551 STANDARD ELECTRICAL DICTIONARY.Ultra-gaseous Matter.Gas so rarefied that its molecules do not collide or very rarely do so.Experiments of very striking nature have been devised by Crookes andothers to illustrate the peculiar phenomena that this matter presents.The general lines of this work are similar to the methods used inGeissler tube experiments, except that the vacua used are very muchhigher.When the vacuum is increased so that but one-millionth of the originalgas is left the radiant state is reached. The molecules in their kineticmovements beat back and forth in straight lines without colliding, orwith very rare collisions. Their motions can be guided and renderedvisible by electrification. A tube or small glass bulb with platinumelectrodes sealed in it, is exhausted to the requisite degree and ishermetically sealed by melting the glass. The electrodes are connectedto the terminals of an induction coil or other source of high tensionelectrification. The molecules which come in contact with a negativelyelectrified pole are repelled from it in directions normal to itssurface. They produce different phosphorescent or luminous effects intheir mutual collisions.Thus if they are made to impinge upon glass, diamond or ruby, intensephosphorescence is produced. A piece of platinum subjected to molecularbombardment is brought to white heat. A movable body can be made to moveunder their effects. Two streams proceeding from one negative pole repeleach other. The stream of molecules can be drawn out of their course bya magnet.The experiments are all done on a small scale in tubes and bulbs,resembling to a certain extent Geissler tubes.[Transcriber's note: These effects are caused by plasma--ionized gas andelectrons.]552 STANDARD ELECTRICAL DICTIONARY.Unbuilding.The loss of its charge or excitation by a self-exciting dynamo. It isthe reverse of building-up. The latter indicates the exciting of thefield by the action of the machine itself; the former the spontaneousloss of charge on open circuit or from other cause.Underground Conductor.An electric conductor insulated and placed under the surface of theearth, as distinguished from aerial conductors.Underground Electric Subway.A subway for the enclosing of electric telegraph and other conductorsunder the surface, generally in the line of streets, to do away withtelegraph poles and aerial lines of wire. Many systems have beendevised. The general type includes tubes called ducts in sets, calledconduits, bedded in concrete or otherwise protected. Every two or threehundred feet the sets lead into a cistern-like cavity called a manhole.The insulated wires or cables, generally sheathed with a lead alloy areintroduced into the tubes through the man-holes. A rope is first fedthrough the tube. To do this short rods which screw together aregenerally employed. One by one they are introduced, and each end one isscrewed to the series of rods already in the duct. When the end of theduct is reached the rope is fastened to the last rod, and the rods arethen drawn through, unscrewed one by one and removed, the rope followingthem. By means of the rope a windlass or capstan may be applied to drawthe cable into the duct. At least at every second man-hole the cableshave to be spliced.Each cable may contain a large number of conductors of small size fortelephoning, or a smaller number for electric light and power. Thetendency is now to separate the different classes of wires in importantlines, placing the heavier wires on one side of the street and thetelephone and telegraph wires on the other. This of course necessitatestwo separate conduits.The advantage of underground distribution affects not only theappearance of streets in doing away with unsightly telegraph poles, butit also removes an element of danger at fires. Aerial wires interferegreatly with the handling of ladders at fires, and expose the firemenwho attempt to cut them to danger to their lives from shock.533 STANDARD ELECTRICAL DICTIONARY.Unidirectional. adj.Having one direction as a "unidirectional current" or "unidirectionalleak." The term is descriptive, and applicable to many cases.Uniform. adj.Unvarying; as a uniform potential difference, uniform current orconductor of uniform resistance per unit of length. The term isdescriptive, and its application and meaning are obvious.Uniform Field of Force.A field of evenly distributed force; one in which the number of lines offorce per unit of area of any equipotential surface is the same.Unipolar. adj.Strictly speaking this term means having only one pole, and is appliedto magnets, armatures and the like. In its use a solecism is involved,for there is no such condition possible as unipolar magnetism ordistribution of magnetism. An example of its use is shown in unipolarmagnets. (See Magnet, Unipolar.)Unipolar Armature.An armature of a unipolar dynamo; an armature whose windingscontinuously cut the lines of force about the one pole, and hence whosepolarity is unchanged in its rotation.Unipolar Current Induction.Current induction produced by moving a conductor through a magneticfield of force so that it always cuts the lines in similar relation toitself. Thus it produces a constant current through its own circuit, ifa closed one, and no commutator is required. As this case always inpractice amounts to the cutting of lines of force in the neighborhood ofa single pole the term unipolar is employed to designate the action.The simplest representation of unipolar induction is the rotating of aconductor around the end of a bar magnet, its axis of rotationcorresponding with the axis of the magnet.Unipolar Dynamo.A dynamo in which one part of the conductor slides on or around themagnet, so as