined without fear of injury.

The only faults which have been observed are the collecting of dirt between the shells of the commutator and the commutator springs, want of contact between them and the collecting of metallic dust between the two shells of the commutator. Each of these faults may be remedied in a moment. It is proper to say that these faults have never occurred when the machines were turned by hand and seldom when turned by power at a high rate of speed.

Some of the wire connections inside the machine might be severed by the breaking of a soldered joint, of which there are five. A fault of this kind would be readily found and easily remedied. In soldering electrical connections, resin, and not acid, should be used.

The effect of any of these faults is to cause a break in the continuity of the electrical circuit of the machine. This circuit is as follows: starting from one binding-screw, a wire leads to the field-of-force coils, or electro-magnet coils, traverses them and passes to one of the commutator springs; thence to one shell of the commutator; thence to the coil around the armature, through this coil to the other shell of the commutator; thence to the other commutator spring and, by a wire, to the second binding-screw, thus forming a complete circuit, when the binding-screws are joined together. If they are left unconnected, there is no closed circuit, no current is generated and the armature, therefore, turns easily. When the circuit is closed by connecting the terminals by a conductor of not too great resistance, the current generated excites the electro-magnets and this leads, in turn, to the generation of a stronger current until a maximum is reached depending on the resistance of the circuit and the speed with which the crank is turned. The electrical energy thus developed when the circuit is closed requires, of course, that extra work should be done to turn the crank. When the circuit is broken, inside or outside of the machine, it is necessary to overcome only the friction of the machine and the armature, therefore, turns easily.

=The Purpose of the Firing-Key.= (_Plate XVI._)—The full power of the electro-magnets of the D. E. machine will be reached soonest and will be greatest when the two binding-screws are joined by a piece of metal of practically no resistance as, for instance, a short wire. If this short-circuit is kept closed until the moment of firing and is at that, moment replaced by the circuit containing the detonator, we will have the machine working with its magnets fully excited in the circuit in which useful work is to be done. In order to accomplish this change of circuit, without allowing the magnetism of the machine to fall, the second circuit must be completed before the first is broken. If we had no more convenient method we could take advantage of this property of the machine by connecting the two ends of the fuze-circuit to the two binding-screws of the machine, and laying a piece of metal across the two binding-screws. When the crank is turned a strong current is generated, the magnets reach their full strength and, on removing the piece of metal, the machine is thrown upon the fuze-circuit with its magnets strongly excited, generating sufficient current to fire the detonator.

The firing-key furnishes a convenient method for making this change of circuit and also a means for testing the continuity of the fuze-circuit at any time before firing. When the firing-key is connected to the machine by wires between the binding-screws of the latter and those marked B, B, of the former and the binding-screws, marked T, T, of the former, are joined by a wire, there are three circuits which may be closed or broken by manipulation of the keys T and F of the firing-key. (_Plate XVII._)

=The Short-Circuit.=—The current follows the path shown in Fig. 1.

=The Test-Circuit.=—When the key T is pressed, the short-circuit is broken and the current follows the path shown in Fig. 2.

=The Firing-Circuit.=—When the keys F and T are pressed, the current follows the path shown in Fig. 3.

=To Test the Firing-Key.=—Connect as above and place the firing-key about ten or twelve feet from the machine, and so that the compass-needle points in the direction of the length of the box; ship the crank and turn it rapidly; if it turn hard the short-circuit is in good condition; then press the key T; if the crank turn easily and the compass-needle be deflected, the test-circuit is complete; then press the key F (the key T being already down); if the crank turn hard and the needle be no longer deflected, the firing-circuit is complete.

FARMER‘S DYNAMO-ELECTRIC MACHINE.

=Pattern C.—Plate XVI.=

This machine, intended for use in boats, has less power than the large machine, and may generally be considered as having an electro-motive force of eight volts, and a resistance of four ohms, and to be capable of firing eight to ten detonators in series, or two to three arranged in as many branches, or a single detonator through 1500 feet of such cable as is now issued.

This pattern combines within itself the firing and testing apparatus,—that is, the firing-key is permanently connected to the machine and the binding-screws of the C machine occupy a position analogous to that of the binding-screws T, T, of the firing-key.

=To Test the Machine.=—Ship the crank and turn it rapidly with the sun; if it turn somewhat hard the short-circuit is complete; press the key T; the crank should turn with ease; connect the binding-screws by a short wire; turn the crank as before and press the key T; if the crank turn easier and a small bell be heard to strike inside, the test-circuit is complete. Continue turning the crank, press the key F and then the key T; if it continue to turn somewhat hard, and the bell does not sound, the firing-circuit is complete. The difference of force necessary to turn the crank during the several tests is not so apparent as with the larger machine. If any of the tests fail the machine should be taken from its case and the fault treated as with the larger machines.

WIRES.

=Insulation.=—Insulation is for the purpose of confining the electric current to the path we wish it to take and should be carefully looked after at all points not covered by the rubber or other permanent insulating matter. Faults in the insulation of the wires leading from the testing or firing apparatus to the torpedo may be so situated as to cause, in the former case, false tests and, in the latter, a sufficient weakening of the current through the detonator to prevent its firing; or, they may be so situated as to cause accidental explosion of the torpedo. The insulation of the wires, as well as that of the testing or firing apparatus, must therefore be carefully preserved.

In order to preserve good insulation, all binding-screws should be kept clean and dry. Rain water has little effect, but salt water is bad. Wires which make short angles should be protected from chafe and all splices should be very carefully insulated by rubber tubing.

Particular care must be taken to prevent metallic contact of the two legs of the detonator. Any such contact at that point would not be detected by testing and would be fatal to success.

=Splicing Wires.=—Remove the jute braiding and rubber tape from the two ends to be spliced for such a distance as to be clear of the rubber tubing used to insulate the splices and whip the braiding. Bare the conductors of the two wires for about an inch and a half, lay them up and brighten them. Slip the piece of rubber tubing over the end of one of the wires. Unite the wires by a square-knot or sheet-bend, soldering the splice if it is to be permanent. Slip the rubber tubing over the splice so that its ends will overlap the rubber insulation of the wires and pass a snug seizing around each end of it.

If the splice is to be permanent a better junction may be made as follows: Prepare the wires as before, bend up slightly the two ends, lay them side by side, and bind them tightly together with a whipping of fine wire; then turn the ends back on the splice and solder the whole together. Another good joint may be made as follows: Prepare the wires, but allow a greater length; lay them together and twist each about the other at right angles and in opposite directions; then solder all together.

In all cases trim the splices so that there shall be no projecting wires to cut through the insulation.

=Continuity.=—It is possible that a wire may be cut or broken at some point where such cut or break cannot be seen. If there be any reason to suspect such a break, the continuity of that wire may be readily tested by connecting it to the testing-magneto, using leading-wires known to be good, and proceeding as in other testing.