The Standard Electrical Dictionary Part 60

The decomposition proceeds subject to the laws of electrolysis. (See Electrolysis, Laws of.) For decomposition to be produced there is for each compound a minimum electro-motive force or potential difference required. The current pa.s.ses through the electrolyte or substance undergoing decomposition entirely by Electrolytic Conduction, q. v. in accordance with Groth?ss' Hypothesis, q. v. The electrolyte therefore must be susceptible of diffusion and must be a fluid.

The general theory holds that under the influence of a potential difference between electrodes immersed in an electrolyte, the molecules touching the electrodes are polarized, in the opposite sense for each electrode. If the potential difference is sufficient the molecules will give up one of their binary const.i.tuents to the electrode, and the other const.i.tuent will decompose the adjoining molecule, and that one being separated into the same two const.i.tuents will decompose its neighbor, and so on through the ma.s.s until the other electrode is reached. This one separates definitely the second binary const.i.tuent from the molecules touching it.

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Thus there is an exact balance preserved. Just as many molecules are decomposed at one electrode as at the other, and the exact chain of decomposition runs through the ma.s.s. Each compound electrolyzed develops a binary or two-fold composition, and gives up one const.i.tuent to one electrode and the other to the other.

Fig. 144. ACTION OF MOLECULES IN A SOLUTION BEFORE AND DURING ELECTROLYSIS.

The cut shows the a.s.sumed polarization of an electrolyte. The upper row shows the molecules in irregular order before any potential difference has been produced, in other words, before the circuit is closed. The next row shows the first effects of closing the circuit, and also indicates the polarization of the ma.s.s, when the potential difference is insufficient for decomposition. The third row indicates the decomposition of a chain of molecules, one const.i.tuent separating at each pole.

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Electrolysis, Laws of.

The following are the princ.i.p.al laws, originally discovered by Faraday, and sometimes called Faraday's Laws of Electrolysis:

1. Electrolysis cannot take place unless the electrolyte is a conductor.

Conductor here means an electrolytic conductor, one that conducts by its own molecules traveling, and being decomposed. (See Groth?ss'

Hypothesis.)

II. The energy of the electrolytic action of the current is the same wherever exercised in different parts of the circuit.

III. The same quant.i.ty of electricity--that is the same current for the same period----- decomposes chemically equivalent quant.i.ties of the bodies it decomposes, or the weights of elements separated in electrolytes by the same quant.i.ty of electricity (in coulombs or some equivalent unit) are to each other as their chemical equivalent.

IV. The quant.i.ty of a body decomposed in a given time is proportional to the strength of the current.

To these may be added the following:

V. A definite and fixed electro-motive force is required for the decomposition of each compound, greater for some and less for others.

Without sufficient electro-motive force expended on the molecule no decomposition will take place. (See Current, Convective.)

Electrolyte.

A body susceptible of decomposition by the electric current, and capable of electrolytic conduction. It must be a fluid body and therefore capable of diffusion, and composite in composition. An elemental body cannot be an electrolyte.

Electrolytic a.n.a.lysis.

Chemical a.n.a.lysis by electrolysis. The quant.i.tative separation of a number of metals can be very effectively executed. Thus, suppose that a solution of copper sulphate was to be a.n.a.lyzed. A measured portion of the solution would be introduced into a weighed platinum vessel. The vessel would be connected to the zinc plate terminal of a battery. From the other terminal of the battery a wire would be brought and would terminate in a plate of platinum. This would be immersed in the solution in the vessel. As the current would pa.s.s the copper sulphate would be decomposed and eventually all the copper would be deposited in a firm coating on the platinum. The next operations would be to wash the metal with distilled water, and eventually with alcohol, to dry and to weigh the dish with the adherent copper. On subtracting the weight of the dish alone from the weight of the dish and copper, the weight of the metallic copper in the solution would be obtained.

In similar ways many other determinations are effected. The processes of a.n.a.lysis include solution of the ores or other substances to be a.n.a.lyzed and their conversion into proper form for electrolysis. Copper as just described can be precipitated from the solution of its sulphate. For iron and many other metals solutions of their double alkaline oxalates are especially available forms for a.n.a.lysis.

The entire subject has been worked out in considerable detail by Cla.s.sen, to whose works reference should be made for details of processes.

