Muscle Shoals the plant for liquefying air, in order to get the nitrogen
out of it, consisted of two dozen towers each capable of producing 1765
cubic feet of pure nitrogen per hour. The air was drawn in through two
pipes, a yard across, and passed through scrubbing towers to remove
impurities. The air was then compressed to 600 pounds per square inch.
Nine tenths of the air was permitted to expand to 50 pounds and this
expansion cooled down the other tenth, still under high pressure, to the
liquefying point. Rectifying towers 24 feet high were stacked with trays
of liquid air from which the nitrogen was continually bubbling off since
its boiling point is twelve degrees centigrade lower than that of
oxygen. Pure nitrogen gas collected at the top of the tower and the
residual liquid air, now about half oxygen, was allowed to escape at the
bottom.

The nitrogen was then run through pipes into the lime-nitrogen ovens.
There were 1536 of these about four feet square and each holding 1600
pounds of pulverized calcium carbide. This is at first heated by an
electrical current to start the reaction which afterwards produces
enough heat to keep it going. As the stream of nitrogen gas passes over
the finely divided carbide it is absorbed to form calcium cyanamid as
described on a previous page. This product is cooled, powdered and wet
to destroy any quicklime or carbide left unchanged. Then it is charged
into autoclaves and steam at high temperature and pressure is admitted.
The steam acting on the cyanamid sets free ammonia gas which is carried
to towers down which cold water is sprayed, giving the ammonia water,
familiar to the kitchen and the bathroom.

But since nitric acid rather than ammonia was needed for munitions, the
oxygen of the air had to be called into play. This process, as already
explained, is carried on by aid of a catalyzer, in this case platinum