electrolytic separation A method
of separating isotopes by exploiting
the different rates at which they are
released in electrolysis. It was for-
merly used for separating deuterium
and hydrogen. On electrolysis of
water, hydrogen is formed at the
cathode more readily than deu-
terium, thus the water becomes en-
riched with deuterium oxide.electromagnetic radiation En-
ergy resulting from the acceleration
of electric charge and the associated
electricÜelds and magneticÜelds.
The energy can be regarded as waves
propagated through space (requiring
no supporting medium) involving os-
cillating electric and magneticÜelds
at right angles to each other and to
the direction of propagation. In a vac-
uum the waves travel with a con-
stant speed (the speed of light) of
2.9979× 108 metres per second; if
material is present they are slower.
Alternatively, the energy can be re-
garded as a stream of *photons trav-
elling at the speed of light, each
photon having an energy hc/λ, where
h is the Planck constant, c is the
speed of light, and λis the wave-
length of the associated wave. A fu-
sion of these apparently conÛicting
concepts is possible using the meth-
ods of *quantum mechanics. The
characteristics of the radiation de-
pend on its wavelength. See electro-
magnetic spectrum.
electromagnetic spectrum The
range of wavelengths over which
electromagnetic radiation extends.
The longest waves (10^5 –10–3metres)
are radio waves, the next longest
(10–3–10–6m) are infrared waves,
then comes the narrow band (4–7 ×
10 –7m) of visible radiation, followed
by ultraviolet waves (10–7–10–9m)
and *X-rays and gamma radiation
(10–9–10–14m).electromeric effect See elec-
tronic effects.electrometallurgy The uses of
electrical processes in the separation
of metals from their ores, the reÜn-
ing of metals, or the forming or plat-
ing of metals.
electromotive force (e.m.f.)The
greatest potential difference that can
be generated by a particular source
of electric current. In practice this
may be observable only when the
source is not supplying current, be-
cause of its internal resistance.electromotive series (electro-
chemical series)A series of chemical
elements arranged in order of their
*electrode potentials. The hydrogen
electrode (H++ e →½H 2 ) is taken as
having zero electrode potential. El-
ements that have a greater tendency
than hydrogen to lose electrons to
their solution are taken as elec-
tropositive; those that gain electrons
from their solution are below hydro-
gen in the series and are called elec-
tronegative. The series shows the
order in which metals replace one
another from their salts; electroposi-
tive metals will replace hydrogen
from acids. The chief metals and hy-
drogen, placed in order in the series,
are: potassium, calcium, sodium,
magnesium, aluminium, zinc,
cadmium, iron, nickel, tin, lead,
hydrogen, copper, mercury, silver,
platinum, gold. This type of series is
sometimes referred to as an activity
series.electron An elementary particle
with a rest mass of 9.109 3897(54) ×
10 –31kg and a negative charge of
1.602 177 33(49) × 10 –19coulomb.
Electrons are present in all atoms in
groupings called shells around the
nucleus; when they are detached
from the atom they are called freeelectrolytic separation 196e