“Metals crystallize, if they have just the right conditions. Each metal has its own form; so, if you could find a single crystal, you would recognize it by its form.
“But when melted iron grows solid, the crystals are crowded so close together that, when it is prepared for the microscope, and polished like this, the surface looks as if it were made up of ‘crystal grains.’
“Sometimes crystallization takes place in steel if it is subjected to long repeated jar. Many accidents in engines are due to that.”
As he took the cover off his microscope, Mr. Farnsworth said:
“I suppose, Harry, that your ‘pygmies’ are the elements that are found in the various kinds of iron?”
“The same,” answered Mr. Prescott.
“Then I shall tell Billy Bradford that some of the pygmies are enemies and others are friends; some need to be driven away, and others should be invited to come in.
“The most numerous enemies are the Carbon pygmies. The blast furnace drives most of them off, but they have to be fought in the pig iron, too.
“Sulphur pygmies are about the worst of all, because they make the iron brittle. They are practically the hardest to drive away.
“Phosphorus pygmies haven’t a good reputation, but they are in much better standing than the Sulphur enemies.