always to cut lines of force near the same pole of themagnet.Unit.A directly or indirectly conventional and arbitrary quantity, in termsof which measurements of things with dimensions expressible in thechosen units are executed.Thus for length the c. g. s. unit is the centimeter; the B. E. unit isthe foot.554 STANDARD ELECTRICAL DICTIONARY.Unit, Absolute.A unit based on the three fundamental units of length, mass and time.These units are the centimeter, gram and second. Each one in itself maybe termed a fundamental absolute unit. The system of such units istermed the centimeter-gram-second system.Unit, Angle.A factor or datum in angular velocity, q. v. It is the angle subtendedby a portion of the circumference equal in length to the radius of thecircle. It is equal very nearly to 57.29578° or 57° 17' 44.8".Unit, B. A.This term, while logically applicable to any of the British Associationunits, is often restricted to the ohm as formerly defined by the BritishAssociation, the B. A. Unit of Resistance, q. v.Unit, Fundamental.The three units of length, mass and time, the centimeter, gram andsecond, are termed fundamental units. On them is based the absolutesystem of units, and on multiples of them the practical system of units.Unit Jar.A Leyden jar which is used as a unit of measure of charge.It consists of a Leyden jar about 4 inches long and 3/4 inch diameter,with about 6 square inches of its outer and the same of its innersurface coated with tinfoil. It is placed between a source ofelectricity and a larger jar or battery of jars which is to be charged.The inner coating connects with the machine; the outer coating with thejars to be charged. Short conductors terminating in knobs connect withinner and outer coatings, and the knobs are adjusted at any desireddistance apart.By the charging operation the large jar or battery of jars receives acharge by induction, and the charge of the small jar is at first equalto this quantity. After a while a spark passes from knob to knob,discharging the small jar. This indicates the reception by the largejars of the quantity of electricity represented by the charge of thesmall jar. The charging goes on, and for every spark approximately thesame quantity of electricity is received by the larger jars.The sparking distance m is directly proportional to the quantity ofelectricity, and inversely proportional to the area of coated surface,or is proportional to the potential difference of the two coats. This isonly true for short sparking distance, hence for accuracy the knobsshould be adjusted not too far from each other.555 STANDARD ELECTRICAL DICTIONARY.Unit of Supply.A commercial unit for the sale of electric energy, as definedprovisionally by the English Board of Trade; 1,000 amperes flowing forone hour under an E. M. F. of 1 volt; 3,600,000 volt-coulombs, or 1,000watt-hours, are its equivalent. It is equal to 1000/746 = 1.34 electrichorse power.Synonym--Board of Trade Unit.[Transcriber's note: Now called a kilowatt-hour.]Units, Circular.A system of units of cross-sectional area, designed especially for usein describing wire conductors. The cross-sectional area of such isuniversally a circle, and the areas of two wires of different sizes varywith the square of their radii or diameters. Hence if the area of acircle of known diameter is determined it may be used as a unit for thedimensions of other circles. Any other circle will have an areaproportioned to the area of the unit circle, as the squares of thediameters are to each other.In practise the commonest circular unit is the circular mil. This is thearea of a circle one mil, 1/1000 inch, in diameter and is equal to.0000007854 square inch. A wire two mils in diameter has an area of fourcircular mils; one ten mils in diameter has an area of one hundredcircular mils.Thus if the resistance of a given length of wire 1 mil in diameter isstated, the corresponding resistance of the same length of wire of thesame material, but of other diameter, is given by dividing the firstwire's resistance by the square of the diameter in mils of the wire inquestion.As it is a basic unit, most conveniently applied by multiplication, thesmaller units are used; these are the circular mil, and circularmillimeter.Units, Derived.Units derived by compounding or other processes, from the threefundamental units. Such are the units of area, volume, energy and work,momentum and electric units generally. In some cases the dimensions ofthe derived unit may reduce to those of a simple unit as inductancereduces to length, but the unit, as deduced from the fundamental ones,is still a derived unit.Units, Practical.A system of units employed in practical computation. The absolute units,especially in electricity, have been found too large or too small, andthe attempt to make them more convenient has resulted in this system. Itis based on exactly the same considerations as the absolute system ofunits, except that multiples of the original fundamental units oflength, mass, and time have been taken as the base of the new system.These basic units are multiples of the fundamental units. They are thefollowing: The unit of length is 1E9 centimeters; the unit of mass is1E-11 gram; the unit of time remains 1 second.While this has conduced to convenience in giving better sized units,micro- and mega-units and other multiples or fractions have to be used.The following are the principal practical electric units:Electrostatic ElectromagneticC. G. S Units. C. G. S. Units.Intensity-Ampere equal to 3E9 1E-1Quantity-Coulomb " 3E9 1E-1Potential-Volt " (1/3)* E-2 1E8Resistance-Ohm " (1/9)* E-11 1E9Capacity-Farad " 9E11 1E-9556 STANDARD ELECTRICAL DICTIONARY.Universal Battery System.A term in