He placed the test tube in a support, clamping it fast, so that
it would be held steady over the flame. Then he turned on more
of the illuminating gas, which, coming through the Bunsen burner,
was made intensely hot. A little column of flame now enveloped
the big test tube containing the powder.

There was a little crackling sound as the heat expanded the
powder, and the end of the test tube became quite red from the
flame.

"That tube'll melt!" exclaimed Mark, peering over the pile of
books. "It's too near the flame."

"Guess you're right," admitted Jack. "I'll raise it up a bit."

He turned down the flame and elevated the tube slightly. Then he
took a position where he could watch the process of making what
he hoped would be a new kind of gas. He wanted to be where he
could see the vapor beginning to collect in the top of the tube,
pass off through the glass in the cork, and then through the
little rubber hose to the bell glass held by Mark. If the gas
was generated too quickly, Jack knew he would have to turn down
the heat slightly.

The crackling sound continued. Then, as Jack watched, he saw a
thick, yellowish vapor collecting in the top of the test tube
near the cork.

"It's coming!" he cried. "There's my new gas!"