“Now,” said Tom to himself, as he mixed two kinds of acid in a jar, to produce a new sort of electrical current, “I will see if this is any better than the first way in which I did it.”

He was careful about pouring out the powerful stuff, but, in spite of this, he spilled a drop on his finger.  It burned like fire, and, instinctively, he jerked his hand back.

The next instant there was a series of happenings.  Tom’s elbow came in contact with another jar of acid, knocking it over, and spilling it into the retort where he had been mixing the first two liquids.  There was a hissing sound, as the acids combined, and a thick, white vapor arose, puffing into Tom’s face, and making him gasp.

He staggered back, brushed against the heavy iron shaft in the corner, and it fell sideways against him, knocking him to the floor, and dropping across his thighs.  The padding on it saved him from broken bones, but the shaft was so heavy, that after it was on him, Tom could not move.  He was held fast on the floor of his shop, unable to use his legs, and prevented from getting up.

For a moment Tom was stunned, and then he called: 

“Help!  Help!  Eradicate!  Koku!  Help!”

He waited a moment, but there was only a silence.

And then Tom smelled a strange odor—­an odor of a choking gas that seemed to smother him.

“It’s the acids!” he cried.  “They’re generating gas!  And I’m held fast here!  The place is closed up tight, and I can’t move!  Help!  Help!”

But there was no one at hand to aid Tom, and every moment the fumes of the gas became stronger.  Desperately the youth struggled to rid himself of the weight of the shaft, but he could not.  And then he felt his senses leaving him, for the powerful gas was making him unconscious.

CHAPTER V — TOM GETS A WARNING

“Bless my shoe buttons!” exclaimed a voice, as a man came toward Tom’s shop, a little later.  “Bless my very necktie!  This is odd.  I go to the house, and find no one there.  I come out here, and not a soul is about.  Tom Swift can’t have gone off on another one of his wonderful trips, without sending me word.  I know he wouldn’t do that.  And yet, bless my watch and chain, I can’t find any one!”

It was Mr. Damon who spoke, as my old readers have already guessed.  He peered into one of the shop windows, and saw something like a fog filling the place.

“That’s strange,” he went on.  “I don’t see Tom there, and yet it looks as if an experiment was going on.  I wonder—­”

Mr. Damon heard some one coming up behind him, and turned to see Koku the giant, who was returning . from the errand on which Tom had sent him.

“Oh, Koku, it’s you; is it?” the odd man asked.  “Bless my cuff buttons!  Where is Tom?”

“In shop I guess.”

“I don’t see him.  Still I had better look.  There doesn’t seem to be any one about.”