The high temperature changing the chlorate into a chloride, the oxygen was disengaged gradually but abundantly, every eighteen pounds of chlorate of potash, furnishing the seven pounds of oxygen necessary for the daily consumption of the inmates of the Projectile.
Still--as the reader need hardly be reminded--it was not sufficient to renew the exhausted oxygen; the complete purification of the air required the absorption of the carbonic acid, exhaled from the lungs.
For nearly 12 hours the atmosphere had been gradually becoming more and more charged with this deleterious gas, produced from the combustion of the blood by the inspired oxygen.

The Captain soon saw this, by noticing with what difficulty Diana was panting.

She even appeared to be smothering, for the carbonic acid--as in the famous _Grotto del Cane_ on the banks of Lake Agnano, near Naples--was collecting like water on the floor of the Projectile, on account of its great specific gravity.

It already threatened the poor dog's life, though not yet endangering that of her masters.

The Captain, seeing this state of things, hastily laid on the floor one or two cups containing caustic potash and water, and stirred the mixture gently: this substance, having a powerful affinity for carbonic acid, greedily absorbed it, and after a few moments the air was completely purified.
The others had begun by this time to check off the state of the instruments.