"Quick—Elaine!" he cried, taking her arm. "Stand back!"
We all retreated. The safe door, powerful as it was, had actually begun to warp and bend. The plates were bulging. A moment later, with a loud report and concussion the door blew off.
A blast of cold air and flakes like snow flew out. Papers were scattered on every side.
We stood gazing, aghast, a second, then ran forward. Kennedy quickly examined the safe. He bent down and from the wreck took up a package, now covered with white.
As quickly he dropped it.
"That is the package that was sent," cried Elaine.
Taking it in a table cover, he laid it on the table and opened it. Inside was a peculiar shaped flask, open at the top, but like a vacuum bottle.
"A Dewar flask!" ejaculated Craig.
"What is it?" asked Elaine, appealing to him.
"Liquid air!" he answered. "As it evaporated, the terrific pressure of expanding air in the safe increased until it blew out the door. That is what caused the cold sweating and the groans."