be sure to keep the edge of the jar below the surface of the
water. I don't want any of the gas to escape."

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--"