First plunge the articles in nitric acid and then wash rapidly in a large quantity of water, then dip them with constant movement for a few seconds in a mixture which has been allowed to stand at least twelve hours, composed of:
53 ounces Sulphuric Acid,
70 1/2 ounces Nitric Acid,
2 82-100 ounces Hydro-chloric Acid,
3 17-100 ounces Sal-ammoniac, 5 29-100 ounces Alum,
3 1/2 ounces Lampblack.
Take the articles from this bath and wash same rapidly in a large quantity of water. The method of preparing this bath is as follows: First pour the nitric acid into the vessel, next adding the finely pulverized salts, followed by the hydro-chloric acid, and after an hour or so, gradually add the sulphuric acid. Care should be taken in mixing these acids, as a large amount of heat is originated and fumes injurious to the lungs are developed; hence, the mixture is best made out of doors or under a chimney with an excellent draught. A large vessel should be used, because otherwise the sulphuric acid might run over. This mixture can be used for a considerably long time, as it is only necessary to add a little sulphuric acid and by and by a little nitric acid and sal-ammoniac.