An allotropic form of oxygen. It possesses much more energetic chemical
properties than oxygen. It is supposed to contain three atoms of oxygen
in its molecule, represented thus:
O
/ \
O—O

It is produced by electric discharges and it is its peculiar odor which
is noticed about an electric machine, and sometimes in a thunderstorm
near the path of a lightning flash.

In the electrolysis of water some ozone may be produced, thus
diminishing the volume of the oxygen or of the mixed gases given off.
This is a source of inaccuracy in a gas voltameter.