Brown bronze dip, for coating hat-hooks and similar small hardware articles, is made of iron scales 1 lb., arsenic 1 oz., muriatic acid 1 lb., zinc, solid, 10 ozs. The zinc should be kept in only when the bath is used. The castings must be perfectly free from sand and grease.

CasE-hardening, to be quickly performed, is done by the use of prussiate of potash. This is powdered and spread upon the surface of the iron to be hardened, after the iron is heated to a bright red. It almost instantly fluxes and flows over the surface; and when the iron is cooled to a dull red, it is plunged in cold water. Some prefer a mixture of prussiate of potash 3 parts, sal-ammoniac 1 part; or prussiate 1 part, sal-ammoniac 2 parts, and finely-powdered bone-dust (unburned) 2 parts. The application is the same in each case. Proper case hardening, when a deep coating of steel is desired, is done by packing the article in an iron box with horn, hoof, bone-dust, shreds of leather or raw hide, or either of these, and heating to a red heat for from 1 to 3 hours, then plunging the box into water.