All these mechanical appliances, admirably set, worked with the greatest ease, and the engineers had not shown themselves less intelligent in the arrangement of the projectile compartment.

Lockers solidly fastened were destined to contain the water and provisions necessary for the three travellers; they could even procure themselves fire and light by means of gas stored up in a special case under a pressure of several atmospheres.  All they had to do was to turn a tap, and the gas would light and warm this comfortable vehicle for six days.  It will be seen that none of the things essential to life, or even to comfort, were wanting.  More, thanks to the instincts of Michel Ardan, the agreeable was joined to the useful under the form of objects of art; he would have made a veritable artist’s studio of his projectile if room had not been wanting.  It would be mistaken to suppose that three persons would be restricted for space in that metal tower.  It had a surface of 54 square feet, and was nearly 10 feet high, and allowed its occupiers a certain liberty of movement.  They would not have been so much at their ease in the most comfortable railway compartment of the United States.

The question of provisions and lighting having been solved, there remained the question of air.  It was evident that the air confined in the projectile would not be sufficient for the travellers’ respiration for four days; each man, in fact, consumes in one hour all the oxygen contained in 100 litres of air.  Barbicane, his two companions, and two dogs that he meant to take, would consume every twenty-four hours 2,400 litres of oxygen, or a weight equal to 7 lbs.  The air in the projectile must, therefore, be renewed.  How?  By a very simple method, that of Messrs. Reiset and Regnault, indicated by Michel Ardan during the discussion of the meeting.

It is known that the air is composed principally of twenty-one parts of oxygen and seventy-nine parts of azote.  Now what happens in the act of respiration?  A very simple phenomenon, Man absorbs the oxygen of the air, eminently adapted for sustaining life, and throws out the azote intact.  The air breathed out has lost nearly five per cent, of its oxygen, and then contains a nearly equal volume of carbonic acid, the definitive product of the combustion of the elements of the blood by the oxygen breathed in it.  It happens, therefore, that in a confined space and after a certain time all the oxygen of the air is replaced by carbonic acid, an essentially deleterious gas.

The question was then reduced to this, the azote being conserved intact—­1.  To remake the oxygen absorbed; 2.  To destroy the carbonic acid breathed out.  Nothing easier to do by means of chlorate of potash and caustic potash.  The former is a salt which appears under the form of white crystals; when heated to a temperature of 400 deg. it is transformed into chlorine of potassium, and the oxygen which it contains is given off freely.  Now 18 lbs. of chlorate of potash give 7 lbs of oxygen—­that is to say, the quantity necessary to the travellers for twenty-four hours.