TREATMENT OF SILVER-BEARING ORES. 12? 



iron. In the other, the oxide ore, containing some sulphur, 

 is roasted with common salt, cupric chloride resulting, which 

 can be leached out by the addition of water, the residues 

 being subsequently extracted by the hydrochloric acid, which 

 forms a bye product of this process. 



To extract lead from galena, in a manner akin to that 

 referred to in assaying, is a comparatively simple process. 

 To do so, however, in the most economical manner, many 

 operations and much plant may be necessary, the very lead 

 fumes being in some instances turned to account. It must 

 be remembered that galena contains silver, not always in 

 such quantity as to demand much consideration; but 

 frequently the reverse : indeed, often a galena ore may be 

 only valuable for its silver. As the lead obtained from the 

 smelting furnace contains also the silver (and gold), the 

 cupellation process, the principle of which has been men- 

 tioned in page 117, or other methods are made use of to 

 obtain the precious metals. 



In the Pattinson process, with the various ladlings from 

 one pot to another, the principle involved is that when a 

 lead-silver alloy is allowed to cool slowly, crystals of lead 

 separate out, and these are very poor in silver, this metal 

 becoming concentrated in the residual " mother liquid." 



In the Parkes method, which now is much made use of, 

 metallic zinc is stirred into the lead, and, this cooling down, 

 the zinc rises to the top and solidifies. It is then found 

 to contain both the silver and gold originally in the lead. 



Treatment of Silver-bearing Ores. 



The extraction of silver from certain lead ore has been 

 referred to in the foregoing remarks. When the ore is 

 a carbonate, the ore can be smelted with oxide of iron and 

 limestone to obtain all the lead with the silver. 



Some silver-bearing ores containing sulphides are treated 

 after the manner referred to in the description of the treat- 

 ment of copper ores, so that there may be obtained a 

 regulus, which may either be roasted direct to form 

 sulphate, the silver sulphate being washed out with water 

 (Ziervogel's method). In the Augustin method, the ore is 

 roasted with salt, the silver chloride extracted by brine, 