telegraphy. If several equal and high resistance telegraphiccircuits are connected in parallel with each other from terminal toterminal of a battery of comparatively low resistance each circuit willreceive the same current, and of practically the same strength as ifonly one circuit was connected. This is termed the universal batterysystem. It is a practical corollary of Ohm's law. The battery being ofvery low resistance compared to the lines the joining of several linesin parallel practically diminishes the total resistance of the circuitin proportion to their own number. Thus suppose a battery of ten ohmsresistance and ten volts E. M. F. is working a single line of onehundred ohms resistance. The total resistance of the circuit is then onehundred and ten ohms. The total current of the circuit, all of which isreceived by the one line is 10/110 = .09 ampere, or 90 milliamperes. Nowsuppose that a second line of identical resistance is connected to thebattery in parallel with the first. This reduces the external resistanceto fifty ohms, giving a total resistance of the circuit of sixty ohms.The total current of the circuit, all of which is received by the twolines in equal parts, is 10/60 = .166 amperes. But this is equallydivided between two lines, so that each one receives .083 ampere or 83milliamperes; practically the same current as that given by the samebattery to the single line. It will be seen that high line resistanceand low battery resistance, relatively speaking, are required for thesystem. For this reason the storage battery is particularly available.The rule is that the resistance of the battery shall be less than thecombined resistance of all the circuits worked by it.Unmarked End.The south-seeking pole of a magnet, so called because the other end,called the marked end, is usually marked with a scratch or notch by themaker, while the south pole is unmarked.
556 STANDARD ELECTRICAL DICTIONARY.V.(a) Symbol for velocity.(b) Symbol or abbreviation for volume.(c) Symbol or abbreviation for volt.557 STANDARD ELECTRICAL DICTIONARY.V. A.Symbol or abbreviation for voltaic alternatives, q. v.Vacuum.A space destitute of any substance. The great pervading substance is ingeneral sense the atmosphere. It is the gaseous mixture which surroundsand envelopes the earth and its inhabitants. It consists of a simplemixture of oxygen, 1 part, nitrogen, 4 parts, with 4 to 6 volumes ofcarbonic acid gas in 10,000 volumes of air, or about one cubic inch toone cubic foot. It presses with a force of about 14.7 lbs. per squareinch under the influence of the force of gravity. The term vacuum inpractise refers to any space from which air has been removed. It may beproduced chemically. Air may be displaced by carbonic acid gas and thelatter may be absorbed by caustic alkali or other chemical. The air maybe expelled and the space may be filled with steam which is condensed toproduce the vacuum. Of course in all cases the space must be included inan hermetically sealed vessel, such as the bulb of an incandescent lamp.But the universal method of producing a vacuum is by air pumps. Anabsolute vacuum means the entire absence of gas or air, something almostimpossible to produce. A high vacuum is sometimes understood to mean onein which the path of the molecules is equal in length to the diameter ofthe containing vessels, as in Crookes' Radiometer and other apparatusfor illustrating the radiant condition of matter. The air left afterexhaustion is termed residual air or residual atmosphere.[Transcriber's note: Dry air is about .78 nitrogen, .21 oxygen, .01argon, .00038 carbon dioxide, and trace amounts of other gases. Argonwas suspected by Henry Cavendish in 1785. It was discovered in 1894 byLord Rayleigh and Sir William Ramsay.]Vacuum, Absolute.A space free of all material substance. It is doubtful whether anabsolute vacuum has ever been produced.Vacuum, High.An approximate vacuum, so nearly perfect that the molecules of theresidual gas in their kinetic motions rarely collide, and beat back andforth between the walls of the containing vessel, or between any solidobject contained in the vessel and the walls of the vessel. The gas insuch a vacuum is in the radiant or ultra-gaseous state. (SeeUltra-gaseous Matter.)Vacuum, Low.A vacuum inferior to a high vacuum; a vacuum in which the moleculescollide with each other and do not move directly from side to side ofthe containing vessel.Vacuum, Partial.A space partially exhausted of air so as to contain less than an equalvolume of the surrounding atmosphere. It really should come below a lowvacuum, but is often treated as synonymous therewith.Vacuum, Torricellian.The vacuum existing above the mercurial column in a barometer tube. Theprinciple of this vacuum is applied in the Geissler and other air pumps.(See Pump, Geissler--Pump, Sprengel--Pump, Swinburne.)558 STANDARD ELECTRICAL DICTIONARY.Valency.The relative power of replacing hydrogen or combining therewithpossessed by different elements; the number of atomic bonds belonging toany element. Thus oxygen has a twofold valency, is bivalent or is adyad, and combines with two atoms of hydrogen because the latter has aunitary atomicity, is monovalent or is a monad.Valve, Electrically Controlled.A valve which is moved by or whose movements are regulated byelectricity.In the block system of railroad signaling the semaphores are worked byweights and pneumatic cylinders and pistons. The valves for admitting orreleasing the compressed air are operated by coil and plunger mechanism.There are many other instances of the control of valves by the electriccurrent.Vapor Globe.A protecting glass globe surrounding an incandescent lamp, when the lampis to be used in