Agricola, Georgius, De re metallica, 1912/1950

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      <text>
        <body>
          <chap>
            <p type="main">
              <s>
                <pb pagenum="208"/>
              or by a horse or by water-power; if by a man, the lower board of a large bellows is
                <lb/>
              fixed to the timbers above the conduit which projects out of the shaft, and so
                <lb/>
              placed that when the blast is blown through the conduit, its nozzle is
                <lb/>
              set in the conduit. </s>
              <s>When it is desired to suck out heavy or pestilential
                <lb/>
              vapours, the blow-hole of the bellows is fitted all round the mouth of the
                <lb/>
              conduit. </s>
              <s>Fixed to the upper bellows board is a lever which couples
                <lb/>
              with another running downward from a little axle, into which it is
                <lb/>
              mortised so that it may remain immovable; the iron journals of this little
                <lb/>
              axle revolve in openings of upright posts; and so when the workman pulls
                <lb/>
              down the lever the upper board of the bellows is raised, and at the same time
                <lb/>
              the flap of the blow-hole is dragged open by the force of the wind. </s>
              <s>If the
                <lb/>
              nozzle of the bellows is enclosed in the conduit it draws pure air into itself,
                <lb/>
              but if its blow-hole is fitted all round the mouth of the conduit it exhausts
                <lb/>
              the heavy and pestilential vapours out of the conduit and thus from the
                <lb/>
              shaft, even if it is one hundred and twenty feet deep. </s>
              <s>A stone placed on the
                <lb/>
              upper board of the bellows depresses it and then the flap of the blow-hole is </s>
            </p>
            <figure number="121"/>
            <p type="caption">
              <s>A—SMALLER PART OF SHAFT. B—SQUARE CONDUIT. C—BELLOWS. D—LARGER PART
                <lb/>
              OF SHAFT.</s>
            </p>
          </chap>
        </body>
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