28 THE ELEMENTS.
METALS BY ELECTROLYSIS.
- Lithium from Fused Lithium Chloride.
Fused lithium chloride, like the aqueous solution of this salt, is largely-
ionized and consequently can act as an electrolyte. According to the present
theory, the passage of an electric current represents a movement of tiny
particles of negative electricity called electrons (cf. p. 9). If an electric current
passes through an electrolyte there is always chemical decomposition at each
electrode, an oxidation at the anode and a reduction at the cathode. Thus
the electrolysis of fused lithium chloride results in the simultaneous formation
of metallic lithium at the cathode and chlorine gas at the anode. At the
cathode, where the negatively-charged electrons pass from the wire to the
electrolyte, the positively-charged lithium ions are neutralized and neutral,
or free, lithium is formed. At the anode, where electrons leave the fused salt
and pass to the anode and thence to the conducting wire, each negatively-
charged chloride ion gives up one electron and neutral, or free, chlorine results.
These reactions of reduction (lithium) and oxidation (chlorine) can be ex-
pressed by the following equations in which the symbol e is used to represent
the electron, or unit charge of negative electricity
2 Li+ + 2 e = 2 Li 2 Cl~ .= CI 2 + 2 t.The electron, therefore, represents one unit negative charge, such as is repre-
sented by the negative charge on one atom of chlorine in the chloride ion.
Although it seems probable from the results of several methods of experimen-
tation that there are about 6.1 X 10^23 atoms of lithium in one gram atom, so
that we have a fairly good idea as to the actual magnitude of the unit charge
of electricity, it is more advantageous to think in terms of the gram atom
which, in the case of lithium or any other univalent ion, bears a charge of
6.1 X 10^23 units of electricity. This larger value corresponds to 96,500
coulombs or 26.82 ampere hours and represents the quantity of electricity
required to set free 6.940 grams of lithium and 35.46 grams of chlorine when
all of the electrical current passing through fused lithium chloride is utilized
for producing lithium at the cathode and chlorine at the anode. Thus, with
100% current yield, a current of one ampere passing through lithium chloride
a 04.0 v QAOO
for one hour (3600 seconds) will set free " n = °-^2589 S- of lithium
y Oj ouu
and^35 "^4 -^6 ,^-.^3600 = 1.322 g. of chlorine. Or, since at 0° and 760 mm.
pressure, one molecule of chlorine or any other gas occupies a volume of about
22.4 liters, one can say that 96,500 coulombs will liberate 11.2 liters of chlorine
gas. This quantity of electricity, 96,500 coulombs, is called one Faraday,
because Michael Faraday recognized about the year 1835 that the quantities
of different elements liberated by a given quantity of electricity were propor-
tional to the atomic weights, or simple multiples of the atomic weights, of
the elements (Faraday's law).