Agricola, Georgius
,
De re metallica
,
1912/1950
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Mix one part of this ore, when it has been roasted, crushed, and washed, with
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three parts of some powder compound which melts ore, and six parts of lead.
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<
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>Put the charge into the triangular crucible, place it in the iron hoop to which
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the double bellows reaches, and heat first in a slow fire, and afterward
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gradually in a fiercer fire, till it melts and flows like water. </
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<
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>If the ore does
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not melt, add to it a little more of these fluxes, mixed with an equal portion
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of yellow litharge, and stir it with a hot iron rod until it all melts. </
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<
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>Then
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take the crucible out of the hoop, shake off the button when it has cooled,
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and when it has been cleansed, melt first in the scorifier and afterward in
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the cupel. </
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<
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>Finally, rub the gold which has settled in the bottom of the cupel,
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after it has been taken out and cooled, on the touchstone, in order to find out
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what proportion of silver it contains. </
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<
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>Another method is to put a
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centumĀ
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pondium
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(of the lesser weights) of gold ore into the triangular crucible, and
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add to it a
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drachma
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(of the larger weights) of glass-galls. </
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<
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>If it resists melting,
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add half a
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drachma
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of roasted argol, and if even then it resists, add the
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same quantity of roasted lees of vinegar, or lees of the
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aqua
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which separates
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gold from silver, and the button will settle in the bottom of the crucible.
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</
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<
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>Melt this button again in the scorifier and a third time in the cupel.</
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<
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>We determine in the following way, before it is melted in the muffle
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furnace, whether pyrites contains gold in it or not: if, after being three times
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roasted and three times quenched in sharp vinegar, it has not broken nor
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changed its colour, there is gold in it. </
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<
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>The vinegar by which it is quenched
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should be mixed with salt that is put in it, and frequently stirred and dissolved
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for three days. </
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<
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>Nor is pyrites devoid of gold, when, after being roasted and
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then rubbed on the touchstone, it colours the touchstone in the same way that
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it coloured it when rubbed in its crude state. </
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<
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>Nor is gold lacking in that,
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whose concentrates from washing, when heated in the fire, easily melt, giving
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forth little smell and remaining bright; such concentrates are heated in the
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fire in a hollowed piece of charcoal covered over with another charcoal.</
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<
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>We also assay gold ore without fire, but more often its sand or the conĀ
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centrates which have been made by washing, or the dust gathered up by
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some other means. </
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<
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>A little of it is slightly moistened with water and heated
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until it begins to exhale an odour, and then to one portion of ore are placed
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two portions of quicksilver
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28
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in a wooden dish as deep as a basin. </
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<
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>They are
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mixed together with a little brine, and are then ground with a wooden pestle
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for the space of two hours, until the mixture becomes of the thickness of dough,
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and the quicksilver can no longer be distinguished from the concentrates
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made by the washing, nor the concentrates from the quicksilver. </
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>
<
s
>Warm, or
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at least tepid, water is poured into the dish and the material is washed until
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the water runs out clear. </
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>
<
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>Afterward cold water is poured into the same dish,
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and soon the quicksilver, which has absorbed all the gold, runs together
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into a separate place away from the rest of the concentrates made by
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washing. </
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>
<
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>The quicksilver is afterward separated from the gold by means
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of a pot covered with soft leather, or with canvas made of woven
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threads of cotton; the amalgam is poured into the middle of the cloth or </
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>
</
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</
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