We are concerned with a chemical phenomenon of the simplest possible
kind. Gaseous nitrogen combines with gaseous hydrogen in simple quantitative
proportions to produce gaseous ammonia. The three substances involved
have been well known to the chemist for over a hundred years. During the
second half of the last century each of them has been studied hundreds of
times in its behaviour under various conditions during a period in which a
flood of new chemical knowledge became available. If it has not been until
the present century that the production of ammonia from the elements has
been discovered, this is due to the fact that very special equipment must be
used and strict conditions must be adhered to if one is to succeed in obtaining
spontaneous combination of nitrogen and hydrogen on a substantial scale,
and that a combination of experimental success with thermodynamic considerations
was needed.