riRE-GILDING OF IRON AND STEEL. 73 



are added to the solution, 'which assumes a greenish color and 

 becomes a little cloudy. 



Barral (Memoire sur la Precipitation de I'Or a TEtat Mdtal- 

 lique, Paris, 1846) gives his experiments ; among others, the 

 following. A bright article of silver, connected by copper 

 wire with a piece of copper, which has been ignited and 

 quenched in dilute sulphuric acid, is beautifully gilt, of any 

 desired thickness, in the liquid. The bright article forms the 

 negative, and the dull copper, the positive pole. Brought in 

 contact with zinc, the silver is gilt more rapidly, arid the action 

 is strongest when the silver is connected with lead. The me- 

 tal serving as positive pole is covered with a strong precipitate 

 of pulverulent gold. By connecting copper with zinc, or iron 

 with lead, the former is powerfully gilt. Bright copper is 

 strongly gilt in connection with dull copper (ignited), while the 

 latter is covered with a powdery deposit. 



Crilding on Iron and Steel. — Eisner showed, in 1841, that 

 steel pens may be heavily gilt, by first removing their blue 

 coating by dilute muriatic acid, and then dipping them into a 

 solution of chloride of gold rendered alkaline by carbonate of 

 soda. Schoppler gives the following method for coating larger 

 articles. (Polytech. Notizbl. 1847.) The surface of iron or 

 steel, being brightened by the file, and coated with lack- varnish, 

 those portions to be gilt are freed from the lacquer, etched 

 by dilute sulphuric acid, dried, and dipped into a very dilute 

 solution of blue vitriol until they are coated with copper. The 

 metal is then dipped into a solution of 100 pts. gold in 13,000 

 pts. water, to which 370 pts. carbonate of soda are added. The 

 gilding may be polished. 



Fire-gilding of Wrought and Cast-iron, and Steel. — This 

 operation, readily performed on bronze and copper by amal- 

 gamating their surface, has not been applied to iron, on account 

 of the difficulty of amalgamating its surface ; but R. Bcittger 

 has contrived the following good method of effecting it. A 

 mixture is made in a porcelain vessel, of 12 pts. mercury, 1 pt. 

 zinc, 2 pts. copperas, 12 pts. water, and 1| pt. muriatic acid 

 of spec. grav. 1.2. The article of iron or steel to be gilded 



