"Bless my cartridge belt, Tom, you don't really mean to say that stuff is powder!" exclaimed Mr. Damon.

"That's what I hope it will prove to be--and powerful powder at that."

"Why, it looks more like excelsior than anything else," went on the odd man, gingerly taking up some yellowish shreds in his fingers.

"And it will burn as harmlessly as excelsior in the open air," went on Tom. "But I hope to prove, when it is confined in a chamber, that it will be highly explosive. I'm going to make a test of it soon."

"Give me good notice, so I can get over in the next State!" exclaimed Ned Newton, with a laugh.

This was several days after our friends had returned from the disastrous gun test at Sandy Hook. Tom had at once gotten to work on the problem that confronted him--a problem of his own making-- to build a giant cannon that would make the longest shots on record. And he had first turned his attention to the powder, or explosive, to be used.

"For," he said, "there is no use having a big gun unless you can fire it. And the gun I am planning will need something more powerful in the powder line than any I've ever heard of."

"Stronger than the kind General Wailer used?" inquired Ned.

"Yes, but I'll make my cannon correspondingly stronger, too, so there will be no danger."

"Bless my shoe buttons!" exclaimed Mr. Damon. "You boys must have had your nerve with you to stay around Sandy Hook after that gun went up in the air."

"Oh, the danger was all over soon after it began," spoke Tom, with a smile. "But now I'm going to test some of this powder. If you want to run away, Mr. Damon, I'll have Koku take you up in one of the airships, and you'll certainly be safe a mile or so in the air," for Tom had instructed his giant servant how to run one of the simpler biplanes.

"No--no, Tom, I'll stick!" exclaimed the eccentric man. "I'll not promise not to hide behind the fence, or something like that, though, Tom; but I'll stick."

"So will I," added Ned. "How are you going to make the test, Tom?"

"I'll tell you in a minute. I want to do a little figuring first."

Tom had, before going to Sandy Hook, made some experiments in powder manufacturing, but they had not been very satisfactory. He had not been able to get power enough. On his return he had undertaken rather a daring innovation. He had mingled two varieties of powder, and the resulting combination would, he hoped, prove just what he wanted.

The powder was in gelatin form, being made with nitro-glycerine as a base. It looked, as Mr. Damon had said, like a bunch of excelsior, only it was yellow instead of white, and it felt not unlike pieces of dry macaroni.

"I have shredded the powder in this manner," Tom explained, "so that it will explode more evenly and quickly. I want it to burn as nearly instantaneously as possible, and I think it will in this form."

"But how are you going to tell how powerful it is unless you fire it in a cannon?" asked Ned. "And you haven't even started your big gun yet."

"Oh, I'll show you," declared Tom. "There are several ways of making a test, but I have one of my own. I am going to take a solid block of steel, of known weight--say about a hundred pounds. This I will put into a sort of square cylinder, or well, closed at the bottom somewhat like the breech of a gun. The block of steel fits so closely in the square well that no air or powder gas can pass it.

"In the bottom of this well, which may be a foot square, I will put a small charge of this new powder. On top of that will come the steel block. Then by means of electric wires I can fire the charge.

"Attached to the steel well, or chamber, will be a gauge, a pressure recorder and other apparatus. When the powder, of which I will use only a pinch, carefully weighing it, goes off, it will raise the hundred-pound weight a certain distance. This will be noted on the scale. There will also be shown the amount of pressure released in the gas given off by the powder. In that way I can make some calculations."

"How?" asked Ned, who was much interested.

"Well, for instance, if one ounce of powder raises the weight three feet, and gives a muzzle pressure of, say, five hundred pounds, I can easily compute what a thousand pounds of powder, acting on a projectile weighing two tons and a half, would do, and how far it would shoot it."

"Bless my differential gear!" cried Mr. Damon. "A projectile weighing two and a half, tons! Tom, it's impossible!"

"That's what General Waller said about his gun; but it burst, just the same," declared Ned. "Poor man, I felt sorry for him. He seemed rather put out at you, Tom."

"I guess he was--a bit--though I didn't mean anything disrespectful in what I said. But now we'll have this test. Koku, take the rest of this powder back. I'll only keep a small quantity."

The giant, who, being more active than Eradicate, had rather supplanted the aged colored man, did as he was bid, and soon Tom, with Ned and Mr. Damon to help him, was preparing for the test.

They went some distance away from any of the buildings, for, though Tom was only going to use a small quantity of the explosive, he did not just know what the result would be, and he wanted to take no chances.

"I know from personal experience what the two kinds of powder from which I made this sample will do," he said; "but it is like taking two known quantities and getting a third unknown one from them. There is an unequal force between the two samples that may make an entirely new compound."

The steel chamber that was to receive the hundred-pound steel block had been prepared in advance, as had the various gauges and registering apparatus.

"Well, I guess we'll start things moving now," went on Tom, as he looked over the things he had brought from his shops to the deserted meadow. The fact of the test had been kept a secret, so there were no spectators. "Ned, give me a hand with this block" Tom went on. "It's a little too heavy to lift alone." He was straining and tugging at the heavy piece of steel.

"Me do!" exclaimed Koku the giant, gently pushing Tom to one side. Then the big man, with one hand, raised the hundred-pound weight as easily as if it were a loaf of bread, and deposited it where Tom wanted it.

"Thanks!" exclaimed our hero, with a laugh. "I didn't make any mistake when I brought you home with me, Koku."

"Huh! I could hab lifted dat weight when I was a young feller!" exclaimed Eradicate, who was, it is needless to say, jealous of the giant.

The powder had been put in the firing chamber. The steel socket had been firmly fixed in the earth, so that if the force of the explosion was in a lateral direction, instead of straight up, no damage would result. The weight, even if it shot from the muzzle of the improvised "cannon," would only go harmlessly up in the air, and then drop back. The firing wires were so long that Tom and his friends could stand some distance away.

"Are you all ready?" cried Tom, as he looked to see that the wiring was clear.

"As ready as we ever shall be," replied Mr. Damon, who, with Ned and the others, had taken refuge behind a low hill.

"Oh, this isn't going to be much of an explosion," laughed Tom. "It won't be any worse than a Fourth of July cannon. Here she goes!"

He pressed the electric button, there was a flash, a dull, muffled report and, for a moment, something black showed at the top of the steel chamber. Then it dropped back inside again.

"Pshaw!" cried Tom, in disappointed tones. "It didn't even blow the weight out of the tube. That powder's no good! It's a failure!"

Followed by the others, the young inventor started toward the small square "cannon." Tom wanted to read the records made by the gases.

Suddenly Koku cried:

"There him be, master! There him be!" and he pointed toward a distant path that traversed the meadow.

"He? Whom do you mean?" asked Tom, startled the giant's excited manner.

"That man what come and look at Master's new powder," was the unexpected answer. "Him say he want to surprise you, and he come today, but no speak. He run away. Look--him go!" and he pointed toward a figure of distinctly military bearing hurrying along the road that led to Shopton.