om. "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 entirel