100 ECONOMIC GEOLOGY 



present. This material is all remelted and recrystallized. 

 This process is continued until only about 0.002 per cent, of 

 silver remains in the lead. 



The Rosan process is largely like the Pattinson only the liquid 

 alloy is drawn off leaving the solidified portion. The process is 

 less delicate or efficient than the Pattinson, giving 0.003 per cent, 

 of silver waste in the lead. 



The Parke's process depends upon the formation of compounds 

 of zinc and silver when these metals are melted together. The 

 alloy of zinc and silver is formed containing about 12 per cent, of 

 silver. The zinc is added in small amounts at different times. 

 In the first solidification practically all the gold and copper so- 

 lidify with the zinc. Upon the addition of more zinc the silver 

 unites directly with the zinc in the formation of the alloy AgZni2. 

 The efficiency of this method is proven by the amount of silver 

 remaining in the lead which is about 0.005 per cent. The 

 final step in the treatment of the alloys thus obtained is cupel- 

 lation, in which process the lead is volatilized, and the gold or 

 silver remains in the cupel. 



Lixiviation Process. The silver is dissolved, and after filtering, 

 is precipitated from the clear liquid into metallic form by some 

 reagent. The process is as follows: 



In the treatment of argentiferous copper matter the Ziervogel 

 process has been largely utilized, in which copper, iron and silver 

 are present and converted into their sulphates, then into their 

 oxides. The iron is the first to oxidize, copper second, silver 

 third. Just as the silver begins to oxidize it is treated with 

 water, and the silver is precipitated by scrap copper. The copper 

 still in solution is recovered by the more electro-positive metal, 

 scrap iron. The process is complete when the solution yields 

 with ammonium hydroxide only a faint blue coloration, and when 

 no dense white curdy precipitate is obtained upon the addition of 

 common salt. 



In the treatment of the ores containing copper and iron, so- 

 dium chloride was first used for the conversion of the silver into 

 silver chloride. This process is known as the Augustine proc- 

 ess. This, because of its general inefficiency, was supplanted by 

 the sodium thiosulphate, otherwise known as the Patera process. 

 This process is more efficacious, because of its greater solvent 

 power, especially upon the arsenates, and antimonates of silver 

 which are practically insoluble in the presence of the sodium 



