C
C. An abbreviation for centigrade when speaking of thermal temperature. In chemistry the centigrade scale is used extensively, but in air temperatures the Fahrenheit scale is universally employed.
Cable, Aerial. A cable that contains a number of wires separately insulated, the entire mass being protected by an external insulation. It is suspended in the air from pole to pole, and sometimes its weight is so great that a supporting wire is carried along with it (usually overhead), the large cable being suspended from it by cable-hangers.
Cable Box. A box to receive cable ends and protect them; also, the box in which cable ends and line-wires are joined. Submarine cable boxes are usually near the ground, while telephone and telegraph cable boxes are mounted on poles, the cables running from the ground and up the poles to the boxes.
Cable-core. The conductors of a cable which make up its interior mass. For the convenience of linemen the wires are often insulated with different-colored materials so that testing is not necessary when making connections.
Cable-hanger. A metallic grip, usually of sheet metal, arranged to clasp two or more wires. It is fastened to the supporting wire by a hook and eye, or by small bolts with thumb-nuts.
Cable-head. A rectangular board equipped with binding-posts and fuse wires so that the connections may be made between the cable ends and the overhead or line-wires of a system.
Cables. An insulated electric conductor of large diameter, often protected by armor or metallic sheathing, and generally containing, or made up, of several separately insulated wires. Cables supply current to traction lines; power, through subterranean passages; communication, by submarine connection; and light, by overhead or underground conduits.
Call-bell. A bell that is rung by pressing a button, and which is operated by electricity.
Calling-drop. A drop-shutter which is worked by electricity in a telegraph or telephone exchange; it denotes the location from which the call was sent in. Small red incandescent lamps have taken the place of the drops in most of the large telephone exchanges, for they are noiseless and do not annoy the operators as the drops and buzzers did.
Candle-power. The amount of light given by the standard candle. The legal English and American standard is a sperm candle burning two grains a minute.
Candle, Standard. The standard of illuminating power; a flame which consumes two grains of sperm wax per minute, and produces a light of a brightness equal to one candle-power.
Caoutchouc. India-rubber. So named because originally its chief use was to erase or rub off pencil marks. It is a substance existing, in a thick fluid state, in the sap or juices of certain tropical trees and vines; it possesses a very high value as an insulator for wire and circuits. The unworked, crude rubber is called virgin gum, but after it is kneaded it is called masticated or pure gum rubber.
Capacity. A term used when speaking of the carrying power of a wire or circuit. The capacity of a wire, rod, bar, or other conductor is sufficient so long as the current does not heat it. Directly electric heat is generated, we speak of the conductor as being overloaded or having its capacity overtaxed.
Capacity of a Telegraph Conductor. The electric capacity may be identical in quality with that of any other conductor. In quantity it varies not only in different wires, but for the same wire under different conditions. A wire reacting through the surrounding air, or other dielectric, upon the earth represents one element of a condenser, the earth in general representing the other. A wire placed near the earth has greater capacity than one strung upon high poles, although the wires may be of identical length and size and of the same metal. The effect of high capacity is to retard the transmission of current, the low capacity facilitates transmission.
Capacity, Storage. In secondary batteries, the quantity of electric current they can supply, when fully charged, without exhaustion. This capacity is measured or reckoned in ampere-hours.
Carbon. One of the elements in graphitic form used as an electric-current conductor. It is the only substance which conducts electricity, and which cannot be melted with comparative ease by increase of current. It exists in three modifications—charcoal, graphite, and the diamond. In its graphitic form it is used as an electro-current conductor, as in batteries and arc-light electrodes, and as filaments in incandescent lamps. In arc-lamp use the carbons are usually electro-plated on the outside with a film of copper which acts as a better conductor.
Carbon, Artificial. Carbon-dust, powdered coke, or gas carbon is mixed with molasses, coal-tar, syrup, or some similar carbonaceous fluid, so that the mass is plastic. It can then be moulded or pressed into shapes, and heated to full redness for several hours by artificial or electric heat. For lamp-carbons the mixture is forced through a round die by heavy pressure, and is cut into suitable lengths, then fired or baked.
After removing and cooling, the carbons are sometimes dipped again into the fluid used for cementing the original mass and re-ignited. This process is termed “nourishing.” All carbon is a resisting medium, but at high temperature the resistance is only about one-third as great; that is, the current will pass through a red-hot carbon three times better than through the cold carbon; or a current of thirty amperes will be conducted as easily through a hot carbon as ten amperes through a cold one.
