124 NATURAL HISTORY OF PRECIOUS METALS, &c.
Had
the Romans been aware of the mineral wealth of Silesia, they would
certainly have made more vigorous efforts for the conquest of Germany ;
but the rich silver-mines of that province were first opened in' the
10th century. In Norway also the Kongsberg mine during the last entury
rivalled in productiveness any of the Mexican.
Silver
was never met with Native (adds Pliny), or even betraying its presence,
like gold, by particles sparkling in a stony matrix: it only occurred
as a reddish or ash-coloured earth. This could not be reduced unless it
were mixed either with lead or with the lead-ore, called Galena (Sulphuret
of Lead), usually obtained in the same mines. (The chief produce of
these Spanish mines at present is silver-lead ore.) By the same
operation, in the smelting, part of this mineral was reduced to lead,
whilst the silver floated on the top, like oil on the surface of water.
Pliny (xxxiv. 47) notices the separation of the silver from the 7ead
in the same melting at different temperatures—a property, only recently
again taken advantage of in the extraction of silver from argentiferous
lead-ore (Pattinson's Process), but thus proved known to the profit of
the old Spanish miners. " Lead is either produced pure naturally in an
ore of its own, giving nothing else, or else united with silver, and
the two ores are smelted together. Of this mixture that which first
runs off in the furnace is called ' Stagnum ;' the next that comes off
is Silver : the residuum in the furnace is Galena, amounting to a
third of the charge of ore. This melted over again produces Lead, with
a loss of two parts in nine." (This residuum, therefore, must have
been Litharge, or lead oxidised by the great heat required to smelt the
combined ores. As charcoal was the only fuel then used, this oxide
gained sufficient carbon in the second melting to convert it into
metallic lead.)
