"That can't be Koku and Rad in one of their periodic squabbles, can it?" asked Ned.

"No. It's probably Mr. Baxter," Tom answered. "The doctor said he might get violent once or twice, until the effects of his shock wore off. There is some quieting medicine I can give him. I'll run up."

"Guess I'd better go along," remarked Ned. "Sounds as if you'd need help."

And it did appear so, for again the frenzied shouts sounded:

"I'll get 'em! I'll get the scoundrels who stole my secret formulae that I worked over so many years! Come back now! Don't put the match near the powder!"

Tom and Ned hurried to the room where the unfortunate chemist had been put to bed, to find him out in the hall, wrapped in a bedquilt, and with Mrs. Baggert vainly trying to quiet him. Mr. Baxter stared at Tom and Ned without seeing them, for he was in a delirium of fever.

"Have you my formulae?" he asked. "I want them back!"

"You shall have them in the morning," replied Tom soothingly. "Lie down, and I'll bring them to you in the morning. And drink this," he added, holding out a glass of soothing mixture which the doctor had ordered in case the patient should become violent.

Josephus Baxter glared about with wild eyes, but between them Tom and Mrs. Baggert managed to get him to drink the mixture.

"Bah! It's as bad as some of my chemicals!" spluttered the chemist, as he handed back the glass. "You are sure you'll have my formulae in the morning?" he asked, as he turned to go back to his room.

"I'll do my best," declared Tom cheerfully. "Now please lie down."

Which, after some urging, Mr. Baxter consented to do. Eradicate wanted to lie down in the hall outside the excited chemist's door to guard against his emerging again, but Tom decided on Koku. The giant, though not as intelligent as the colored man, was more efficient in an emergency because of his great strength. Eradicate was getting old, and there was a pathetic droop to his figure as he shuffled off when Koku superseded him.

"Ah done guess Ah ain't wanted much mo'," muttered Rad sadly.

"Oh, yes, you are!" cried Tom, as, the excitement over, he walked downstairs with Ned. "I'm going to start something new, Rad, and I'll need your help."

"Will yo', really, Massa Tom?" exclaimed faithful Rad, his face lighting up. "Dat's good! Is yo' goin' off after mo' diamonds, or up to de caves of ice?"

"Not quite that," answered the young inventor, recalling the stirring experiences that had fallen to him when on those voyages. "I'm going to work around home, Rad, and I'll need your help."

"Anyt'ing yo' wants, Massa Tom! Anyt'ing yo' wants!" offered the now delighted Rad, and he went to bed much happier.

"Well, to resume where we left off," began Ned, when he and Tom were once more by themselves, "what's the game?"

"Oh, I don't know that it's much of a game," was the answer. "But I just have an idea that a big fire in a towering building can be fought from above with chemicals, as well as from the ground with streams of water.

"Well, I guess it could be," Ned agreed. "But how are you going to get your chemicals in at the top? Shoot 'em up through a hose? If you do that you'll need a special kind of hose, for the chemicals will rot anything like rubber or canvas."

"I wasn't thinking of a hose," returned Tom. "What then?" asked the young financial manager.

"An airship!" Tom exclaimed with such sudden energy that Ned started. "It just came to me!" explained the youthful inventor. "I was wondering how we could get the chemicals in from the top, and an airship is the solution. I can sail over the burning building and drop the chemicals down. That will douse the blaze if my plans go right."

Ned was silent a moment, considering Tom's daring plan and project. Then, as it became clearer, the young banker cried:

"Blamed if I don't think that's just the thing, Tom! It ought to work, and, if it does, it will save a lot of lives, to say nothing of property! A fire in a sky-scraper ought to be fought from above. Then the extinguisher element, whether chemicals or water, could be dropped where they'd do the most good. As it is now, with water, a lot of it is wasted. Some of it never reaches the heart of the fire, being splashed on the outside of the building. A lot more turns to steam before it hits the flames, and only a small percentage is really effective."

"That's my notion," Tom said.

"Then go ahead and do it!" urged his friend. "You have my permission!"

"Thanks," commented Tom dryly. "But there are several things to be worked out before we can start. I've got to devise some scheme for carrying a sufficient quantity of chemicals, and invent some way of releasing them from an airship over the blaze. But that last part ought to be easy, for I think I can alter my warfare bomb-dropping attachment to serve the purpose.

"What I really need, however, is some new chemical combination that will quickly put a really big blaze out of business. There are any number of these chemicals, but most of them depend on the production of carbon dioxide. This is the product of some solution of a carbonate and sulphuric acid, and I suppose, eventually, I'll work out something on that order. But I hope I may get something better."

"You haven't delved much into chemistry, have you?"

