In the center of this hole would be a small "core" made of asbestos and concrete mixed. Around this would be poured the molten steel from great caldrons. It would flow into the hole. The sides of earth—lined with fire-clay—would hold it in, and the middle core would make a hole throughout the length of the central part of the gun. Afterward this hole would be bored and rifled to the proper calibre.
After this central part was done, steel jackets or sleeves would be put on, red-hot, and allowed to shrink. Then would come a winding of wire, to further strengthen the tube, and then more sleeves or jackets. In this way the gun would be made very strong.
As the greatest pressure would come at the breech, or in the powder chamber there, the gun would be thickest at this point, decreasing in size to the muzzle.
It took many weary weeks to get ready for the first cast, but finally Tom received word that it was to be made, and with Ned, and Mr. Damon, he proceeded to the plant of the steel concern.
There was some delay, but finally the manager gave the word. Tom and his friends, standing on a high gallery, watched the tapping of the combined furnaces that were to let the molten steel into the caldrons. There were several of these, and their melted contents were to be poured into the mould at the same time.
Out gushed the liquid steel, giving off a myriad of sparks. The workers, as well as the visitors, had to wear violet-tinted glasses to protect their eyes from the glare.
"Hoist away!" cried the manager, and the electric cranes started off with the caldrons of liquid fire, weighing many tons.
"Pour!" came the command, and into the pit in the earth splashed the melted steel that was to form the big cannon. From each caldron there issued a stream of liquid metal of intense heat. There were numerous explosions as the air bubbles burst—explosions almost like a battery in action.
"So far so good!" exclaimed the manager, with a sigh of relief as the last of the melted stuff ran into the mould. "Now, when it cools, which won't be for some days, we'll see what we have."
"I hope it contains no flaws," spoke Tom, "That is the worst of big guns—you never can tell when a flaw will develop. But I hope—"