NN + OO --> NO + NO
nitrogen oxygen nitric oxide

The --> represents Jove's thunderbolt, a stroke of artificial
lightning. We see on the left the molecules of oxygen and nitrogen,
before taking the electric treatment, as separate elemental pairs, and
then to the right of the arrow we find them as compound molecules of
nitric oxide. This takes up another atom of oxygen from the air and
becomes NOO, or using a subscript figure to indicate the number of atoms
and so avoid repeating the letter, NO_{2} which is the familiar nitro
group of nitric acid (HO--NO_{2}) and of its salts, the nitrates, and of
its organic compounds, the high explosives. The NO_{2} is a brown and
evil-smelling gas which when dissolved in water (HOH) and further
oxidized is completely converted into nitric acid.

The apparatus which effects this transformation is essentially a
gigantic arc light in a chimney through which a current of hot air is
blown. The more thoroughly the air comes under the action of the
electric arc the more molecules of nitrogen and oxygen will be broken up
and rearranged, but on the other hand if the mixture of gases remains in
the path of the discharge the NO molecules are also broken up and go
back into their original form of NN and OO. So the object is to spread
out the electric arc as widely as possible and then run the air through
it rapidly. In the Schönherr process the electric arc is a spiral flame
twenty-three feet long through which the air streams with a vortex
motion. In the Birkeland-Eyde furnace there is a series of semi-circular
arcs spread out by the repellent force of a powerful electric magnet in
a flaming disc seven feet in diameter with a temperature of 6300° F. In
the Pauling furnace the electrodes between which the current strikes