84 HYDKOMETALLURGT. [ HI. 



It is only necessary to use the zincking solution dilute, and 

 the electric current proportionally feebler. The zinc coating 

 had the thickness of writing paper. The results with hyposul- 

 phite of zinc were unsatisfactory. 



4. The arts of design may be applied to metallic surfaces by 

 etching, and in other ways, a feAY hints on which, of a chemical 

 character, we here present. 



Niello-ivork. — A metallic plate of iron, copper, &c. is 

 covered with an etching ground, the design graved through 

 it with a point, and these portions etched out by acid. The 

 etching ground being removed, the plate is put into a galvano- 

 plastic apparatus, and coated thickly with metal. The whole 

 surface is ground down, until the precipitated metal is only 

 left in the etched lines. Copper or silver is thus precipitated 

 on steel or copper ; and several metals may be precipitated on 

 the same plate. (Vogel in Polytech. Notizbl. 1847.) 



Etching on Cojjper and Steel. — To avoid the disagreeable 

 nitrous fumes arising from the employment of nitric acid for 

 etching, as is ordinarily done, Schwartz and Btihme propose 

 for steel, 10 pts. fuming muriatic acid, diluted with 70 pts. 

 water, mixed with a boiling solution of 2 pts. chlorate of po- 

 tassa in 20 pts. water. The liquid is diluted, before using, 

 with 100 to 200 pts. water. For copper, 2 pts. iodine and 5 

 pts. iodide of potassium are dissolved in 4 pts. water for a 

 strong action, or in 8 pts. water for feebler action. (An. d. 

 Ch. u. Pharm. Ixvi. 63.) 



Engraving ujwn Silvered or Gilded Coj)per. — Becquerel 

 (Comptes Rendus, xxvi. 153) gives an abstract of Victor's 

 method of copying drawings upon metal, glass, or paper ; and 

 also of Poiterin's ingenious improvement, by which these 

 drawings may be transferred in a few hours to metal plates, 

 so that they will furnish impressions. The process in detail 

 may be found in the Philosophical Magazine for 1848. 



The drawing or writing, previously subjected to the action 

 of iodine vapors, is gently and carefully pressed upon a highly 

 polished daguerreotype plate. The black lines, being the only 

 portions which are iodized, imprint the silver with a corre- 



