Agricola, Georgius, De re metallica, 1912/1950
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              of the bellows, and blows up the fire with the bellows; thus within the space
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              of half an hour the forehearth, as well as the hearth, becomes warmed, and
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              of course more quickly if on the preceding day ores have been smelted in the
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              same furnace, but if not then it warms more slowly. </s>
              <s>If the hearth and
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              forehearth are not warmed before the ore to be smelted is thrown in, the furnace
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              is injured and the metals lost; or if the powder from which both are made
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              is damp in summer or frozen in winter, they will be cracked, and, giving
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              out a sound like thunder, they will blow out the metals and other substances
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              with great peril to the workmen. </s>
              <s>After the furnace has been warmed, the
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              master throws in slags, and these, when melted, flow out through the tap­
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              hole into the forehearth. </s>
              <s>Then he closes up the tap-hole at once with
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              mixed lute and charcoal dust; this plug he fastens with his hand to a
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              round wooden rammer that is five digits thick, two palms high, with a handle
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              three feet long. </s>
              <s>The smelter extracts the slags from the forehearth with a
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              hooked bar; if the ore to be smelted is rich in gold or silver he puts into the
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              forehearth a
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              centumpondíum
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              of lead, or half as much if the ore is poor,
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              because the former requires much lead, the latter little; he immediately
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              throws burning firebrands on to the lead so that it melts. </s>
              <s>Afterward he
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              performs everything according to the usual manner and order, whereby he
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              first throws into the furnace as many cakes melted from pyrites
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              12
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              , as he
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              requires to smelt the ore; then he puts in two wicker baskets full of ore
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              with litharge and hearth-lead
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              13
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              , and stones which fuse easily by fire of the
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              second order, all mixed together; then one wicker basket full of charcoal,
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              and lastly the slags. </s>
              <s>The furnace now being filled with all the things I
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              have mentioned, the ore is slowly smelted; he does not put too much of it
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              against the back wall of the furnace, lest sows should form around the nozzles
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              of the bellows and the blast be impeded and the fire burn less fiercely.</s>
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              <s>This, indeed, is the custom of many most excellent smelters, who know
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              how to govern the four elements
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              14
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              . </s>
              <s>They combine in right proportion the
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              ores, which are part earth, placing no more than is suitable in the furnaces;
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              they pour in the needful quantity of water; they moderate with skill the air
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              from the bellows; they throw the ore into that part of the fire which burns
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              fiercely. </s>
              <s>The master sprinkles water into each part of the furnace to dampen
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              the charcoal slightly, so that the minute parts of ore may adhere to it,
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              which otherwise the blast of the bellows and the force of the fire would agitate
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              and blow away with the fumes. </s>
              <s>But as the nature of the ores to be smelted
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              varies, the smelters have to arrange the hearth now high, now low, and to
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              place the pipe in which the nozzles of the bellows are inserted sometimes on a
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              great and sometimes at a slight angle, so that the blast of the bellows may
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              </s>
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