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.