on, in utter unconcern, drew a pipe out of one of
his pockets, filled it, and stuck the stem between his lips. Next, he
struck a safety match, softly, against the side of the match-box, and
lighted his pipe, drawing in great whiffs.

"Just how far does this practice go!" inquired the machinist, still
sitting on the keg and smoking contentedly.

At that moment Captain Jack Benson caught, in his nostrils, the scent
of burning tobacco.

In an instant a steely glitter shone in the young captain's eyes. Firm,
strong lines appeared about his mouth. All that part of the face showed
white and pallid. Just a second or two later Hal Hastings also turned.
Like a flash his lower jaw dropped, as though the hinge thereof had
broken.

When Captain Jack's voice came to him it sounded low, yet hard and
metallic. One would have wondered whether he had suddenly become ugly.

"Williamson," he directed, "just step outside and see if Eph is there!"

Hardly noting the unusual ring in the young commander's voice, the
machinist, still with the pipe-stem between his teeth, rose and walked
out into the open. With an almost inarticulate yell Captain Jack
Benson leaped after him, striking the man in the back and sending him
spinning a dozen feet beyond.

Hal Hastings, too, dashed through the door way; then paused, grasping
the edge of the door and shutting it with a bang.

"What on earth do you mean by knocking a fellow down like that?" demanded
the machinist, angrily, leaping to his feet and wheeling about, leaving
the lighted pipe on the snowcrust.

"Look at the sign on this door," ordered Hal Hastings, pointing to the
big white letters.

"Danger, eh?" asked Williamson, speaking more quietly. "Well, that door
was open and swung back when I came along, so I couldn't see any
warning. But what is there in the shed that's so mighty dangerous?"

"What do you suppose is in the half-open keg that you were sitting on?"
demanded Captain Jack, rather hoarsely.

"What!" queried the machinist, curiously.

"The head of that keg is half off," Jack continued. "Now, if any sparks
from your pipe had dropped down and set the bagging afire--well, that
keg is almost full of cubes of gun-cotton!"

"Whew!" gasped Williamson, beginning to look pallid himself.

"Nor is that all," Hal took up. "Of course, if you had touched off that
gun-cotton in the keg, it would have sent us all through the roof. But
the smaller explosion would have touched