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BOOK X.
467
of the works in which ore is smelted. In the space between the middle and
the front long walls and between the second27 and the third transverse walls are the bellows, the machinery for depressing and the instrument for raising them. A drum on the axle of a water-wheel has rundles which turn the toothed drum of an axle, whose long cams depress the levers of the bellows, and also another toothed drum on an axle, whose cams raise the tappets of the stamps, but in the opposite direction. So that if the cams which depress the levers of the bellows turn from north to south, the cams of the stamps turn from south to north. Lead is separated from gold or silver in a cupellation furnace, of
which the structure consists of rectangular stones, of two interior walls of which the one intersects the other transversely, of a round sole, and of a dome. Its crucible is made from powder of earth and ash ; but I will first speak of the structure and also of the rectangular stones. A circular wall is built four feet and three palms high, and one foot thick ; from the height of two feet and three palms from the bottom, the upper part of the interior is cut away to the width of one palm, so that the stone sole may rest upon it. There are usually as many as fourteen stones ; on the outside they are a foot and a palm wide, and on the inside narrower, because the inner circle is much smaller than the outer ; if the stones are wider, fewer are required, if narrower more ; they are sunk into the earth to a depth of a foot and a palm. At the top each one is joined to the next by an iron staple, the points of which are embedded in holes, and into each hole is poured molten lead. This stone structure has six air-holes near the ground, at a height of a foot above the ground ; they are two feet and a palm from the bottom of the stones ; each of these air-holes is in two stones, and is two palms high, and a palm and three digits wide. One of them is on the right side, between the wall which protects the main wall from the fire, and the channel through which the litharge flows out of the furnace crucible ; the other five air-holes are distributed all round at equal distances apart ; through these escapes the moisture which the earth exhales when heated, and if it were not for these openings the crucible would absorb the moisture and be damaged. In such a case a lump would be raised, like that which a mole throws up from the earth, and the ash would float on the top, and the crucible would absorb the silver-lead alloy ; there are some who, because of this, make the rear part of the structure entirely open. The two inner walls, of which one intersects the other, are built of bricks, and are a brick in thickness. There are four air-holes in these, one in each part, which are about one digit's breadth higher and wider than the others. Into the four compartments is thrown a wheelbarrowful of slag, and over this is placed a large wicker basket full of charcoal dust. These walls extend a cubit above the ground, and on these, and on the ledge cut in the rectangular stones, is placed the stone sole ; this sole is a palm and three digits thick, and on all sides touches the rectangular stones ; if there are any cracks in it they are filled up with fragments of stone or brick. The front part of the sole is sloped so that a channel can be made, through which |
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*Vn Agricolas' text this is "ßrst, "—obviously an error.
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