"Lighter than the kind Professor Henderson made for use in the
Flying Mermaid, in which we went to the center of the earth?"

"No, I'm afraid I can't equal his gas; but then, no one can ever
hope to. I'm going to make a new gas, though, and I'll show you
that it will be much lighter and more powerful than hydrogen."

"More powerful, eh? Then I wish you'd have some one else hold
this. I'm afraid the test tube will burst."

"What if it does? It can't hurt you--very much. But here, since
you're so nervous, I'll put a pile of books all around the tube
and the burner. Then, if it bursts, the books will prevent the
pieces of glass from flying all about. Does that satisfy you?"
and Jack began heaping some books about the burner, over which he
was about to suspend the test tube containing the queer chemical.

"Yes," returned Mark doubtfully. "I suppose it's all right--unless
the books will be blown all over."

"Well, I'll be jig-sawed!" exclaimed Jack with a laugh. "There's
no satisfying you. You're too particular, Mark."

"Maybe; but I don't want to get hurt."

"You'll not be injured in the least. Look, you're quite a
distance away, and even if it does explode and the books are
scattered away, it can't hurt much to be hit by one of these
volumes. There, I'm all ready now. Hold the tube firmly."