Then pieces of the calcium
are spread out in an oven heated by electricity and a current of dry
hydrogen passed through. The gas is absorbed by the metal, forming the
hydride (CaH_{2}). This is packed up in cans and when hydrogen is
desired it is simply dropped into water, when it gives off the gas just
as calcium carbide gives off acetylene.
This last reaction was also used in Germany for filling Zeppelins. For
calcium carbide is convenient and portable and acetylene, when it is
once started, as by an electric shock, decomposes spontaneously by its
own internal heat into hydrogen and carbon. The latter is left as a
fine, pure lampblack, suitable for printer's ink.
Napoleon, who was always on the lookout for new inventions that could be
utilized for military purposes, seized immediately upon the balloon as
an observation station. Within a few years after the first ascent had
been made in Paris Napoleon took balloons and apparatus for generating
hydrogen with him on his "archeological expedition" to Egypt in which he
hoped to conquer Asia.
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