Case-hardening

The proce of converting the surface of iron into steel. Formerly much used in making small-arms. The parts to be hardened, such as the hammer , tumbler , etc., were inclosed in an airtight iron box, filled with charcoal, bones, particles of horn, or other carbonizing substance. The box and its contents were then submitted to prolonged heat. The proce is that of incomplete cementation (which see).