IV. — Remarks upon the Coating of Iron with Magnetic 

 Oxide, and a Suggestion of a probably New Method of 

 producing it — By John Forbes. 



(Read February 0th, ISOl.) 



In the production of articles of metal, it is frequently desirable 

 that the condition or color of the surface be chano-ed, sometimes 

 as a matter of taste, the natural color of the metal not comport- 

 ing with its associations, or with its purposed use ; sometimes 

 as a protection of the article from deterioration by natural oxi- 

 dation, and, in some cases, with both of these aims in view^ 



Often the surfaces of such articles are intentionally oxidized, 

 and a more uniform and more durable, as well as a more beauti- 

 ful, oxidation, produced by the artificial means, than that which 

 would result if Nature were left to do the work herself in the 

 ordinary course of wear or of exposure. 



Silver articles are frequently artificially coated with a film of 

 sulphuret of silver, whicli, while being- of a more even character 

 both in constitution and color, is also more tasteful and probably 

 more durable than a natural result would produce. 



Tin and zinc articles frequently have their surfaces treated in 

 such a manner as to produce a crystalline effect, which is pre- 

 served by a thin covering of lacquer, giving a better and more 

 durable effect than if left to the natural action of the atmosphere 

 or other causes. 



Copper, after being polished, is made darker, and the natural 

 metallic lustre and redness changed to a dark chocolate color, tlie 

 surface being thus improved and made more duraljle. 



Iron is frequently covered with tin or zinc, by lieing dipj^ed 

 '(after proper preparation of its surface) into a melted liatli of 

 •one of those metals. 



Steel and iron articles are also frequently treated in such a 

 ananner as to produce upon them a thin scale or film of magnetic 

 ^oxide, FcgO^, which, being a different degree of oxidation than 



(27) 



