Ozone is a form of oxygen. It is different from ordinary oxygen in that the molecule consists of three atoms of oxygen instead of two. It is a bluish gas that can be formed by passing an electrical discharge through oxygen. Thus lightning is a natural means of producing ozone. Ozone can be produced mechanically by passing air between highly-charged electrical plates of a special machine. Ozone is also formed by the arcs from electric motor brushes, and can be identified by the rather penetrating odor associated with running motors.
In the upper atmosphere, ozone is produced when ultraviolet sunlight strikes oxygen. Because these rays are harmful in great amounts, it is advantageous that they are absorbed. The ozone which is produced in the upper atmosphere is wafted downward by convection currents. Only minute quantities are in the atmosphere man breathes, however, and in small amounts this poisonous gas gives an invigorating touch to the air and can be tolerated.
Ozone is chemically active because the extra atom of oxygen is loosely held and combines readily with substances. It is used for certain cleaning and purifying processes.