"No. And I wish now that I had. I see my limitations and realize my weakness. But I can brush up a little on my chemistry. As for the mechanical part, that of dropping the extinguisher on the blaze, I'm not worrying over that end."

"No," agreed Ned. "You have enough types of airships to be able to select just the best one for the purpose. But, say, Tom!" he suddenly cried, "why not ask him to help you?"

"Who?"

"Mr. Baxter. He's a chemist. And though he says his formulae are about dyes and fireworks, maybe he can put you in the way of inventing a chemical solution that will be death to fires."

"He might," Tom agreed. "But I think he'll be out of business for some time. This shock--being overcome by smoke and his secret formulae having been stolen--seem to have affected his mind. I don't know that I could depend on him."

"It's worth trying," declared Ned. "What do you suppose he means, Tom, saying that Field and Melling stole his formulae?"

"Haven't the least idea. I only know those fireworks firm members slightly, if at all. I'm not sure I'd recognize them if I met them. But they are reputed to be wealthy, and I hardly think they would stoop to stealing some inventor's formulae.

"We inventors are a suspicious lot, Ned, as you probably have found out," he added with a smile. "We imagine the rest of the world is out to cheat us, and I presume Josephus Baxter is no exception. Still, there may be some truth in his story. I'll give him all the help I can. But I'm going into the aerial fire- fighting game. I've been waiting for something new, and this may be it."

"You may count on me!" declared Ned. "And now, unless you're going to sit up all night and start studying chemistry, you'd better come to bed."

"That's right. Tomorrow is another day. I hope Mr. Baxter gets some rest. Sleep will improve him a lot, the doctor said."

"I know one friend of yours who will be glad to know that you are going to start something," remarked Ned, as he and Tom started for their rooms, for the young manager was staying with his friend for the night.

"Who?" Tom wanted to know.

"Mr. Wakefield Damon," was the answer. "He hasn't been over lately, Tom."

"No, he's been off on a little trip, blessing everything from his baggage check to his suspender buttons," laughed the young inventor, as he recalled his eccentric acquaintance. "I shall be glad to see him again."

"He'll be right over as soon as he learns what's in the wind," predicted Ned.

The hopes that Mr. Baxter would be greatly improved in the morning were doomed to disappointment. He was in no actual danger, the doctor said, but his recovery from the effects of the smoke he had breathed was not as rapid as desired or hoped for.

"He's suffering from some shock," said the physician, "and his mental condition is against him. He ought to be kept quiet, and if you can't have him here, Mr. Swift, I can arrange to have him sent to a hospital."

"I wouldn't dream of it!" Tom exclaimed. "Let him stay here by all means. We have plenty of room, and Mrs. Baggert has been wishing for some one to nurse. Now she has him."

So it was arranged that the chemist should remain at the Swift home, and he gave a languid assent when they spoke to him of the matter. He really was much more ill than seemed at first.

But as everything possible had been done, Tom decided to go ahead with the new idea that had come to him--that of inventing an aerial chemical fire-fighting machine.

"And if we get a chance, Ned, we'll try to get back those secret formulae Mr. Baxter claims to have lost," Tom declared. "I have heard some stories about that fireworks firm, which make me believe there may be something in Baxter's story."

"All right, Tom, I'm with you any time you need me," Ned promised.

The young inventor lost little time in beginning his operations. As he had said, the chief need was a fire extinguishing chemical solution or powder. Tom resolved to try the solution first, as it was easier to make. With this end in view he proceeded to delve into old and new chemistry books. He also sought the advice of his father.

And one day, when Ned called, Tom electrified his chum with the exclamation:

"Well, I'm going to give it a try!"

"What?"

"My aerial chemical fire-fighting apparatus. Of course I only have the chemical yet. I haven't worked on the carrying apparatus nor decided how I will attach it to an airship. But I'm going up now with some of my new solution and drop it on a blaze from above."

"Where are you going to get the fire?" asked Ned. "You can't have a sky-scraper blaze made to order, you know."

"No, but as this is only an experiment," Tom said, "a big bonfire will answer the purpose. I'm having Koku and Rad make one now down in our big meadow. As soon as it gets hot enough and fierce enough, I'll sail over it in my small machine, drop the extinguisher on it, and see what happens. Want to come?"

"Sure thing!" cried Ned. "And I hope the experiment is a success!"

"Thanks," murmured Tom. "I'm about ready to start. All I have to do is to take this tank up with me," and he pointed to one containing his new mixture. "Of course the arrangement for dumping it out of the aircraft is very crude," Tom said. "But I can work on that later."

Ned and he were busy putting the can of Tom's new chemical extinguisher in the airship when the door of the hangar was suddenly opened and a very much excited man entered crying:

"Fire! Fire! Bless my kitchen sink, your meadow's on fire, Tom Swift! It's blazing high! Fire! Fire!"