Carbon-cored. A carbon for arc-lamps, the core being of softer carbon than the outer surface. It is supposed to give a steadier light, and fixes the position of the arc.
Carbon-dioxide. A compound gas, or carbonic-acid gas. It is a dielectric.
Carbon-holders. In arc-lamps, the clamps arranged to hold the carbon-pencils.
Carbonization. The ignition of an organic substance in a closed vessel, so as to expel all constituents from it except the carbon.
A destructive distillation.
Carbon Resistance. (See [Resistance, Carbon].)
Carbon Volatilization. In arc-lamps the heat is so intense that it is believed a part of the carbon-pencil is volatilized, as vapor, before being burned or oxidized by the oxygen of the air.
Carbons, Bare. (See [Bare Carbons].)
Carrying Capacity. In a current-conductor, its carrying capacity up to the heating-point. It is expressed in amperes.
Cascade. The arrangement of a series of Leyden-jars in properly insulated stools, or supports, for accumulating frictional electricity. They are arranged in a manner somewhat similar to a battery of galvanic cells, the inner coating of one being connected to the outer coating of the next, and so on through the series.
Case-hardening, Electric. A process by which the surface of iron is converted into steel by applying a proper carbonaceous material to it while it is being heated by an electric current.
Cautery, Electric. An electro-surgical appliance for removing diseased parts or arresting hemorrhages. It takes the place of the knife or other cutting instrument. It is a loop of platinum wire heated to whiteness by an electric current.
C.C. An abbreviation commonly used for cubic-centimeter. It is usually written in small letters, as 50 c.c., meaning 50 cubic-centimeters.
Cell, Electrolytic. A vessel containing the electrolyte used for electro-plating.
Cell, Regenerated. A cell restored to its proper functions by a process of recharging.
Cell, Standard. Meaning the same as battery. The vessel, including its contents, in which electricity is generated.
Cell, Storage. Two plates of metal, or compounds of metal, whose chemical relations are changed by the passage of an electric current from one plate to the other through an electrolyte in which they are immersed.
Cements, Electrical. Cements of a non-conducting nature, such as marine glue and sticky compounds, used in electrical work.
Centrifugal Force. A diametric revolving force which throws a body away from its axis of rotation. A merry-go-round is a simple example of this force. The more rapidly the platform revolves the greater the tendency for those on it to be thrown off and out from the centre. The high velocity attained by the armatures in motors and dynamos would throw the wires out of place and cause them to rub against the surfaces of the field-magnets. Consequently, wire bands or binders are necessary to keep the coils of wire from spreading under the influence of the centrifugal force.
Charge. The quantity of electricity that is present on the surface of a body or conductor.
The component chemical parts that are employed to excite the elements of a cell in generating electric current.
Charge, Residual. After a Leyden-jar, or other condenser, has been discharged by the ordinary methods, a second discharge (of less amount) can be had after a few minutes’ waiting. This is due to what is known as the residual charge, and is connected in some way with the molecular distortion of the dielectric.
Chemical Change. When bodies unite so as to satisfy affinity, or to bring about the freeing of thermal or other energy, the union is usually accompanied by sensible heat or light. Sulphuric acid added to water produces heat; a match in burning produces light. Another form of chemical change is decomposition or separation (the reverse of combination), such as takes place in the voltaic-battery, the electro-plating bath, and other forms of electrolysis. This is not accompanied by heat or light, but by the evolution of electricity.
Chemical Element. (See [Element, Chemical].)
Chemistry. The science which treats of the atomic and molecular relations of the elements and their chemical compounds. Chemistry is divided into many departments, but electro-chemistry treats only of the science wherein electricity plays an active part, such as batteries, electro-plating, and electro-metallurgy.
Choking-coil. (See [Coil, Choking].)
Circle, Magic. A form of electro-magnet. It is a thick circle of round iron used in connection with a magnetized coil to illustrate electro-magnetic attraction.
Circuit. A conducting-path for electric currents. Properly speaking, a complete circuit has the ends joined, and includes a source of current, an apparatus, and other elements introduced in the path. When the circuit is complete it is called active. The term circuit is also applied to portions of a true circuit—as, an internal or external circuit.
