Agricola, Georgius, De re metallica, 1912/1950

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              in the middle of it. </s>
              <s>As soon as the borax crackles and the lead-stone melts,
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              which soon occurs, remove the coal from the crucible, and the lead will settle
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              to the bottom of it; weigh it out, and take account of that portion of it
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              which the fire has consumed. </s>
              <s>If you also wish to know what portion of silver
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              is contained in the lead, melt the lead in the cupel until all of it exhales.</s>
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              <s>Another way is to roast the lead ore, of whatsoever quality it be, wash
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              it, and put into the crucible one
                <emph type="italics"/>
              centumpondium
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              of the concentrates, together
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              with three
                <emph type="italics"/>
              centumpondia
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              of the powdered compound which melts ore, mixed
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              together, and place it in the iron hoop that it may melt; when it has cooled,
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              cleanse it of its slag, and complete the test as I have already said. </s>
              <s>Another way is
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              to take two
                <emph type="italics"/>
              unciae
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              of prepared ore, five
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              drachmae
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              of roasted copper, one
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              uncia
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              of
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              glass, or glass-galls reduced to powder, a
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              semi-uncia
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              of salt, and mix them. </s>
              <s>Put
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              the mixture into the triangular crucible, and heat it over a gentle fire to
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              prevent it from breaking; when the mixture has melted, blow the fire
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              vigorously with the bellows; then take the crucible off the live coals and
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              let it cool in the open air; do not pour water on it, lest the lead button being
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              acted upon by the excessive cold should become mixed with the slag, and the
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              assay in this way be erroneous. </s>
              <s>When the crucible has cooled, you will find
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              in the bottom of it the lead button. </s>
              <s>Another way is to take two
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              unciae
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              of
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              ore, a
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              semi-uncia
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              of litharge, two
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              drachmae
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              of Venetian glass and a
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              semi-uncia
                <emph.end type="italics"/>
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              of saltpetre. </s>
              <s>If there is difficulty in melting the ore, add to it iron filings,
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              which, since they increase the heat, easily separate the waste from lead and
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              other metals. </s>
              <s>By the last way, lead ore properly prepared is placed in the
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              crucible, and there is added to it only the sand made from stones which easily
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              melt, or iron filings, and then the assay is completed as formerly.</s>
            </p>
            <p type="main">
              <s>You can assay tin ore by the following method. </s>
              <s>First roast it, then
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              crush, and afterward wash it; the concentrates are again roasted, crushed,
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              and washed. </s>
              <s>Mix one and a half
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              centumpondia
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              of this with one
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              centum­
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              pondium
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              of the
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              chrysocolla
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              which they call borax; from the mixture,
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              when it has been moistened with water, make a lump. </s>
              <s>Afterwards,
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              perforate a large round piece of charcoal, making this opening a palm deep,
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              three digits wide on the upper side and narrower on the lower side; when
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              the charcoal is put in its place the latter should be on the bottom and the
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              former uppermost. </s>
              <s>Let it be placed in a crucible, and let glowing coal be
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              put round it on all sides; when the perforated piece of coal begins to burn,
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              the lump is placed in the upper part of the opening, and it is covered with a
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              wide piece of glowing coal, and after many pieces of coal have been put round
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              it, a hot fire is blown up with the bellows, until all the tin has run out
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              of the lower opening of the charcoal into the crucible. </s>
              <s>Another way is to
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              take a large piece of charcoal, hollow it out, and smear it with lute, that the
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              ore may not leap out when white hot. </s>
              <s>Next, make a small hole through the
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              middle of it, then fill up the large opening with small charcoal, and put the
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              ore upon this; put fire in the small hole and blow the fire with the nozzle of
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              a hand bellows; place the piece of charcoal in a small crucible, smeared
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              with lute, in which, when the melting is finished, you will find a button
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              of tin.</s>
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