under the table. Ha, ha! It was awfully funny!"

"Humph! Maybe you think so, but I don't," responded Mark with
rather a serious air. "I noticed that you got behind a chair."

"Well, of course. I didn't want broken glass in my eyes. Come
on, are you going to hand me that test tube, or will I have to
come and get it? We haven't much more time to-day."

"Oh, here's the tube," said Mark as he passed it over. "But
please be careful, Jack."

Jack measured out some black chemical that resembled gunpowder,
and poured it into the test tube which Mark handed him. Then he
inserted in the opening a cork, from which extended a glass tube,
to the outer end of which was fastened a rubber pipe.

He paused in his experiment to laugh again.

"What are you making--laughing gas?" asked Mark.

"No. But--excuse me--ha, ha! I can't help laughing when I
think of the way you ducked under the table the other day."

"Maybe you'll laugh on the other side of your countenance, as
Washington White would say," commented Mark; "especially if that
big tube bursts."

"But it isn't going to burst."