form round about the nozzles of the bellows. This process of smelting is very
ancient among the Tyrolese18, but not so old among the Bohemians.
The second method of smelting ores stands in a measure midway between
that one performed in a furnace of which the tap-hole is closed intermittently,
and the first of the methods performed in a furnace where the tap-hole is
always open. In this manner are smelted the ores of gold and silver that are
neither very rich nor very poor, but mediocre, which fuse easily and are
readily absorbed by the lead. It was found that in this way a large quantity
of ore could be smelted at one operation without much labour or great expense,
and could thus be alloyed with lead. This furnace has two crucibles, one of
which is half inside the furnace and half outside, so that the lead being put
into this crucible, the part of the lead which is in the furnace absorbs
the metals of the ores which easily fuse ; the other crucible is lower, and
the alloy and the molten pyrites run into it. Those who make use of this
method of smelting, tap the alloy of gold or silver with lead from the upper
crucible once or twice if need be, and throw in other lead or litharge, and
each absorbs that flux which is nearest. This method of smelting is in use
in Styria19.
The furnace in the third method of smelting ores has the tap-hole likewise open, but the furnace is higher and wider than the others, and its bellows
are larger ; for these reasons a larger charge of the ore can be thrown into
it. When the mines yield a great abundance of ore for the smelter, they
smelt in the same furnace continuously for three days and three nights,
providing there be no defect either in the hearth or in the forehearth. In this
kind of a furnace almost every kind of accretion will be found. The forehearth of the furnace is not unlike the forehearth of the first furnace of all,
except that it has a tap-hole. However, because large charges of ore
are smelted uninterruptedly, and the melted material runs out and the slags
are skimmed off, there is need for a second forehearth crucible, into which the
molten material runs through an opened tap-hole when the first is full. When
a smelter has spent twelve hours' labour on this work, another always takes his
place. The ores of copper and lead and the poorest ores of gold and silver
are smelted by this method, because they cannot be smelted by the other
three methods on account of the greater expense occasioned. Yet by this
method a centumpondium of ore containing only one or two drachmae of
gold, or only a half to one uncia of silver,20 can be smelted ; because there
is a large amount of ore in each charge, smelting is continuous, and without
expensive fluxes such as lead, litharge, and hearth-lead. In this method
of smelting we must use only cupriferous pyrites which easily melt in the
fire, in truth the cakes melted out from this, if they no longer absorb
iaRhetos. The ancient Rhaetia comprised not only the greater part of Tyrol,
but also parts of Switzerland and Lombardy. The mining section was, however, in
Tyrol.
^Noricum was a region south of the Danube, embracing not only modern Styria, but
also parts of Austria, Salzberg, and Carinthia.
20One drachma of gold to a centumpondium would be (if we assume these were Roman
weights) 3 ozs. ι dwt. Troy per short ton. One-half uncia of silver would be 12 ozs. 3 dwts.
per short ton.
