of carbonic acid, produced by the combustion of the elements of
the blood. In an air-tight enclosure, then, after a certain
time, all the oxygen of the air will be replaced by the carbonic
acid-- a gas fatal to life. There were two things to be done
then-- first, to replace the absorbed oxygen; secondly, to
destroy the expired carbonic acid; both easy enough to do, by
means of chlorate of potassium and caustic potash. The former
is a salt which appears under the form of white crystals; when
raised to a temperature of 400 degrees it is transformed into
chlorure of potassium, and the oxygen which it contains is
entirely liberated. Now twenty-eight pounds of chlorate of
potassium produces seven pounds of oxygen, or 2,400 litres-- the
quantity necessary for the travelers during twenty-four hours.

Caustic potash has a great affinity for carbonic acid; and it is
sufficient to shake it in order for it to seize upon the acid
and form bicarbonate of potassium. By these two means they
would be enabled to restore to the vitiated air its life-
supporting properties.

It is necessary, however, to add that the experiments had
hitherto been made _in anima vili_. Whatever its scientific
accuracy was, they were at present ignorant how it would answer
with human beings. The honor of putting it to the proof was
energetically claimed by J. T. Maston.

"Since I am not to go," said the brave artillerist, "I may at
least live for a week in the projectile."

It would have been hard to refuse him; so they consented to