Circuit, Astatic. A circuit so wound, with reference to the direction of the currents passing through it, that the terrestrial or other lines of force have no directive effect upon it.
Circuit-breaker. Any apparatus for opening and closing a circuit, such as switches, automatic cut-outs, lightning-arresters, and the like.
A ratchet-wheel engaged with a spring, or wire, which rests against the teeth. The current passes through the wire, the wheel, and axle. The wheel is revolved by a crank, and as the ratchets pass the spring, or wire, an instantaneous make-and-break occurs. The speed of the wheel regulates the frequency of the interruptions.
Circuit, External. A portion of the circuit not included within the generator, such as a secondary telegraph key and sounder.
Circuit, Grounded. A circuit in which the ground is used as a conductor. This is common in telegraph and telephone lines, particularly for short distances where the conductivity of the earth does not offer too much resistance.
Circuit, Incandescent. A circuit in which incandescent lamps are installed.
Circuit Indicator. A pocket-compass, galvanometer, or other device for indicating or detecting the condition of a wire, whether it is active or dead, and, if active, in which direction the current is flowing. It may also give a general idea of its strength.
Circuit, Internal. That portion of an electric circuit which is included within the generator.
Circuit Loop. A minor circuit introduced, in series, into another circuit by a switch or cut-out, so that it becomes a part of the main circuit.
Circuit, Main. a circuit or main line, includes the apparatus supplying current to it. Thus distinguished from a local circuit.
Circuit, Metallic. A circuit in which the current outside the generator passes through metal parts or wire, but not through the ground. Electric light and power lines are always metallic circuits. An electro-plating apparatus may be properly termed a metallic circuit, although a part of the circuit is formed by the electrolyte in the bath. The essential meaning of the words metallic circuit is that the earth does not form a part of the return circuit.
Circuit, Open. A circuit in which a switch has been opened to prevent the continuous flow of current, such as an electric-bell circuit, which normally remains open, and which is active only when the push-button is pressed, thereby closing the circuit and operating the bell. An open-circuit battery is one that remains inactive when the circuit is open.
Circuit, Parallel. A term signifying a multiple circuit.
Circuit, Quadruple. A single circuit capable of having four messages transmitted over it simultaneously—two in one direction, and two in the other.
Circuit, Return. In telegraphy the ground is used as the return circuit. It is also that portion of a circuit which leads from an apparatus back to the terminal of a dynamo or battery, usually the negative wire.
Circuit, Short. A connection between two parts of a circuit, causing the current to skip a great part of its appointed path. Short-circuits prevent the proper working of any electrical apparatus.
Circuit, Simple. A circuit containing a single generator, the proper wire for carrying the current, and a switch to operate it. An electric-bell line, a single telegraph line, or a direct telephone line are all simple circuits.
Clamp. A tool for grasping and holding the ends of wires while joining them.
The appliance for holding the carbon-pencils in arc-lamps.
Cleats. Blocks of wood, porcelain, or other insulating material used to hold wires against a wall or beam. They have one, two, and three notches at one side, for single, double, and three wire systems.
Clutch, Electric. A form of magnetic brake applied to car-wheels, the armatures of motors, and other revolving mechanism, whereby the current, passing through a coil, magnetizes a mass of cast-iron, and brings it to bear frictionally upon the moving parts of the mechanism.
Code, Cipher. A set of disconnected words which, in accordance with a prearranged key, stand for whole sentences and phrases. Commercially the system is used as a short-cut—ten words perhaps meaning what otherwise it would take forty or fifty words to express. It is used extensively in telegraphy, both as an abbreviated message and as a means for securing secrecy.
Coherer. Conducting particles constituting a semi-conducting bridge between two electrodes, and serving to detect electro-magnetic waves. The coherer in wireless telegraphy is understood to mean that form of radio-receiver which, being normally at high resistance, is, under the influence of Hertzian-waves, changed to a low resistance, thus becoming relatively a conductor. Tubes of various kinds have been used for this purpose. Within them is a filling of carbon granules, copper filings, nickel and silver filings, and other substances. Marconi’s coherer consists of a tube one and one-half inches long and one-twelfth inch internal diameter. This is filled with filings—90 per cent. of nickel, 10 per cent. of silver. A globule of mercury coats the outer surface of each grain with a thin film of the quicksilver. Into both ends a piece of pure silver wire is plugged. These latter are a quarter of an inch long, and fit the tube very accurately. The tube is thus sealed, and it is considered preferable to have a slight vacuum within it.