Electrolytic Convection.

It is sometimes observed that a single cell of Daniell battery, for instance, or other source of electric current establis.h.i.+ng too low a potential difference for the decomposition of water seems to produce a feeble but continuous decomposition. This is very unsatisfactorily accounted for by the hydrogen as liberated combining with dissolved oxygen. (Ganot.) The whole matter is obscure. (See Current, Convection.)

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Electrolytic Conduction.

Conduction by the travel of atoms or radicals from molecule to molecule of a substance with eventual setting free at the electrodes of the atoms or radicals as elementary molecules or const.i.tuent radicals. A substance to be capable of acting as an electrolytic conductor must be capable of diffusion, and must also have electrolytic conductivity. Such a body is called an electrolyte. (See Groth?ss' Hypothesis--Electrolysis-- Electrolysis, Laws of--Electro-chemical Equivalent.)

Electro-magnet.

A ma.s.s, in practice always of iron, around which an electric circuit is carried, insulated from the iron. When a current is pa.s.sed through the circuit the iron presents the characteristics of a magnet. (See Magnetism, Amp?re's Theory of--Solenoid--Lines of Force.) In general terms the action of a circular current is to establish lines of force that run through the axis of the circuit approximately parallel thereto, and curving out of and over the circuit, return into themselves outside of the circuit. If a ma.s.s of iron is inserted in the axis or elsewhere near such current, it multiplies within itself the lines of force, q. v.

(See also Magnetic Permeability--Permeance--Magnetic Induction, Coefficient of Magnetic Susceptibility--Magnetization, Coefficient of Induced.) These lines of force make it a magnet. On their direction, which again depends on the direction of the magnetizing current, depends the polarity of the iron. The strength of an electro-magnet, below saturation of the core (see Magnetic Saturation), is proportional nearly to the ampere-turns, q. v. More turns for the same current or more current for the same turns increase its strength.

In the cut is shown the general relation of current, coils, core and line of force. a.s.sume that the magnet is looked at endwise, the observer facing one of the poles; then if the current goes around the core in the direction opposite to that of the hands of a clock, such pole will be the north pole. If the current is in the direction of the hands of a clock the pole facing the observer will be the south pole. The whole relation is exactly that of the theoretical Amp?rian currents, already explained. The direction and course of the lines of force created are shown in the cut.

The shapes of electro-magnets vary greatly. The cuts show several forms of electro-magnets. A more usual form is the horseshoe or double limb magnet, consisting generally of two straight cores, wound with wire and connected and held parallel to each other by a bar across one end, which bar is called the yoke.

In winding such a magnet the wire coils must conform, as regards direction of the current in them to the rule for polarity already cited.

If both poles are north or both are south poles, then the magnet cannot be termed a horseshoe magnet, but is merely an anomalous magnet. In the field magnets of dynamos the most varied types of electro-magnets have been used. Consequent poles are often produced in them by the direction of the windings and connections.

To obtain the most powerful magnet the iron core should be as short and thick as possible in order to diminish the reluctance of the magnetic circuit. To obtain a greater range of action a long thin shape is better, although it involves waste of energy in its excitation.

216 STANDARD ELECTRICAL DICTIONARY.

Fig. 145 DIAGRAM OF AN ELECTRO-MAGNET SHOWING RELATION OF CURRENT AND WINDING TO ITS POLARITY AND LINES OF FORCE.

Fig. 146. ANNULAR ELECTRO-MAGNET

Electro-magnet, Annular.

An electro-magnet consisting of a cylinder with a circular groove cut in its face, in which groove a coil of insulated wire is placed. On the pa.s.sage of a current the iron becomes polarized and attracts an armature towards or against its grooved face. The cut shows the construction of an experimental one. It is in practice applied to brakes and clutches.

In the cut of the electro-magnetic brake (see Brake, Electro-magnetic), C is the annular magnet receiving its current through the brushes, and pressed when braking action is required against the face of the moving wheel. The same arrangement, it can be seen, may apply to a clutch.

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Fig. 147. BAR ELECTRO-MAGNET.

Electro-magnet, Bar.

A straight bar of iron surrounded with a magnetizing coil of wire. Bar electromagnets are not much used, the horseshoe type being by far the more usual.