"An explosive mixture?" echoed Orton.
"Yes, Jack, the blow-outs that you have had at the end of the tunnel were not blow-outs at all, properly speaking. They were explosions."
We sat aghast at this revelation.
"And, furthermore," added Kennedy, "I should, if I were you, call back all the men from the tunnel until the cause for the presence of this explosive mixture is discovered and remedied."
Orton reached mechanically for the telephone to give the order, but
Taylor laid his hand on his arm. "One moment, Orton," he said.
"Let's hear Professor Kennedy out. He may be mistaken, and there
is no use frightening the men, until we are certain.
"Shelton," asked Kennedy, "what sort of flash oil is used to lubricate the machinery?"
"It is three-hundred-and-sixty-degree Fahrenheit flash test," he answered tersely.
"And are the pipes leading air down into the tunnel perfectly straight?"
"Straight?
"Yes, straight - no joints, no pockets where oil, moisture, and gases can collect."