Through Space to Mars; Or, the Longest Journey on Record

Mark, hand me that test tube, will you, please?
The lad who had made the request looked over at his companion, a boy of about his own age, who was on the other side of the laboratory table.
The big one, or the small one? questioned Mark Sampson.
The large one, answered Jack Darrow. I want to put plenty of the chemical in this time and give it a good try.
Now be careful, Jack. You know what happened the last time.
You mean what nearly happened. The tube burst, but we didn't get hurt. I have to laugh when I think of the way you ducked 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.