Coil. A strand of wire wound in circular form about a spool, a soft-iron core, or in layers, as a coil of rope.
An electro-magnetic generator.
A helix. (See also [Induction], [Resistance], [Magnetizing].)
Coil, Choking. A form of resistance to regulate the flow of current. Any coil of insulated wire wound upon a laminated or divided iron core forms a choking-coil. In alternating-current work special choking-coils are used. They have a movable iron core, and by thrusting it in or out the power is increased or diminished, thus raising or lowering the lights, the same as gas is regulated.
Coil, Faradic. The name given to a medical induction-coil or faradic machine.
Coil, Induction. A coil in which the electro-motive force of a portion of a circuit is, by induction, made to produce higher or lower electro-motive forces in an adjacent circuit, or in a circuit a part of which adjoins the original circuit. There are three principal parts to all induction-coils—the core, the primary coil, and the secondary coil. The core is a mass of soft iron, cast or wrought, but preferably divided—for example, a bundle of rods or bars. The primary coil of comparatively larger wire is wound about this core, each layer being properly insulated and varnished, or coated with melted paraffine, to bind the wires. The secondary coil is of fine wire, and is wound about the primary coil. A great many turns of the fine wire are necessary, and care must be taken to properly insulate each layer and shellac the wires. The primary must be well insulated from the secondary coil, so as to prevent sparking, which would destroy the insulation. A make-and-break is operated by the primary coil, and is constructed upon the general form of an electric bell or buzzer movement. Extra currents which interfere with the action of an induction-coil are avoided by the use of a condenser. (See also [Condenser].) The induction-coil produces a rapid succession of sparks which may spring across a gap of thirty or forty inches, according to the size of the coil. Induction-coils are used extensively in electric work, especially in telephone transmitters, wireless telegraphy, electric welding, and in the alternating-current system.
Coil, Magnetizing. A coil of insulated wire so wound that a well or aperture will be formed. Within this well a piece of steel is placed, so that an electric current, passing through the wires, will magnetize the steel; or a steel rod may be passed in and out of the hole several times while a strong current is travelling through the coil, thus magnetizing the rod.
Coil, Resistance. A coil so constructed that it will offer resistance to a steady current of too great electro-motive force for the safety of the apparatus. Generally the coil is made by doubling the wire without breaking it, then starting at the doubled end to wind it in coil or spring fashion. If the wire is too heavy to wind double, a single strand is wound on a square or triangular insulator in which notches are made. Then, alternately between the coils, the second strand is wound. The strands are joined at one end of the coil, but those at the other are left free for unions with other wires. (See also [Resistance].)
Coil, Retarding. A choking-coil. A resistance-coil.
Coil, Ribbon. Instead of wire, flat, thin strips of sheet-metal are sometimes used for resistance-coils, doubled, as explained above. The wraps are insulated with sheet-mica, micanite, or asbestos, to prevent short-circuiting.
Coil, Ruhmkorff. A common type of induction-coil with a vibrator or circuit-breaker. Used with constant and direct current.
A step-up transformer with a circuit-breaker attachment.
Coils, Idle. Coils in a dynamo in which no electro-motive force is being generated or developed.
Coils that, through broken connections or short circuits, are inactive.
Column, Electric. An old name for the voltaic pile. The apparatus made up of a pile of disks of copper and zinc, separated by pieces of flannel wet with acidulated water.
Comb. A bar from which a number of teeth project like the teeth of a comb. It is used as a collector of electricity from the plate of a frictional electric machine.
Commutator. An apparatus used on motors and dynamos and induction-coils for changing the direction of currents. It is made in a variety of types, but usually in the shape of insulated bars closely packed about an armature shaft.
Commutator-bars. The metallic segments of a dynamo or motor-commutator.
Commutators, Quiet. Commutators that do not spark during the revolutions of the armature.
Compass. An apparatus for indicating the directive force of the earth upon the magnetic needle. It consists of a case covered with glass, in which a magnetized needle, normally pointing to the north, is balanced on a point at the centre. Under the needle a card is arranged on which the degrees or points of the compass are inscribed. A valuable instrument in electrical work, magnetism, etc.
Compass, Liquid. A form of marine compass. The needle is attached to a card or disk which floats in alcohol or other spirits, so as to check undue oscillation.
