Page:Tom Swift and His Giant Cannon.djvu/112

102 It was in thin sheets, with holes pierced through it here and there, irregularly.

"The idea is," Tom explained, "to make a quick-burning explosive. I want the concussion to be scattered through it all at once. It is set off by concussion, you see," he went on, "A sort of cartridge is buried in the middle of it, after it has been inserted in the cannon breech. The cartridge is exploded by a primer, which responds to an electric current. The thin plates, with holes corresponding to the centre hole in a big grain of the hexagonal powder, will, I hope, cause the stuff to burn quickly, and give a tremendous pressure. Now we'll put some in the steel tube, and see what happens."

Even Tom was a little nervous as he prepared for this latest test. But he was not nervous enough to drop any of those queer, cheese-like slabs. For, though he knew that a considerable percussion was needed to set them off, it would not do to take chances. High explosives do not always act alike, even under the same given conditions. What might with perfect safety be done at one time, could not be repeated at another. Tom knew this, and was very careful.

The powder, as I shall occasionally call it for the sake of convenience, though it was not such in the strict sense of the word—the powder was