Agricola, Georgius, De re metallica, 1912/1950
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              <s>
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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. </s>
              <s>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. </s>
              <s>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. </s>
              <s>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. </s>
              <s>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. </s>
              <s>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. </s>
              <s>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. </s>
              <s>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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              </s>
              <s>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. </s>
              <s>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. </s>
              <s>With regard to this test I will speak later.</s>
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              <s>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. </s>
              <s>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. </s>
              <s>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.</s>
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              <s>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 </s>
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