Compass, Mariners’. A compass in which the needle is attached to a card that rotates in pointing to the north. A mark, called the “lubber’s mark,” is made upon the case, and this is in line with the ship’s keel, so that a glance at the card will indicate the direction in which the ship is headed.
Compass, Spirit. A form of mariners’ compass in which the bowl, or case, is sealed and filled with alcohol. The compass-card works as a spindle, and, by a series of air compartments, floats on the alcohol. The friction of the pivot is thereby greatly diminished, making the compass a very sensitive one.
Compass, Standard. A compass employed as a standard by which to compare other compasses.
Condenser. An appliance for storing up electro-static charges; it is also called a static accumulator. The telegraphic condenser consists of a box packed full of sheets of tin-foil having a sheet of paraffined paper or sheet-mica between every two sheets. The alternate sheets of tin-foil are connected together, and each set has its binding-post. (See also [Electrostatic Accumulator].)
Condenser, Air. (See [Air-condenser].)
Condenser, Ayrton’s. (See [Ayrton’s Condenser].)
Condenser-plate. (See [Plate, Condenser].)
Condenser, Sliding. An apparatus in the form of a Leyden-jar whose coatings can be slid past each other to diminish or increase the face area, and also to diminish or increase the capacity of the condenser.
Conductance. The conducting power of a mass of material, varying according to its shape and dimensions. The cylindrical or round conductor is the best type for the conveyance of electric currents.
Conduction. The transmission of electricity through an immobile medium, such as a wire, or rod, or a bar.
Conductivity. Ability to conduct electric currents. The conductivity of a wire is its power to conduct or transmit a current. Glass has no conductivity, and it is therefore a non-conductor.
Conductivity, Variable. The change in the conducting or transmitting powers of metals and substances under different temperatures. Hot metal conducts an electric current better than cold. A hot carbon-pencil in an arc-light conducts the current better than when the light is first started, for as it warms up under the influence of the arc-flame the current passes more freely. Five minutes after the current is turned on the lamps in the circuit give a steady light, and do not sputter as when they first start up.
Conductor. Anything which permits the passage of electric current. The term conductor is a relative one, and, excepting a vacuum, there is probably no substance that has not some conductive power. Metals, beginning with silver, are the best conductors, liquids next, glass the worst. The ether, or air, is a conductor of sound and electric vibratory disturbances, but not in the same sense as the ground. The air conducts frictional electricity, while the ground acts as a conductor for the galvanic current, or “current electricity.” By this last term is meant electricity which flows continually, instead of discharging all at once, with an accompanying spark or flash.
Conductor, Overhead. Overhead electric lines, wires or cables, for conducting current. Generally poles are erected for this purpose.
Conductor, Prime. A cylindrical or spherical body with no points or angles, but rounded everywhere and generally of metal. If made of other material, such as wood, glass, or composition, its entire surface is rendered conductive by being covered with sheet-metal, such as tin-foil, gold-leaf or tinsel, applied to it with paste, shellac, or glue. A prime conductor should be mounted on an insulated stand; it is employed to collect and retain frictional electricity generated by a static machine.
Conductor, Underground. An insulated conductor which is placed under the surface of the earth, passing through conduits.
Connect. The act of bringing two ends of wire together, either temporarily or permanently. Bringing one end of a conductor into contact with another so as to establish an electric connection.
Connector. A sleeve, with screws or other clamping device, into which the ends of wires or rods may be passed and held securely. A binding-post and spring-jack comes under this head.
Contact. The electrical union of two conductors, whether temporary or permanent. It may be established by touching the ends or terminals of a circuit through the agency of a push-button, a telegraph-key, an electric switch, etc.
Contact-breaker. (The same as [Circuit-breaker], which see.)
Contact, Loose. A contact formed by two or several surfaces imposed one upon another and held by their weight alone.
Contact-point. A point, or stud, often of silver or platinum, arranged to come into touch with a contact-spring, such as the vibrating armature of an electric bell.
Contact-spring. A spring connected at one end of a lead and arranged to press against another spring or plate, so that a plug may be inserted between the contact-points.
Controller. The lever or handle on the switch-board of a resistance-coil, by means of which electric current is let in or kept out of a circuit.
Controlling Force. In galvanometers and similar instruments, the force used to bring the needle or indicator back to zero.
