A manual of electro-metallurgy

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1844 Excerpt: ...the chemical process called " dipping," or by the mechanical process called " scratching." It often happens that the nature of the articles will not admit of this rough surface, and when thin films of metal are to be deposited, it is obviously impracticable; in such cases the end must be attained by carefully cleaning the surface. 231. The most effectual cleaning is effected by immersion in an acid liquor, called " dipping liquor." The composition of this liquid is as follows:--Sulphuric Acid 64 Nitric Acid 32 Hydro-chloric (muriatic) acid.... 1 Water 64 If the surface of the article to be cleaned, is covered with oily or greasy matters, the process of dipping will be of little avail, the metal being effectually defended from the action of the acid, by the film of greasy matter-In such cases it is necessary to remove the oil, or grease, before the process of dipping. This may be done in a variety of ways; the most convenient, and a very effectual one, is that of boiling the articles in a strong solution of pearlash; after such treatment, the dipping acid will take effect. 232. Metallic surfaces may be made clean by means of the voltaic battery. It has been already more than once stated (6), that when a metal, having an affinity for oxygen, is connected with the copper or silver end of the batter', and made one of the electrodes in an acid or saline solution, the oxygen evolved there by the passage of the voltaic current, combines with the metal, and forms an oxide; an excellent method of cleaning surfaces to receive voltaic deposites, is founded on this fact. In order to clean a metallic surface by means of the battery, the article must be attached by a wire to the copper, or negative metal, of the instrument; and a metallic su...