The Standard Electrical Dictionary / A Popular Dictionary of Words and Terms Used in the Practice of Electrical Engineering

by T. O'Conor Sloane

Fig. 144. ACTION OF MOLECULES IN A SOLUTION
BEFORE AND DURING ELECTROLYSIS.
The cut shows the assumed 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 mass, when the potential difference is
insufficient for decomposition. The third row indicates the
decomposition of a chain of molecules, one constituent separating at
each pole.
214 STANDARD ELECTRICAL DICTIONARY.
Electrolysis, Laws of.
The following are the principal 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 Grothüss'
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 quantity of electricity--that is the same current for the
same period----- decomposes chemically equivalent quantities of the
bodies it decomposes, or the weights of elements separated in
electrolytes by the same quantity of electricity (in coulombs or some
equivalent unit) are to each other as their chemical equivalent.
IV. The quantity 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 Analysis.
Chemical analysis by electrolysis. The quantitative separation of a
number of metals can be very effectively executed. Thus, suppose that a
solution of copper sulphate was to be analyzed. 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 pass 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
analysis include solution of the ores or other substances to be analyzed
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 analysis.
The entire subject has been worked out in considerable detail by
Classen, 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 establishing 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.)
215 STANDARD ELECTRICAL DICTIONARY.
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 constituent 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 Grothüss' Hypothesis--Electrolysis--
Electrolysis, Laws of--Electro-chemical Equivalent.)
Electro-magnet.
A mass, in practice always of iron, around which an electric circuit is
carried, insulated from the iron. When a current is passed through the
circuit the iron presents the characteristics of a magnet. (See
Magnetism, Ampére'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 mass 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. Assume 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 Ampérian 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
passage 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.
217 STANDARD ELECTRICAL DICTIONARY.

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.
Electro-magnet, Club-foot.
An electro-magnet, one of whose legs only is wound with wire, the other
being bare.

Fig. 148. CLUB-FOOT ELECTRO-MAGNETS WITH HINGED ARMATURES.
Electro-magnet, Hinged.
An electro-magnet whose limbs are hinged at the yoke. On excitation by a
current the poles tend to approach each other.