588 ANNUAL EECORD OF SCIENCE AND INDUSTRY. 



hot, though not glowing, molten zinc, for a short time, until 

 they acquire the temperature of the zinc, the surface of the 

 zinc having been cleaned with an iron spoon. They are then 

 removed and beaten, to cause the excess of zinc to fall off. 

 12 (7, February, 1873, 12. 



COATING CAST AND WROUGHT IKON AND STEEL WITH COPPER. 



For this purpose the three following methods are given by 

 Gaudoin : 1. Dry method : To coat wrought or cast iron with 

 a heavy film of copper, brass, or bronze, when it is not nec- 

 essary that it should be perfectly uniform (as in printing roll- 

 ers, sockets, etc.), the object, after having been heated to the 

 same temperature, is dipped into a bath formed of the neces- 

 sary quantity of metal, melted in a crucible of suitable shape, 

 and covered with a layer of pulverized cryolite and phos- 

 phoric acid. 2. A second dry method, with or without an 

 electric current, applicable with advantage to fancy articles 

 requiring only a slight coating : A mixture of one part dry 

 subchloride or subfluoride of copper and five to six parts of 

 cryolite is fused in a crucible, to which a certain amount of 

 chloride of barium may be added to increase its fusibility. 

 The articles, previously cleansed by dipping in acid solution, 

 when immersed in the perfectly fluid mass, become coated 

 with an adhesive layer of copper (displaced from its combina- 

 tion), of a thickness dependent upon the length of the immer- 

 sion and the concentration of the bath. Employing an elec- 

 tric current has the advantao-e of maintaining: the streno-th of 

 the bath constant, as well as facilitating the dej^osition of 

 copper. 3. The Avet process : The cause of the failure to 

 produce heavy, adhesive, tough films of copper on wrought 

 or cast iron and steel by any of the numerous alkaline and 

 neutral solutions of salts of copper proposed for this purpose, 

 lies in the fact that such baths have not the property of com- 

 pleting the cleansing of the surface of the iron, only partially 

 brought about, especially with cast iron, by the previous dip- 

 ping. Investigations on copper-coating, on a large scale, in- 

 dicate that decidedly acid copperiijg solutions must be em- 

 ployed, which may cleanse the oxidized portions unafiected 

 by the dipping, without, how^ever, attacking the underlying 

 metal, thus acting continually upon the parts not coated with 

 copper, and finally removing the oxide which prevents its 



