"Mark, hand me that test tube, will you, please?"
The lad who had made the request looked over at his companion, aboy of about his own age, who was on the other side of thelaboratory table.
"The big one, or the small one?" questioned Mark Sampson.
"The large one," answered Jack Darrow. "I want to put plenty ofthe 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'tget hurt. I have to laugh when I think of the way you duckedunder the table. Ha, ha! It was awfully funny!"
"Humph! Maybe you think so, but I don't," responded Mark withrather a serious air. "I noticed that you got behind a chair."
"Well, of course. I didn't want broken glass in my eyes. Comeon, are you going to hand me that test tube, or will I have tocome and get it? We haven't much more time to–day."
"Oh, here's the tube," said Mark as he passed it over. "Butplease be careful, Jack."
Jack measured out some black chemical that resembled gunpowder,and poured it into the test tube which Mark handed him. Then heinserted 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 Ithink of the way you ducked under the table the other day."
"Maybe you'll laugh on the other side of your countenance, asWashington White would say," commented Mark; "especially if thatbig tube bursts."
"But it isn't going to burst."
"How do you know?"
"Well, I worked out this experiment carefully. I've calculatedjust how strong the new gas will be, and—"
"Ah, that's just it. It's a new gas, and you've never yetsucceeded in making it, have you?"
"No; but—"
"And it takes a different combination of chemicals to make itfrom any you ever experimented with before, doesn't it?" askedMark.
"It does. But—"
"Yes, and I don't see how you can tell, with any amount ofcalculation, just how much force will develop from thosechemicals, as no one ever put them together before."
"Well, maybe I can't," admitted Jack. "But this tube is verystrong, and even if it does break nothing very serious canhappen."
"Unless the gas you expect to generate is stronger than you haveany idea of."
"Well, I'm going to do it. I've got half an hour beforeProfessor Lenton and his class comes in, and that's time enough.Here, just hold this rubber tube under this jar, will you? Andbe sure to keep the edge of the jar below the surface of thewater. I don't want any of the gas to escape."
He handed Mark the end of the rubber tube, and the somewhatnervous student, who was helping his chum Jack in the experiment,inserted it under the edge of a large bell–glass, the open mouthof which was placed just under the surface of water in a shallowpan.
The two lads were students at the Universal Electrical andChemical College. They stood high in their classes, and wereoften allowed to conduct experiments on their own responsibility,this being one of those occasions. Jack, who was somewhat olderthan his companion, was of a more adventurous turn of mind, andwas constantly trying new things. Not always safe ones, either,for often he had produced small explosions in the laboratory ofthe college. Only minor damage had been