Agricola, Georgius
,
De re metallica
,
1912/1950
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is first roasted in a hot fire for about six or eight hours; next, when it has
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cooled, it is crushed and washed; then the concentrates made by washing
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are again roasted, crushed, washed, dried, and weighed. </
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<
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>The portion which
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it has lost whilst it is being roasted and washed is taken into account, and
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these concentrates by washing represent the cake which will be melted out
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of the copper ore. </
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<
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>Place three
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centumpondia
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(lesser weights) of this, mixed
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with three
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centumpondia
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(lesser weights) each of copper scales
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30
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, saltpetre,
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and Venetian glass, mixed, into the triangular crucible, and place it in the iron
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hoop which is set on the hearth in front of the double bellows. </
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<
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>Cover the crucible
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with charcoal in such a way that nothing may fall into the ore which is to be
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melted, and so that it may melt more quickly. </
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<
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>At first blow a gentle blast with
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the bellows in order that the ore may be heated gradually in the fire; then
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blow strongly till it melts, and the fire consumes that which has been added to
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it, and the ore itself exudes whatever slag it possesses. </
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>Next, cool
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the crucible which has been taken out, and when this is broken you will find
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the copper; weigh this, in order to ascertain how great a portion of the ore
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the fire has consumed. </
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>Some ore is only once roasted, crushed, and washed;
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and of this kind of concentrates, three
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centumpondia
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(lesser weights) are
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taken with one
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centumpondíum
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each of common salt, argol and glass
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galls. </
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<
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>Heat them in the triangular crucible, and when the mixture has
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cooled a button of pure copper will be found, if the ore is rich in this metal.
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</
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>If, however, it is less rich, a stony lump results, with which the copper is
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intermixed; this lump is again roasted, crushed, and, after adding stones
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which easily melt and saltpetre, it is again melted in another crucible, and
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there settles in the bottom of the crucible a button of pure copper. </
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<
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>If you
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wish to know what proportion of silver is in this copper button, melt it in a
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cupel after adding lead. </
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<
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>With regard to this test I will speak later.</
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>Those who wish to know quickly what portion of silver the copper ore
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contains, roast the ore, crush and wash it, then mix a little yellow litharge
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with one
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centumpondium
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(lesser weights) of the concentrates, and put the
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mixture into a scorifier, which they place under the muffle in a hot furnace for
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the space of half an hour. </
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<
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>When the slag exudes, by reason of the melting force
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which is in the litharge, they take the scorifier out; when it has cooled, they
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cleanse it of slag and again crush it, and with one
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centumpondíum
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of it they
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mix one and a half
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uncíae
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of lead granules. </
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<
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>They then put it into another
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scorifier, which they place under the muffle in a hot furnace, adding to the
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mixture a little of the powder of some one of the fluxes which cause ore to
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melt; when it has melted they take it out, and after it has cooled, cleanse
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it of slag; lastly, they heat it in the cupel till it has exhaled all of the lead,
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and only silver remains.</
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<
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>Lead ore may be assayed by this method: crush half an
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uncía
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of
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pure lead-stone and the same quantity of the
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chrysocolla
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which they call
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borax, mix them together, place them in a crucible, and put a glowing coal </
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