of all.

"Oh, for one breath of fresh air!" cried Mr. Damon, who seemed to
suffer more than any of the others. Grim death was hovering around
them, imprisoned as they were on the ocean's bed, over a mile from the
surface.

Chapter Thirteen

Off for the Treasure

Suddenly Tom, after a moment's pause, seized a wrench and began
loosening some nuts.

"What are you doing?" asked his father faintly, for he was being
weakened by the vitiated atmosphere.

"I'm going to take this valve apart," replied his son. "We haven't
looked there for the trouble. Maybe it's out of order."

He attacked the valve with energy, but his hands soon lagged. The lack
of oxygen was telling on him. He could no longer work quickly.

"I'll help," murmured Mr. Sharp thickly. He took a wrench, but no
sooner had he loosened one nut than he toppled over. "I'm all in," he
murmured feebly.

"Is he dead?" cried Mr. Damon, himself gasping.

"No, only fainted. But he soon will be dead, and so will all of us, if
we don't get fresh air," remarked Captain Weston. "Lie down on the
floor, every one. There is a little fairly good air there. It's heavier
than the air we've breathed, and we can exist on it for a little
longer. Poor Sharp was so used to breathing the rarified air of high
altitudes that he can't stand this heavy atmosphere."

Mr. Damon was gasping worse than ever, and so was Mr. Swift. The
balloonist lay an inert heap on the floor, with Captain Weston trying
to force a few drops of stimulant down his throat.

With a fierce determination in his heart, but with fingers that almost
refused to do his bidding, Tom once more sought to open the big valve.
He felt sure the trouble was located there, as they had tried to locate
it in every other place without avail.

"I'll help," said Mr. Jackson in a whisper. He, too, was hardly able to
move.

More and more devoid of oxygen grew the air. It gave Tom a sense as if
his head was filled, and ready to burst with every breath he drew.
Still he struggled to loosen the nuts. There were but four more now,
and he took off three while Mr. Jackson removed one. The young inventor
lifted off the valve cover, though it felt like a ton weight to him. He
gave a glance inside.

"Here's the trouble!" he murmured. "The valve's clogged. No wonder it
wouldn't work. The pumps couldn't force the water out."

It was the work of only a minute to adjust the valve. Then Tom and the
engineer managed to get