SILVER. 251 



its separation from lead is founded on the different oxidability of 

 lead and silver, and on the ready fusibility of litharge. The lead 

 obtained from those kinds of galena which are rich in sulphuret of 

 silver, is kept at a red heat in a flat furnace, with a draught of air 

 constantly playing on its surface ; the lead is thus rapidly 

 oxidated ; and as the oxide, at the moment of its formation, is 

 fused, and runs off through an aperture in the side of the furnace, 

 the production of litharge goes on uninterruptedly till all the lead 

 is removed. The button of silver is again fused in a smaller fur- 

 nace, resting on a porous earthen dish, made with lixiviated wood- 

 ashes, called a test, the porosity of which is so great, that it absorbs 

 any remaining portions of litharge, which may be formed on the 

 silver." 



"The ores commonly employed in the process of amalgamation, 

 which has been long used at Freyberg, in Saxony, and is exten- 

 sively practised in the silver and gold mines of South America, are 

 native silver and its sulphuret. The ore in fine powder is mixed 

 with sea salt, and carefully roasted in a reverberating furnace. 

 The production of sulphuric acid leads to the formation of sulphate 

 of soda, while the chlorine of the sea salt combines with silver. 

 The roasted mass is ground to a fine powder, and, together with 

 mercury, water, and fragments of iron, is put into barrels, which 

 are made to revolve by machinery. In this operation, intended to 

 insure perfect contact between the materials, chloride of silver is 

 decomposed by the iron, the silver unites with the mercury, and 

 the chloride of lime is dissolved by the water. The mercury is 

 then squeezed through leathern bags, through the pores of which 

 the pure mercury passes, while the amalgam of silver is retained. 

 The combined mercury is then distilled in close vessels, and the 

 metal obtained in a separate state.*" 



Silver may be obtained free from copper, for chemical and phar- 

 maceutical purposes, by dissolving it in nitric acid, diluted with 

 its weight of water ; then adding a solution of muriate of soda, 

 and exposing the precipitate to heat, with three parts of the carbo- 

 nate of potash. Pure silver has considerable lustre, and a brighter 



* Turner's Elements of Chemistry, p. 560. 



