"Now then," said Sturgis to his companion, "the last chance lies in the speaking-tube. But first help me move this box."
"What do you want to do with the box?" asked Sprague, who, however, did as he was bid.
"It may help us to gain a little time. Put it down here."
Sturgis struck a match and pointed out the spot.
"On the hot-air register?"
"On what looks like a hot-air register. Did you ever see a hot-air register with no apparent means of shutting off the heat?"
Sprague, who stood almost over the register, suddenly threw back his head and gasped for breath.
"You have discovered the secret of this death trap," said Sturgis, observing him.
"Gas!" spluttered the artist.
"Yes, he is going to asphyxiate us. Now, quick, to the speaking-tube! The box will somewhat retard the rush of gas; but, at the best, it is only a question of minutes before the air becomes so charged as to render respiration impossible."