udden demand for immense quantities of hydrogen and all manner of means
was taken to get it. Water is easily decomposed into hydrogen and oxygen
by passing an electric current through it. In various electrolytical
processes hydrogen has been a wasted by-product since the balloon demand
was slight and it was more bother than it was worth to collect and
purify the hydrogen. Another way of getting hydrogen in quantity is by
passing steam over red-hot coke. This produces the blue water-gas, which
contains about 50 per cent. hydrogen, 40 per cent. carbon monoxide and
the rest nitrogen and carbon dioxide. The last is removed by running the
mixed gases through lime. Then the nitrogen and carbon monoxide are
frozen out in an air-liquefying apparatus and the hydrogen escapes to
the storage tank. The liquefied carbon monoxide, allowed to regain its
gaseous form, is used in an internal combustion engine to run the plant.

There are then many ways of producing hydrogen, but it is so light and
bulky that it is difficult to get it where it is wanted. The American
Government in the war made use of steel cylinders each holding 161 cubic
feet of the gas under a pressure of 2000 pounds per square inch. Even
the hydrogen used by the troops in France was shipped from America in
this form. For field use the ferro-silicon and soda process was adopted.
A portable generator of this type was capable of producing 10,000 cubic
feet of the gas per hour.

The discovery by a Kansas chemist of natural sources of helium may make
it possible to free ballooning of its great danger, for helium is
non-inflammable and almost as light as hydrogen.

Other uses of hydrogen besides ballooning have already been referred to
in other chapters. It is combined with nitrogen to form synthetic
ammonia. It is combined with oxygen in the oxy-hydrogen blowpipe to
produce heat. It is combined with vegetable and animal oils to convert
them into solid fats. There is also the possibility of using it as a
fuel in the internal combustion engine in place of gasoline, but for
this purpose we must find some way of getting hydrogen portable or
producible in a compact form.

Aluminum, like silicon, sodium and calcium, has been rescued by violence
from its attachment to oxygen and like these metals it reverts with
readiness to its former affinity. Dr. Goldschmidt made use of this
reaction in his thermit process. Powdered aluminum is mixed with iron
oxide (rust). If the mixture i