“Are you all ready, Tom?”
“All ready, Mr. Sharp,” replied a young man, who was stationed near some complicated apparatus, while the questioner, a dark man, with a nervous manner, leaned over a large tank.
“I’m going to turn on the gas now,” went on the man. “Look out for yourself. I’m not sure what may happen.”
“Neither am I, but I’m ready for it. If it does explode it can’t do much damage.”
“Oh, I hope it doesn’t explode. We’ve had so much trouble with the airship, I trust nothing goes wrong now.”
“Well, turn on the gas, Mr. Sharp,” advised Tom Swift. “I’ll watch the pressure gauge, and, if it goes too high, I’ll warn you, and you can shut it off.”
The man nodded, and, with a small wrench in his hand, went to one end of the tank. The youth, looking anxiously at him, turned his gaze now and then toward a gauge, somewhat like those on steam boilers, which gauge was attached to an aluminum, cigar-shaped affair, about five feet long.
Presently there was a hissing sound in the small frame building where the two were conducting an experiment which meant much to them. The hissing grew louder.
“Be ready to jump,” advised Mr. Sharp.
“I will,” answered the lad. “But the pressure is going up very slowly. Maybe you’d better turn on more gas.”
“I will. Here she goes! Look out now. You can’t tell what is going to happen.”
With a sudden hiss, as the powerful gas, under pressure, passed from the tank, through the pipes, and into the aluminum container, the hand on the gauge swept past figure after figure on the dial.
“Shut it off!” cried Tom quickly. “It’s coming too fast! Shut her off!”
The man sprang to obey the command, and, with nervous fingers, sought to fit the wrench over the nipple of the controlling valve. Then his face seemed to turn white with fear.
“I can’t move it!” Mr. Sharp yelled. “It’s jammed! I can’t shut off the gas! Run! Look out! She’ll explode!”