Several powders have been placed on market for the purpose of casehardening. The principles to be adopted in compounding them will be obvious from what we have just written. The following are a few of the best: -

1. Prussiate of potash, dried, finely powdered, and mixed with any simple coloring-matter to disguise its appearance.

2. Prussiate of potash, 3 parts; sal ammoniac, 1 part. Powder finely, and mix thoroughly. A little very finely powdered animal-charcoal is sometimes added.

3. Sal ammoniac and bone-dust, of each 2 parts; prussiate of potash, 1 part. Grind to fine powder, and mix thoroughly.

4. The powder suggested by the author of this work, namely, animal charcoal, soaked in a solution of prussiate of potash and finely powdered, we believe to be the most convenient and efficient. It is cheap, easily made, and, if put up in packets of different sizes, would find a ready though limited sale.