Converter. An induction-coil used with the alternating current for changing the potential difference and inverting the available current. High alternating voltage may be converted into lower direct-current voltage, thereby increasing the amperage or current. A converter consists of a core of thin iron sheets, wound with a primary coil of fine insulated wire, with many convolutions or turns. Also, a secondary coil made up of coarse insulated wire with fewer convolutions. The coil may be jacketed with iron to increase the permanence.
Converter, Rotary. A combined motor and dynamo whose function is to transform a current of high or low voltage (A-C., or D-C.) into any other kind of current desired.
Convolution. The state of being convolved; a turn, wrap, fold, or whorl. A clock-spring is a familiar example.
Copper-bath. A solution of sulphate of copper used in electro-plating, electrotyping, and copper-refining by electricity.
Cord, Flexible. A flexible-wire conductor made up of many strands of fine wire and properly insulated so that it may be easily twisted, bent, or wrapped. Flexible wire is used as the conductors for portable electric lights, push-buttons, medical coils, etc.
Core. The iron mass (generally located in the centre of a coil or helix) which becomes highly magnetic when a current is flowing around it, but which looses its magnetism immediately that the current ceases to flow.
A conductor or the conductors of an electric cable made up of a single strand or many strands laid together and twisted. These may be of bare metal, or each one insulated from the others.
Core-disks. Disks of thin wire, for building up armature-cores. The usual form of a core is round or cylindrical. A number of thin disks, or laminations, of iron strung upon the central shaft, and pressed firmly together by the end-nuts or keys. This arrangement gives a cylinder as a base on which to wind the insulated wire that forms a part of the armature.
Core-disks, Pierced. Core-disks for an armature of a motor or dynamo, which have been pierced or bored out around the periphery. Tubes of insulating material, such as fibre, rubber, or paraffined paper, are inserted in the holes and through these the windings of wire are carried. The coils are thus imbedded in the solid mass of iron, and are protected from eddy currents; also they act to reduce the reluctance of the air-gaps. This arrangement is very good, from a mechanical point of view, but in practice its use is confined to small motors only, and dynamos generating under one hundred volts.
Core-disks, Toothed. Core-disks of an armature or motor where notches are cut from the periphery. When they are locked together, to form the armature-core, the coils of wire lie in the grooves formed by a number of the disks bound together. This construction reduces the actual air-gaps and keeps the coils equally spaced.
Core, Laminated. The core of an armature, an induction-coil, a converter, or any similar piece of apparatus, which is made up of plates or disks, insulated more or less perfectly from one another by means of mica or paraffined paper. The object of laminations is to prevent the formation of Foucault currents. A core built up of disks is sometimes called a radially laminated core.
Core, Ring. A dynamo or motor armature-core which forms a complete ring.
Core, Stranded. The core of a cable, or a conducting core made up of a number of separate wires or strands laid or twisted together.
Core, Tubular. Tubes used as cores for electro-magnets, and also to produce small magnetizing power. Tubular cores are nearly as efficient as solid ones in straight magnets, because the principal reluctance is due to the air-path. On increasing the current, however, the tubular core becomes less efficient.
Coulomb. The practical unit of electrical quantity. It is the quantity passed by a current of one ampere intensity in one second.
Couple. The combination of two electrodes and a liquid, the electrodes being immersed in the latter, and being acted on differentially by the liquid. This combination constitutes a source of electro-motive force, and, consequently of current, and is called the galvanic or voltaic cell or battery.
Couple, Astatic.. A term sometimes applied to astatic needles when working in pairs.
Coupling. The union of cells or generators constituting a battery; the volume of current, or electro-motive force, is thereby increased.
C. P. An abbreviation for “candle power”; also meaning “chemically pure,” when speaking of chemicals.
Crater. The depression that forms in the positive carbon of a voltaic-arc.
Creeping. A phenomena met with in solution batteries. The electrolyte creeps up the sides of the containing jar and evaporates, leaving a deposit of salts. Still more solution creeps up through the salts until it gets clear to the top and runs over. To prevent this the tops of the jars should be brushed with hot paraffine for a distance of two inches from the upper edge. The salts will not form on paraffine. Oil is sometimes poured on the top of the battery solution, but this affects the elements if it touches them, and makes their surfaces non-conducting.
