"Gun-metal," said the other, "is an alloy of copper and tin and once was used almost exclusively for cannon and big guns generally. But you're right about all guns having a bluish tinge. That is all steel, but it is treated by a process called coloring or bluing. I'll show you—both the old way and the new."
Going down the stairs and crossing the yard, he took Hamilton into a small building where there were a couple of open charcoal furnaces, in which the charcoal was intensely hot, but not hot enough to catch fire. The pieces of finished steel were buried in this charcoal, and every few minutes the men in charge would draw them out, wipe them over with a bunch of oiled waste, and thrust them back into the fire. It was about the dirtiest, blackest, grimiest work the boy had ever seen.
"That is the old way," Hamilton was told, "and although it is handwork instead of machine work it is not a bit better in its results than the new way. The modern system, besides, is much simpler and cleaner."
In the next building was a row of charcoal ovens, revolving in such a way that the parts to be blued were alternately covered and released from the superheated charcoal, the effect of the greasing also being done at every automatic revolution Each furnace door bore an asbestos clock.
"What are those clocks for?" asked Hamilton. "The same as those others, I suppose, so that the man in charge can put in a number of certain parts of a gun and leave them in for a regular length of time at a certain heat, and pull them out all done?"
"Just that," was the reply. "The only gain in the old style is that each part being handled separately, if there is ever so little difference in the metal, the bluer can give it a shorter or a longer time, whereas the machine treats all alike."
"Then when the gun is assembled, all the work is done?" queried Hamilton, who was becoming a little tired from his long tramp through the works and among the furnace-heated shops.
"No," said the other. "That wouldn't do at all. A gun has not only got to shoot, but it has got to shoot straight."
"But how in the world," said Hamilton, "can you tell whether a gun will shoot straight or not?"
"One of the most important ways," said his informant, "is to let an expert look through the barrel. One of our best men, for example, has done nothing else all his life; his father before him was a barrel-sighter and his son has just entered the works. He does it this way—here, you try," and he handed a barrel to Hamilton. "Rest the barrel in this crotch," he continued, "and look at the window. You see there is a piece of ground glass with a thin black line running across it. Point the barrel so that it is aimed just below that line, and if you get it right, you will see a reflection of that line running lengthways up the barrel."