M. TECHNOLOGY. 515 



by heating a copper article thus coated carefully to about 

 248 to 284 (best under olive-oil), when the zinc will unite 

 with the copper support to form a gold-tinted tombac, and 

 the article need only be quickly cooled in water, or some 

 other suitable liquid, as soon as the desired color is apparent. 

 18 (7, VII., 345. 



ENAMELING ON BRASS AND GERMAN SILVER. 



The adhesion of enamel to brass and German silver, it is 

 said, may be most perfectly effected by first engraving or 

 pressing the design to be enameled into the alloy, and then 

 coating the whole object, or only the depressed design, gal- 

 vanically with copper. The enamel can be fused upon this 

 surface as usual, and may then be bronzed or silvered, or 

 treated in any usual way. 5 6", XL., 399. 



BRONZING IRON CASTINGS. 



A process for bronzing iron castings, patented in different 

 countries by Gaudoin, Mignon, and Bouart, differs from pre- 

 ceding ones in dispensing with the intervention of a third 

 substance, and at the same time rendering the film of copper 

 so adherent that it will not scale off; but in some cases the 

 iron and copper have been found to scale off together. The 

 film is also said to be perfectly uniform in thickness upon the 

 elevations and depressions, and on the undercut portions, and 

 capable, in the hands of a skillful workman, of acquiring a 

 close resemblance to bronze. The process has been employed 

 at the large foundery of ornamental iron-work at Val d'Osne 

 on castings of all sizes up to colossal statues, some of which 

 have withstood the weather for a summer and two winters 

 without the least injury. The cost is not more than double 

 that by the usual process. A similar method may also be 

 employed for tinning copper and cast-iron vessels. 5 C, 

 ^Lj., 383. 



NICKEL-PLATING PROCESS. 



Plazenet employs a bath composed of 87.5 grammes of 

 sulphate of nickel, 20 grammes of sulphate of ammonia, 17.5 

 grammes of citric acid dissolved in 2 liters of water. Another 

 recipe much used in France is formed of a solution of 4 parts 