an atmosphere of explosive vapor, as in mines orsimilar places; or when in a place where it is exposed to dripping waterwhich would break the hot lamp bulb if it fell upon it.Variable Period.The period of adjustment when a current is started through a conductorof some capacity. It is the period of duration of the variable state, q.v., in a conductor. As indicated in the next definition in a cable ofhigh electrostatic capacity a variable period of nearly two minutes mayexist. This indicates the retardation in signaling to be anticipated incables and other lines of high capacity.Variable State.When an electric circuit is closed the current starts through theconductor with its full strength from the point of closure, and advanceswith a species of wave front so that some time elapses before it attainsits full strength in the most distant parts of the conductor, owing toits having to charge the conductor to its full capacity at the givenpotential. The state of the line while the current thus varies is calledthe variable state.A long telegraph line when a message is being transmitted may be alwaysin the variable state. The current at the receiving end may never attainits full strength.In the case of such a conductor as the Atlantic cable, 108 seconds wouldbe required for a current to attain 9/10 of its full strength at thedistant end, and but 1/5 second to attain 1/100 of its final value.During the period of increase of current the variable state exists.Variation of the Compass.The declination of the magnetic needle. (See Elements, Magnetic.) As thedeclination is subject to daily, annual and secular variations, it isunfortunate that this term is synonymous with declination. Thus thevariation of the compass means its declination, while there is also thevariation of the declination and of other elements. The term variationof the compass is more colloquial than the more definite expression"declination," or "magnetic declination."559 STANDARD ELECTRICAL DICTIONARY.Variometer.An apparatus used in determining the relative values of the horizontalcomponent of the earth's magnetic field in different places.Varley's Condenser.A static condenser whose conducting surfaces are platinum electrodesimmersed in dilute sulphuric acid. When the potential difference is1/50th that of a Daniell's cell, two square inches of platinum have acapacity equal to that of an air condenser whose plates have an area of80,000,000 square inches, and separated 1/8th of an inch from eachother. As the E. M. F. increases the capacity also increases.Varley's Resistances.Variable resistances formed of discs of carbonized cloth, q. v., piledup, and pressed together more or less firmly to vary the resistance asdesired.Varnish.A glossy transparent coating of the nature of paint, applied as aprotective, or ornamental coating to objects.Varnish, Electric.Alcoholic or etherial varnishes are the best for electrical apparatus.They dry quickly and perfectly, and tend to form surfaces unfavorable tothe hygroscopic collection of water. Sealing wax dissolved in alcohol,or shellac dissolved in the same solvent are used for electricalapparatus, although the first is rather a lacquer than a varnish.Etherial solution of gum-copal is used to agglomerate coils of wire. Itis well to bake varnished objects to harden the coating.Varnish, Red.A solution of sealing wax in 90 per cent. alcohol. It is best made thinand applied in several coats, each coat being allowed to dry perfectlybefore the next is applied. It is often seen on Leyden jars. It is aprotector from surface leakage.Vat.A vessel for chemical or other solutions. A depositing vat is one inwhich a plating solution is worked, for the deposition of electroplateupon articles immersed in the liquid, and electrolyzed by an electriccurrent.Velocity.The rate of motion of a body. It is usually expressed in distancetraversed per second of time. The absolute unit is one centimeter persecond or kine. The foot per second is very largely used also.The dimensions of velocity are length (L) divided by time (T) or L/T.Velocity, Angular.Velocity in a circle defined by the unit angle, or the angle whichsubtends a circular arc equal in length to itself. The radius of thecircle traversed by the moving body does not enter into this definition,as the real velocity of the object is not stated. If its angularvelocity and the radius of the path it travels are given its actualvelocity can be deduced.560 STANDARD ELECTRICAL DICTIONARY.Velocity of Signaling.The speed of transmission of electric signals is affected by the natureof the line, as regards its static capacity, and by the delicacy of thereceiving instruments, which may need a more or less strong current tobe affected. Thus of an original current one per cent. may suffice tooperate a sensitive instrument. This might give almost the velocity oflight, while if the instrument would only respond to the full currentnearly two minutes (see Variable State) might be required for theproduction of a signal.Velocity Ratio.A term applied to the ratios existing between the electrostatic andelectro-magnetic units. If we take as numerators the dimensions of thedifferent qualities in the electrostatic system, and their dimensions inthe electro-magnetic system as denominators, the fractions thus obtainedreduce to expressions containing only velocity or V in some form. Thusif we divide the dimensions of the electrostatic quantity by thedimensions of electro-magnetic quantity the quotient is simply V orvelocity. A like division for potential, electrostatic andelectro-magnetic gives (1/V), and so on.The value of the velocity ratio is very nearly 3E10 (sometimes given as2.98E10) centimeters per second. This is almost exactly that of light(2.9992E10 centimeters per second.) This is one of the proofs of ClerkMaxwell's magnetic theory of light. (See Maxwell's Theory of Light.)