evidence of my experiment, I find it most convenient to destroy you as I have done with the mouse.
'These large test tubes were made for such an experiment as this. One tube for each of you. After that,
we shall attach these lengths of hose, invert the carboy and let the solvent do its work.'
CLYDE BURKE chewed his lips. Cliff Marsland stared steadily ahead. Each man realized now the
fiendishness of Professor Urlich's cunning, scheming mind. More horrible death could scarcely be
imagined. To be dissolved, while totally helpless, within a mammoth tube of glass!
Both of The Shadow's agents could feel the terrible sensation of that vitriolic fluid that was to come!
Professor Urlich cackled wickedly. He saw the consternation on the faces of his intended victims. He
was joyed by the thought of the swift, silent death that was to be theirs.
Even more did he relish the cunningness of his scheme. To reduce these living men to nothing but a slimy
sediment; then to pour out the remains that could leave no vestige of a clew to the crime that he had
perpetrated!
This was death supreme; crime raised to the level of scientific achievement. Professor Urlich had no
desire to question his victims. Let them call out for mercy if they would; babble secrets of The Shadow. If
their words seemed important, the experiment could be delayed. If not, it would go on.
The Shadow meant little to Professor Urlich now. The very fact that he held one — possibly two — of The
Shadow's agents in his power meant that The Shadow must have died from the fumes of Thomas
Jocelyn's sighing death.
Clyde Burke was staring hopelessly at the merciless countenance of the professor. Cliff Marsland was
looking beyond, toward the distant rear of the laboratory. His eyes blinked suddenly. Had he seen a
motion by what appeared to be a doorway? Had he seen a barrier open; then close?
Was it imagination, or did Cliff catch a glimpse of a moving form that glided along the hazy wall, unseen
by any of the others present? The thought, at least, offered a ray of hope.
Cliff heard a nervous gasp from the man beside him. He spoke in an undertone, without moving his lips:
'Steady, Clyde. Steady. Stick it out, old man.'
The reporter nodded. The test tubes were swinging forward, on swivels from the tripod pedestals.
Professor Urlich's servants approached and lifted Cliff Marsland.
The Shadow's agent offered no resistance. His body slid into the tube; it swiveled upright, and Cliff could
see the attendants going to get Clyde Burke. Helpless, he watched them slide the reporter into the other
tube.
BOTH containers were upright now. Professor Urlich and his minions seemed grotesque shapes through
the curved walls of the tube. Clyde Burke, inspired by Cliff's bravery, was staring at them also. Professor
Urlich was pointing toward the caps.
Suddenly, the scientist stopped. He was staring upward toward the row of lights above the central
stairway. The red incandescent had become suddenly illuminated.
Some one was within the outer zone of death — the portico that surrounded the circular building!
Harsh orders burst from the professor's lips. Sanoja and Rasch nodded as each caught the message
intended for him. They were to proceed with the experiment. Their master had other work to do.
Hastily, Professor Urlich crossed the laboratory, and opened the door that led to the hollow cylinder.
Rasch brought forward a ladder and mounted it. He stood beside Cliff's tube and motioned to Sanoja to
pass him the first cap.
Clyde Burke groaned within the mammoth test tube that held him prisoner. This was the beginning of the
end. One cap; then the other; after that death that would be terrible despite its rapidity.
Then, suddenly, Clyde's eyes opened wide. Coming into the realm of concentrated light was a mass of
blackness that bore only the grotesque semblance of a human form, when viewed through the curving
glass.
Clyde emitted a cry of exultation. It escaped his lips despite his effort to restrain it. The shout caused a
hollow echo from the huge test tube. Sanoja turned; so did Rasch. Terrified gasps came from Professor
Urlich's henchmen.
Standing before the tubes of death stood a tall figure clad in black. Menacing eyes glared from beneath
the broad brim of a slouch hat. From the folds of a black cloak extended a gloved hand that held a
powerful automatic, ready for action.
Rasch cowered, with upraised hands, as he stood upon the ladder. The metal cap clattered from
Sanoja's fists as the man on the floor also raised his arms. Steadily, The Shadow approached. His
mocking laugh came in clear, fantastic tones of triumph.
Professor Folcroft Urlich would find no victims here when he returned; nor would he find tubes of
colorless liquid where living men had come. The Shadow had arrived to foil the scheme of silent death!
The Shadow's glowing eyes brought terror to the enemies who viewed them. Those eyes were glaring
now. They knew all; they saw all. Not only did they observe the cowering minions of Professor Urlich;
they also perceived the cause of the scientist's sudden departure.
The Shadow had seen the red light that still glowed above the central staircase! Again, his laugh reechoed
through that laboratory where death had been frustrated!
CHAPTER XXII. THE SWITCH OF DEATH
PROFESSOR FOLCROFT URLICH stood beside the huge death machine in the pit beneath his
laboratory. His hand was on the control switch; his eyes watched the row of glowing incandescents.
Not yet did the cruel scientist intend to loose the terrific shock of death. Only the red bulb was lighted. It
meant that invaders had come no farther than the outer portico.
Well had the professor designed his three zones of death. He did not intend to use the power at his
disposal merely to dispose of some prowler; nor did he choose to employ it indiscreetly.
So long as the first zone alone had been entered, there could be no danger. Perhaps these intruders
would go away. If they sought to enter, they could be allowed to do so, if they came as friends.
That was the reason why the scientist had ordered his men to proceed with the experiment that would
bring death to the captives in the laboratory. If merely harmless investigators had come to this coliseum of
doom, Urlich could welcome them with clean hands.
The muffled thuds of heavy battering suddenly impressed themselves upon the professor's ears. A frown
furrowed the evil brow. That sound meant enemies. The scientist's hand wavered upon the control
switch. It paused.
This was not the time to kill. If death were dealt now, some watchers beyond the range of the hidden
portico might be clear; they might witness the end of their companions.
Urlich grinned wickedly. He would let these invaders enter. Once inside, within the second zone; yes,
even in the third, he could pull the switch of death!
Silent death! The death that Urlich had longed to deal. This coming upon the heels of his laboratory
experiment caused the fiend to chortle with glee.
The Shadow was dead; his agents were on their way to destruction; and other enemies were entering the
door to meet their end.
WHO could these foes be? Professor Urlich nodded as he thought. The police? Yes! Somehow, they
had trailed the path of Larry Ricordo.
