Man's physical universe

xanabras

AIR AND WATER AS RAW MATERIALS 659

on a commercial scale.

Four fifths of the air is nitrogen, but nitrogen

is so inert that up to a few years before 1914 all efforts to combine it

(this process is called fixation) with other elements on a large scale had

met with failure. Here was a job which required the aid of a catalyst.

Fritz Haber's nitrogen-fixation method, which involved the heating

of nitrogen and hydrogen under pressure in the presence of certain

catalysts, was rapidly developed on a large scale in Germany when it

became evident that the war was going to last longer than was expected.

The hydrogen for this reaction may be prepared from water by electrolysis

or by the action of steam on coke.

C + 2H2O —>- CO2 + 2H2

coke steam carbon dioxide hydrogen

The first commercially successful nitrogen-fixation process was the

arc process, in which nitrogen and oxygen combine when passed

through an electric arc. This process is too expensive except where

very cheap power is available, as in Norway.

The next process to be developed was the cyanamide process.

Cyanamide plants were built throughout the world during the eight

years preceding World War I. This process, it will be recalled, consists

in

heating calcium carbide with nitrogen to form calcium cyanamide.

After the war broke out, it became difficult to obtain information

concerning the new Haber process; so the United States, forced to

provide a nitrogen supply that would not have to be transported by

steamer from Chile, selected the cyanamide process.

It therefore constructed

the largest cyanamide plant in the world at Muscle Shoals,

Alabama, which, however, had never been in operation up to 1941 due

to economic and political reasons.

During the war Germany constructed several cyanamide plants, the

one at Merseburg alone having a production capacity corresponding

to about two thirds of the previous total annual shipments from Chile.

In recent years several new processes for the fixation of nitrogen have

been developed, and nitrogen-fixation plants have entered into competition

with Chilean nitrates throughout the world. Today about

20 per cent of the world's nitrogen supply comes from Chile; 10 per cent

comes from coal in the by-product coke ovens; and the rest comes

from nitrogen-fixation processes.

Nitric Acid Is Now Prepared from Ammonia.

Ammonia, prepared by the Haber process, may be oxidized by passing

a mixture of ammonia and air through chambers containing such

catalysts as iron oxide or platinum gauze to form nitrogen dioxide,

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