There now remained only the question of air; for allowing for the consumption of air by Barbicane, his two companions, and two dogs which he proposed taking with him, it was necessary to renew the air of the projectile. Now air consists principally of twenty-one parts of oxygen and seventy-nine of nitrogen. The lungs absorb the oxygen, which is indispensable for the support of life, and reject the nitrogen. The air expired loses nearly five per cent. of the former and contains nearly an equal volume 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° it is transformed into chlorate of potass, and the oxygen which it contains is entirely liberated. Now twenty-eight pounds of chlorate of potassium produce seven pounds of oxygen, or 2400 _litres_—the quantity necessary for the travellers 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 bi-carbonate of potass. 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 honour 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 his wish. A sufficient quantity of chlorate of potassium and of caustic potash was placed at his disposal, together with provisions for eight days. And having shaken hands with his friends, on the 12th November, at six o'clock a.m., after strictly informing them not to open his prison before the 20th, at six o'clock p.m., he slid down the projectile, the plate of which was at once hermetically sealed. What did he do with himself during that week? They could get no information. The thickness of the walls of the projectile prevented any sound reaching from the inside to the outside. On the 20th of November, at six p.m. exactly, the plate was opened. The friends of J. T. Maston had been all along in a state of much anxiety; but they were promptly reassured on hearing a jolly voice shouting a boisterous hurrah. Presently afterwards the secretary of the Gun Club appeared at the top of the cone in a triumphant attitude. He had grown fat!