Agricola, Georgius
,
De re metallica
,
1912/1950
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the channel, mixed with charcoal, the scum, as one might say, of the lead;
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the lead makes this scum when it becomes hot, but that less of it may be
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made it must be stirred frequently with the bar.</
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<
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>Within the space of a quarter of an hour the crucible absorbs the lead;
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at the time when it penetrates into the crucible it leaps and bubbles. </
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>Then
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the master takes out a little lead with an iron ladle, which he assays, in order
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to find what proportion of silver there is in the whole of the alloy; the
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ladle is five digits wide, the iron part of its handle is three feet long and the
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wooden part the same. </
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<
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>Afterward, when they are heated, he extracts with
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a bar the litharge which comes from the lead and the copper, if there be any
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of it in the alloy. </
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<
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>Wherefore, it might more rightly be called
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spuma
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of lead
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than of silver
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34
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. </
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<
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>There is no injury to the silver, when the lead and copper
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are separated from it. </
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<
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>In truth the lead becomes much purer in the crucible
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of the other furnace, in which silver is refined. </
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<
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>In ancient times, as the
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author Pliny
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35
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relates, there was under the channel of the crucible another
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crucible, and the litharge flowed down from the upper one into the lower
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one, out of which it was lifted up and rolled round with a stick in order that
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it might be of moderate weight. </
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>For which reason, they formerly made it
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into small tubes or pipes, but now, since it is not rolled round a stick, they
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make it into bars.</
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>If there be any danger that the alloy might flow out with the litharge, the
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foreman keeps on hand a piece of lute, shaped like a cylinder and pointed at
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both ends; fastening this to a hooked bar he opposes it to the alloy so that
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it will not flow out.</
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<
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>Now when the colour begins to show in the silver, bright spots appear,
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some of them being almost white, and a moment afterward it becomes
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absolutely white. </
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<
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>Then the assistant lets down the water-gates, so that, the
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race being closed, the water-wheel ceases to turn and the bellows are still.
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</
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<
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>Then the master pours several buckets of water on to the silver to cool it;
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others pour beer over it to make it whiter, but this is of no importance since
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the silver has yet to be refined. </
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<
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>Afterward, the cake of silver is raised with
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the pointed iron bar, which is three feet long and two digits wide, and has a
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wooden handle four feet long fixed in its socket. </
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<
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>When the cake of silver has
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been taken from the crucible, it is laid upon a stone, and from part of it the
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hearth-lead, and from the other part the litharge, is chipped away with a
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hammer; then it is cleansed with a bundle of brass wire dipped in water.
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</
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<
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>When the lead is separated from the silver, more silver is frequently found
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than when it was assayed; for instance, if before there were three
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uncíae
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and
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as many
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drachmae
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in a
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centumpondíum,
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they now sometimes find three
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uncíae
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and a half
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36
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. </
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<
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>Often the hearth-lead remaining in the crucible is a palm
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deep; it is taken out with the rest of the ashes and is sifted, and that which
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remains in the sieve, since it is hearth-lead, is added to the hearth-lead
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37
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