140 EECENT C0PPEE-EXTRACTI2?"G PEOCESSES. 



metals not previously in a soluble condition ; in tlie precipitating 

 stage the liquor is passed over iron pyrites or other metallic sul- 

 phides with a view to precipitate any gold and silver present in 

 solution, ferrous sulphate being sometimes added to facilitate 

 such precipitation. The liquor is next passed over metallic iron, 

 copper, or zinc (according to its composition), to precipitate 

 other metals present, in such order as may be most convenient ; 

 and, finally, if any other metals in solution, the liquor is treated 

 ^\dth an alkali, to precipitate them, and then concentrated, or 

 evaporated to dryness, to recover the saline substances for use in 

 successive operations. A jet of steam is used during the two 

 latter stages, to accelerate the reaction. When silver is present 

 in the ore, salt is dispensed mth and saltpetre substituted, to 

 avoid its precipitation and loss in the lixiviating stage, or 

 sufficient salt is used to ensure a saturated solution ; it being 

 well known to metallurgists that, while any chloride in dilute 

 solution will precipitate the silver present, a saturated solution 

 will arrest its precipitation. If no gold or silver were present, 

 the liquor would not have to pass over metallic sulphides. 



The process appears to possess great merit and value, especially 

 in Australia, where copper is found associated with other valuable 

 metals, the presence of which has hitherto detracted from their 

 value instead of adding thereto. 



Claxjdet's Peocess 



for the extraction of copper and the precious metals from their 

 ores is one Qf the notable economic methods for the treatment of 

 particular kinds of mineral. Hitherto it has been principally 

 applied to the treatment of cupreous pyrites with great success, 

 the average contents being about 4 per cent, of copper and 18 

 dwts. of silver. The pyi'ites is roasted with salt, which converts 

 the metals into soluble chlorides ; it is then put into vats and 

 subjected to eight or nine washings to extract the copper and 

 silver. The first three washings take out 95 per 'cent, of the 

 metals ; this is all that is sought to extract of the precious 

 metals, but the remainder is returned to the vats for re-treat- 

 ment. 



The silver present is precipitated by iodide of potassium, as an 

 insoluble iodide, after pre^dous titration, to ascertain the quan- 

 tity required and avoid waste ; acetate of lead in solution is 

 also added, which ensures a precipitation of the chloride and aids 

 in collecting the silver. It is then thoroughly shaken,* and allowed 

 to stand for forty-eight hours, when the copper liquor is drawn 

 off clear ; the tanks are filled for a further operation, and finally 

 cleaned out once a fortnight. The precipitate contains a consid- 

 erable quantity of copper, which is readily washed out with dilute 

 hydro -chloric acid. The precipitate is next decomposed by the 

 addition of metallic zinc, wdiich reduces the silver to the metallic 



