"What's the name of it?" asked Mark.

"I haven't named it yet. I want to collect it in the jar and
show it to Professor Lenton. He said he didn't believe I could
make it."

The boys resumed their careful watching of the experiment. It
was a nervous moment, for, from experience, Mark knew you never
could tell what would happen when Jack began to try new
combinations of chemicals. He was ready to drop down on an
instant's warning, out of the way of flying missiles.

"See any bubbles in that pan of water yet?" cried Jack.

"No, not yet."

"That's queer. The test tube is full of the yellow gas, and some
ought to be over to where you are now. I'm going to turn on some
more heat."

He increased the Bunsen flame. The crackling noise was louder.
The test tube became a fiery red.

"It's bubbling now!" suddenly called Mark.

"That's good! The experiment is a success! I knew I could make
it. Is any of the gas coming up in the glass jar?"

Mark bent over to make a closer examination. There were a few