opinion as to how much longer it could burn without getting entirely beyond control, Tom set off on a run toward another large structure. Ned, glancing toward his chum, observed:

"The dirigible shed! I wonder what his game is? Surely that can't be in danger—it's too far off!"

Ned was right as to the last statement. The shed, where was housed a great dirigible balloon Tom had made, but which he seldom used of late, was sufficiently removed from the zone of fire to be out of danger.

Meanwhile several members of the fire-fighting force that had been summoned from the various shops by the alarm, had made an effort to save from the red shed some of the more valuable of the contents. There were some machines in there, as well as explosives and chemicals, in addition to the store of carbide.

But the fire was now too hot to enable much to be done in the way of salvage. One or two small things were carried out from a little addition to the main structure, and then the rescuers were driven back by the heat of the flames, as well as by the rolling clouds of black smoke.

"Keep away!" warned Mr. Swift. "It will explode soon. Keep back!"

"That's right!" added Mr. Damon. "Bless my powder-horn! We may all be going sky-high soon, and without aid from any of Tom Swift's aeroplanes, either."

Warned by the aged inventor, the throng of men began slowly moving away from the immediate neighborhood of the blazing shed. Though it may seem to the reader that some time has elapsed since the first sounding of the alarm, all that I have set down took place in a very short period—hardly three minutes elapsing since Tom and the others came rushing out of the aerial warship building.

Suddenly a cry arose from the crowd of men near the red shed. Ned, who stood ready with several lines of hose, in charge of Koku, Eradicate and others, to turn them on the airship shed, in case of need, looked in the direction of the excited throng.

The young bank clerk saw a strange sight. From the top of the dirigible balloon shed a long, black, cigar-shaped body arose, floating gradually upward. The very roof of the shed slid back out of the way, as Tom pressed the operating lever, and the dirigible was free to rise—as free as though it had been in an open field.

"He's going up!" cried Ned in surprise. "Making an ascent at a time like this, when he ought to stay here to fight the fire! What's gotten into Tom, I'd like to know? I wonder if he can be—"

Ned did not finish his half-formed sentence. A dreadful thought came into his mind. What if the sudden fire, and the threatened danger, as well as the prospective loss that confronted Tom, had affected his mind?

"It certainly looks so," mused Ned, as he saw the big balloon float free from the shed. There was no doubt but that Tom was in it. He could be seen standing within the pilot-house, operating the various wheels and levers that controlled the ship of the air.

"What can he be up to?" marveled Ned. "Is he going to run away from the fire?"

Koku, Eradicate and several others were attracted by the sight of the great dirigible, now a considerable distance up in the air. Certainly it looked as though Tom Swift were running away. Yet Ned knew his chum better than that.

Then, as they watched, Ned and the others saw the direction of the balloon change. She turned around in response to the influence of the rudders and propellers, and was headed straight for the blazing shed, but some distance above it.

"What can he be planning?" wondered Ned.

He did not have long to wait to find out.

An instant later Tom's plan was made clear to his chum. He saw Tom circling over the burning red shed, and then the bank clerk saw what looked like fine rain dropping from the lower part of the balloon straight into the flames.

"He can't be dousing water on from up above there," reasoned Ned. "Pouring water on carbide from a height is just as bad as spurting it on from a hose, though perhaps not so dangerous to the persons doing it. But it can't be—"

"By Jove!" suddenly exclaimed Ned, as he had a better view of what was going on. "It's sand, that's what it is! Tom is giving battle to the flames with sand from the ballast bags of the dirigible! Hurray? That's the ticket! Sand! The only thing safe to use in case of an explosive chemical fire.

"Fine for you. Tom Swift! Fine!"

CHAPTER IV

SUSPICIONS

High up aloft, over the blazing red shed, with its dangerous contents that any moment might explode, Tom Swift continued to hold his big dirigible balloon as near the flames as possible. And as he stood outside on the small deck in front of the pilot-house, where were located the various controls, the young inventor pulled the levers that emptied bag after bag of fine sand on the spouting flames that, already, were beginning to die down as a result of this effectual quenching.

"Tom's done the trick!" yelled Ned, paying little attention now to the big airship shed, since he saw that the danger was about over.

"Dhat's what he suah hab done!" agreed Eradicate. "Mah ole mule Boomerang couldn't 'a' done any better."

"Huh! Your mule afraid of fire," remarked Koku.

"What's dat? Mah mule afraid ob fire?" cried the colored man. "Look heah, yo' great, big, overgrowed specimen ob an equilateral quadruped, I'll hab yo' all understand dat when yo' all speaks dat way about a friend ob mine dat yo'—"

"That'll do, Rad!" broke in Ned, with a laugh. He knew that when Tom's helper grew excited on the subject of his mule there was no stopping him, and Boomerang was a point on which Eradicate and Koku were always arguing. "The fire is under control now."

"Yes, it seems to have gone visiting," observed Koku.

"Visiting?" queried Ned, in some surprise.

"Yes, that is, it is going out," went on Koku.

"Oh, I understand!" laughed Ned. "Yes, and I hope it doesn't pay us another visit soon. Oh, look at Tom, would you!" he cried, for the young aviator had swung his ship about over the flames, to bring another row of sand bags directly above a place where the fire was hottest.

Down showered more sand from the bags which Tom opened. No fire could long continue to blaze under that treatment. The supply of air was cut off, and without that no fire can exist. Water would have been worse than useless, because of the carbide, but the sand covered it up so that it was made perfectly harmless.

Moving slowly, the airship hovered over every part of the now slowly expiring flames, the burned opening in the roof of the shed making it possible for the sand to reach the spots where it was most needed. The flames died out in section after section, until no more could be seen—only clouds of black smoke.

"How is it now?" came Tom's voice, as he spoke from the deck of the balloon through a megaphone.

"Almost out," answered Mr. Damon. "A little more sand, Tom."

The eccentric man had caught up a piece of paper and, rolling it into a cone, made an improvised megaphone of that.

"Haven't much more sand left," was Tom's comment, as he sent down a last shower. "That will have to do. Hustle that carbide and other explosive stuff out of there now, while you have a chance."

"That's it!" cried Ned, who caught his chums meaning. "Come on, Koku. There's work for you."

"Me like work," answered the giant, stretching out his great arms.

The last of the sand had completely smothered the fire, and Tom, observing from aloft that his work was well done, moved away in the dirigible, sending it to a landing space some little distance away from the shed whence it had arisen. It was impossible to drop it back again through the roof of the hangar, as the balloon was of such bulk that even a little breeze would deflect it so that it could not be accurately anchored. But Tom had it under very good control, and soon it was being held down on the