178 SILVER. 
sidered by the Spaniards as the purest that is known. 
A range of mountains near Potosi, about twenty miles 
in circumference, is said to be perforated by more than 
300 shafts, or openings of mines, and to produce, in the 
whole, from 30,000 to 40,000 dollars 7 worth of ore per 
week. The annual produce of the silver mines in 
America has been estimated at near 2,400,000/. sterling. 
Silver is also found in several parts of Europe ; and, 
some years ago, there were mines of this metal, worked 
to a great extent, at Konigsberg in Norway. These 
were discovered in 1623, and they were found so pro- 
fitable, that in 1751 forty-one shafts and twelve veins 
were wrought there ; and 3,500 officers, artificers, and 
labourers, were employed. The perpendicular depth 
of the principal shaft was more than 750 feet. Speci- 
mens of native silver are not uncommon from some of 
the copper-mines of Cornwall ; and, many years ago, a 
vein of silver ore was, for a short time, wrought with 
considerable advantage in the parish of Alva, Sterling- 
shire, Scotland. It is said that from 40,000/. to 
50,000^. worth of silver was obtained from it before the 
repository was exhausted. We are informed that a 
mass of capillary native silver was found, in veins tra- 
versing the blue-coloured limestone of Isla, one of the 
Western Islands of Scotland. Great quantities of silver 
are extracted from lead. There was lately melted in 
one refining house in London 50,000/. worth of this 
metal, from lead of the Beralston mines in Devonshire. 
Different methods are employed, in different coun- 
tries, to extract silver from its ore. In Mexico and 
Peru the mineral is pounded, roasted, washed, and 
then mixed with mercury in vessels filled with water; 
& mill being employed for* the more perfectly agitating 
and mingling them. By this process the silver com- 
bines with the mercury. The alloy thus obtained, 
after undergoing some further processes, is submitted 
to the action of heat, by which the mercury passes off 
In a state of vapour, leaving the silver behind. The 
silver is then melted and cast into bars or ingots. In 
