M. TECHNOLOGY. 559 







short of that of polished silver. One of the chief advantages 

 of the new method is that it obviates the liability of iron and 

 steel goods to rust, and it is proj^osed that Avhere articles are 

 to be silver-plated, a white under-coat shall be first given by 

 means of this new material, so that when the silver wears 

 off it will show the silver-white appearance beneath. 



The process is now being applied to coating various sub- 

 stances, such as harness-fittings, spurs, bedstead-springs, sew- 

 ing-machines, gas-fittings, locks, keys, etc. 8 A, December 2, 

 1872, 185. _^ 



HOT-GILDIXG OF IRO?f. 



The process of hot-gilding of iron, and similar metals, has 

 been lately much simplified by Kirchmann, who produces 

 gilt designs which are very uniform, and which bear polish- 

 ing. This is done by rubbing the surface with soda-amalgam 

 (which amalgamates it immediately, even if the surface be 

 oxidized), and then quickly applying a concentrated solution 

 of chloride of gold, and expelling the mercury by the heat 

 of a lamp or furnace. Similar results may be obtained with 

 platinum and silver salts. 13 C, December 15, 1872, 1624. 



PYRO-PLATIXG. 



The term pyro-plating has been applied to a method of 

 coating one metal with another by the action of heat, to dis- 

 tinguish it from the electro-plating, close-plating, and amal- 

 gamation processes ; the peculiarity being that the coating, 

 after deposition, is driven into the surfiice of the metal by 

 the aid of heat and atmosj^heric pressure. It is nsed, there- 

 fore, wherever the other processes indicated are unsuited or 

 impracticable, and is applicable not only for coating with sil- 

 ver, but also with gold, platinum, aluminium, copper, alu- 

 minium-bronze, etc. 



The object to be coated must be rendered chemically clean, 

 this being efi*ected in various Avays, according to the metal 

 to be operated upon. Thus articles of iron or steel are first 

 boiled in caustic alkali, and then cleaned, nnder water, with 

 emery and wire brushes, and finally by ireneratinc: nascent 

 hydrogen upon the surface, the articles being suspended in a 

 hot alkaline solution, and made the negative pole of a some- 

 what powerful battery. When perfectly clean, they are 



