REACTIONS OF OXIDATION AND REDUCTION 125the cathode. If the anode were of an unattackable material, such
as platinum, the current would have to pass the anode surface by
some different mechanism. As a matter of fact, oxygen gas es-
capes at a platinum anode in a CuSO 4 solution, the mechanism
being indicated in the equation
sor~ + H 2 O -»2H+sor~ + ^o 2 + 20It should be remarked that just as the symbol Cu stands for
63.6 grams of copper or 6.06 X 10^23 actual atoms, the symbol ©
stands for 96,500 coulombs of electricity or 6.06 X 10^23 actual
electrons.
It should also be stated, to make the relation of positive and
negative electricity clearer, that neutral atoms of elements ap-
parently contain both positive and negative electricity in equal
amounts. The positive electricity is confined within the structure
of the atom. In chemical changes atoms may alter their net
charge by the loss or gain of a small number of electrons without
destroying their identity.
Electric currents forced through chemical cells from an outside
source of energy such as a dynamo can force chemical reactions of
oxidation and reduction to take place. Reactions of oxidation
and reduction which will take place spontaneously under their
own power may on the other hand cause a current to flow through
an external metallic conductor if the solutions and electrodes are
properly arranged. For example, if zinc is placed in a copper
sulphate solution, zinc passes into solution and copper is deposited.
No useful electric current is thereby generated. To dispose the
materials of this reaction so that an external current will flow let
us place a porous clay jar in a beaker; in the porous jar let us place
a copper sulphate solution in which dips a copper electrode; out-
side the porous jar in the beaker let us place zinc sulphate solution
in which dips a zinc electrode. The pores of the clay jar become
filled with solution so that ions can pass through, but the jar pre-
vents the copper sulphate solution mixing with the solution in con-
tact with the zinc. The oxidizing agent, Cu++ ions, and the re-
ducing agent, Zn, are remote from each other. Now if the zinc
and copper electrodes are connected by a wire, a current flows,
and zinc dissolves from the zinc electrode and copper deposits on
the copper electrode: Zn -> Zn++ + 28; 20 + Cu++ -> Cu.
The electrons passing through the wire constitute the current in