When using the "acid dip" method on copper and brass the work must be fastened to a piece of copper or brass wire (do not use iron wire), and hung in the solution for about five to thirty seconds, the length of time depending upon the strength of the solution. The work must then be thoroly washed off in cold running water. Care must be taken to avoid getting any of the solution upon the hands or clothing. A few of the best of these dipping solutions are as follows:

No. 1. Sulphuric acid, one part. Nitric acid, one part.

No. 2. Sulphuric acid, one part. Nitre, one part, Water, one part.

No. 3. Yellow aqua fortis, 1 quart, Sulphuric acid, 1 quart, Muriatic acid, 1 gill, Water, 1 pint.

No. 4. Sulphuric acid, 1 quart, Nitric acid, 1 pint.

No. 5. Hydrofluoric acid, 4 quarts, Nitric acid, 3 quarts, Common salt, 2 tablespoonfuls.