The steel cylinders standing in the background are packed with the
carbide and then put into the ovens sunk in the floor. When these are
heated internally by electricity to 2000 degrees Fahrenheit pure
nitrogen is let in and absorbed by the carbide, making cyanamid, which
may be used as a fertilizer or for ammonia.]
[Illustration: Photo by International Film Service
A BARROW FULL OF POTASH SALTS EXTRACTED FROM SIX TONS OF GREEN KELP BY
THE GOVERNMENT CHEMISTS]
[Illustration: NATURE'S SILENT METHOD OF NITROGEN FIXATION
The nodules on the vetch roots contain colonies of bacteria which have
the power of taking the free nitrogen out of the air and putting it in
compounds suitable for plant food.]
The modern agriculturist realizes that the soil is a laboratory for the
production of plant food and he ordinarily takes more pains to provide a
balanced ration for it than he does for his family. Of course the
necessity of feeding the soil has been known ever since man began to
settle down and the ancient methods of maintaining its fertility, though
discovered accidentally and followed blindly, were sound and
efficacious.
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