are waiting for something to turn up in regard
to them, you may be glad to assist me."

"I will, and without pay," said the chemist.

But Tom would not hear of that, and together he and Mr. Baxter set
about putting the finishing touches to Tom's latest invention.

CHAPTER XIX

ON THE TRAIL

"There, Tom Swift, it ought to work now!"

Josephus Baxter held up a large laboratory test tube, in which seethed
and bubbled some strange mixture, turning from green to purple, then to
red, and next to a white, milky mixture.

"Do you think you've hit on the right combination?" asked the young
inventor, whose latest idea, the plan of fighting fires in skyscrapers
from an airship as a vantage point, was taking up all his spare moments.

"I'm positive of it," said Mr. Baxter. "I've dabbled in chemicals long
enough to be certain of this, even if I can't get on the track of the
missing dye formulae."

"That certainly is too bad," declared Tom. "I wish I could help you as
much as you have helped me."

"Oh, you have helped me a lot," said the chemist. "You have given me a
place to work, much better than the laboratory I had in the old
fireworks factory of Field and Melling. And you have paid me, more than
liberally, for what little I have done for you."

"You've done a lot for me," declared Tom. "If it had not been for your
help this chemical compound would not be nearly as satisfactory as it
is, nor as cheap to manufacture, which is a big item."

"Oh, you were on the right track," said Mr. Baxter. "You would have
stumbled on it yourself in a short time, I believe. But I will say, Tom
Swift, that, between us, we have made a compound that is absolutely
fatal to fires. Even a small quantity of it, dropped in the heart of a
large blaze, will stop combustion."

"And that's what I want," declared Tom. "I think I shall go ahead now,
and proceed with the manufacture of the stuff on a large scale."

"And what do you propose doing with it?" asked Mr. Baxter.

"I'm going to sell the patent and the idea that goes with it to as many
large cities as I can," Tom answered. "I'll even manufacture the
airships that are needed to carry the stuff over the tops of blazing
skyscrapers, dropping it down. I'll supply complete aerial
fire-fighting plants."

"And I think you'll do a good business," said the chemist.

It was the conclusion of the final tests of an improved chemical
mixture, and the reaction that had taken place in the