In the formation of new compounds they
unite, and in the breaking up of existing compounds they separate.
The uniting of oxygen is no exception to this general law. All of its
combinations are brought about by the uniting of its atoms. In the burning
of carbon, for example, the atoms of oxygen and the atoms of carbon unite,
forming molecules of the compound known as carbon dioxide. The chemical
formula of this compound, which is CO_2, shows the proportion in which the
atoms unite--one atom of carbon uniting with two atoms of oxygen in each of
the molecules. The affinity of oxygen for other elements, and the affinity
of other elements for oxygen, and for each other, resides in their atoms.
*Oxidation.*--The uniting of oxygen with other elements is termed
_oxidation_. This may take place slowly or rapidly, the two rates being
designated as _slow_ oxidation and _rapid_ oxidation. Examples of slow
oxidation are found in certain kinds of decay and in the rusting of iron.
Combustion is an example of rapid oxidation. Slow and rapid oxidation,
while differing widely in their effects upon surrounding objects, are
alike in that both produce heat and form compounds of oxygen. In slow
oxidation, however, the heat may come off so gradually that it is not
observed.
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