Put the articles requiring to be hardened, after being finished but not polished, into an iron box in layers with animal carbon, that is, horns, hoofs, skins, or leather, partly burned so as to be capable of being reduced to powder, taking care that every part of the iron is completely surrounded; make the box tight with a lute of sand and clay in equal parts, put the whole into the tire, and keep it at a light red heat for half an hour to two hours, according to the depth of hardened surface required, then empty the contents of the box into water, care being taken that any articles liable to buckle be put in separately and carefully, end in first.

Cast iron may be case hardened as follows: -

Bring to a red heat, and roll it in a mixture of powdered prussiate of potash, saltpetre and sal-ammoniac in equal parts, then plunge it into a bath containing 2 oz. prussiate of potash, and 4 oz. sal-ammoniac per gallon of water.