He handed Mark the end of the rubber tube, and the somewhat nervous student, who was helping his chum Jack in the experiment, inserted it under the edge of a large bell-glass, the open mouth of which was placed just under the surface of water in a shallow pan. The two lads were students at the Universal Electrical and Chemical College. They stood high in their classes, and were often allowed to conduct experiments on their own responsibility, this being one of those occasions. Jack, who was somewhat older than his companion, was of a more adventurous turn of mind, and was constantly trying new things. Not always safe ones, either, for often he had produced small explosions in the laboratory of the college. Only minor damage had been done thus far, but, as Mark said, one could never tell what was going to happen when Jack mixed certain things in test tubes and placed them over a spirit lamp, or the flame of a Bunsen burner. "Have you got that tube under the jar?" asked Jack as he lighted a large Bunsen flame. "It's under," answered Mark. "But say, what are you going to do in case you prove that your theory is right, and that you can make a new kind of gas? What good will it be?" "Lots of good. If I'm right, this will be the lightest gas ever made. Much lighter than hydrogen--" "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." 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.