Mix this well, and let it stand for about three hours, or until the action of the battery becomes weak, when it is in order to work with a very uniform action.

Put one pound of sulphate of copper in one quart of water; stir it until the sulphate of copper is all dissolved, and then add one half ounce of sulphuric acid and a quarter of an ounce of nitric acid.

This solution, well mixed, should be filtered, and it is ready for use.

It is very important that the solution should be kept clean, clear, and free from all foreign substance.

The above quantity of this solution will be found sufficient for electrotyping a dozen of the sixth-size plates.