"And we're rapidly breathing that up," added Captain Weston solemnly.
"Can't you make more?" cried Mr. Damon. "I thought you said you could make oxygen aboard the ship."
"We can," answered Mr. Swift, "but I did not bring along a supply of the necessary chemicals. I did not think we would be submerged long enough for that. But there should have been enough in the reserve tank to last several days. How about it, Tom?"
"It's all leaked out, or else it wasn't filled," was the despairing answer. "All the air we have is what's in the ship, and we can't make more."
The treasure-seekers looked at each other. It was an awful situation.
"Then the only thing to do is to fix the machinery and rise to the surface," said Mr. Sharp simply. "We can have all the air we want, then."
"Yes, but the machinery doesn't seem possible of being fixed," spoke Tom in a low voice.
"We must do it!" cried his father.
They set to work again with fierce energy, laboring for their very lives. They all knew that they could not long remain in the ship without oxygen. Nor could they desert it to go to the surface, for the moment they left the protection of the thick steel sides the terrible pressure of the water would kill them. Nor were the diving suits available. They must stay in the craft and die a miserable death—unless the machinery could be repaired and the Advance sent to the surface. The emergency expanding lifting tank was not yet in working order.
More frantically they toiled, trying every device that was suggested to the mechanical minds of Tom, his father, Mr. Sharp or Mr. Jackson, to make the pumps work. But something was wrong. More and more foul grew the air. They were fairly gasping now. It was difficult to breathe, to say nothing of working, in that atmosphere. The thought of their terrible position was in the minds of all.