Agricola, Georgius, De re metallica, 1912/1950

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              <s>
                <pb pagenum="235"/>
              assay ores, we can without great expense add to them a small portion of any
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              sort of flux, but when we smelt them we cannot add a large portion without
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              great expense. </s>
              <s>We must, therefore, consider how great the cost is, to avoid
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              incurring a greater expense on smelting an ore than the profit we make out of
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              the metals which it yields.</s>
            </p>
            <p type="main">
              <s>The colour of the fumes which the ore emits after being placed on a hot
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              shovel or an iron plate, indicates what flux is needed in addition to the lead,
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              for the purpose of either assaying or smelting. </s>
              <s>If the fumes have a purple
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              tint, it is best of all, and the ore does not generally require any flux whatever.
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              </s>
              <s>If the fumes are blue, there should be added cakes melted out of pyrites or
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              other cupriferous rock; if yellow, litharge and sulphur should be added; if
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              red, glass-galls
                <emph type="sup"/>
              17
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              and salt; if green, then cakes melted from cupriferous stones,
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              litharge, and glass-galls; if the fumes are black, melted salt or iron slag,
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              litharge and white lime rock. </s>
              <s>If they are white, sulphur and iron which is
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              eaten with rust; if they are white with green patches, iron slag and
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              sand obtained from stones which easily melt; if the middle part of the
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              fumes are yellow and thick, but the outer parts green, the same sand and
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              iron slag. </s>
              <s>The colour of the fumes not only gives us information as to the
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              proper remedies which should be applied to each ore, but also more or less
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              indication as to the solidified juices which are mixed with it, and which give
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              forth such fumes. </s>
              <s>Generally, blue fumes signify that the ore contains azure;
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              yellow, orpiment; red, realgar; green, chrysocolla; black, black bitumen;
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              white, tin
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              18
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              ; white with green patches, the same mixed with chrysocolla;
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              the middle part yellow and other parts green show that it contains sulphur.
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              </s>
              <s>Earth, however, and other things dug up which contain metals, some­
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              times emit similarly coloured fumes.</s>
            </p>
            <p type="main">
              <s>If the ore contains any
                <emph type="italics"/>
              stíbíum,
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              then iron slag is added to it; if pyrites,
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              then are added cakes melted from a cupriferous stone and sand made from
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              stones which easily melt. </s>
              <s>If the ore contains iron, then pyrites and sulphur
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              are added; for just as iron slag is the flux for an ore mixed with sulphur, so
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              on the contrary, to a gold or silver ore containing iron, from which they are
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              </s>
            </p>
          </chap>
        </body>
      </text>
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