“The gas produced by the furnace used to be wasted. Now they utilize it in the hot-blast stoves. That accounts for some of the huge pipes attached to the furnace. Come this way, and I’ll show you a stove.
“Here it is, almost as tall as the furnace itself. This giant, also, is encased in an armor of iron plates. If we could look inside, we should see that it is almost filled with open brick work that resembles a honeycomb.
“They send hot gas over the brick work till the stove is hot, then they shut off the gas and start the engine that blows in cold air. That, heated by the bricks, is forced into the furnace.
“One of those great pipes up there is where they draw off the slag. It is so much lighter than the iron that it rises to the top, like cream on milk.
“Down here they draw off the iron. Sometimes they keep it hot for the next process; sometimes it is made into pig iron.”
“What,” asked Dr. Crandon, “becomes of the slag?”
“That depends somewhat on the chemical composition of the slag. Some kinds are broken up to be used as foundation for roads; others are granulated by being run into water, and so made into cement. Over in Germany, where the ores are rich in phosphorus, they grind up the linings of the furnace to make phosphatic fertilizers for the farmers.”
“Then,” said Dr. Crandon, “the making of iron involves the use of chemistry, doesn’t it?”
“It certainly does,” answered Mr. Prescott; “from the chemical composition of ores to the finished product. We are learning a great deal just now from the chemists about steel alloys.
“I didn’t tell you that from the gas they sometimes save ammonia, tar, and oils, before it is fed to the hot-blast stoves.”