[Transcriber's note: The SI metre was defined in 1983 such that thespeed of light in a vacuum is exactly 299,792,458 metres per second orabout 186,282.397 miles per second.]Ventilation of Armature.In a dynamo or motor ventilation of the armature is often provided forby apertures through it in order to prevent heating. This heating iscaused by Foucault currents. By proper disposition of the interior ofthe armature with properly disposed vanes and orifices an action likethat of a fan blower can be produced, which by creating a current of aircools the machine very efficiently.Verticity, Poles of.Points upon the earth's surface where the horizontal component ofmagnetic force disappears, leaving only the vertical component active.The term is derived from the verticity of the dipping needle when overeither of them.561 STANDARD ELECTRICAL DICTIONARY.Vibration Period.In electrical resonance the period of a vibration in an electricalresonator. The length of this period indicates the quality of theresonator in responding to electrical oscillations by sympatheticvibration. For conductors of small resistance the period is thuscalculated. Let T be the period of one-half a full vibration; L theabsolute coefficient of self-induction expressed in centimeters or inhenries X 10-9; C the electrostatic capacity of the terminals, alsoexpressed in the same unit; v the velocity of light in centimeters persecond. Then we have the formulaT = PI * SquareRoot( L * C ) / v[Transcriber's note: If the inductance is in henries and the capacitancein farads, frequency in hertz = 1/(2 * PI * squareRoot( L * C ) )]Vibration, Sympathetic.A vibration in a cord or other body susceptible of elastic vibrationproduced by the vibrations of exactly the same period in a neighboringvibrating body. Thus if two tuning forks are tuned to precisely the samepitch, and are placed near each other, if one is sounded it will startthe other into vibration by sympathy.In electricity its application is found in electric resonanceexperiments. The resonator has a definite period of electric resonance,and is made to give a spark by the exciter of identical period. This isby what may be called electric sympathetic vibration, and is exactlyanalogous to the action of the tuning forks upon each other.Vibrator, Electro-magnetic.The make and break mechanism used on induction coils, or other similarapparatus in which by alternate attractions by and releases from anelectro-magnet an arm or spring is kept in motion. In most cases thework is done by a single magnet, whose armature is attracted to themagnet, when the latter is excited, but against the action of a springwhich tends to pull it away from the magnet. In its motions a make andbreak action is produced, to give the requisite alternations ofattraction and release. Two electro-magnets may be connected so asalternately to be excited and keep an arm carrying a mutual armature invibration, or the same result may be attained by a polarized relay. Themake and break is illustrated under Bell, Electric--Coil, Induction--Anvil.Villari's Critical Value.Magnetization induced or residual in a wire is diminished on stretching,provided that the magnetization corresponds to an inducing force above acertain critical value, known as above; this being (Sir Wm. Thomson)about 24 times the terrestrial intensity. Below that critical valuetension increases the magnetization of a magnetized wire. The effects oftransverse expansive stress are opposed to those of longitudinalstretching. (Daniell.)Viole's Standard of Illuminating Power.A standard authorized by the International Congress of 1881. It is thelight given by one square centimeter of platinum, melted, but just atthe point of solidification. It is equal to 20 English standard candlesalmost exactly.It has not been very widely accepted, the tendency among photometristsbeing to adhere to the old standards, carcel or candle. It is obviousthat actual use of the Viole would be very inconvenient and wouldinvolve expensive apparatus, difficult to work with.Synonym--Viole.562 STANDARD ELECTRICAL DICTIONARY.Vis Viva.The kinetic energy of a body in motion; "mechanical energy."Vitreous Electricity.Positive electricity; the electricity produced on the surface of glassby rubbing it with silk and other substances. (See ElectrostaticSeries.)The term "positive electricity" should be allowed to supplant it. It isthe analogue and opposite of resinous electricity.Vitriol, Blue.A colloquial or trade name for copper sulphate (Cu SO4).Vitriol, Green.A colloquial or trade name for ferrous sulphate (Fe SO4).Vitriol, White.A colloquial or trade name for zinc sulphate (Zn SO4).Volt.The practical unit of electro-motive force or potential difference. Itmay be referred to various data.An electro-motive force of one volt will cause a current of one ampereto flow through a resistance of one ohm.A condenser of one farad capacity charged with one coulomb will have arise of potential of one volt.The cutting of 100,000,000 lines of force per second by a conductorinduces one volt E. M. F.A Daniell's battery gives an E. M. F. of 1.07 volts; about the mostfamiliar approximate standard that can be cited.It is equal to 1/300 absolute electrostatic unit.It is equal to 1E8 absolute electro-magnetic units.