Agricola, Georgius
,
De re metallica
,
1912/1950
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is bent down the same distance as it was bent up the last time; the other
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end of it, which also acts as a journal, is straight. </
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<
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>This part which protrudes
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through the wood is protected by two iron washers in the shape of discs, to
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which are fastened two leather washers of the same shape and size, in order
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to prevent the water which is drawn into the box from gushing out. </
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<
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>These
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discs are around the axle; one of them is inside the box and the other
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outside. </
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>Beyond this, the end of the axle is square and has two eyes, in
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which are fixed two iron rods, and to their ends are weighted lumps of lead,
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so that the axle may have a greater propensity to revolve; this axle can
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easily be turned when its end has been mortised in a crank. </
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<
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>The upper part
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of the box is the shallower one, and the lower part the deeper, the upper
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part is bored out once straight down through the middle, the diameter of the
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opening being the same as the outside diameter of the column pipe; the
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lower box has, side by side, two apertures also bored straight down;
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these are for two pipes, the space of whose openings therefore is twice as
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great as that of the upper part; this lower part of the box is placed
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upon the two pipes, which are fitted into it at their upper ends, and the
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lower ends of these pipes penetrate into trunks which stand in the
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sump. </
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<
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>These trunks have perforations through which the water flows into
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them. </
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<
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>The iron axle is placed in the inside of the box, then the two iron
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piston-rods which hang from it are let down through the two pipes to the depth
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of a foot. </
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<
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>Each piston has a screw at its lower end which holds a thick iron
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plate, shaped like a disc and full of openings, covered with a leather, and
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similarly to the other pump it has a round valve in a little box. </
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<
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>Then the
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upper part of the box is placed upon the lower one and properly fitted to it on
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every side, and where they join they are bound by wide thick iron plates, and
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held with small wide iron wedges, which are driven in and are fastened with
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clamps. </
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<
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>The first length of column pipe is fixed into the upper part of the
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box, and another length of pipe extends it, and a third again extends this one,
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and so on, another extending on another, until the uppermost one reaches the
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drain of the tunnel. </
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<
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>When the crank worker turns the axle, the pistons in
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turn draw the water through their discs; since this is done quickly, and
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since the area of openings of the two pipes over which the box is set, is twice
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as large as the opening of the column pipe which rises from the box, and since
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the pistons do not lift the water far up, the impetus of the water from the
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lower pipes forces it to rise and flow out of the column pipe into the drain of
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the tunnel. </
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<
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>Since a wooden box frequently cracks open, it is better to
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make it of lead or copper or brass.</
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<
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>The fifth kind of pump is still less simple, for it is composed of two or
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three pumps whose pistons are raised by a machine turned by men, for each
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piston-rod has a tappet which is raised, each in succession, by two cams on
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a barrel; two or four strong men turn it. </
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<
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>When the pistons descend into
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the pipes their discs draw the water; when they are raised these force the
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water out through the pipes. </
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<
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>The upper part of each of these piston-rods,
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which is half a foot square, is held in a slot in a cross-beam; the lower part,
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which drops down into the pipes, is made of another piece of wood and is
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round. </
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<
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>Each of these three pumps is composed of two lengths of pipe fixed </
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