WELDING POWDER. 69 



bones, and 3 pts. ignited and ground flints. The mixture is 

 then ground with water, spread over the first coat and burned 

 in. The third and last coat (which is similarly treated) con- 

 sists of 12 pts. powdered feldspar, 4| pts. kaolin, 18 pts. 

 borax, 3 pts. saltpeter, 1| pt. potash, and 1| pt. oxide of tin. 



Soldering Salt (chloride of zinc and ammonium). — Vessels 

 may be tinned with this salt without previously cleansing their 

 surfaces. It is made by dissolving IR) zinc in muriatic acid, 

 adding 22 pts. salammoniac to the solution, and evaporating 

 to dryness ; the yield is 2 Jib of the double salt. To use it, the 

 salt, moistened with water, is brushed on the surface to be 

 tinned, a little solder laid on it here and there, and the surface 

 heated until the solder fuses, when it flows wherever the salt 

 was put, and unites with the metallic surface. (Journ. f. 

 Buchdruckerk. 1847, No. vii.) 



. Tinning. — According to Becquerel, well-cleansed vessels of 

 iron and copper may be tinned by dipping them into a solution 

 of the double salt of chloride of tin and sodium, at a heat of 

 160° assisted by contact with zinc. 



Soldering Wrought and Cast-iron. — Filings of soft cast-iron 

 are melted with calcined borax, the mass pulverized and 

 sprinkled on the parts to be united. They are then separately 

 heated and welded together on an anvil by gentle blows. 

 (Journ. Fr. Inst. (3) xviii. 50.) 



Welding Powder. — To melted borax, J^ salammoniac is 

 added, the mixture poured on an iron plate, and an equal 

 weight of quicklime ground up with it. Iron or steel to be 

 welded is first heated to redness, the mixture laid on the weld- 

 ing surfaces, and the metal again heated, but far below the 

 usual welding heat. The pieces unite firmly by hammering. 

 (Lond. Builder, 1848.) 



2. IIydrometallurgy 



Embraces those processes performed by liquid agents on 

 metals, by which they are procured again from combinations 

 in the metallic state. .Some of these operations arc included 



