“Using your eyes, are you, Billy? That’s quite likely to set your mind to working.
“I suppose you’ve heard them talking around here about testing machinery. That isn’t the first testing. They test iron all the way along, from the ore in the mine to the sticks of pig iron piled up in our yard.”
“Some of it is in cakes,” said Billy.
“Is that so?” asked Uncle John, as he took another sandwich out of his pail. “Now I think of it, they did tell me that cakes are the new style in pig iron.
“Well,” continued Uncle John, “there are men testing and experimenting all the time; and some of them found out that old iron and pig iron together make better new iron than they can make from pig iron alone. Since they found that out, scrap iron has kept on going up in price.
“Did you happen, Billy, to see any other heaps lying around?”
“I saw a pile of coke, over in the corner,” answered Billy.
“Somewhere,” said Uncle John, “there must have been a heap of limestone. They use that for what they call a flux. That unites with the waste things, the ashes of the coke and any sand that may have stuck to the pig iron. Those things together make slag. The slag is so much lighter than the iron that it floats on top, and there are tap holes in the cupola where they draw it off. Limestone helps the iron to melt, that’s another reason why they use it.”
“I saw some scales,” said Billy.
“Those,” said Uncle John, “are to weigh the things that they put into the cupola. There are rules for making cast iron. It all depends on what kind of machinery we want to make.