"What? Don't you believe Sam guilty?" asked Bert.

"No, I can't say that I do."

"But he is!" a.s.serted Jack. "It was his sweater the farmer saw instead of yours. You're both about the same height and build. Of course Sam did it, Tom."

"No, I can't agree with you. I'll admit I did wear my sweater when I left here the night the horses were poisoned, and I came back without it, but------"

"What in the world happened to it?" demanded Jack.

"That I can't say--yet."

"Will you ever be able to?" Bert wanted to know.

"I hope to in time--perhaps soon now. Mr. Appleby picked it up--that much I'll have to admit."

"And can you clear your name?" asked Jack, rather rueful that the fine theory he had built up was thus easily pa.s.sed over by his chum.

"I hope to, Jack."

"Have you any new clews?" asked Bert. "I presume that's what you've been looking for?"

"Yes, I did go off hunting for them," said Tom slowly.

"Well, did you find any?" burst out Jack. "Can't you relieve the suspense?"

"I found this," said Tom, placing an empty bottle on the table.

"Why--why, there's nothing in it!" exclaimed Jack, looking at it. "How can that form a clew?"

"Not because of what is in it but what _was_ in it," said Tom with a smile. "Unless I'm mistaken this will help to prove my innocence--that is, if the experiment I'm going to try works out. We'll soon see. I wonder if the laboratory is closed," and he went out into the corridor.

CHAPTER XVIII

ON THE TRAIL

"What's he up to now?" asked Bert of Jack, as the two stood in the room, looking at one another.

"Give up. We'll have to wait and see. It's something important though, to judge by Tom's actions."

"Yes, but an empty bottle! What can he hope to do with that for a clew?"

"I don't know. Leave it to Tom."

The latter came back in a little while, carrying several bottles, test tubes and an alcohol lamp.

"Well, for the cla.s.s's sake!" cried Jack. "Are you going to give us a demonstration of the action of liquids on solids?"

"No, I'm going to prove that mind is superior to matter," laughed Tom.

"Say, it sounds good to hear that!" cried Jack. "You haven't laughed before in two weeks."

"Well, I feel a bit like it now," said Tom. "I'm beginning to get a glimpse of daylight in this darkness."

He arranged his material on the table in front of him, having removed the books and papers. Then, taking a bottle of some colorless liquid which he had brought from the college laboratory, he poured some into the apparently empty bottle he had first exhibited.

"What's that?" asked Bert.

"Sterilized water."

"Say, where did you find that bottle?" demanded Jack.

"In Farmer Appleby's barn," was the calm rejoinder. "I picked it up just by chance, but it may mean something big."

"What?" cried Jack. "You don't mean to say you've been around there?"

"Surely. Why not?"

"Why, he might think you wanted to do away with the rest of his horses."

"He didn't see me. I took care of that. Besides that's the only place where I can consistently look for clews. I was sure whoever poisoned the horses must have left some trace behind him, and this may be it."

"The empty bottle?" asked Bert incredulously.

"It may not be altogether empty," replied Tom. "That's what I'm going to test for. I saw traces of some powder on the sides, and I want to see if my suspicions are true."

"Then you think it contained----" began Jack.

"I'm not going to think anything until I finish this experiment,"

laughed Tom.

He shook the sterilized water about in the bottle, rinsing it well, and the contents he then poured into a test tube. This, after heating, he mixed with some other chemicals.

"Would you mind telling us what you're testing for?" asked Jack.

"Not at all," said Tom quietly. "I'm trying to see if this bottle had any cyanide of pota.s.sium in it."

"What! Cyanide?" gasped Bert.

"The stuff that killed the one horse and sickened the others?" asked Jack.

"That's it. I may find it--I may not."

Tom poured a few drops of another chemical into the test tube. There was a reaction, and at once he uttered a cry:

"There it is!" he fairly shouted. "I'm on the right trail at last!