To Case-Harden
Make a paste with a concentrated solution of prussiate of potash and loam, and coat the iron therewith; then expose it to a strong red heat, and when it has fallen to a dull red, plunge the whole into cold water. which steel becomes hard is indubitably the best, the mode here recommended will be found the only one by which the process of hardening can be effected with a less portion of fire than is, or can be, required in any other way. These observations are decisive, and will, in all probability, tend to establish in general use what cannot but be regarded as a very important improvement in the manufacturing of edge steel instruments. 3303. To Case-Harden Small Articles of Iron. Fuse together, in an iron vessel or crucible, 1 part prussiate of potash and 10 parts common salt, and allow the article to remain in the liquid 30 minutes, then put them in cold water and they will be case-hardened.