In only one respect has the study of indirect methods of synthesizing ammonia
from the elements been able to get round the difficulties. Frank and
Caro obtained the important calcium cyanamide through the action of nitrogen
on calcium carbide obtained from lime and coal in the electric arc.
Splitting the calcium cyanamide with water produces ammonia, and the
process takes place in the soil without any particular help from us, once the
cyanamide has been added to the soil as fertilizer. The saving in factory processing
achieved by this, plus the fact that the only raw materials required
are lime, coal and nitrogen, have been important factors in the establishment
of the process