a 1 8 Natural Hiftcry of Silver. [Book VI. 



yields half its weight of filver ; it varies in its appear- 

 ance, being fometrmes of a grey and brilliant afpe<5r a 

 but often of a dull and tarnifhed colour, with erfloref- 

 cences of cobalt. The goofe dung ore belongs to this 

 ipecies. The grey ore of filver contains a large quan- 

 tity of copper. The black filver ore, called nigrillo by 

 the Spaniards, feems to be a middle ftate between na- 

 tive filver and fome of its ores, or thofe ores in a ftate 

 of imperfect decompofition. The corneous fiiver ore 

 is a natural combination of filver and muriatic acid 

 with a finall quantity of vitriolic acid. Silver is alfo 

 found in confiderable quantity in the ores of other 

 metals, particularly thofe of antimony, zinc, lead, and 

 copper. 



In the allaying of filver ores different procefTes arfc 

 iiied, according to their nature. When found in its 

 metallic ftate, nothing more is neceffary than to fepa- 

 rate it from the earthy or ftony matter in which it is, 

 embedded. With this view it is firft expofed to heat, 

 to render the ftony matter friable. The mafs is then 

 mixed and ground with quickfilver. Thus the filver 

 is converted into an amalgam, which, from the inti- 

 mate union of the particles of the metals, is fpecifically 

 heavier than quickfilver itfelf. The ftony matters are 

 now eafily warned off, without lofing any of the metal. 

 The quickfilver is afterwards partly feparated by 

 fqueezing it through a piece of leather, and the re- 

 mainder by diftillation. Sulphureous filver ores re- 

 quire to be firft roafted, and then mixed with a 

 quantity of flux. In order to feparate lead, copper, 

 iron, &c. from filver, a particular procefs is employed, 

 which is called cupellation, from the veiTel ia which it 

 is performed, called a cupel, and which is chiefly 

 formed of calcined bones, and is very porous. The 

 metallic mats containing filver is mixed with a confi- 



