of increasing its volume. Such inconveniences become serious with
dirigible balloons, whose surface, on the contrary, it is necessary to
diminish as much as possible. When the increasing interest taken in
aerostation at Paris was observed, an assured annual output of some
hundreds of cubic meters of eras for the sole use of balloons was
foreseen, the adoption of pure hydrogen being only a question of the
net cost.

Pure or slightly carbureted hydrogen is capable of being substituted
to advantage for coal gas for heating or lighting. Such an application
is doubtless somewhat premature, but we shall see that it has already
got out of the domain of Utopia. Finally the oxyhydrogen blowpipe,
which is indispensable for the treatment of very refractory metals,
consumes large quantities of hydrogen and oxygen.

For a few years past, oxygen has been employed in therapeutics; it is
found in commerce either in a gaseous state or in solution in water
(in siphons); it notably relieves persons afflicted with asthma or
depression; and the use of it is recommended in the treatment of
albumenuria. Does it cure, or at least does it contribute to cure,
anæmia, that terrible affection of large cities, and the prime source
of so many other troubles? Here the opinions of physicians and
physiologists are divided, and we limit ourselves to a mention of the
question without discussing it.

Only fifteen years ago it would have been folly to desire to obtain
remunerative results through the electrolysis of water. Such research
was subordinated to the industrial production of electric energy.

We shall not endeavor to establish the priority of the experiments and