Crucible, Electric. A crucible for melting refractory substances, or for reducing ores by means of the electric arc produced within it. Probably the result obtained is due more to current incandescence than to the action of the arc.
Crystallization, Electric. Under proper conditions many substances and liquids take a crystalline form. When such action is brought about by means of electricity the term electric crystallization may be applied to the phenomenon. A solution of nitrate of silver, when decomposed by a current, will give crystals of metallic silver. A solution of common salt or brine, when electrically decomposed, will produce sodium and chlorine. The sodium appears at the leading-out electrode and readily unites with carbonic-acid gas, which is injected into the apparatus. The result of the combination is carbonate of soda, one of the most important products of the alkali industry.
Current, Alternating. A current flowing alternately in opposite directions. It is a succession of currents, each of short duration and of direction opposite to that of its predecessor. Abbreviation, A-C.
Current, Amperage. The volume of electricity passing through any circuit per second, the flow being uniform.
Current, Constant. An unvarying current. A constant-current system is one in which the current is uniformly maintained—for example, in electric light, power, and heat plants.
Current, Continuous. A current of one direction only, or the reverse of an alternating current.
Current, Direct. A current of unvarying direction, as distinguished from the alternating. Abbreviation, D-C.
Current Distribution, Uniform. A steady current; a current whose density in a conductor is always the same at all points.
Current, Induced. A current caused by electro-dynamic induction.
Current, Low Potential. A current of low pressure.
A term applied to low electro-motive force.
Current, Make-and-break. A current which is continually broken or interrupted and started again. The term is applied only where the interruptions occur in rapid succession, as in the action of an induction-coil or pole-changer.
The alternating current.
Current-meter. An apparatus for indicating the strength of a current, such as an ammeter.
Current, Oscillating. A current periodically alternating.
Current, Periodic. A current with periodically varying strength or direction. A current alternating periodically.
Current, Polarizing. A current which causes polarization.
Current-reverser. A switch or other contrivance for reversing the direction of a current in a conductor.
Current, Undulating. A current whose direction is constant but whose strength is continuously varying.
Currents, Eddy. Useless currents in an armature, in the pole pieces, and in the magnetic cores of dynamos and motors. They are created by the high speed of the armature in its rotation, or by other electric currents induced by the armature’s motion through magnetic fields.
Currents, Faradic. Induced currents. They take their name from Michael Faraday, the original investigator of the phenomena of electro-magnetic induction. The secondary or induced electro-magnetic currents and their accompanying phenomena.
A series of alternating electro-static discharges from influence machine, such as the Holtz and Wimshurst.
The simple and commonly understood Faradic currents are those produced in the medical battery, and used in medical therapeutics.
Currents, Foucault. A form of currents produced in revolving armature-cores; sometimes called eddy currents. They are useless.
Currents, Harmonic. Currents which alternate periodically, and vary harmonically. Currents which vibrate at certain pitches, as, for instance, the currents in wireless telegraphy. Two instruments must be tuned to the same pitch in order to be responsive. Thus an instrument sending out waves of 70,000 vibrations cannot be recorded by one tuned much below or above the same number.
Sound waves of sympathetic or harmonic vibrations.
Currents, Positive. (See [Positive Currents].)
Cut-in. To electrically connect a piece of mechanism or a conductor with a circuit.
Cut-out. The reverse of the cut-in. To remove from a circuit any conducting device. The cut-out may be so arranged as to leave the circuit complete in some other way.
An appliance for removing a piece of apparatus from a circuit so that no more current shall pass through the former.
Cut-out, Automatic. A safety device for automatically cutting out a circuit to prevent accident or the burning-out of an apparatus, due to an overload of current. It is worked by an electro-magnet and spring. An overload of current causes a magnet of high resistance to draw an armature towards it, and this, in turn, releases the spring of the cut-out device. Sometimes a strip or wire of fusible metal is employed which is in circuit with a switch. The excess of current fuses the metal, and the broken circuit releases a spring-jack, which, in turn, breaks the circuit.
Cut-out, Safety. A block of non-conducting material, such as marble, slate, or porcelain, carrying a safety-fuse or plugs. In these is enclosed a piece of fusible wire, which burns out or melts and breaks the circuit before the apparatus is damaged.
Cut-out, Wedge. A cut-out operated by a wedge, such as a spring-jack or the plugs at the end of the flexible wires on the switch-boards of telephone exchanges.