[Transcriber's note: The SI definition of a volt: The potentialdifference across a conductor when a current of one ampere dissipatesone watt of power.]Voltage.Potential difference or electro-motive force expressed in volts; as avoltage of 100 volts. Thus voltage may express the electro-motive forceabsorbed in a conductor, while electro-motive force is a term generallyapplied where it is produced, evolved or present in the object. The termvoltage of a lamp expresses simply the volts required, but does notsuggest the possession of electromotive force.563 STANDARD ELECTRICAL DICTIONARY.Voltage, Terminal.The voltage or potential difference at the terminals of an electriccurrent generator, such as a dynamo, as distinguished from the totalelectro-motive force of the dynamo or generator.In batteries the distinction is not generally made in practice; thetotal electro-motive force of the battery is made the basis ofcalculations.Voltaic. adj.This adjective is used to qualify a great many things appertaining to orconnected with current electricity. It is derived from Volta, theinventor of the voltaic battery, and now tends to displace the term"galvanic," formerly in general use.Voltaic Alternatives.A term used in electro-therapeutics or medical electricity to indicatean alternating battery current.Synonym--Alternative current.Voltaic Effect.The potential difference developed by contact of different conductors.It is the basis of the contact theory, q. v., of electricity, althoughit may be accepted as the expression for a condition of things by thosewho reject the above theory. This potential difference is slight whenthe conductors are separated, but it is calculated that it would beenormous could the metals be so quickly separated as to hold each itsown charge.Thus if a copper and a zinc plate are assumed to be in contact, really1/20000000 centimeter or 1/50000000 inch apart, they may be treated as apair of condenser plates. Being so near, their density of charge, whichis a strongly bound charge, is enormous. If it were possible to separatethem without permitting any discharge, their potential would rise by theseparation, on the principle of Epinus' condenser, q. v., to such anextent that they would spark through twenty feet of air. (See Volta'sFundamental Experiment.)Voltaic Electricity.Electricity of low potential difference and large current intensity;electricity such as produced by a voltaic battery; current or dynamicelectricity as opposed to static electricity.Voltameter.In general an apparatus for determining the quantity of electricitypassing through a conductor by measuring the electrolytic action it canperform.Voltameter, Copper.An apparatus which may be of similar construction with the silvervoltameter (see Voltameter, Silver), but in which a copper anode and asolution of copper sulphate are substituted for the silver anode andsilver nitrate solution. One coulomb corresponds to .329 milligram or.005084 grain of copper deposited. It is not accepted as of as high astandard as the silver voltameter.The electrodes should be placed half an inch from each other. Two squareplate electrodes may conveniently be used, and not less than two squareinches on each plate should be the area per ampere of current.564 STANDARD ELECTRICAL DICTIONARY.Voltameter, Differential, Siemens'.A volume or gas voltameter with duplicate eudiometers and pairs ofelectrodes. It is used for determining the resistance of the platinumconductor used in his pyrometer. A current divides between the twovoltameters; in one branch of the circuit the platinum conductor isplaced, in the other a known resistance. The current strength varyinginversely with the resistance, the resistances of the two conductors areinversely proportional to the gas evolved.Voltameter, Gas.A voltameter whose indications are based on the electrolysis of water,made an electrolyte by the addition of sulphuric acid. The gases evolvedare measured. It may take several forms.In one form it is an apparatus consisting of a single eudiometer orgraduated glass tube with upper end closed and its lower end or mouthopen, collecting the mixture of hydrogen and oxygen.In the form shown in the cut three tubes are connected, the side tubesrepresenting eudiometers. For each side tube there is a platinumelectrode. In this apparatus the oxygen and hydrogen are connected inopposite tubes. A is an open tube filled with dilute sulphuric acid. Byopening the cocks on B and C they can both be completely filled withacid. As shown in the cut, this operation is not yet completed. Thehydrogen alone may in this case be measured.The mixed gas voltameter has only one eudiometer.The exact equivalents are only approximately known. The volume of mixedgases per coulomb is given as .1738 cubic centimeters (Ayrton); .172cubic centimeters (Hospitalier); and other values by other authorities.The hydrogen is equal to 1/3 of the mixed gases almost exactly.Synonyms--Volume Voltameter--Sulphuric Acid Voltameter.The gas is measured at 0º (32º F.) and 76 centimeters, or 30 inchesbarometer.Fig. 341. GAS VOLTAMETER.565 STANDARD ELECTRICAL DICTIONARY.If the gas is measured in cubic inches, the temperature in degrees F.,and the barometric height in inches, the following formula may be usedfor reduction to standard pressure and temperature. It is the volumecorresponding to one coulomb.( .01058 * 30 * (491 + Fº - 32) ) / (h* 491)For the metric measurements and degrees C.