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 potassium 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!
There was cyanide in the bottle!"

"There sure was," agreed Jack, who had seen the same test made in one
of the classes a few days before.

"But I don't see what good that is," remarked Bert. "Everyone knew
that cyanide was used on the horses. It's a common enough poison.
Naturally whoever used it would have it in a bottle. Then you
accidentally find the bottle in the stable, but that doesn't tell you
who dropped it there."

"No, but this may," said Tom quietly, taking a small piece of paper
from his pocket and smoothing it out on the table.

"What is it?" asked Jack, and then, before he could be answered he
added. "Oh, I see, part of a druggist's label."

"Yes," admitted Tom. "It was near the bottle. It had been washed off,
I imagine. I didn't show it to you at first, for I wanted to make sure
of what the bottle had contained."

"And now that you're sure," began Bert, "I suppose------"

"I'm going to the druggist who sold this, and ask if he can remember
who bought it," went on Tom, for, though the label from the bottle was
torn, there was enough of it left to show part of the firm name. And,
as there were but three drug shops in Elmwood, it was not difficult to
pick out the one represented.

"We'll go with you!" exclaimed Jack. "Hurray, Tom! I do believe
you're on the trail at last."

"Sure," assented Bert. "Let's go at once."

"I'd like to have you along," explained Tom, "but I think maybe I'd
better go by myself. I've got to go at this thing quie