"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.