seconds of silence, broken only by the roaring of the burner and
the crackling of the black powder.

"Yes, there is vapor in the jar," he said.

"Good! That's the stuff!" cried Jack. "Now I guess Professor
Lenton will admit that I'm right."

He turned the Bunsen flame up higher. A moment later he uttered
a cry, for he saw the cork being forced from the test tube. The
pressure of the new gas was too much for it.

"Lookout!" cried Jack. "She's going up!"

Then followed a sharp explosion, and the laboratory seemed filled
with fragments of broken glass and torn books.





CHAPTER II

JACK MAKES OXYGEN


"There it goes! There it goes!" cried Mark, making a dive for
the laboratory door, but slipping and sprawling on the floor.
"There it goes, Jack!"