(.1738 * 76 * (273 + Cº)) / (h X 273)Voltameter, Silver.An apparatus consisting of a platinum vessel containing a solution ofsilver nitrate into which solution a silver anode dips, whose end iswrapped in muslin to prevent the detachment of any particles. When acurrent is passed by connecting one terminal to the dish and the otherto the rod, securing a proper direction of current, silver will bedeposited on the dish and the same amount will be dissolved from therod. The dish is weighed before and after the test. Its increase inweight gives the silver deposited.FIG. 342. SILVER VOLTAMETER.In the cut Ag is the silver anode, Pt is the platinum dish, r is theconducting rod, p is a wooden standard, Cu is a copper plate on whichthe dish rests and which also serves as a conductor and contact surface,b is a muslin cloth to place over the silver plate to prevent detachedparticles falling in the dish; s s' are the binding screws.The weight of silver corresponding to a coulomb is given variously bydifferent authorities. Ayrton and Daniell take 1.11815 milligrams or.017253 grain of metallic silver. Other determinations are as follows:1.1183 milligrams (Kohlrausch).1.124 " (Merscart).The solution of silver nitrate should be from 15 to 30 per cent. ofstrength. The current should not exceed one ampere per six squareinches; or in other words not more than about 3/1000 grain of silvershould be deposited per second on a square inch area of the dish. Theedge of the silver disc or anode should be about equidistant from theside and bottom of the dish. The latter notes are due to Lord Rayleigh.566 STANDARD ELECTRICAL DICTIONARY.Voltameter, Weight.A voltameter in which the amount of decomposition is determined byweighing the products, or one of the products of the electrolysis. Thetitles Voltameter, Copper, and Voltameter, Silver, may be cited.Fig. 343. WEIGHT VOLTAMETERS.In the cuts are shown examples of weight gas voltameters. These aretubes light enough to be weighed when charged. Each contains adecomposition cell T, with its platinum electrodes, and charged withdilute sulphuric acid, while t is calcium chloride or other drying agentto collect any water carried off as vapor or as spray by the escapinggases; c are corks placed in position when the weighing is beingexecuted, so as to prevent the calcium chloride from absorbing moisturefrom the air.In use the tubes are weighed. They are then connected to the circuit,after removal of the corks, and the decomposition proceeds. After asufficient time they are removed, the corks put in place, and they areweighed again. The loss gives the water decomposed.The water corresponding to one coulomb is.09326 milligram .001430 grain, Ayrton,.092 " Hospitalier,.0935 " Daniell.567 STANDARD ELECTRICAL DICTIONARY.Voltametric Law.The law on which voltameters are based. The amount of chemicaldecomposition produced by an electric current in a given electrolyte isproportional to the quantity of electricity passed through the solution.Fig. 344. VOLTA'S FUNDAMENTAL EXPERIMENT.Volta's Fundamental Experiment.The moistened finger is placed on the upper plate of a condensing orelectrophorous electroscope. The other hand holds a plate of zinc z,soldered to a plate of copper c. The lower plate is touched with thecopper. On removing the cover the gold leaves l diverge and withnegative electricity. Hence zinc is supposed to be positivelyelectrified when in contact with copper. The experiment is used todemonstrate the contact theory of electricity.568 STANDARD ELECTRICAL DICTIONARY.Volta's Law of Galvanic Action.The electro-motive force between any two metals in an electro-chemicalseries (see Electro-Chemical Series) is equal to the sum of theelectro-motive forces between all the intervening metals.Volta's Law of Thermo-electricity.In a compound circuit, consisting of a number of different metals, allpoints of which are at the same temperature, there is no current.Volt, B. A.The volt based on the B. A. ohm. It is equal to .9889 legal volt.Volt, Congress.The volt based upon the congress or legal ohm; the legal volt.Volt-coulomb.The unit of electric work; the watt-second; it is equivalent to1.0E7 ergs..24068 gram degree C. (calorie).737337 foot lbs.,.00134 horse power seconds.Volt Indicator.A form of easily read voltameter for use in electric light stations andfor similar work.Volt, Legal.The legal volt based upon the legal ohm. It is equal to 1.00112 B. A.volt.Voltmeter.An instrument for determining the potential difference of any twopoints.In many cases it is a calibrated galvanometer wound with a coil of highresistance. The object to be attained is that it shall receive only aninsignificant portion of current and that such portion shall suffice toactuate it. If connected in parallel with any portion of a circuit, itshould not noticeably diminish its resistance.The divisions into which ammeters range themselves answer forvoltmeters. In practice the same construction is adopted for both. Thedifferent definitions of ammeters in disclosing the general lines ofthese instruments are in general applicable to voltmeters, except thatthe wire winding of the coils must be of thin wire of great length. Thedefinitions of ammeters may be consulted with the above understandingfor voltmeters.In the use made of voltmeters there is a distinction from ammeters. Anammeter is a current measurer and all the current measured must bepassed through it. But while a voltmeter is in fact a current measurer,it is so graduated and so used that it gives in its readings thedifference of potential existing between two places on a circuit, andwhile measuring the current passing through its own coils, it is bycalibration made to give not the current intensity, but theelectro-motive force producing such current.In use it may be connected to two terminals of an open circuit, when asit only permits an inconsiderable current to pass, it indicates thepotential difference existing between such points on open circuit. Or itmay be connected to any two parts of a closed circuit. Owing to its highresistance, although it is in parallel with the intervening portion ofthe circuit, as it is often connected in practice, it is without anyappreciable effect upon the current. It will then indicate the