17B Ohservations on Lead Ores. 



At Patterdale, the ore yields fifty or sixty ounces of sil- 

 ver to a ton. 



The poorest lead ores yield most silver. 



From seven to ten thousand tons of lead are smelted an- 

 mially in Derbyshire. 



The tests or cupels are made of four parts of calcined 

 bones, and one part unwashed fern ashes; wood ashes are 

 sometimes used without washing. 



If galena be free from pyrites the lead may be melted 

 out without roasting, otherwise not. (Bl. II. 620.) 



One-eighth of an ounce, or less, of gold or silver may be 

 separated from one hundred pounds of lead by scorification. 



The lead is recovered from the cupels by pounding thera 

 up, and mixing the powder with inflammable matters by 

 the aid of heat. 



Fourcroy (VI. 74) asserts that every sulphuret of lead 

 contains silver ; we believe very (ew are without it. 



Galena, with small facets, or of a granulated texture, is 

 apt to contain most silver ; but this is, in our view, not an 

 infallible criterion. 



Fourcroy (VI. 82) gives the following process. Roast 

 the ore, weigh, and fuse with two parts of black flux, or bo- 

 rax and charcoal and a little decrepitated salt, and try the 

 button on the cupel, (pa. 84,) after the nitric solution is 

 made, precipitate it by carbonat of soda, one hundred and 

 thirty parts of the carbonat of lead contain one hundred of 

 lead — ammonia dissolves out the silver,* but cupellation 

 is best. 



Iron precipitates both lead and silver. (Fourcroy.) 



The proportion of silver in lead, varies from one-three 

 hundreth to one-twelth. 



The lustre of galena is impaired by silver ; this metal is 

 more commonly found in the octohedral than the cubical 

 varieties. 



Blende and calamine often occur with galena. 



Antimony is commonly in argentiferous lead ores, which 

 hardens the lead ; and the processes for getting rid of the 

 antimony are the same as for extracting the silver. 



Cupels may be made of any infusible earth of little co- 

 hesion, (Aikin, I. 110,)— -cores of ox horns are preferred at 

 the tower. 



* This mw^liowever be dangerousj as fulminating silver mffT/ be formed. 



