54 PYROMETALLURGT. [ill. 



generally worked for the small fraction of gold it contains. 

 Hence, both in extracting and refining, the mixed hydro and 

 pyro-metallurgic processes are adopted. 



The processes of separation or parting are by nitric or 

 sulphuric acid. In the former case, the gold is melted "with 

 2 or 3 times its weight of silver, granulated by pouring into 

 water, and then treated with pure nitric acid, which extracts 

 not only the silver added, but also more or less of that originally 

 contained in the gold ; for gold has such a covering power that 

 acid could not extract the silver originally present, but by 

 adding more silver, the gold is so disseminated, that as the 

 silver is extracted, the gold is left in a spongy state. For 

 parting by sulphuric acid, the gold is melted with more silver 

 than for nitric acid, granulated, and then heated with un- 

 diluted oil of vitriol in vessels of platinum or iron, whereby 

 silver and copper are extracted and the gold untouched. This 

 method is especially applicable to silver containing only traces 

 of gold. 



The silver dissolved out from gold is recovered either by 

 precipitating it in the metallic state by copper, or it is pre- 

 cipitated as a chloride by common salt, and the chloride re- 

 duced most conveniently and neatly by zinc and dilute acid. 



Silver. — An important series of essays on this metal, by 

 Malaguti and others, especially with reference to its extraction 

 from the ore, has been presented to the " Academic des 

 Sciences" of Paris, abstracts of which have appeared in the 

 Comptes Rendus, Chemical Gazette, London Journal, &c. We 

 refer to them for the details. 



Reduction of Silver from its Ores. — A new method of ef- 

 fecting this is to roast the ores with common salt, which forms 

 chloride of silver, and to lixiviate the roasted ore with a hot 

 solution of common salt, which dissolves out the chloride of 

 silver. The solution is precipitated by metallic copper. 



According to another method, the sulphuretted ores are 

 carefully roasted in a reverberatory, to change them into sul- 

 phates ; the sulphates lixiviated by boiling water, and the 

 silver precipitated by metallic copper. 