potentialdifference existing between the two points.569 STANDARD ELECTRICAL DICTIONARY.Voltmeter, Battery.A voltmeter for use in running batteries. In one form (Wirt's) it isconstructed for a low range of voltage, reading up to two and a halfvolts and having exactly one ohm resistance, thus giving the batterysome work to do.Voltmeter, Cardew.A voltmeter in which the current passing through its conductor heatssuch conductor, causing it to expand. Its expansion is caused to move anindex needle. By calibration the movements of the needle are made tocorrespond to the potential differences producing the actuating currentsthrough it. The magnetic action of the current plays no part in itsoperation. It is the invention of Capt. Cardew, R. E.The construction of the instrument in one of its most recent forms isshown in the cut. On each side of the drum-like case of the instrumentare the binding screws. These connect with the blocks m and n. To thesethe fine wire conductor is connected and is carried down and up over thetwo pulleys seen at the lowest extremity, its centre being attached toc. From c a wire is carried to the drum p, shown on an enlarged scale onthe left of the cut. A second wire from the same drum or pulley connectsto the spring S. The winding of the two wires is shown in the separatefigure of c, where it is seen that they are screwed fast to theperiphery of the little drum, and are virtually continuations of eachother. By the screw A the tension of the spring S is adjusted.On the shaft of the little drum p is a pinion, which works into theteeth of the cog-wheel r. The shaft of r is extended through the dialof the instrument, and carries an index. The dial is marked off forvolts; g g and h h are standards for carrying the pulleys.570 STANDARD ELECTRICAL DICTIONARY.The action of the instrument is as follows. The current passing throughthe wire heats it. This current by Ohm's law is proportional to theelectro-motive force between the terminals. As it is heated it expandsand as it cools contracts, definite expanding and contractingcorresponding to definite potential differences. As the wire expands andcontracts the block or pin c moves back and forth, thus turning the drump and cogwheel r one way or permitting it to turn the other way underthe pull of the spring S.Fig. 345. CARDEW VOLTMETER.In this construction for a given expansion of the wire the piece c onlymoves one half as much. The advantage of using a wire twice as long aswould be required for the same degree of movement were the fullexpansion utilized is that a very thin wire can be employed. Such a wireheats and cools more readily, and hence the instrument reaches itsreading more quickly or is more deadbeat, if we borrow a phraseologyproperly applicable only to instruments with oscillating indexes.In the most recent instruments about thirteen feet of wire .0025 inch indiameter, and made of platinum-silver alloy is used.571 STANDARD ELECTRICAL DICTIONARY.If the potential difference to be measured lies between 30 and 120 voltsthe wire as described suffices. But to extend the range of theinstrument a resistance in series is required. If such resistance isdouble that of the instrument wire, and remains double whether thelatter is hot or cold the readings on the scale will correspond toexactly twice the number of volts. This is brought about in someinstruments by the introduction in series of a duplicate wire, preciselysimilar to the other wire, and like it, carried around pulleys and keptstretched by a spring.[Transcriber's note: If the series resistance is twice that of thevoltmeter, the indicated voltage will be ONE THIRD of the totalvoltage.]Thus whatever ratio of resistance exists between the two wires cold, itis always the same at any temperature, as they both increase intemperature at exactly the same rate. Tubes are provided to enclose thestretched wires and pulleys, which tubes are blackened.The voltmeter is unaffected by magnetic fields, and, as itsself-induction is very slight, it is much used for alternating currents.The tubes containing the wire may be three feet long.Its disadvantages are thus summarized by Ayrton. It absorbs a good dealof energy; it cannot be constructed for small potential differences, asthe wire cannot be made thicker, as it would make it more sluggish;there is vagueness in the readings near the zero point and sometimesinaccuracy in the upper part of the scale.Volts, Lost.The volts at the terminals of a dynamo at full load fall short of theirvalue on open circuit. The difference of the two values are termed lostvolts.Voltmeter, Electrostatic.A voltmeter based on the lines of the quadrant electrometer. It includestwo sets of quadrants, each oppositely excited by one of the two parts,whose potential difference is to be determined. They attract each otheragainst a controlling force as of gravity.One form has the two sets poised on horizontal axes, bringing the partsso that the flat quadrants move in vertical planes.In another form a number of quadrants are used in each set, the membersof the two sets alternating with each other. One set is fixed, theothers move and carry the index.Vulcanite.Vulcanized india rubber which by high proportion of sulphur and propervulcanization has been made hard. It is sometimes distinguished fromebonite as being comparatively light in color, often a dull red, whileebonite is black. For its electrical properties see Ebonite.Both substances have their defects, in producing surface leakage.Washing with weak ammonia, or with dilute soda solution, followed bydistilled water, is recommended for the surface, if there is any troublewith surface leakage. It may also be rubbed over with melted paraffinewax.